Proceedings


EFFECTS OF COVER CROPS ON WEED SUPPRESSION IN SUB-TROPICAL SOUTH TEXAS. S. Rugg*; University of Texas Rio Grande, Edinburg, TX (1)

ABSTRACT


ESTABLISHMENT OF COVER CROP SPECIES FOLLOWING RESIDUAL HERBICIDES APPLIED IN CORN AND SOYBEAN. K. B. Pittman*1, M. L. Flessner1, C. W. Cahoon2, T. Hines2; 1Virginia Tech, Blacksburg, VA, 2Virginia Tech, Painter, VA (2)

ABSTRACT

Establishment of Cover Crop Species Following Residual Herbicides Applied in Corn and Soybean. K. B. Pittman*, M. L. Flessner, C. W. Cahoon, and T. Hines; Virginia Polytechnic Institute and State University, Blacksburg, VA.

 

ABSTRACT

 

Cover crops have been shown to reduce soil erosion and compaction, increase water-holding capacity and soil organic matter, and suppress pests. One major consideration when choosing a cover crop is the sensitivity of species to previously applied herbicides, as herbicide carryover may result in reduced cover crop establishment. Research was conducted to evaluate the establishment of eight cover crop species following herbicide application in corn and soybean.

 

Multiple studies were conducted in Montgomery and Accomack Counties in Virginia in 2015. In each study, herbicides were applied at a typical timing for the location and crop. Herbicide applications in Montgomery County for corn preemergent and postemergent herbicides were May 18th and August 22nd, respectively, and May 20th and August 23rd for soybean preemergent and postemergent herbicides, respectively. In Accomack County, applications were made on May 7th for corn preemergent studies and on May 26th for corn postemergent studies; soybean studies were not conducted in Accomack County. Subsequently, strips of cover crops were planting into the treated area using a drill at a typical timing for the location: October 20th and November 5th for Accomack and Montgomery Counties, respectively. Treatments in the corn preemergent study were atrazine (AAtrex) at 2240 g ai ha-1, simazine (Princep) at 2240 g ai ha-1, atrazine + simazine (AAtrex + Princep) at 1344 g ai ha-1 each, atrazine + S-metolachlor (Bicep II Magnum) at 1806 + 1428 g ai ha-1, mesotrione (Callisto) at 105 g ai ha-1, isoxaflutole + thiencarbazone-methyl (Corvus) at 49.3 + 19.7 g ai ha-1, acetochlor (Warrant) at 2100 g ai ha-1, S-metolachlor (Cinch) at 2139 g ai ha-1, atrazine + S-metolachlor + mesotrione (Lumax EZ) at 771.7 + 2104 + 210.4 g ai ha-1, dimethenamid-P (Outlook) at 735 g ai ha-1, pendimethalin (Prowl H2O) at 1596 g ai ha-1, acetochlor + clopyralid + flumetsulam (SureStart II) at 1050 + 107.6 + 32.7 g ai ha-1, pyroxasulfone (Zidua) at 178 g ai ha-1, and saflufenacil (Sharpen) at 69 g ai ha-1. Treatments for the corn postemergent herbicide study were 2,4-D (2,4-D LV ester) at 1120 g ae ha-1, atrazine (AAtrex) at 2240 g ai ha-1, isoxaflutole (Balance Flexx) at 70 g ai ha-1, primisulfuron-methyl (Beacon) at 40 g ai ha-1, bromoxynil (Buctril) at 420 g ai ha-1, fluthiacet-methyl (Cadet) at 6 g ai ha-1, mesotrione (Callisto) at 105 g ai ha-1, tembotrione + thiencarbazone-methyl (Capreno) at 76.8 + 15.2 g ai ha-1, ametryn (Evik DF) at 1770 g ai ha-1, prosulfuron (Peak) at 30 g ai ha-1, glyphosate (Touchdown Total) at 1170 g ae ha-1, topramezone (Impact) at 18.4 g ae ha-1, tembotrione (Laudis) at 92 g ai ha-1, rimsulfuron + thifensulfuron-methyl (Resolve Q) at 16.1 + 3.5 g ai ha-1, and dicamba + difluenzopyr  (Status) at 246.3 + 95.7 g ai ha-1. Treatments in the soybean preemergent herbicide evaluation were fluthiacet-methyl + pyroxasulfone  (Anthem) at 2.2 + 73.1 g ai ha-1, S-metolachlor + sulfentrazone (Authority Elite) at 1379 + 152.5 g ai ha-1, sulfentrazone + cloransulam-methyl (Authority First) at 278.1 + 35.4 g ai ha-1, fluthiacet-methyl (Cadet) at 6 g ai ha-1, metribuzin + chlorimuron-ethyl (Canopy) at 270 + 44.9 g ai ha-1, S-metolachlor (Cinch) at 1378 g ai ha-1, flumioxazin + pyroxasulfone (Fierce) at 87.7 + 111.3 g ai ha-1, linuron (Linex) at 1120 g ai ha-1, metribuzin (TriCor) at 313.5 g ai ha-1, saflufenacil (Sharpen) at 68.6 g ai ha-1, sulfentrazone (Spartan) at 210 g ai ha-1, flumioxazin (Valor) at 142.7 g ai ha-1, and pyroxasulfone (Zidua) at 178 g ai ha-1. For the soybean postemergent herbicide evaluation, treatments were bentazon (Broadloom) at 840 g ai ha-1, chlorimuron-ethyl (Classic) at 11.7 g ai ha-1, lactofen (Cobra) at 2207 g ai ha-1, cloransulam-methyl (FirstRate) at 17.7 g ai ha-1, fomesafen (Reflex) at 420 g ai ha-1, fluazifop-P-butyl (Fusilade DX) at 175 g ai ha-1, glyphosate (Touchdown Total) at 1170 g ae ha-1, thifensulfuron-methyl (Harmony SG) at 6.6 g ai ha-1, imazethapyr (Pursuit) at 70 g ai ha-1, imazamox (Raptor) at 44 g ai ha-1, clethodim (Select Max) at 102 g ai ha-1, bentazon + acifluorfen (Storm) at 383.8 + 176.2 g ai ha-1, thifensulfuron + chlorimuron-ethyl (Synchrony XP) at 1.8 + 5.6 g ai ha-1, aciflurofen (Ultra Blazer) at 420 g ai ha-1, and glufosinate (Liberty) at 594 g ai ha-1. Cover crop species included winter wheat (Triticum aestivum, Southern States, 520), barley (Hordeum vulgare, Southern States, variety not stated), cereal rye (Secale cereale, Southern States, variety not stated), oats (Avena sativa, Southern States, variety not stated), forage radish (Raphanus sp., Southern States, Eco-till), crimson clover (Trifolium incarnatum, Green Cover Seed, variety not stated), hairy vetch (Vicia villosa, Green Cover Seed, TNT), and mustard (Brassica sp., Green Cover Seed, Caliente). Planting rates were based on recommendations from the 2015 Virginia Agricultural Cost-Share BMP Manual. Stand counts were conducted 6 and 9 weeks after planting in Montgomery and Accomack Counties, respectively, counting plants in 0.9 m of row per plot. Visual injury was assessed 9 weeks after planting at both locations relative to the nontreated check on a scale of 0 (no injury) to 100 (complete plant necrosis). Studies were conducted using a randomized complete split plot design with a minimum of three replications. Data were analyzed using JMP software (SAS Institute Inc., Cary, NC) and were subjected to ANOVA and effects were considered significant when P<0.05 followed by means comparison of each treatment to the nontreated check using Dunnett’s Method (P<0.05).

 

There was a location difference between corn research sites in Montgomery and Accomack counties so data were considered separately. In corn, no differences were detected in visible injury or establishment relative to the check in Montgomery County. In Accomack County, atrazine treatment resulted in visual injury on oats in the corn preemergent study (10%). Bromoxynil applied in the corn postemergent trial injured crimson clover (60%). In the soybean postemergent trial in Montgomery County, glufosinate treatment resulted in an increase in the mean emergence count for hairy vetch and barley relative to the check. This difference was attributed to planting error; more seed was lost when the drill would start and stop. No other differences were found in establishment or injury where soybean preemergent or postemergent herbicides were applied. Under the conditions in Montgomery County, no differences in visible injury or decreases in establishment population were observed. Conversely, in Accomack County, herbicides were more injurious to the cover crop species. Therefore, cover crop injury due to herbicide carryover was heavily dependent on location, application timings, and weather conditions inherent to these locations. Herbicide carryover can vary with different soil temperature and moisture and vary from year-to-year.  Future research is needed to corroborate herbicide carryover findings in more environments and soil types and test more cover crop species.

 

kbpittma@vt.edu

 


SEASONAL BIOMASS AND STARCH CONTENT OF PASPALUM FASCICULATUM IN PUERTO RICO. M. Y. Berrios Rivera*1, W. Robles2, J. O'Hallorans3, G. Ortiz4; 1University of Puerto Rico, Mayaguez, Barranquitas, PR, 2University of Puerto Rico, Mayaguez, Dorado, PR, 3University of Puerto Rico, Mayaguez, San Juan, PR, 4University of Puerto Rico, Mayaguez, Mayaguez, PR (3)

ABSTRACT

The Mexican crowngrass (Paspalum fasciculatum) is considered an invasive species in the humid zones of Puerto Rico. This Neotropical species was introduced in Puerto Rico during the 1940’s for use in pasturing and for erosion control. The use of this weed as forage was ineffective because of its poor nutritional quality. This weed establishes and distributes easily due to its rapid horizontal growth through runners, causing degradation in pastures by displacing desirable foraging species. Little is known about its growth and development in colonized ground, information that is important to establish management programs.  Two naturally colonized grounds by this weed were selected in the Agricultural Experiment Stations in Gurabo and Corozal for documentation of the seasonal fluctuations of the aboveground and belowground biomass of this weed; and also to determine changes in the starch content.  Each experimental site consisted of approximately one acre of naturally colonized Mexican crowngrass where samples of the aboveground and belowground biomass were collected monthly during a period of two years using a 0.25m2 quadrant.  The amount of aboveground and belowground starch was determined using extraction through the hydrolysis enzyme method (Starch Assay Kit). In February 2014, results in Gurabo showed an average maximum aboveground and belowground biomass of 2,158 and 1,117 g m-2, respectively. In Corozal the average maximum aboveground biomass was 1,464 g m-2, in June 2014. The maximum belowground biomass of 1,326 g m-2 was achieved in February 2014. Starch content is an energy indicator for the regrowth of perennial and annual foraging species. In Gurabo the starch content fluctuated between 0.12 to 18% in the aboveground tissue, and from 0.19 to 26% in the belowground tissue.  In Corozal the starch content in the aboveground tissue fluctuated from 0.38 to 21% and in the belowground tissue from 0.41 to 24%.  By understanding these data and considering the life cycle of the plant, we can infer that starch accumulates in greater quantities in the aboveground tissue of the Mexican crowngrass.  This finding suggests that managing practices of this weed should be focused on the removal of aboveground biomass.


VALUE OF VARIOUS COVER CROPS IN SUPPRESING WEED EMERGENCE AND PROTECTING COTTON YIELD. M. G. Palhano*, J. K. Norsworthy, Z. Lancaster, S. Martin, G. T. Jones; University of Arkansas, Fayetteville, AR (4)

ABSTRACT

With the recent confirmation of PPO-resistant Palmer amaranth (Palmer amaranth) in the Midsouth, there is increased concern about the sustainability of weed management in cotton production systems. The use of cover crops can be a worthy option to alleviate this problem since cover crops can suppress weed emergence through allelochemicals and/or a physical residue barrier. A field experiments was conducted in 2014 and 2015 at the Arkansas Agricultural Research and Extension Center in Fayetteville to evaluate the value of various cover crops in suppressing weed emergence and protecting cotton yield. Experiments were designed as a randomized complete block with a split plot with 7 cover crops serving as a main plot and the residual and nonresidual herbicide programs as a sub-plot. The non-residual herbicide program was designed to assess weed emergence in each cover crop throughout the growing season, and the residual side was used to assess the effect of cover crop on seedcotton yield. No cover, cereal rye, wheat, oats, hairy vetch, crimson clover, Austrian winterpea, and rapeseed were used as cover crop treatments. Biomass of each cover crop was collected at cotton planting. Cotton stand counts were collected at 2 weeks after planting. Palmer amaranth density and visual estimates of weed control were evaluated 2, 4, 6, and 8 weeks after cotton planting. Seedcotton yield was also determined. In both years, cereal rye and wheat had the highest biomass production whereas the amount of biomass present in spring did not differ among the remaining cover crops. All cover crops initially diminished Palmer amaranth emergence. However, cereal rye had the greatest suppression, with 83% less emergence than in no cover crop plots. Brassica and legume cover crops had only a minor impact on Palmer amaranth emergence. For these cover crops, physical suppression of the Palmer amaranth and other weeds from the cereal residues is most likely the greatest contributor to reducing weed emergence in this experiment. Similar to weed suppression, as biomass production increased there was greater difficulty in establishing a stand of cotton, which led to a negative impact of all cover crops on seedcotton yield in 2014. It is possible that the reduced stand was a result of the moist conditions that occurred at the time of planting. In 2015, only a minor negative effect of cover crop on cotton stands was observed. Seedcotton yield in the legume and brassica cover crop plots were statistically similar when compared with the no cover crop treatment. However, the seedcotton yield collected from cereal cover crop plots was significantly lower than from other treatments. It is likely that the cereal residue triggered nitrogen immobilization, leading to reduced yield. Special nitrogen management may be needed to alleviate this problem.

 


EVALUATION OF TILLAGE, COVER CROP, & HERBICIDE EFFECTS ON WEED CONTROL, YIELD AND GRADE IN PEANUT. J. P. Williams*1, A. J. Price2, J. S. McElroy1, E. A. Guertal1, J. Tredaway-Ducar1, S. Xi1, R. S. Tubbs3; 1Auburn University, Auburn, AL, 2USDA-ARS, Auburn, AL, 3University of Georgia, Tifton, GA (7)

ABSTRACT

Peanut production continues to play a large role in agriculture in the Southeastern United States and weed challenges persist. Therefore, it is important to reduce weed competition in peanut to protect yield and grade. With traditional use of herbicides for weed control in peanut and rotational crops, the frequency of herbicide resistant weeds has grown. Because of this, alternative integrated methods of weed control must be investigated to maintain crop yield and quality, and increasingly to combat herbicide resistant weeds and their development.  Conservation tillage is a production method that can offer weed suppression through use of high-residue cover crops and needs further investigation due to agronomic and cover crop/herbicide interference concerns. Thus, an experiment was established evaluating tillage, cover crop, and herbicide use intensity conducted as a split-plot design with tillage type as the main plot and herbicide application intensity as the sub plot. The main plot treatments were 1) conventional tillage including a moldboard plow, 2) conservation tillage winter weedy fallow utilizing spring within-row non-inversion tillage, and 3) conservation tillage using cereal rye as a cover crop and spring within-row non-inversion tillage. Sub plot treatments included: 1) Flumioxazin (3 oz/acre) early PRE, 2) Diclosulam (.45 oz/acre) PRE at planting, and 3) Imazapic (4 fl oz/acre) early POST, 4) Flumioxazin (3 oz/acre) early PRE followed by Imazapic (4 fl oz/acre) early POST, 5) Diclosulam (.45 oz/acre) PRE followed by Imazapic (4 oz/acre) early POST, or 6) non-treated. Weed control ratings were taken along with yield. Yield from conventional tillage (4113 kg/ha) was shown to be significantly higher than winter fallow (3328 kg/ha), but not significantly higher than conservational tillage (3792 kg/ha). Results also show that a PRE and POST herbicide system are the most effective at improving yield (5103 kg/ha), whereas applying herbicide only at the time of planting or late POST is less effective (2903 kg/ha and 3967 kg/ha, respectively). Weed control was highet under the conventional tillage system for crabgrass (Digitaria sanguinalis), palmer amaranth (Amaranthus palmeri), and morningglory (Jaquemontia tamnifolia) (95%, 84%, and 87%, respectively). Conservation tillage provided comparable control relative to conventional tillage for sicklepod (Senna obtusifolia) and nutsedge (Cyperus rotundus) (93% and 93% respectively in conservation tillage and 91% and 94% in conventional tillage). In general, integrated weed management systems provided adequate weed control and yield protection in conservation systems as compared to winter fallow or conventional peanut systems.


IDENTIFYING MOLECULAR MARKERS ASSOCIATED WITH HERBICIDE TOLERANCE IN TOMATO. G. Sharma*, T. Tseng; Mississippi State University, Starkville, MS (8)

ABSTRACT

Identifying Molecular Markers Associated With Herbicide Tolerance In Tomato. G. Sharma*1, T.M. Tseng 1, 1 Mississippi State University, Starkville, MS

The United States is one of the world's leading producers of tomatoes, second only to China. Fresh and processed tomatoes account for more than $2 billion in annual farm cash receipts. In terms of consumption, tomato is the nation's fourth most popular fresh-market vegetable behind potatoes, lettuce, and onions. In Mississippi it is grown on over 444 acres across 627 farms. Unfortunately, tomato yield is reduced by up to 25% because of herbicide drift mostly from row crops, and because of this growers near Mississippi delta region are not able to grow tomatoes even in the greenhouse. Major drifted herbicides are 2, 4-D, and glyphosate. Wild cultivars are good source of genetic variability. In this study we selected 50 wild tomato cultivars (obtained from Tomato Genetic Resource Center) which are resistant to abiotic stresses such as drought, cold or salt. These cultivars were screened for tolerance to 2, 4-D at two different concentrations 0.5 % (0.0056 kg ai/hectare) and 1 % (0.0112 kg ai/hectare) of the recommended rate in soybean, in a spray chamber. Injury, stunting, and mortality, were recorded at 12 days after treatment (DAT). Thirty (17 wild, and 13 abiotic stress tolerant), and eleven (7 wild, and 4 abiotic stress tolerant) accessions showed no sign of injury and stunting at 0.5 and 1 % concentration of 2, 4-D, respectively. Tolerant cultivars selected from screening were then used for QTL analysis to identify molecular markers associated with herbicide resistance, using RFLP and SSR markers linked to abiotic stress tolerance. Potential lines selected from the herbicide screening and molecular marker identification can be used for breeding experiments to develop tomato lines with improved herbicide tolerance and high yield potential. These markers associated with herbicide tolerance will be summarized and submitted to Tomato Genetic Resource Center public database and made available to researchers.


NON-DESTRUCTIVE, RAPID LEAF ASSAY FOR RESISTANCE TO ALS HERBICIDES IN ECHINOCHLOA. T. M. Penka*1, N. Burgos2, R. A. Salas2; 1University of Arkansas, Amarillo, AR, 2University of Arkansas, Fayetteville, AR (9)

ABSTRACT

Echinochloa is a troublesome weed for not only rice producers around the world but also for producers of other food crops. Some acetolactate synthase (ALS) inhibiting herbicides are effective on Echinochloa, but resistance to ALS inhibitors had evolved in this genus. Assays had been created to identify ALS-resistant plants rapidly; however, most assays are destructive or tedious and involve complex laboratory methods. An ALS assay for Echinochloa was adapted from the method of Gerwick (1993) that was developed for broadleaf plants.The goals of this assay were: 1) to quickly distinguish resistant and suceptible Echinochloa plants using a nondestructive assay, and 2) for such assay to be conducted with minimal instrumentation or training and produce reliable results. Known resistant (R) and susceptible (S) ecotypes, identified and maintained in Dr. Burgos’ laboratory at the University of Arkansas-Fayetteville, were used. The herbicide tested was imazethapyr. The assay used 0.3 g leaf tissue incubated in a solution containing CPCA, a KARI enzyme inhibitor, and 10 µM imazethapyr for 4 h. After incubation, leaf tissues were ground and filtered through glass filter paper. The filtrate was acidified to convert acetolactate into acetoin. Napthol dye was added to the solution, centrifuged for 10min, and absorbance of the supernatant was read at 530 nm with a Shimadzu, UV-1600 spectrophotometer. The mean absorbance of six replications of R plants was significantly higher than that of S plants, with 95% confidence of obtaining the same result when the assay is conducted with other plants. All S plants had an absorbance level <0.442. All plants with absorbance values ≥0.442 were resistant. In a few cases, however, R plants had absorbance values between 0.42 and 0.442, falling into the S group. Overall, in a ‘blind’ color evaluation of samples (light-dark pink=R; green-brown=S), the R individuals were identified correctly 80% of the time and S individuals were identified correctly 83% of the time. This ambiguity factor reflected the occasional overlap in absorbance between R and S plants, when R plants (unexplicably) showed low level of acetoin, producing a brown-colored supernatant. Nevertheless, all pink-colored supernatants were from R plants. Further research is needed to define the conditions that contribute to variability in the assay and the minimum number of technical and biological replicates needed to achieve high accuracy (e.g. 99%) of detection for Echinochloa.

 


ROLLED COVER CROP MULCH FOR SUPPRESSION OF AMARANTHUS PALMERI IN PICKLING CUCUMBER. S. J. McGowen*, K. M. Jennings, D. W. Monks, N. T. Basinger, S. C. Beam, M. B. Bertucci, S. Chaudhari, S. C. Reberg-Horton; North Carolina State University, Raleigh, NC (10)

ABSTRACT

Palmer amaranth (Amaranthus palmeri S. Wats.) has been ranked the most common and troublesome weed in pickling cucumber (Cucumis sativus L.) in NC. In addition to reducing cucumber yield and quality, Palmer amaranth can interfere with harvest and increase harvest costs. Herbicide options for controlling Palmer amaranth in pickling cucumber are limited, thus supplemental control by cultural tactics is warranted. A study was conducted at the Horticultural Crops Research Station in Clinton, NC to determine if cereal rye (Secale cereale L. ‘Wrens Abruzzi’) and oat (Avena sativa L.) cover crops suppress the emergence of Palmer amaranth in a no-till cucumber production system. Cover crops were planted in November, 2014 and terminated in March, 2015 with a broadcast application of 1,060 g ai ha­­-1 potassium salt of glyphosate and later rolled with a tractor mounted roller-crimper. On May 18, 2015, pickling cucumber was seeded using a no-till planter. Main plot treatments consisted of rye, oat, and no cover crop. Subplot treatments consisted of combinations of 1,260 g ai ha­­-1 ethalfluralin, 780 g ai ha­­-1 ethalfluralin plus 250 g ai ha­­-1 clomazone, and 40 g ai ha­­-1 halosulfuron applied preemergence (PRE) after seeding; 410 g ai ha­­-1 S-metolachlor and 530 g ai ha­­-1 pendimethalin applied postemergence (POST) at 1 to 2 lf cucumber stage; and 40 g ha­­-1 halosulfuron applied POST at 3 to 5 lf cucumber. Percent ground cover by cover crop residue and cucumber yield were greatest in the cereal rye cover crop, followed by oat and then bare ground, regardless of herbicide treatment. Averaged over the main plot treatments, cucumber yield and Palmer amaranth control were greatest in the weed-free treatment followed by 1,260 g ha­­-1 ethalfluralin PRE with 40 g ha­­-1 halosulfuron POST at 3 to 5 lf cucumber treatment and the 1,260 g ha­­-1 ethalfluralin PRE alone treatment.

*sjmcgowe@ncsu.edu

 


SUSTAINABLE CROPPING SYSTEMS FOR AVS-8080 VEGETABLE SOYBEAN IN ARKANSAS. S. E. Abugho*1, N. R. Burgos1, J. Ross1, T. Roberts1, D. Motes1, L. Earnest2, L. E. Estorninos Jr1; 1University of Arkansas, Fayetteville, AR, 2University of Arkansas, Rohwer, AR (11)

ABSTRACT

Sustainable cropping systems for AVS-8080 vegetable soybean in Arkansas*

S. E. Abugho, N. R. Burgos, T. Roberts, J. Ross, D. Motes, L. Earnest, L. E. Estorninos Jr.

Department of Crop, Soil and Environmental Sciences

University of Arkansas-Fayetteville

 

Vegetable soybean, popularly known as edamame, is increasing its popularity in the United States due to its health benefits. AVS-8080 edamame is commercially grown in Arkansas. It matures early and has large seed size.  Crop rotation, coupled with appropriate herbicide programs, is a potential tool for sustainable weed management in edamame, which can increase farm income and diversify local food sources.  A study was conducted at Kibler, Arkansas in 2014 and 2015 to determine feasible crop rotations with edamame including greenbeans (rotation 1), short season soybean (rotation 2), sweet corn (rotation 3), and edamame monoculture (rotation 4). S-metolachlor (1.12 kg ai ha-1) was applied to edamame and greenbeans as preemergence herbicide. Wheat was planted as fall cover crop on rotations 1, 2, and 4. Spinach was planted as fall-spring cash crop for rotation 3. Mesotrione (0.21 kg ai ha-1) and pyroxasulfone (0.12 kg ai ha-1) was applied preemergence for sweet corn and soybean, respectively. Fomesafen (0.26 kg ai ha-1) was applied to edamame at third trifoliate. Crop stand count, yield, and weed control were recorded. Fomesafen caused transient foliar necrosis (<20%) on edamame. Weed control and crop stand were good in both years. In 2014 edamame yield ranged from 167.5 - 352.3 kg ha-1. In 2015 edamame yield ranged from 163.8 - 282.7 kg ha-1. This study demonstrated that edamame can be grown as a double crop with sweet corn, greenbeans and soybean grown in Arkansas. Analyses of partial budgets to determine profitability will be included.

Nomenclature: edamame, crop rotation, yield

 


CROP SAFETY ASSESSMENT OF MUTAGENESIS-DERIVED ACCASE RESISTANT WHEAT LINES. C. M. Hildebrandt*, P. Westra, S. Haley, T. A. Gaines; Colorado State University, Fort Collins, CO (12)

ABSTRACT

In wheat cropping systems, competition with winter annual grass species such as jointed goatgrass (Aegilops cylindrica), downy brome (Bromus tectorum), and feral rye (Secale cereale) can be a major problem for managers.  To combat this problem, new technologies and chemistries are needed in order to give managers multiple options for grass control.  Through a forward genetics screen using an induced mutagenesis method, mutant lines of wheat resistant to the ACCase inhibitor quizalofop p-ethyl were previously characterized, and further crosses were performed to create breeding lines.  During the 2014-2015 growing season, a field crop safety trial was performed to assess these lines for relative levels of resistance and performance under two application timings, applied with and without a safener.  One quizalofop susceptible line, four two-gene (mutation on two genomes) breeding lines, and three one-gene parent lines were compared.  A split-split plot design was used in which quizalofop p-ethyl was applied at 92.5 g ai ha-1 with 1% MSO corresponding to the highest likely label application rate.  Applications were made at either tillering or jointing growth stages.  The two-gene breeding line CO14A065 showed the highest crop safety, with no changes from untreated control for any application timing or safener combination for yield, height, or visual injury (p<0.05).  The best performing one-gene parent line, AF28, showed reduced yield and height, as well as higher visual injury ratings without the presence of the safener, but was not different from the control when safener was applied (p<0.05).  Application after jointing made these reductions more pronounced.  The susceptible line showed 100% mortality in all treatments.  These results indicate that 2-gene lines will provide sufficient crop safety for likely quizalofop-p-ethyl applications to control winter annual grass weeds.

 


EVALUATION OF TANK-MIX OPTIONS FOR PROVISIA HERBICIDE IN PROVISIA RICE. J. S. Rose*, L. T. Barber, J. K. Norsworthy, R. C. Scott, Z. Lancaster, M. S. McCown; University of Arkansas, Fayetteville, AR (13)

ABSTRACT

Evaluation of Tank-Mix Options for Provisia Herbicide in Provisia Rice J.S. Rose*, L.T. Barber, J.K. Norsworthy, R.C. Scott, Z.D. Lancaster, M.S. McCown.

Barnyardgrass control in rice is becoming increasingly difficult as a result of increased resistance to common herbicides.  BASF is currently developing a new non-GMO rice trait that will provide rice tolerance to quizalofop, an acetyl coenzyme A carboxylase (ACCase)-inhibiting herbicide. Along with this new trait BASF will be marketing the herbicide quizalofop under the tradename Provisia. An experiment was conducted in 2015 at the Southeast Research and Extension Center in Rowher, AR (SEREC) and at the Rice Research and Extension Center (RREC) near Stuttgart, AR to evaluate early postemergence (EPOST) tank mixtures containing Provisia herbicide in Provisia rice. In this study, nine common rice herbicides were evaluated in combination with Provisia herbicide for weed control and crop tolerance. Tank mixture candidates included: quinclorac at 0.042 kg ai/ha (32 oz/A) (Facet), pendimethalin at 1.12 kg ai/ha (46.5 oz/A) (Prowl 3.3), saflufenacil at 0.0187 kg ai/ha (0.75 oz/A) (Sharpen), carfentrazone at 0.056 kg ai/ha (0.75 oz/A) (Aim), penoxsulam at 0.042 lb ai/A (2.4 oz/A) (Grasp), bispyribac at 0.052 kg ai/ha (0.93 oz/A) (Regiment), halosulfuron at 0.052 kg ai/ha (1 oz/A) (Permit), propanil+quinclorac at 3.0+0.0233 kg ai/ha (96 oz/A) (Duet), and propanil+thiobencarb at 2.25+2.25 kg ai/ha (96 oz/A) (Ricebeaux). All treatments were applied at the 1- to 3-leaf stage of rice (EPOST) and followed by (fb) quizalofop at .120 kg ai/ha (15.5 oz/A) (Provisia) applied prior to flooding (PREFLD). As a result of some tank mixes (Aim or Sharpen), slight injury was observed on Provisia rice at both locations; however, no more than 10% injury was observed with any tank mixture. At both locations, weed control was evaluated on barnyardgrass and red rice. In addition, Amazon sprangletop and some off-type rice cultivars were evaluated at Rowher location. At 22 days after the EPOST application, the greatest barnyardgrass control was seen in those tank mixes that contained more than one mode of action, such as the addition of halosulfuron, at both locations, however these differences were no longer present 10 days following a mid-post application. There was a similar story with the control of Amazon sprangletop where increased control was seen when a tank mix was made with Provisia. At the Rohwer, location there was some possible antagonism seen when propanil+quinclorac was mixed with Provisia with ≤ 60% control of barnyardgrass or Amazon sprangletop being observed. There was some variation in red rice control seen between locations at the Rohwer location, >89% red rice control was observed with all tank mixtures and Provisia alone after the first application and 99% control after the second application timing. Whereas in Stuttgart, only 75%-90% control of red rice was seen after the first application and similar results after the second application timing. After the two application timings, 99% control was seen of all off-type rice cultivars. From these results, we conclude that having a tank mixing partner, with Provisia is beneficial in controlling weedy grasses and off-type rice cultivars, including red rice.


EVAULATION OF A BENZOBICYCLON PLUS HALOSULFURON PREMIX FOR WEED CONTROL IN DRILL-SEEDED RICE. M. L. Young*, J. K. Norsworthy, C. J. Meyer, J. A. Godwin, R. R. Hale; University of Arkansas, Fayetteville, AR (14)

ABSTRACT

Gowan Company is developing a new rice herbicide for post-flood control of problematic weeds that will likely be sold under the tradename of Rogue. Rogue will contain a mixture of halosulfuron (Group 2) and benzobicyclon (Group 27) herbicides and will control a broad-spectrum of grasses, aquatics, broadleaves, and sedges, including those currently resistant to Group 2 herbicides.  If labeled as expected, this will be the first 4-hydroxyphenylpyruvate dioxygenase (HPPD) herbicide commercially available in U.S. rice production. A field study was conducted in 2014 and 2015 at the Rice Research and Extension Center near Stuttgart, Arkansas to understand if the addition of halosulfuron (Permit) to benzobicyclon would increase the level of weed control compared to benzobicyclon alone for many of the most common and problematic weeds of rice. Herbicide treatments included halosulfuron at 35 and 53 g ai/ha, benzobicyclon at 247 and 371 g ai/ha, and a mixture of the two low rates and two high rates of both herbicides along with a nontreated. Benzobicyclon alone was effective in controlling Amazon sprangletop, ducksalad, California arrowhead, rice flatsedge, and smallflower umbrellasedge.  The addition of halosulfuron to benzobicyclon generally improved control of weeds that were marginally controlled by benzobicyclon alone.  The low rate combination of benzobicyclon plus halosulfuron was often as effective as the high rate of benzobicyclon alone.  The results of this study suggest that benzobicyclon premixed with halosulfuron has potential for control of a wide array of problematic weeds in Arkansas rice and could be used as an additional tool for control of herbicide-resistant weeds.

 


EXAMINING THE POTENTIAL FOR INSECTICIDE SEED TREATMENTS TO REDUCE INJURY ASSOCIATED WITH HERBICIDE APPLICATION IN SOYBEAN AND GRAIN SORGHUM. N. R. Steppig*, J. K. Norsworthy, M. L. Young, R. R. Hale, S. Martin, J. A. Godwin; University of Arkansas, Fayetteville, AR (15)

ABSTRACT

Insecticide seed treatments have been shown to partially safen rice against drift from imazethapyr or glyphosate.  These results are of great interest as herbicide programs diversify to better control herbicide-resistant weeds. Diversification includes use of non-selective, postemergence herbicides like glyphosate and glufosinate, as well as herbicides with soil-residual activity. Both types of herbicides can potentially damage crops, either via drift or carryover in soil, and a method for reducing off-target injury in crops would provide benefits for producers who find themselves in situations where crops are particularly injury-prone. In order to examine potential similarities to results demonstrated earlier in rice, field studies were conducted at the Lon Mann Cotton Research Station in Marianna, Arkansas in 2015 with soybean and grain sorghum. Two field trials were conducted to evaluate the potential for insecticide seed treatment to lessen injury following drift to soybean and grain sorghum. Drift events were simulated by applying 1/10x labeled rates of 8 herbicides in soybean and 3 in grain sorghum to plants approximately three weeks after planting (WAP). Two insecticide seed treatments, thiamethoxam+fludioxonil+mefonoxam (CruiserMaxx®) and clothianidin (NipsIt INSIDE®) were applied to soybean and sorghum, with grain sorghum trial having imidacloprid (Gaucho®) as an additional seed treatment. Two other field trials were conducted to evaluate injury reduction from herbicide carryover with 9 herbicides in soybean and 3 in grain sorghum with the thiamethoxam+fludioxonil+mefonoxam seed treatment in both crops. Herbicide carryover was simulated by applying reduced rates of soil-residual herbicides the same day both crops were planted. All four tests consisted of a randomized complete block design and visual estimates of crop injury were taken at 1, 2, and 4 weeks after application. There was minimal safening in soybean and grain sorghum to most of the herbicides evaluated. In soybean, there was a significant reduction in injury caused by halosulfuron when the seed were treated with clothianidin or thiamethoxam+fludioxonil+mefonoxam. No other herbicide/insecticide combination resulted in reduced a significant reduction in injury.  These trials will be repeated in 2016 across multiple sites to see if there is an environmental interaction that could have impacted the 2015 results.     


WILL AN INSECTICIDE SEED TREATMENT REDUCE INJURY TO CLEARFIELD RICE CAUSED BY ALS-INHIBITING HERBICIDES? S. M. Martin*1, J. K. Norsworthy1, G. M. Lorenz2, J. Hardke3, R. C. Scott1, C. J. Meyer1, P. Tehranchian1; 1University of Arkansas, Fayetteville, AR, 2University of Arkansas, Lonoke, AR, 3University of Arkansas, Stuttgart, AR (16)

ABSTRACT

Increased use of insecticide seed treatments in rice have brought up many questions about the potential benefits of these products.  In 2014 and 2015, a field experiment was conducted at the Rice Research and Extension Center near Stuttgart, Arkansas and at the University of Arkansas Pine Bluff Farm near Lonoke, Arkansas, to evaluate whether an insecticide seed treatment could lessen injury from acetolactate synthase (ALS)-inhibiting herbicides in Clearfield® rice.  Two varieties were tested (a hybrid variety, CLXL 745 and a conventional variety, CL152) with and without an insecticide seed treatment (CruiserMaxx® Rice).  Four different herbicide combinations were evaluated (a non-treated check, two applications of Regiment®, two applications of Newpath®, and two applications of Newpath® plus Regiment®).  The first herbicide application was early postemergence (1- to 2-leaf rice), and the second application was prior to establishing the permanent flood (preflood).  At 2 and 4 WAT, the rice treated with CruiserMaxx Rice and two applications of Newpath plus Regiment showed less injury than the rice treated with the fungicide-only seed treatment with the same herbicide program when averaged across varieties.  At 4 WAT, CLXL 745 had significantly more injury than CL 152 when averaged over herbicide treatments. Rice did recover from the herbicide injury in all plots by the end of the season and yields within a variety were similar with and without a seed treatment across all herbicide treatments.  Rough rice yields averaged over seed treatments and herbicides were 160 bu/A for CL152 and 230 bu/A for CLXL745.  These results show that repeated applications of ALS-inhibiting herbicides can cause injury to Clearfield® rice, especially CLXL745, but rice is able to recover from this injury without an adverse effect on yield. 

 


RICE TOLERANCE TO SHARPEN: INFLUENCE OF RATE, TIMING, AND ADJUVANTS. R. R. Hale*, J. K. Norsworthy, L. T. Barber, M. G. Palhano, J. A. Godwin Jr., M. R. Miller; University of Arkansas, Fayetteville, AR (17)

ABSTRACT

Sharpen is a contact herbicide and a postemergence option for broadleaf weed control in rice.  To achieve optimum weed control, it is beneficial to include an adjuvant in combination with Sharpen.  Currently in AR, Sharpen at 1 oz/A + methylated seed oil (MSO) at 1 pt/A is recommended as a pre-plant or preemergence option.  Sharpen at 1 oz/A + 1% v/v crop oil concentrate (COC) can be applied in crop from the 2-lf rice stage through panicle initiation.  Current recommendations do not include the use of MSO in crop nor the use of COC at 1 qt/A, but this additional adjuvant may aid in weed control which would be beneficial.  Hence, a field study was conducted at the Pine Tree Research Station near Colt, AR to evaluate the rice tolerance to Sharpen with COC and MSO at 1 pt/A and 1 qt/A, and when tank-mixed with Facet L at 43 fl oz/A.  Applications were made using a CO2-pressurized backpack sprayer calibrated to 15 GPA.  Treatments were arranged in a randomized complete block design and applied at different growth stages including: 1-lf rice, 3-lf rice, 0.5-inch internode elongation, and 3 to 4 inch joint.  Only main effects of adjuvant, Facet use, and application timing were significant for rice yield.  In general, rice injury increased with the addition of MSO to Sharpen over the addition of COC to Sharpen; however, this increase in injury did not translate into a reduction in yield.  Plots receiving applications containing Sharpen plus COC at 1 pt/A had yields of 163 bu/A while rice yields of 155 bu/A were observed when Sharpen was applied with MSO at 1 pt/A.  The 1 qt/A rate of MSO and COC resulted in rice yields comparable to the lower use rate for each adjuvant.  Applications made at the 0.5-inch internode elongation stage or earlier showed no differences in rice yield which was 20 to 23 bu/A greater than when Sharpen was applied at the 3 to 4 inch joint stage.  Based on these results, a reduction in yield can be observed when Sharpen is applied beyond the 0.5-inch internode elongation growth stage, and while MSO may increase rice injury this does not translate to yield loss.


WEED CONTROL AND CROP TOLERANCE OF INZEN GRAIN SORGHUM WHEN TREATED WITH ALS INHIBITING HERBICIDES. H. C. Foster*1, D. B. Reynolds1, J. D. Smith2; 1Mississippi State University, Starkville, MS, 2DuPont Crop Protection, Madison, MS (18)

ABSTRACT

WEED CONTROL AND CROP TOLERANCE OF INZEN GRAIN SORGHUM WHEN TREATED WITH ALS INHIBITING HERBICIDES.  H. C. Foster1, D. B. Reynolds2, J. D. Smith3, 1Mississippi State University, Starkville, MS, 2Mississippi State University, Starkville, AR, 3DuPont Crop Protection, Madison, MS.

ABSTRACT

Weed management is a continuous challenge for growers, and continual innovation is essential to maintain the effectiveness of management technologies.  With the creation of InzenTM Z herbicide-tolerant sorghum trait, there is hope that growers will have greater ability to control yield-limiting grass weeds in grain sorghum, or milo.  Inzen is a non-genetically modified (GMO) trait, meaning it will not be subject to the regulations imposed on transgenic products by USDA and unaccepted by some international communities.  That presents international marketing opportunity for sorghum crops that will be grown from hybrids containing the traits.  Some of the herbicides to be used for control of grass weeds in the grain sorghum include: nicosulfuron (Zest), rimsulfuron (Leadoff®), thifensulfuron and metolachlor + atrazine (Cinch ATZ®).

This study was conducted to observe the effectiveness of Zest, Leadoff ®, and Cinch ATZ ® on grasses and broadleaves, as well as observe any injury to the sorghum.  The study was conducted in Brooksville, MS.  The Inzen sorghum was arranged in plots 3.85 m x 12.19 m (four row plots) with the two middle rows being treated.  Zest, Leadoff® and Cinch ATZ® were applied at different application times to determine if weed control and crop safety would vary.  Visual evaluations were collected 7, 14, 21, 28, and 35 days after treatment (DAT).  The study was analyzed in SAS 9.4 using PROC GLIMMIX with α =0.05.

The results of this study show that at 14 DAT, Cinch ATZ at 3.20 pt./A + Abundit Extra at 32 fl oz./A applied at pre-emergence and Zest at 12 fl oz./A + Atrazine 4L at 0.75 qt./A + Crop Oil at 1.0% v/v + Amsul at 2.0 lbs./A applied at mid-post had slightly less significant control of the pitted morning glory population.  Likewise, Abundit Extra at 32 fl oz./A applied at pre-emergence and Zest at 12 fl oz./A + Atrazine 4L at 0.75 qt./A + Crop Oil at 1.0% v/v + Amsul at 2.0 lbs./A applied at early post showed slightly less control of the pitted morning glory population.  By 28 DAT, all treatments showed equal control of the pitted morningglory population.  There was slight injury shown 28 DAT to the sorghum applied with each herbicide treatment, but injury was insignificant.  Overall, the effectiveness of Zest, Leadoff®, and Cinch ATZ® on grasses and broadleaves was excellent compared to the untreated check.  

 


EVALUATION OF DOUBLE-CROPPED PEANUT AND TOBACCO AFTER AUTUMN OR WINTER APPLICATIONS OF PYRASULFOTOLE TO WINTER WHEAT. A. A. Diera*1, T. L. Grey2, K. S. Rucker3, W. Vencill1, T. M. Webster4, C. L. Butts5, J. Moore2; 1University of Georgia, Athens, GA, 2University of Georgia, Tifton, GA, 3Bayer Crop Science, Tifton, GA, 4USDA-ARS, Tifton, GA, 5USDA-ARS, Dawson, GA (19)

ABSTRACT

Acetolactate synthase (ALS)-resistant annual weeds have become more prevalent  in winter wheat (Triticum aestivum L.) production in the southeastern United States, investigating alternative herbicide mechanisms of action to control broadleaf weed species grows increasingly more critical.  Little information is known about the residual activity of the herbicide pyrasulfotole used in wheat production.  This study was designed to examine pyrasulfotole residual activity on peanut (Arachis hypogaea L.) and tobacco (Nictoiana tabacum L.) when rotated with winter wheat.  Trials were conducted from November 2014 through October 2015 at three locations in southern Georgia:  Tifton (Tift loamy sand); Dawson (Greenville sandy loam); and Plains (Faceville sandy clay loam).  After killing wheat with glyphosate, peanut beds were strip-tilled, planted, and evaluated for emerged plant counts, leaf diameter (cm), and yield (kg/ha).  In Tifton and Dawson, tobacco was conventionally tilled, planted, and evaluated for emerged plant emerged plant counts, leaf and plant diameter (cm), leaf count, fresh stalk weight (kg), and fresh cut plant weight (kg).   At the labeled use rate of 300 g ai/ha, pyrasulfotole did not cause peanut and tobacco injury from November and January applications (3 and 5 months prior to planting).  Differences in peanut and tobacco yields were observed among locations, but this was most likely due to environmental conditions unaccounted for within the scope of this study.  Future work will continue to evaluate the safety of pyrasulfotole on other crops rotated with winter wheat.


 


PRE HERBICDES APPLIED EPOST IN SORGHUM: EFFICACY AND CROP TOLERANCE. W. J. Everman, L. Vincent, J. T. Sanders*; North Carolina State University, Raleigh, NC (20)

ABSTRACT

 

Grass weed control continues to be one of the greatest challenges in sorghum production in North Carolina. Several products are currently labeled for POST broadleaf weed control, however, only one product is currently labeled for POST grass control. In order to determine the best use pattern for quinclorac, a series of experiments were conducted. In 2015, a study was performed at two research stations in North Carolina which evaluated the performance of atrazine and several preemergence (PRE) herbicides paired with quinclorac at the EPOST timing in order to gauge crop safety, weed control and yield in grain sorghum. At each location, the study was arranged as a randomized complete block design with 8 treatments and 4 replications. Treatments consisted of an atrazine PRE followed by quinclorac, quinclorac + a residual herbicide, or quinclorac + a residual +atrazine applied to sorghum 10-18cm in height. The addition of atrazine caused significant but transient stunting of the crop in its early stages, but significantly improved yield. In addition, control of Urochloa platyphylla (broadleaf signalgrass) and Digitaria sanguinalis (large crabgrass) was enhanced with both the addition of residual herbicides to quinclorac and with the further addition of atrazine to those mixtures.


SURVEYING FOR HERBICIDE RESISTANCE IN ITALIAN RYEGRASS COLLECTED FROM EASTERN TEXAS WHEAT FIELDS. R. A. Garetson*1, J. Swart2, P. Baumann3, C. Jones4, M. V. Bagavathiannan1; 1Texas A&M University, College Station, TX, 2Texas A&M AgriLife Extension, Commerce, TX, 3Texas A&M AgriLife Extension, College Station, TX, 4Texas A&M University, Commerce, TX (21)

ABSTRACT

Italian ryegrass (Lolium perenne ssp. multiflorum) is a serious weed issue in Northeast Texas wheat production. Herbicides, particularly the acetolactatesynthase (ALS)- and acetyl-CoA carboxylase (ACCase)-inhibitors have been relied on heavily for effective management of this species. Growers and crop consultants have reported failure of these herbicides on Italian ryegrass due likely to the evolution of resistance in this species. The goal of this research was to survey the distribution of Italian ryegrass in the region and determine the prevalence of herbicide resistance in them. A semi-stratified survey methodology was followed.  A total of 116 survey sites were visited across the eastern and central Texas Blacklands prior to wheat harvest in spring 2015. Ryegrass seed samples were collected from across 15 to 20 randomly selected plants in each field. The samples were brought to the laboratory, air dried, thrashed and planted in greenhouse beds for conducting herbicide assays. Seeds from each population were planted in pots (4 replications) containing potting soil mix and thinned to five healthy seedlings per pot prior to herbicide application at the 2-3 leaf seedling stage. Herbicide assays were conducted at 2X the field rate for mesosulfuron-methyl (Osprey®; 1X rate – 14.5g ai/ha), diclofop-methyl (Hoelon®; 1X rate - 375g ai/ha), and pinoxaden (Axial® XL; 1X rate - 59g ai/ha). A non-treated control and a known susceptible population were used as standards for comparison. Results reveal the widespread infestation of Italian ryegrass in the region, found infesting 58 out of the 116 survey sites (50%). Preliminary herbicide evaluations on a handful of samples have indicated the presence of herbicide resistance in these samples. One population, collected near Commerce, TX has exhibited resistance to all the three herbicides at the 2X rate. Dose-response assays have confirmed survival of this population for up to 64X rate of diclofop-methyl and mesosulfuron-methyl, and for up to 4X for pinoxaden. The spread of multiple herbicide resistant ryegrass will limit the herbicide options available for effective control of this species and emphasizes the critical need for diversified tactics.



TRINEXAPAC-ETHYL WINTER WHEAT CULTIVAR EVALUATIONS WITH VARIABLE RATES OF NITROGEN. D. B. Simmons*1, T. L. Grey2, W. Faircloth3, W. Vencill1, T. M. Webster4; 1University of Georgia, Athens, GA, 2University of Georgia, Tifton, GA, 3Sygenta, Albany, GA, 4USDA-ARS, Tifton, GA (22)

ABSTRACT

Trinexapac-ethyl Winter Wheat Cultivar Evaluations with Variable Rates of Nitrogen.1Danielle Simmons*, 2Timothy L. Grey, 3Wilson Faircloth, 2William Vencill, 4Theodore M Webster; 1Graduate Student, University of Georgia, Athens, GA, 2University of Georgia, Athens, GA, 3Syngenta Crop Protection, Greensboro, NC, 4USDA-ARS, Tifton, GA.

In Georgia, winter wheat (Triticum aestivum) is a widely used grain crop for many row cropping systems. From 2012 to 2015 Georgia farmers planted approximately 127,481 ha each year while harvesting 98,882 ha. Plant growth regulators for wheat, such as trinexapac-ethyl, could assist growers by improving yield, canopy development, harvest ability, and reduce potential for lodging of the stalk. The objectives of this study were to evaluate the effect of trinexapac-ethyl (TE), nitrogen fertilization (N), and cultivars on plant growth and yields of winter wheat. The experiment was carried out in a randomized block design with four replications that have three factorials that include: four trinexapac-ethyl rates (non-treated, 233 g ai ha-1, 256 g ai ha-1, and 128 g ai ha-1 + 128 g ai ha-1) rates, two N fertilizer rates (112 kg/ha N and 168 kg/ha N), and five cultivars (Coker 9550, Coker 9700, Cypress, AGS 2060, and AGS 2026) of winter wheat. Two way interactions were done with each of the three factorial categories and combined across all variables, but none of the interactions between the factorials were statistically significant. The study suggested that the only significant TE rate was the split application of 128 g ai ha-1 + 128 g ai ha-1 in which height, or stem length, was reduced. Winter what yield ranged from 2957 kg/ha to 3918 kg/ha in the five cultivars, with Coker 95 having the greatest yield and AGS 2060 having the smallest yield. The two different N fertilizer rates have distinct yield differences with the larger rate creating the larger yield, but overall those differences were not significant. Winter wheat yield ranged between 3468 kg/ha and 3656 kg/ha from the four trinexapac-ethyl treatments; however, the highest yield of 3656 kg/ha came from the non-treated treatment, so it can be stated that none of the treatments improved yield. Future studies should include different varieties and treatments of plant growth regulators, along with different fertilizer amounts to see if N fertilizer or PGRs have an effect on the yield and growth of winter wheat. Email:dsimmo10@uga.edu

  

 


RESIDUAL AMARANTHUS SPP. CONTROL WITH VLCFA HERBICIDES. M. M. Hay*, D. E. Peterson, D. E. Shoup; Kansas State University, Manhattan, KS (23)

ABSTRACT

Increased herbicide resistance in Palmer amaranth (Amaranthus palmeri) and common waterhemp (Amaranthus rudis) across multiple herbicide sites of action (SOA) has required a change in management to facilitate weed control. Very Long-Chain Fatty Acid Inhibitor (WSSA SOA 15) and, Microtubule Inhibitor (WSSA SOA 3) herbicides commonly have been used for residual grass control for many years, but also can provide residual control of Amaranthus spp.  In general, there is minimal confirmed weed resistance and no confirmed Amaranthus spp. resistance to these SOA’s in Kansas. Therefore, these herbicides could be very beneficial to help manage Amaranthus spp. in Kansas. Field experiments were established in 2015 near Manhattan and Ottawa, Kansas, to assess residual control of Amaranthus spp. with SOA 3 and 15 herbicides. Pyroxasulfone, dimenthenamid-P, s-metolachlor, metolachlor, acetachlor, and pendimethalin were applied at three different field use rates (high, mid, and low) to tilled soil based on labeled rate ranges for use for soybeans. The experiment was a randomized complete block design with a factorial arrangement of herbicides and rates with four replications. All treatments were applied pre-emerge (PRE) after the plot was clean tilled with a field cultivator and herbicide applications were made June 1 at Manhattan and June 8 at Ottawa. Percent weed control was visually evaluated weekly from two to eight weeks after treatment (WAT) on a scale of 0% for no control and 100% for complete control. Soil was a silt loam texture at both locations.  All data were subjected to ANOVA PROC MIXED SAS at α = 0.05 to test for significance of herbicide, rate, and time main effects and their interactions, with time treated as a repeated measure.

All treatments at Ottawa, except the low and mid rates of pendimethalin, were not significantly different due to a sparse and inconsistent population of common waterhemp. Palmer amaranth populations at Manhattan exceeded 100 plants m-1. Factorial analysis at each evaluation date revealed significant interaction between herbicide and rate only at 3 and 5 WAT, and analysis over all evaluations with time as a repeated measure revealed no significant 2- or 3-way interactions involving herbicide, rate, or time. Therefore, herbicide efficacy was compared using grand means across all evaluation times and rates. Pyroxasulfone, s-metolachlor, and dimenthenamid-P resulted in greater than 90% efficacy of Palmer amaranth control, followed by metolachlor, acetachlor, and pendimethalin in descending order of efficacy. Using the grand means, herbicides at the low rate resulted in significantly reduced efficacy with 72% control of Palmer amaranth compared to the mid and high rates; however, weed suppression at the mid and high rates were not significantly different with near 80% control of Palmer amaranth.

As a result of these observations, SOA 15 herbicides such pyroxasulfone, s-metolachlor, and dimenthenamid-P offered the highest level of Palmer amaranth control as opposed to metolachlor, acetachlor, and pendimethalin. Regardless of active ingredient, the low rate resulted in the reduced Palmer amaranth control when compared to the mid and high rates.

 


CULTURAL PRACTICES TO SUPPORT PALMER AMARANTH MANAGEMENT IN MICHIGAN. K. M. Rogers*, C. L. Sprague, K. A. Renner; Michigan State University, East Lansing, MI (24)

ABSTRACT

Cultural Practices to Support Palmer Amaranth Management in Michigan

Herbicide-resistant Palmer amaranth continues to be a threat to Michigan field crop growers. In addition to herbicide-resistant issues, Palmer amaranth’s ability to emerge throughout the growing season and its rapid growth rate makes it extremely difficult to manage with herbicides alone. One potential approach to improve management of herbicide-resistant Palmer amaranth in soybean is to incorporate the use of additional cultural practices, such as narrow row widths and cover crops. A field experiment was established in the fall of 2014 near Middleville, Michigan in a field with a confirmed glyphosate-resistant Palmer amaranth population. The objectives of this research were to examine the effects of: 1) a cereal rye cover crop, 2) cover crop termination method, 3) soybean row width and 4) herbicide programs on Palmer amaranth management and soybean yield. The experiment was a split-split-plot design with the main plots: 1) cereal rye cover crop terminated in the spring with flail mowing, 2) cereal rye cover crop terminated in the spring with glyphosate, and 3) no cereal rye cover. The sub-plots were soybean planted in two different row widths: 1) 19 cm and 2) 76 cm rows. The sub-sub-plots included three different Palmer amaranth management strategies: 1) no management, 2) low management strategy (flumioxazin PRE fb. glufosinate POST), and 3) high management strategy (flumioxazin PRE fb. glufosinate + acetochlor POST). Each plot was replicated 4 times. Cereal rye planted on October 23 produced 120 g m-2 of dry biomass (1200 kg/ha) and suppressed winter annual and early summer annual weed biomass 77% compared with the no cover control at the time of termination in mid-April at the Feeke’s stage 6. Cereal rye was not controlled by flail mowing and produced an additional 128 g m-2 of dry biomass by the following week before being terminated by glyphosate. Overall, the cereal rye cover crop and termination method had minimal effects on Palmer amaranth control. Palmer amaranth was controlled throughout most of the season in the low and high Palmer amaranth management systems. Soybean canopy closure occurred 16 days earlier in the 19 cm row width which reduced the number of late emerging Palmer amaranth plants by 52% compared with 76 cm rows. Soybean yields were highest in the high management system in narrow rows (3874 kg ha-1) and with no cover crop (4002 kg ha-1). The lack of cover crop effect on Palmer amaranth management in this study may be due to the low cereal rye biomass produced. Palmer amaranth emergence occurred on June 16, 33 days after cereal rye termination. Planting soybean in narrow rows was a more effective management strategy than planting a cereal rye cover crop in the first year of our research.

 


SEQUENTIAL TIMING APPLICATIONS FOR RESCUE CONTROL OF PALMER AMARANTH. D. Denton*1, D. M. Dodds1, C. A. Samples2, M. T. Plumblee2, L. X. Franca2, A. L. Catchot1, T. Irby2, J. A. Bond3, D. B. Reynolds2; 1Mississippi State University, Mississippi State, MS, 2Mississippi State University, Starkville, MS, 3Mississippi State University, Stoneville, MS (26)

ABSTRACT

Sequential Timing Applications for Rescue Control of Palmer Amaranth (Amaranthus palmeri).  A.B. Denton, D.M. Dodds, C.A. Samples, M.T. Plumblee, L.X. Franca, A.L. Catchot, T. Irby, J.A. Bond, D.B. Reynolds; Mississippi State University, Mississippi State, Mississippi.

 

            Glyphosate-resistant (GR) Palmer amaranth was first reported in 2005 in Georgia.  Since that time, GR-Palmer amaranth has spread throughout the Mid-South and southeastern U.S.  Growers have been forced to dramatically alter weed control practices in areas where this weed is problematic.  Crops that are tolerant to glyphosate, glufosinate, and dicamba are under development.  While timely herbicide applications will be critical with this technology, timely herbicide applications are not always feasible due to unforeseen circumstances such as weather.  Therefore, data is needed regarding control of GR-Palmer amaranth that is larger than recommended at the time of herbicide application.

            This research was conducted in 2014 and 2015 at Hood Farms in Dundee, MS and at the Delta Research and Extension Center in Stoneville, MS in 2015 to determine the effect of timing between sequential applications and herbicide combinations on GR-Palmer amaranth control.  The experiment was initiated in fields with heavy natural infestations of GR-Palmer amaranth.  Herbicide applications were initiated when Palmer amaranth plants were 20 to 25 cm in height and 40 to 50 cm in height. A sequential application for each growth stage was made at five different timings which included 1, 2, 3, 4 and 5 weeks after initial treatment of each growth stage.  Treatments utilized in this experiment included: glyphosate + dicamba at 0.8 kg ae/ha and 0.6 kg ai/ha as well as glufosinate + dicamba at 0.6 kg ai/ha each.

            Treatments containing glyphosate + dicamba significantly increased height reduction (≥48%) when applied to 20 to 25 cm GR-Palmer amaranth when data were pooled across sequential timing as well as two weeks after final application.  Four weeks after final applications, GR-Palmer amaranth height reduction was significantly greater when applications were made ≤ 1 week after initial treatment with height reductions ranging from 55 to 56% for plants initially treated at 20 to 25 cm in height.  Sequential applications containing glufosinate + dicamba provided more consistent control of 40 to 50 cm Palmer amaranth.  Sequential herbicide applications provided effective rescue control of Palmer amaranth which may help facilitate crop harvest and minimize Palmer amaranth seed production.  abd93@msstate.edu

 


COMMON RAGWEED (AMBROSIA ARTEMISIIFOLIA L) INTERFERENCE IN NEBRASKA SOYBEANS. E. R. Barnes*1, A. Jhala1, S. Knezevic1, P. H. Sikkema2, J. L. Lindquist1; 1University of Nebraska-Lincoln, Lincoln, NE, 2University of Guelph, Ridgetown, ON (27)

ABSTRACT

Common ragweed (Ambrosia artemisifolia L.) is an early emerging and competitive annual weed species in soybean (Glycine max) production fields in much of the north central US and Canada. A field experiment was conducted in 2015 at the University of Nebraska-Lincoln’s Agriculture Research and Development Center to assess common ragweed interference in soybean as influenced by variable water supply. Experimental treatments included common ragweed sown at densities of 0, 2, 6, and 12 weeds/m-1 row in soybean and a density of 2 weeds/m-1 without soybean. Three irrigation treatments were established to achieve full, half, or zero replacement of predicted evapotranspiration using SoyWater (http://hprcc-agron0.unl.edu/soywater/). Irrigation treatments were established based on distance from a solid set sprinkler irrigation system. Periodic destructive sampling of crop and weed leaf area index and dry biomass, and regular measurements of plant height, soil water content, and final yield were taken. Because of adequate rainfall in 2015, there was no significant effect of irrigation treatment. Soybean yield was reduced up to 100% as common ragweed density increased, and yield loss was tightly correlated to common ragweed density, LAI, and total aboveground biomass. These relationships were best described using a hyperbolic yield loss model. The study will be repeated in 2016.

 


NEXT DAY AIR: WATERFOWL AND WEED SEED DISTRIBUTION. J. A. Farmer*, M. D. Bish, A. Long, M. Biggs, K. W. Bradley; University of Missouri, Columbia, MO (28)

ABSTRACT

Migratory waterfowl have often been implicated in the movement of troublesome agronomic weed species. Previous research has shown that migratory waterfowl have the ability to transport invasive wetland weed species. However, little to no research has been conducted to investigate the long-distance dispersal of agronomic weed species such as Palmer amaranth and waterhemp. Thus, two objectives were set forth for this research project. The first was to determine what weed species are being transported throughout Missouri by ducks and snow geese. Beginning in the fall of 2014, 238 ducks and 111 snow geese were collected from Missouri waterfowl hunters. These birds were dissected to remove weed seed from each bird’s esophagus, gizzard and intestines. Recovered seeds from each section were then planted by individual organ section in the greenhouse. Emerged seedlings were identified by species, counted, and removed from the flats every 2 weeks for 3 months. Almost 14,400 weeds representing over 50 distinct species emerged from the digestive tract contents of the hunter-harvested ducks. The three species representing the largest portion of the emerged weeds were barnyardgrass, Amaranthus species, and smartweed species at 5494, 4311, and 3454, plants respectively. Waterhemp made up the second largest recovered species within the esophagus, gizzard and intestines at 38, 11, and 19%, respectively. From the hunter-harvested snow geese, 87 plants emerged representing 12 species. The three plants most commonly recovered from all dissected organs were corn, smartweed species and Amaranthus species at 45, 30, and 9% respectively. Palmer amaranth was one of the Amaranthus species recovered from the snow goose intestines. These results indicate that waterfowl, particularly ducks, are consuming many agronomic weeds, including waterhemp and Palmer amaranth, and transporting them throughout Missouri with the potential to disperse these seeds over long distances. The second objective of this study was to determine the recovery rate and viability of 13 agronomic weed species after passage through a duck’s digestive system. A feeding study was conducted on live mallards in the summer of 2015 and repeated in the fall of 2015. Adult mallards were precision fed 1-gram meals of a known quantity of seed from 1 of 13 different agronomically important weed species. The ducks were placed into individual cages immediately after feeding where each duck’s fecal samples were collected every 4 hours up to 48 hours after feeding. The experimental design consisted of an incomplete block design of 13 treatments and 4 replications of the feeding experiment.  Across the 4 replications, no two ducks were fed the same 4 weed species as another duck. Each weed species was fed to an equal number of male and female mallards. The fecal samples were rinsed in sieves and recovered seed was collected, counted, and stored for future viability testing. Data was subjected to analysis through a PROC GLIMMIX procedure in SAS using a logit link function and means were separated using Fisher’s Protected LSD (P<0.05). Data from the feeding study also supported the potential for long-distance dispersal of weed seed through waterfowl consumption.  Intact seed was recovered from 11 of the 13 weed species fed. Waterhemp and Palmer amaranth seed recovery was 19 and 12%, respectively, within the 48 hour monitoring period. These preliminary results show the potential for waterfowl to provide long-distance dispersal of agronomic weed species. Future plans include testing the viability of seed recovered in the feeding study as well as a second year of collecting ducks and snow geese from Missouri waterfowl hunters.

 


WATERHEMP GROWTH AND DEVELOPMENT IN A COMMON GARDEN. J. M. Heneghan*, W. G. Johnson; Purdue University, West Lafayette, IN (29)

ABSTRACT

Waterhemp (Amaranthus tuberculatus var. rudis) is a small-seeded broadleaf weed that is problematic in agronomic crops across much of the Midwest. Waterhemp exhibits discontinuous germination and produces large amounts of seed. These characteristics can lead to plants of varying sizes to be present in field settings and can also lead to rapid growth and dense populations. A common garden experiment was established in 2014 and 2015 to evaluate the phenology of waterhemp populations from Indiana, Illinois, Missouri, Iowa, and Nebraska. Seeds were germinated in the greenhouse and later transplanted in the field at three different timings to simulate discontinuous germination. The first planting was planted to simulate initial spring emergence in early May. The second and third planting were planted 21 days before and after the summer solstice, respectively. Seedlings were transplanted to the field 12-15 days after greenhouse planting. Weekly height measurements were taken from 12 plants in every plot and end of season biomass accumulation and seed yield was recorded. In the pooled data set, there were no differences between the first and second plantings in biomass accumulation, but the third planting accumulated less. In 2014, there were no differences between the first and second planting in seeds g-1, but there were fewer seeds g-1 from the third planting, indicating larger seeds. Within the first and second planting, there were no differences among populations in biomass accumulation. In the third planting, Missouri and Illinois biotypes accumulated the greatest biomass with 338 and 283 g plant-1, respectively, while the Iowa biotype accumulated the least with 195 g plant-1. Within the first planting, there were no differences among biotypes in seeds g-1 with an overall mean of 4860 seeds g-1.  In the second and third planting, the Iowa biotype had the fewest seeds g-1, with 4100 and 3370, respectively. The highest total seed production in the first planting was from the Nebraska, Illinois, and Iowa biotypes with 1,255,000, 1,085,000, and 881,300 seeds plant-1, respectively. In the second planting, the Iowa biotype produced the greatest number of seeds and the Indiana biotype the fewest with 1,275,000 and 862,000 seeds plant-1, respectively. In the third planting, the Missouri and Illinois biotypes produced the greatest number of seeds with 396,000 and 385,000 seeds plant-1, respectively, and the Iowa biotype the fewest with 192,000 seeds plant-1.  

 


ALS AND GLYPHOSATE RESISTANCE MECHANISMS IN PALMER AMARANTH POPULATIONS FROM ARKANSAS. S. Singh*1, V. Singh2, J. C. Argenta1, P. C. De Lima1, N. R. Burgos1, A. Lawton- Rauh3, V. Shivrain4, L. Glasgow5; 1University of Arkansas, Fayetteville, AR, 2Texas A&M University, College Station, TX, 3Clemson University, Clemson, SC, 4Syngenta Crop Protection, Singapore, Singapore, 5Syngenta Crop Protection, Greensboro, NC (30)

ABSTRACT


SEED RETENTION OF PALMER AMARANTH AND BARNYARDGRASS IN SOYBEAN. J. K. Green*, J. K. Norsworthy, M. G. Palhano, C. J. Meyer, S. M. Martin, L. M. Schwartz; University of Arkansas, Fayetteville, AR (31)

ABSTRACT

Narrow-windrow burning of soybean chaff is currently being evaluated as a means of reducing the return of weed seed to the soil seedbank at soybean harvest. The success of narrow-windrow burning is dependent upon the amount of seed retained by weeds at crop harvest. In 2015, experiments were conducted in Fayetteville, Arkansas, to determine the retention of Palmer amaranth and barnyardgrass seed over the course of a growing season when grown in conjunction with a soybean crop that was planted in late May. The weeds were evaluated in separate experiments but adjacent to one another so that the weather conditions were similar throughout the season. Barnyardgrass seeds were sown in the greenhouse on the day of soybean planting. At approximately 4 weeks after planting, barnyardgrass seedlings were transplanted into the row middles approximately 1.2 m apart along the soybean row in the field. Palmer amaranth seedlings were allowed to emerge naturally from the soil with the crop. Emerged seedlings were thinned to a spacing of approximately 1.2 m within the soybean row.  The trials were kept weed-free with the exception of the plants being used in the experiment. Within a few weeks of observing reproductive development, trays and cups lined with fabric were placed underneath 16 randomly selected plants in each experiment in order to allow for the capture of seeds that may be released from the plant. The contents of the trays and cups were collected on a weekly basis to allow for calculation of periodicity of seed shed from the plants over time. Additionally, 10 plants were collected weekly and threshed to determine the amount of seed present on each plant over time.  Data were regressed over time, and it was observed that Palmer amaranth retained approximately 98% of the seed at crop maturity, with an additional 7% loss of seed over the four-week period following crop maturity.  Conversely, barnyardgrass was less able to retain seed, with only 43% of the total seed production remaining at crop maturity. Over the four-weeks following soybean maturity, barnyardgrass shed an additional 8% of the total seed produced during the growing season.  When measuring seed production over time through weekly harvest of Palmer amaranth plants, the number of seeds on each plant increased over the course of the growing season.  These results indicate seed production continues to increase throughout the season when conditions are conducive for plant growth.  Based on these data, Palmer amaranth will be an excellent candidate for at harvest weed seed collection and destruction because a high percentage of seed are retained through crop maturity whereas harvest weed seed control tactics would be less impactful in managing the barnyardgrass soil seedbank.  

 


GLYPHOSATE-RESISTANT PALMER AMARANTH MANAGEMENT WITH ENGENIA HERBICIDE IN BOLLGARD II® XTENDFLEXTM COTTON. A. T. Koonce*1, W. Keeling2, P. A. Dotray3, J. D. Reed4, A. C. Hixson5; 1Texas A&M AgriLife, Lubbock, TX, 2Texas A&M, Lubbock, TX, 3Texas Tech University, Lubbock, TX, 4BASF Corporation, Wolfforth, TX, 5BASF Corporation, Lubbock, TX (32)

ABSTRACT

GLYPHOSATE-RESISTANT PALMER AMARANTH MANAGEMENT WITH ENGENIA™ HERBICIDE IN BOLLGARD II® XTENDFLEX® COTTON  A.T. Koonce1, J.W. Keeling1, P.A. Dotray1, J.D. Reed2, A.C. Hixson2, Texas A&M Agrilife Research , Lubbock TX1, BASF Corporation2

EngeniaTM herbicide, a new dicamba formulation (BAMPA) is under development by BASF for use in Bollgard II XtendFlexTM cotton. Engenia, applied either pre- or postemergence could improve control of glyphosate tolerant Palmer amaranth (Amaranthus palmeri), morningglory (Ipomoea spp.), Russian thistle (Salsola tragus L.), kochia (Kochia scoparia), woolyleaf bursage (Ambrosia grayi), and field bindweed (Convolvulus arvensis L.) compared to glyphosate or glufosinate alone. The objectives of these studies were to 1) evaluate weed management in a mixed population of glyphosate-susceptible and glyphosate-resistant Palmer amaranth with Engenia in both glyphosate and glufosinate systems, 2) determine the value of residual herbicides applied pre-plant incorporated (PPI) or postemergence (POST) for season-long Palmer amaranth management. Field trials conducted near Lubbock, TX in 2015 included treatments with or without pendimethalin PPI followed by glyphosate (32 oz/A) + Engenia (12.8 oz/A) or glufosinate (29 oz/A) + Engenia POST. Dimethenamid (14 oz/A), acetochlor (48 oz/A), or S-metolachlor (20 oz/A) were applied as in-season residuals. Early-postemergence (EPOST) treatments were applied June 8 to Palmer amaranth 2-4” tall, while weeds were 6-8” tall at the delayed mid-postemergence (MPOST) application timing. All treatments were applied at 15 gallons per acre using TTI 110015 nozzles. Weed control was estimated at 30, 50, and 70 DAP for both studies. In the glyphosate/Engenia systems, the most effective Palmer amaranth control and greatest cotton yields were produced with treatments which included glyphosate + Engenia applied EPOST with either a PPI or POST residual herbicide. Less effective weed control and reduced cotton yields resulted when POST treatments were delayed to the MPOST timing. In the glufosinate/Engenia system, the addition of Engenia improved Palmer amaranth control compared to glufosinate alone or tank-mixed with dimethenamid. These studies demonstrate the value of residual herbicides such as pendimethalin and dimethenamid, and the importance of timely Engenia applications when weeds are small (<4”).  

 


RELATING DICAMBA INJURY AND RESIDUE TO YIELD IN DRY BEAN. T. A. Reinhardt*, R. Zollinger; North Dakota State University, Fargo, ND (33)

ABSTRACT

Dicamba has the potential for higher use rates on more acres but is still detrimental to dry bean. Susceptibility of soybean to dicamba has been quantified, but dry bean threshold for dicamba drift or tank contamination is uncertain. The purpose of this study is to relate visual injury and yield loss to mg kg-1 herbicide concentration in leaf tissue. Treatments were applied to the center 2 meters of 3 by 12 meter plots using a CO2 backpack sprayer fitted with 11002 Turbo TeeJet nozzles at rates of 0.175, 1.75, and 17.5 g ai ha-1 of dicamba alone and in combination with glyphosate at 0.366, 3.66, 36.6 g ai ha-1, respectively. These low rates simulate the amount of dicamba that could be misapplied by improperly cleaning the spray tank or drift from another field, and the proportions correspond to the proposed herbicide mixture applied to dicamba tolerant soybean. Leaf tissue samples and evaluation of visible injury was taken at 10 and 20 days after treatment (DAT). Final grain yield was taken from the center two treated rows that had no samples taken.

While injury appeared across all treated plots, final yield was only reduced in plots treated with 17 g ai ha-1. Plots treated with 1.75 g dicamba had a consistent delay in physiological maturity that could require an extra desiccation application in order for a timely harvest. Dicamba residue found in the leaf was too variable by environment to create a predictive model for North Dakota growers. 

 


APPEARANCE OF AUXIN-LIKE SYMPTOMOLOGY ON SOYBEAN PROGENY EXPOSED TO AN ACTUAL DICAMBA DRIFT EVENT THE PREVIOUS YEAR. G. T. Jones*, J. K. Norsworthy, M. G. Palhano, N. R. Steppig, Z. Lancaster, R. R. Hale; University of Arkansas, Fayetteville, AR (34)

ABSTRACT

Soybean is highly sensitive to dicamba as even low drift rates may result in leaf and pod malformation. Exposure at vegetation stages typically shows more injury than exposure at reproductive stages; however, yield has been documented to be reduced more at reproductive stages than vegetative stages. With the advent of dicamba-resistant crops, there will be greater possibility for off-target movement of dicamba; therefore, probable effects on progeny are of great interest. It is not well understood what measurements from soybean plants following an actual dicamba drift event would correlate with damage to soybean progeny.  Eight dicamba drift trials were established at the Northeast Research and Extension Center in Keiser, AR in 2014. A single 30 m pass with a high clearance sprayer was made in each drift trial to simulate a drift event. Six of these drift events occurred at the R1 growth stage of soybean and two were at the R3 growth stage. At 2 weeks after application, transects with 6 m plot lengths were established parallel to the sprayer path every 4 rows until no visible injury was observed. Measurements on the parent plants (those exposed to dicamba drift) included visual estimates of leaf malformation at 14 and 28 days after application (DAA), soybean height at 28 DAA and maturity, percentage of malformed pods, and yield taken from the grid-sampled field. Seed were collected from each drift trial and planted at the Arkansas Agriculture Research & Extension Center in Fayetteville, AR, in 2015 at 346,000 seeds/ha in 6 m single row plots on 91 cm spacing. Measurements from the progeny included emergence (%), vigor (1-5), injury at 21 days after planting (DAP) (%), plants malformed (#/plot), and yield (kg/ha). Data were subjected to the multivariate and correlation analysis using JMP Pro 12 to determine pairwise correlations among parent and progeny observations. Auxin-like symptomology appeared in plots at the unifoliate and first trifoliate stages. Auxin-like symptoms were more prevalent in progeny collected from plants from the R3 than the R1 drift events. When dicamba drift occurred at R1, progeny emergence, progeny vigor, injury to progeny at 21 DAP, and number of progeny plants malformed were most closely correlated with height of parent plants at 28 DAA. When dicamba drift occurred at the R3 stage of soybean, progeny vigor and number of progeny plants malformed were correlated with injury from dicamba at 28 days after the drift event. Progeny injury was most strongly correlated with parent height at 28 days after the drift event while progeny yield loss was most closely correlated with percentage of pod malformation on parent plants. This research shows that soybean damaged from dicamba drift during early stages of reproductive development can negatively impact progeny, and that some measurements taken on the parent plants are better indicators of the progeny response than others.  The greatest concern for progeny would be when dicamba drift occurs on seed production fields, causing seed quality to suffer or growers to be alarmed by the occurrence of auxin-like symptoms on plants soon after emergence.     


COMPARISON OF POSTEMERGENT HERBICIDES IN CORN AND SOYBEAN. R. S. Randhawa*1, M. L. Flessner1, C. W. Cahoon2, K. M. Vollmer3, T. Hines2; 1Virginia Tech, Blacksburg, VA, 2Virginia Tech, Painter, VA, 3University of Delaware, Georgetown, DE (35)

ABSTRACT

Comparison of Postemergent Herbicides in Corn and Soybean. R. S. Randhawa*1, M. L. Flessner1, C. W. Cahoon1, T. Hines1, K. M. Vollmer2; 1Virginia Polytechnic Institute and State University, Blacksburg, VA, 2University of Delaware, Newark, DE. 

 ABSTRACT

 Weed control is necessary for protecting yield in every crop. Weed control is critical until canopy closure in corn and R3 growth stage in soybean, respectively, to prevent yield loss, which frequently requires a postemergent herbicide. This study was conducted to compare postemergent herbicides in corn and soybean for weed control efficacy.

Separate field experiments were conducted for corn and soybean. Corn experiments were conducted at Kentland Farm, Blacksburg, VA and soybean experiments at the Eastern Shore Agricultural Research and Extension Center (AREC), Painter, VA. Corn and soybean were planted on May 12, 2015 and June 22, 2015, respectively. Applications were made on June 22, 2015 and July 8, 2015 for corn and soybean, respectively. Weeds assessed in corn included morning glory (Ipomoea spp.) and redroot pigweed (Amaranthus retroflexus). Treatments evaluated included 2,4-D (2,4-D LV4) at 1120 g ae ha-1, atrazine (AAtrex) at 2240 g ai ha-1, isoxaflutole (Balance Flexx) at 70 g ai ha-1, primisulfuron (Beacon) at 40 g ai ha-1, bromoxynil (Buctril) at 420 g ai ha-1, fluthiacet (Cadet) at 6 g ai ha-1, mesotrione (Callisto) at 105 g ai ha-1, thiencarbazone (Capreno) at 92 g ai ha-1, ametryn (Evik DF) at 1770 g ai ha-1, prosulfuron (Peak) at 30 g ai ha-1, glyphosate (Touchdown Total) at 1170 g ae ha-1, topramezone (Impact) at 18.4 ae ha-1, tembotrione (Laudis) at 92 g ai ha-1, rimsulfuron + thifensulfuron (Resolve Q) at 16.1 + 3.5 g ai ha-1, dicamba + diflufenzopyr (Status) at 246.3 + 95.7 g ai ha-1. Weeds evaluated in soybean included morning glory (Ipomoea spp.) and common ragweed (Ambrosia artemisiifolia). Treatments included bentazon (Broadloom) at 840 g ai ha-1, chlorimuron (Classic) at 11.7 g ai ha-1, lactofen (Cobra) at 220 g ai ha-1, cloransulam (FirstRate) at 17.7 g ai ha-1, fomesafen (Reflex) at 420 g ai ha-1, glyphosate (Touchdown Total) at 1170 g ae ha-1, thifensulfuron (Harmony) at 6.6 g ai ha-1, imazethapyr (Pursuit) at 70 g ai ha-1, imazamox (Raptor) at 44 g ai ha-1, bentazon + acifluorfen (Storm) at 384 + 176 g ai ha-1, chlorimuron + thifensulfuron (Synchrony XP) at 5.6 + 1.81 g ai ha-1, acifluorfen (Ultra Blazer) at 420 g ai ha-1, glufosinate (Liberty) at 594 g ai ha-1. Both studies included a non-treated check and had a minimum of three replications per treatment per location. Plot size was 3 by 7.6 m for both studies and applications were made at 140 L ha-1 at 193 kPa with a boom equipped with four TeeJet 8002 nozzles. Experiments utilized a randomized complete block design. Weed control was visually evaluated relative to the non-treated check on a 0 (no control) to 100 (complete plant necrosis) scale. Visible control was assessed at 2 and 4 weeks after treatment (WAT) for soybean and corn, respectively. Data analyses were performed using SAS PROC GLM (SAS® Institute v. 9.1). ANOVA was performed and effects were considered significant when P < 0.05. Subsequently, data were also subjected to means separation using Fisher’s protected LSD (P < 0.05).

For morning glory control in corn, 2,4-D, atrazine, bromoxynil, mesotrione, thiencarbazone, ametryn, prosulfuron, diflufenzopyr resulted in >75% control; conversely, glyphosate, topramezone, tembotrione, rimsulfuron + thifensulfuron all resulted in <50% control 4 WAT. For redroot pigweed all treatments except fluthiacet, bromoxynil, and isoxaflutole resulted in similar control (65 to 100%). Fluthiacet, bromoxynil, and isoxaflutole all resulted in <35% control 4 WAT. For morning glory control in soybean, all treatments resulted in >85% control 2 WAT. For common ragweed all treatments except chlorimuron + thifensulfuron resulted in >89% control. Chlorimuron + thifensulfuron resulted in 73% control. Overall, herbicide application at labeled weed height resulted in excellent weed control, underscoring the need for timely application. Furthermore, results clearly indicated that many herbicide modes of action (MOA) other than glyphosate were effective, thus giving producers the ability to rotate MOA or use multiple MOA. Doing so will help mitigate both the spread and development of herbicide resistant weeds. Future research should evaluate more weed species and include herbicide resistant populations.

 


DO INDETERMINATE AND DETERMINATE SOYBEAN CULTIVARS DIFFER IN RESPONSE TO LOW RATES OF DICAMBA? M. S. McCown*1, L. T. Barber1, J. K. Norsworthy1, J. S. Rose1, A. W. Ross2, L. M. Collie2; 1University of Arkansas, Fayetteville, AR, 2University of Arkansas, Little Rock, AR (36)

ABSTRACT

Commercial introduction of soybean cultivars genetically modified with resistance to the synthetic auxin herbicide dicamba will provide growers an alternative weed management option, but may expose susceptible soybean cultivars to non-target herbicide movement and tank contamination. A study was conducted to simulate tank contamination by applying low rates of dicamba to susceptible soybean cultivars. Two identical trials were conducted in 2015 at Lon Mann Cotton Research Station in Marianna, Arkansas. The purpose of this study was to determine if determinate vs. indeterminate soybean cultivar has an influence on recovery from dicamba injury. Five susceptible soybean cultivars were chosen based on relative maturity and included three indeterminate cultivars (CZ 4105, CA 4950, Armor 501) and two determinate cultivars (CZ 5147 and CZ 5445). Dicamba was applied at 1.42g ae ha-1 (1/64x rate) and 0.35g ae ha-1 (1/256x) at R1 soybean growth stage. This experiment was set up as a split-plot design with growth habit (indeterminate vs. determinate) as the main plot and dicamba rate (1/64x or 1/256x) as the split plot. Treatments were applied depending on when the cultivar reached each growth stage. Crop injury was visually evaluated at 2 and 4 weeks after treatment and average heights were gathered using five randomly chosen plants from each plot. After plants had reached full maturity the middle two rows of each plot were harvested and yield was determined. During this experiment weeds were managed with a glufosinate herbicide weed control program consisting of pre-emerge herbicides and glufosinate plus metolachlor POST. Due to large window (approx. a month) between planting date of the two trials, overall yields were significantly different between the two site locations resulting in separate analysis of variance. No interaction between dicamba rates and growth habit were observed at either location.  At Location A (planted May 13, 2015) regardless of dicamba rate, a significant difference in yield was observed between the indeterminate and determinate cultivars with the determinate cultivars yielding 6 bushels higher than the indeterminate cultivars.  As expected, at both locations a significant difference in yield and height was observed between dicamba rates across all cultivars when compared to the untreated plots.  From these results we can conclude that indeterminate vs. determinate soybean cultivars can differ in response from low rates of dicamba; however, other factors may influence yield more significantly such as planting date and rate of dicamba applied. 

 


CHARACTERIZATION OF AVENA STERILIS POPULATION TOLERANT TO GLYPHOSATE. P. T. Fernandez*1, R. Alcantara-de la Cruz1, A. M. Rojano-Delgado1, H. E. Cruz-Hipolito2, J. M. de Portugal3, R. Smeda4, D. Rafael1; 1University of Cordoba, Cordoba, Spain, 2Bayer CropScience, Mexico City, Mexico, 3Agrarian Superior College of Beja, Beja, Portugal, 4University of Missouri, Columbia, MO (37)

ABSTRACT

Characterization of Avena sterilis Population Tolerant to Glyphosate. P.T. Fernandez*1, R. Alcantara1, A.M. Rojano-Delgado1, H.E. Cruz-Hipolito2, J.M. de Portugal3, R.J. Smeda4, R. De Prado1; 1University of Cordoba, Cordoba, Spain, 2Bayer CropScience, Col. Ampl. Granada, Mexico, 3Agrarian Superior College of Beja, Portugal, 4University of Missouri, MO.

Sterile wild oat (Avena sterilis L.) is an autogamous grass that infests areas in warm climate regions. This species has been used as a cover crop in perennial crops such as olive groves throughout the Mediterranean region.  Prior to initiation of spring growth of the olive trees, control of the A. sterilis with glyphosate or use of tillage is necessary to avoid undesirable competition. In 2011, the olive grove farmers of southern Spain expressed dissatisfaction with the activity of glyphosate on A. sterilis. Experiments were conducted to determine continuous use of glyphosate over a 5 year period had selected for a new resistant or tolerant biotype. The concentration of glyphosate to reduce A. sterilis shoot growth by 50% (GR50) were 297.12 and 283.74 g ae ha-1 for E (seeds exposed to glyphosate applications) and UE (never exposed to glyphosate applications) accessions, respectively. The spray retention and shikimic acid accumulation demonstrated a non-significant difference between the two accessions. Absorption of 14C- glyphosate was the same between the two accessions, and translocation out of the treated leaf (48.3 to 51.8 %) to the rest of the shoots (25.6 to 23.9 %) and roots (25.9 to 24.2 %) was also similar. Glyphosate metabolism to AMPA and glyoxylate was similar in both accessions, but increased after treatment with glyphosate, indicating metabolism was significant. Both A. sterilis populations exhibited similarity in changes in EPSPS activity in the presence and absence of glyphosate, indicating both accessions have the same genomic characteristics. The above-mentioned results indicate that innate tolerance to glyphosate in A. sterilis is partially the result of reduced absorption, translocation, and metabolism compared to other grasses weeds such as Chloris inflata, Eleusine indica and Lolium rigidum.

Keywords: Avena sterilis, glyphosate-tolerant, NRST, RST.

E-mail Address: pablotomas91@hotmail.es

 


A SURVEY OF CROP WEED MANAGEMENT IN VIRGINIA. S. C. Haring*, M. L. Flessner; Virginia Tech, Blacksburg, VA (38)

ABSTRACT

A Survey of Crop Weed Management in Virginia. S. C. Haring*, M. L. Flessner; Virginia Tech, Blacksburg, VA.

ABSTRACT

The development of high-impact Extension education and outreach programs relies on awareness of how to best communicate to growers. Understanding how growers source, obtain, and process new knowledge is critical in the efficient dissemination of that knowledge. A survey was conducted to gain information regarding these issues directly from growers in Virginia.

Surveys were conducted online and in-person (on paper). Online subject recruitment occurred through email lists, including email lists maintained by the Virginia Soybean Producers Association and the Virginia Grain Producers Association, among others. In-person subject recruitment occurred at county and regional agriculture conferences organized by Virginia Cooperative Extension and the Virginia Crop Production Association. These populations were selected because, together, they comprise a representative sample of crop growers in Virginia. Surveys were administered between February and April 2015. Online surveys were administered through Qualtrics Research Suite software (Qualtrics, LLC, Provo, UT). Paper survey data were entered into this software, as well. Data were analyzed using JMP (SAS Institute Inc., Cary, NC) and R (R Core Team, Vienna, AT). Responses from ranking or scoring questions were subjected to the Kruskall-Wallace H test and the Steel-Dwass All Pairs test. Responses from multiple choice questions were analyzed using Pearson’s Chi-Square test. The survey was completed by 97 growers, who collectively farm about 10% of corn, soybean, and small grains acreage in Virginia.

Growers reported that Extension specialists should focus their efforts on herbicide resistant weed management, new herbicide evaluation, herbicide resistant crop technology evaluation, and weed management with multiple modes of herbicidal action, while the proper use of tillage, cover crops, and alternative technologies in weed management were less important. When asked what information was most likely to influence growers to change how weeds are managed, growers overwhelmingly reported on-farm demonstrations to be the most influential. The next most influential information was data regarding weed population changes over time in response to management practices. Yield data, economic assessments, and weed control efficacy data were all reported to be less effective than these other two methods. Similarly, when asked what was the best format to spread information, growers preferred field days, Extension meetings, or Extension publications over websites and on-farm demonstrations. The least-preferred options were YouTube videos, Twitter or Facebook posts, and blog posts. Agricultural retailers were reported to be the primary source of weed management information. Crop consultants, sales representatives, and Extension agents and specialists were reported to be less important information sources than retailers, but more important than magazines or commercial publications, the internet, and neighbors or friends. This pattern was repeated when growers were asked who was the key influencer when making an herbicide purchase decision. The retailer was again reported to be most important at the time of herbicide purchase, with greater influence than any other source. Growers reported crop consultants, sales representatives, and Extension agents and specialists to be as influential as the growers themselves. Finally, magazines or commercial publications, the internet, and neighbors or friends were reported to be the least influential groups in an herbicide purchase decision.  Overall, these data indicate that Extension specialists should communicate research results in-person to growers and agricultural retailers through on-farm demonstrations and Extension presentations. Future research should examine if these preferred means of communication affect greater or more rapid change in weed management practices relative to less preferable options.

sharing@vt.edu


 

 


INVESTIGATIONS OF MULTIPLE HERBICIDE RESISTANCE IN A MISSOURI WATERHEMP POPULATION. B. R. Barlow*, M. D. Bish, A. Long, M. Biggs, K. W. Bradley; University of Missouri, Columbia, MO (39)

ABSTRACT

ABSTRACT

Investigations of Multiple Herbicide Resistance in a Missouri Waterhemp Population

Blake R. Barlow*, Meghan E. Biggs, Alex R. Long, Mandy D. Bish, and Kevin W. Bradley; University of Missouri Columbia

A field and greenhouse study was conducted in 2015 to investigate the potential for multiple herbicide resistance in a waterhemp population from Missouri (designated MOR). In the field trial, the following treatments were applied in a bare-ground setting to waterhemp 10-cm in height:  2,4-D and dicamba at 0.56, 1.12, 2.24, and 4.48 kg ai/ha; glyphosate at 0.84, 1.68, and 3.36 kg ai/ha, mesotrione at 0.11, 0.21 and 0.42 kg ai/ha; atrazine at 1.12, 2.24, and 4.48 kg ai/ha; fomesafen at 0.34, 0.68, and 1.36 kg ai/ha; glufosinate at 0.59, 1.19, and 2.38 kg ai/ha; and chlorimuron at 0.01, 0.02, and 0.05 kg ai/ha. The experiment was conducted in a randomized complete block design with 4 replications. Visual control ratings and waterhemp survival counts were determined 28 and 42 days after application (DAA). Based on the results from the field experiment, resistance to 2,4-D, glyphosate, mesotrione, atrazine, fomesafen, and chlorimuron was suspected in this waterhemp population.  Across all rates evaluated in the field study, waterhemp control ranged from 29 to 71% with 2,4-D, from 6 to 23% with glyphosate, from 31 to 76% with mesotrione, from 18 to 27% with atrazine, from 22 to 47% with fomesafen, and from 6 to 7% with chlorimuron 42 DAA.  Dicamba and glufosinate were the only herbicides that provided acceptable control of the waterhemp population.  To further examine the possibility of multiple herbicide resistance in this waterhemp population, a greenhouse herbicide screening was conducted using seed harvested from the MOR waterhemp population in comparison to seed harvested from a population harvested near Columbia, Missouri. Seed were planted in greenhouse flats containing a commercial potting medium and all treatments were applied once waterhemp reached 10 cm in height.  The experiment was conducted in a completely randomized design with four replications. Based on visual control and waterhemp biomass reduction 21 DAA, the results from one run of the greenhouse experiment suggest that the MOR population exhibits resistance to 2,4-D, glyphosate, atrazine, fomesafen, and chlorimuron, but not mesotrione.  The 1.12 kg/ha rate of 2,4-D resulted in only 31% control and 50% biomass reduction of the MOR population, but provided 72% control and 95% biomass reduction of the Columbia population.  Additional field and greenhouse experiments will be conducted in 2016 in order to better understand the levels of herbicide resistance in the MOR waterhemp population.

 


GROUP VI SOYBEAN RESPONSE TO SUB-LETHAL RATES OF DICAMBA. A. M. Growe*1, M. K. Bansal1, D. Copeland2, J. T. Sanders1, B. W. Schrage1, L. Vincent1, W. J. Everman1; 1North Carolina State University, Raleigh, NC, 2North Carolina State University, Cary, NC (40)

ABSTRACT

Group VI Soybean Response to Sub-lethal Rates of Dicamba

Abstract

Dicamba-resistant crop varieties have the potential to become utilized in North Carolina as a tool to control glyphosate-resistant weeds.  Current soybean cultivars, commonly glyphosate or glufosinate-resistant varieties, are highly susceptible to dicamba. There is growing concern of off-site movement of this broadleaf herbicide to sensitive cultivars.  Tank contamination, wind drift, and volatility of dicamba can cause injury and reduce soybean yields. To date, there has been little information reported on soybean varietal responses to sub-lethal doses of dicamba. 

The objective of this study was to evaluate the effects of sub-lethal rates of dicamba on various group VI soybean cultivars at vegetative and reproductive growth stages.  Effects of dicamba were determined by collecting visual injury ratings, height reductions and yield.  Experiments were conducted in Lewiston-Woodville and Kinston, North Carolina during 2015.  Five soybean varieties were treated with dicamba at 1.1, 2.2, 4.4, 8.8, 17.5, 35, and 70 g ae ha (1/512 to 1/8 of the labeled use rate for weed control in corn) during V4 and R2 growth stages.  Experiments were conducted using a factorial arrangement of treatments in a randomized complete block design, with three factors being dicamba rate, soybean cultivar and growth stage. All data were subjected to analysis of variance and means were separated using Fisher’s Protected LSD at p= 0.05.

Statistical analysis showed a wide range of visual injury and height reduction 2 and 4 WAT for all 5 varieties. Higher level of injury was associated with increasing dicamba rates. Height reduction and injury were more severe when dicamba was applied to the V4 growth stage compared to R2.  Statistical analysis revealed a variety by timing interaction.  When averaged across all dicamba rates, height reduction 4 WAT ranged from 15-22 % for the V4 timing and 8-22% for the R2 timing.  This data suggest the potential for a varietal response to sub-lethal rates of dicamba.  Dicamba effects on soybean yield have not yet been analyzed.


WEED CONTROL AND TOLERANCE OF “BOLT” SOYBEAN (GLYCINE MAX L.) TO APPLICATION OF VARIOUS ALS INHIBITING HERBICIDES. Z. A. Carpenter*1, D. B. Reynolds2, J. D. Smith3; 1Mississippi State University, Mississippi State, MS, 2Mississippi State University, Starkville, MS, 3DuPont Crop Protection, Madison, MS (41)

ABSTRACT

Weed Control and Tolerance of “Bolt” Soybean (Glycine max L.) to Applications of Various ALS Inhibiting Herbicides. Z.A. Carpenter*1, D. B. Reynolds1, and J. D. Smith2; 1Mississippi State University, Mississippi State, MS, 2DuPont Crop Protection, Madison, MS

ABSTRACT

The launch of Bolt™ soybeans from DuPont Crop Protection introduced a new herbicide resistance trait to help grower’s combat glyphosate resistant weeds. Bolt™ soybeans offer an increased level of tolerance to the sulfonylurea class of ALS herbicides when compared to STS varieties. Bolt™ soybean are also the only soybean varieties with no plant back restrictions following burndown applications of DuPont’s LeadOff® (rimsulfuron + thifensulfuron-methyl) and Basis Blend® (rimsulfuron + thifensulfuron-methyl) herbicides, which have a plant back restriction of 30 to 60 days depending on rate. This new technology will provide grower’s with greater flexibility in combating glyphosate resistant weeds and timings of preplant burndown applications.

The objectives of this study were to analyze the tolerance of Bolt™ soybeans to applications of various sulfonylurea herbicides as well as to determine which treatments provided the best season long weed control. The study was conducted in Brooksville, Mississippi in 2015. The experimental design was a randomized complete block with four replications. Plots were 3.85 m by 12.19 m. The experimental site was heavily populated with pitted morningglory (Ipomoea lacunose).  Applications were made at two timings; preemergence (PRE) and postemergence (POST) when weeds were 10 to 15 cm in height. All applications were made using a backpack sprayer calibrated to deliver 141 l ha-1 at 276 KPa. The center two rows of each plot were treated. Twenty-two treatments were evaluated.  Treatments included an untreated check as well as Staple LX (pyrithiobac), Resolve DF (rimsulfuron), Classic DG (chlorimuron-ethyl), Finesse (chloramsulfuron + metsulfuron-methyl), Express TSG (tibenuron-methyl), Valor SX (flumioxazin), Envive (chlorimuron-ethyl + flumioxazin + thifensulfuron-methyl), LeadOff (rimsulfuron + thifensulfuron-methyl), Diligent (chlorimuron-ethyl + flumioxazin + rimsulfuron),   Authority MTZ (metribuzin + sulfentrazone), Synchrony XP (chlorimuron-ethyl + thifensulfuron-methyl), Envoke (trifloxysulfuron), Accent WG (nicosulfuron), and Permit (halosulfuron). Roundup PowerMax® (glyphosate) was tankmixed with all postemergence treatments.  Visual rating and weed control data were collected 7 and 14 days after treatment (DAT) with PRE applications and 7, 14, 28, and 56 days after POST. Plots were harvested at the end of the growing season and yield data were collected.

The greatest visual injury (6%) was observed 7 days after a POST application of Envoke. Staple LX also displayed an average of 4% visual injury 7 DAT. Soybeans quickly grew out of any injury and by 14 DAT only averaged 1 to 2%. When compared to the untreated check, all treatments had an average yield increase of 43%. The untreated check averaged 2,065 kg ha-1.  Diligent PRE and Synchrony XP POST averaged yield 2,824 kg ha-1. Eighteen out of 22 treatments had greater than 85 percent control 56 DAT.


EFFECTS OF DICAMBA AND GLYPHOSATE COMBINATIONS ON PEANUT. D. L. Teeter*1, T. A. Baughman1, P. A. Dotray2, W. Grichar3, R. W. Peterson1; 1Oklahoma State University, Ardmore, OK, 2Texas Tech University, Lubbock, TX, 3Texas AgriLife Research, Yoakum, TX (42)

ABSTRACT

Effects of Dicamba and Glyphosate Combinations on Peanut. D. L. Teeter*1, T. A. Baughman1, P. A. Dotray2, W. Grichar3, R. W. Peterson1; 1 Oklahoma State University, Ardmore, OK, 2 Texas Tech University, Lubbock, TX, 3 Texas A&M AgriLife Research, Yoakum, TX.

ABSTRACT

The potential release of crops tolerant to dicamba and glyphosate have many concerned with the effect of off-site movement and tank contamination to non-tolerant crops.  Peanuts (Arachis hypogaea) are one of the crops that will be grown in close proximity to this new technology. Studies were conducted in Oklahoma (Fort Cobb), Texas Southern High Plains (Seagraves) and South Texas (Yoakum) to evaluate the effects of various rates and timings of dicamba + glyphosate on peanuts.  Applications were based on the proposed 1X rate of dicamba at 0.56 kg ae/ha + glyphosate at 1.12 kg ae/ha.  Additional rates were 0.5X, 0.25X, 0.125X and 0.0625X of the 1X rate.  Each of these were applied 30 (8-10 node), 60 (beginning pod), and 90 (full pod) days after planting (DAP).  Traditional small plot techniques were used and trials were established as a randomized complete block design.  All treatments were applied with a CO2 backpack sprayer in 93 to 187 L ha-1 carrier volume.  Visual injury was evaluated at each location.  Peanuts were dug and allowed to field dry to 10% moisture and harvested with a commercial combine equipped with a sacking attachment.  Data was subjected to analysis of variance and treatments were separated using a protected LSD of P = 0.05.  Peanut stand reduction was 1% or less with all application timings when dicamba + glyphosate was applied at the 0X, 1/16X, 1/8X, and 1/4X rate and when 1/2X and 1X rates were applied at 60 and 90 DAP in both 2014 and 2015 at Fort Cobb.  Stand reduction was 10 to 20% with the 1/2X rate applied 30 DAP early season and 5 to 20% late season.  Stand reduction increased to greater than 70% with 1X rate applied 30 DAP early season and was 45 to 70% late season.  All 30 DAP application rates resulted in visual injury of greater than 10% in both 2014 and 2015 at Fort Cobb.  Visual injury was greater than 25% with 1/4X and greater than 60% with 1X both years.  All treatments reduced yield compared to the untreated check except the 1/16X (2014 and 2015) and 1/8X (2015) rate applied at 30 DAP.  Peanut injury at Seagraves was greater than 25% when evaluated within 2 weeks after treatment (WAT) with all rates applied 30 and 60 DAP in both 2014 and 2015.  The only treatments applied 90 DAP that injured peanuts 2 WAT were the 1/2X and 1X rate. Peanut injury was greater than 50% late season with 1/2X and 1X rate applied at 30 and 60 DAP in both years.  Late season injury was less than 10% with 1/16X rate at 30 DAP in 2014 and 2015, 1/16X rate at 60 DAP in 2015, and 1/8X rate at 30 DAP in 2014. Peanut yields at Seagraves were reduced with all treatments applied at 30 and 60 DAP except the 1/16X rate in 2014.  The only 90 DAP treatments that reduced yield in 2014 were those applied at 1/2X and 1X.  Unlike 2014 only the 1/2X and 1X rate applied at 30, 60, and 90 DAP, the 1/4X rate at 60 and 90 DAP, and the 1/8X rate at 90 DAP reduced peanut yields in 2015.  Peanut injury at Yoakum was greater than 15% with all rates applied 30 and 60 DAP both in 2014 and 2015.  Late season injury at Yoakum was greater than 20% with 1/4X rate and greater than 35% with 1/2X and 1X rate regardless of application timing.  All application timings of dicamba + glyphosate at 1/4X, 1/2X, and 1X rate reduced peanut yield except 1/4X rate applied 60 DAP in 2014.

 


THE EFFECT OF COTTON (GOSSYPIUM HIRSUTUM L.) GROWTH STAGE ON SUSCEPTIBILITY TO INJURY AND YIELD EFFECTS FROM EXPOSURE TO A SUB-LETHAL CONCENTRATION OF DICAMBA. J. Buol*1, D. B. Reynolds2; 1Mississippi State University, Mississippi State, MS, 2Mississippi State University, Starkville, MS (43)

ABSTRACT

THE EFFECT OF COTTON (Gossypium hirsutum L.) GROWTH STAGE ON INJURY AND YIELD WHEN SUBJECTED TO A SUB-LETHAL CONCENTRATION OF DICAMBA. J. Buol and D.B. Reynolds. Department of Plant and Soil Sciences, Mississippi State University, Mississippi State, MS 39762.

ABSTRACT

The pending registration and commercialization of novel auxin-herbicide-tolerant crop biotechnologies may hold great promise in helping address the compounding issue of herbicide-resistance. New weed management systems such as the Enlist™ and Extend™ platforms will allow producers of the major row crops to enjoy an additional herbicide mode-of-action (MOA) in their weed control arsenals. These systems will also allow more flexible herbicide application logistics, hopefully culminating in a more integrated and robust approach to herbicide-resistance stewardship. However, because implementation of these weed-control systems will likely promote an increased use of the auxin-mimic herbicides 2,4-D (2,4-dichlorophenoxyacetic acid) and dicamba (3,6-dichloro-2-methoxybenzoic acid), a corresponding increase in the risks associated with these herbicides will likely ensue. Due to their effects on plant hormone physiology, 2,4-D and dicamba are capable of negatively affecting susceptible species even if exposure is to low sub-lethal concentrations. Thus, off-target exposure to the auxin-herbicides such as would manifest with herbicide drift, volatility, or spray-tank contamination events are important when considering the production of auxin-sensitive crops such as non-transgenic cotton cultivars.

Previous research has characterized a complex relationship between cotton and the auxin-herbicides. It has been shown that 2,4-D is generally more injurious to cotton than dicamba. However, growth stage at the time of exposure appears to have an effect on cotton response to sub-lethal rates of auxin-herbicides. Current research shows that exposure to sub-lethal concentrations of 2,4-D is more injurious to cotton early in its growth and development. Conversely, exposure to sub-lethal concentrations of dicamba appears to result in the most severe injury and yield loss when it occurs in the middle of cotton’s growth and development.

Upland cotton (Gossypium hirsutum L) remains an economically important crop in the United States as over 3.5 million hectares of land in the United States were planted in 2015. Thus, an experiment was conducted to assess the effect of cotton growth stage on susceptibility to injury and yield effects from a sub-lethal concentration of dicamba. Research was conducted in 2014 and 2015 at the R.R. Foil Plant Research Facility in Starkville, MS and the Black Belt Research Station in Brooksville, MS, where the experimental layout was a randomized complete block design with four replications with an untreated check. The diglycolamine salt formulation of dicamba (Clarity™) was applied at a rate of 0.035 kg ae ha-1 to the center two rows of four-row plots measuring 3.9 m by 12.2 m. One preemergence (PRE) application was included in the experiment, with the rest of the applications occurring weekly from 1 to 14 weeks after emergence (WAE). Crop growth stage and height were recorded at each application timing along with environmental data. Data collection included visual injury assessment ratings taken 7, 14, 21, and 28 days after treatment (DAT); plant heights; nodes above cracked boll (NACB) and nodes above white flower (NAWF) measurements; and both hand and machine-harvested seed cotton yield. Hand-harvested yield data were analyzed on the basis of Position (horizontal location of a boll on each branch relative to the main stem), Zone (vertical node of the branch on which a boll is found), and maturity cohort (combination of Position and Zone), with all yield found on monopodial (vegetative) branches or aborted terminals treated as discrete Positions. All data were analyzed in SAS 9.4 PROC MIXED, and means were separated using Fisher’s Protected LSD at the α = 0.05 level of significance.

Cotton injury 28 DAT was greatest when dicamba was applied 5 to 7 WAE, with a decrease in plant height from an application at 5 WAE, and increases in plant height from applications made 10 and 11 WAE. Machine-harvested yield reductions occurred from exposure to dicamba at 6 and 7 WAE. Seed cotton yield partitioned in Position 1 and 2 bolls decreased as yield partitioned on monopodial branches and aborted terminals increased from applications of dicamba made 3 to 7 WAE. Similarly, yield partitioned in Zone 1 (nodes 5 to 8) and Zone 2 (nodes 9 to 12) decreased as yield partitioned in Zone 3 (nodes > 12) increased from applications of dicamba made 3 to 7 WAE. Thus, our data suggest that cotton growth stage is a significant factor in relation to yield reduction and partitioning in response to exposure to sub-lethal concentrations of dicamba. Furthermore, cotton appears to be most susceptible to injury, yield reduction, and yield partitioning effects when it is exposed to sub-lethal concentrations of dicamba in the middle of its growth and development, around the blooming stage. 

 


EVALUATION OF STAPLE LX IN ENLIST COTTON. Z. D. Lancaster*, J. K. Norsworthy, N. R. Steppig, M. L. Young, S. Martin; University of Arkansas, Fayetteville, AR (44)

ABSTRACT

 

With no new herbicide modes of action available in the foreseeable future, new herbicide-resistant crop technologies are needed to effectively control these troublesome weeds.  The introduction of the Enlist™ technology provides an additional mode of action to combat these difficult-to-control weeds, but proper stewardship will need to be taken to slow the development of resistance to this new technology.  The addition of residual herbicides is essential to proper stewardship of a technology.  Staple LX™ (pyrithiobac) is a residual herbicide which can be used pre-plant and postemergence in cotton.  An experiment was conducted in the summer of 2015 at the Lon Mann Cotton Research Station near Marianna, AR to determine if the addition of Staple LX to the Enlist system improves season-long weed control.  The experiment was set up as a single factor randomized complete block design with the factor being herbicide program.  Treatments were applied to a bare-ground field with applications at preemergence (PRE), early postemergence (EPOST – 14 to 21 days after PRE), and mid-postemergence (MPOST - 14 to 21 days after EPOST).  Treatments consisted of combinations of Cotoran 4™ and Staple LX applied PRE; Roundup PowerMax™, 2,4-D Amine, Dual Magnum™, and Liberty™ applied EPOST, and Roundup PowerMax, 2,4-D, Staple LX, and Liberty applied MPOST.  Data were collected on Palmer amaranth (Amaranthus palmeri), barnyardgrass (Echinochloa crus-galli), large crabgrass (Digitaria sanguinalis), goosegrass (Eleusine indica), entireleaf morningglory (Ipomoea purpurea), and pitted morningglory (Ipomoea lacunosa) control at 14 to 21 days after each application.  Data were analyzed with JMP 12.1 using Proc Mixed, with means separated using Fisher’s protected LSD (α=0.05).  Treatments including Staple LX were found to have no significant difference in weed control when compared to treatments containing the industry standard of Dual Magnum.  All herbicide programs showed no significant difference for late season Palmer amaranth control, except for the program of Staple LX/Cotoran (PRE) followed by Roundup PowerMax/2,4-D/Dual Magnum (EPOST), followed by Liberty/Staple LX (MPOST) which resulted in lower control at 85%.  The industry standard treatment (no 2,4-D) showed equally effective control of Palmer amaranth compared to the most effective 2,4-D-containing programs.  This research shows that Staple LX does not bring added value to the Enlist system compared to currently used residual herbicides, and that current industry standards without 2,4-D are still able to provide exceptional season-long weed control.

 


AVOIDING LIVESTOCK SUICIDES. D. P. Russell*, J. D. Byrd, Jr.; Mississippi State University, Mississippi State, MS (45)

ABSTRACT

Perilla mint (Perilla frutescens) is an erect, herbaceous annual herb from eastern Asia that escaped cultivation and threatens grazing livestock throughout the central and southeastern United States. Plants are often found in areas of partial shade, low-lying areas, and woodland edges. Toxicity levels increase during the plants’ reproductive growth stage in late summer, consequently putting livestock at risk. The goal of these studies was to evaluate efficacy of several preemergence and postemergence herbicide treatments to reduce the potential threat to livestock.

A field experiment to evaluate postemergence treatments was initiated in August 2014 and June 2015 in east-central Mississippi. Per acre herbicide treatments included Perspective (39.5% aminocyclopyrachlor + 15.8% chlorsulfuron) at 4 oz, Rejuvra (44.5% aminocyclopyrachlor + 6.67% metsulfuron) at 2.5 oz, Invora (7.3% aminocyclopyrachlor + 14.6% triclopyr) at 12 fl oz, Grazon P+D (10.2% picloram + 39.6% 2,4-D) at 1 and 2 pts, GrazonNext HL (8.24% aminopyralid + 41.26% 2,4-D) at 1.2 pts, Roundup Powermax (48.7% glyphosate) at 1.3 pts, Remedy Ultra (60.45% triclopyr) at 1 pt, Cimarron (60% metsulfuron) at 0.1 oz, Weedmaster (12.4% dicamba + 35.7% 2,4-D) at 1 and 2 pts, and 2,4-D Amine (47.3% 2,4-D) at 2 pts. Treatments were applied with a CO2 backpack calibrated to deliver 14 GPA. An untreated control was included in the design.

Preemergence herbicides were evaluated in 2014 and 2015 in the greenhouse on local seed with a germination percentage of 69%. Preemergence herbicides were applied through a controlled environment spray chamber at 23 GPA. Herbicides used on a per acre basis included Perspective (39.5% aminocyclopyrachlor + 15.8% chlorsulfuron) at 16 fl oz, Grazon P+D (10.2% picloram + 39.6% 2,4-D) at 2 pts, GrazonNext HL (8.24% aminopyralid + 41.26% 2,4-D) at 1.2 pts, Weedmaster (12.4% dicamba + 35.7% 2,4-D) at 2 pts, Prowl H2O (38.7% pendimethalin) at 4.2 qts, and Plateau (23.6% imazapic) at 6 fl oz. An untreated control was also included.

2014 and 2015 postemergence results indicated Roundup Powermax exhibited the quickest response with 100% perilla mint control 14 and 28 days after treatment (DAT) respectively. In 2014, complete control was achieved by every treatment except Remedy Ultra and Cimarron 42 DAT. Postemergence herbicide results in 2015 indicated all treatments except Weedmaster at 2 pts, Invora, and Cimarron controlled perilla mint up to 94 DAT with at least 73% visual control. Preemergence evaluations from 2014 and 2015 indicated all treatments except Prowl H20 provided acceptable visual control (>85%), and were not significantly different through 49 DAT. Perspective, Grazon P+D, GrazonNext HL, and Weedmaster provided complete control and are recommended applications prior to perilla mint germination.

 


CONTROL OF CADILLO IN GRAZINGLANDS. J. C. Dias*1, G. E. Duarte2, B. A. Sellers1, L. J. Martin1; 1University of Florida, Ona, FL, 2UNESP-Jaboticabal, Jaboticabal, Brazil (46)

ABSTRACT

ControL of Cadillo (Urena lobata) in Grazinglands. J.L.C.S. Dias*1; G.E. Duarte2; B.A. Sellers3; L.J. Martin4; University of Florida, 33865, FL

 

ABSTRACT

 

Cadillo (Urena lobata) is a perennial invasive species which has become increasingly troublesome in Florida pastures and natural areas. Cadillo seeds can germinate under a wide range of environmental conditions, contributing to the competitiveness of this weed. Despite this, little information is available regarding chemical control. Thus, the objective of this research was to evaluate different POST herbicide treatments for the control of cadillo. Field and greenhouse studies were conducted at the Range Cattle Research and Education Center, Ona, FL, in 2015. Both studies were conducted twice using a randomized complete block design. Data were subjected to analysis of variance and means were separated using Fisher’s protected LSD (P ≤ 0.05). Treatments in the greenhouse study consisted of broadcast applications of triclopyr-ester (280; 561 and 1,121 g ae ha-1); aminopyralid (61 and 122 g ae ha-1); metsulfuron (11 and 21 g ai ha-1); 2,4-D (561; 1121 and 2,242 g ae ha-1); aminocyclopyrachlor (17; 35 and 70 g ai ha-1); aminopyralid + metsulfuron (7 + 44; 13 + 86 and 20 + 131 g ai ha-1); aminocyclopyrachlor + metsulfuron (125 + 40 and 263 + 84 g ai ha-1) and imazapyr + aminocyclopyrachlor + metsulfuron (288 + 208 + 66 and 443 + 319 + 102 g ai ha-1). The appropriate adjuvants were added to each spray solution as provided by the manufacturer. Plants were treated at the 5 to 8-leaf stage in the greenhouse using a track sprayer calibrated to deliver 187 L ha-1.  Visual estimations of cadillo injury were recorded at 14, 21 and 28 days after treatment (DAT) and above ground dry biomass was recorded at 28 DAT. The field study consisted of broadcast applications of triclopyr-ester (561 and 1,121 g ae ha-1); aminopyralid (122 g ae ha-1); 2,4-D (1,121 and 2,242 g ae ha-1); aminocyclopyrachlor (35 and 70 g ai ha-1) and triclopyr + fluroxypyr (420 + 140 and 841 + 280 g ae ha-1). Nonionic surfactant was added to each herbicide solution at 0.25% v/v. Plants were approximately 2 m tall at the time of application and were treated using a tractor mounted, compressed air broadcast sprayer calibrated to deliver 233 L ha-1. Visual estimations of injury were recorded at 15, 30 and 60 DAT. In the greenhouse study, all treatments resulted in at least 83% control by 28 DAT, except aminocyclopyrachlor at 17 g ai ha-1 (67%) and at 35 g ai ha-1 (73%). In addition, triclopyr and 2,4-D containing treatments performed exceedingly well with 99-100% control. Dry biomass was reduced by at least 74% of the untreated in all treatments. All rates of triclopyr, 2,4-D at 1,121 and 2,242 g ha-1 and metsulfuron at 21 g ha-1 resulted in at least 90% less dry biomass compared to the untreated. In the field study, all treatments provided >90% control of Cadillo by 30 DAT, except aminocyclopyrachlor at 35 g ha-1 (29%) and 70 g ha-1 (48%) as well as aminopyralid at 122 g ae ha-1 (71%). By 60 DAT, all herbicide treatments resulted in 100% control.  These data indicate that Cadillo is susceptible to  many common herbicides utilized in grazinglands. sellersb@ufl.edu

Key words: Bahiagrass, pastures, postemergence, triclopyr, aminopyralid, metsulfuron, 2,4-D, aminocyclopyrachlor, imazapyr

 


DOSE RESPONSE OF BLACK MEDIC TO CLOPYRALID. S. M. Sharpe*1, N. Boyd2, P. J. Dittmar1; 1University of Florida, Gainesville, FL, 2University of Florida, Wimauma, FL (47)

ABSTRACT

Black medic is a problematic weed within the Florida strawberry industry.  Emergence occurs through the planting hole of the plastic covered beds while the crop establishes.  Clopyralid is registered for post-transplant control of weeds at rates of 140 to 280 g ae ha-1 though suppression of black medic is generally reported by growers.  An outdoor potted experiment was established to generate the dose response curve of black medic to clopyralid, determine the rate required to achieve 90% control and study the effect of plant size on control.  There was significant interaction between black medic stem length and clopyralid rate at 22 days after treatment (DAT) for epinasty (p=0.0022) and chlorosis (p=0.0055).  The effective dosage to induce 90% (ED90) epinasty varied between plant sizes, valued at 249.5 g ha-1 for 0.5 to 1 cm stem length and 398.3 g ha-1 for 3 to 6 cm stem length.  The chlorosis ED90 was 748.2 g ha-1 for the 0.5 to 1 cm stem length while the 3 to 6 cm stem length value was beyond the measured range.  Necrosis was not significantly affected by stem length during application.  The ED90 value was 1856.3 g ha-1.  The aboveground dry biomass ED90 was 197.3 g ha-1 for the 0.5 to 1 cm stem length and was outside the measured range for the 3 to 6 cm stem length.  The maximum label rate (240 g ha-1) did reduce aboveground biomass by 90% when applied to the 0.5 to 1 cm growth stage but not for the larger growth stage.  Clopyralid activity on black medic appears to continue past 42 DAT and may well result in total plant death though such is outside the bounds of the current study.  Overall, clopyralid remains a viable option for control of black medic within Florida strawberry production.


HERBICIDE SCREENING FOR LATE SEASON APPLICATION IN TOBACCO. M. D. Inman*, T. Whaley, M. Vann, L. Fisher; North Carolina State University, Raleigh, NC (48)

ABSTRACT

In recent years viable weed seed has been found in tobacco exported from the United States.  This has initiated concern over jeoporadizing sales of tobacco in these markets.  The majority of contamination from weed seed is most likely associated with mechanical harvest.  Historically, when tobacco was harvested by hand, less non-tobacco vegetation and weed seed would have entered the drying and curing process and subsequent export.  Farmers deploy a variety of management options that include herbicides applied at planting, several in-season cultivations,  and hand-removal of weeds to reduce weed interference, maintain leaf quality, and decrease seed populations for future years. Cultivation is ineffective in the tobacco row and hand removal is expensive.  The herbicides currently used in tobacco are often effective early in the season but do not provide complete control, in part because options post-transplant are limited and as tobacco is harvested throughout the season weeds will emerge as sunlight enters the canopy and residual effects of herbicides decrease.  Developing new herbicide alernatives for posy-transplant application could lead to more effective weed management in tobacco.  Field research was conducted during 2014 and 2015 at two locations to evaluate herbicides not currently lableled for tobacco to determine efficacy and tobacco injury.  Treatments were arranged in a randomized complete block design and replicated four times.  Eight herbicides were evaluated, each applied before topping (approximately 60 days after transplanting) and after the first harvest (approximately 90 days after transplanting).  Herbicides included carfentrazone, fomesafen, glufosinate, mesotrione, linuron, S-metolachlor, sulfentrazone, and trifloxysulfuron.  A final herbicide treatment was sethoxydim applied after first harvest and control treatment of sulfentrazone plus clomazone (pre-transplant only).  These respective treatments served to create a broadleaf weed control and a commercial standard.  Herbicides applied using a CO2 pressurized backpack sprayer equipped with Teejet VisiFlow flat-fan nozzles calibrated to deliver 147 L ha-1 157 kpa.  Spray applications covered the row middles as well as a portion of the tobacco bed.  Product rates were based upon the manusfactuer’s suggested use rate either for tobacco or for other crops.  Visable estimates of percent weed control and tobacco injury and tobacco yield and quaility were dtermined.  Visible injury was noted when glufosinate, (4%), mesotrione (13%), and carfentrazone (3%) were applied prior to topping at one of two locations but not when applied after the first harvest.  S-metolachlor, sulfentrazone, trifloxysulfuron, fomesafen, and linuron did not injure tobacco at either location regardless of timing of application.  However, tobacco leaf yield and quality were not affcted by herbicides at either location or year regardless of timing of application when compared with the commercial standard of sulfentrazone plus clomazone.  Palmer amaranth control was almost complete regardless of herbicide treatment when comapred with the sethoxydim-alone control.

 


IMPROVE SOIL QUALITY, DECREASE COSTS, OR REDUCE THE WEED SEEDBANK? INSIGHTS FROM A SYSTEMS COMPARISON OF PROMINENT ORGANIC WEED MANAGEMENT STRATEGIES. B. Brown*, E. R. Gallandt; University of Maine, Orono, ME (49)

ABSTRACT

Several prominent organic weed management strategies are fundamentally distinct: Critical Period Weed Control (CPWC) prioritizes cultivation during the crop’s sensitive “critical period” to avoid yield loss; Zero Seed Rain (ZSR) involves frequent cultivation to preempt seed rain; and intensive mulching utilizes black plastic, straw, or hay to suppress weeds. In 2014 and 2015 we aimed to quantify the benefits and drawbacks of each strategy by implementing each in a RCBD with four replicates using yellow onions as our test crop. CPWC plots required the least amount of labor. Plastic-mulched plots required three hand-weedings to control grasses penetrating the planting holes. Soil temperatures under the black plastic were consistently higher than other plots and onions matured several weeks earlier, which may have contributed to decreased bulb size in 2014. The straw mulching strategy involved the greatest expenditure per acre for both years of the experiment. An average of 59.5 oats/m2 germinated in the straw and necessitated hand pulling. Conversely, hay brought in weed seed but little emerged through the mulch. As expected, mulched plots performed favorably in several indicators of soil quality, however, the only significant predictor of yield was aboveground weed biomass. Unexpectedly, ZSR and mulch hay were more profitable than most of the other strategies. In 2015, uniformly managed sweet corn experienced yield loss where CPWC was implemented in 2014, likely due to ten times the weed germination as the other plots. Unlike aboveground weed biomass, strategy was not a significant covariate explaining sweet corn yields.

 


IMPROVED WEED MANAGEMENT AND CROP ESTABLISHMENT IN DRY DIRECT SEEDED SYSTEM USING ANAEROBIC GERMINATION TOLERANT RICE (ORYZA SATIVA L.) CULTIVARS. H. S. Chamara*1, V. Kumar1, B. Marambe2, B. S. Chauhan3; 1International Rice Research Institute, Los Banos, Philippines, 2University of Peradeniya, Peradeniya, Sri Lanka, 3University of Queensland, Toowoomba, Australia (50)

ABSTRACT

Direct-seeded rice (DSR) is becoming popular in both irrigated and rainfed areas in Asia due to its efficient resource utilization. However, weed emergence at the time of rice seedling emergence is the major concern in dry DSR. Though flooding immediately after DSR planting effectively controls weeds, the germination of rice seeds is affected. However, the crop establishment under flooded conditions can be enhanced with the use of anaerobic germination-tolerant (AG) rice cultivars. A field study was conducted at the International Rice Research Institute (IRRI), Philippines during the wet season of 2014 to evaluate the effect of flooding on weed suppression and crop establishment using AG rice (Oryza sativa L.) cultivars in dry direct seeding conditions. The experiment was laid in a split-split plot arrangement in a randomized complete block design with three replicates having three flooding depths (3 cm, 5 cm, and non-flooded control) as main plots, two weed levels (weedy and weed-free) as subplots, and four rice cultivars i.e. three AG cultivars, namely IR64-AG1, WTR-16RF2-AG4 and WTR-5-RF12-AG6, and a traditional flood tolerant cultivar Khao-Hlan-On, as sub-subplots.

The total above ground weed biomass in non-flooded control plots was 18, 144, and 281 g m-2 at 21, 35, and 49 days after seeding (DAS), respectively. At 3 cm flooding depth, weed biomass was reduced by 90, 70, and 40 %, respectively while at 5 cm flooding depth, these values were 95, 80, and 50% at 21, 35, and 49 DAS, respectively.

The density of different rice cultivars varied from 258 to 324 plants m-2 in the non-flooded control plots. At 35 DAS, Khao-Hlan-On and IR64-AG1 showed similar plant densities at 3 cm flooding depth (57 plants m-2) while lower plant densities were reported in WTR-16RF2-AG4 (30 plants m-2) and WTR-5-RF12-AG6 (23 plants m-2). At the higher flooding depth of 5 cm, the densities declined further to 10-41 plants m-2.

Flooding the fields soon after rice planting significantly controlled the weeds. However, it also affected crop establishment in all the tested cultivars.  The results suggest that there is further need to improve the tolerance of the rice cultivars to flooded conditions.  

 


SOIL SOLARIZATION FOR IMPROVED STALE SEEDBED PREPARATION IN THE NORTHEAST. S. K. Birthisel*, E. R. Gallandt; University of Maine, Orono, ME (51)

ABSTRACT

Soil solarization using clear plastic is an established weed management practice in arid and Mediterranean climates.  Its efficacy in northern temperate regions, however, is relatively unknown.  We conducted field experiments at two sites in Maine using soil solarization to augment stale seedbed preparation.  Fields were tilled, irrigated, and three replicates of four treatments were established at each site: Tilled; Tilled + Cultipacked; Tilled + Solarized for two weeks; and Tilled + Cultipacked + Solarized.  Cumulative weed emergence was recorded during the solarization period.  Following plastic removal, all plots were flamed to establish a stale seedbed.  Post-flaming, plots were left fallow for two weeks and then a final weed census was recorded.  During two weeks of treatment, soil solarization (with or without cultipacking) reduced cumulative weed emergence by over 70% in comparison to un-solarized controls.  In the final census, weed emergence was approximately 80% less in solarized treatments as compared with control stale seedbed preparations.  Soil temperatures during these field trials were consistently higher in solarized plots as compared to controls, reaching a maximum of 47 C at a depth of 5 cm.  Across treatments, there was a negative relationship between maximum soil temperature and weed emergence.  We expected clear plastic to encourage more rapid and extensive weed establishment which would improve the efficacy of a subsequent stale seedbed operation.  However, the surprisingly high soil temperatures apparently killed weed seeds and/or newly germinated seedlings, preempting establishment.  Solarization is a very promising strategy to create a stale seedbed prior to sowing high-value vegetable crops. 

 


JAPANESE STILTGRASS CONTROL IN LAWNS. J. R. Brewer*, S. S. Rana, S. Askew; Virginia Tech, Blacksburg, VA (52)

ABSTRACT

Japanese Stiltgrass Control in Turf

J. R. Brewer, S. S. Rana, and S. D. Askew

 

Past research related to Japanese stiltgrass (Microstegium vimineum) (JSG) control has been conducted in forest, woodlands, or wetlands using different chemical and mechanical controls including fenoxaprop, imazapic, sethoxydim, mowing, and hand-pulling.  Although JSG is the most common weed of lawns submitted to the Virginia Weed Clinic, little is known about JSG control in managed lawns.  Research to evaluate JSG response to herbicides commonly used in managed turfgrass systems on mown turfgrass areas is warranted. We conducted two studies in Newport, Virginia in the summer of 2014 and 2015 on a residential lawn site to evaluate turf herbicides for possible Japanese stiltgrass control. The two sites were 0.16 km apart, and both consisted of a cool-season turfgrass (turf) mix infested with JSG. In 2014, the trial was initiated on August 15 with a follow-up application 3 weeks later on September 6. In 2015, the trial was initiated on July 17 with a follow-up application on August 5. Treatments for both trials included: mesotrione at 280 g ai/ha-1 (single app), mesotrione at 140 g ai/ha-1 (seq app- sequential application 3 weeks after initial), topramezone at 57 g ai/ha-1 (single app), topramezone 24 g ai/ha-1 (seq app), quinclorac at 1120 g ai/ha-1 (single app), quinclorac at 660 g ai/ha-1 (seq app), fenoxaprop at 140 (HR), 70 (MR), and 35 g ai/ha-1 (LR) once, triclopyr at 1120 g ai/ha-1 once, mesotrione at 280 g ai/ha-1 + triclopyr at 1120 once, topramezone at 54 g ai/ha-1 + triclopyr once.  Treatments containing topramezone or quinclorac included methylated seed oil adjuvant at 1% v/v.  Additional adjuvant was not mixed with fenoxaprop and triclopyr applied alone.  All other treatments were mixed with nonionic surfactant at 0.25% v/v.  Treatments were applied with a hooded sprayer at 280 L/ha-1 and 4.8 km/h containing two flat fan 11002XR nozzles that generated a 71-cm spray width.

The interaction of year by treatment was significant for all measured responses and data are presented separately for 2014 and 2015. In 2014, no treatment injured turf greater than 20% at any rating. In 2015 at 1 week after initial treatment (WAIT), only mesotrione (single app) injured turf greater than 30%. In 2015, we had four treatments injure turf greater than 30%, which included mesotrione (single app), mesotrione + triclopyr, mesotrione (seq app), and topramezone + triclopyr at 48%, 47%, 38%, and 30%, respectively. The difference in injury observed between the two years could be partially due to differences in moisture and temperature of the two locations. The trial in 2014 was initiated later in the summer during hotter and dryer weather compared to the trial in 2015. In 2014 2 WAIT, mesotrione + triclopyr, fenoxaprop (HR), quinclorac (single app), and topramezone + triclopyr controlled JSG greater than 45% with mesotrione + triclopyr having the best control at 63%. In 2015, all treatments except quinclorac (seq. app) and triclopyr alone controlled JSG greater than 45%. Three treatments in 2015 controlled JSG greater than 70% 2 WAIT, which included topramezone (single app), topramezone + triclopyr, and fenoxaprop (HR) at 77%, 75%, and 73%, respectively. In 2014 at 6 WAIT, all rates of fenoxaprop controlled JSG greater than 95%, while all other treatments controlled JSG less than 70%. Topramezone (seq. app) and topramezone + triclopyr had the second highest control at 68% and 65%. In 2015, all fenoxaprop and topramezone-containing treatments controlled JSG greater than 95% while all other treatments had less than 70% control. Stiltgrass shoots were counted at the conclusion of both trials. In 2014, all rates of fenoxaprop contained less than 10 shoots per plot, and all other treatments had more than 240 shoots. In 2015, all topramezone and fenoxaprop-containing treatments contained less than 20 shoots per plot while all other treatments had greater than 250 shoots.

 


SOURCES OF ERROR THAT INTERFERE WITH MEASURING ANNUAL BLUEGRASS INFLUENCE ON BALL ROLL TRAJECTORY. S. S. Rana*, S. Askew, J. R. Brewer; Virginia Tech, Blacksburg, VA (53)

ABSTRACT

Annual bluegrass (Poa annua L.) is often speculated to impact ball roll direction and distance; and, golfers repeatedly blame it for missed putts.  However, the majority of these accusations are anecdotal and there is a lack of peer-reviewed research that supports the case against annual bluegrass.  After two years of research and rolling over 10,000 golf balls in the laboratory and on several Virginia golf courses, we have found that measuring the influence of annual bluegrass on ball roll trajectory is an extremely difficult task to execute.  And, possible effects of annual bluegrass are too subtle to be evaluated by commercially-available ball roll devices.  The inability to detect differences in ball roll trajectory due to annual bluegrass is primarily because of several sources of error that severely limit the utility of commercially-available ball roll devices for evaluating ball roll consistency following a simulated golf putt.  The first such error source is ball center of gravity.  When the center of mass is skewed to one side, balls can roll erratically, especially when ball momentum decreases.  Using a brine-solution method, we found that only 10 out of 180 balls, representing 13 different manufacturers and ball construction techniques, were off-centered.  The second source of error is terminal deceleration.  As the ball’s forward momentum decreases and can no longer overcome frictional forces, the ball can come to an erratic stop as determined by the green's surface characteristics.  Therefore, golfers are trained to putt 30-45 cm past the cup to overcome the erratic ball behavior and make successful putts.  Following the same technique, we overcame this error source from our field ball dispersion study by placing a pressure-sensitive paper on a strike plate positioned 30 cm short of the total putt distance.  The third source of error was ball roll legacy or "tracking" effects.  To evaluate legacy effects from consecutive ball rolls as influenced by brushing the green’s surface, research was conducted on two creeping bentgrass greens managed at 3 mm.  This research indicated that when a green canopy is not brushed, subsequent balls rolled in the same transect not only followed the track created by previous balls but also rolled further in a curvilinear trend, reaching 20-30 cm greater roll distance after just 2 previous balls had been rolled.  We overcame this source of error by brushing the canopy between each ball roll.  Previously, laboratory studies were conducted at Virginia Tech to select among six ball roll devices and 13 gall ball types from leading manufacturers for consistency of ball roll distance and trajectory.  The six ball roll devices included three commercially-available devices with linear or curvilinear inclined ramps: USGA stimpmeter® (USM), Pelz Meter (PM), and Greenstester (GT); and three custom prototypes built at Virginia Tech: Putting Robot (PR) and two devices that used curvilinear inclined ramps with a flexible ramp (FR) and carpet ramp (CR) to provide smooth roll.  These laboratory studies indicated that ball wobble or oscillations while rolling down the linear or curvilinear ramp of commercially-available ball roll devices were causing imprecision in ball direction upon leaving the device.  Assessments with a high-speed camera indicated that the area of ball wobble was positively correlated and accounted for approximately half of the error associated with directional imprecision.  The wobble effect was eliminated by selecting the PR for use in subsequent field studies to detect small patches of annual bluegrass on pure creeping bentgrass greens and evaluate the ball roll consistency.  All the above-mentioned error sources were minimized in the field to measure the impact of annual bluegrass on ball roll trajectory from a golf putt.

 


EFFECT OF HERBICIDE APPLICATION TIMING AND MOWING ON POST VASEYGRASS CONTROL. M. D. Jeffries*, T. Gannon, F. H. Yelverton; North Carolina State University, Raleigh, NC (54)

ABSTRACT

Vaseygrass (Paspalum urvillei Steud.) is an invasive, perennial C4-grass commonly found on roadsides in areas with poorly drained soils.  Due to its upright growth habit and prolific seedhead production, vaseygrass can impair motorist sightlines and subsequently, require increased management inputs to maintain vegetation at an acceptable height.  Two field experiments were conducted from 2012 to 2015 on North Carolina roadsides to evaluate the effect of mowing and mowing timing with respect to applications of various herbicides on vaseygrass control.  Both experiments evaluated clethodim (280 g ai ha-1), imazapic (140 g ai ha-1), foramsulfuron + halosulfuron + thiencarbazone (44 + 69 + 22 g ai ha-1), metsulfuron + nicosulfuron (16 + 59 g ai ha-1) and sulfosulfuron (105 g ai ha-1) with a non-ionic surfactant at 0.25% v v-1.  Experiment 1 focused on the effect of mowing (routinely mown or non-mown) and herbicide application timing (fall–only, fall–plus–spring or spring–only), while experiment 2 focused on pre-herbicide application mowing intervals [6, 4, 3, 2, 1 or 0 wk before treatment (WBT)].  From experiment 1, vaseygrass cover in nontreated plots was reduced 55% at 52 wk after fall treatment (WAFT) when routinely mown, suggesting this cultural practice should be employed where possible.  Additionally, routine mowing and herbicide application season affected herbicide efficacy.  Treatments providing > 70% vaseygrass cover reduction at 52 WAFT included routinely mown fall–only clethodim and fall–plus–spring imazapic, and fall–plus–spring metsulfuron + nicosulfuron across mowing regimes.  Experiments 1 and 2 data aligned with respect to clethodim being the most efficacious herbicide at a fall–only application timing.  Within clethodim, mowing vaseygrass 2 or 1 WBT resulted in the lowest cover at 40 (1 to 2%) and 52 (4 to 6%) wk after treatment (WAT) compared to other intervals, which aligns with current label recommendations.  Across all evaluated treatments in this research, vaseygrass persisted through 52 WAT, suggesting eradication of this species will require inputs over multiple growing seasons.

 


INDAZIFLAM: POTENTIAL NEW HERBICIDE TO CONTROL INVASIVE WINTER ANNUAL GRASSES. D. J. Sebastian*, C. T. Hicks, K. C. Kessler, S. J. Nissen; Colorado State University, Fort Collins, CO (55)

ABSTRACT

Managing invasive winter annual grasses on non-crop and rangeland remains a constant challenge throughout many regions of the US.  During the winter and early spring months, these species exploit moisture and nutrients before native plant communities break dormancy in the spring.  This results in dense, monotypic stands of winter annual grasses invading roadsides, abandoned crop fields, overgrazed grasslands, and open space properties.  Currently, there are limited management options for controlling winter annual grasses that work consistently, provide multiple years of control, and do not injure desirable plant communities.  Imazapic has been one of the most-widely used herbicides on rangeland, but this herbicide lacks consistency beyond the year of application and can cause injury to perennial grasses.  Indaziflam, a new herbicide mode of action for rangeland weed management, has provided long-term residual winter annual grass control in several field experiments.  A greenhouse study was conducted to compare indaziflam and imazapic pre-emergence control of downy brome (Bromus tectorum L.), feral rye (Secale cereale L.), jointed goatgrass (Aegilops cylindrical L.), Japanese brome (Bromus japonicus Thunb.), medusahead (Taeniatherum caput-medusae [L.] Nevski), and ventenata (Ventenata dubia (Leers) Coss).  For each herbicide, seven rates were used to develop dose-response curves for each species.  Log-logistic regression was conducted to determine GR50 values.  Indaziflam provided superior winter annual grass control across all species, compared to imazapic.  The GR50 values for imazapic were up to 25 times greater than indaziflam.  Jointed goatgrass was the most difficult winter annual grass to control for both herbicides.  This research provides evidence of a potential new tool and mode of action for land managers to control invasive winter annual grasses on US rangeland. 


EFFECT OF DELAYED DICAMBA/GLUFOSINATE APPLICATION ON PALMER AMARANTH CONTROL AND COTTON YIELD. R. A. Atwell*, A. C. York, R. W. Seagroves; North Carolina State University, Raleigh, NC (56)

ABSTRACT

Glyphosate-resistant Palmer amaranth (AMAPA) is a serious problem for cotton producers.  Growers currently depend heavily on glufosinate to control this weed, leading to concerns for selection of glufosinate-resistant biotypes. AMAPA must be 7.5 cm or less for consistent control by glufosinate. Growers struggle to make timely applications and often experience inadequate control. XtendFlex® cotton, tolerant of dicamba, glufosinate, and glyphosate, will provide growers another tool to manage AMAPA. Concurrent use of dicamba and glufosinate will reduce selection pressure on glufosinate and may widen the window for application. The objective of this experiment was to evaluate AMAPA control, cotton growth, and cotton yield in an AMAPA salvage situation created by delaying first POST application timing of dicamba plus glufosinate.

The experiment was conducted in 2015 at two locations in Clayton, North Carolina. No PRE herbicides were used in order to have dense weed pressure for POST treatments. Timings of the first POST application of dicamba plus glufosinate-ammonium (560 + 880 g ai ha-1) included timely application and delays of 7, 14, 21, or 28 d.  The timely application was made to 1-leaf cotton and AMAPA no larger than 7.5 cm tall.  A second POST application of dicamba plus glufosinate-ammonium (560 + 590 g ai ha-1) was made 14 d after the first application. A layby application of glyphosate potassium salt (1260 g ae ha-1) plus S-metolachlor (1070 g ai ha-1) plus diuron (1120 g ai ha-1) was made 72 d after planting. A non-treated check was included. The experimental design was a RCBD with four replications.

AMAPA was controlled 99% with 0- and 7-d timing delays 14 d after first POST application. Control declined to 93, 74, and 70% with 14-, 21-, and 28-d timing delays, respectively. AMAPA control greater than 88% was achieved across all timing delays 14 d after the second POST application. Greater than 99% control was observed in all treatments after layby and late in the season, but competition from AMAPA as first POST application timing was delayed reduced cotton growth, maturity, and yield. Cotton stunting at layby time increased linearly with each delay in first POST application timing. Compared to timely application, cotton was stunted 11, 31, 40, and 63% with 7-, 14-, 21-, and 28-d delays in first POST application timing, repectively. The percentage of open cotton bolls and cotton lint yield were reduced with each delay in first POST application timing. Yield reductions of 9, 30, 45, and 56% were observed with 7-, 14-, 21-, and 28-d delays in first POST application timing, respectively. This research demonstrates that “salvage” control of AMAPA is possible with two applications of dicamba plus glufosinate, but timely application will be emphasized to maximize cotton yield and reduce selection pressure.  

 


CONTROL OF CHLORIS SPP. WITH FOUR DIFFERENT SPRAY QUALITY PRODUCING NOZZLES ACROSS SIX POST-EMERGENCE HERBICIDES. J. Ferguson*1, R. G. Chechetto2, A. J. Hewitt3, B. S. Chauhan4, S. W. Adkins1, G. R. Kruger5, C. C. O'Donnell1; 1University of Queensland, Gatton, Australia, 2University of Queensland and UNESP - Botucatu, Gatton, Australia, 3University of Queensland and University of Nebraska-Lincoln, Gatton, Australia, 4The University of Queensland, Toowoomba, Australia, 5University of Nebraska-Lincoln, North Platte, NE (57)

ABSTRACT

A study to compare the effect of spray quality on the herbicide efficacy for control of windmill grass (Chloris truncata R. Br.) and its domestic cousin, Rhodes grass (Chloris gayana Kunth) var ‘Callide’ was conducted at the University of Queensland in Gatton, Queensland (QLD), Australia. The study compared across four different spray qualities using six nozzles (Fine – XR 11002; Medium – TT 11002; Coarse – AIXR 11002, TADF 11002, MiniDrift 11002; Extremely Coarse – TTI 11002). The herbicides selected were: clodinafop-propargyl + a methylated seed oil at 50.4 g ai ha-1 + 0.5 % v/v; imazamox and imazapyr + exthoxylated vegetable oil at 25 g ai ha-1 and 11.4 g ai ha-1  0.5 % v/v; metribuzin, at 330 g ai ha-1; glyphosate at 570 g ai ha-1; paraquat at 300 g ai ha-1; and amitrole + soyal surfactant at 1,400 g ai ha-1 + 0.1 % v/v . Rates were selected based on recommended control for Chloris spp. at the four leaf to tillering growth stage in Queensland. Plants were grown outside and irrigated twice daily. Plants were sprayed at the tillering growth stage on 11 August and the study replicated and sprayed on 6 October, 2015. Treatments were applied at 10.4 km hr-1 to achieve the 100 L ha-1 application volume. Nozzles were operated at 350 kPa, which produce a Fine, Medium, Coarse and Extremely-Coarse spray according to the catalogue from their manufacturers. Applications were made with 6m a towed sprayer and boom height was 50 cm above plants and nozzle spacing was 50 cm. After application, pots were returned to their original growing location, and watered daily as described above. Plants were watered daily for four weeks, and ratings were taken at 7, 14, 21 and 28 days after treatment (DAT). At 28 DAT, the remaining individual plants were clipped at the soil level and put into a paper sack and placed in a drier at 65°C, dried for 48 hours, and weights were recorded. Results showed no difference in dry weight reductions and spray quality in windmillgrass, but observed decreased dry weight reductions changing from a Fine to Extremely Coarse spray across all herbicides in Rhodes grass. Glyphosate, imazamox + imazapyr and clodinafop resulted in commercially acceptable control for both species, regardless of the spray quality. Proper nozzle selection can result in control of hard to control weed species, while reducing occurrence of spray drift.

 


CONTROL OF GLYPHOSATE-RESISTANT GIANT RAGWEED (AMBROSIA TRIFIDA L.) IN 2,4-D CHOLINE PLUS GLYPHOSATE-RESISTANT (ENLIST™) SOYBEAN. P. S. Chahal*1, K. Rosenbaum2, A. Jhala1; 1University of Nebraska-Lincoln, Lincoln, NE, 2DowAgrosciences, Crete, NE (58)

ABSTRACT

The early season emergence and vigorous growth habit of giant ragweed makes it one of the most competitive weeds in corn and soybean. With the intent to control glyphosate–resistant (GR) and hard to control weeds, a formulation of 2,4-D choline (24.4%) plus glyphosate (22.1%) (Enlist Duo® herbicide) has been developed recently to be used post-emergence in corn, soybean and cotton tolerant to Enlist Duo. In 2013, a field experiment was conducted in a soybean field infested with GR giant ragweed near McCool Junction, Nebraska. The study was laid out in a randomized completed block design with fifteen herbicide treatments and four replications in soybean tolerant to 2,4-D choline, glufosinate, and glyphosate (Enlist E3™ soybeans). Herbicide treatments included different POST herbicides applied early POST (E–POST) or late POST (L–POST) applications. At 14 days after E–POST, GR giant ragweed was controlled ≥99% with all the POST herbicides used in this study. Similarly, at 14 days after L–POST or 28 daysafter E-POST, all the herbicide treatments controlled GR giant ragweed ≥ 99%. No soybean injury was observed with any of the herbicide treatment applications during the growing season. No aboveground biomass of giant ragweed was observed in any of the herbicide treatment plots except in the nontreated control plots. Soybean crop was destructed at R3 growth stage. Results suggested that herbicide options are available for effective control of GR giant ragweed in Enlist E3™ soybean.

™Enlist, Enlist Duo, and Enlist E3 are registered trademarks of The Dow Chemical Company (“Dow”) or an affiliated company of Dow. Enlist E3 soybeans are jointly developed by Dow AgroSciences LLC and M.S. Technologies, LLC.

 


COTTON VARIETAL RESPONSE TO GLUFOSINATE TANK MIX COMBINATIONS. M. T. Plumblee*1, D. M. Dodds2, B. Blanche3, C. A. Samples1, D. Denton2, L. X. Franca1; 1Mississippi State University, Starkville, MS, 2Mississippi State University, Mississippi State, MS, 3Dow AgroSciences, Tensas Parrish, LA (59)

ABSTRACT

Cotton Varietal Response to Glufosinate Tank Mix Combinations. Michael T. Plumblee*1, Darrin M. Dodds1, Brooks Blanche2, Chase A. Samples1, and Andrew B. Denton1; 1Mississippi State University, Mississippi State, MS, 2Dow AgroSciences, Tensas Parrish, LA.

                                                                                         

ABSTRACT

 

Glufosinate-resistant cotton (Liberty Link) was commercialized in 2004 by Bayer Crop Sciences. Liberty Link cotton was developed through the insertion of the bialaphos resistance (BAR) gene, which provides resistance to glufosinate. Widestrike, which provides resistance to lepidopteron pests, was released in 2005 by Dow AgroSciences. The phosphinothricin acetyltransferase (PAT) gene, which also provides resistance to glufosinate, was used as a selectable marker during plant formation. Therefore, the objective of this research was to evaluate the effects of glufosinate tank mix combinations on four commercially available Liberty Link and Widestrike cultivars.

 

This experiment was conducted in 2015 at the R.R. Foil Plant Science Research Center in Starkville, MS to evaluate Widestrike™ cotton varieties and their tolerance to glufosinate and glufosinate tank mix combinations. Phytogen 312 WRF, 333 WRF, 444 WRF, and 499 WRF were planted May 8, 2015 in 4-row plots 3.86 m wide x 12.2 m long. Applications of glufosinate (Liberty), glufosinate + glyphosate (Durango), or glufosinate + glyphosate (Roundup PowerMax) at rates of 2.34 L ha-1 were made to 4-leaf cotton on June 10, 2015. Additional applications of the same tank mixes were made 14 days after the initial application. Phytotoxicity data were collected at 7 days after both the initial and secondary applications. End of season data collected included plant height, total nodes, and node above cracked boll, and lint yield. Data were subjected to analysis of variance using PROC Mixed procedure in SAS 9.2 and means were separated using Fishers protected LSD at p = 0.05.

 

Visual crop injury in PHY 333 WRF and PHY 444 WRF did not differ due to tank mix combinations 7 days after the initial application. PHY 312 WRF displayed a 3% increase in crop injury when glufosinate was applied alone rather than either of the other glufosinate + glyphosate treatments. PHY 499 WRF displayed a 2% increase in crop injury when glufosinate (Liberty) + glyphosate (Roundup PowerMax) was applied rather than glufosinate alone or glufosinate (Liberty) + glyphosate (Durango). Visual crop injury 7 days after the second application revealed that glufosinate (Liberty) + glyphosate (Durango) (44-50%) had significantly higher crop injury than glufosinate (Liberty) + glyphosate (Roundup PowerMax) (14-21%) in every variety. PHY 333 WRF and PHY 499 WRF also had higher percentage of crop injury from glufosinate (Liberty) treatments alone than glufosinate (Liberty) + glyphosate (Roundup PowerMax). PHY 312 WRF and PHY 444 WRF heights were not significantly different due to tank mix combinations. PHY 333 WRF was taller following glufosinate + glyphosate (Roundup PowerMax) tank mix application of herbicide. Compared to the other herbicide applications PHY 499 WRF was taller when untreated than when sprayed with glufosinate + glyphosate (Durango). The number of nodes per plant were only different in PHY 333 WRF and PHY 444 WRF following glufosinate + glyphosate (Roundup PowerMax) had more nodes than the untreated. PHY 444 WRF Glufosinate application also resulted in more nodes per plant in PHY 444 WRF. Cottonseed yield was not significantly due to herbicide application in any variety.

 


PALMER AMARANTH CONTROL PROGRAMS IN ENLIST COTTON. L. X. Franca*1, D. M. Dodds2, L. C. Walton3, M. T. Plumblee1, C. A. Samples1, D. Denton2; 1Mississippi State University, Starkville, MS, 2Mississippi State University, Mississippi State, MS, 3Dow AgroSciences, Tupelo, MS (60)

ABSTRACT

Palmer Amaranth (Amaranthus palmeri) Control Programs in Enlist Cotton. L. X. Franca*1, D. M. Dodds1, M. T. Plumblee1, C. A. Samples1, D. B. Denton1, L. C. Walton2; 1Mississippi State University, Mississippi State, MS, 2Dow AgroSciences, Tupelo, MS.

ABSTRACT

Given the proliferation of glyphosate-resistant Palmer amaranth (Amaranthus palmeri S. Wats.) throughout the Mid-South and Southeast United States, efficacious and cost effective means of control are needed. New technologies are being developed to combat glyphosate-resistant Palmer amaranth. The Enlist weed control system under development by Dow AgroSciences will allow for postemergence application of 2,4-D, glyphosate, and glufosinate to cotton containing Enlisttechnology. Dow AgroSciences has developed 2,4-D choline, a new form of 2,4-D which offers reduced volatility and reduced drift potential. Enlist Duo® herbicide is a premix of 2,4-D choline and glyphosate.

Experiments were conducted in 2012, 2013, and 2014 to evaluate Palmer amaranth control programs in Mississippi. Experiments were conducted at Hood Farms in Dundee, MS which was had a natural infestation of glyphosate resistant Palmer amaranth. The following POST herbicide programs were applied in conjunction with fluometuron at 1.1 kg ai/ha as a PRE: 1) fluometuron at 1.1 kg ai/ha only; 2) two applications of glyphosate at 1.1 kg ae/ha; 3) two applications of glufosinate at 0.5 kg ae/ha; 4) two applications of GF-2726 (2,4-D choline + glyphosate DMA) at 1.6 kg ae/ha; 5) two applications of GF-2726 at 2.2 kg ae/ha; 6) GF-2726 at 2.2 kg ae/ha + acetochlor at 1.3 kg ai/ha followed by GF-2726 at 2.2 kg ae/ha; 7) acetochlor at 1.3 kg ai/ha + glufosinate at 0.5 kg ae/ha followed by glyphosate at 1.1 kg ae/ha; 8) acetochlor at 1.3 kg ai/ha + glufosinate at 0.5 kg ae/ha followed by glufosinate at 0.5 kg ae/ha and 9) two applications of 2,4-D choline at 1.1 kg ae/ha + glufosinate at 0.5 kg ae/ha. The first POST application was applied to 5 to 10 cm Palmer amaranth followed by a second POST application two weeks after. All applications were made with a CO2-powered backpack sprayer equipped with Turbo Teejet induction spray tips utilizing 324 kPa pressure. Visual ratings of Palmer amaranth and cotton injury were taken 2 weeks after each application. Data was subjected to analysis of variance and means were separated using Fischer’s Protected LSD at α = 0.05.

Greater than 95% Palmer amaranth control was observed two weeks after the 10 cm Palmer amaranth application after the following treatments, fluometuron PRE plus: 3) two applications of glufosinate; 4) two applications of GF-2726 at 1.6 kg ae/ha; 5) two applications of GF-2726 at 2.2 kg ae/ha; 6) GF-2726 + acetochlor followed by GF-2726; 8) acetochlor + glufosinate followed by glufosinate and 9) two applications of 2,4-D choline + glufosinate (P < 0.0001). Glyphosate applied alone to 10 cm Palmer amaranth resulted in 77% control; however, fluometuron PRE alone resulted in 63% control indicating that glyphosate applied alone provided an additional 14% control over fluometuron PRE alone. Two weeks after the second POST application greater than 92% Palmer amaranth control was observed after the following treatments (all treatments had fluometuron applied PRE): 3) two applications of glufosinate; 4) two applications of GF-2726 at 1.6 kg ae/ha; 5) two applications of GF-2726 at 2.2 kg ae/ha; 6) GF-2726 + acetochlor followed by GF-2726; 7) acetochlor + glufosinate followed by glyphosate; 8) acetochlor + glufosinate followed by glufosinate and 9) two applications of 2,4-D choline + glufosinate. Applications of glyphosate and fluometuron alone resulted in 48 and 37% Palmer amaranth control, respectively (P < 0.0001). Cotton injury at two weeks after the second POST application was less than 3% for all treatments (P = 0.463).

 Glyphosate-resistant Palmer amaranth can be effectively controlled through planned PRE and POST weed management programs comprised of multiple modes of action. Sequential applications containing GF-2726 provided consistently high levels of Palmer amaranth control. Soil residual herbicides are recommended as part of a total weed management program to promote herbicide resistance management.

 ™® Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow.


WEED MANAGEMENT IN DICAMBA-RESISTANT SOYBEAN. D. Sarangi*1, M. S. Malik2, A. Jhala1; 1University of Nebraska-Lincoln, Lincoln, NE, 2Monsanto Company, St. Louis, MO (61)

ABSTRACT

The evolution of glyphosate and multiple-herbicide resistant weed species has left very few effective postemergence (POST) herbicide options for soybean growers. Pending regulatory approvals, the Roundup Ready 2 XtendTM soybeans, soybean trait providing both dicamba and glyphosate tolerance, are anticipated to be commercialized in near future. This technology will provide growers a new weed management tool to control multiple-herbicide resistant broadleaf weeds. The proposed dicamba application window will be from preplant application up to R1 stage (beginning of flowering) in soybean. Field experiments were conducted in 2015 at Clay County and Seward County, NE to evaluate herbicide programs in dicamba-tolerant soybean and to compare the results with the glufosinate-based weed management system. Environment effect was significant; therefore data from two experiment sites were presented separately. All herbicide programs included flumioxazin applied alone preemergence (PRE) or tank mixed with chlorimuron ethyl, or glyphosate, or MON 119096 (560 g ai ha-1, an experimental low-volatility formulation of dicamba or XtendiMaxTM). Results suggested that all the herbicide programs resulted in similar (≥ 84%) level of common waterhemp control at 21 d after PRE. Applications of MON 119096, MON 76832 (1,680 g ai ha-1, an experimental low-volatility premix formulation of dicamba plus glyphosate or Roundup XtendTM), and MON 76832 plus micro-encapsulated acetochlor (Warrant®) applied POST resulted in ≥ 98% control of common waterhemp control at 35 d after early-POST application at Clay County. Averaged across all the treatments from Seward County, common waterhemp control was higher (80%) with dicamba-based herbicide programs compared to the glufosinate-based programs (73%) at harvest. Similar trend was observed in yield data, where dicamba-based herbicide programs resulted in higher soybean yield (1,915 kg ha-1) compared to the glufosinate-based programs (1,583 kg ha-1). Dicamba-tolerant soybean technology should be used along with other herbicide modes-of-action to gain its full-benefit for control of herbicide-resistant weeds.


EFFECT OF TEMPERATURE ON EFFICACY OF 2,4-D AND GLYPHOSATE FOR CONTROL OF COMMON RAGWEED. Z. A. Ganie*1, M. Jugulam2, A. Jhala1; 1University of Nebraska-Lincoln, Lincoln, NE, 2Kansas State University, Manhattan, KS (62)

ABSTRACT

Common ragweed (Ambrosia artemisiifolia L.) is an important broadleaf weed in diverse agroecosystems, roadsides, and wastelands. Limited herbicide options are available for control of common ragweed resistant to ALS-, EPSPS-, PS II- and PPO-inhibitors in several states in the United States.  Glyphosate and 2,4-D are very effective for control of common ragweed, however, environmental factors including temperature may influence efficacy of these herbicides. The objective of this study was to evaluate the efficacy of 2,4-D and glyphosate for common ragweed control under different growth temperatures. Using glyphosate-susceptible and –resistant common ragweed biotypes, 2,4-D and glyphosate dose-response studies were conducted under two growth temperatures (day/night, 0C): low (LT) 20/11 and high (HT) 29/17. Plants were treated at 8 to 12 cm height with 2,4-D or glyphosate rates varying from 0.06x to 8x (1x of 2,4-D and glyphosate were 560 and 1,260 g ae ha-1, respectively). Visual control estimates and above ground biomass reduction (21 days after treatment) data were fit to a four-parameter log logistic model in drc package of R software. Additionally, uptake and translocation studies were conducted by applying approximately 20,000 dpm 14C labelled 2,4-D or glyphosate on two newly mature leaves of 8 to 10 cm plants grown at LT and HT. Radioactivity was determined in treated leaf, tissues above and below treated leaf at 24, 48, 72 and 96 h after treatment. Results of visual control estimates of 2,4-D dose-response study suggested ED90 of 331 and 7,270 g ae ha-1 at HT and LT, respectively. Similarly, glyphosate dose-response study suggested ED90 of 587 and 6,963 g ae ha-1 for susceptible biotype and 8,354 and 218, 014 g ae ha-1 for resistant biotype at HT and LT, respectively. Uptake and translocation experiments indicated more translocation for both 2,4-D and glyphosate at HT compared to LT. In conclusion, the efficacy of 2,4-D and glyphosate for common ragweed control improved at warm temperature (29/17 0C d/n) due to increase in translocation of these herbicides compared to cooler temperatures (20/11 0C d/n).


EFFECT OF SPRAY WATER PH, FOLIAR FERTILIZERS, AND AMMONIUM SULFATE ON EFFICACY OF A 2,4-D PLUS GLYPHOSATE FORMULATION. P. Devkota*, W. G. Johnson; Purdue University, West Lafayette, IN (63)

ABSTRACT

Carrier water pH is a critical factor for optimum herbicide efficacy. Foliar fertilizers are often co-applied with POST herbicides which could influence herbicide efficacy. Field and greenhouse studies were conducted to evaluate the effect of carrier water pH, foliar fertilizer, and ammonium sulfate (AMS) on premixed 2,4-D plus glyphosate efficacy on horseweed and Palmer amaranth. In the field study, treatments consisted of two factor combinations: carrier water pH (at 4, 6.5, or 9) and foliar fertilizer (zinc or manganese fertilizer at 2.5 or 3.75 L ha-1, respectively). In the greenhouse study, AMS was applied at 0 or 2.5% v/v in addition to the carrier water pH and foliar fertilizer treatments. Premixed 2,4-D plus glyphosate was applied at 0.785 and 0.834 kg ae ha-1; and 0.266 plus 0.283 kg ae ha-1 in field and greenhouse studies, respectively. In the field study, horseweed control and plant density reduction was 11% or greater with 2,4-D plus glyphosate applied at water pH 4 compared to 6.5 or 9 at 4 WAT in 2014. Horseweed control and plant density reduction was reduced with 2,4-D plus glyphosate co-applied with Mn compared to Zn fertilizer in 2015. In the greenhouse study, effect of carrier water pH, foliar fertilizer, or AMS was significant for horseweed and Palmer amaranth control with 2,4-D plus glyphosate. Premixed 2,4-D plus glyphosate showed 7% or greater control of horseweed and Palmer amaranth with carrier water pH 4 compared to 9. Co-applied Mn fertilizer reduced horseweed or Palmer amaranth control compared to without fertilizer. Horseweed or Palmer amaranth control with premixed 2,4-D plus glyphosate was increased by 10% with the addition of AMS. In conclusion, 2,4-D plus glyphosate formulation applied with carrier water pH 4 and addition of AMS resulted in greater control of horseweed and Palmer amaranth. 

 


OPTIMIZING RATE AND INTERVAL BETWEEN SEQUENTIAL APPLICATIONS OF GLUFOSINATE IN LIBERTYLINK SOYBEAN. C. J. Meyer*, J. K. Norsworthy, J. K. Green, S. M. Martin; University of Arkansas, Fayetteville, AR (64)

ABSTRACT

The use of glufosinate in U.S. agriculture is increasing in response to the rising number of row crop acres with confirmed cases of resistance common soybean herbicides. Furthermore, the anticipated release of new technologies that include glufosinate-resistant traits (e.g. Enlist, RoundupReady Xtend) will likely continue to intensify the use of glufosinate. An experiment was conducted at the Arkansas Agricultural Research and Extension Center in Fayetteville, AR, in 2015 to identify POST-application strategies that maximize the utility of glufosinate. A RCBD with a factorial treatment structure was used for the experiment, in which factor 1 was glufosinate rate (451, 595, 738, 882 g ai ha-1) and factor 2 was sequential application structure. The five levels for the sequential application structure were: no sequential application, initial application followed by (fb) a sequential application 7 days after the initial application (DAI), initial fb sequential 10 DAI, initial fb sequential 14 DAI, and initial fb sequential 21 DAI. The plot area was planted to LibertyLink® (glufosinate-resistant) soybean and the first herbicide application occurred when weeds reached approximately 25 cm in height. For treatments that contained a sequential application, the same rate used in the initial application (e.g. 451 g ai ha-1) was also used in the sequential. A single application of 451 g ai ha-1 controlled Palmer amaranth and barnyardgrass 70% and 78%, respectively, 2 weeks after the final application (21 DAI) occurred. A sequential application, of the same rate, improved control for both Palmer amaranth (96%) and broadleaf signalgrass (97%). A single application of 882 g ai ha-1 controlled Palmer amaranth 74% and broadleaf signalgrass 86%, showing that a treatment with a sequential application of a low rate (451 g ai ha-1) is more effective than a single application of a high rate (882 g ai ha-1). Thus, to maximize weed control, glufosinate should be applied sequentially at the desired rate with a 7-14 day interval between applications. If sequential applications of glufosinate are used in combination with a comprehensive weed control management program (using residual herbicides PRE and POST, tillage, etc.) the likelihood of evolving glufosinate-resistant weeds should be greatly reduced, and the LibertyLink technology should remain a valuable weed management tool. 

 


GLYPHOSATE RESISTANT GIANT RAGWEED (AMBROSIA TRIFIDA): PHENOTYPIC VARIATION, GENOTYPIC DIVERSITY, AND RESISTANCE MECHANISMS. J. C. Walker*1, T. Tseng2, D. B. Reynolds2, D. R. Shaw1; 1Mississippi State University, Mississippi State, MS, 2Mississippi State University, Starkville, MS (65)

ABSTRACT

Giant Ragweed (Ambrosia trifida) is a problematic weed that occurs throughout North America. Significant crop losses can occur where infestations are not properly controlled. Giant ragweed is very competitive due to its aggressive growth habits. In recent years, giant ragweed has developed resistance to several herbicides including glyphosate. The objectives of this study are to, 1) confirm glyphosate resistance in several biotypes from MS (Hayes, Hemphill, and Younger), TN, and OH, having survived field doses of glyphosate; 2) measure shikimate accumulations in biotypes and compare to a susceptible MS biotype; and, 3) conduct study to evaluate growth and development of the various biotypes. Whole plant bioassays confirmed all suspected resistant biotypes to be glyphosate resistant, and provided complete control of the susceptible MS biotype at 14 DAT. Shikimate accumulation levels were measured and results show 20% higher shikimate accumulation in the susceptible biotype as compared to resistant MS biotypes. Six individual plants from each biotype were established in greenhouse and transplanted outside into global buckets where they were maintained on an automatic watering system for eight weeks. Height, number leaves on main stem, and number of nodes was measured weekly. Total leaf area, and, dry leaf and stem weights, were recorded at the end of eight weeks. The patterns of growth for all biotypes were similar for the first two weeks but from third week onwards, the Ohio biotype grew at a faster pace than all other biotypes, until the fifth week where the Ohio biotype slowed its growth and overall height stayed about the same throughout the rest of the study. There were no significant differences in total leaf area, or dry stem and leaf weights, for the Hayes, Hemphill, and susceptible MS biotypes. The TN and Younger biotypes had significantly less leaf area (50%) as compared to Hayes, Hemphill, and MS susceptible biotypes. The Ohio biotype had the smallest average leaf area (966 sq cm). Dry leaf and stem weights followed similar patterns. These results suggest there were no fitness penalties associated with the development of glyphosate resistance, as two of the resistant biotypes from MS (Hayes and Hemphill) showed very similar plant measurements 9944 and 11228 sq cm, respectively, as compared to the susceptible MS biotype (9070 sq cm). However, the biotypes that originated from Northern environments (TN and OH) had smaller leaf areas (5359 and 966 sq cm, respectively).


RNA-SEQ TRANSCRIPTOME ANALYSIS FOR GLUFOSINATE TOLERANCE IN PALMER AMARANTH. R. A. Salas*1, N. R. Burgos1, A. Lawton-Rauh2, R. Noorai2, C. Saski2; 1University of Arkansas, Fayetteville, AR, 2Clemson University, Clemson, SC (66)

ABSTRACT

Palmer amaranth (Amaranthus palmeri) is an economically aggressive weed plaguing cotton and soybean farmers in the southern United States. The widespread occurrence of glyphosate-resistant weeds prompted the use of alternative herbicides such as glufosinate for controlling herbicide-resistant weeds. This study aimed to generate the transcriptome sequence of Palmer amaranth, elucidate genes involved in glufosinate response, and determine non-target site-based tolerance mechanisms in glufosinate-tolerant Palmer amaranth using analyses of RNA-Seq data. Glufosinate at 0.55 kg ai ha-1 was applied to 3- to 4-inch susceptible (S) and tolerant (T) plants. Leaf tissues from both treated and nontreated seedlings were harvested after 24 h for RNA extractions and RNA-Seq analysis. An ammonia accumulation assay was conducted and glutamine synthetase (GS) gene copy number was determined. The S plants accumulated two times more ammonia than the T plants. GS copy number ranged from one to three in both S and T plants.  A reference transcriptome consisting of 72,794 contigs was generated using Illumina sequencing. Relative to the respective nontreated checks, 8,154 genes were affected by herbicide application in the T plants and 6,034 genes in the S plants. Comparisons between treated S and T plants revealed 567 differentially expressed genes, 210 of which were more abundant in T plants than in the S plants. The majority of these genes were related to metabolic processes, oxidoreductase activity, transferase activity, and nucleotide binding. Candidate genes that are potentially associated with non-target site-based tolerance to glufosinate include genes coding for the NAC transcription factor, glutathione S-transferase, cytochrome P450 (cyp7a2192, 794a1, 86b1, 82g1, 71a3), ABC transporter, glycosyl transferase, and acyltransferase. Increased expression of detoxification-related and transporter genes suggest that glufosinate is either metabolized or differentially translocated in the T plants. Further study will involve validation of these candidate genes using quantitative real-time PCR, verification of differential glufosinate degradation between S and T plants, and evaluation of stability of this trait across generations.

 


USING TRANSCRIPTOMICS TO INVESTIGATE GLYPHOSATE RESISTANCE AND THE RAPID NECROSIS RESPONSE IN GIANT RAGWEED. C. R. Van Horn*, P. Westra; Colorado State University, Fort Collins, CO (67)

ABSTRACT

The introduction of glyphosate resistant crops along with widespread multiple in-season applications of glyphosate as part of weed management strategies that fail to address long-term weed control have provided the perfect scenario to foster the recent boom in glyphosate resistant weeds. In order to implement best strategies to manage glyphosate resistant weeds, it is important to understand the mechanism of resistance. Glyphosate resistance in giant ragweed (Ambrosia trifida) was first discovered in 2004 and we still do not know the mechanism of this resistance today. Glyphosate targets and inhibits the enzyme 5-enolpyruvalshikimate-3-phosphate synthase (EPSPS), which prevents the synthesis of essential aromatic amino acids. We have investigated the mechanism of glyphosate resistance using twenty-two geographically diverse giant ragweed populations. From these populations we have characterized three phenotypic responses to glyphosate treatment: susceptible, resistant slow response, and resistant rapid necrosis. Observational data suggests that a carbon source, whether from photosynthesis or an artificial source is a necessary component to stimulate the rapid necrosis response. Sequence analysis showed no nucleotide mutation at the Proline-106 target site region across all populations sequenced. Analysis of EPSPS copy number using qPCR shows no evidence of increased EPSPS in either glyphosate resistant or susceptible populations. Shikimate data suggests a translocation-based resistance mechanism may be involved. Currently we hypothesize that a very rapid transcriptional signal is causing an upregulation of stress/defense response genes in the glyphosate resistant biotype to a greater extent than the glyphosate susceptible biotype. Current research involves a transcriptomics approach to investigate gene expression patterns during this response. Our RNA-Sequencing experimental design consists of 48 samples comparing gene expression patterns across phenotype, plant replicates, tissue type, and time points after glyphosate treatment. With this next generation sequencing data, we hope to identify candidate genes involved in the glyphosate resistance mechanism. These initial results provide a much needed framework for the future of giant ragweed glyphosate resistance research, which becomes increasingly important as the use of glyphosate-resistant crops develops world-wide. With this research, we can continue to work toward sustainable forms of herbicide weed management.

 


ENVIRONMENTAL FATE OF RINSKORTM ACTIVE: FIELD DISSIPATION AND REPLANT INTERVAL FOR SOYBEAN. M. R. Miller*1, J. K. Norsworthy1, M. R. Weimer2, R. Huang2, Z. Lancaster1, S. Martin1; 1University of Arkansas, Fayetteville, AR, 2Dow AgroSciences, Indianapolis, IN (68)

ABSTRACT

Herbicides are the primary method used to control barnyardgrass  (Echinochloa crus-galli) in rice. As a result, this troublesome weed has evolved resistance to at least 9 modes of action globally and at least 7 modes of action in the United States. LoyantTM is a new rice herbicide being developed by Dow AgroSciences which contains RinskorTM active, the second herbicide in a new structural class of synthetic auxins in the arylpicolinate herbicide family. This new herbicide provides broad-spectrum post-emergence control of broadleaf, grass, and sedge species at low use rates with an alternative mode of action for rice. A field experiment was conducted in 2014 and repeated in 2015 to evaluate potential plant-back restrictions for soybean following an application of Rinskor. The experimental design was a randomized complete block with a two factor factorial treatment structure comprised of Rinskor applied at 30 and 60 g ai ha-1 at 56, 28, 14, and 0 days prior to planting soybean. The concentration of Rinskor acid in soil at the time of planting was determined by collecting 5 soil cores at a 15-cm depth in each plot at the time of planting and quantified in the laboratory using LC-MS/MS. Visual estimates of soybean injury were highest 21 days after planting when Rinskor was applied 0 days before planting.  These injury assessments corresponded to the highest concentration of Rinskor acid recovered from soil at the time of planting. Conversely, soybean injury was reduced when Rinskor was applied at increasing intervals before planting. By the end of season, soybean injured by Rinskor had not recovered and there was stand loss. Soybean yield was similar to the non-treated control when 30 or 60 g ha-1 of Rinskor was applied 56 days prior to planting whereas all other treatments significantly lowered yield.  The replant interval following an application of Rinskor will likely be determined by several factors including soil moisture, amount of herbicide applied, and the crop selected for replanting. These results support a relatively short replant interval for soybean after Rinskor application compared to other herbicides commonly used in rice. It appears unlikely that there will be rotational crop restrictions when planting of soybean the year following a Rinskor application in rice.

 

TMTrademark of the Dow Chemical Company (“Dow”) or an affiliated company of Dow. LoyantTM is not registered with the US EPA at the time of this presentation. The information presented is intended to provide technical information only.

 


HERBICIDE AND NITROGEN APPLICATIONS IMPACT NITROUS OXIDE EMISSIONS. A. M. Knight*, W. J. Everman, S. C. Reberg-Horton, S. Hu, D. L. Jordan, N. Creamer; North Carolina State University, Raleigh, NC (69)

ABSTRACT

Estimates of greenhouse gas emissions indicate that agriculture accounts for approximately 10 percent of these emissions.  Agriculture is estimated to contribute largely to the output of one of the main greenhouse gases, nitrous oxide, which is suspected to be 59% of those emissions caused via agriculture.  Additionally, this gas is thought to be contributing to climate change.  While these large percentages are evidenced to be largely due to nitrogen application and tillage, little research has been conducted to determine if herbicides play a role in greenhouse gas emissions.  An incubation study was conducted with treatments of the herbicides nicosulfuron, chlorimuron, flumioxazin, atrazine, glyphosate, glufosinate, pendimethalin, paraquat, mesotrione, isoxaflutole, s-metalochlor, 2,4-D, dicamba and a non-treated control.  Additionally, high (22.5 kg ha-1) and low (135 kg ha-1) rates of urea ammonium nitrate were applied.  Lab studies were conducted using a Tarboro Loamy Sand soil from Goldsboro, NC maintained at a water filled pore space of 70%.  Gas flux was measured following treatment application at 12, 25, 48, 72, 120, and 168 hours for the greenhouse gas N2O using gas chromatography.  Results indicated that differences in N2O emissions were present for both nitrogen rates, herbicides applied and the interaction.  A field study was also conducted to quantify herbicide differences in the field following USDA-ARS GRACEnet Project Protocols.  Gas measurements were taken at 24 hour increments for a week and, field results showed evidence of herbicide differences in N2O emissions.


EVALUATING THE PHYSIOLOGICAL BASIS OF 2,4-D TOLERANCE IN HYBRID WATERMILFOIL (MYRIOPHYLLUM SPICATUM X SIBIRICUM). K. C. Kessler*1, S. J. Nissen1, R. A. Thum2, T. A. Gaines1; 1Colorado State University, Fort Collins, CO, 2Montana State University, Bozeman, MT (70)

ABSTRACT

Managing invasive aquatic plants, like Eurasian watermilfoil (EWM; Myriophyllum spicatum), is vital to maintaining the health and quality of our freshwater resources. Invaded sites have decreased biodiversity, altered flow regimes, increased sedimentation, and further eutrophication. The most cost effective herbicide labeled for EWM management is 2,4-D; however, the discovery of 2,4-D tolerant milfoil hybrids (M. spicatum X M. sibiricum) has raised concerns about future management options. The objective of this research was to explore the physiological basis of 2,4-D tolerance in hybrid populations by evaluating 2,4-D absorption, translocation and metabolism.  Two experiments were conducted, one to evaluate absorption and translocation and the other metabolism.  In both experiments, plants were placed in 4 L mesocosm filled with 3 L of tap water and treated with 1 mg L-1 2,4-D amine supplemented with 7.4 KBq 14C 2,4-D (ring-labeled).  At the following time points: 6, 12, 24, 48, 96, and 192 hours after treatment (HAT), three plants from each population were randomly selected and harvested.  To evaluate shoot absorption and root translocation, the shoot and root tissue were oxidized separately. Herbicide metabolism was quantified using HPLC paired with radioactive detection.  All data were analyzed using nonlinear regression.  Foliar absorption and root translocation were compared using fresh biomass Plant Concentration Factors (PCF) (Concentration in plant µg g-1/Concentration in water µg mL-1).  Maximum absorption (Amax) values could not be compared as neither population reached Amax over the time course; however, absorption for EWM and hybrid populations at 192 HAT were similar (16.3 PCF ± 1.6 SE and 22.1 PCF ± 2.5 SE, respectively).  Less than 1% of absorbed 2,4-D was translocated to root tissue in both populations.  Additionally, there was no difference between the 2,4-D metabolism rate between the two populations and metabolite profiles were similar. The mechanism of tolerance remains unknown.  Future studies will determine 2,4-D metabolism rates at lower herbicide concentrations as field and mesocosm studies suggest that the greatest differential sensitivity between hybrid and EWM occurs at application rates of 0.5 mg L-1 or less. 

 


COMPARATIVE FLUX ANALYSIS OF NITROGEN METABOLISM IN GLYPHOSATE RESISTANT AND SUSCEPTIBLE AMARANTHUS PALMERI BIOTYPES. A. S. Maroli*1, N. Tharayil1, V. K. Nandula2; 1Clemson University, Clemson, SC, 2USDA-ARS, Stoneville, MS (71)

ABSTRACT

Amino acids, the building blocks of proteins, are found to be elevated in most plants growing under sub-optimal environments, a strategy thought to be part of an efficient stress mitigation physiology. Despite their paramount influence on the survival of plants under stressful environments, we currently lack a robust understanding about the relative contribution of catabolic vs anabolic pathways that contribute to this buildup of amino acid pool. Using stable isotope-resolved metabolomics (SIRM), the present study characterized the differential contribution of anabolic (de novo synthesis) vs catabolic (protein degradation) process by examining the fluxes in amino acid pools in Amaranthus palmeri biotypes susceptible (S) and resistant (R) to glyphosate, an EPSPS targeting herbicide.

Following exposure to glyphosate (0.4 kg ai ha-1), the proportion of 15N amino acids (15N-AA) in the total amino acid pool increased in the S-biotype, compared to R-biotype, which indicates a potential increase in the de novo amino acid synthesis, coupled with a lower protein synthesis rate in this biotype. Consistent with other plant stress studies, the 15N amino acid enrichment profile of the S- biotype, compared to that of the R-biotype, showed a significant decrease in the abundance of the 15N-AA with the exception of four shikimate pathway-independent amino acids- asparagine, glutamine, alanine and serine. The potential causes for the higher de novo synthesis of Asn and Gln in the herbicide treated S-biotype could be attributed to their primary role of inorganic nitrogen assimilation while the abundance of Ala and Ser can be attributed to the transamination of glycolytic intermediates of pyruvate and 3-phosphoglycerate respectively via carboxylation of phosphoenolpyruvate. Furthermore, the efficiency of GS/GOGAT cycle evaluated as a function of Gln/Glu ratio indicates that though there is regular functioning of the initial nitrogen assimilation in the chloroplasts of herbicide treated S-biotype, with the synthesis of glutamine using glutamate as a substrate, subsequent transamination reactions for de novo amino acid synthesis is disproportionately disrupted. In contrast, the herbicide treated R-biotype had a Gln/Glu ratio of about 1.4, similar to that of non-herbicide treated S- and R-biotypes. However, the herbicide treated S-biotype had a 10 fold increase in the Gln/Glu ratio, indicating that there is a significant accumulation of nitrogen-rich amino acids (Gln, Asn) during the early process of nitrogen assimilation and decreased synthesis of amino acids downstream of glutamine. 

The observations from this study categorically points to the fact that the toxic effect of EPSPS inhibiting herbicide is not restricted to inhibition of biosynthesis of aromatic amino acid alone but also disrupts the de novo biosynthesis of most non-aromatic acids. Furthermore, it can be concluded that the abiotic stress induced increase in total amino acid pool in the S-biotype, though primarily contributed by protein catabolism, is also a result of anabolism of amino acids majorly involved in transamination reactions (Gln, Asn, Glu) facilitating subsequent amino acid biosynthesis.


POLLEN-MEDIATED RESISTANCE TRANSFER FROM HPPD-RESISTANT WATERHEMP TO PALMER AMARANTH IN NEBRASKA. M. C. Oliveira*1, T. A. Gaines2, A. Jhala1, S. Z. Knezevic3; 1University of Nebraska-Lincoln, Lincoln, NE, 2Colorado State University, Fort Collins, CO, 3University of Nebraska-Lincoln, Concord, NE (72)

ABSTRACT

The dioecious and anemophily natures of common waterhemp and Palmer amaranth are plant characteristics that help the rapid spreading of herbicide resistant genes. The objective of this study was to evaluate the gene transfer from HPPD-resistant common waterhemp to HPPD-susceptible Palmer amaranth. The experiments were conducted in 2014 in Dixon County, NE using a square design in which the pollen donor (male plants of HPPD-resistant common waterhemp) is surrounded with pollen receptor (female plants HPPD-susceptible Palmer amaranth) in eight geographical block directions (N, NE, E, SE, S, SW, W, NW). In October 2014, Palmer amaranth’s seeds were harvested and then planted during the summer of 2015. The F1 seedlings (5-7 cm tall) were sprayed with a label rate (175 g ai ha-1) of HPPD-inhibiting herbicide (mesotrione), which was used as phenotypic marker. Based on the first year of data, the proportion of the HPPD-resistant F1 survivors was the highest in the center of the source population and reduced exponentially with the increasing distance from the source in all directions. For example, there was 1.7% survivors at 0.5 m from the source population, which was then reduced among all direction to 0.4% at 5 m and to 0.2% at 30 m and 45 m from the source of HPPD resistance. Results from the first year study indicated that interspecific hybridization between waterhemp and Palmer amaranth do occur under field conditions, therefore the HPPD-resistant gene can be transferred among these Amaranthus species. Next step is verify that these are true F1 hybrids, using the PCR-RFLP molecular marker.


POPULATION GENOMICS OF GLYPHOSATE-RESISTANT PALMER AMARANTH (AMARANTHUS PALMERI) USING GENOTYPING-BY-SEQUENCING (GBS). A. Kuepper*1, W. McCloskey2, H. Manmathan1, E. L. Patterson1, S. J. Nissen1, S. Haley1, T. A. Gaines1; 1Colorado State University, Fort Collins, CO, 2University of Arizona, Tucson, AZ (73)

ABSTRACT

Throughout the southeastern and southwestern United States, populations of Palmer amaranth (Amaranthus palmeri) have been identified with evolved resistance to the herbicide glyphosate. This project aims to determine the degree of genetic relatedness among a set of glyphosate-resistant and –susceptible lines by analyzing patterns of phylogeography and diversity on an intraspecific level. Seven different lines of Palmer amaranth from different geographic regions were tested against a glyphosate-resistant line from an Arizona locality for glyphosate resistance. The goal is to ascertain whether resistance evolved independently in the Arizona locality, or whether resistance spread from outside to the location. For example, the transportation of resistant seeds in harvesting equipment could be a source of gene flow via seed migration. The accumulation of shikimic acid and EPSPS copy number were tested to confirm resistance. The susceptible lines showed an average of 41 mg/ml shikimic acid accumulation while the resistant lines showed an average of 0.1 mg/ml after exposure to a 500µm solution of glyphosate. Individuals from the Arizona glyphosate-resistant locality had increased copies of EPSPS in the range of 20 – 290-fold. This is the same mechanism previously identified in the Palmer amaranth lines from the southeastern US, therefore it is possible that resistance was introduced from elsewhere. DNA samples were collected for genotyping by sequencing (GBS) to perform single nucleotide polymorphism (SNP) calling, which will be used to determine the genetic structure of the different lines. Currently, neighbor joining trees and principle component analysis are being performed. This information about the evolution and migration of glyphosate resistance will be useful to design better strategies for herbicide resistance management. 

TARGET-SITE RESISTANCE TO ALS-INHIBITORS IN WEEDY SORGHUM SPECIES. R. Werle*, K. Begcy, M. K. Yerka, J. L. Lindquist; University of Nebraska-Lincoln, Lincoln, NE (74)

ABSTRACT

Traditional breeding technology is currently being used to develop grain sorghum germplasm that will be tolerant to acetolactate synthase (ALS)-inhibiting herbicides. This technology (Inzen, DuPont) has the potential to improve sorghum production by allowing for the postemergence control of traditionally hard-to-control grasses in the United States. However, grain sorghum and shattercane can interbreed and introduced traits such as herbicide tolerance could increase the invasiveness of the weedy relative. Moreover, ALS-resistance in shattercane populations has been reported, indicating that over-reliance on ALS-chemistry may also select for resistant biotypes. Inzen sorghum will carry a double mutation in the ALS gene (Val531Ile and Trp574Leu), which confers high levels of resistance to herbicides in the ALS sulfonylurea and imidazolinone families. In 2013, seeds from 190 shattercane and 59 johnsongrass populations were collected with the objective to evaluate the distribution of ALS-resistance in weedy-sorghum populations across northern Kansas, northwestern Missouri, and southern Nebraska. Five shattercane and five johnsongrass populations were confirmed resistant to imazethapyr. Four shattercane and three johnsongrass populations were confirmed resistant to nicosulfuron. All ALS-resistant shattercane and johnsongrass populations were collected in Nebraska except for one nicosulfuron-resistant johnsongrass population collected in Kansas. The objective of this study was to determine whether the amino acid substitutions present in Inzen sorghum were also present in the ALS-resistant weedy populations. Primers specific to the Val531 and Trp574 region of the ALS-gene were used to screen the populations in PCR. The Trp574Leu mutation was present in one ALS-resistant johnsongrass population and the Val531Ile was detected in three ALS-resistant shattercane, one susceptible shattercane used as control in our study, and one ALS-resistant johnsongrass population. Moreover, Val531Ile was present in resistant and/or susceptible individuals within johnsongrass and shattercane populations that were segregating for ALS-resistance, indicating that by itself, Val531Ile amino acid substitution does not confer resistance to ALS-inhibiting herbicides. None of our populations presented both mutations simultaneously, as does Inzen sorghum. This research indicates that the ALS mutations present in Inzen sorghum already exist individually in weedy sorghum populations. Thus, pollen-mediated gene flow from Inzen sorghum to related weed species would increase the frequency of ALS-resistance alleles in wild populations, especially where mitigating strategies are not deployed; but use of the technology will not transfer novel or unprecedented ALS mutations to weeds.  


INFLUENCE OF SOIL TYPE AND GROWING ENVIRONMENT ON THE SELECTIVITY INDEX IN HERBICIDE RESISTANCE STUDIES. C. W. Coburn*, A. R. Kniss; University of Wyoming, Laramie, WY (75)

ABSTRACT

The selectivity index (SI) is frequently used as a measure of herbicide resistance, and it is important to understand how experimental factors may influence it. Previous research suggests that soil type and growing environment can influence the SI in herbicide resistance studies. The objective of the present research was to determine the influence of environment (indoor vs. outdoor) and soil type (field soil vs. potting media) on the SI using Chenopodium album L. (CHEAL) biotypes treated with glyphosate. Plants were grown in 1500 cm3 pots containing either field or potting media in a hoop house (indoor) or on the exterior of the hoop house (outdoor). Glyphosate-susceptible and –tolerant biotypes were planted in plugs in pots to prevent native seed bank influences. Glyphosate was applied at the 14 true-leaf stage at rates of 0, 105, 210, 420, 840, 1260 and 1680 g ae ha-1. Injury at 7 and 14 days after treatment (DAT), above ground dry-weight, and mortality were assessed. The susceptible biotype exhibited less injury 7 DAT when grown indoor compared to outdoor, which influenced the SI. The injury SI for outdoor plants was 2.9 and 1.2 for potting media and field soil, respectively.  For indoor plants, the injury SI was 0.1 and 0.8 for potting media and field soil, respectively. Tolerant plants grown indoor had a higher injury (P=0.001) than tolerant plants grown outdoor. Thus, plants tended to be less affected by the herbicide when grown indoor and in potting media. These results, in combination with previous work, indicate that growing conditions can affect the SI in herbicide resistance studies, and this should be considered when quantifying resistance levels from field collected populations.


COMBINING COVER CROPS AND FALL APPLIED HERBICIDES FOR ITALIAN RYEGRASS CONTROL. G. Montgomery*1, L. Steckel1, J. A. Bond2, H. M. Edwards2; 1University of Tennessee, Jackson, TN, 2Mississippi State University, Stoneville, MS (76)

ABSTRACT

Herbicides are the foundation for weed control in commercial agricultural production systems of the United States.  Reliance on a small number of these herbicides has resulted in extreme selection pressure leading to a number of herbicide-resistant weed species.  Planting cover crops in the fall is one tactic to help mitigate herbicide resistance developing in weeds. In part due to this, integrating cover crops as part of a total weed management system has become more popular in recent years in the State of Tennessee.  Italian ryegrass, primarily a fall germinating weed species, has become more of a troublesome weed in the Mid-Southern United States.  It is very competitive to crops and has developed a biotype in that region that is resistant to a number of herbicides including glyphosate. Growers who utilize cover crops are concerned that Italian ryegrass could become established in their cover crops.  The focus of the research was to determine if fall applied herbicides can be implemented onto a wheat or vetch cover crop to control Italian ryegrass (Lolium multiflorum).

A study to investigate cover crop tolerance to fall applied herbicides and Italian ryegrass control was conducted from 2014-2015 at the Delta Research and Extension Center in Stoneville, Mississippi and at the West Tennessee Research and Education Center in Jackson, Tennessee.  A wheat cover crop was evaluated in Stoneville and wheat and vetch covers were evaluated in Jackson.  Treatments were arranged as a two factor factorial within a randomized complete block design with four replications. The first factor level consisted of cover or no cover and the second factor level was herbicide and consisted of flumioxazin at 89 g ai ha-1 and pendimethalin at 1123 g ai ha-1 applied preemergence (PRE) and acetochlor at 1263 g ai ha-1, flufenacet at 382 g ai ha-1, metribuzin at 263 g ai ha-1, pyroxasulfone at 15 g ai ha-1, and s-metolachlor at 1069 g ai ha-1 applied at the one- to two-leaf cover crop stage (POST).  Applications to cover and no cover plots were made simultaneously and paraquat was applied immediately after cover planting to insure a clean seed bed.  Cover crop injury and Italian ryegrass control were visually assessed 10, 30, 60, 90, and 150 d after the POST application.  Data were subjected to an analysis of variance with p value = 0.05.  Wheat data was pooled across location.

Injury for hairy vetch and wheat was greatest from flumioxazin (38% and 15%, respectively) 10 DAT.  A interaction of herbicide and cover was detected for Italian ryegrass control in vetch 90 DAT.  Control was greatest from pyroxasulfone with or without (87% and 86%, respectively) a hairy vetch cover.  Control from these treatments declined to 76% and 72%, respectively, at the 150 DAT interval (data not shown).  A wheat cover significantly improved Italian ryegrass control at the 90 and 150 DAT rating intervals.  In the wheat study Italian ryegrass control at 30, 90, and 150 DAT was greatest with pyroxasulfone (79%, 88%, and 87%, respectively) followed by s-metolachlor (76%, 85%, and 74%, respectively), pooled across cover and no cover treatments.  At 90 DAT and 150 DAT rating intervals, cover plots provided 71% and 62% control, respectively, compared to no cover plots providing 63% and 52% control, respectively, when pooled across herbicide treatments.

In summary, early season cover crop injury was reflective of late season cover crop injury (data not shown) and indicates that fall applied herbicide options for a wheat or vetch cover crop can be utilized without causing detrimental impacts to the cover crop.  However, only a limited number of herbicide options are available to provide adequate control of Italian ryegrass.  For maximum control of Italian ryegrass in a hairy vetch or wheat cover crop, pyroxasulfone should be used.

  

 


CONTROL OF PALMER AMARANTH WITH RESIDUAL HERBICIDES PLUS COVER CROPS IN SOYBEAN. D. J. Spaunhorst*, W. G. Johnson; Purdue University, West Lafayette, IN (77)

ABSTRACT

During two growing seasons a field study evaluating fall planted annual ryegrass and cereal rye cover crops and spring applied soil residual herbicides for management of Palmer amaranth was conducted at Throckmorton Purdue Agricultural Center near Lafayette, Indiana. Glufosinate and glyphosate-resistant soybean were established in an area infested with a mixed population of glyphosate-resistant and susceptible Palmer amaranth seed to determine if soybean system, cover crop type, and or herbicide strategy influence Palmer amaranth biomass, density, and soybean grain yield. Early emerging summer and winter annual weeds were reduced more with a cereal rye cover crop than an annual ryegrass or no cover treatment. Burndown treatments which contained flumioxazin reduced Palmer amaranth density 85% or more than burndown treatments without flumioxazin. We also observed that cover crops can inhibit soil residual herbicides on target weeds. For example, in 2014 the cereal rye cover crop plus a burndown treatment mixed with glyphosate plus 2,4-D plus flumioxazin had 8 more Palmer amaranth plants when compared to a burndown treatment mixed with glyphosate plus 2,4-D plus flumioxazin with no cover crop. In both years cover crops did not reduce Palmer amaranth biomass. However, Palmer amaranth biomass was reduced by 98% or more with a burndown treatment of glyphosate plus 2,4-D plus flumioxazin plus a one or two pass post with residual strategy compared to a burndown strategy alone that consisted of glyphosate plus 2,4-D. Moreover, a burndown strategy mixing glyphosate plus 2,4-D resulted in 1,656 and 1,505 kg ha-1 less soybean grain yield compared to a burndown strategy of glyphosate plus 2,4-D plus flumioxazin plus a one or two pass post with residual in 2014 and 2015, respectively. Soybean grain yield was similar among cover crop types in 2014. However in 2015, treatments with an annual ryegrass or cereal rye cover crop resulted in 1,174 and 1622 kg ha-1, respectively, more soybean grain yield than treatments without a cover crop. Results from this study suggests that soybean grain yield in response to cover crops is variable between years while herbicide strategy was consistent between years and was more significant than cover crop type and soybean system for reducing Palmer amaranth density and biomass. Soybean system did not impact soybean grain yield and Palmer amaranth biomass. The cereal rye cover crop was more effective than the annual ryegrass cover crop in suppressing winter and early emerging summer annual weeds prior to a burndown application.


MODELING GROWTH OF ECHINOCHLOA PHYLLOPOGON (LATE WATERGRASS) IN CALIFORNIA RICE. W. B. Brim-DeForest*, A. Fischer, K. Al-Khatib; University of California, Davis, Davis, CA (78)

ABSTRACT

Late watergrass (Echinochloa phyllopogon (Stapf.) Koss (synonym E. oryzicola Vasinger)) is one of the most competitive weeds in the California rice agroecosystem. It emerges under both aerobic and anaerobic conditions and multiple-herbicide resistant biotypes are widespread throughout California rice lands. In order to better time herbicide applications and to make cultural management decisions, it is necessary to better understand the effects of soil moisture, temperature and resistance status on the emergence and early growth of late watergrass. The objectives of this research were: 1) To quantify differences in emergence and early growth between resistant and susceptible biotypes at different soil depths, irrigation systems and planting dates; and 2) To develop and validate a model to predict emergence to the 2 leaf stage using Growing Degree Days (GDD).

Studies were conducted in 2013 and 2014 at the Rice Experiment Station in Biggs, CA. Seeds from one known resistant and one known susceptible biotype were collected in the fall of 2012 and the fall of 2013. Starting in May 2013, incubator-germinated seeds from each biotype were planted in pots outside at four depths (0.5 cm, 2 cm, 4 cm and 5 cm) in three different irrigation systems: continuously flooded (CF), daily flush (DF), and intermittent flush (IF). The continuously flooded treatment was flooded to 10 cm above the soil surface, the daily flush treatment was watered daily to soil saturation, and the intermittent flush was watered every three days to soil saturation. The experiment was arranged as a Randomized Complete Block Design, with four replications of each irrigation-planting depth combination. Two seeds were planted per pot. After planting, height measurements were taken and leaf stage was noted daily until plants reached the 5-leaf stage. At the 5-leaf stage, aboveground biomass was harvested, dried until constant weight, and dry weight was recorded. The experiment was repeated three times, at planting dates corresponding to rice planting dates in California (May to June). Model construction and validation in the field will be carried out in 2016 and 2017 under two irrigation systems: continuously flooded, and intermittently flushed.

Both Resistant (R) and Susceptible (S) plants emerged from all depths in the daily and intermittent flush treatments. In the flooded treatment, both biotypes emerged only from the 0.5 and 2 cm depths. Both R and S plants in the flooded systems had significantly less biomass than plants in the flushed systems (p < 0.05). R biotypes better tolerated later planting dates, with a greater percentage of R plants emerging from all three irrigation systems (p < 0.05). The greatest number of plants (both R and S) emerged from all depths in the daily flush system (p < 0.05), independent of planting date. The differences between the R and S biotypes may indicate that herbicide resistance is related to general stress tolerance in the R biotypes, which may have important implications for management in the current California drought. 


CHARACTERIZATION AND BIOLOGY OF A NEW ARKANSAS RICE WEED: SCHOENOPLECTUS SPP. C. E. Rouse*1, N. Burgos1, Z. T. Hill2; 1University of Arkansas, Fayetteville, AR, 2University of Arkansas-Monticello, Monticello, AR (79)

ABSTRACT

Arkansas’ flood-irrigated rice production system presents a unique environment for a variety of weeds to proliferate and for atypical species to arise. In 2014, a report of an unknown Cyperaceae species in a zero-grade, or continuously flooded system, was brought to the attention of University of Arkansas researchers and extension personnel. According to the producer, this species survived/escaped applications of common rice herbicides and had invaded a large majority of his fields in less than 3 years. This research aims to identify the species, understand its biology, and identify potential herbicides for management. Three accessions were collected and brought to the Altheimer Laboratory at the University of Arkansas, Fayetteville, for further investigation and identification. The field-collected plants were grown separately by accession in a greenhouse during the summer of 2015 to produce homogenous seed. Plants used for evaluation were produced from either seed or via clonally propagated shoots from the greenhouse-grown specimen. The plant was identified as a Schoenoplectus spp. with fibrous roots and rhizomes, 3-ranked triangular shaped leaves, with the leaf blade flat on the edge and triangular at the cross section. The inflorescence initiates on the adaxial leaf surface approximately 3 to 5 cm from the leaf tip, forming a branched spike or cluster of 6-8 spikes. Plants that were clonally propagated initiated new shoots within 2 weeks and flowered by 12 weeks. Under greenhouse conditions this species grew an average of 2.9 cm per week, and at maturity averaged approximately 41 cm in height. In the field, it could grow up to 1 m tall. Four assays were conducted to evaluate potential methods for alleviating dormancy imposed by the seed- physical scarification (sandpaper), acid scarification (sulfuric acid), chemical scarification (bleach), and ethylene exposure; a nontreated control was included. Overall, physical scarification and ethylene exposure resulted in the highest germination (61%), which was 40% more than the nontreated controls. Weed control using 9 rice herbicides was evaluated: 2,4-D (1065 g ae ha-1), bentazon (841 g ha-1), halosulfuron (52 g ha-1), imazethapyr (105 g ha-1), propanil (4486 g ha-1), quinclorac (565 g ha-1), saflufenacil (25 g ha-1 & 50 g ha-1), and triclopyr (278 g ae ha-1). By 5 WAP, 2,4-D, triclopyr, saflufenacil (50 g ha-1), and bentazon resulted in the greatest control (>85%); however, regrowth was observed with the saflufenacil treatment. This species is not yet wide spread, but it can spread quickly by seeds or clones. It is necessary to take preventive measures to curtail its spread to new areas and use effective herbicides to reduce the seed bank. 

 


DETERMINING SEED RETENTION OF KEY ANNUAL WEEDS AT WHEAT HARVEST, AND THE POTENTIAL FOR HARVEST WEED SEED CONTROL. N. Soni*, T. A. Gaines; Colorado State University, Fort Collins, CO (80)

ABSTRACT

Annual winter grasses such as feral rye (Secale cereale), downy brome (Bromus tectorum), and jointed goatgrass (Aegilops cylindrica) are the major problematic grass weed species in Colorado wheat fields. Currently, those species are managed with herbicides and crop rotation. A complementary weed control tool is needed to diversify weed management techniques. One approach is harvest weed seed control (HWSC). HWSC methods destroy, burn or remove weed seeds from the field. Target weed species need to retain seed at harvest height for HWSC to be effective. Feral rye, downy brome, and jointed goatgrass have a similar growth habit as wheat. These species have similar height and reach maturity at wheat harvest. Therefore, we hypothesized that the majority of seeds from these weed species are retained in the harvestable wheat fraction of the canopy. Our main objective was to quantify seed retention by comparing the amount of weed seeds retained in the upper wheat canopy with the shattered seed on the soil surface. To accomplish this objective, 21 wheat field located around eastern Colorado were sampled. In each field, 4 replicate samples were collected containing the weed species present at the site. There were 14, 6, and 7 fields containing feral rye, jointed goatgrass, and downy brome, respectively. Plant height, density and seed amount were quantified per weed species to compare retained weed seeds in the above 15 cm of wheat with shattered weed seeds. In addition, biomass and grain yield were recorded for wheat. In order for HWSC to be successful, the majority of weed seeds located in the wheat canopy should not shatter before harvest. As an integrated pest management practice, implementation of HWSC approaches substantially decrease weed pressure for the next wheat season. Potential benefits of HWSC include reduced herbicide use, improved management of herbicide resistance, and reduced production costs in the long term for wheat fields.


OPTICAL PROPERTIES OF COMMON LAMBSQUARTERS, REDROOT PIGWEED AND TOMATO LEAVES. L. Ma*, M. K. Upadhyaya; University of British Columbia, Vancouver, BC (81)

ABSTRACT

Optical Properties of Common Lamb’s-quarters, Redroot Pigweed and Tomato Leaves.  

Li Ma and Mahesh K. Upadhyaya, University of British Columbia, Vancouver, Canada.

Effects of leaf age and position on optical properties (reflectance, transmittance, and absorptance) for red (R) and far-red (FR) lights in common lamb’s-quarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.) and tomato (Lycopersicon esculentum L.; cv. Gold Nugget Cherry) leaves were studied. Reflectance, transmittance and absorptance of leaves of plants grown in growth chambers were measured at red (660 nm) and far-red (730 nm) wavelengths using a CI-710 Miniature Leaf Spectrometer. The 3, 5, 7, 9 and 11th true leaves of lamb’s-quarters and pigweed, and 1, 3, 5 and 7th true leaves of tomato were chosen to study the effect of leaf position on optical properties. To study the effect of leaf age on optical properties, periodical observations were taken on the 3rd true leaf. Leaves at a higher position generally reflected and transmitted less radiation at 660 and 730 nm in lamb’s-quarters and pigweed. Reflectance at 730 nm was not affected. In tomato, reflectance did not change with leaf position at either 660 nm or 730 nm. Interestingly, species differed in this regard. The magnitude of the position effect was the greatest in pigweed, which also reflected and transmitted more radiation at 660 nm. With the exception of R/FR ratio of the reflected light in tomato, R/FR ratios of the reflected and transmitted lights were significantly influenced by leaf position. R/FR ratio and the magnitude of change were the greatest in pigweed compared to other species.  Leaf age also influenced leaf optical properties and species differed in this regard.  Some differences in optical properties at 730 nm were also observed in these species. The results of this study suggest that the same area of leaves of different species may influence R/FR ratio in a plant canopy differently, inducing different magnitudes of the shade-avoidance response.  The leaf area index alone, therefore, should not be used to assess the potential plant competition. Effects of leaf age and position on leaf optical properties, and species-specific differences must be considered.  

 


ROLE OF SHADE AVOIDANCE IN CRITICAL PERIOD OF WEED CONTROL IN BETA VULGARIS. A. T. Adjesiwor*, T. J. Schambow, A. R. Kniss; University of Wyoming, Laramie, WY (82)

ABSTRACT

Plants are able to perceive presence of neighboring plants through changes in reflected red:far-red light ratio (R:FR). Being sessile, plants modify their morphology and physiology to avoid the perceived impending competition, a phenomenon termed shade avoidance. This usually occurs before direct competition for light, nutrients, and water, and therefore, can influence the critical period of weed control in crops. This study evaluated effects of reflected R:FR from grass (Kentucky bluegrass) on morphology of Beta vulgaris. Grass treatments were initiated at crop emergence, four true-leaf (TL), and 6 TL growth stages, and compared to a grass-free control treatment. Grass was clipped frequently to prevent shading and competition for light. Grass roots were isolated from B. vulgaris to ensure there was no competition for water or nutrients. Grass treatments resulted in longer B. vulagris leaves that were more erect relative to the control treatment. While this may have improved light interception, this modified morphology came with a concomitant reduction in number of leaves per plant. Sugarbeet morphology was affected more when treatments were initiated at emergence compared to grass treatments initiated at the 4 TL or 6 TL stage. These results showed that shade avoidance responses can be triggered early in the B. vulgaris life cycle, and may play a substantial role in the critical period of weed control in this crop.


STAKEHOLDER PERSPECTIVES ON WEED MANAGEMENT ISSUES IN TEXAS RICE. R. Liu*1, J. Samford2, V. Singh2, X. Zhou3, M. V. Bagavathiannan1; 1Texas A&M University, College Station, TX, 2Texas A&M Universtiy, College Station, TX, 3Texas A&M University, Beaumont, TX (83)

ABSTRACT

Weeds present a major constraint to rice production in Texas. To understand the stakeholders’ perspectives on weed management issues and research needs in Texas rice, a paper-based survey was carried out during summer 2015, especially targeting rice growers, crop consultants, county extension personnel, and distributors. A questionnaire was designed to acquire specific information on farm size, crop rotation, herbicide program, problematic weed species, and factors that influence weed management decision making in rice. A total of 110 questionnaires were distributed during rice field days that were widely attended by stakeholders in the region. Of the 42 responses received, 30 were complete and usable. Twenty-four out of the 30 respondents were growers, and the rest were extension personnel and distributors. Results revealed that the average land holding was 355 ha. Barnyardgrass (Echinochloa crus-galli), hemp sesbania (Sesbania herbacea), sprangletops (Leptochloa Spp.) and red rice (Oryza sativa) were among the most problematic rice weeds judged by the respondents. Among the sprangletops, the Nealley’s sprangletop (Leptochloa nealleyi), a relatively new species to the region, was raised as an emerging concern. Clomazone was the most often used (90%) pre-emergence herbicide, whereas propanil (55%), bispyribac-sodium (54%), and quinclorac (45%) were the important post-emergence herbicides of choice. Most respondents made weed control decisions based on economic threshold (57%), weed problems from previous years (50%), and recommendations from dealers (47%). Sixty-three percent of the respondents expressed moderate to high concern for herbicide-resistant weeds, while only 10% of the respondents indicated that herbicide resistance is not a concern for them. Strategies to manage herbicide-resistant weeds (63%) and economical weed management practices (63%) were among the top research priorities. Results of this survey will help direct future research and outreach efforts for sustainable weed management in Texas rice production. 

 


SORGOLEONE PHYTOTOXICITY ON DIFFERENT WEED AND CROP SPECIES. M. K. Bansal*; North Carolina State University, Raleigh, NC (84)

ABSTRACT

Sorghum is known to produce allelochemical called ‘Sorgoleone’. Plants can produce these chemicals either by roots when they are still alive or by dead decaying matter and are known to have negative impact on weeds and following crops. There are concerns about sorghum affecting following winter wheat growth when grown in rotation in North Carolina. Lab studies were conducted in 2015 to evaluate the impact of sorgoleone on growth of wheat and different weed species. Seeds of wheat (Shirley) and four weed species, large crabgrass, Italian ryegrass, velvetleaf, and sicklepod were pre-germinated and then transferred to 20x100mm petri dishes treated with varying concentrations of sorgoleone. Sorgoleone was applied @ 0 (control), 25, 50, 100, 150, 200, and 300 µg ml-1. 10 days after placing seeds on the petri dishes, growth was measured in terms of shoot length. Significant sorgoleone treatment effects were observed for shoot growth when pooled over species. Shoot length was reduced at higher rates of sorgoleone compared to control. Wheat shoot length was not significantly affected by sorgoleone concentration. Velvetleaf shoot length was lower at all concentration compared to control. At higher rates of sorgoleone, large crabgrass, Italian ryegrass, and sicklepod growth was reduced when compared to lower rates. Preliminary analysis suggests that sorgoleone has a negative impact on growth of weed species, however wheat is not impacted. 

 


TRENDS IN HERBICIDE DIVERSITY IN UNITED STATES CROP PRODUCTION, 1991 TO 2014. A. R. Kniss*; University of Wyoming, Laramie, WY (85)

ABSTRACT

Using multiple herbicide modes of action is a common recommentation for proactive and reactive herbicide resistant weed management. However, few studies have attempted to quantify the diversity of herbicides being used. Shannon diversity index (H) and Shannon equitibility (EH) were calculated using national-level USDA-NASS survey data from 1990 to 2012 for soybean, spring wheat, and winter wheat, and 1990 to 2014 for corn. These measures of diversity are commonly used to quantify species diversity, and are well known to many plant ecologists. Herbicide site of action diversity and evenness, as quantified by H and EH, respectively, declined significantly in US soybean between 1990 and 2012 (P<0.001). This change was due, in large part, to glyphosate use in glyphosate-resistant soybean. In contrast, herbicide site of action diversity increased over a similar time period for corn, spring wheat, and winter wheat (P≤0.001). Evenness of herbicide site of action significantly increased between 1990 and 2012 in spring wheat (P=0.002) but decreased in soybean (P<0.001). No trends in site of action evenness were observed for corn or winter wheat. 


TRENDS IN FARMING PRACTICES AND CHANGES IN WEED FLORA ON ARABLE LAND: A FARM SURVEY IN CZECH REPUBLIC. J. Soukup*, K. Hamouzova, M. Jursik; Czech University of Life Sciences Prague, Prague, Czech Republic (86)

ABSTRACT

The aim of the study was an identification of recent developments in weed communities on arable land in the Czech Republic (Central Europe) and evaluation of factors influencing occurrence of troublesome weeds. Two years survey was conducted on 80+ farms across the country and questionnaires have been collected containing data on soil and weather conditions, crop acreage, soil tillage system, fertilization, weed control practices (independent variables) and weed species occurrence and tendencies, herbicide resistance status and development (dependent variables). The data was analysed by exploratory analysis and multivariate methods (DCA, RDA and PCA) in R-project and CANOCO 4.5 statistical packages. Silky bentgrass was considered the most frequent species but increasing importance for other weed grasses such as barren brome, wild oat and barnyard grass was mentioned as well. From dicots, small-flowered cranesbill and wild buckwheat are emerging issues. On the contrary, decreased importance was found for wild poppy and cornflower, creeping thistle and broad-leaved dock.  The percentage of winter oil-seed rape in crop rotation was the most important factor explaining 10.6% of data variability. Growing of this crop stimulated an occurrence of winter annual weeds (mainly cleavers, mayweed, and small-flowered cranesbill) and brassicaceous species (before all the field pennycress and flixweed).  Other factor supporting mainly the occurrence of grass weeds was reduced tillage compared to usage of mouldboard ploughing. The results show that the current farming systems with high share of winter crops and omitting of ploughing generate higher occurrence of hard to control weeds and herbicide resistance in many cases.


HERBICIDE WEED RESISTANCE IN MEXICO. AN UPDATE. R. Alcantara-de la Cruz1, P. T. Fernandez*1, H. E. Cruz-Hipolito2, I. Travlos3, J. A. Dominguez-Valenzuela4, D. Rafael1; 1University of Cordoba, Cordoba, Spain, 2Bayer CropScience, Mexico City, Mexico, 3Agricultural University of Athens, Athens, Greece, 4Chapingo Autonomous University, Texcoco, Mexico (87)

ABSTRACT

Herbicide Weed Resistance in Mexico. An Update. R. Alcántara-de la Cruz1, P.T. Fernandez*1, H.E. Cruz-Hipolito2, I. Travlos3, J.A. Dominguez-Valenzuela4, R. De Prado1; 1University of Cordoba, Cordoba, Spain, 2Bayer CropScience, Col. Ampl. Granada, Mexico, 3Agricultural University of Athens, Athens, Greece, 4Chapingo Autonomous University, Mexico.

 

Chemical weed control is increasingly common in Mexico. Continued use of herbicides has resulted to the appearance of weed resistant species. However, in Mexico only a few cases have been reported. According to The International Survey of Herbicide Resistant Weeds (Heap, 2015), there are seven weed species resistant to herbicides confirmed in the country.  Phalaris minor was the first recorded case in 1996, showing cross-resistance to ACCase-inhibiting herbicides. Subsequently, Avena fatua and P. paradoxa biotypes also showed resistance to this group of herbicides. The main resistance mechanism involved in these species is due to a point mutation at the site of action. The most recent cases of resistance correspond to Sorghum halepense and Ixophorus unisetus reported in 2009 and 2014, respectively, with resistance to ALS-inhibiting herbicides; and Leptochloa virgata and Bidens pilosa with glyphosate resistance reported in 2010 and 2014, respectively. Local reports and communications in national congresses indicate that at least nine other biotypes of P. minor, P. paradoxa and A. fatua are resistant to ACCase-inhibiting herbicides. One of these A. fatua biotypes exhibited multiple resistance (both to ACCase- and ALS-inhibiting herbicides). Other species such as Echinochloa colona and Euphorbia heterophylla have been reported as having resistance to herbicides that are inhibitors of the photosystem II, P. brachystachys has been characterized as resistant to ACCase inhibitors, while Chloris elata and Parthenium hysterophorus are glyposate resistant. To date, there is no source including all the resistant weed biotypes in Mexico. This is due to the lack of prospection works allowing the identification of new cases; existence of weed catalogs in which descriptions, distribution areas and synonyms of these plants are included; and their weak dissemination by researchers.

Keywords: Herbicide resistance; ACCase; ALS; glyphosate; Mexico; photosystem II.

Email address: pablotomas91@hotmail.es

 


ADZUKI BEAN SENSITIVITY TO PREEMERGENCE HERBICIDES. N. Soltani*1, R. E. Nurse2, C. Shropshire1, P. H. Sikkema1; 1University of Guelph, Ridgetown, ON, 2Agriculture Canada, Harrow, ON (88)

ABSTRACT

Limited preemergence herbicide options are available for weed management in adzuki bean in Ontario. Eight field trials were conducted in Ontario over a three-year period (2012, 2013, 2014) to evaluate the tolerance of adzuki bean to pyroxasulfone (150 and 300 g ai ha-1), flumioxazin (71 and 142 g ai ha-1), sulfentrazone (420 and 840 g ai ha-1), fomesafen (240 and 480 g ai ha-1), imazethapyr (75 and 150 g ai ha-1), and cloransulam-methyl (35 and 70 g ai ha-1) applied preemergence.  Pyroxasulfone, flumioxazin and sulfentrazone applied preemergence at the proposed 1X and 2X rates caused 25-96% injury and reduced plant stand up to 78%, shoot dry weight up to 95%, plant height up to 67% and seed yield up to 76% in adzuki bean. Cloransulam-methyl resulted in 1 to 9% injury with no adverse effect on plant stand, shoot dry weight, plant height, seed moisture content and seed yield of adzuki bean. Fomesafen and imazethapyr resulted in 1-3% injury with no adverse effect on plant stand, shoot dry weight, plant height, seed moisture content and seed yield of adzuki bean. Based on these results, pyroxasulfone, flumioxazin and sulfentrazone do not have an adequate margin of crop safety for weed management in adzuki bean. Cloransulam-methyl has potential for use in adzuki bean especially at the lower rate. Imazethapyr and fomesafen at the rates evaluated can be used safely in adzuki bean production under Ontario environmental conditions. 


EFFICACY OF ACURON AND ARMEZON FLEX IN CORN. A. W. Ross*1, T. Barber1, R. C. Doherty2, L. M. Collie1, Z. T. Hill3; 1University of Arkansas, Little Rock, AR, 2University of Arkansas-Monticello, Lonoke, AR, 3University of Arkansas-Monticello, Monticello, AR (89)

ABSTRACT

Efficacy of Acuron and Armezon Flex in Corn

A.W. Ross

L.T. Barber

L.M. Collie

University of Arkansas- Lonoke, Arkansas

R.C. Doherty

Z.T. Hill

University of Arkansas- Monticello, Arkansas

 

Abstract

 

In 2015 two separate trials were conducted to evaluate weed control using Acuron and Armezon Pro when compared to common corn herbicide programs in Arkansas. A study was initiated to determine weed control effectiveness between Acuron (a pre-mix containing s-metolachlor, mesotrione, bicyclopyrone and atrazine) and other corn herbicide standards when applied pre-emerge followed by common post emergence herbicides. An additional study was conducted evaluating postemergence weed control effectiveness between Armezon Pro (a pre-mix of topramezone and dimethenamid) and typical post emergence corn herbicide options for Arkansas. These trials were conducted at the University of Arkansas Rohwer Research Station on a Herbert silt loam soil. Both trials were planted on four 38 inch rows 40 ft. in length using DKC67-87 corn hybrid. Each study was arranged as a randomized complete block design and data were analyzed using Fisher’s protected LSD at P≤0.05 for significance. Applications were made using a tractor mounted, compressed air broadcast sprayer with 110015 Greenleaf Air-Mix nozzles on 19 inch spacing at 12 gallons per acre. Palmer amaranth (Amaranthus palmeri), morningglory (Ipomea sp.), and barnyardgrass (Echinochla crus-galli) were over seeded at planting to provide consistent and adequate weed population. Barnyardgrass control was significantly less in treatment consisting of Dual II Magnum followed by Bicep II Magnum 44 days after preemerge application and 12 DAT (days after post treatment)  while Palmar amaranth and morningglory control remained similar among treatments. Acuron herbicide performed consistently with other standard herbicide programs when applied PRE in corn. Armezon Pro and other standard corn postemergence herbicides were applied with and without atrazine at the V4 corn growth stage.  No significant differences were noted in Palmar amaranth or barnyardgrass control at 14 DAT (days after treatment). Morningglory control was slightly less in treatments of Armezon Pro and Capreno without the addition of Atrazine. By 27 DAT all treatments without the addition of Atrazine POST did not provide equivalent control of Palmar amaranth as treatments that included Atrazine. Armezon Pro alone did not control morningglory as well as all other treatments. Barnyardgrass control was significantly reduced with treatments of Capreno with or without Atrazine. All herbicide program controlled Palmar amaranth better postemergence when applied in combination with Atrazine, and it remains a crucial component of a successful corn weed control program.


ALFALFA SEED DEVELOPMENT IMPAIRED BY AUXIN DISRUPTER HERBICIDES. R. A. Boydston*1, S. Kesoju2, S. Greene3; 1USDA-Agricultural Research Service, Prosser, WA, 2Washington State University, Prosser, WA, 3USDA-Agricultural Research Service, Fort Collins, CO (90)

ABSTRACT

Feral alfalfa is a common weed on along roads, irrigation ditches, and field borders throughout alfalfa production regions. Feral alfalfa contributes to pollen contamination and lowers genetic purity of alfalfa seed when it is located in the vicinity of alfalfa seed production fields. Of particular concern is glyphosate resistant (GR) feral alfalfa in conventional and organic alfalfa seed growing regions. If a pollinator visits a flowering GR feral alfalfa plant and moves on to a conventional plant, the seed produced by the conventional plant may carry the GR trait resulting in adventitious presence. An important strategy to limit adventitious presence is to control feral alfalfa plants in alfalfa seed production areas. Feral alfalfa plants are often treated with herbicides in later developmental stages when plants are easier to detect and often flowering or have already formed early seed pods when herbicides are applied. This study was conducted to determine the effect of four auxin inhibitor herbicides; dicamba, 2,4-D, triclopyr and aminopyralid on seed development in alfalfa when applied to plants in the early seed development stage (green seed pods). Glyphosate resistant alfalfa, var. Genuity (R44BD16), was treated July 25, 2012, July 10, 2013, and July 11, 2014 with dicamba (0.8 kg ae ha-1), 2,4-D (1.1 kg ae ha-1), triclopyr (0.8 kg ae ha-1), and aminopyralid (0.09 kg ae ha-1) when alfalfa plants contained primarily green seed pods and 5% or less tan colored (mature) seed pods. Nontreated control plants were included for comparison. Two weeks after herbicide application, plants were harvested, air dried, and seed yield determined. Seed viability was assessed with germination tests and seedling growth abnormalities were recorded. The ability of seedlings to emerge from planted seed was tested by planting into soil in greenhouse containers. Averaged over three years, the four auxin inhibitor herbicides applied during the early pod fill period decreased alfalfa seed yield per plant 34 to 56% (by weight) compared to nontreated plants.  Seed germination averaged 42, 48, and 72% in 2012, 2013, and 2014, respectively, and was not significantly affected by treating with the four herbicides during early pod fill stage.  However, seedlings grown from seed collected from plants treated with dicamba, 2,4-D, and triclopyr were often deformed with abnormal growth. In 2013 and 2014, dicamba tended to cause the greatest percentage of deformed seedlings (16 and 37%respectively). Normal seedlings developed from seeds collected from aminopyralid treated and nontreated plants.  In 2012 and 2014, seedling emergence from seed planted into soil was reduced by 57 to 77% from dicamba treated plants; 44 to 69% from 2,4-D and triclopyr treated plants, but was not significantly reduced in 2013 compared to nontreated. Seedling emergence from seed collected from aminopyralid treated plants was similar to nontreated checks in all three years. The combined effects of reduced seed yield and lower percent seedling emergence from seed from dicamba, 2,4-D, and triclopyr treated plants could greatly reduce ability of feral alfalfa plants to reproduce. These three herbicides could be useful components of an integrated management program for feral alfalfa.  rick.boydston@ars.usda.gov


RESPONSE OF WHITE CLOVER TO AUXINIC HERBICIDES. W. Vencill*, A. Missaoi; University of Georgia, Athens, GA (91)

ABSTRACT


EFFICACY AND TOLERANCE TO HERBICIDE PROGRAMS IN CORN. R. W. Peterson*1, D. L. Teeter1, P. Baumann2, M. Matocha2, T. A. Baughman1; 1Oklahoma State University, Ardmore, OK, 2Texas A&M AgriLife Extension, College Station, TX (92)

ABSTRACT

Efficacy and Tolerance to Herbicide Programs in Corn. R. W. Peterson*1, D. L. Teeter1, P. Baumann2, M. Matocha2, T. A. Baughman1; 1 Oklahoma State University, Ardmore, OK, 2 Texas A&M AgriLife Extension, College Station, TX (92)

ABSTRACT

Controlling multiple species of weeds can be difficult to do without sustaining problematic injury to corn. Using a preemergence herbicide program followed by a post herbicide program can be an effective way to control various weeds. In some cases this approach will allow the introduction of differing herbicide modes of action in the overall corn weed control program.  Research trials were conducted at the Caddo Research Station near Fort Cobb, OK and at the Texas A&M University Research and Extension Center near College Station, TX.

Typical small plot research methods and materials were used to conduct these trials. Various preemergence and post emergence herbicides were tested. These herbicides included: Aatrex (atrazine), Acuron (atrazine + bicyclopyrone + mesotrione + metolachlor), Anthem ATZ (atrazine + pyroxasulfone + fluthiacet-methyl), Balance Flex (isoxaflutole), Cinch (metolachlor), Cinch ATZ (metolachlor + atrazine), Corvus (isoxaflutole + thiencarbazone-methyl), Diflexx (dicamba), Halex GT (metolachlor + glyphosate + mesotrione), Impact (topramezone), Laudis (tembotrione),Laudis Flexx (tembotrione + dicamba), Revulin Q (nicosulfuron + mesotrione + isoxadifen-ethyl), Roundup Powermax (glyphosate), Status (dicamba + diflufenzopyr), Surestart II (cetochlor + clopyralid + flumetsulam), Touchdown Total (glyphosate), Verdict (dimethenamid-p + saflufenacil).

No corn injury was observed with any Revulin Q herbicide combination at College Station.  Palmer amaranth (AMAPA) efficacy was 100% with all Revulin Q combinations for the entire growing season. Any treatment with Cinch ATZ pre followed by Revulin Q or Laudis post controlled browntop panicum (PANFA) greater than 98% the entire season. Revulin Q tank mixed with atrazine controlled entireleaf morningglory (IPOHG) the entire season. There was less than 1% injury at Fort Cobb for all combinations of Revulin Q in the late season. Cinch pre followed by Revulin Q tank mixed with atrazine plus Impact controlled Texas millet (PANTE) 98% the entire season. All treatments Had greater than 99% control on wild poinsettia (EPHHL) all season. Any treatment that included a PRE followed by a POST treatment controlled AMAPA and ivyleaf morningglory (IPOHE) season long at least 97% except Cinch followed by Revulin Q applied alone POST.

Acuron and Acuron + Aatrex had greater than 93% efficacy on PANTE at Fort Cobb. Acuron pre followed by Halex GT post controlled PANTE, AMAPA, and EPHHL greater than 90% late season.  Two applications of Acuron was the only treatment that controlled IPOHE and AMAPA season long. There was less than 8%injury early season and no injury was recorded late season. There was no visible injury at College Station season long. All treatments containing Acuron controlled AMAPA greater than 99% season long. Acuron pre followed by either Halex GT or Touchdown Total was the only treatment to control PANFA greater than 97% early season. All treatments controlled IPOHG greater than 82% early season except Surestart II and Corvus. There was no treatment that controlled IPOHG greater than 75% late season.

Balance Flex + atrazine pre controlled AMAPA and PANFA greater than 96% early season in College Station. Balance Flex + atrazine pre followed by Roundup Powermax post was the only treatment to control PANFA greater than 96% late season. Balance Flex + atrazine pre followed by Roundup Powermax + Laudis + DiFlexx post was the only treatment to control AMAPA greater than 95% in late season. No visible injury was recorded season long. Less than 11% injury was recorded early season and no injury was recorded late season for all treatments at Fort Cobb. PANTE control was greater than 97% season long except before the post where applied and the treatment containing Balance Flex + atrazine followed by Roundup Powermax. Control of AMAPA, IPOHE, and 

 


PERFORMANCE REVIEW: IMPACT(R) PROGRAMS FOR WEED MANAGEMENT IN CORN IN THE SOUTHERN US. N. M. French*; AMVAC Chemical Co., LIttle Rock, AR (93)

ABSTRACT

PERFORMANCE REVIEW: IMPACT® PROGRAMS FOR WEED MANAGEMENT IN CORN IN THE SOUTHERN US.  Ned M. French, AMVAC Chemical Corporation, Newport Beach, CA

ABSTRACT

Interference of weeds, such as Palmer amaranth, limits yield in field corn, and herbicides continue to be a key tool for minimizing weed competition.  As a consequence of selection for glyphosate-resistant weeds, corn growers are modifying herbicide programs to successfully manage key broadleaf weeds.  A series of field trials was conducted to compare Impact® based herbicide programs with a competitive program.

Ten trials were conducted by University and Extension weed scientists across the southern US from North Carolina to west Texas.  The objective was to evaluate the influence of Impact® and other herbicide programs on management of difficult to control weeds and yield in glyphosate tolerant field corn.  Each experiment was arranged in a randomized completed block design with four replications.  Across locations, glyphosate-tolerant corn hybrids were planted from Apr-1 to 4-June 2015.  Herbicide programs of Impact® (topramezone) at 0.75 oz./A + Sequence® (s-metolachlor + glyphosate) at 2.5 pt./A + AAtrex® at 1 qt./A, Halex® GT (s-metolachlor + glyphosate + mesotrione) at 3.6 pt./A + AAtrex® at 1qt./A, and Impact® at 0.75 oz./A + Roundup PowerMAX® at 22 oz./A + AAtrex® at 1 qt./A + Zidua® (pyroxasulfone) at 2 oz./A were assessed.  A nontreated check was included for comparison.  All herbicide programs included ammonium sulfate at 8.5 lbs./100 gal. or liquid equivalent and adjuvants (methylated seed oil or non-ionic surfactant) as directed by herbicide label. Post-emergence application timings were scheduled to target 2-4” weeds and corn at V2-V4. Numerous weed species were observed, and herbicide efficacy findings focus on weed species observed at two or more locations.  Measurements included plant stand, visual estimates of crop safety, weed control, lodging, and yield.  Nine trial locations were harvested.  Data were subjected to ANOVA, and means were separated using Student-Newman-Keuls test (p=0.05, protected). 

All herbicide programs averaged 94-100% control of pigweed (primarily Palmer amaranth), morningglory spp., sicklepod, and crabgrass compared with the untreated check, and results against teaweed and barnyardgrass were quite good (88-93% control).  All herbicide programs averaged an increase in grain yield of 58 bushels per acre above the untreated check, which yielded 92 bu./A.

Across ten replicated, small plot trials designed to investigate herbicide performance in field corn, Impact® based herbicide programs provided excellent weed control and corn yields compared with a commercial herbicide program.  Similar favorable results with Impact® based herbicide programs were reported at prior SWSS meetings; therefore, in three consecutive years of extensive testing by University and Extension weed scientists across the southern US, Impact® based herbicide programs have performed well.


EXAMINING THE PLANT-BACK INTERVAL FOR GLYPHOSATE- AND GLUFOSINATE-RESISTANT CORN AFTER GROUP 1 HERBICIDE APPLICATION. N. Soltani*1, K. J. Mahoney2, C. Shropshire1, P. H. Sikkema1; 1University of Guelph, Ridgetown, ON, 2University of Guelph Ridgetown Campus, Ridgetown, ON (94)

ABSTRACT

Studies in 2013 and 2014 examined the tolerance of corn to Group 1 herbicides when they were used to terminate a failed stand of glyphosate- and glufosinate-resistant corn.  To simulate this scenario, Group 1 herbicides were applied 1 wk or 1 d preplant (PP) and several parameters were measured.  Corn injury 1, 2, 4, or 8 wk after emergence (WAE) was similar to the untreated control, regardless of herbicide treatment, dose, or application timing.  Across herbicides and doses, application timing did not affect plant stand or aboveground biomass 2 WAE, plant height 4 WAE, or yield.  Across application timings, plant stand and aboveground biomass were similar to the untreated control, regardless of herbicide treatment or dose; however, some herbicides reduced height and/or yield.  For example, compared to the untreated control, fluazifop-p-butyl (75 and 150 g a.i. ha-1) and sethoxydim (300 g a.i. ha-1) each reduced height by about 3% while clethodim (30 and 60 g a.i. ha-1), fluazifop-p-butyl (150 g a.i. ha-1), and quizalofop-p-ethyl (72 g a.i. ha-1) each reduced yield by about 2%.  Therefore, in the rare situation where a grower may need to terminate a failed corn stand, Group 1 herbicide selection should be based on efficacy rather than plant-back restrictions.


PRE-AND POSTEMERGENCE HERBICIDE COMBINATIONS IN BOLLGARD II(R) XTENDFLEX(TM) COTTON. C. J. Webb*1, W. Keeling2, J. D. Everitt3; 1Texas A&M Research, Lubbock, TX, 2Texas A&M, Lubbock, TX, 3Monsanto Company, Shallowater, TX (95)

ABSTRACT

PREEMERGENCE AND POSTEMERGENCE HERBICIDE COMBINATIONS IN BOLLGARD II® XTENDFLEX® COTTON. C. J. Webb1, J.W. Keeling1, J.D. Everitt2, Texas A&M Agrilife Research1, Monsanto Company2, Lubbock, TX1,2

Bollgard II® XtendFlex® cotton is an innovative technology with tolerance to dicamba, glyphosate and glufosinate. Combining three different modes of action could improve control of glyphosate resistant Palmer amaranth (Amaranthus palmeri S. Wats), and other troublesome weeds including morningglory (Ipomoea spp.), Russian-thistle (Salsola tragus L.), kochia (Kochia scoparia L.), field bindweed (Convolvulus arvensis L.), woollyleaf bursage (Ambrosia grayi A. Nels.), and Texas blueweed (Helianthus ciliaris DC.) compared to glyphosate applied alone.  In 2015 studies were conducted on the Texas High Plains at two locations to evaluate Palmer amaranth and Texas millet (Urochloa texana Buckl.) control following preemergence and postemergence applications of a dicamba formulation alone (MON 119096) and a dicamba/glyphosate premix (MON 76832). Preemergence and postemergence residual herbicides also were compared. The objectives of this study were to evaluate Palmer amaranth and Texas millet control with MON 76832 and MON 119096 applied preemergence or postemergence in combination with residual herbicides in Bollgard II® XtendFlex® cotton. Field trials conducted near Lubbock and New Deal, TX in 2015 compared application timings and tank-mix combinations of MON 76832 and MON 119096. Preemergence treatments included Caparol 4L (32oz/A) + MON 119096 (22oz/A) and MON 119096 + Warrant (48oz). Early-postemergence treatments included MON 76832 (64oz/A) + Warrant, MON 76832 fb MON 76832, MON 76832 fb Liberty 280 SL (29oz/A), and MON 119096 + Warrant. Mid-postemergence treatments included MON 76832, Warrant, and Liberty 280 SL. Treatments were applied using a CO2-pressurized backpack sprayer calibrated to deliver 15 gallons per acre. Weed control was estimated visually and recorded at each location. Season-long control (100%) was achieved with a PRE application followed by sequential MON 76832 treatments tank-mixed with Warrant at one of the POST application timings. Palmer amaranth control was 98-100% when PRE application were followed by sequential MON 76832 treatments. Preemergence applications followed by MON 76832 EPOST fb Liberty 280 SL MPOST provided Palmer amaranth control ranging from 88-89%. The addition of Warrant improved Palmer amaranth control to 93-99%. Texas millet control ranged from 96-100% with all treatments; however, control was less than 80% when MON 119096 was applied POST, indicating the need for glyphosate to be included in the system.


DETERMINING THE MOST EFFECTIVE AND ECONOMICAL PRE HERBICIDES FOR GLB2 COTTON. T. B. Buck*1, A. C. York1, A. S. Culpepper2, L. E. Steckel3; 1North Carolina State University, Raleigh, NC, 2University of Georgia, Tifton, GA, 3University of Tennessee, Jackson, TN (96)

ABSTRACT

DETERMINING THE MOST EFFECTIVE AND ECONOMICAL PREEMERGENCE HERBICIDES FOR GLB2 COTTON.  T.B. Buck*1, A.C. York1, A.S. Culpepper2, L.E. Steckel3; 1North Carolina State University, Raleigh, NC, 2University of Georgia, Tifton, GA, 3University of Tennessee, Jackson, TN

 

ABSTRACT

 

Glyphosate-resistant Palmer amaranth (GR-AMAPA) is controlled in cotton with well-timed glufosinate applications plus residual PRE and POST herbicides. PRE herbicides are essential components of management systems but they sometimes injure cotton. The objective of this research was to evaluate PRE herbicide combinations and rates as components of an overall management system to control GR-AMAPA while minimizing cotton injury. 

 

An experiment was conducted in 2015 at Macon and Moultrie, GA and three fields near Clayton, NC. Cotton was no-till at one Clayton site and conventionally tilled at other sites. Twelve PRE herbicide combinations included the following: Warrant + Reflex at 840 + 140, 840 + 210, and 1260 + 280 g ai ha-1; Warrant + Direx at 840 + 560 and 1260 + 560 g ai ha-1; Warrant + Cotoran at 1260 + 1120 g ai ha-1; Reflex + Direx at 140 + 560, 210 + 560, and 280 + 560 g ai ha-1; Reflex + Cotoran at 210 + 1120 g ai ha-1; Brake F16 at 378 g ai ha-1; and Cotoran + Caparol at 840 + 840 g ha-1. A no-PRE treatment was included. Full use rates (g ha-1) of PRE herbicides on the soils in this experiment include the following: Brake F16 (fluridone + fomesafen), 378; Cotoran (fluometuron), 1120; Direx (diuron), 560 if in a combination; Reflex (fomesafen), 280; and Warrant (acetochlor), 1260.

 

Roundup PowerMax (glyphosate) 1260 g ae ha-1 + Liberty (glufosinate-amonium) 660 g ai ha-1  were applied POST 18 to 35 d after planting when GR-AMAPA averaged 10 cm tall and again 18 to 25 d later. Direx + MSMA at 1120 + 1680 g ai/ha were directed at layby 14 d after the second POST application. The experimental design was a RCB with three or four replications.

 

Overall, greatest control was achieved by Warrant + Reflex at 1260 + 280 g ha-1 and Brake F16 while poorest control was with Cotoran + Caparol and Reflex+ Direx at 140 + 560 g ha-1. At four of the five locations, prior to the first POST application, GR-AMAPA was controlled 90% or greater by all PRE herbicides except Reflex + Direx at 140 + 560 g ha-1 and Cotoran + Caparol. At Macon, only Warrant + Reflex at 840 + 210 or 1260 + 280 g ha-1 and Brake F16 gave greater than 90% control. Following the two POST and the layby applications, GR-AMAPA was controlled greater than 90% by all PRE herbicides. Poorest control (75-81%) was observed in the system without PRE herbicides. All PRE herbicides reduced late-season GR-AMAPA biomass and density greater than 99% compared to the system with no PRE herbicide.

 

Cotton injury was minor with all treatments but generally increased as the rate of Reflex increased. Cotton yield in the system without PRE herbicides reflected the reduced GR-AMAPA control. Cotton in the system without PRE herbicides yielded only 75 to 82% as much as the average of all systems with PRE herbicides.  The value of PRE herbicides in a management system with POST and layby herbicides was demonstrated. Systems with PRE herbicides had greater GR-AMAPA control, greater cotton yield, and greatly reduced numbers of weeds to replenish the seed.

 


EVALUATION OF WEED CONTROL USING ENGENIA IN XTEND COTTON. L. M. Collie*1, L. T. Barber2, R. C. Doherty3, Z. T. Hill4, A. W. Ross1; 1University of Arkansas, Little Rock, AR, 2University of Arkansas, Fayetteville, AR, 3University of Arkansas, Monticello, AR, 4University of Arkansas-Monticello, Monticello, AR (97)

ABSTRACT

Engenia is a new and improved formulation of dicamba developed by BASF specifically for use on Roundup Ready Xtend soybean and XtendFlex cotton.   This new formulation of dicamba has reduced volatility characteristics due to the formulation of the BAPMA salt and is expected to be labeled both preemergence and postemergence to tolerant crops. Trials were conducted at the Lon Mann Cotton Branch Station in Marianna, AR and the Southeast Research and Extension Center near Rohwer, AR. These trials were conducted to evaluate performance of Engenia in a full program with preemergence and other postemergence herbicides in XtendFlex cotton.  Trials were set up in a randomized complete block design with four 38in row plots 30 ft in length.  Palmer amaranth (Amaranthis palmeri L.) and pitted morningglory (Ipomoea lacunose L.) were over seeded at planting to provide consistent weed populations. Weed efficacy and crop response was recorded 14 days after each application. The trial consisted of 8 herbicide programs comprised of preemergence (PRE), early postemergence (EPOST), and late postemergence (LPOST) applications. The EPOST timing showed minimal crop injury and no significant difference was noted. Programs that contained Prowl H2O (0.95 lb ai/acre) or Cotoran 4L (1.0 lb ai/acre) applied PRE provided better season-long control of Palmer amaranth than programs not having these residuals at planting. In LPOST applications Palmer amaranth control was maintained when Engenia was used in conjunction with a residual herbicide. Treatments that used a PRE produced the highest yields, while LPOST only applications suffered yield reduction. Engenia provided more suitable control of Palmer amaranth and morningglory in Xtend cotton when used in a full herbicide program rather than a POST only program. Residual herbicides are crucial to the PRE and EPOST applications to make Engenia programs successful in the XtendFlex system. 

 


USING LEAF HYPERSPECTRAL DATA TO DISTINGUISH TWO PIGWEEDS FROM COTTON WITH DIFFERENT LEAF COLORS. R. S. Fletcher*1, K. N. Reddy2; 1USDA, Stoneville, MS, 2USDA-ARS, Stoneville, MS (98)

ABSTRACT


PEANUT RESPONSE TO POSTEMERGENCE HERBICIDES IN PRESENCE AND ABSENCE OF THRIPS INJURY. M. D. Inman*, D. L. Jordan; North Carolina State University, Raleigh, NC (99)

ABSTRACT

Injury to peanut (Arachis hypogaea) caused by thrips (Frankliniella spp.) and early season interference from weeds can reduce peanut yield.  In a survey of peanut growers in North Carolina and Virginia for the 2013 peanut growing season, approximately 65% of growers applied the insecticide acephate 2-3 weeks after peanut emergence to suppress thrips and minimize injury regardless of insecticide applied at planting.  Presence of Palmer amaranth (Amaranthus palmeri) in many peanut fields requires frequent herbicide applications early in the season.  Postemergence (POST) herbicides included bentazon, imazapic, lactofen, and paraquat in various combinations applied within the first month of the season to control weeds, and these herbicides are often applied with residual herbicides including acetochlor and S-metolachlor.  There is also interest in applying prothioconazole to suppress soil-borne disease within this tie period.  While compatibility of acephate and paraquat applied with residual herbicides has been evaluated, interactions of residual herbicides applied with POST herbicides other than paraquat are understood less well.  Three experiments were conducted to determine interactions of POST herbicides with acephate, residual herbicides, and prothioconazole in the field.  All pesticide combinations were applied when phorate was applied in the seed furrow at planting or when phorate was not applied at planting.  In the first experiment all possible combinations of no POST herbicide, paraquat plus bentazon, and paraquat plus bentazon plus S-metolachlor with two levels of acephate (0 and 0.7 kg ai/ha), prothioconazole (0 and 0.2 kg ai/ha), and S-metolachlor (0 and 1.1 kg ai/ha).  In a second experiment, treatments consisted of no herbicide applied POST, lactofen plus bentazon plus 2,4-DB, and lactofen plus imazapic plus 2,4-DB applied alone or with acephate (0 and 0.7 kg/ha) and S-metolachlor (0 and 1.1 kg/ha).  In a final experiment, peanut response to paraquat plus bentazon applied alone and with all possible combination of acephate (0 and 0.7 kg/ha) and the residual herbicides acetochlor (0 and 1.3 kg ai/ha) and pyrosulfone (0 and 0.12 kg ai/ha).  Nonionic surfactant was applied with paraquat at 0.125% (v/v) while all other herbicides were applied with nonionic surfactant at 0.25% (v/v).  Pesticides in experiments 1 and 3 were applied 3 wks after peanut emergence while pesticides in experiment 2 were applied 4 wks after peanuts emerged.  Peanut were maintained weed-free to determine the effects of pesticides and injury from thrips on visible injury and peanut yield.  Data for visible estimates of percent stunting caused by a combination of herbicide injury and thrips feeding were subjected to ANOVA with partitioning appropriate for the factorial arrangement of treatment.  The first two experiments were repeated with the final experiment conducted only once during 2015.

In the first experiment, interactions of herbicide treatment (none, paraquat plus bentazon, and paraquat plus bentazon plus S-metolachlor) with phorate, prothioconazole, and acephate were noted for peanut injury caused by thrips feeding and herbicide phytotoxicity.  However, peanut yield was not affected by these interactions.  When pooled over other treatment factors, peanut yield was lower in absence of phorate compared with applying phorate at planting.  No other main effects or interactions impacted yield.  Applying acephate with paraquat plus bentazon alone or with S-metolachlor reduced injury compared with application of these herbicides without acephate.  Injury associated with these herbicides increased slightly when applied with prothioconazole or following phorate.  While interactions of location, phorate, and acephate were noted for peanut injury in the second experiment, herbicide treatments (no herbicide applied POST, lactofen plus bentazon plus 2,4-DB, lactofen plus imazapic plus 2,4-DB) did not interact with acephate or phorate.  However, more injury was noted when lactofen plus imazapic plus 2,4-DB were applied with S-metolachlor compared with this herbicide mixture applied alone.  Yield was higher when phorate was applied irrespective of other treatments.  Injury caused by herbicides did not translate into reduction in peanut yield.  In the final experiment, peanut response in the form of visible injury or yield was not affected by interactions of herbicide mixtures and acephate irrespective of phorate treatment at planting.  Results from these experiments indicate that while combinations of pesticides applied early in the season may cause phytotoxicty or prevent injury from thrips, the levels observed in these experiments most likely will not translate into negative impacts on peanut yield. 

 


EVALUATION OF APPLICATION INTERVALS OF POSTEMERGENCE GRAMINICIDES FOR COMMON BERMUDAGRASS CONTROL IN PEANUT. M. W. Durham*1, J. A. Ferrell1, J. Taylor2, P. Munoz1; 1University of Florida, Gainesville, FL, 2Syngenta, North Palm Beach, FL (100)

ABSTRACT

Common bermudagrass (Cynodon dactylon (L.) Pers.) infestations in peanut (Arachis hypogaea) can negatively impact yield.  The graminicide, clethodim, is commonly used for grass control because it is effective on both annual and perennial grasses.  However, there is some indication that fluazifop-p is more effective on common bermudagrass than clethodim.  The objectives of this study were to evaluate the efficacy of bermudagrass control with the two graminicides and to evaluate the impact of single vs sequential applications of each of the graminicides and the intervals between the applications.    This experiment was designed as a randomized complete block with a factorial arrangement.  The first factor was the two graminicides,  fluazifop-p (0.21 kg ai ha-1) and clethodim (0.28 kg ai ha-1)  and the second factor was the three timings:  (1) one application, (2) a second application two weeks after the initial treatment (WAT), and (3) a second application 4 WAT.  The data sets were analyzed by year due to a significant year-by-treatment interaction. In 2014, fluazifop-p, averaged across all three timings, resulted in 45% greater bermudagrass control than clethodim at 8 WAT and 24% at 9 WAT.  No differences in graminicides were detected in 2015.   For both years, sequential applications of graminicide, averaged across both graminicides, resulted in greater bermudagrass control after  5 WAT than the single application.  However, no differences were detected between the 2 and 4 WAT application intervals.  These data indicate that some years, fluazifop-p can be more effective than clethodim for controlling common bermudagrass, especially at the critical period of canopy closure.  These data also indicate that two applications are more effective than one, regardless of the interval between the applications.

 


HERBICIDE INJURY AND WEED CONTROL IN RICE. X. Zhou*1, J. Samford2, J. Vawter2; 1Texas A&M AgriLife Research, Beaumont, TX, 2Texas A&M AgriLife Research, Eagle Lake, TX (101)

ABSTRACT

Weeds are among the most important factors limiting rice production. Currently, barnyardgrass and red rice have been considered the most troublesome weed species in rice in the southern U. S. because of their significant impacts on yield, lodging and grain quality. Since the introduction of Clearfield® rice in 2002, rice farmers have had a new and powerful tool to combat against red rice, barnyardgrass and many other weeds. Numerous herbicides are available, but improper use of herbicides may result in crop injury causing chlorosis, growth stunting and even death. Therefore, farmers are in need of information concerning the herbicides and their best timings of application that are not only effective for control of target weeds but also safe to the rice crop. The objective of this study was to evaluate the impact of selected herbicides on crop injury and yield potential in conventional and Clearfield® rice.

A field trial was conducted using a split plot design with variety as main plots and herbicide as subplots at Eagle Lake, Texas in 2014 and 2015. This trial evaluated six herbicides [Command 3ME (clomazone), Facet 75DF (quinclorac), Regiment (bispyribac-sodium), Grasp  (penoxsulam), Sharpen (saflufenacil) and Newpath (imazethapyr)] and five rice varieties (three conventional varieties, Presidio, Cheniere and XL753; two Clearfield® varieties, CL152 and CL XL745). Rice was drill seeded at 70 lb/A for Presidio, Cheniere and CL152 and at 35 lb/A for XL753 and CL XL745. Command (11 oz/A) and Facet (0.44 lb/A) were applied at preemergence; Regiment (0.4 oz/A) and Grasp (2.3 oz/A) were applied at late postemergence (3 to 5 leaf); Sharpen was applied at 2 and 1 oz/A at preemergence and late postemergence, respectively; Newpath (6 oz/A) was applied at both early (emergence to 2 leaf) and late postemergence. Percent plant injury caused by herbicides was visually rated at weekly intervals after treatment. Rice grain yield and milling quality (% head rice and % total milled rice ) were determined.  

In 2014 and 2015, Facet, Regiment and Grasp did not cause any injury to rice plants on all assessment dates. Command and Sharpen caused 5 to 40%  injury on the early assessment dates but no injury symptoms were observed on the last assessment date (33 days after planting). In 2014, none of the herbicide treatments significantly affected yield. In 2015,  all herbicide treatments equally increased yield compared to the untreated control. None of the herbicides evaluated significantly affected percent whole and total milled rice in either year. There were no differences in crop tolerance to herbicide treatments among the varieties evaluated. Results of this study demonstrate that Facet, Regiment and Grasp were safe for use to control weeds in conventional inbred and hybrid varieties. Facet, Regiment, Grasp and Newpath also were safe to Clearfield® rice varieties. Command and Sharpen might cause some degree of injury to conventional and Clearfield® rice varieties. However, plants treated with command or Sharpen were able to recover with time, resulting in no negative impacts on grain yield and milling quality.


MANAGEMENT OF COMMON WEEDS FOUND IN LOUISIANA RICE PRODUCTION WITH BENZOBICYCLON. B. M. McKnight*, E. P. Webster, E. A. Bergeron, S. Y. Rustom Jr; Louisiana State University, Baton Rouge, LA (102)

ABSTRACT

Benzobicyclon is a HPPD inhibitor that has been registered for use in Japan since 2001. This herbicide must be applied in flood-water to be active and benzobicyclon is primarily taken up by plants through root and shoot tissue. The requirement of a flood being present at application makes Louisiana rice production ideal for benzobicyclon use because 35% of the rice acreage in Louisiana is water-seeded. Water-seeded production systems utilizing either continuous or pinpoint flooding practices may benefit from a herbicide with these characteristics since the permanent flood is established much earlier than is recommended for drill-seeded production. A field study was established to evaluate benzobicyclon activity when applied at various rates.

This study was conducted in 2015 at the H. Rouse Caffey Rice Research Station (RRS) on a Crowley silt loam soil, and on a Midland silt loam soil. The same study was also conducted at the Northeast Research Station (NERS) near St. Joseph, Louisiana in the 2015 growing season on a Sharkey clay soil. Following seedbed preparation, a permanent flood was established and a natural infestation of weeds emerged. No rice was planted in the plot area in order to encourage weed pressure without competition.  Prior to flooding, 90-cm diameter by 30-cm tall galvanized metal rings were installed into individual plots to contain benzobicyclon and prevent herbicide dilution. The application timing at all locations occurred when ducksalad [Heteranthera limosa (Sw.) Willd.] had reached the expanded leaf growth stage, or spoon stage. Other weeds present at the Crowley and St. Joseph location included Indian jointvetch (Aeschynomene indica L.), yellow nutsedge (Cyperus esculentus L.), barnyardgrass [Echinochloa crus-galli (L.) Beauv.], purple ammania (Ammannia coccinea Rottb.), Indian toothcup [Rotala ramosior (L.) Koehne],  and Lindernia spp. Benzobicyclon was applied at 10 different rates: 0, 31, 62, 123, 185, 246, 493, 739, 986 and 1232 g ai ha­­­­-1. Applications were made using a CO-pressurized backpack sprayer calibrated to deliver 140-L ha­­­­-1.  The design was a randomized complete block with four replications. At the study conclusion in all locations weeds were hand-harvested, separated by species, and fresh weights were recorded.

Ducksalad fresh weight at the conclusion of the study conducted on the Crowley silt loam was highest in the nontreated and the 31 g ha-1 rate of benzobicyclon. Any treatments receiving a 62 g ha-1 rate of benzobicyclon and higher yielded less weed biomass, on a fresh weight basis. In treatments receiving an application rate of 246 g ha-1 and higher, consistent ducksalad control was achieved. In the study established on the Sharkey clay soil barnyardgrass, Indian toothcup, purple ammania and Lindernia spp. control was inconsistent and no differences in fresh weight were detected among any benzobicyclon treatment. Ducksalad and total weed fresh weight was greater than 500 g in all treatments applied at a rate of 739 g ha-1 and less. On the Midland silt loam soil barnyardgrass, Indian toothcup, and Lindernia spp. plants were absent in benzobicyclon treatmened plots of 739 g ha-1 and higher. Purple ammania fresh weight was highest in rings receiving the 31 g ha-1 benzobicyclon treatment and was reduced to 3 g in rings receiving 1232 g ha-1. Ducksalad fresh weight was reduced with any rate of benzobicyclon compared with the nontreated. The most consistent ducksalad control based on fresh weight was from rates of 185 g ha-1 of benzobicyclon and higher.


EVALUATION OF RICE TOLERANCE TO PETHOXAMID APPLIED ALONE AND IN COMBINATION WITH OTHER RICE HERBICIDES. J. A. Godwin Jr.*, J. K. Norsworthy, M. Palhano, R. R. Hale, P. Tehranchian, J. S. Rose; University of Arkansas, Fayetteville, AR (103)

ABSTRACT

Pethoxamid is a very-long chain fatty acid-inhibiting herbicide (WSSA Group 15) belonging to the chloroacetamide family. Due to the evolution of herbicide resistance, it is essential to integrate new herbicide modes of action whenever possible. No Group 15 herbicides are currently labeled in U.S. rice production; however, Group 15 herbicides have been used with great success in Asian rice culture.  Considering the success of Group 15 herbicides in Asian rice culture and many other U.S. crops, it is believed that herbicides such as pethoxamid may have a potential fit in U.S. rice. Pethoxamid has been found to be very effective in controlling grasses such as barnyardgrass (Echinochloa crus-galli) and red rice (Oryza sativa) along with small-seeded broadleaves.  Pethoxamid may be a viable option to combat herbicide-resistant weeds in rice if crop tolerance can be established.  Pethoxamid was applied alone and in combination with several common U.S. rice herbicide regimes which included: clomazone (340 g ai/ha), quinclorac (420g ai/ha), propanil (4,480 g ai/ha), imazethapyr (71 g ai/ha), and cafentrazone (18 g ai/ha).  In each herbicide regime, pethoxamid was applied at 560 g ai/ha.  Injury of up to 30% was observed for pethoxamid plus propanil; however, pethoxamid applied alone only resulted in 3% injury.  Rough rice yields from all treatments were statistically similar to the yield of the nontreated control (9,195 kg/ha).  Due to the low amount of injury and little yield loss observed for pethoxamid when integrated into common U.S. rice herbicide regimes, the use of pethoxamid in rice merits further investigation.  

 


WEED CONTROL ATTRIBUTES AND TOLERANCE OF RINSKOR ACTIVE IN MIDSOUTH RICE . D. H. Perry1, D. T. Ellis*1, J. M. Ellis2, L. C. Walton3, M. R. Weimer4; 1Dow AgroSciences, Greenville, MS, 2Dow AgroSciences, Sterlington, LA, 3Dow AgroSciences, Tupelo, MS, 4Dow AgroSciences, Indianapolis, IN (104)

ABSTRACT


GRASS CONTROL WITH MIXTURES OF QUIZALOFOP AND BROADLEAF HERBICIDES IN PROVISIATM RICE. H. T. Hydrick*, B. Lawrence, H. M. Edwards, T. L. Phillips, J. A. Bond, J. D. Peeples; Mississippi State University, Stoneville, MS (105)

ABSTRACT

Provisia is a new non-genetically modified rice (Oryza sativa) developed by BASF that is resistant to quizalofop.  Research was conducted in 2014 and 2015 at the Mississippi State University Delta Research and Extension Center in Stoneville, MS, to evaluate control of red rice (Oryza sativa), volunteer rice, and Amazon sprangletop (Leptochloa panicoides) with mixtures of quizalofop and broadleaf herbicides.  Individual plots included four rows of Provisia rice and one row each of red rice, ‘CL 151’, ‘Rex’, and ‘CL XL745’.  Rex, CL 151, and CL XL745 were included to simulate volunteer rice.  The experimental design each year was a randomized complete block with four replications.  Herbicide treatments varied from 2014 to 2015, but all included two applications of quizalofop at 0.1 and 0.12 kg ai/ha in 2014 and 2015, respectively.  Sequential applications were made early-postemergence (EPOST) to rice in the two- to three-leaf stage and late-postemergence (LPOST) to rice in the four-leaf to one-tiller stage.  Broadleaf herbicides were mixed with quizalofop in the EPOST timing only and included a variety of herbicides common in southern U.S. rice production.  Control of red rice, CL 151, Rex, CL XL745, and Amazon sprangletop was visually estimated 7 and 14 d after the EPOST application and 7, 14, and 21 d after the LPOST application.  All data were subjected to ANOVA with means separated by Duncan’s New MRT at P=0.05.  At 14 d after EPOST applications in both years, all treatments controlled Amazon sprangletop ≥ 95%.  Quizalofop alone controlled red rice 89% in 2014 and 97% in 2015 at 14 d after EPOST applications.  In 2014, red rice control 14 d after EPOST applications was reduced 8 to 79% when quinclorac, propanil plus thiobencarb, or halosulfuron plus thifensulfuron were added to quizalofop.  However, red rice control was similar among all herbicide treatments 14 d after EPOST applications in 2015.  Red rice control with quizalofop plus saflufenacil, pensoxsulam, and halosulfuron was similar to that with quizalofop alone at 14 d after EPOST application both years.  In both years, no differences in red rice control were observed after LPOST treatments.  The cultivars CL 151, Rex, and CL XL745 were controlled ≥ 96% with all treatments both years.  Because control varied across years, caution should be exercised when quizalofop is applied in mixtures with broadleaf herbicides.  

 


EVALUATING RATE AND TIMING EFFECTS OF FACET L APPLICATIONS ON GRASS SPECIES IN THE GREENHOUSE. L. Vincent, W. J. Everman, J. Copeland*; North Carolina State University, Raleigh, NC (106)

ABSTRACT

EVALUATING RATE AND TIMING EFFECTS OF FACET L APPLICATIONS ON GRASS SPECIES IN THE GREENHOUSE

J. Drake Copeland 

W.J. Vincent

W.J. Everman

North Carolina State University

Raleigh, North Carolina

 

Abstract

 

Due to limited options, grass weed management in grain sorghum (Sorghum bicolor) production is challenging. Facet L (quinclorac), released in 2013, is an option for control of grass weed species that can be applied preplant incorporated, preemergence, and postemergence. Previous research has provided that herbicide rate and timing can affect overall herbicide efficacy on target grass weed species. BASF label for Facet L provides that applications should be made on grass weed species no larger than 5.08 cm in height. Given the recent rise in acres of grain sorghum in North Carolina, growers should be aware of the importance of timeliness and rate for controlling the grassy weeds spectrum. Therefore, the objective of this study was to evaluate the response of six grassy weed species at three distinct growth stages with applications of quinclorac at various rates.

 

Studies were conducted at the Method Greenhouse Facility in Raleigh, North Carolina in 2015 to evaluate the rate and timing effects of quinclorac applications on six grass weed species commonly found in grain sorghum production in North Carolina. Grass weed species included large crabgrass (Digitaria sanguinalis), goosegrass (Eleusine indica), broadleaf signalgrass (Urochloa platyphylla), fall panicum (Panicum dichotomiflorum), Texas millet (Urochloa texana), and crowfootgrass (Dactyloctenium aegytium). Quinclorac was applied at 290 and 420 g ai ha-1 with the addition of crop oil concentrate (COC) at 2.34 L ha-1 as well as an untreated check. Applications were made when species reached 2.54, 5.08, and 10.16 cm in height. Experiments were conducted using a factorial arrangement of treatments in a randomized complete block design with three factors being species, rate, and timing. All data were subjected to analysis of variance and means were separated using Fisher’s Protected LSD at p=0.05.

 

Visual control 14 DAT of large crabgrass (92%) and fall panicum (87%) was significantly greater than compared to applications at 5.08 and 10.16 cm. Crowfootgrass and goosegrass were not controlled by quinclorac applications 14 DAT regardless of timing or rate. Height reductions 14 DAT at the 2.54 cm timing of large crabgrass (97%) and broadleaf signalgrass (96%) were significantly greater than later timings, 5.08 cm and 10.16 cm, ranging from 60-81% height reduction. Dry weight reductions for broadleaf signalgrass at all timings ranged from 92-99%. Dry weight reductions of large crabgrass with applications of quinclorac at the 2.54 cm (99%) and 5.08 cm (96%) were significantly greater than the 10.16 cm (83%) timing. These data provide the importance of timely applications of quinclorac for grass weed species, specifically broadleaf signalgrass, large crabgrass, and fall panicum.

 


SCREENING OF ALS-RESISTANCE IN ECHINOCHLOA SPP. FROM RICE FIELDS IN PORTUGAL. D. Oliveira1, T. Marina1, A. Monteiro1, I. M. Calha2, D. Rafael*3; 1University of Lisbon, Lisbon, Portugal, 2National Institute of Biological Resources (INIAV I.P.), Lisbon, Portugal, 3University of Cordoba, Cordoba, Spain (107)

ABSTRACT

Screening of ALS-resistance in Echinochloa spp. from Rice Fields in Portugal. D. Oliveira1, M. Triviño1, A. Monteiro2, R. DePrado*3, I.M. Calha1; 1 INIAV, Oeiras, Portugal, 2 ISA / University of Lisboa, Lisboa, Portugal, 3 University of Cordoba, Cordoba, Spain.

 

 

In the Mediterranean basin Echinochloa species are major paddy rice weeds. The intensive use of herbicides and lack of crop and herbicide rotation. S were responsible for selection of resistance in more than 61 Echinochloa accessions worldwide. Growers` complaints about poor efficacy of ACCase and ALS-inhibiting herbicides in Echinochloa raises the question of herbicide resistance, an issue not yet confirmed in these species in Portugal.  Seed samples were collected before harvest (October 2014) in 12 rice fields from Tagus basin (Central Portugal). Species identification was based on biometric characterization of spikelet. Three pre-treatments were studied for breaking dormancy: PEG, GA3 and H2SO4. Dose-response Petri-dish bioassays with seeds for screening of penoxsulam resistance in Echinochloa spp. Germination, radicle and coleoptile length were measured. The GR50 was estimated using non-linear regression analysis with R, drc package. Three species were identified: E. crusgalli ssp. hispidulaE. oryzoides and E. phyllopogon. Germination ranged from 32 % to 88 %. Coleoptile length was the parameter most sensitive to penoxsulam. A susceptible population (GR50= 6.5 mg L-1) was used as reference. Three populations were confirmed as being resistant to penoxsulam with Resistant Indices (RI= GR50 R / GR50 S) of 2.2, 3.2 and 5.6.

Keywords: Echinochloa, rice, ALS-resistance, Dose-response.

E-mail address: qe1pramr@uco.es

 


MANAGEMENT OF WEEDY RICE UTILIZING CROP ROTATION. S. Y. Rustom Jr*, E. P. Webster, E. A. Bergeron, B. M. McKnight; Louisiana State University, Baton Rouge, LA (108)

ABSTRACT

Hybrid rice seed (Oryza sativa L.) has a history of dormancy, and it can become a weedy plant if allowed to establish the following growing season as an F2. Clearfield F2 plants can vary in phenotype and are often resistant to imazethapyr and imazamox. These resistant F2 plants can become a tremendous weed problem when Clearfield hybrid rice is grown in consecutive years. Another problem with the Clearfield rice technology is outcrossing with red rice (O. sativa L.). The outcrosses and the F2 rice plants coupled with red rice form a complex of rice weeds that will be referred to as weedy rice.

A producer location was identified near Esterwood, Louisiana with a history of 3 consecutive growing seasons of Clearfield hybrid rice production. This location was determined to have a complex weedy rice infestation. In 2013, a four year study was established consisting of five different rotations and utilizes the use of Provisia Rice which contains a non-genetically modified trait allowing for the use of quizalofop. The study also added Liberty Link soybean which allows the use of glufosinate. The utilization of these two herbicides in conjunction with the other herbicides further expands the flexibility of active ingredient and differing mode of action rotation. The rotations used were: Rotation 1) Roundup Ready soybean (2013)/Provisia Rice (2014)/Roundup Ready soybean (2015)/Clearfield Hybrid Rice (2016); Rotation 2) Fallow (2013)/Provisia Rice (2014)/Roundup Ready soybean (2015)/Clearfield Hybrid Rice (2016); Rotation 3) Clearfield Hybrid Rice (2013)/Liberty Link soybean (2014)/Provisia Rice (2015)/Clearfield Hybrid Rice (2016); Rotation 4) Roundup Ready soybean (2013)/Liberty Link soybean (2014)/Roundup Ready soybean (2015)/Clearfield Hybrid Rice (2016); Rotation 5) Roundup Ready soybean (2013)/Clearfield Hybrid Rice (2014)/Roundup Ready soybean (2015)/Clearfield Hybrid Rice (2016). Herbicide programs and cultural practices were consistent across a given rotation.

In 2013, 2014, and 2015 each 0.2 ha block followed the rotations listed above, and herbicide programs employed are listed below. The Clearfield ‘CLXL 745’ was treated with clomazone at 336 g ai/ha plus imazethapyr at 105 g ai/ha on one- to two-leaf rice, followed by (fb) imazethapyr at 105 g ai/ha on three- to four-leaf rice fb a panicle initiation (PI) application of imazamox at 44 g ai/ha. Provisia rice was treated with quizalofop at 115 g ai/ha plus halosulfuron at 53 g ai/ha on 2- to 3-leaf rice fb quizalofop at 115 g ai/ha on 4-leaf to 1-tiller rice. Roundup Ready soybean was treated with glyphosate at 1120 g ai/ha plus dimethenamid at 945 g ai/ha at the first trifoliate leaf. A second application of glyphosate at 1120 g ai/ha was applied at 21 days later. Rotation 4 was treated with pyroxasulfone at 150 g ai/ha added to first application of glyphosate plus dimethenamid in 2013. Liberty Link soybean was treated with glufosinate at 820 g ai/ha plus dimethenamid at 945 g ai/ha on soybean in the first trifoliate leaf stage fb glufosinate at 820 g ai/ha. Rotation 4 was treated with pyroxasulfone at 150 g ai/ha added to first application of glufosinate plus dimethenamid in 2014. The fallow area, Rotation 2 in 2013, was treated with glyphosate at 1120 g ai/ha at the same time the soybeans were treated with glyphosate. A tillage operation occurred in the fallow area 2 weeks after the second glyphosate application. A third glyphosate application at 1120 g ai/ha occurred 4 weeks later in the fallow area. Prior to rice harvest weedy rice plant counts were determined.

In 2013, weedy rice plants for each rotation were: Rotation 1 - 17.2 plants/m²; Rotation 2 - 25.1 plants/m²; Rotation 3 - 0.3 plants/m²; Rotation 4 - 5.2 plants/m²; Rotation 5 - 7.8 plants/m². In 2014, weedy rice weedy rice plants for each rotation were: Rotation 1 - 0.005 plants/m²; Rotation 2 - 0.004 plants/m²; Rotation 3 - 2.6 plants/m²; Rotation 4 - 3.1 plants/m²; Rotation 5 - 39.6 plants/m².

In 2015, rotations 1, 2, and 4 were planted with Roundup Ready soybean, treated as previously mentioned, and contained 0 weedy rice plants/m2 at the end of the growing season. Rotation 5 was also planted with Roundup Ready soybean and contained 2.5 weedy rice plants/m2 at the end of the growing season. Rotation 3 was planted with Provisia Rice and contained 0 weedy rice plants/m2 at the end of the 2015 growing season. The utilization of Roundup Ready and Provisia technology vastly improved rotational flexibility in 2015 and will serve as excellent rotational tools in conjunction with Clearfield technology for weedy rice management. This research indicates that long term crop rotation, herbicide active ingredient rotation, and employing different production practices can be used to manage weedy rice and reduce the weedy rice population in future growing seasons.

 


SESAME RESPONSE TO POST TIMING APPLICATIONS. W. Grichar*1, P. A. Dotray2, J. Rose3, D. Langham4, T. Baughman5; 1Texas AgriLife Research, Yoakum, TX, 2Texas Tech University, Lubbock, TX, 3Sesaco Corp, Austin, TX, 4Sesame Research LLC, San Antonio, TX, 5Oklahoma State University, Ardmore, OK (109)

ABSTRACT


WEED CONTROL PROGRAMS IN ARKANSAS GRAIN SORGHUM. M. T. Bararpour*, J. K. Norsworthy, Z. Lancaster, G. T. Jones; University of Arkansas, Fayetteville, AR (110)

ABSTRACT

Weed management programs are an essential component of grain sorghum production. A field study was conducted at the Northeast Research and Extension Center, Keiser, Arkansas, in 2015 to evaluate various herbicide applications for broadleaf and grass weed control in grain sorghum. The experiment was designed as a randomized complete block with 20 treatments and four replications. The experiment was established in a natural weed population of Palmer amaranth (Amaranthus palmeri), pitted morningglory (Ipomoea lacunosa), prickly sida (Sida spinosa), horse purslane (Trianthema portulacastrum), and barnyardgrass (Echinochloa crus-galli). All postemergence (POST) treatments were applied at 2- to 3-leaf grain sorghum stage (5- to 10-cm weeds).

Only 1 to 3% grain sorghum injury was observed from some herbicide applications. A single POST application of Huskie (bromoxynil + pyrasulfotole) at 0.27 kg ai/ha + AAtrex (atrazine) at 2.24 kg ai/ha provided excellent control (94 to 97%) of Palmer amaranth, pitted morningglory, prickly sida, and barnyardgrass (except horse purslane 85%). Preemergence (PRE) application of Lexar (S-metolachlor + atrazine + mesotrione) at 3.11 kg ai/ha provided 86 to 97% control of all broadleaf weeds. However, Lexar only controlled barnyardgrass 75%. Applications [PRE followed by (fb) POST] of Sharpen (saflufenacil) at 0.05 kg ai/ha PRE fb Bicep II Magnum (S-metolachlor + atrazine) at 2.47 kg ai/ha POST, Warrant (acetochlor) at 1.26 kg ai/ha PRE fb Bicep II Magnum POST, Verdict (saflufenacil + dimethenamid) at 0.49 kg ai/ha PRE fb Bicep II Magnum POST, and Dual II Magnum (S-metolachlor) at 1.07 kg ai/ha PRE fb Peak (prosulfuron) at 0.03 kg ai/ha + AAtrex 1.12 kg ai/ha POST provided 97, 69, 96, and 80% control of Palmer amaranth; 95, 73, 93, and 61% control of pitted morningglory; 95, 81, 95, and 73% control of prickly sida; 93, 93, 96, and 90% control of horse purslane; and 94, 85, 91, and 81% control of barnyardgrass, respectively. For the weed spectrum present in this trial, Verdict PRE fb Bicep II Magnum POST or Huskie + AAtrex (2.24 kg ai/ha) POST appeared to provide effective weed control and high yield.


BROADLEAF WEEDS MANAGEMENT IN GRAIN SORGHUM AS AFFECTED BY AGRONOMIC PRACTICES AND HERBICIDE PROGRAM. T. E. Besancon*, W. J. Everman, R. W. Heiniger; North Carolina State University, Raleigh, NC (111)

ABSTRACT

Weed control remains a major challenge for economically viable sorghum production in the Southeastern region of the United States because of sorghum sensitivity to weed competition during early growth stages. Field experiments were conducted in 2012, 2013, and 2014 to determine the effects of row spacing, sorghum population, and herbicide programs on Palmer amaranth, sicklepod and morningglory control as well as on sorghum growth and grain yield. Treatments included: three row spacing, 19, 38, and 76 cm; four sorghum populations, 99,000, 198,000, 297,000, and 396,000 plants ha-1; and three herbicide programs, (1) a non-treated control, (2) a PRE application of prepackaged S‑metolachlor plus atrazine at 100% of the recommended rate, referred to as PRE, and (3) a PRE application of prepackaged S‑metolachlor plus atrazine at 75% of the recommended rate followed by early POST application of 2,4-D, referred to as PRE followed by POST (PRE fb POST). Palmer amaranth control for all locations benefited from the addition of a POST herbicide and also by increasing the sorghum population from 99,000 to at least 297,000 plants ha-1. Palmer amaranth response to row spacing was variable across rating dates and years. Narrower row spacing or increased sorghum population did not affect Palmer amaranth density but caused significant dry biomass reduction by 33% with 19 and 38 cm compared to 76 cm, and by 43% with 297,000 or 396,000 compared to 99,000 plants ha-1. Our results underscored the need for a POST application combined to sorghum population ≥ 297,000 plants ha-1 to consistently maintain ≥90% late season morningglory control. Light interception by the sorghum canopy was little or not affected by row spacing. However, sorghum population had large influence with canopy closure occurring one and a half weeks earlier for 297,000 or 396,000 plants ha-1 density compared to 99,000 plants ha-1. Consistent grain yield increase by 18% on average was observed for 19 cm rows compared to 38 and 76 cm whereas sorghum plant populations used here had little or no effect. Overall, results from these experiments indicate that in the absence of POST application, narrow row spacing and sorghum populations of 297,000 plants ha-1 or more provide greater broadleaf weed control and biomass reduction.


IDENTIFICATION OF  HPPD-TOLERANT SORGHUM GENOTYPES FROM A DIVERSITY PANEL. A. Varanasi, C. R. Thompson, P. Prasad, M. Jugulam*; Kansas State University, Manhattan, KS (112)

ABSTRACT

Weed control in grain sorghum is a major challenge for producers across the US. Because of a limited number of herbicide options, POST emergence management of weeds, especially grasses is a challenge in grain sorghum production. HPPD-inhibitors are effective in controlling a wide spectrum of broadleaf and some grass weeds in many crops. The overall goal of this research was to screen and identify HPPD-inhibitor (e.g. mesotrione or tembotrione) tolerant genotypes from a sorghum diversity panel. We have screened a total of 317 genotypes from this germplasm for tolerance to mesotrione or tembotrione. Initial in vitro screening was performed in culture vessels containing solidified agar supplemented with 0.6x mesotrione (1x is 105 g ha-1) or 0.025x tembotrione (1x is 92 g ha-1). Herbicide doses were selected based on the concentration that discriminated a known sensitive vs tolerant plant in vitro. Thirty-five genotypes that had ≤ 50% visual injury to mesotrione and/or tembotrione in the in vitro assay were selected for preliminary evaluation under greenhouse (2x mesotrione or 0.5x tembotrione) and field (1x and 2x mesotrione or tembotrione) conditions. Upon screening in the greenhouse and field, two genotypes (SC319 and SC420) were found more tolerant (≤ 30% injury) to mesotrione compared to Pioneer 84G62, a widely grown commercial sorghum hybrid. Based on further dose-response experiments under greenhouse conditions, when compared to Pioneer 84G62, these two genotypes exhibited 6.8- and 2.6-fold level of tolerance, respectively to mesotrione. Experiments are in progress to identify sorghum genotypes tolerant to tembotrione.  Successful completion of this research will enable the use of tolerant lines in breeding programs to develop HPPD-inhibitor-tolerant sorghum technology to help manage POST-emergent weed control.

 


SOYBEAN YIELD COMPARISON IN LIBERTY LINK SYSTEMS VERSUS ROUNDUP READY SYSTEMS. N. D. Pearrow*1, W. J. Ross2, R. C. Scott3; 1University of Arkansas, Newport, AR, 2University of Arkansas, Lonoke, AR, 3University of Arkansas, Fayetteville, AR (113)

ABSTRACT

YIELD COMPARISON IN LIBERTY LINK SOYBEANS VERSUS ROUNDUP READY SYSTEMS.   N. D. Pearrow, W. J. Ross, R. C. Scott, University of Arkansas Division of Agriculture, Little Rock, AR

 

ABSTRACT

 

With the introduction of Roundup Ready® soybean in 1996, producers were provided with one of the most valuable technologies for weed control in the 20th and 21st centuries.  This technology was rapidly and widely accepted across North America.  However, the sole use of this technology magnified the selection pressure for biotypes of glyphosate-resistant weed species.  To date there are 32 weed species in the United States that are resistant to glyphosate, seven of which occur in Arkansas.  The rapid adoption of the Roundup Ready® technology also resulted in some inferior varieties of soybeans being planted resulting in lower than normal yields. 

LibertyLink® soybean varieties were introduced in 2009, which provided producers a new, but similar technology for weed control.  Studies were conducted from 2011 to 2015 in Arkansas to compare yields of Roundup Ready® and LibertyLink® technologies, and to determine if there was an associated “yield lag” with the LibertyLink® technology.  Average soybean yields for the LibertyLink® varieties were comparable to the Roundup Ready® soybean varieties tested during the five years for maturity group IV and V varieties.  For the maturity group IV varieties, average yields for both the LibertyLink® and Roundup Ready® varieties were 64 bushels per acre.  A similar trend was seen with the maturity group V tests, where the average Liberty Link soybean yield was 66 bushels per acre compared to 65 bushels per acre for the Roundup Ready soybean varieties.  Results from these studies indicate that LibertyLink® soybean varieties can yield as well as Roundup Ready® soybean varieties.

 


MANAGEMENT OF GLYPHOSATE-RESISTANT PALMER AMARANTH IN LIBERTY-LINK SOYBEAN. D. D. Joseph*, M. W. Marshall, C. H. Sanders; Clemson University, Blackville, SC (114)

ABSTRACT

Recent introductions of Liberty-Link soybean varieties that are tolerant to postemergence applications of glufosinate (Liberty) in the Southeastern United States has allowed producers in South Carolina to manage glyphosate-resistant Palmer amaranth populations effectively.  Combined with a diverse soil residual herbicide program (i.e., one that does not rely heavily of PPO-inhibitors), a timely glufosinate program is providing an effective alternative to glyphosate-based systems.  Field experiments were conducted at the Clemson University Edisto Research and Education Center (EREC) located near Blackville, SC in 2015.  Glufosinate-tolerant soybean variety Credenz 7007LL was planted on 6/8/15.  Treatments included combinations of soil residual herbicides including Authority MTZ at 13 oz/A, Envive at 4.0 oz/A, Canopy at 6.0 oz/A, Broadaxe at 25 oz/A, Boundary at 2 pt/A, Zidua at 2.0 oz/A, Valor XLT at 3.5 oz/A, Fierce 3.5 oz/A; and postemergence herbicide was Liberty at 29 oz/A.  Percent weed control and crop injury ratings were collected at 14, 28, and 56 days after treatment (DAT).  Palmer amaranth, pitted morningglory, and goosegrass percent control and soybean injury data were analyzed using ANOVA and means separated at the P = 0.05 level.  No significant (less than 5%) soybean injury was noted with any of the herbicide program.  A soil residual herbicide followed by a Liberty (glufosinate) postemergence provided excellent control (100%) of Palmer amaranth, pitted morningglory, and goosegrass in the glufosinate-tolerant system.  In general, soybean yield in the glufosinate-tolerant system were higher with the Envive-based treatement compared to the Canopy-based programs.  In the glyphosate-tolerant system, Broadaxe, Authority MTZ, Envive and Canopy provided longer residual control of Palmer amaranth.  In systems where a preemergence herbicide is left out, more weed escapes were observed after the first postemergence application of Liberty.  No soil effects from metribuzin containing herbicide treatments were observed with the Credenz 7007 variety.  Due to the excessive rainfall during the fall of 2015, soybean yield were not collected because the beans in the pods rotted from high humidity.  In summary, a robust soil residual program is important in the LibertyLink production system to prevent early season weed competition and reduce the amount of weed that Liberty has to control at the first postemergence application.

 


COMPARING NON-GMO HERBICIDE PROGRAMS TO GLYPHOSATE-BASED ONES IN CORN AND SOYBEAN. D. Lingenfelter*, W. S. Curran; Pennsylvania State University, University Park, PA (115)

ABSTRACT

Recent trends indicate that non-GMO crops are making a comeback and the public may greatly increase consumption. In order to keep up with the non-GMO movement, herbicide programs must be aligned with these crops to provide adequate weed control and avoid crop injury that limits yield. In 2015, field studies were conducted in Pennsylvania to examine non-glyphosate-based herbicide programs (i.e., non-GMO options) for weed control in corn and soybean. To allow for a direct comparison of the treatments, the trials were conducted in Roundup Ready crop varieties and featured many one- (PRE) and two-pass (PRE fb POST) competitive programs that targeted both broadleaf and grassy weeds. In the corn study, one-pass PRE programs provided 75-87% control of giant foxtail (Setaria faberi) and large crabgrass (Digitaria sanguinalis); while all of the two-pass systems (with and without glyphosate) provided ≥95% control of these species. Annual broadleaf weed including velvetleaf (Abutilon theophrasti) and common lambsquarters (Chenopodium album) control was >90% control with all treatments. None of the herbicide caused notable lasting injury to the corn. In the soybean study, all of the treatments provided >90% control of giant foxtail. In the two-pass programs that contained glyphosate, common lambsquarters and common ragweed control was 99%. However, in the non-glyphosate programs, annual broadleaf weed control was less consistent and ranged from 75-99%. Also, depending on the mixture, soybean injury ranged from 3-25% from the herbicide application. Most of the injury was caused by treatments that contained an ALS (group 2) or PPO (group 14) herbicides. Yield ranged from 36 to 51 bu/A. The herbicide only costs in systems with or without glyphosate typically range from $25 to 54/A in corn and $22 to 52 in soybean. In summary, weed control in conventional varieties varies depending on the crop. There are more broadleaf herbicide options in corn but POST control of grasses in some cases may be more challenging. Furthermore, there are fewer herbicide choices in soybean with POST broadleaf options being more limited than corn. In conjunction, more soybean injury might be expected compared to GMO varieties. Also, perennial weeds and resistant species can be problematic especially in continuous no-till systems. In most cases, production costs can be less and yields competitive. However, other features of GMO crops such as insect protection traits, enhanced crop safety, elite variety lines, among others provide additional value to these crops. Therefore, farmers must consider all aspects of each system before deciding which type of crop to grow.


ROUNDUP READY XTEND SOYBEAN TECHNOLOGY IN OKLAHOMA. T. A. Baughman*, D. L. Teeter, R. W. Peterson; Oklahoma State University, Ardmore, OK (116)

ABSTRACT

Roundup Ready Xtend Soybean Technology in Oklahoma.  T. A. Baughman*, D. L. Teeter and R. W. Peterson.  Oklahoma State University, Ardmore, OK 73401.

ABSTRACT

The increased occurrence of weed resistance has made achieving a successful weed management program extremely difficult in Oklahoma soybean.   This is particularly true with the spread of Palmer amaranth (Amaranthus palmeri) resistance to glyphosate.  With that being said research has been conducted at the Vegetable Research Station near Bixby, OK to evaluate the Roundup Ready Xtend (dicamba tolerance) soybean technology for the management of glyphosate resistant Palmer amaranth in Oklahoma soybean.

Typical small plot research techniques were employed in all trials. Various preemergence herbicide programs were investigated including:  acetochlor, dimethenamid, flumioxazin, imazethapyr, pyroxasulfone, and saflufenacil.  These were followed by postemergence application of dicamba and/or glyphosate.  Soybean injury and Palmer amaranth (AMAPA) efficacy was evaluated in 2015 and 2015, and soybean yield was only recorded in 2015.

No soybean injury was observed in the one trial conducted in 2014.  This was regardless of preemergence herbicide combination.  These included dimethenamid + imazethapyr + saflufenacil, flumioxazin, and pyroxasulfone + saflufenacil.  Initial AMAPA control was at least 90% with all PRE herbicides.  However, this control was less than 75% 4 weeks after planting and prior to POST applications of dicamba + glyphosate.  Following these PRE treatments with either dicamba + glyphosate alone or in combination with dimethenamid increased AMAPA control to greater than 95% season long.  Acetochlor + dicamba + glyphosate early POST controlled AMAPA 99% season long.  This was compared to glyphosate POST alone or following flumioxazin PRE controlling AMAPA less than 50% late season.

Soybean injury was 10% early season with pyroxasulfone + saflufenacil with or without imazethapyr in 2015.  The increased injury in 2015 was the result of increased rainfall immediately after planting (6.57 inches within 10 DAP).  This injury had subsided by the end of the season.  AMAPA control 15 DAP was 100% with all PRE treatments except dicamba + glyphosate.  These treatments included pyroxasulfone + saflufenacil with or without imazethapyr, dimethenamid + imazethapyr + saflufenacil, flumioxazin, and dicamba + glyphosate.  Late season AMAPA control was at least 99% with pyroxasulfone PRE combinations followed by two and three applications of dicamba + glyphosate POST.  Glyphosate POST alone or following a PRE application of flumioxazin controlled AMAPA less than 40% late season.  Soybean yield was greater than 50 bushels/A with two and three applications of dicamba + glyphosate.

Soybean injury was 5% or less season long with all flumioxazin PRE treatment in a second trial conducted in 2015.  The PRE treatments were followed by dicamba + glyphosate + acetochlor.  All PRE followed by POST treatments controlled AMAPA at least 99% season long.  Soybean yield was greater than 45 bushels/A compared to 26 bushels/A for the untreated control.

The final study evaluated various application timings of dicamba for AMAPA control in soybean.  Four application timings were evaluated PRE, POST1 (soybean = V3-V4, AMAPA = 0.5-6 in), POST2 (soybean = V4-V5, AMAPA = 0.5-24 in), and POST3 (soybean = R3, AMAPA = 0.5-36 in).  Soybean injury was less than 5% with all application timings of dicamba.  Initial AMAPA control was 63% and decreased over time with dicamba PRE.  AMAPA control was 99% with dicamba POST1 2 WAT and was 92% by the end of the season.  Dicamba POST 3 controlled AMAPA 96% and POST 4 controlled AMAPA 86% when evaluated 4 WAT.  The highest soybean yields occurred with the POST1 (46 bushels/A) and POST2 (44 bushels/A) application timings of dicamba.

These trials indicate that glyphosate resistant Palmer amaranth can be managed with the Roundup Xtend soybean technology.  The most effective programs were when a preemergence program was used in combination with dicamba.  This type of herbicide program will most protect the technology from future weed resistance to dicamba.

 

 


FOUR YEARS OF BALANCETM GT SOYBEANS IN KENTUCKY. S. K. Lawson*; University of Kentucky, Lexington, KY (117)

ABSTRACT

The University of Kentucky has conducted field trials examining overall crop tolerance and weed control of a new GMO soybean trait developed from collaboration between MS Technologies and Bayer Cropscience, Balance™ GT.  These soybeans are tolerant to glyphosate and isoxaflutole, an HPPD-inhibiting herbicide.  By incorporating HPPD tolerance, we now have additional options for controlling resistant and problematic weeds in soybean production. Treatments included isoxaflutole at varying rates with and without other herbicides at preemergence followed by tank mix standards at V2 in 2012 and 2013, mid-postemergence in 2014 and V4 in 2015.  Weed species evaluated were common lambsquarters (Chenopodium album) (2012-13), smooth pigweed (Amaranthus hybridus), morning glory (Ipomoea spp) (2012-15) and giant foxtail (Setaria faberi) (2013-15).  All treatments that included isoxaflutole provided 94% control of weed species evaluated by the final observation. Due to vastly different environmental conditions, visual ratings for crop tolerance varied year to year. 


ISOXAFLUTOLE-BASED HERBICIDE PROGRAMS IN HPPD-TOLERANT SOYBEAN. M. W. Marshall, C. H. Sanders*; Clemson University, Blackville, SC (118)

ABSTRACT


GROWER PERCEPTION OF FIERCE XLT HERBICIDE: COLLABORATION BETWEEN ASA AND VALENT USA. D. Refsell*1, J. Pawlak2, F. Carey3, E. Ott4, R. Estes5, J. Cranmer6, J. Smith7; 1Valent USA, Lathrop, MO, 2Valent USA, Lansing, MI, 3Valent USA, Olive Branch, MS, 4Valent USA, Greenfield, IN, 5Valent USA, Champaign, IL, 6Valent USA, Morrisville, NC, 7Valent USA, Peach Tree City, GA (119)

ABSTRACT

In the spring of 2015, 93 growers signed up to participate in collaboration between the American Soybean Association and Valent USA to evaluate Fierce XLT (flumioxazin + pyroxasulfone + chlorimuron) on their farms to gain experience with the product.  Due to weather circumstances across the Midwest, 58 growers were able to complete applications and participate in the results survey.   Overall we had a 62% participation rate, which was above expectations due to uncooperative rainfall events.   Growers were asked to respond to nine questions and submit yield results.  Results from the survey indicated that over 90% of growers rated their overall satisfaction and the length of residual with Fierce XLT as Good-Excellent using a scale of Excellent, Good, Fair, Poor, or Neutral.   When comparing Fierce XLT to their standard program; 40% found it to be better than, 53% equal to, and only 7% inferior to their current preemergence herbicide.   This was emphasized by the difference in weed escapes, with 29% fewer weed escapes observed in the Fierce XLT treated areas of fields.  Weeds most commonly observed included Amaranthus spp., Ambrosia spp., Conyza canadesis, and Setaria spp.   Final yields reported indicated no difference in yields between the grower standard and the Fierce XLT treated area.   Grower expectations for 2016 following this program suggested that 71% of growers will either likely or definitely add Fierce XLT to their herbicide program.   

 


EFFECT OF LATE-SEASON DIPHENYL ETHER HERBICIDE APPLICATION ON SOYBEAN. M. L. Flessner*; Virginia Tech, Blacksburg, VA (120)

ABSTRACT

Effect of Late-Season Diphenyl Ether Herbicide Application on Soybean. M. L. Flessner*. Virginia Polytechnic Institute and State University, Blacksburg, VA.

ABSRACT

Weeds resistant to both WSSA group 2 and 9 herbicides limit producers’ postemergent herbicide options in soybeans, leading to many postemergent WSSA group 14 applications, specifically diphenyl ether herbicides. Weather, improper scouting, equipment, and other issues too often prevent timely application, which research indicates results in poor weed control. However, effects of so-called “rescue applications” on soybean flower and seed pod production, as well as yield, have not been fully evaluated. The objective of this research was to evaluate soybean response to late-season diphenyl ether herbicide application.

Research was conducted at the Eastern Virginia Agricultural Research and Extension Center near Warsaw, Virginia. Soybeans (Pioneer 46T21R) were planted May 25, 2015 at 321k seed ha-1. Glyphosate (Roundup Powermax; Monsanto Co., St. Louis, MO) at 870 g ae ha-1 + S-metolachlor (Cinch; DuPont Co., Wilmington, DE) at 1390 g ai ha-1 was applied across the trial area to prevent weed infestation on June 24, 2015. A factorial treatment arrangement was used with two factors: herbicide treatment and application timing. Application timings were R1 (July 7, 2015), R3 (July 23, 2015), and R5 (August 20, 2015) growth stages.  Treatments included lactofen (Cobra; Valent USA Corp., Walnut Creek, CA) applied at 220 g ai ha-1, acifluorfen (Ultra Blazer, United Phosphorus Inc., King of Prussia, PA) at 420 g ai ha-1, and fomesafen (Flexstar, Syngenta Crop Protection LLC, Greensboro, NC) in addition to a nontreated check. Crop oil concentrate at 1.75 L ha-1 and ammonium sulfate at 2240 g ha-1 were applied with lactofen. Nonionic surfactant was applied at 0.25 % v v-1 with acifluorfen and fomesafen. A nontreated check was included. Treatments were applied in 140 L ha-1 using a hand-held boom equipped with four, TeeJet 8002VS nozzles on 46 cm spacing at 197 kPa. A randomized complete block design with four replications was used. Plot sizes were 3 by 7.6 m. Data collected included visual injury, flower or seed pod counts, and yield. Visual injury was assessed on a 0 to 100% scale with 0 corresponding to no visible injury and 100 to complete plant necrosis, relative to the nontreated check 1 week after each application timing. Differences in flower or seed pod counts were taken by counting prior to each application timing and 1 week later. Flower counts were taken for the R1 timing, while seed pod counts were taken for the R3 and R5 timings. Yield data were collected by harvesting the center two rows of each plot and adjusting to 13% moisture. Data analysis was conducted using SAS (SAS SAS® Institute v. 9.3, Cary, NC). ANOVA was performed for visible injury and yield data, which were subsequently subjected to means separation using Fisher’s protected LSD0.05. Flower or seed pod counts were compared to the nontreated check at each timing respectively, using t-tests0.05.

Consistent with previous research, visible necrosis was greatest from lactofen (35 to 43%) 1 week after application. Visible necrosis from both aciflourfen and fomesafen was less than lactofen and was 5 to 7% from aciflourfen and 3 to 7% from fomesafen, 1 week after application. Data analysis failed to detect a difference in flower or seed pod counts relative to the nontreated check from any treatment at any application timing. Yield averaged 3288 kg ha-1 and analysis failed to detect a difference between any treatment and the nontreated check. Analysis did indicate that lactofen applied at R1 and aciflourfen applied at R1 yielded greater than lactofen applied at R3 or R5. Overall, while visible leaf necrosis was observed from all treatments, these failed to result in a flower or seed pod reduction or a yield penalty relative to the check, suggesting that yield losses observed in other research is a result of weed competition rather than from soybean injury. Future research should corroborate this effort at multiple site-years.

flessner@vt.edu


EFFECT OF RICE HERBICIDES ON SOYBEAN WITH BOLTTM  TECHNOLOGY. H. M. Edwards*, J. D. Peeples, B. Lawrence, H. T. Hydrick, T. L. Phillips, J. A. Bond; Mississippi State University, Stoneville, MS (121)

ABSTRACT

In 2015, research was conducted to compare the response of Roundup Ready, STS, and BOLT soybean cultivars to low rates of acetolactate synthase (ALS)-inhibiting herbicides common in southern U.S. rice production.  The experimental design was a split block with three replications.  Whole plots were ALS rice herbicides applied at 12.5% of the labeled application rate to simulate an off-target drift event.  Herbicide treatments included imazosulfuron (League) at 0.019 lb ai/A, a prepackaged mixture of halosulfuron plus thifensulfuron (Permit Plus) at 0.0044 lb ai/A, bispyribac (Regiment) at 0.0042 lb ai/A, and a prepackaged mixture of orthosulfamuron plus halosulfuron (Strada Pro) at 0.011 lb ai/A.  Sub plots were soybean cultivars and included ‘Pioneer P49T09BR’ and ‘Pioneer P50T15R” (BOLT cultivars), ‘Asgrow AG4632’ (STS cultivar) and ‘Pioneer P95Y10’ (Roundup Ready cultivar).  Pioneer 95Y10 was injured more than BOLT cultivars with each herbicide 7, 14, and 28 DAT. Injury to Pioneer 95Y10 and Asgrow 4632 was similar with bispyribac 7, 14, and 28 DAT, and the level of injury was greater than that exhibited by the BOLT cultivars.  Bispyribac injured Asgrow 4632 and both BOLT cultivars more than other herbicides at all evaluations.  Injury to Pioneer 49T09BR was greater than that for Asgrow 4632 and Pioneer 50T15BR with orthosulfamuron plus halosulfuron 14 DAT.  Problematically, the response to some of the herbicides varied between the BOLT cultivars.  Injury to Pioneer 49T09BR with bispyribac was greater than that for Pioneer 50T15BR at all evaluations. The same trend was observed with orthosulfamuron plus halosulfuron 14 DAT.  Roundup Ready, STS, and BOLT soybean cultivars responded differently to ALS herbicides used in southern U.S. rice.  The STS cultivar Asgrow 4632 was as tolerant as the BOLT cultivar Pioneer 50T15BR following applications of imazosulfuron, halosulfuron plus thifensulfuron, and orthosulfamuron plus halosulfuron applied at 12.5% of labeled rates.  Among the four cultivars evaluated, response to bispyribac was most variable with injury ranging from 23 to 85% 28 DAT.  Although not completely tolerant to all herbicides evaluated, Pioneer 50T15BR could planted adjacent to rice fields and lessen the potential effects of drift of ALS herbicides.


BOLT™ TECHNOLOGY SOYBEANS FOR IMPROVED PLANT-BACK FLEXIBILITY AFTER DUPONT™ FINESSE® HERBICIDE APPLICATION TO WHEAT. K. A. Backscheider*1, L. H. Hageman2, J. T. Krumm3, S. E. Swanson2, B. Steward4, M. T. Edwards5, R. N. Rupp6, R. W. Williams7, D. Edmund8, V. A. Kleczewski9, D. H. Johnson10; 1DuPont Crop Protection, Shelbyville, IN, 2DuPont Crop Protection, Rochelle, IL, 3DuPont Crop Protection, Hastings, NE, 4DuPont Crop Protection, Overland Park, KS, 5DuPont Crop Protection, Pierre Part, LA, 6DuPont Crop Protection, Edmond, OK, 7DuPont Crop Protection, Raleigh, NC, 8DuPont Crop Protection, Little Rock, AR, 9DuPont Crop Protection, Middletown, DE, 10DuPont Crop Protection, Johnston, IA (122)

ABSTRACT


WINTER WHEAT RESPONSE AND WEED CONTROL WITH EARLY POSTEMERGENCE APPLICATIONS OF FIERCE HERBICIDE. F. Sanders Jr.*1, A. S. Culpepper2, M. S. Riffle3, J. Smith4; 1Valent U.S.A. Corporation, Tifton, GA, 2University of Georgia, Tifton, GA, 3Valent U.S.A. Corporation, Tallahassee, FL, 4Valent USA, Peach Tree City, GA (123)

ABSTRACT

Managing Italian ryegrass (IRG) (Lolium multiflorum) in winter wheat has become extremely challenging.  Resistance of IRG to ALS and ACCase-inhibiting herbicides across the Southeast limits a grower’s ability to manage the weed effectively or economically.  Fierce herbicide, a premix of flumioxazin and pyroxasulfone produced by Valent U.S.A. Corporation, provides excellent control of herbicide resistant IRG as well as broadleaf weeds such as henbit, chickweed, and wild radish.  To achieve optimal weed control, Fierce should be applied when weeds are less than 0.25”, and the herbicide must be activated by rainfall or irrigation (0.5 inch for most soils).  Crop response with Fierce is influenced by planting depth, application timing, soil type, and excessive rainfall (>2in) after application.  To help avoid crop injury to wheat, planting depth should be at least 1 inch, Fierce should be applied between the spike and 2 leaf stages, and Fierce should not be applied to fields with extremely sandy soils.  Currently, Section 24(c) Special Local Need labels are available for use of Fierce in wheat production in Georgia, South Carolina, and North Carolina.  

 


MONITORING HERBICIDE RESISTANCE IN CEREAL WEEDS: A SYNGENTA PERSPECTIVE. R. Jain*1, M. A. Cutulle1, C. L. Dunne1, D. J. Porter2; 1Syngenta Crop Protection, Vero Beach, FL, 2Syngenta Crop Protection, Greensboro, NC (124)

ABSTRACT

Wild oat (Avena fatua) and Italian ryegrass (Lolium multiflorum) are problematic weeds in cereal production. Group 1 herbicides that are commonly used to control these weeds include Acetyl CoA carboxylase (ACCase) inhibitors such as Aryloxyphenoxy propionates (FOPs) and Phenylpyrazolins (DENs). Resistance to these chemistries has been known to occur in grass weeds in cereals. Syngenta is dedicated to monitoring resistance to ACCase inhibitors and other modes of action in these weeds. Wild oat and Italian ryegrass seed samples were collected from fields where weeds were not adequately controlled by Syngenta cereal herbicide products. The samples were screened for sensitivity to multiple Group 1 and Group 2 (Acetolactate synthase or ALS-inhibitor) herbicides in the greenhouse. Results of samples analyzed in 2005 indicated that greater than 50% of the wild oat populations were resistant to FOP herbicides; comparatively, only 12% were resistant to the DEN herbicide pinoxaden. By 2014, approximately 75% of the collected populations were resistant to FOP herbicides, but only approximately 30% were resistant to pinoxaden. Despite resistance to Group 1 herbicides, Group 2 herbicides controlled a majority of the wild oat non-performance samples. Syngenta will continue to provide herbicide sensitivity diagnostics and recommendations to growers dealing with herbicide resistant weeds.


PYROXSULAM PRODUCTS FOR WEED CONTROL IN NORTH AMERICAN WHEAT. J. P. Yenish*1, R. E. Gast2, P. Prasifka3, M. Moechnig4, R. Degenhardt5, L. Juras6; 1Dow AgroSciences, Billings, MT, 2Dow AgroSciences, Indianapolis, IN, 3Dow AgroSciences, West Fargo, ND, 4Dow AgroSciences, Toronto, SD, 5Dow AgroSciences, Edmonton, AB, 6Dow AgroSciences, Saskatoon, SK (125)

ABSTRACT

Pyroxsulam Herbicides or Weed Control in U.S Wheat, Joseph P. Yenish, Roger E. Gast, Patricia L. Prasifka, Michael J. Moechnig, Rory F. Degenhardt, and Len T. Juras.

Dow AgroSciences is planning to introduce three pyroxsulam-based herbicide products for the U.S. spring and winter wheat markets during the 2016 and 2017 growing seasons, which include PerfectMatchTM, TeamMateTM, and TarzecTM herbicides.  PerfectMatch, to be introduced for the 2016 season, is a new premix herbicide formulation for spring and winter wheat that combines the broadleaf activity of clopyralid and fluroxypyr with the added grass and broadleaf activity of pyroxsulam.  PerfectMatch will be labeled at a single application rate of 1.17 liters/ha (1 pint/A), which delivers 15 g ai pyroxsulam, 105 g ae clopyralid, and 105 g ae fluroxypyr/ha.  In field trials conducted in 2013, 2014, and 2015 from Washington to Minnesota, PerfectMatch provided greater control of wild buckwheat, mayweed chamomile, common lambsquarters, prickly lettuce, and Canada thistle compared to GoldSkyTM  herbicide, a premix of pyroxsulam, fluroxypyr, and florasulam. The new formulation will provide the same excellent crop safety to both spring wheat (including durum) and winter wheat as GoldSky herbicide.

 The second herbicide available will be TeamMate, a pyroxsulam WDG formulation for grass and broadleaf weed control in winter and spring wheat, including durum, which will provide flexible tank mix options to allow customization for broad-spectrum grass and broadleaf weed control.  TeamMate will be labeled at a single rate of 70 g product/ha (1 oz/A) which delivers 15 g ai pyroxsulam/ha.  Trials conducted in 2014 and 2015 demonstrated excellent crop safety of TeamMate with less than 5% injury observed 1 and 2 weeks after treatment and no effect on wheat yield. Moreover, TeamMate efficacy was similar to GoldSky on wild oats, Italian ryegrass, Persian darnel, yellow foxtail, and green foxtail in those same trials.

 The third new herbicide is Tarzec, a premix WDG formulation for use in winter wheat only.  Tarzec will provide greater crop safety under conditions of cold temperatures or large differences in diurnal temperatures with a greater broadleaf spectrum than PowerFlex HL.  Tarzec will be labeled at a single rate of 70 g product/ha (1 oz/A) that delivers 17.5 g ai pyroxsulam and 4.7 g ae ArylexTM active/ha.  Trials conducted in the 2014/2015 winter wheat growing season demonstrated excellent crop safety of Tarzec with less than 2% injury observed 1 to 6 weeks after application.  Tarzec provided equal or greater downy brome control as PowerFlex HL with fall or spring application timings.  Tarzec also provided greater downy brome and Italian ryegrass control than Osprey with spring applications, and greater fumitory control than all comparative treatments.

 ™Trademark of The Dow Chemical Company ("DOW") or an affiliated company of Dow.


MULTIPLE RESISTANCE TO IMAZAMOX AND GLUFOSINATE IN WHEAT IN EUROPE. A. M. Rojano-Delgado1, P. T. Fernandez*1, R. Alcantara-de la Cruz1, J. Menendez2, D. Rafael1; 1University of Cordoba, Cordoba, Spain, 2University of Huelva, Huelva, Spain (126)

ABSTRACT

Multiple Resistance to Imazamox and Glufosinate in Wheat in Europe. A.M. Rojano-Delgado1, P.T. Fernandez*1, R. Alcantara-de la Cruz1, J. Menendez2, R. De Prado11University of Cordoba, Cordoba, Spain; 2University of Huelva, Palos, Spain.

The economic importance of wheat at the global level results from its use for a large number of processed foods for humans and animals. Two lines (line 24 and line 42) from Clearfield® imazamox-resistant wheat ’Pantera’ and transgenic glufosinate-resistant wheat ‘Anza’ crossings were selected for being highly resistant to the herbicides glufosinate and imazamox. Line 24 showed a phenotype similar to Pantera cultivar, while line 42 was similar to Anza. Dose-response experiments using imazamox plus glufosinate mixture formulations (IMI/GS) showed that the ED50 value of line 24 was 51,72/517,26 g of active ingredient IMI/GS per hectare (g ai ha-1) and for line 42 was 95,81/958,16 g of active ingredient IMI/GS per hectare (g ai ha-1), 28-fold and 15-fold higher than the susceptible cultivar, respectively. A study of the gluthamine synthetase activity in both lines showed I50 values 62-fold (39.95 µM, line 24) and 100-fold (64.97 µM, line 42) higher than the susceptible variety (0.62 µM). For ALS enzyme activity, the values for both lines were 23-fold (70.85 µM, line 24) and 5-fold (15.70µM, line 42) higher than the susceptible variety (3.56 µM). Both results were consistent with the correspondence between line and parental phenotypes observed.

These results suggest that glufosinate and imazamox tolerance may be explained in terms of loss of affinity in their target site. However, the metabolism of glufosinate by the bar gene, a key mechanism of glufosinate resistance, cannot be discarded.

Keywords: Clearfield®, imazamox, glufosinate, gluthamine synthetase.

Email address: pablotomas91@hotmail.es

 


ALS RESISTANT ITALIAN RYEGRASS CONTROL IN WINTER WHEAT. J. T. Copes*1, D. K. Miller2, T. M. Batts2, M. Mathews1, J. L. Griffin3; 1LSU AgCenter, Saint Joseph, LA, 2LSU AgCenter, St Joseph, LA, 3LSU AgCenter, Baton Rouge, LA (127)

ABSTRACT

ALS RESISTANT ITALIAN RYEGRASS CONTROL IN WINTER WHEAT. J.T. Copes, D.K. Miller, T.M. Batts, M.M. Mathews, and J.L. Griffin; School of Plant, Environmental, and Soil Sciences, Louisiana State University Agricultural Center, Baton Rouge, LA 70803.

 

Abstract

 

Research was conducted at the LSU AgCenter Northeast Research Station near Saint Joseph to determine if a single fall applied herbicide application could provide season long control of Italian ryegrass. Soil type was a Commerce silt loam, and the test area contained a natural dense Italian ryegrass population that is suspected acetolactate synthase resistant. The experiment was conducted in a randomized complete block design with four replications. Wheat was planted on November 26, 2014 using a Marliss drill calibrated to sow 90 pounds of seed per acre. Treatments were pyroxasulfone applied at spiking and 2-leaf wheat, pyroxasulfone applied at spiking and 2-leaf wheat followed by pinoxaden, pyroxasulfone/carfentrazone (premix) applied at spiking and 2-leaf wheat, pyroxasulfone/carfentrazone + metribuzin applied at 2-leaf wheat, metribuzin applied at 2-leaf wheat, metribuzin applied at 2-leaf wheat followed by pinoxaden, pyroxasulfone + metribuzin applied at 2-leaf wheat. Spiking treatments were made to one inch wheat on December 9, 2014 and the 2-leaf application was made on December 17, 2014. Pinoxaden was applied on January 21, 2015 to 2 leaf to 3 tiller Italian ryegrass with wheat in the early tillering (1 to 3 tiller) growth stage. Wheat was harvested on June 2, 2015 to determine yield.

 

End of season Italian ryegrass control is discussed. Pyroxasulfone applied to spiking or 2-leaf wheat and metribuzin applied at 2-leaf wheat controlled Italian ryegrass 73, 63, and 73%, respectively. Pyroxasulfone applied to spiking or 2-leaf wheat and followed by pinoxaden, controlled Italian ryegrass 94 to 95%. Metribuzin followed by pinoxaden and pyroxasulfone + metribuzin controlled Italian ryegrass 89 and 93%, respectively. Pyroxasulfone/carfentrazone (premix) applied to spiking or 2-leaf wheat controlled Italian ryegrass 93 and 87%, respectively. Whereas, pyroxasulfone/carfentrazone + metribuzin controlled Italian ryegrass 96%. Wheat injury occurred only for herbicide treatments containing metribuzin, with wheat injury ranging from 20 to 27% and 25 to 36% 56 DAA and 76 DAA, respectively. No injury was observed at any time for treatments not containing metribuzin. No yield differences were detected among treatments; this was a result of Fusarium wilt (head Scab) infecting wheat during the wheat pollination period.

 

Results show that a single herbicide application made in the fall to spiking or 2-leaf wheat controlled Italian ryegrass as well as two shot programs. Also, results show the importance of planting a metribuzin tolerant wheat variety when this herbicide will be applied for weed control in winter wheat.  


RYEGRASS IN NORTHEAST TEXAS WHEAT. C. Jones*; Texas A&M University, Commerce, TX (128)

ABSTRACT

A trial was conducted in Hunt County, Texas to evaluate the control of ryegrass (Lolium multiflorum) that is tolerant to ALS and ACC’ase herbicides.   Treatments included pyroxasulfone at 124 g ai/ha delayed PRE (dPRE), pyroxasulfone at 93 and 124 g ai/ha dPRE fb pinoxaden at 60 g ai/ha LPOST, pyroxasulfone at 93 g ai/ha dPRE fb metribuzin at 220 g ai/ha POST, pyroxasulfone plus carfentrazone at 82 + 5.86 g ai/ha and 115 plus 8.2 g ai/ha dPRE, pyroxasulfone plus carfentrazone at 82 + 5.86 g ai/ha and 115 plus 8.2 g ai/ha dPRE fb pinoxaden at 60 g ai/ha LPOST, flufenacet plus metribuzin at 240 + 60 g ai/ha dPRE, flufenacet plus metribuzin at 240 + 60 g ai/ha dPRE fb pinoxaden at 60 g ai/ha LPOST, and pyroxasulfone at 93 and 124 g ai/ha plus metribuzin at 110 g ai/ha plus pinoxaden at 60 g ai/ha ePOST, and pinoxaden at 60 g ai/ha LPOST.  Delayed PRE treatments were made when wheat radical was about 1 cm long, ePOST treatments were made when ryegrass was at 1 leaf stage, POST treatments were made to 3 to 4 leaf ryegrass, and LPOST treatments were made to 2 to 3 tiller ryegrass 50 days after .

Pyroxasulfone and pyroxasulfone plus carfentrazone controlled ryegrass 48 to 58% 50 days after delayed PRE (DADP)  47 to 58% 110 DADP and ryegrass control decreased to 31 to 36% at 170 DADP.  When following pyroxasulfone at 124g ai/ha or pyroxasulfone plus carfentrazone at 115 plus 8.2 g ai/ha with pinoxaden increased ryegrass control to70 to 72% at 110 DADP, but control was not increased at 170 DADP.  When following the lower rate of pyroxasulfone plus carfentrazone, pinoxaden did not increase ryegrass control.  At 110 DADP, pyroxasulfone fb metribuzin  and pyroxasulfone at 124 g ai/ha plus metribuzin plus pinoxaden controlled ryegrass 94 and 86%, respectively.  By 170 DADP, no treatment controlled rye grass better than 65% and pinoxaden alone controlled ryegrass 13%.

 


FALL HERBICIDE APPLICATIONS ALLOW FOR FROST-SEEDING OF RED CLOVER IN WINTER WHEAT. G. E. Powell*, C. L. Sprague; Michigan State University, East Lansing, MI (129)

ABSTRACT

Frost-seeding red clover into winter wheat has been time-honored practice that has been beneficial for wheat growers since the early 1900s. However, many growers moved away from this practice because clover was not compatible with the practices used for weed control in wheat. Including red clover back into crop rotations has been an interest expressed by many Michigan growers. Therefore, the objectives of this research were to evaluate several new herbicides and determine the impact of fall and spring herbicide applications on frost-seeded clover survival, weed control, and winter wheat yield. A field experiment was conducted in Michigan by planting wheat in the fall of 2013 and 2014. The experiment was set up as a split-split plot design with herbicide application timing (fall or spring) as the main plot and herbicide treatment as the sub plot. All plots were replicated 4 times. Fall herbicide applications were made when winter wheat was at the 3-leaf stage (Feeke’s stage 1.3) and spring herbicide applications were made at when wheat was at Feeke’s stage 5, approximately 4-6 weeks after medium red clover was frost seeded. The herbicides that were examined were: 1) thifensulfuron + tribenuron (13 + 13 g ha-2), 2) pyrasulfotole + bromoxynil (45 + 258 g ha-2), 3) mesosulfuron (14.5 g ha-2), 4) pyroxsulam (18 g ha-2), 5) dicamba (140 g ha-2), 6) 2,4-D ester (560 g ha-2), and 7) MCPA (213 g ha-2).  A non-ionic surfactant plus ammonium sulfate was included in the thifensulfuron + tribenuron, pyrasulfotole + bromoxynil, mesosulfuron, and pyroxsulam treatments. Winter wheat injury, red clover establishment and survival, and weed control were assessed several times throughout the growing season. Wheat was harvested for yield in the second year of this experiment. Winter wheat injury was less than 10% with all herbicide treatments with the exception of fall-applied 2,4-D ester, which resulted in over a 25% reduction in yield. Common lambsquarters was the predominant weed in this trial and spring applications of all herbicides with the exception of mesosulfuron provided greater than 80% control of common lambsquarters after wheat harvest. Unexpectantly, fall-applied thifensulfuron + tribenuron also provided 80% common lambsquarters control. Red clover was able to tolerate fall applications of all the herbicides. However, fall-applied mesosulfuron did cause significant red clover injury (20%) and reduced stand by 30% compared untreated control. All spring herbicide applications, with the exception of MCPA injured red clover by 75% and reduced the clover stand by at least 58%. From this research, growers do have weed control options in winter wheat that are compatible with the frost-seeding of red clover. Spring-applied MCPA and fall applications of several of the herbicides examined were compatible with frost-seeding red clover. However, due to concerns with reduced yield growers should not apply 2,4-D in the fall. 

 


PRELIMINARY FINDINGS ON THE EFFECT OF FOLIAGE ON 2,4-D VOLATILITY. G. Oakley*1, D. B. Reynolds2, B. Bruss3; 1Mississippi State University, Mississippi State, MS, 2Mississippi State University, Starkville, MS, 3NuFarm, Morrisville, NC (130)

ABSTRACT


DEACTIVATION OF CONTAMINATE CONCENTRATIONS OF 2,4-D AND DICAMBA BY USING THE FENTON REACTION. G. T. Cundiff*1, D. B. Reynolds1, T. C. Mueller2; 1Mississippi State University, Starkville, MS, 2University of Tennessee, Knoxville, TN (131)

ABSTRACT

Deactivation of Contaminate Rates of 2,4-D and Dicamba by Using The Fenton Reaction. G.T. Cundiff1, D.B. Reynolds1, and T.C. Mueller2, 1Mississippi State University, Mississippi State, MS., 2University of Tennessee, Knoxville, TN.

ABSTRACT

The introduction of new herbicide tolerant crops may provide many benefits for producers such as alternative control options for resistant weed species, decreased costs, and different modes of action.  Along with these benefits, the use of auxin containing herbicides may also increase concern for issues such as herbicide drift, volatilization, and tank contamination.  The adjuvant and solvent system utilized in several commercial herbicides often result in the release of herbicides which have been sequestered within the spray system thus resulting in injury to sensitive crops.  Roundup WeatherMax and PowerMax (glyphosate) are two such products that have been observed to have this effect.

Field studies were conducted to evaluate the effect of the Fenton Reaction on various rates of dicamba and 2,4-D while using soybean and cotton as a bio-indicator.  Treatments were arranged as a split plot design with four replications.  Each experimental unit consisted of 4-91cm rows 12.2 m in length.  The center two rows of each experimental unit were treated.  Factor A main plots consisted of two cleanout procedures (none and a chemical deactivation procedure of the Fenton Reaction).  Factor B sub-plots consisted of seven rates of dicamba (0.56, 0.14, 0.035, 0.009, 0.00218, 0.000549, and 0 kg ae/ha) and six rates of 2,4-D (0.56, 0.14, 0.035, 0.009, 0.00218 and 0 kg ae/ha).  The soybeans were sprayed at the R2 growth stage and cotton at the pinhead square growth stage with applications made at 140 L/ha using a two row boom with TTI 110015 tips.

Each rate of dicamba and 2,4-D was mixed in a spray solution of 3.785 liters and applied to soybean and cotton, respectively. The remaining solution for each rate was adjusted to a volume of 1.875 liters and then the Fenton Reaction was added to the spray solution.  Following the deactivation reaction, the resulting solution was sprayed to plots adjacent to experimental units previously sprayed with the corresponding rates.  The deactivation treatment consisted of iron sulfate hepta-hydrate added to the original spray solution and agitated for one minute and then 30% H2O2 was added and allowed to react for 20 minutes.  Each dicamba and 2,4-D solution treated with the cleanout method was then applied. Weekly visual ratings were taken 7, 14, 21, and 28 days after treatment (DAT), plant height reductions calculated, yield was taken and percent yield reductions were calculated.  Analytical samples were taken before and after the Fenton Reaction and analyzed on High Performance Liquid Chromatography (HPLC) to the mass spec.

Soybean experiments from 2014 and 2015 showed an interaction with cleanout procedure and rate with respect to percent visual estimation of injury (VEOI), height reduction, yield reduction and ppm analyte retained.  At 28 DAT, VEOI at the 1X (0.56 kg ha-1) and 1/4X rate of dicamba alone showed 100 and 84% compared to 89 and 58% injury when the Fenton Reaction was applied, respectively.  Soybean yield reduction at the 1/4X rate was 94% with dicamba alone and showed a 56% reduction from the check when the Fenton Reaction was applied. At the 1/16X rate, dicamba alone showed a 62% yield reduction from the check when compared to 32% with the Fenton Reaction.  Cotton experiments from 2014 and 2015 showed an interaction with cleanout procedure and rate with respect to VEOI, height reduction, yield reduction and ppm 2,4-D analyte retained.  At 28 DAT, the rates of 1X (0.56 kg ha-1), 1/4X, 1/16X, 1/64X, and 1/256X of 2,4-D alone are significantly greater at 89, 57, 37, 27, and 13% visual injury when compared to the Fenton Reaction of 49, 31, 21, 14 and 4%. At the 1X, 1/4X, 1/16X, and 1/256X rates of 2,4-D alone yield reductions were 95, 83, 61, and 39% when compared to the Fenton Reaction of 77, 53, 31, and 8%.  These data show that the Fenton Reaction coupled with a dilution process reduced the occurrence of tank contamination.

 


WEED CONTROL, CROP TOLERANCE AND POTENTIAL TANK CONTAMINATION IN DICAMBA RESISTANT SOYBEANS. J. E. Scott1, L. D. Charvat2, S. Z. Knezevic*1; 1University of Nebraska-Lincoln, Concord, NE, 2BASF Corporation, Lincoln, NE (132)

ABSTRACT

Weed resistance is on the increase, therefore, introduction of dicamba-tolerant soybeans could provide another option for weed control. Four studies were conducted in 2015 in northeast Nebraska, including: (1) Herbicide programs for dicamba-tolerant soybeans based on PRE followed by POST application of EngeniaTM (BAPMA-dicamba); (2) efficacy of BAPMA-dicamba as influenced by weed heights; (3) tolerance of dicamba-tolerant soybeans to other auxin-type herbicides; and (4) tolerance of non-dicamba-tolerant soybeans to various levels of BAPMA-dicamba residues as potential tank contaminants. Preemergence herbicides, which included: sulfentrazone, dimethenamid-p, flumioxazin, pyroxasulfone, metribuzin, metolachlor, and saflufenacil provided good-to-excellent control of waterhemp and lambsquarters. The POST application of BAPMA-dicamba tank mixed with glyphosate provided complete control of all weed species tested.  

BAPMA-dicamba tankmixed with glyphosate provide excellent control (>90%) of the weed species tested when applied early-POST and mid-POST (5-20cm tall weeds). Late-POST application (20-30cm weeds) was less effective, especially on velveltleaf.  Dicamba-tolerant soybeans were temporarily speckled by BAPMA-dicamba+glyphosate when ultra course droplets were delivered using TTI nozzles.  Dicamba-tolerant soybean sprayed with dicamba+diflufenzopyr or 2,4-D amine exhibited 90% and 75% injury levels, respectively. Non-dicamba-tolerant soybean exhibited high level of sensitivity to BAPMA-dicamba as a tank contaminant. For example, at 10DAT of BAPMA-dicamba, there was 40% injury at 1/100 of the label rate and 20% injury at 1/1000 of the label rate (560 ai/ha) applied at V3 soybeans. Similar injury occurred with applications at V6 and R2 stages. The injuries were evident season long in the form of overall canopy stunting and leaf cupping, which further delayed crop maturity.  These results indicated potential use of BAPMA-dicamba to control various weed species; however repeated use of BAPMA-dicamba alone or in combination with glyphosate should be avoided to reduce probabilities for dicamba resistance, as there is already dicamba-resistant kochia in Western Nebraska, eastern Colorado and eastern Wyoming.


KNOWING WHEN TO SPRAY:  MONITORING SURFACE TEMPERATURE INVERSIONS AND DAILY WIND SPEED PROFILES IN MISSOURI. M. D. Bish*, K. W. Bradley; University of Missouri, Columbia, MO (133)

ABSTRACT

The group 4 synthetic auxin herbicides are commonly associated with drift and injury to non-target plants, such as tomatoes, grapes, and soybean.  The impending introduction of dicamba and 2,4-D-resistant traits into the soybean and cotton markets is likely to cause increased usage of synthetic auxin herbicides.  The focus of this ongoing research is to monitor factors associated with the risk of synthetic auxin herbicide drift in Missouri by analyzing historical wind speed data and investigating the frequencies and intensities of surface temperature inversions.

High wind speeds can lead to physical drift of herbicide particles in which the chemical never reaches the intended plants. The Environmental Protection Agency (EPA) considers herbicide applications made during wind speeds exceeding 16 km/hour as high risk for off-target herbicide movement.  To identify times throughout the growing season that wind speeds are most likely to surpass the 16 km/hour threshold, the average hourly wind speeds for every March to August day from the years 2000 to 2015 were retrieved from the Missouri Historical Agricultural Weather Database for 5 regions within the state.  For each region, the hourly wind speeds for all March days within the 15 years were averaged together and graphed to profile the wind speeds throughout a typical March day.  Similarly, hourly wind speed graphs were generated to represent typical April, May, June, July and August days for each of the 5 regions.  In 3 out of the 5 regions analyzed, average wind speeds during mid-day hours of March, April, and May exceeded 16 km/hour.

Surface temperature inversions occur when air nearest the earth’s surface is cooler than the air above it; they create a stable atmosphere that is conducive for herbicide volatilization. To monitor surface temperature inversions, weather stations at 3 regions within Missouri were fitted with temperature sensors at 46, 168, and 305 cm above the soil surface in January of 2015.  Temperatures were recorded every 3 seconds, and those temperatures were averaged to generate a 5-minute temperature reading at each height.  The 5-minute temperatures were compared to identify inversions in which the 46 cm temperature was coolest and the 305 cm temperature was warmest.  Preliminary results from March to July of 2015 indicated that inversions occurred at all 3 locations in each of the 5 months.  The intensity of most inversions was 1 to 3° C different between the 46 and 305 cm heights.  The average duration of inversion varied across month and location, but was shorter during June and July than in the earlier months analyzed.

 This ongoing research will be useful to equip herbicide applicators with information to help steward the new weed control technologies.  Preliminary results of the temperature inversion study support the importance of using the new, low-volatile formulations of 2,4-D and dicamba to help minimize the potential impact of temperature inversions on volatilization of these active ingredients.

 


INFERRING THE OUTCROSSING RATE AMONG DIFFERENT ECHINOCHLOA SP. USING THE ALS-INHIBITING HERBICIDE RESISTANCE MARKER. A. Pisoni, T. Kaspary, R. S. Rafaeli, C. Menegaz, A. Merotto Junior*; Federal University of Rio Grande do Sul - UFRGS, Porto Alegre, RS, Brazil (134)

ABSTRACT

Barnyardgrass (Echinochloa crus-galli) is a selfing specie, but small outcrossing rate could occur. Gene flow through pollen is important for the spreading of the herbicide resistance, which has occurred with high frequency in Echinochloa species. In addition, several plants from the main Echinochloa species have been found with mixtures of morphological discriminant traits indicating the possibility of gene introgression. The objectives of this study were to evaluate the outcrossing rate of barnyardgrass and the occurrence of introgression between E. crus-galli and E. colona. The resistance to imidazolinone herbicides was used as a marker for quantifying the occurrence of cross-fertilization. An imidazoline-herbicide resistant biotype (ALS gene mutation Trp574) of E. crus-gally was used as pollen donor and a susceptible biotype of the species E. crus-gally and E. colona was used as pollen receptor. Each plot consisted 20 donor and 12 receptor plants separated by 1m. Seeds from the receptor plants were harvest at maturity at intervals of 5 days. The outcrossing rate identification was based on 2,500 plants per experimental area. The identification of resistant individuals was performed by applying the herbicide imazethapyr in three to four-leaf stage plants. The evaluations were performed at 21 days after herbicide application, where it was considered plants with heterozygous alleles those who survive the herbicide application. The average out-crossing rate in E. crus-galli was 3.46%, ranging from 2.96% to 4.41%. The production of E. crus-galli seeds reached 23.107 seeds per plant when grown under field conditions at a plant density of 1.0 m2. The survival of E. colona plants originated from seeds of the receptor plants was of 0,8%, whose occurrence of introgression is currently been confirmed through cpDNA molecular markers. Although E. crus-galli is an autogamous plant significant outcrossing occurs at field condition, which could be associated with the rapid evolution of the multiple herbicide resistance.


VEGETATIVE PROPAGATION OF AMBROSIA ARTEMISIIFOLIA FOR RAPID RESISTANCE TESTING. B. W. Schrage*, W. J. Everman; North Carolina State University, Raleigh, NC (135)

ABSTRACT

Vegetative Propagation of Ambrosia artemisiifolia for Rapid Resistance Testing.  B.W. Schrage, W.J. Everman, R. Richardson; North Carolina State University, Raleigh, NC.

ABSTRACT

During the summer of 2015, soybean producers in Northeastern North Carolina began experiencing insufficient control of common ragweed (Ambrosia artemisiifoia) with the use of labeled PPO-inhibiting herbicides.  The existence of confirmed PPO-resistant common ragweed in Delaware and Ohio prompted an immediate investigation.  Distance from experimental stations and the documented difficulty associated with screening common ragweed from seed collected previously in the same year created a need for a simple, albeit effective, resistance screening method. 

Live samples were collected, transplanted, propagated and an accelerated resistance screening was conducted.  A completely randomized design including five herbicide treatments (fomesafen, fomesafen+glyphosate, lactofen, aciflourifen at respective full labeled rates and an non-treated check), two putative resistant populations (Moyock and Sunbury, NC), and five replications was employed at the Method Greenhouse facilities in Raleigh, NC.

Significant differences in plant height and injury were observed among herbicide treatments (P > 0.0001) although all plants survived and showed potential to recover.  Numeric trends suggest that lactofen had the greatest toxicity on specimens; whereas acifluorfen had the least.  Sample locations in Moyock and Sunbury, NC both suggest the existence of PPO-resistant common ragweed; although more detailed screening methods need to be conducted.  Initial results from this research raise concerns that PPO-Inhibiting herbicides may become ineffective should over-reliance continue in North Carolina soybean production.

 


POSTEMERGENCE HERBICIDE OPTIONS FOR NEALLEY’S SPRANGLETOP (LEPTOCHLOA NEALLEYI) CONTROL. E. A. Bergeron*, E. P. Webster, B. M. McKnight, S. Y. Rustom Jr; Louisiana State University, Baton Rouge, LA (136)

ABSTRACT

In 2014 and 2015, a study was initiated to evaluate Nealley's sprangletop (Leptochloa nealleyi Vasey) control when treated with a single application of cyhalofop or fenoxoprop or a sequential application of either herbicide. This study was established at the LSU AgCenter H. Rouse Caffey Rice Research Station (RRS) near Crowley, LA in 2014 and 2015 and a grower location near Estherwood, LA in 2015. The initial application was applied to rice in the two- to three-leaf stage or early-POST (EPOST), or an EPOST application followed by an application 2 weeks after on four- to five-leaf rice, or late-POST (LPOST). Cyhalofop rates were 208, 314, or 417 g ai/ha. Fenoxoprop rates were 66, 86, or 122 g ai/ha. Previous research indicated quinclorac plus halosulfuron had no activity on Nealley's sprangletop; therefore, quinclorac at 420 g ai/ha plus halosulfuron at 53 g ai/ha was applied delayed preemergence (DPRE) to control grass, sedge, and broadleaf weeds in the research area. All herbicides were applied with a CO2-pressurized backpack sprayer calibrated to deliver 140 L/ha.

At 21 DAT, the Nealley's sprangletop treated with fenoxaprop at 66, 86, or 122 g/ha, applied EPOST, was controlled 80 to 85%, compared with the cyhalofop applied EPOST at 208, 314, or 417 g/ha treated Nealley's sprangletop with 64 to 76% control. At 35 DAT, all Nealley's sprangletop treated with an EPOST fb LPOST application of fenoxoprop or cyhalofop was controlled 92%. At 21 DAT, cyhalofop at 208 g/ha applied EPOST resulted in the lowest control of Nealley's sprangletop, 64%. Although at 54 DAT, the control of Nealley's sprangletop was similar from both herbicides, the higher control observed at 21 DAT with fenoxoprop at 122 g/ha yielded 8090 kg/ha compared with rice treated with cyhalofop at 208 and 314 g/ha with a rice yield at 6520 and 7180 kg/ha, respectively. Rice treated with the highest rate of cyhalofop evaluated, 417 g/ha, resulted in a yield similar to rice treated with fenoxoprop at 122 g/ha. Rice treated with fenoxoprop at 66, 86, or 122 g/ha or cyhalofop at 208, 314, or 417 g/ha yielded 970 to 1020 kg/ha higher than the nontreated. 

A study was established at the RRS in 2014 and 2015 and a grower location near Estherwood, LA in 2015. This study evaluated Nealley’s sprangletop control when treated with imazethapyr plus propanil applied at different rates. The experimental design was a randomized complete block with a factorial arrangement of treatments with four replications. Factor A was imazethapyr at 0 or 70 g ai/ha and Factor B was an emulsifiable concentrate propanil at 0, 2240, 3360, or 4480 g ai/ha. In April 2014, Clearfield ‘CL 151’ rice was drill-seeded at 90 kg/ha and Clearfield ‘CL 111’ rice was planted at the same rate in March 2015. Herbicide treatments were applied as previously described.  All treatments were applied mid-postemergence (MPOST) to three- to four-leaf rice. A crop oil concentrate at 1% v/v was added to imazethapyr when applied alone, and no adjuvant was added to any mixture containing propanil.

At 49 DAT, a single application of imazethapyr controlled Nealley's sprangletop 75% while the imazethapyr plus propanil at 2240, 3360, or 4480 g/ha controlled Nealley's sprangletop 92, 89, and 81%, respectively. Rice treated with a single application of imazethapyr yielded 4960 kg/ha compared with rice treated with imazethapyr plus propanil at 2240, 3360, or 4480 g/ha yielded 7490, 6290, and 7018 kg/ha, respectively.

Nealley’s sprangletop is a prolific seed producer with high seed viability. It is important to correctly identify this weed in order to select the appropriate weed management program. Imazethapyr alone will not control Nealley's sprangletop and may be the reason this weed has spread in Louisiana. A POST application of fenoxaprop applied at 122 g/ha should be used on small actively growing Nealley's sprangletop when it is present in rice.


HERBICIDE PROGRAMS TO CONTROL HPPD-RESISTANT COMMON WATERHEMP IN NEBRASKA. M. C. Oliveira*1, J. E. Scott2, A. Jhala1, T. A. Gaines3, S. Z. Knezevic2; 1University of Nebraska-Lincoln, Lincoln, NE, 2University of Nebraska-Lincoln, Concord, NE, 3Colorado State University, Fort Collins, CO (137)

ABSTRACT

Common waterhemp (Amaranthus rudis) populations from Nebraska have been confirmed to be resistant to five modes of action (glycine, growth regulators, PSII, ALS, and HPPD). Series of field experiments were conducted in corn during the 2013 and 2014 seasons to evaluate various herbicides for control of HPPD-resistant waterhemp with premergence (PRE), postemergence (POST), and PRE followed by POST treatments. The experimental design for all studies was RCBD with treatments replicated three times. One of the best PRE treatments was a tankmix of s-metolachlor+atrazine+mesotrione with acetochlor, which provided 96% control at 50 DAT. POST alone treatments based on glyphosate, and combinations of mesotrione+atrazine with PSII inhibitors, or growth regulators, or glufosinate, provided 92% control of HPPD-resistant common waterhemp at 22 DAT. The combinations of PRE applications of s-metolachlor+atrazine+mesotrione followed by POST applications of glyphosate or glufosinate mixtures provided excellent control (> 97%) at 32 days after the POST application. In addition, PRE applications of acetochlor + atrazine followed by POST applications of topramezone, atrazine and synthetic auxins provided also > 97% control at 32 days after the POST treatment. Most of tested herbicide provided very good waterhemp control (>90%), suggesting that excellent herbicides are still available to combat the spread of HPPD-resistant waterhemp in corn.


SCREENING OF SUSPECTED PPO-RESISTANT PALMER AMARANTH POPULATIONS IN SOUTH CAROLINA. M. W. Marshall*, C. H. Sanders; Clemson University, Blackville, SC (138)

ABSTRACT

Herbicides, including fomesafen and flumioxazin, have provided excellent soil residual and/or postemergence control of glyphosate and ALS-resistant Palmer amaranth in cotton and soybean over the past ten years (since the confirmation of glyphosate-resistance).  Recently, several areas in the Mid-South and Southeast have found and confirmed PPO-resistant Palmer amaranth populations.  In 2015, several growers in South Carolina observed Palmer amaranth populations that survived both soil and postemergence applications of fomesafen and flumioxazin in cotton and soybean.  Seeds were collected from 3 sites in South Carolina and grown in the greenhouse facility at Edisto Research and Education Center.  Seedheads from each site were dried, threshed, and cleaned.  In a dose response study, the three biotype populations were planted in the greenhouse in 10 by 10 cm pots.  At the 4-leaf growth stage, plants were sprayed with following rates of fomesafen:  0, 0.5, 1, 2 X where X equals 0.25 lb ai/A rate.  The populations that were treated with any rate of fomesafen were controlled.  Therefore, the three populations collected from the South Carolina sites were not resistant to the X rate of fomesafen.  In addition, plants showed injury at the 0.125 lb ai/A rate of fomesafen.  All treated plants died within a few days of application with no differences among the treatment except the untreated control.  Although, none of the samples we tested had PPO-resistance, we only sampled a small portion of cotton and soybean production areas.  In 2016, a more extensive seed collection survey will be conducted in cotton and soybean fields.  The ability of these resistance genes to travel in pollen has been documented in Palmer amaranth and explains why glyphosate resistance spread rapidly throughout the Southern United States (in a matter of a few years).  With PPO-resistance on the horizon in the Southeastern United States, effective soil applied programs will need to be developed which delay (where we do not have PPO resistance) and/or manage (where we do) PPO-resistant Palmer amaranth populations in cotton and soybean.


PRE- AND POSTEMERGENCE CONTROL OF GLYPHOSATE-RESISTANT AMARANTHUS SPP. WITH SINISTER. M. C. Cox*, K. Ward, J. R. Roberts; Helena Chemical Company, Memphis, TN (139)

ABSTRACT

Sinister™ is an herbicide developed with Helena Chemical Company’s free acid formulation technology and contains over 30% more fomesafen acid per liter than competitor fomesafen products.  Sinister™ also contains additional proprietary, compatibility and tank-stabilizing adjuvants lacking in other commercial sodium salt formulations.  Recent field studies evaluated pre- and postemergence control of various pigweed species (Amaranthus spp.) with Sinister™ and comparison sodium salt formulations of fomesafen.  From 2013-2015, field trials in Arkansas, Georgia, Minnesota, Mississippi, Missouri, North Carolina, South Carolina, and Tennessee demonstrated equivalent or better Palmer amaranth (Amaranthus palmeri), tall waterhemp (Amaranthus tuberculatus), or redroot pigweed (Amaranthus retroflexus) control with Sinister™ at 0.80-1.2 L haˉ¹ compared to other commercial sodium salt fomesafen formulations at 1.2-1.8 L haˉ¹, out to 28 DAA.  Sinister™ produced a lower contact angle and higher surface tension value than two commercial sodium salt formulations of fomesafen in laboratory evaluations, corroborating previous experimental results where Sinister™ appeared to be superior in wetting and spreading.  Sinister™ demonstrated better solution stability in -10C cold storage testing, decreased foaming, and prevention of crystallization and dissolution of spray mixture components, when compared to two sodium salt formulations of fomesafen and mixed with a glyphosate isopropylamine (IPA) salt.  Decreased weed control was recently reported at several locations with tank-mixes of a sodium salt fomesafen and glyphosate IPA salt, with the efficacy loss attributed to a compatibility problem linked to pH.  No occurrences of spray mixture incompatibility or reduced field performance with Sinister™ have been reported since product launch in 2014.


PALMER AMARANTH MANAGEMENT WITH LIBERTY® AND RESIDUAL HERBICIDE SYSTEMS. M. R. Zwonitzer*1, W. Keeling2, P. A. Dotray3, R. Perkins4; 1Texas A&M AgriLife Research, Lubbock, TX, 2Texas A&M, Lubbock, TX, 3Texas Tech University, Lubbock, TX, 4Bayer CropScience, Idalou, TX (140)

ABSTRACT

GlyTol® LibertyLink® is the first double-stacked herbicide tolerant technology providing tolerance to both Liberty® 280 SL (glufosinate) and glyphosate herbicides. This technology allows growers to make over-the-top applications with two modes of action to effectively control weeds and reduce the potential for resistance as part of a comprehensive, full-season herbicide program. Increasing populations of glyphosate-resistant Palmer amaranth require new postemergence weed management options. In the Texas High Plains, studies were conducted in 2015 at four sites to evaluate control of partially resistant Palmer amaranth populations in GlyTol® LibertyLink® cotton following single and sequential applications of Liberty® with and without Dual Magnum® or Roundup PowerMAX®. Applications were made at 15 GPA using Turbo TeeJet® 110015 nozzles at 38 PSI. Results showed that Liberty® effectively controlled Palmer amaranth where applied POST to 4-6” tall weeds and that effective season long control (95-100%) was observed when sequential POST applications of Liberty® + Dual Magnum® were applied. When Liberty® was applied tank-mixtured with glyphosate antagonism was observed. In 2015, weather conditions during the first half of the growing season (above average rainfall, higher humidity, and below average temperatures) influenced Liberty® activity in the Southern High Plains. 

 


SURVEY OF GLYPHOSATE-RESISTANT KOCHIA IN EASTERN OREGON SUGAR BEET FIELDS. P. Jha*1, J. Felix2, D. Morishita3; 1Montana State University-Bozeman, Huntley, MT, 2Oregon State University, Ontario, OR, 3University of Idaho, Kimberly, ID (141)

ABSTRACT

Glyphosate-resistant kochia (Kochia scoparia L. Schrad) was confirmed in sugar beet fields in Oregon and Idaho in 2014. A random field survey was conducted in eastern OR sugar beet fields, field edges/fence lines, ditch banks, and beet dump area during the summer of 2015. Live plant samples were collected and immediately placed in a – 80 C freezer until they were analyzed. The objective of this survey was to confirm and determine the level of evolved glyphosate resistance on the basis of relative EPSPS gene copy numbers in the selected kochia samples. The levels of glyphosate resistance in kochia positively correlated with the EPSPS gene copy numbers. The susceptible plants had a single EPSPS gene copy. The 10 kochia plant samples from the Payette beet dump area had relative EPSPS gene copies ranging from 1.5 to 2.6, which indicates “developing (very low levels) resistance” in the population. Out of the 10 samples collected from Ontario sugar beet fields, the EPSPS gene copy numbers ranged from 2.0 to 4.1, indicating “low levels of resistance” to glyphosate. The 10 additional populations collected from Ontario along Highway 201 had EPSPS gene copy numbers of 2.4 to 6.6, indicating “low to moderate levels of resistance”. None of the populations collected in the 2015 survey had >7 copies of the EPSPS gene (highly resistant). The GR kochia populations from sugar beet fields in eastern OR in 2014 had ~ 3 to 8 copies of the EPSPS gene. The 2015 survey results indicate that the development of GR kochia in eastern OR sugar beet fields can still be managed. It is advisable to use full use rates of glyphosate per application, with multiple applications (total in-crop of 3,954 g ha-1 glyphosate) to prevent further development of kochia populations with low levels of resistance (2 to 4 EPSPS copies) to glyphosate. A “zero seed tolerance” approach for glyphosate survivors needs to be implemented in sugar beet fields. Growers need to proactively manage the GR kochia seed bank with alternative, effective modes of action herbicides in crops grown in rotation with GR sugar beet, with the integration of tillage.


JUNGLERICE (ECHINOCHLOA COLONA) POPULATIONS DOSE-RESPONSE CURVES TO GLYPHOSATE HERBICIDE. G. Picapietra, H. A. Acciaresi*; Instituto Nacional Tecnologia Agropecuaria, Pergamino, Argentina (142)

ABSTRACT

Herbicide resistance has evolved so increasing worldwide. Although herbicides inhibitors of the enzyme acetolactate synthase (ALS) inhibitors of photosystem two (PS II) present the most prominent global cases (157 and 105 species, respectively), in Argentina ten of the sixteen total cases involve the herbicide glyphosate. One of the species concerned is Junglerice (Echinochloa colona), which was detected in the province of Santa Fe in 2009 and in the province of Tucuman in 2010. In order to evaluate the possible resistance of barnyard grass in the northwest of the province of Buenos Aires, seeds mature plants were harvested in different establishments in Rancagua (33 ° 59 'S, 60 ° 29' W), Tambo Nuevo (33 ° 57 'S, 60 ° 34' W), Pergamino (33 ° 56 ' S, 60 ° 34 'W) and Manuel Ocampo (33 ° 45' S, 60 ° 40 'W). Seeds were sown in Petri dishes, on solutions having different concentrations of glyphosate. The existence of one  resistant population to glyphosate was observed in each of the sites tested.


THE ROLE OF PPO CHEMISTRY IN A DICAMBA-RESISTANT WORLD. C. Smith*1, J. Pawlak2, M. Everett3, F. Carey4, M. Griffin1, R. Jones5; 1Valent USA, Cleveland, MS, 2Valent USA, Lansing, MI, 3Valent USA, Wynne, AR, 4Valent USA, Olive Branch, MS, 5Valent USA, Plano, TX (143)

ABSTRACT

The release of dicamba-resistant technology will alter future weed control methods in soybean. With the adoption of dicamba-resistant technology, more producers could continue to adopt and practice POST based weed control programs. The potential shift toward dicamba-centered, POST programs would be a similar trend that occurred with the development of glyphosate-resistant soybean.

Using multiple modes of action, including residual herbicide programs, are crucial to longevity of the dicamba-resistant technology. Trials were conducted across the US and Canada to determine the impact of PPO herbicides when utilized in dicamba based programs. Separate studies were developed for varying tillage regimes, with 16 conducted as no-till and six under conventional tillage. All herbicide programs utilized PRE treatment combinations of dicamba (560 g ae/ha), glyphosate (1260 g ae/ha), flumioxazin (89 g ai/ha) or flumioxazin plus pyroxasulfone (71.5 g ai/ha and 89 g ai/ha). The POST treatments were applied 28 days after planting and utilized combinations dicamba (560 g ae/ha), glyphosate (1260 g ae/ha), and lactofen (220 g ai/ha). Studies were evaluated at 42 and 56 DAP.

Evaluations of the no-till studies at 42 DAP found no differences among herbicide programs in controlling horseweed (Conyza canadensis), giant ragweed (Ambrosia artemisiifolia), giant foxtail (Setaria faberi), or common lambsquarters (Chenopodium album). However, control of ivyleaf morningglory (Ipomoea hederacea) and Palmer amaranth (Amaranthus palmeri) was greater when using a flumioxazin based PRE programs compared to programs without. In conventional tillage systems, the use of a flumioxazin based PRE also resulted in increased control of Palmer amaranth and common waterhemp (Amaranthus rudis) compared to those without flumioxazin. At 56 DAP, a comparison of programs utilizing PRE applications of dicamba and flumioxazin found that the addition of lactofen to a POST application of dicamba plus glyphosate resulted in greater control of Palmer amaranth, when compared to a POST application without.

 


ORGANIC WEED CONTROL PRODUCTS FOR VEGETABLE CROPS. J. O'Sullivan*1, R. C. Van Acker2, S. Harris2, P. H. White1, R. N. Riddle1; 1University of Guelph, Simcoe, ON, 2University of Guelph, Guelph, ON (144)

ABSTRACT

Conventional agricultural practices rely on highly effective synthetic herbicides for managing weeds. However, public acceptance of synthetic herbicides is increasingly negative and new regulations have contributed to a reduction in the number of new products commercialized by agrichemical manufacturers. While demand for organic foods has increased, weed control remains the most significant agronomic problem associated with organic crop production. Only a limited number of products are currently acceptable in organic agriculture and they have limited efficacy. This study focused on crop safety and the enhanced weed control efficacy of Manuka oil when applied in mixtures with other natural weed control products to control or effectively suppress weeds in organic crop production. Manuka oil was applied directed-postemergence alone or tank mixed with other products three weeks after planting tomato, sweet corn and pepper and again four weeks later. The best overall weed control was from a combination of Manuka oil plus Weed Zap and Manuka oil plus Vinegar. This control was significantly improved compared to each product used alone. These results were comparable to control with a combination of Callisto and Vinegar. Yields from combinations of Manuka oil plus Weed Zap and Manuka oil plus Vinegar were comparable to yields obtained with Callisto plus Vinegar and the hand weeded control. This research will satisfy weed control needs for organic crop production with effective and environmentally responsible natural biological weed control solutions that will improve productivity, increase yield potential and profitability.  Unlike currently approved products, Manuka oil displays systemic and soil activity and has pre-emergence activity on weeds. Innovative weed management solutions with natural source-products will provide alternatives to synthetic herbicides that will reduce risk to human health and the environment and will enhance sustainability of organic crop production. 

 


DURATION OF WEED-FREE PERIODS IN ORGANIC ROMAINE LETTUCE: AFFECT ON CROP YIELD AND QUALITY. S. Parry, R. Cox, L. Larocca de Souza, A. Shrestha*; California State University, Fresno, CA (145)

ABSTRACT

Field studies were conducted in fall 2014 and spring 2015 at Fresno, CA to determine the effect of the duration of weed-free periods on crop yield and quality of transplanted organic Romaine lettuce (Lactuca sativa L.). The crop was grown for 8 weeks with 8 different weed-free periods [0 (no weed control), 1, 2, 3, 4, 5, 6, weeks and weed-free entire 8 weeks]. Weeding was done manually with hand hoes and time taken to weed each plot was recorded. All standard organically-acceptable production practices were followed. Data were collected on total and marketable yield, hand weeding costs, weed density, weed biomass, crop quality rating at harvest, and anthocyanin and organic acids (chlorogenic acid, ferulic acid, and protocatechuic acid). Total stand counts, disease incidence, anthocyanin and organic acid composition of the leaves were not affected by the durations of weed-free period.  The critical weed-free duration for lettuce yield and quality was estimated as four weeks after transplant. Weed biomass data also showed that there was no benefit in controlling weeds beyond four weeks after lettuce transplant. The major weed species differed between the seasons. It can be concluded that a weed-free duration of four weeks after transplanting will be sufficient to produce organic Romaine lettuce without compromising yield or crop quality.


EVALUATION OF ORGANIC COVER CROP TERMINATION METHODS: FLAME OR FICTION? A. J. Price*1, J. S. McElroy2, L. M. Duzy1; 1USDA-ARS, Auburn, AL, 2Auburn University, Auburn, AL (146)

ABSTRACT

Use of winter cover crops is an integral component of organic vegetable systems. However, timely spring termination currently relies on tillage in most instances due to time constraints.  Thus, the use of conservation practices in organic systems is usually disjointed with some tillage required between crop transitions.  Field experiments were conducted from autumn of 2012 through cover crop termination in spring 2014 at the Alabama Agricultural Experiment Station’s E.V. Smith Research Center at Shorter, AL to evaluate organic cover crop termination practices compared to an effective conventional standard, all managed using conservation practices including a cover crop roller-crimper.  The experiment was a strip plot design with a factorial arrangement of cover crop, termination month, and termination method.  Cover crops included hairy vetch, crimson clover, cereal rye, Austrian winter pea, and rape, terminated in late February, March, and April. The termination treatments applied over the entire plot included:  1) 20% vinegar solution, 2) 45% clove oil /45% cinnamon oil solution, 3) 3 mil clear plastic sheeting, 4) broadcast flame utilizing a boxed directed propane flame apparatus, and 5) 1.12 kg ae/ha glyphosate.  Prior to termination application, the entire experimental area including non-treated was rolled with a cover crop roller-crimper.  Cover crop termination was then evaluated one, two, and three weeks after application.  In 2013, averaged over termination date, hairy vetch, Austrian winter pea, and cereal rye provided the highest biomass followed by clover and rape.  Three weeks after treatment, results show that utilizing broadcast flaming was >90% effective and similar to glyphosate, except for crimson clover in which no organic treatment provided greater than 76% control due to regrowth. Clear plastic mulch terminated hairy vetch and winter peas > 90%. Vinegar and oil treatments provided little additional termination.  In 2013 biomass was higher and three weeks after treatment, termination results show that all treatments were more effective than 2012 with similar trends. Thus, organic producers needing to terminate winter covers would most likely be successful using a broadcast flamer in most any winter cover or utilizing clear plastic in hairy vetch, winter peas, or cereal rye as ambient temperature increase along with solar radiation, both in combination with a roller/crimper.  Commercially available vinegar and clove/cinnamon oil solutions provided little predictable termination and producers are likely to resort to tillage if no other material or practice is readily available.

 

 


WEED CONTROL AND SNAP BEAN RESPONSE TO FOMESAFEN AND S-METOLACHLOR ON ORGANIC SOIL. D. C. Odero*1, A. L. Wright2, J. V. Fernandez1; 1University of Florida, Belle Glade, FL, 2University of Florida, Ft. Pierce, FL (147)

ABSTRACT

Field studies were conducted to evaluate the response of snap bean grown on organic soils of the Everglades Agricultural Area to preemergence and postemergence fomesafen applied alone or in combination with preemergence S-metolachlor or postemergence bentazon. Fomesafen (0.28 and 0.42 kg/ha) and S-metolachlor (1.42 kg/ha) were applied preemergence either alone or in combination. These preemergence herbicides were followed by postemergence application of bentazon (0.56 kg/ha) at the first trifoliate stage of snap bean. Similarly, fomesafen was applied postemergence alone at 0.28 and 0.42 kg/ha. Predominant weed species were common lambsquarters (Chenopodium album) and fall panicum (Panicum dichotomiflorum). Preemergence fomesafen and S-metolachlor did not result in snap bean injury at 14 and 28 days after treatment (DAT). Postemergence fomesafen resulted in <3% snap bean injury at 28 DAT. However, postemergence bentazon resulted in up to 14% snap bean injury at 28 DAT. Preemergence S-metolachlor alone or in combination with fomesafen provided >91% fall panicum control at 28 DAT compared to 26% control provided by fomesafen applied alone. In contrast, preemergence fomesafen provided up to 90% common lambsquarters control at 28 DAT compared to 39% control provided by S-metolachlor. Similarly, postemergence fomesafen provided <27% control of fall panicum compared to postemergence treatments that followed preemergence S-metolachlor (>93% fall panicum control). Postemergence fomesafen and bentazon provided up to 99% common lambsquarters control. Postemergence treatments that included bentazon had lower yields compared to other treatments. These results indicate that a tank-mix of preemergence fomesafen with S-metolachlor resulted in better weed control compared to either herbicide applied alone. Also, although postemergence bentazon resulted in better common lambsquarters control, injury from it resulted in reduction in snap bean yield. 


EFFECT OF OXYFLUORFEN POSTTRANSPLANT ON CABBAGE SAFETY AND COMMON LAMBSQUARTERS CONTROL. P. J. Dittmar*, C. E. Barrett, L. Zotarelli; University of Florida, Gainesville, FL (148)

ABSTRACT

Common lambsquarters is one of the most problematic weeds in Florida cabbage production. Currently registered postemergence herbicides do not provide control of common lambsquarters. The objective of this experiment was to establish crop tolerance and common lambsquarters control of oxyfluorfen applied posttransplant. Oxyfluorfen at 0.21 kg ha-1 was applied at pretransplant, <4 lf, 4 to 6 lf, and 6 to 10 lf growth stage, preplant f.b. 4 to 6 lf., and preplant f.b. 6 to 10 lf. Crop injury (0%=no injury, 100%= crop death) and weed control was evaluated at 7 to 10 day after treatment (DAT) interval. Cabbage injury by oxyfluorfen POST was chlorotic spotting and was <10%. Cabbage was harvested once and no delay in harvest was observed. No differences in individual head weight and total yield. Common lambsquarters control was 85 to 100% control and was greater than the nontreated. Oxyfluorfen at 0.21 kg ha-1 applied at the 4-6 lf stage would provide POST control of common lambsquarters and would not affect cabbage yield.

 


EFFECT OF PREEMERGENCE HERBICIDES FOR WEED CONTROL IN YAM (DIOSCOREA ALATA). R. Couto*1, M. Lugo Torres1, W. Robles2; 1University of Puerto Rico, Mayaguez, Mayaguez, PR, 2University of Puerto Rico, Mayaguez, Dorado, PR (149)

ABSTRACT

Yam (Dioscorea alata) is the most important root crop in Puerto Rico. Clomazone is the 
only pre-emergence herbicide available for this crop.  A field study was conducted at 
Gurabo, Puerto Rico to evaluate efficacy and phytotoxicity of several preemergence 
herbicides in yam. The preemergence herbicide treatments were clomazone at 0.62 and 
1.24 kg ai/ha; metolachlor at 1.6 and 3.2 kg ai/ha; fomesafen at 0.42 and 0.84 kg ai/ha; 
linuron at 1.12 and 2.24 kg ai/ha; sulfentrazone at 0.21 and 0.42 kg ai/ha; sulfentrazone + 
s-metolachlor at 1.83 and 3.66 kg ai/ha. Two control treatments were included; a hand-
weeded weed free control, and weeded control. Herbicides treatments were applied a day 
after planting with a portable CO2 -pressured backpack sprayer, delivering 187 L /ha 
spray volume.  A randomized complete block with four replications was used. Data of 
weed control and phytotoxicity was collected twice during the first two months after 
herbicide applications. Yield was recorded nine months after planting. At four weeks 
after application, linuron at 2.24kg ai/ha and sulfentrazone + metolachlor at 3.66 kg ai/ha 
controlled 100% of grasses and broadleaves, whereas clomazone at 2.54 kg ai/ha that 
controlled 43% of them. No significant differences were observed among treatments for 
yam yield, not for crop injury at 4 WAA and at 8 WAA. 

EVALUATION OF PREEMERGENCE AND EARLY POSTMERGENCE HERBICIDES ON SWEETPOTATO AND CASSAVA IN TROPICAL CONDITIONS. M. L. Lugo Torres*1, R. Couto1, W. Robles2; 1University of Puerto Rico, Gurabo, PR, 2University of Puerto Rico, Mayaguez, PR (150)

ABSTRACT

In Puerto Rico a combination of herbicides and hand weeding is the most common practice for weed control of root crops. Currently, herbicides registered for these crops are limited to clomazone and clethodim. Two field studies were conducted at Gurabo, Puerto Rico, to evaluate efficacy and phytotoxicity of several preemergence herbicides on sweet potato and cassava plantations.  The preemergence herbicide treatments were clomazone at 0.62 and 1.24 kg ai/ha; metolachlor at 1.6 and 3.2 kg ai/ha; fomesafen at 0.42 and 0.84 kg ai/ha; linuron at 1.12 and 2.24 kg ai/ha; sulfentrazone at 0.21 and 0.42 kg ai/ha; sulfentrazone + s-metolachlor at 1.83 and 3.66 kg ai/ha. As early post-emergent, metolachlor at 1.60 kg ai/ha followed the preemergence treatments: clomazone at 0.62 kg ai/ha; fomesafen at 0.42 kg ai/ha; linuron at 1.12 kg ai/ha and sulfentrazone at 0.21 kg ai/ha. Preemergence treatments were applied one day after planting using a portable CO2-pressurized backpack sprayer, delivering 187 L/ha spray volume.  A randomized complete block design with four replications was used. Weed control rating and crop injury were recorded three times during the first two months after planting.  Sweet potato and cassava yields were recorded five and 10 months after planting, respectively. Predominant weeds were junglerice (Echinochloa colona), purple nutsedge (Cyperus rotundus), and Asian spiderflower (Arivela viscosa). Sweet potato plants were susceptible to metolachlor+sulfentrazone at 3.66 kg ia/ha.  At 2 WAA and 4 WAA the majority of the treatments controlled more than 80% of weeds. When metolachlor was applied early postemergence, efficacy increased in the majority of treatments. Results indicated that no significant differences were found among herbicide treatments for sweet potato yield. Cassava plants were highly tolerant to the herbicide treatments evaluated in this study. Fomesafen and sulfentrazone and metolachlor + sulfentrazone at the highest rate was lightly toxic to the plants. Contrary to the observations for sweet potato, in the cassava study, linuron at both rates controlled grasses less than 50% at 4 WAA and 8 WAA. Higher yields of cassava were obtained using sulfentrazone followed by metolachlor compared to yields with clomazone at both rates. This treatment combination controlled between 94 and 100% of the weeds.

 


FIELD EVALUATION OF SULFENTRAZONE FOR SOUTHERN PEA WEED MANAGEMENT IN ARKANSAS. C. E. Rouse*, N. Burgos; University of Arkansas, Fayetteville, AR (151)

ABSTRACT

Southernpea’s represent a major alternative specialty crop for Arkansas producers. Unfortunately, due to a lack of production acreage nationwide, research on potential new herbicides and herbicide-based weed control programs for southernpea production is limited. Sulfentrazone, is a new herbicide for southernpea, registered as a premix with carfentrazone. Further evaluation is needed to determine the efficacy of, and southernpea tolerance to, this compound. A study was conducted in 2014 and 2015 at the Arkansas Agriculture Research and Extension Center (AAREC), Fayetteville, AR and the Vegetable Research Station (VRS), Kibler, AR, to evaluate the utility of sulfentrazone in southernpea production systems. Sulfentrazone (0.21 kg ha-1) was evaluated alone and as the premix of sulfentrazone (0.14 kg ha-1) + carfentrazone (0.02 kg ha-1). The sulfentrazone products were included in the program as either preplant (PPL) or PRE applications with the currently registered herbicides: S-metolachlor (1.12 kg ha-1), imazethapyr (0.07 kg ha-1), imazamox (0.04 kg ha-1), and sethoxydim (0.32 kg ha-1). Some programs included fluthiacet-methyl (0.0067 kg ha-1), another potential herbicide for southernpea. Commercial standards- trifluralin (0.84 kg ha-1, PPI) fb imazethapyr (POST) and S-metolachlor + imazethapyr (PRE) fb bentazon/ imazamox + sethoxydim (POST), as well as nontreated weedy and a weed-free checks were included for comparison. Herbicides were applied PPL-1 week before planting, preplant incorporated (PPI), preemergence (PRE), or postemergence (3 to 4 trifoliate). Data collected included crop stand (2 WAP), weed density (3 WAP), crop injury (%), total weed control (%), and yield. Data were analyzed as a RCBD using an ANOVA. For both crop injury and weed control, years were analyzed separately; for injury-related data, locations were analyzed together; and for weed control, locations were analyzed separately. None of the herbicides reduced crop stand in either year compared to the nontreated plots. By 6 WAP, minimal crop injury (13% or less) was observed only in 2015, with the application of S-metolachlor + fluthiacet-methyl (POST) causing visual burning.  Yield was not affected by any treatment in either year. For both years and locations weed control 6 WAP was relatively high (>80%) for the sulfentrazone-containing treatments, which was consistently greater than the commercial standard of trifluralin fb imazethapyr. All of the programs containing sulfentrazone or the premix of sulfentrazone + carfentrazone provided excellent season-long control with no adverse effects on crop health.

 


SEED PRODUCTION AND INTERFERENCE FROM LATE-SEASON TALL MORNINGGLORY IN CHILE PEPPER. B. J. Schutte*; New Mexico State University, Las Cruces, NM (152)

ABSTRACT

Tall morningglory (Ipomoea purpurea L.) is an annual weed in chile pepper that emerges near the time of crop thinning (9 to 10 weeks after seeding).  Previous studies have shown that tall morningglory is not controlled by pendimethalin, which is a soil-applied herbicide often used for postemergence directed applications in chile pepper.  The objective of this study was to determine pendimethalin effects on interference and seed production for tall morningglory plants that emerge at chile pepper thinning.  A field study was conducted during the summers of 2014 and 2015 near Las Cruces, NM.  Prior to the start of each annual run, a field was subjected to a sequence of preparatory procedures that included: tilling, laser leveling, listing and shaping raised beds into rows spaced 1 m apart.  Chile pepper was seeded into raised beds on May 2, 2014 and April 23, 2015.  At 9.5 weeks after seeding, the crop was thinned and treatments were installed.  Study treatments were factorial combinations of herbicide (pendimethalin-treated [1.6 kg ai ha-1] and untreated) and tall morningglory density (0, 4, 8, 12, 16, 20 plants 10-m row-1).  Treatments were arranged in a randomized complete block design with four replications.  Experimental units were four raised beds by 10 m and are hereafter referred to as “plots”.  Throughout the study period, weeds other than tall morningglory were controlled.  Data collected at harvest included: tall morningglory seed production, fresh weight of marketable chile peppers and time required for one individual to harvest 10-m of crop row, which was used to calculate the amount of chile pepper harvested in 1 min (i.e., “harvest efficiency”).  Results indicated that crop yield was not influenced by tall morningglory density or interactions between tall morningglory density and herbicide treatment.  However, crop yield was influenced by herbicide treatment as pendimethalin-treated plots had greater yields than untreated plots.  Harvest efficiency was influenced by tall morningglory density, but, this response variable was not influenced by either herbicide treatment or interactions between herbicide treatment and tall morningglory density.  In general, each additional tall morningglory plant decreased the amount of chile pepper harvested in 1 min by 9.7 g.  Seed production by individual tall morningglory plants was negatively affected by plant density.  At high densities (16, 20 plants 10-m row-1), seed production by individual plants was negatively affected by pendimethalin.  These results indicate that, although tall morningglory is not controlled by pendimethalin, this herbicide influences the short-term and long-term impacts of tall morningglory plants that emerge at chile pepper thinning, with the exception of tall morningglory effects on harvest efficiency.


CHARACTERIZING GLYPHOSATE RESISTANT HORSEWEED (CONYZA CANADENSIS) POPULATIONS FROM OHIO VINEYARDS. M. Mohseni-Moghadam*1, D. Doohan2, L. Fleuridor2; 1Ohio State University, Wooster, OH, 2The Ohio State University, Wooster, OH (153)

ABSTRACT


COMPARING EFFICACY AND CROP SAFETY OF BICYCLOPYRONE AND TOLPYRALATE IN VEGETABLE CROPS. E. Peachey*; Oregon State University, Corvallis, OR (154)

ABSTRACT

Bicyclopyrone and tolpyralate are relatively new HPPD herbicides with selectivity in corn. The objective of this study was determine whether these herbicides also might have utility in vegetable production. Herbicides were applied both PRE and POST to 30 vegetable crops that were direct-seeded into a loam soil. Bicyclopyrone was evaluated for yellow nutsedge control in a greenhouse study. Cilantro, zucchini, and cucumber were tolerant to PRE applications of bicyclopyrone. Cilantro and onions were tolerant to POST applications of bicyclopyrone. Crops tolerant to tolpyralate applied PRE included several brassica crops, cilantro, parsley, carrot, zucchini, and cucumber. Onions were tolerant to tolpyralate applied both PRE and POST. Weed control was good to exceptional with both PRE and POST applications of bicyclopyrone and tolpyralate. 

 


BICYCLOPYRONE PERFORMANCE IN MINOR/ SPECIALTY CROPS; SCREENING CANDIDATES AT THE VERO BEACH RESEARCH STATION. J. Long*1, C. L. Dunne1, G. D. Vail2; 1Syngenta Crop Protection, Vero Beach, FL, 2Syngenta Crop Protection, Greensboro, NC (155)

ABSTRACT

Bicyclopyrone is a newly registered HPPD-inhibiting active ingredient for control of broadleaves and some grasses. Bicyclopyrone is one of the four active ingredients in Acuron herbicide which was registered for sales in corn in 2015.  Syngenta is evaluating the potential for expanding Bicyclopyrone use into minor/specialty crops where options for weed control are limited.  More than 40 crops have been screened in the greenhouse and/or field for pre-emergence and post emergence tolerance to Bicyclopyrone.  The objective of this poster is to discuss the challenges involved with the selection of candidates for evaluation.


THE EVOLUTION OF WEED POPULATIONS IN GOLF TURF OF SOUTHERN CHINA. G. Xue*, D. Rong, M. Jianxia, L. Chunyan; East China Weed Technology Institute, Nanjing, Jiangsu, Peoples Republic (156)

ABSTRACT

The Evolution of Weed Population in Golf of Southern China

Xue Guang, Du Jinrong and Li Chunyan

East China Weed Technology Institute, Nanjing, jiangsu ,210007,China

Abstract : Based on the investigation of weeds in bermudagrass, seashore paspalum and Zoysia of 46 Golf courses during 1998-2000 and 2013-2015 respectively in southern China. More than 159 weeds were determined which includes 39 grasses species 15 sedge species and 105 broad-leaved species. The weed community was set up with 20 kinds of most trouble weed species including 5 kinds of grasses, 2 kinds of sedges and 13 kinds of broad-leaved weeds in 2000 as followings: Digitaria sanguinalis, Panicum repens, Paspalum conjugatum, Axonpus compressus, Poa annua, Cyperus rotundus, Kyllinga brevifolia, Hydrocotyle sibthorpioides, Oxalis corniculata, Kummerwia striata, Alternanthera philoxeroides, Desmodium triflorum, Mimosa pudica, Centella asiatica, Securinega suffiruticosa, Viola japonica, Hedyotis corymbosa,Euphorbia hirta, Lobelia chinensis and Alysicarpus vaginalis.In the second investigation, weed community was set up by other 20 kinds of trouble weed species including 10 kinds of grass, 2 kinds of sedge and 8 kinds of broad-leaved weed which were Alysicarpus vaginalis, Digitaria ischaemum, Digitaria sanguinalis, Poa annua, Panicum repens, Dactyloctenium aegyptium, Axonpus compressus, Cynodon dactylon, Paspalum distichum, Eragrostis pilosa, Kyllinga brevifolia, Cyperus rotundus, Euphorbia humifusa, Hedyotis corymbosa, Desmodium triflorum, Hydrocotyle sibthorpioides, Centella asiatica, Alysicarpus vaginalis Kummerwia striata, Trifolium repens and Lindernia crustacean. The investigation of trouble weeds showed that grassy weeds were increased from 5 to 10 kinds and broad-leaved weeds were decreased from 13 to 8 kinds in 2015 compared with the trouble weed in 2000. There were Alysicarpus vaginalis,Digitaria ischaemum, Digitaria sanguinalis, Panicum repens and Axonpus compressus in most of golf turf of Hainan and Guangdong province. Cynodon dactylon was expanding in seashore paspalum turf of Sanya, Hainan province. Poa annua and Digitaria sanguinalis was getting serious in almost each golf turf in southern China. Kyllinga brevifolia, Euphorbia humifusa and Desmodium triflorum was also expanding in most golf turf of Hainan island. 

The paper introduced some of typical weed community with picture in the seashore paspalum and bermudagrass in the golf of Southern China. Author also analyzed the possible factors to influence the evolution of weed population changing. It was maybe due to competition, climate changing, removing weed by hand, improper maintain and improper herbicide application.


COMPARING COST AND WEED BIOMASS OF TWO WEEDING STRATEGIES IN CONTAINER NURSERIES. C. D. Harlow*, B. P. LeBlanc, J. C. Neal; North Carolina State University, Raleigh, NC (157)

ABSTRACT

Container nurseries rely primarily on two methods of weed control – multiple applications of residual, preemergence herbicides and hand-weeding. As production costs increase, growers are continually looking for ways to reduce expenses, and prior research has demonstrated that hand-weeding every 2 weeks may reduce overall weed biomass and time spent compared to the more typical 6- to 8-week intervals. Four experiments were conducted, one at a research station and three at cooperating container nurseries. Methods were similar at each site. At the research station each experimental unit contained approximately 150 4-L pots consisting of three species of ornamental plants. Experimental unit size at the nursery sites ranged from approximately 650 pots to 1200 pots, and pot sizes ranged from 4-L to 12-L. Species composition varied at each nursery. Experimental treatments were two different hand-weeding intervals – removing weeds more frequently (typically every 2 weeks) or removing weeds less frequently and only immediately prior to a residual herbicide application (typically every 8 weeks). Plants were potted in the spring or early summer, and Snapshot TG at 150 lb/A was applied to all plots immediately after potting for each experiment. Snapshot was applied subsequently to all plots immediately following the 8-week weeding. At each 2-week weeding, weeding crews removed only those weeds which had grown large enough to be removed easily or appeared to have the potential to flower. At 8-week weedings, all weeds were removed. For pots that had very small weeds hard to pull, the substrate surface was “raked” by hand to dislodge those small seedlings. Time required for hand-weeding and fresh weights of the weeds removed were recorded. Some differences between sites were observed. Possible explanations for the differences include weed pressure both within and around the plots; weeding crews and their hand-weeding methods; crop species, sizes and canopies; and weed species composition. Overall, trends in results were similar: hand-weeding more frequently reduced weeding time, weed biomass and projected expense. At the research station, cumulative weed weights over a 25 week span (2, 8-week cycles and 1, 9-week cycle) were 4.75 Kg for plots weeded every 8 weeks compared to 0.36 Kg for plots weeded every 2 weeks. Weeding time was reduced from 1.61 man-hours in 8-week plots to 0.65 man-hours in 2-week plots, a potential savings of 60%. At Johnson Nursery, cumulative weed weights over a 22 week span (2, 8-week cycles and 1, 6-week cycle) were 66.7 Kg for plots weeded every 8 weeks compared to 10.4 Kg for plots weeded every 2 weeks. Weeding time was reduced from 7.53 man-hours in 8-week plots to 3.04 man-hours in 2 week plots, a potential savings of 60%. Results were less dramatic at the other two sites, with weed biomasses reduced from 8.5 Kg to 2.4 Kg and 4.6 Kg to 1.8 Kg and weeding time reductions of approximately 10% at each nursery. While these studies support more frequent hand-weeding of container nursery stock, further investigation is needed to refine recommendations to take into account developmental stages of the weeds, seasonal and temperature differences, weed species composition, crop species and size, and other factors that may influence weeding strategies.


USING FE HEDTA TO REDUCE HANDWEEDING IN NURSERY PRODUCTION. C. Wilen*1, G. Johnson2; 1Univ. of California, San Diego, CA, 2UCCE, Irvine, CA (158)

ABSTRACT

Nursery growers often 1. Apply the preemergent herbicide before weeds start to emerge based on “best-guess” or other experience which would reduce the cost of hand-removal but may increase the overall amount of herbicide actually needed over the course of the production cycle or 2. Wait until the weeds start to emerge, hand weed as best as one can, and then apply the next preemergent herbicide treatment.  Small, newly germinated ones are not remove and these will not be controlled by the preemergent herbicide, increasing production costs for subsequent hand weeding even though another application was made.

In preliminary screens, the contact herbicide with the active ingredient Fe HEDTA (Fiesta) registered as a biopesticide was applied over the top (OTT) to plants in nursery containers Fe HEDTA provided excellent control of all weeds except prostrate spurge and common purslane and little to no crop injury. We then conducted more trials to determine if Fe HEDTA can be used to control newly emerged weed seedlings prior to or in concert with, a preemergent herbicide thereby improving long-term broadleaf weed control.  While this product is not expected to be a stand-alone herbicide, it may fill a much needed niche to control broadleaf weeds between preemergent herbicide applications, improve the reliability of conventional herbicide programs, and reduce the amount of hand weeding.

Fe HEDTA tended to have similar weed control as handweeding, especially when combined with Dimension 2EW, for management of common groundsel and northern willowherb, it was not an effective treatment for ground spurge.  In all other cases, a single application of Fe HEDTA +a preemergent herbicide was generally as good as the handweeded equivalent .  Barring any incompatibility issues, these results can be immediately transferrable to that of other commonly used preemergent nursery herbicides.

 

 

 


PRELIMINARY STUDIES ON THE GERMINATION, EARLY GROWTH AND FLOWERING OF CHAMAESYCE MACULATA IN CONTAINERS. J. C. Neal*, B. LeBlanc, C. D. Harlow; North Carolina State University, Raleigh, NC (159)

ABSTRACT

Weed management in container nurseries is heavily reliant on multiple applications of residual herbicides and frequent hand weeding.  Our recent research has demonstrated that hand weeding every 2 weeks reduced overall weed biomass compared to typical 6- to 8-week hand weeding intervals.  However, contrary to initial assumptions, weed populations continued to increase over time in pots weeded every 2-weeks. Thus, in late-May 2015, we started a preliminary study to investigate the growth and development of weeds in nursery pots.  Pots were filled with a hammer-milled pine bark substrate then hand watered to settle the substrate.  Thereafter pots received about 1.5 cm overhead irrigation daily. Half of the pots were placed in full sun, the other half under 50% shade.  Each pot was surface-seeded with about 30 seeds of Chamesyce maculata (spotted spurge).  Days from seeding to weed germination, first true leaf, branching, flowering, and seed pod formation were recorded.  Seedling emergence increased in a linear fashion between 3 and 9 days after seeding in both shade and sun.  Plants branched 16 to 18 days after seeding.  After branching, plants in both sun and shade experienced exponential growth rates. Flowers were produced within 21 days of seeding, with a very rapid increase in flower production between 21 and 25 days. Plants grown in the sun produced over 300 flowers per plant in less than 30 days after seeding. Shade-grown plants produced fewer than 50 flowers per plant during the same time period.  Seed pods were formed within 7 days after first flowering.  These data suggest that hand weeding every 30 days would be adequate to remove spurge plants before they produce mature seeds.  However, any plants missed in this hand weeding cycle could shed seeds before the next weeding event.


INVESTIGATING AVENUE SOUTH FOR TURF WEED MANAGEMENT. J. R. Brewer*1, A. Estes2, J. Marvin2, S. Askew1; 1Virginia Tech, Blacksburg, VA, 2PBI Gordon, Pendleton, SC (160)

ABSTRACT

Investigating Avenue South for Turf Weed Management

J. R. Brewer, A. Estes, J. Marvin, and S. D. Askew

The turf industry has many potent herbicides for control of broadleaf weeds in both cool and warm-season turf species. These herbicides can be highly injurious to unlabeled turfgrass and even injurious to labeled species. Avenue South is a new product being released by PBI Gordon. It is reported to have superior turf safety while still controlling common broadleaf weeds. At Virginia Tech, multiple trials and demos were conducted in summer 2015 to evaluate Avenue South on weed control and turf safety compared to other industry standards which included MSM Turf, Celsius, Speedzone, and Millennium Ultra. Two trials were initiated on April 8, 2015 and April 13, 2015 on bermudagrass and zoysiagrass. These trials compared Avenue South at 63.7 fl oz/A to Celsius at 3.68 oz wt/A and MSM Turf at 0.33 oz wt/A.  Five other demonstrations were initiated on July 29, 2015 on creeping bentgrass, tall fescue, bermudagrass, tall fescue/Kentucky bluegrass mix, and perennial ryegrass. These demonstrations compared Avenue South to Celsius, MSM Turf, Millennium Ultra at 2.5 pt/A, and Speedzone at 4 pt/A.

Avenue South controlled common chickweed and white clover equivalent to MSM Turf and Celsius (greater than 95%), but was slightly less effective at controlling dandelion. None of the evaluated herbicides injured bermudagrass, but MSM Turf and Celsius injured zoysiagrass 63 and 35%, respectively compared to no injury by Avenue South.  In demonstrations, Avenue South appeared to control ground ivy and white clover equivalent to MSM Turf, Celsius, Speedzone, and Millennium Ultra.  Avenue South also appeared to injure creeping bentgrass putting greens less than other herbicides.  Avenue South appeared to injure perennial ryegrass more than Speedzone and Millennium Ultra but less than MSM Turf and Celsius.

 


COOPERATIVE EFFORTS TO SOLVE TROPICAL SIGNALGRASS CONTROL PROBLEMS IN TURFGRASS. M. Lenhardt*1, S. Wells2, B. Spesard3, R. G. Leon4; 1University of Florida, Cocoa, FL, 2Bayer CropScience, High Springs, FL, 3Bayer CropScience, Research Triangle Park, NC, 4University of Florida, Jay, FL (161)

ABSTRACT

Cooperative Efforts to Solve Tropical Signalgrass Control Problems in Turfgrass. M.A. Lenhardt*1, S. Wells2, B. Spesard3, and R.G. Leon4. 1University of Florida, Cocoa, FL, 2Bayer CropScience, High Springs, FL, 3Bayer CropScience, Research Triangle Park, NC, 4University of Florida, Jay, FL.

 

The banning of MSMA use in urban areas has resulted in a dramatic increase in tropical signalgrass problems in golf courses and turf areas in Florida. Educating industry professionals about recommended turf management strategies is an important component to the overall economic viability of the turf grass industry in Florida.  However, golf course superintendents and sports turf managers are challenging audiences to attract to Extension programs.  Many in this clientele rely on education from golf industry shows, trade journals, or hands-on experience. To reach this clientele, the Brevard County Commercial Horticulture agent partnered with stakeholders and Extension specialists to develop an innovative program called the Space Coast Golf and Turf Association (SCGTA).  A strategy integrating the development of alternative herbicide programs by industry researchers for tropical signalgrass control with the SCGTA trainings by university Extension specialists was implemented to increase stakeholder adoption of new and alternative control programs. Experiments were conducted in golf courses and sod farms to evaluate the use of post-emergent herbicides at different applications timings. The golf courses and sod farms hosting the experiments also provided infrastructure to conduct workshops with participants from several counties.  Two workshops were conducted approximately 5 months apart. The first workshop included talks about tropical signalgrass biology and control alternatives that participants could try on their own golf courses and sports turf.  The second workshop was a field day to see the results of the experiments and to exchange opinions about the participants’ experience with their own control strategies during the previous 5 months. Spot treating with three sequential applications (2 wk. apart) of Tribute Total (99.2 g ai ha-1) plus ammonium sulfate (1.7 kg ha-1) plus methylated seed oil 0.5% v/v -1 during the fall provided >92% and >94% tropical signalgrass control at 4 and 8 months after the initial application (MAIT), respectively. Four sequential applications ensured >90% control 12 MAIT. Witnessing the development of the experiments increased the willingness of the participants to try the herbicide programs, and also helped researchers to receive direct feedback of situations in which the herbicide programs required modifications to meet specific environmental, budget, and turf management situations.


ST. AUGUSTINEGRASS (STENOTAPHRUM SECUNDATUM) GERMPLASM COLLECTION: BREEDING FOR GLYPHOSATE TOLERANCE AND POPULATION STRUCTURE. A. N. Chan1, T. Tseng*2, H. W. Philley1, C. M. Baldwin1, J. McCurdy2; 1Mississippi State University, Mississippi State, MS, 2Mississippi State University, Starkville, MS (162)

ABSTRACT


WHITE CLOVER RECOVERY FOLLOWING BROADLEAF HERBICIDES IN PASTURES. R. E. Strahan*1, S. Gauthier2, E. K. Twidwell1; 1LSU AgCenter, Baton Rouge, LA, 2LSU AgCenter, Breaux Bridge, LA (163)

ABSTRACT

White clover recovery following broadleaf herbicides in pastures

R. E. Strahan, S. Gauthier, E. K. Twidwell, LSU AgCenter, Baton Rouge, LA, 70803.

ABSTRACT

White clover (Trifolium repens L.) is a cool season perennial legume of European origin.  It is highly palatable, nutritious forage for all classes of livestock.  Because of the high quality of white clover, it is well suited for use as complimentary forage in southeastern United States.  However, white clover is highly sensitive to most broadleaf weed herbicides used in pastures.  Selectively removing troublesome broadleaf weeds without reducing white clover stands is very difficult.  The following research evaluates the long-term effect of several common pasture broadleaf herbicides on Durana white clover stands. 

A field study was conducted in 2015 in Vermillion Parish, near the town of Abbeville, LA in in a producer’s Alicia bermudagrass pasture with a heavy well established population of Durana white clover (Trifolium repens).  Our objective was to evaluate long-term Durana white clover recovery following several herbicides known to be highly injurious to pasture legumes.  The study was initiated June 18, 2015.  White clover populations were heavy and in full bloom at the time of the applications.   

Herbicides evaluated in single application included 2,4-D amine at 1 qt/A, Grazon Next HL (aminopyralid + 2,4-D) at 0.75 qt/A, Grazon P+D (picloram + 2,4-D) at 1 qt/A, Remedy (triclopyr) at 1 qt/A, Chaparral (aminopyralid + metsulfuron) at 2.5 oz/A, Pasturegard (fluroxypyr + triclopyr) at 1 qt/A, Surmount (fluroxypyr + picloram) at 1 qt/A, and Cimarron Max (metsulfuron + 2,4-D + dicamba) 0.5 oz/A + 1 qt/A, respectively.  There were 10 total treatments including an unsprayed check.

Herbicides were applied with a CO2 pressurized backpack sprayer equipped with 11003 XR flat fan nozzles that delivered 15 GPA at 25 psi.  Plot size was 8 ft x 30 ft.  The experiment was conducted as a randomized complete block with 3 replications.  Data were subjected to analysis of variance (P=0.05) and means were separated using Fisher’s LSD. 

Initial white clover injury was determined 30 DAT.  All herbicides evaluated caused at least a 90% initial Durana white clover stand reduction with the exception of 2,4-D (45%).  By approximately 200 DAT, all herbicides containing the active ingredient aminopyralid (Grazon Next and Chaparral) reduced clover stands by 95%.  Herbicides with picloram as a component such as Grazon P+D and Surmount reduced clover stands 90 and 95%, respectively.  Herbicides that contain triclopyr (Remedy and Pasturegard) reduced white clover stands 87 and 95%.  Weedmaster, and Cimarron Max reduced clover stands 57 and 85%.  2,4-D was the least injurious herbicide on Durana white clover when evaluated at 200 DAT (40% stand reduction).  Data collection will continue at the location for at least 1 year to determine the long-term effect of these herbicides on Durana white clover stands.


EVALUATION OF SAFLUFENACIL FOR BUTTERCUP CONTROL AND WHITE CLOVER TOLERANCE IN PASTURES. R. E. Strahan*1, S. Gauthier2, E. K. Twidwell1; 1LSU AgCenter, Baton Rouge, LA, 2LSU AgCenter, Breaux Bridge, LA (164)

ABSTRACT

Evaluation of saflufenacil for buttercup control and white clover tolerance in pastures

R. E. Strahan, S. Gauthier, E. K. Twidwell, LSU AgCenter, Baton Rouge, LA, 70803.

ABSTRACT

White clover (Trifolium repens L.) is a cool season perennial legume of European origin.  It is highly palatable, nutritious forage for all classes of livestock.  Because of the high quality of white clover, it is well suited for use as complimentary forage in southeastern United States.  However, white clover is highly sensitive to most broadleaf weed herbicides used in pastures.  Selectively removing troublesome broadleaf weeds such as buttercup (Ranunculus spp.) without reducing white clover stands is very difficult.

Saflufenacil (Sharpen) is pyrimidinedione herbicide that inhibits protoporphyrinogen oxidase (PPO) that disrupts cell membranes.  The herbicide is used as burndown for broadleaf weeds applied preplant and/or preemergence in a wide range of crops.  Additionally, Sharpen is labeled for broadleaf weed control in perennial forage grasses grown in pastures, or in fields grown for forage, silage, and hay production.  The following research evaluates buttercup control and Durana white clover tolerance to Sharpen in a southern Louisiana pasture. 

A field study was conducted in 2015 in Vermillion Parish, near the town of Abbeville, LA in in a bermudagrass pasture well-established stand of over-seeded with Gulf ryegrass and an established population of Durana white clover (Trifolium repens).  Our objective was to evaluate Durana white clover injury and recovery and buttercup control following Sharpen herbicide applications.  The study was initiated February 15, 2015.  White clover populations were heavy with some blooms at the time of treatment.  

Sharpen was evaluated in a single application alone at 1 or 2 oz/A, and in tank-mixes including Sharpen + 2,4-D amine at 1 pt/A, Sharpen + glyphosate at 1 pt/A, or Sharpen + Pastora (metsulfuron + nicosulfuron) at 1 oz/A.  Sharpen was applied at 1 oz/A in the tank-mixtures.   Additional treatments included the standard treatment, 2,4-D at 1 pt/A and an unsprayed check.  There were 7 total treatments including an unsprayed check. 

Herbicides were applied with a CO2 pressurized backpack sprayer equipped with 11003 XR flat fan nozzles that delivered 15 GPA at 25 psi.  Plot size was 8 ft x 30 ft.  The experiment was conducted as a randomized complete block with 4 replications.  Buttercup control and white clover injury and recovery were determined weekly with subjective visual ratings of percent control or injury where 0= no control or injury and 100= complete control or clover destruction.  Data were subjected to analysis of variance (P=0.05) and means were separated using Fisher’s LSD. 

Buttercup control with Sharpen at 1 or 2 oz/A, Sharpen + 2,4-D, and Sharpen + glyphosate were similar (73 – 83% control) 1 WAT (week after treatment).  Buttercup control with 2,4-D alone was approximately 50%.  Clover injury was at least 60% with Sharpen applied alone or tank-mixed.  By 2 WAT, Sharpen applied at 1 or 2 oz/A or with tank-mix partners provided > 85% buttercup control.  Sharpen applied alone at either rate injured white clover at least 65%.  Tank-mixes of Sharpen + glyphosate or Pastora caused 90% clover injury. 

Buttercup and white clover stands were completely destroyed by Sharpen + Pastora by 4 WAT.  Sharpen provided good buttercup control at the 1 and 2 oz/A rate (87 and 92%) but still injured clover at least 30% at the 4 WAT period.   2,4-D provided 93% buttercup control and the least amount of clover injury (10%).  For the duration of the study, there was no advantage to tank-mixing Sharpen with 2,4-D or glyphosate for buttercup control when compared to buttercup control with 2,4-D alone. 

In conclusion, Sharpen was very effective in controlling buttercup but still caused unacceptable white clover injury 28 DAT.  However, clover recovery was inevitable in the test plots where Sharpen alone was applied.  No clover recovery was observed with plots treated with Sharpen + Pastora.  2,4-D provided excellent buttercup control and white clover recovered to acceptable levels within 4 WAT. 


EVALUATION OF COVER CROP COMBINATIONS AND IMAZAPYR APPLICATIONS ON COGONGRASS CONTROL. M. M. Zaccaro*, J. D. Byrd, Jr.; Mississippi State University, Mississippi State, MS (165)

ABSTRACT

Successful cogongrass (Imperata cylindrica (L.) Beauv.) management is an important issue as herbicides provide limited efficacy for an extended period of time. The objective of this experiment was to evaluate the effect of cover cropping system with different herbicide application timings on cogongrass control. The field study started in November 2013, when cogongrass was mowed, aboveground biomass removed from the research plots, and ALS-resistant Italian ryegrass (Lolium perenne ssp. multiflorum (Lam.) Husnot) broadcast seeded at the rate of 33.8 kg ha-1. Imazapyr applications of Polaris 4AC at 0.8 kg ae ha-1 were made at the time of planting (PRE), or May (EPOST) or June (LPOST) of 2014. One month after each herbicide application, white clover ‘Durana’ (Trifolium repens L.) was also broadcast planted at rate of 3.4 kg ha-1. Visual percent control of cogongrass was estimated periodically after the first herbicide application, and biomass samples collected in October 2014. The experiment was replicated in the following season, however, the entire experimental area was tilled prior to ryegrass seeding. The experiment design each season was a 2 x 2 x 3 factorial arrangement of treatments in a randomized complete block design with four replications. The factors were presence or absence of ryegrass cover, presence or absence of white clover cover, and timing of herbicide applications. Data were analyzed with PROC GLIMMIX in SAS 9.4 with α value of 0.05. Data for the two seasons were not combined for analysis. In both seasons, there was no interaction between factors and herbicide timing was the independent factor that affected mean visual cogongrass control, regardless of cover crop use. In the 2013-2014 season, herbicide application in May provided the highest visual percent control (90%), and was significantly better than application in June and November, which was the least effective treatment. Furthermore, the imazapyr application made in May reduced mean cogongrass biomass weight by 92% when compared to the Polaris applied the previous November (2013). Polaris applied in June reduced cogongrass biomass weight by 36% compared to the November treatment. In the 2014-2015 season, herbicide application made in June provided higher visual control (80%) compared to the application made the previous November. The visual control achieved with the application made in May was not significantly different from the other treatments. A similar trend was observed with the cogongrass biomass data. Polaris applied in June reduced mean cogongrass biomass weight by 70% in comparison to Polaris applied in November of the previous year. After two seasons of this research, we concluded that cogongrass elimination would not be achieved by the utilization of this system for a single year only. More research is needed to refine cover crops seeding rates in order to improve development. Imazapyr applications made in May or June would be recommended to provide 80% or higher cogongrass control in October the following year.


TOLERANCE OF ARACHIS PINTOI TO PRE AND POST EMERGENCE HERBICIDES. L. J. Martin*1, B. A. Sellers1, J. A. Ferrell2, J. M. Vendramini2, R. Leon3, J. C. Dias1; 1University of Florida, Ona, FL, 2University of Florida, Gainesville, FL, 3University of Florida, Jay, FL (166)

ABSTRACT

Arachis pintoi is a tropical and subtropical seeded perennial forage peanut. Similar to Arachis glabrata, A. pintoi is a prostrate growing legume commonly used as a supplemental forage crop. Herbicides commonly used for weed control in A. glabrata and other forages may inflict undesirable injury to A. pintoi. Separate experiments were conducted to evaluate pre and post emergence herbicide tolerance by visual estimations of crop injury. Pre-emergence treatments consisted of pendimethalin (Prowl H2O), imazethapyr (Pursuit), imazapic (Impose), and 2,4-D (2,4-D Amine). Post-emergence treatments consisted of imazethapyr, 2,4-D, imazapic, sulfosulfuron (Outrider), and carfentrazone (Aim) applied at emergence and 2 weeks after emergence. Pre-emergence herbicides were applied at .5-x, 1-x, and 2-x; and post-emergence herbicides were applied at .5-x, and 1-x labeled rates. Both experiments were conducted using a randomized complete block design with 4 replications. Overall, low levels of injury were recorded in the pre-emergence study 30 days after treatment with the greatest level of injury resulting from applications of imazapic (28%). In the post-emergence study, imazethapyr resulted in little or no injury when applied at emergence or 2 weeks after emergence. In contrast, herbicides applied at emergence resulted in moderate to severe injury (28-97%). However, 2,4-D and carfentrazone applied 2 weeks after emergence resulted in the most injury (40%) 14 days and (26%) 30 days after treatment compared to all other treatments. Therefore, A. pintoi injury from herbicide applications may be dependent upon application timing as less injury was observed when herbicide treatments were applied 2 weeks after emergence versus at emergence. Additional screening should be conducted to determine if post-emergence timing is critical to avoid injury.

Senior Author: sellersb@ufl.edu

 


CHEROKEE ROSE MANAGEMENT IN CARPETGRASS PASTURES. R. E. Strahan*1, S. Gauthier2, E. K. Twidwell1; 1LSU AgCenter, Baton Rouge, LA, 2LSU AgCenter, Breaux Bridge, LA (167)

ABSTRACT

Cherokee rose management in carpetgrass pastures

R. E. Strahan, S. Gauthier, and E. K. Twidwell, LSU AgCenter, Baton Rouge, LA, 70803.

ABSTRACT

Cherokee rose (Rosa laevigata) originates from China and Southeast Asian countries like Laos and Vietnam and was introduced into the United States as an ornamental, for livestock containment, and in wildlife habitat plantings.   This plant grows in nearly any soil type and produces large, pure white, fragrant flowers with a bright yellow center. Cherokee rose is highly invasive and among the 10 most troublesome weeds to control in pastures in Louisiana.  The overall goal in controlling Cherokee rose is to develop a long-term management system that permanently destroys established stands.  

A field study was conducted in 2015 in St. Martin Parish, near the town of St. Martinville, LA in in a producer’s carpetgrass/bahiagrass mix pasture with a heavy natural population of Cherokee rose.  Our objective was to evaluate the efficacy of several herbicides and herbicide combinations for Cherokee rose management.  The study was initiated April 28, 2015.  Cherokee rose had runners that were 2 to 4 feet in length at the time of treatment. 

Herbicides evaluated in single application included Grazon Next (aminopyralid + 2,4-D) at 1.5 qt/A, Grazon P+D (picloram + 2,4-D) at 2 qt/A, and 4 qt/A, Remedy (triclopyr) at 2 qt/A, Chaparral (aminopyralid + metsulfuron) at 3 oz/A, and Cimarron (metsulfuron) at 1 oz/A.  Tank-mixes were also evaluated including Grazon P+D at 2 qt/A + Remedy at 1 qt/A and Grazon P+D at 4 qt/A + Cimarron at 1 oz/A.  There were 9 total treatments including an unsprayed check.

Herbicides were applied with a CO2 pressurized backpack sprayer equipped with 11003 XR flat fan nozzles that delivered 15 GPA at 25 psi.  Plot size was 8 ft x 30 ft.  Visual ratings of percent Cherokee rose control and percent carpetgrass injury data were collected quarterly.   The experiment was conducted as a randomized complete block with 3 replications.  Data were subjected to analysis of variance (P=0.05) and means were separated using Fisher’s LSD. 

No carpetgrass injury was observed at any rating period.  Approximately 150 DAT, Grazon Next, Grazon P+D, and the Grazon P+D + Cimarron tank-mix provided at least 90% control.  Control with Cimarron or Remedy applied alone was <25%.   The Remedy + Grazon P+D tank-mixture only controlled 45% of Cherokee rose at 150 DAT rating period. 

By 250 DAT, only Grazon + Cimarron provided satisfactory control (75%). Cherokee rose control was <20% for Remedy, Cimarron, and Grazon P+D + Remedy tank-mix.  These results indicate that Cherokee rose is extremely difficult to control in pastures and that a single herbicide application is likely not sufficient for long-term control.


JAPANESE CLIMBING FERN (LYGODIUM JAPONICUM) CONTROL IN LITTLE BLUESTEM (SCHIZACHYRIUM SCOPARIUM) RIGHT OF WAY. V. L. Maddox*1, J. D. Byrd, Jr.1, D. Thompson2; 1Mississippi State University, Mississippi State, MS, 2Mississippi Department of Transportation, Jackson, MS (168)

ABSTRACT

Japanese climbing fern (Lygodium japonicum) is a problematic weed on roadsides in southern Mississippi and other Gulf states.  Although control research has been conducted elsewhere on Japanese climbing fern, more research is needed on herbicides approved for use on Mississippi highway rights of way where grasses are desired.  This study evaluates the efficacy of nine herbicides on Japanese climbing fern in unimproved little bluestem (Schizachyrium scoparium)  turf.  Treatments were foliar applied once on August 8, 2014, and evaluated over a one-year period.  Treatments were Accord XRT (5.4 lb ai gal-1) at 1 gal product A-1; Arsenal (2 lb ae gal-1) at 1% V/V; Escort XP (60% metsulfuron methyl) at 1.0 oz product A-1; Garlon (4 lb ae gal-1) at 4% V/V; Milestone (2 ae gal-1) at 7.0 oz product A-1; MSMA (6 lb ai gal-1) at 0.5 gal product A-1;  Oust XP (75% sulfometuron methyl) at 1.0 oz product A-1; Perspective (39.5% aminocyclopyrachlor plus 15.8% chlorsulfuron) at 5 oz product A-1, Plateau (2 lb ai gal-1) at 1.5% V/V; and an untreated check.  A NIS at 0.25% V/V was added to each herbicide treatment.  MSMA showed the greatest control through 2 WAT.  Despite Japanese climbing fern control, damage to little bluestem was unacceptable as visual injury was 90% at 1 MAT and remained over 60% at 3 MAT.  At 1 MAT, control with MSMA was equal to Garlon, which was followed by control observed with Perspective.  However, Garlon and Perspective caused far less foliar damage to little bluestem during the same period.  Based upon percent visual plot cover, some products showed Japanese climbing fern suppression up to 1 YAT.  Little bluestem did not recover from the Accord XRT treatment, but was released in other treatments based upon cover data evaluated in 2015.  Overall treatment cover in plots was variable 1 YAT.  Although some treatments provided good control, no treatment resulted in 100 percent control at 1 YAT based upon visual cover evaluation.  In addition, some treatments significantly damaged the little bluestem turf severely enough to prevent recovery.  Potential negative damage to turf must be a consideration when using certain treatments despite level of efficacy on Japanese climbing fern to be acceptable treatment for this application site.


KUDZU CONTROL OPTIONS: PRELIMINARY EVALUATION. J. Omielan*1, D. Gumm2, B. Michael1; 1University of Kentucky, Lexington, KY, 2Kentucky Transportation Cabinet, Jackson, KY (169)

ABSTRACT

Kudzu (Pueraria montana) is an invasive deciduous twining, trailing, mat-forming, woody leguminous vine that forms dense infestations along forest edges, rights-of-way, old homesteads, and stream banks.  It colonizes by vines rooting at nodes and spreads by seed dispersal.  The plants have extensive root systems with large tuberous roots which can be 3 to 10 feet deep. Kudzu can dominate a site to the exclusion of other vegetation.   Repeated herbicide applications along with other management measures are required to reduce the infestation.  Picloram is used for kudzu control in many states but has not been used extensively in KY in recent years. What are some of the other selective herbicide control options and how effective are they?

This study was initiated in June, 2014 to answer the questions asked above, by mowing a kudzu infested field near Beattyville KY.  Plots (9 m x 9 m) with 3 m alleys separating them were arranged in a 10 treatment randomized complete block design with 3 replications.  After kudzu regrowth, 9 herbicide treatments were applied at 337 L/ha on July 25, 2014 and two repeat treatments were applied on September 25.  These same treatments were applied in 2015 on July 23 and September 24.  Final assessments will be taken in 2016.  The treatments included the following products (active ingredients):  Transline (clopyralid), Streamline (aminocyclopyrachlor + metsulfuron), Garlon 3A (triclopyr), Rodeo (glyphosate), Opensight (aminopyralid + metsulfuron), BK800 (2,4-D + 2,4-DP + dicamba), and Patron 170 (2,4-D + 2,4-DP).  Garlon 3A and Rodeo were applied again on two sets of plots.  All treatments included a non-ionic surfactant at 0.5% v/v.  Visual assessments of percent kudzu control and green vegetative cover (0-100%) were done 32 (8/26/2014), and 62 (9/25/2014) DAT (days after initial treatment) in 2014.  Visual assessments of percent green vegetative cover by kudzu, grasses, and other broadleaves, as well as percent bare ground were done 363 (7/23/2015), 392 (8/21/2015), and 426 (9/24/2015) DAT.

In 2014, all the treatments had kudzu control greater than 92% 32 DAT.  However by 62 DAT control with Patron 170 had declined to 72%.  Green vegetative cover 62 DAT ranged from 63 to 100% for most treatments except for Streamline with only 13% green cover.

In 2015, Patron 170 had 83% kudzu cover 363 DAT while the other treatments ranged from 28 to 4%.  After this year’s applications the kudzu cover was 67% with Patron 170, 8% with Transline and 0-3% for the other herbicide treatments 426 DAT.  At the end of the season (426 DAT), annual grasses had 77-93% cover in the Garlon 3A, Opensight, and BK 800 treatments.  Broadleaves had 73-77% cover in the two Rodeo treatments.  Streamline had the least green vegetative cover with 44% bare ground at the end of the 2015 season.

Final assessments will be done in 2016.  There are a number of herbicide options which are selective and effective in kudzu control.

 


TOLERANCE OF SWALLOWWORTS (VINCETOXICUM SPP.) TO MULTIPLE YEARS OF ARTIFICIAL DEFOLIATION OR CLIPPING. L. R. Milbrath1, A. DiTommaso*2, J. Biazzo1, S. H. Morris2; 1USDA-ARS Robert W. Holley Center for Agriculture and Health, Ithaca, NY, 2Cornell University, Ithaca, NY (170)

ABSTRACT

The European vines pale swallowwort (Vincetoxicum rossicum) and black swallowwort (V. nigrum) are invading various habitats in northeastern North America. It is unclear how these plants might respond to potential biological control agents, as they experience little herbivore damage in North America, or longer durations of mowing given the reported lack of efficacy of mechanical control. We evaluated the effect of six seasons of artificial defoliation (50% or 100% defoliation once or twice per season) and clipping (once, twice or four times at 8 cm above the soil level) on the survival, growth, and reproduction of mature plants of the two species grown in a common garden field experiment. No plants died from damage after six years. Black swallowwort produced more aboveground biomass, whereas pale swallowwort produced more root biomass and root crown buds, compared with its congener species. For most damage treatments, root biomass and the number of crown buds and stems increased over time whereas aboveground biomass and viable seeds per plant generally did not change. Substantial overlap in plant size and seed production occurred among damage treatments. The most severe defoliation treatment did not substantially limit growth and reproduction compared to undamaged plants. While two clippings per season sometimes prevented seed production, four clippings per season was the only type of damage that consistently prevented plant growth and eliminated seed production. Pale and black swallowwort display a high tolerance to above-ground tissue loss in high-light environments without plant competition. The annual increase in plant size calls into question the potential efficacy of a defoliating insect against field populations of swallowworts, and it seems likely the only benefits of a long-term mowing regime will be to eliminate seed production.


EPA'S ANALYSIS OF VARIABILITY IN TERRESTRIAL PLANT STUDIES SUBMITTED FOR PESTICIDE REGISTRATION. S. Sankula*, B. Kiernan, F. Farruggia, C. Hartless; Environmental Protection Agency, Arlington, VA (171)

ABSTRACT


EPA'S INNOVATIVE RISK MITIGATION APPROACHES IN HERBICIDE REGULATION. S. Sankula*, E. Odenkirchen; Environmental Protection Agency, Arlington, VA (172)

ABSTRACT


EPA'S LISTED TERRESTRIAL PLANT BIOLOGICAL ATTRIBUTE DATABASE FOR PESTICIDE EFFECTS DETERMINATIONS. E. A. Donovan*; US EPA, Arlington, VA (173)

ABSTRACT


AUDREY III- EPA'S TIER II PLANT EXPOSURE ESTIMATION TOOL. E. A. Donovan*; US EPA, Arlington, VA (174)

ABSTRACT

Title: Audrey III- EPA's Tier II Plant Exposure Estimation Tool

Authors: Elizabeth Donovan, Susan Bartow, Jim Carleton, Frank T. Farruggia, Kris Garber, R. David

Jones, Brian D. Kiernan, Ed Odenkirchen, and Chuck Peck



The United States Environmental Protection Agency’s Office of Pesticide Programs Environmental Fate

and Effects Division (EFED) is developing a replacement for the TerrPlant model, which is used to

estimate pesticide exposures to plants inhabiting terrestrial and wetland habitats. Conceptually, this

model considers pesticide transport via spray drift and runoff from treated areas into and onto adjacent

non-target habitats. The new model, Audrey III, makes use of existing models currently employed for

estimating exposure by EPA, including AgDRIFT, the Pesticide Root Zone Model (PRZM5), and the

Variable Volume Water Model (VVWM). In Audrey III, the terrestrial exposure model is focused on a

conceptual Terrestrial Plant Exposure Zone (T-PEZ), whose width is determined by the distance from the

edge of field traveled by overland sheet flow and whose depth is determined by the plant root zone. 

Within the T-PEZ, exposure is estimated separately for loading of pesticide entrained in runoff and sorbed

to eroded sediment, and pesticide deposited directly onto foliage by spray drift. For areas outside of the T-

PEZ, exposure is estimated for pesticide transported via spray drift only. A separate wetland conceptual

model in Audrey III is based on a conceptual Wetland Plant Exposure Zone (W-PEZ), and assumes the

same surface area dimensions used for the “Standard Pond” in PRZM5 (10 ha field and 1 ha body of

water) however has different assumptions of depth. Similar to the T-PEZ, concentrations will be

estimated based on loadings from runoff, eroded sediment, and spray drift; however, the W-PEZ will be

modeled as two completely mixed compartments (variable volume water column and benthos) linked

together via mass-transfer. The aquatic exposure model is also based on pesticide loading from runoff,

erosion, and spray drift to a relevant aquatic plant habitat.

 


2015 NATIONAL WEED CONTEST. B. A. Ackley*; Ohio State University, Columbus, OH (175)

ABSTRACT

A look back on the 2015 National Weed Contest hosted by The Ohio State University.

 


DIGITAL BOOK FOR WEED IDENTIFICATION. B. A. Ackley*; Ohio State University, Columbus, OH (176)

ABSTRACT

Plant identification can be challenging and even intimidating for the inexperienced. Growers do not necessarily need to identify every weed in a field to be effective managers, but should be able to identify the major weeds that are important to their operations and goals.  At first glance, learning how to identify weeds can seem like a daunting task given the number and diversity of species, but it is not as difficult as it may seem. Generally, there is a specific group of weeds that tends to dominate disturbed habitats within any native landscape.  This iBook, “The Ohio State University Guide to Weed Identification”, was created to help people better understand the nature of the weeds they are trying to control, and plant identification is a key component of that understanding.  The iBook provides a new way to use an old tool  - visualization - in the world of weed identification. Plant descriptions contained herein include key identification characteristics, photos of many species at different stages of maturity, and 360-degree movies for most species in the book.  This book is not meant to be a compendium of all weedy plants in the U.S., but rather includes a number of the most common Midwestern U.S. weeds and the basic intellectual tools that are necessary to successfully identify plants.

 


THE GLOBAL HERBICIDE RESISTANCE ACTION COMMITTEE AUXIN WORKING GROUP - PURPOSE AND PROJECTS. M. A. Peterson*1, A. Cotie2, M. J. Horak3, A. Landes4, D. Porter5; 1Dow AgroSciences, West Lafayette, IN, 2Bayer CropScience, Research Triangle Park, NC, 3Monsanto, St. Louis, MO, 4BASF, Limburgerhof, Germany, 5Syngenta Crop Protection, Raleigh, NC (177)

ABSTRACT

The Global Herbicide Resistance Action Committee (HRAC) is an Industry organization with representation from 8 major companies working as a part of Crop Life International.  HRAC’s mission is to maintain the effectiveness and sustainability of herbicides by coordinating and supporting research and communications to prevent and/or delay the onset of weed resistance.  Within HRAC there exist several working groups which have been formed to address specific areas of weed resistance management.  Working groups often focus on specific mechanisms of action (MOA) to develop testing methods, management recommendations, educational efforts, or research programs specific to the MOA of interest.  The Auxin Working Group (AWG) was formed in 2013 with the following broad objectives:  1) Review current understanding of the mechanism of action of auxin herbicides in plants; 2) Evaluate public reports of resistance to auxin herbicides; 3) Facilitate research regarding the auxin MOA and mechanisms of auxin resistance in weeds; 4) Contribute to recommendations that will preserve the auxin MOA as an effective weed control tool; and 5) Support the active exchange of information regarding auxin resistance via public conferences, symposia, and publications. Recent projects of the AWG have included a review of auxin herbicide resistance cases listed in the International Survey of Herbicide Resistant Weeds (www.weedscience.org) and development of fact sheets on specific auxin-resistant weed species that can be used as educational tools for a broad audience.


WATCHDOG SPRAYER STATION DOESN'T RELIABLY MEASURE WIND PARAMETERS. J. D. Byrd, Jr.*1, M. Brown1, D. Jamie1, D. Thompson2; 1Mississippi State University, Mississippi State, MS, 2Mississippi Department of Transportation, Jackson, MS (178)

ABSTRACT

Wind speed data collected with the Spectrum Watchdog Sprayer Station were compared to data recorded with a Young 05103-5 anemometer at the Rodney R. Foil Plant Science Research Center on the Mississippi State University campus June and July, 2014 and 2015.  The manufacturer’s specifications advertise the Sprayer Station wind speed accuracy for wind speeds less than 12 mph is +1.1 mph and wind speeds greater than 12 mph is +2.3 mph.  While the wind speed data recorded by the Watchdog Sprayer Station followed the same trend as the data recorded with the Young anemometer, variations in wind speed both above and below that recorded by the Young anemometer indicate the Watchdog precision is not sufficiently reliable to assist spray equipment operators monitor wind velocity nor direction.  Data recorded by the Young anemometer and Watchdog Sprayer Stations were poorly correlated for collection periods in 2014 and 2015 at 0.61 and 0.49, respectively for wind speed.  These data indicate the Watchdog Sprayer Station does not measure wind speed with sufficient reliability to provide a pesticide applicator, such as a DOT spray truck driver, a true indication when wind speeds are likely to cause off-target movement.

 


INTRODUCTION OF HERBICIDE-RESISTANT PALMER AMARANTH AND WATERHEMP BIOTYPES ACROSS KENTUCKY. J. Green*, J. Martin; University of Kentucky, Lexington, KY (179)

ABSTRACT

The presence of Palmer amaranth (Amaranthus palmeri) and waterhemp (Amaranthus tuberculatus [syn rudis]) was limited except for a few localized areas of west Kentucky prior to the year 2000.  Between 2005 and 2010 isolated problems with control of these Amaranthus species with glyphosate in grain crops began to develop and were reported in counties in west Kentucky adjacent to major rivers including the Mississippi, Ohio, Cumberland, and Green Rivers. Several county extension agents reported that infestations of these pigweeds often occurred in fields within the floodplains. It was thought that excessive flooding caused a rapid spread of both Amaranthus species on bottomlands but weed seed was also spread on some upland areas with equipment, especially combines and other equipment used at harvest.  In 2010 Palmer Amaranth was reported in eight west Kentucky counties and waterhemp in five counties.  Based on a county agent survey during 2011 Palmer amaranth and waterhemp were reported in 17 and 11 counties, respectively, and populations were not effectively controlled by glyphosate.  In 2012 leaf samples were collected from Plamer amaranth and waterhemp in 17 counties to analyze for resistance to glyphosate and other herbicides. These results indicated that most of the plants which had spread across the state were introduced from seed sources that were already genetically resistant to glyphosate and there was evidence indicating ALS-resistance was present in some populations of both species.  By 2013 Palmer amaranth began to spread eastward across the state and was present in 24 counties, including 2 observations near central Kentucky.  Waterhemp was still mostly observed in 10 counties that bordered the lower Ohio River, but was also present in four counties up river between Louisville and Cincinnati.  A survey of county extension agents in 2015 confirmed glyphosate-resistant Palmer amaranth is present in at least 50 counties that extend from west Kentucky eastward to counties within the central parts of Kentucky including three counties northeast of Lexington. Glyphosate-resistant waterhemp is not as widespread compared with Palmer amaranth but now occupies nearly 30 counties that include counties that border the lower and upper Ohio River valley but also several isolated counties throughout the state.  Results this past summer using DNA analysis of leaf tissue indicate PPO-resistant Palmer amaranth and waterhemp are also present in Kentucky. A variety of sources is thought to have contributed to the introduction of Palmer amaranth and waterhemp across Kentucky.  A primary source of introduction is from equipment used in the production and harvest of crops.  Another known source of Palmer amaranth seed is through cotton seed hulls fed to cattle and the subsequent manure spread onto cropland.  Other sources include contamination in cover crop seed, as well as, potentially birds and other animals.  The spread of populations with multiple herbicide resistance, especially cases involving PPO inhibitors, will create new and significant challenges in managing Palmer amaranth and waterhemp.


CONTINUED EVALUATION OF PHYSICAL AND VAPOR DRIFT OF SEVERAL DICAMBA AND 2,4-D FORMULATIONS AND THE IMPACT OF VOLATILITY REDUCTION ADJUVANTS. J. T. Daniel*1, S. K. Parrish2, K. A. Howatt3, P. Westra4; 1Agricultural Consultant, Keenesburg, CO, 2AgraSyst Inc, Spokane, WA, 3North Dakota State University, Fargo, ND, 4Colorado State University, Fort Collins, CO (180)

ABSTRACT

Increased use of phenoxy herbicide tank mixes with glyphosate herbicide as a means to manage developing herbicide resistance has led to the discovery of increased physical and vapor drift of 2,4-D dimethyl amine salt (DMA), dicamba DMA salt and dicamba diglycolamine salt (DGA), when applied with ammonium sulfate (AMS) and/or nonionic surfactant (NIS). New drift reduction and volatility reduction adjuvants are now under development to help manage these issues. Field and greenhouse evaluations have demonstrated the ability of AQ922, AQ889, AQ1000 and AQ2005 to reduce herbicide movement through drift reduction and volatility reduction when applied as adjuvants in the use rate range of 0.125% v/v to 1% v/v of the spray solution.

 


IMPACT OF DEPOSTION AIDS ON HERBICIDE CANOPY PENETRATION. C. A. Samples*1, D. M. Dodds2, A. L. Catchot2, T. Irby1, G. R. Kruger3, D. B. Reynolds1, J. T. Fowler4, D. Denton2, M. T. Plumblee1, L. X. Franca1; 1Mississippi State University, Starkville, MS, 2Mississippi State University, Mississippi State, MS, 3University of Nebraska-Lincoln, North Platte, NE, 4Monsanto Company, St. Louis, MO (181)

ABSTRACT

Effect of Drift Retardants/Deposition Aids and Herbicides on Insecticide Canopy Penetration in Cotton. C.A. Samples1, D.M. Dodds1, A.L. Catchot1, A.B. Denton1, G. Kruger2, J.T. Fowler3. 1Mississippi State Univ., Missippi State, MS, 2Univ. of Nebraska, North Platte, NE. 3Monsanto Company, St. Louis, MO.

 

Abstract

 

Although glyphosate resistance has become more prevalent across much of the southern U.S., glyphosate is still commonly utilized to control non-resistant weed species. In 2010, almost 100 % of the cotton planted in the U.S. was treated at least once with glyphosate (NASS, 2014). However, due to glyphosate resistance, glufosinate tolerant crops are becoming more common. Glufosinate has been observed to increase control of glyphosate resistant Palmer amaranth from 9 to 19% when compared to glyphosate (Whitaker et al., 2011). Two POST applications of glufosinate has been shown to provide up to 96 percent control of Palmer amaranth 2 WAT. A single application of glufosinate applied at 0.6 kg ai/ha has been observed to provide 82 to 94 % control of Palmer amaranth 3 WAT (Ahmed et al. 2012). 

 

Several studies have been conducted evaluating drift retardant/deposition aid effects on drift (Guler et al., 2006, Hewitt, 2003, SDTF 1997, Wolf et al., 2002, 2003, 2005). Most of these studies were conducted with ground application systems or the use of a wind tunnel. Studies focused primarily on different polymer formulations. Very little to no information exists comparing tank mix combinations of insecticides with herbicides or deposition aids and the effect of these tank mixes on crop canopy penetration. With new technologies such as Enlist® or Xtend® under development, data is needed regarding herbicide and insecticide tank mixed with deposition aids and the resultant effects on crop canopy penetration.

 

Experiments were conducted in 2014 at the R.R. Foil Plant Science Research Center located in Starkville, MS. Deltapine 1321 B2RF was planted during early May for this experiment. All applications were made using a Bowman Mudmaster calibrated to deliver 140 L/ha at 4.8 kph. It was equipped with a 4 row multi-boom equipped with 110015 AIXR nozzles spaced 48 cm apart. Applications were made 46 cm above the crop canopy. Insecticides included acephate 97 (SP) @ 0.84 kg ai/ha and lamba-cyhaolthrin (EC) at a rate of 0.05kg ai/ha. Insecticides were applied alone or in combination with glufosinate @ 0.6 kg ai/ha, glyphosate @ 0.9 kg ae/ha, HM 9733 (guargum) applied @ 30 g per 38 L of water; HM 1428 (polymer) applied @ 0.5 % v/v; and HM 9679A (oil) applied @ 1.0% v/v. A red tracer was added to each treatment at a rate of 0.2% v/v. Metal stands 61 cm in height were utilized for this experiment. Card holders were spaced equidistantly from one another spiraling up the stand. Once the crop met the pre-determined height requirement, stands were placed in rows 2 and 3 with stand in row 2 being labeled as the front stand and the lower most position running parallel with the row. The stand in row 3 was labeled as the back stand and was placed with the lowest most positon located perpendicular to the row in an attempt to cover all penetration angles. Once stands were in place, 10 cm x 10 cm mylar cards were placed at the end of each card holder on the stand using clean latex gloves. Approximately 90 -120 seconds after application, cards were removed using another pair of clean latex gloves. Cards were then immediately placed in a dark container due to the dye’s high level of photo degradability. Penetration of each treatment at each position was determined using a fluorimeter and reflectance analysis. Treatments were compared to applications receiving no herbicide or deposition aids in tank combinations. All data were analyzed using the PROC MIXED procedure in SAS 9.4 and means were separated using Fischer’s Protected LSD. Stands were analyzed separately due to changes in penetration angles.

 

When averaged across insecticides and position in the canopy for the back stand, treatments containing a polymer deposition aid provided 34 percent greater deposition than treatments not receiving a deposition aid. In addition, treatments with a polymer deposition aid had significantly greater penetration into the crop canopy than treatments containing the oil, glyphosate, or glufosinate with all three having a negative impact on total deposition in the canopy. However, when analyzing the front stand, treatments containing glyphosate, regardless of insecticide or position had 65 percent greater deposition than treatments receiving no additive. These treatments had significantly greater deposition than all other herbicides and deposition aids used in testing. A three way interaction was present for insecticide, deposition aid/herbicide, and position in the canopy. However, this was only present for deposition at the lowermost position in the canopy. For the back stand, treatments containing acephate + polymer deposition aid had significantly greater deposition than all other insecticide and deposition aid/herbicide combinations. On average, this treatment provided 296 percent greater deposition than acephate with no additive. However, when analyzing the same interaction for the front stand treatments containing acephate + glyphosate had significantly greater deposition compared to all other treatments with deposition being 525 percent greater than that of treatments containing only acephate. Data suggest that glyphosate could be minimizing droplet size allowing for further canopy penetration at position 4 due to less surface area per droplet. 

 


IMPACT OF APPLICATION VOLUME, RATE, AND ADJUVANT USE ON EFFICACY OF RINSKORTM ACTIVE. M. R. Miller*1, J. K. Norsworthy1, D. H. Perry2, G. T. Jones1, C. J. Meyer1; 1University of Arkansas, Fayetteville, AR, 2Dow AgroSciences, Greenville, MS (182)

ABSTRACT

Barnyardgrass (Echinochloa crus-galli), broadleaf signalgrass (Urochloa platyphylla), hemp sesbania (Sesbania herbacea), and yellow nutsedge (Cyperus esculentus) continue to be some of the most troublesome weeds in rice today. As the evolution of herbicide resistance continues and herbicide mechanisms of action that provide control are lost, the development of new herbicide active ingredients are needed. The introduction of LoyantTM herbicide with RinskorTM Active brings a valuable tool to weed control and provides an alternative mechanism of action for use in rice. Rinskor provides broad-spectrum post-emergence control of broadleaf, grass, and sedge species. Studies were conducted in 2014 and 2015 to evaluate Rinskor efficacy as influenced by formulation and adjuvant rate, spray volume, time of flooding, and tank-mix compatibility.  Two formulations of Rinskor were evaluated, an SC and a NeoECTM. Each formulation was applied at 15 and 30 g ai ha-1 with 0, 0.7, 1.4, 2.1, 2.8, or 3.5 L ha-1 MSO. Weeds evaluated included barnyardgrass, broadleaf signalgrass, hemp sesbania, yellow nutsedge, and Palmer amaranth (Amaranthus palmeri) planted in a non-flooded setting. Increasing MSO rate improved weed control with both formulations. The NeoEC formualtion required less MSO to improve control.  Another experiment was conducted to determine the effect of spray volume and adjuvant on control of the same weed species used in the formulation and adjuvant rate experiment. Factors included Rinskor at 15 and 30 g ai ha-1 formulated as an SC applied at 47, 94, or 187 L ha-1 with 0, 1.2, 2.3, and 3.5 L ha-1 MSO. Rinskor at 30 g ai ha-1 provided better control than 15 g ha-1, regardless of spray volume or MSO rate. Control with 30 g ha-1 improved as spray volume and MSO level increased. The addition of Loyant to rice herbicide programs will be beneficial for herbicide resistance management and provides an effective tool to control difficult-to-manage weeds in rice.

 

TMTrademark of the Dow Chemical Company (“Dow”) or an affiliated company of Dow. LoyantTM is not registered with the US EPA at the time of this presentation. The information presented is intended to provide technical information only.

 


IMPACT OF APPLICATION VOLUME AND ADJUVANT SYSTEM ON HARVEST AID EFFICACY IN MID-SOUTH SOYBEAN (GLYCINE MAX). A. B. Scholtes*1, J. Irby2, J. M. Orlowski3, S. G. Flint1, S. M. Carver1; 1Mississippi State University, Starkville, MS, 2Mississippi State University, Mississippi State, MS, 3Mississippi State University, Stoneville, MS (183)

ABSTRACT

Harvest aids have traditionally been used to control weeds, defoliate crops and increase harvest efficiency.  Past research has suggested that the use of adjuvants with a harvest aid may increase the efficacy achieved through such applications.  The use of harvest aids in the Mid-South is increasing to not only assist with pre-harvest weed control, but also to achieve an earlier and more efficient harvest. 

The objectives of this research were to evaluate the efficacy of harvest aids applied in conjunction with various adjuvant systems as well as to evaluate the efficacy of harvest aids applied at various application volumes.  Separate experiments were conducted for each objective with applications in both experiments being made once the crop reached 65% mature pods. In both experiments, harvest aid treatments consisted of paraquat (0.25 lb ai/A), saflufenacil (0.03 lb ai/A), sodium chlorate (6 lb ai/A), paraquat plus saflufenacil (0.02 lb ai/A), and paraquat plus sodium chlorate (3 lb ai/A). For the first objective, the five harvest aid combinations were applied with three different adjuvant combinations (crop oil concentrate at 1% v/v, non-ionic surfactant at 0.25% v/v, or methylated seed oil at 1% v/v). Ammonium sulfate at 0.25% v/v was included with all treatments.  For the second objective, Factor A was the harvest aid that was applied and Factor B was the application volume.  Factor A consisted of the same five harvest aid combinations all applied at volumes (Factor B) of 5, 10, 15 and 20 GPA.  Each experiment contained 3 replicates and an untreated check for comparison purposes. Experimental units were 12.7 feet wide and 40 feet in length (4 row plots).  All four rows were treated and visually evaluated and the center two rows were harvested for yield. 

Visual estimation of desiccation, green stems and green pods were collected for both experiments.  For objective 1, all harvest aid treatments, except for saflufenacil and saflufenacil plus the various adjuvant combinations, resulted in greater desiccation when compared to the untreated 3 DAT with desiccation ranging from 35 to 71%. By 7 DAT, all harvest aid treatments other than saflufenacil applied with no adjuvant provided greater desiccation compared to the untreated with desiccation ranging from 60 to 94%. No differences in desiccation were observed 14 DAT. Furthermore, all harvest aid treatments, except for saflufenacil and saflufenacil plus the various adjuvant combinations, resulted in a lower percentage of green stems present 3 DAT. No differences in green stem were observed 7 or 14 DAT. No differences in green pods were observed at any evaluation timing. In addition, no yield differences were observed.  For objective 2, all harvest aid treatments resulted in greater desiccation at both 3 and 7 DAT when compared to the untreated with desiccation values ranging from 83 to 90% and 95 to 98%, respectively. An application volume of 15 GPA resulted in greater desiccation at 7 DAT compared to both 5 and 10 GPA. Application volumes of 10 and 15 GPA both resulted in less green stem at 3 DAT. By 7 DAT, all harvest aid treatments except saflufenacil + MSO + AMS resulted in decreased green stem. At 3 DAT, application volumes of 10, 15, and 20 GPA resulted in a decrease of green pods present. However, by 7 DAT, application volumes of 5, 15, and 20 GPA all resulted in fewer green pods. No differences in soybean yield were observed for any harvest aid treatment or application volume combination.


EXAMINING NOZZLE EFFECTS ON POST-APPLIED HERBICIDE BURN TO COTTON. J. Reeves, L. E. Steckel, S. Steckel*; University of Tennessee, Jackson, TN (184)

ABSTRACT

Glyphosate-resistant Palmer amaranth (Amaranthus palmeri) continues to be the most troublesome weed Tennessee cotton growers face.  With the adoption of more GlyTol/Liberty Link® and RoundUp Xtend® cottons, there has been an increase in three-way tank mixes of glufosinate plus glyphosate plus s-metolachlor to combat Palmer amaranth.  Glufosinate and glyphosate often have heavy surfactant loads and when added to the oil of s-metolachlor, this tankmixture increases the probability of seedling cotton injury.  One possible way to help mitigate POST herbicide injury to cotton is to use nozzle selection to affect droplet size.  The objective of this research was to evaluate the effect of nozzle type on crop injury and yield from an early-season POST-applied tank mix of glufosinate plus glyphosate plus s-metolachlor on seedling cotton.

Two studies were conducted in 2015 at the West Tennessee Research and Education Center in Jackson, TN.  Treatments were arranged in a randomized complete block design with four replications.  Foliar application was made to cotton at the two leaf growth stage using a high-clearance sprayer equipped with a Capstan pulse-width modulating (PWM) system®.  Four nozzle types were evaluated: Spraying Systems Co. TeeJet XR 11002FF®, (Flat Fan, fine droplets, 200 microns, pulse of 100%); Greenleaf Technology TADF02® (TurboDrop Asymmetrical DualFan, coarse droplets, 350 microns, 50% pulse); Wilger MR11002® (DR nozzle, very coarse droplets, 414 microns, 100% pulse); and the Spraying Systems Co. TTI002® (Turbo TeeJet Induction, ultra-coarse droplets, 800 microns, 100% pulse).  Crop injury was evaluated 7 and 21 days after application (DAA) using a 0 – 100 scale where 0 = no injury and 100 = plant death.  Crop injury and yield were subjected to analysis of variance using appropriate mean separation techniques and α=0.05.

There were differences among all nozzles for crop injury observed 7 DAA.  Injury was greatest with the DualFan nozzle (32%) followed by the Flat Fan (22%), followed by the TTI (18%), and the DR nozzle (13.5%).  At 21 DAA, more injury was seen with the Dual Fan nozzle compared with the TTI and DR nozzles.  The DR treatment yielded more seed cotton than the Dual Fan treatment.

To mitigate crop injury, it is recommended to use single fan nozzles that deliver a larger droplet size (AIXR, AI, DR, TDXL, etc.) and reduce the l/ha-1 to 94 or less.  This decreases the coverage and lessens the area of the leaf that will be injured.  Might this cause Palmer amaranth control to suffer?  Perhaps.  However, less injury to the cotton in the spring could aid the crop from an earliness standpoint.  Also, there are a few options to control any pigweed escapes that may occur from this strategy.  Because Tennessee is in the northern Cotton Belt, it is imperative that growers manage their crop for earliness and avoid crop injury that may cause delay.  Therefore, growers need to be aware how nozzle type may effect crop injury with early-season POST herbicides.

 


NOZZLE EFFECT ON EFFICACY OF GLUFOSINATE AND FOMESAFEN ON PALMER AMARANTH IN SOYBEAN. J. L. Reeves*, G. Montgomery, L. Steckel; University of Tennessee, Jackson, TN (185)

ABSTRACT


EFFECT OF CARRIER VOLUME AND SPRAY QUALITY ON LACTOFEN TANK-MIXTURES. B. E. Meusch*1, L. Sandell2, J. A. Golus3, C. J. Hawley3, G. R. Kruger3; 1Univeristy of Nebraska Lincoln, Lincoln, NE, 2Valent USA, Lincoln, NE, 3University of Nebraska-Lincoln, North Platte, NE (186)

ABSTRACT


GLUFOSINATE TANKMIX EFFICACY AS INFLUENCED BY CARRIER VOLUME AND NOZZLE SELECTION. S. L. Taylor*1, P. A. Dotray1, W. Keeling2, R. M. Merchant1, M. R. Manuchehri1, R. Perkins3; 1Texas Tech University, Lubbock, TX, 2Texas A&M, Lubbock, TX, 3Bayer CropScience, Idalou, TX (187)

ABSTRACT

GLUFOSINATE TANKMIX EFFICACY AS INFLUENCED BY CARRIER VOLUME AND NOZZLE SELECTION. S. L. Taylor*1, P. A. Dotray1,2, J. W. Keeling2, R. M. Merchant1, M. R. Manuchehri1, W. R. Perkins3; 1Texas Tech University, 2Texas A&M AgriLife Research and Extension, 3Bayer CropScience

Glufosinate, 2,4-D, and dicamba are critical components of two new weed management systems that can effectively control a wide range of problem weeds, including glyphosate resistant Palmer amaranth (Amaranthus palmeri S. Wats.). These new systems and associated herbicide labels will require specific nozzle types and carrier volume to reduce off target movement. Herbicide performance can also be greatly influenced by both potential and likely tank-mix combinations. To examine herbicide efficacy of glufosinate, 2,4-D amine, and dicamba applied alone and in tank-mix combinations when using different carrier volumes and nozzle selections, two studies were conducted near Lubbock, TX in 2015. Herbicide treatments were applied at 10, 15, and 20 gallons per acre (GPA) using TTI 11002 nozzles to evaluate carrier volume. To evaluate nozzle selection, three different nozzles at 15 GPA were used. Nozzles were selected based on droplet size: medium = 236-340 microns (TT11002 at 27 psi), very-coarse = 404-502 microns (AIXR 11002 at 27 psi), and ultra-coarse = >665 (TTI 110015 at 37 psi). Herbicide rates included glufosinate at 29 fl oz/A, dicamba at 16 fl oz/A, and 2,4-D at 32 fl oz/A. In the nozzle selection study, glufosinate tank-mixed with 2,4-D or dicamba improved Palmer amaranth control over these herbicides when applied alone. When glufosinate was mixed with 2,4-D or dicamba, Palmer amaranth control using the ultra-coarse nozzle was as effective as current nozzles that produce medium to very coarse droplets. In the carrier volume study, improved Palmer amaranth control was observed with increased carrier volume following glufosinate or 2,4-D alone or glufosinate + 2,4-D. However, carrier volume did not affect control following dicamba alone or glufosinate + dicamba in tank-mix. 

 


TIME OF DAY EFFECTS ON BARNYARDGRASS CONTROL WITH GLUFOSINATE. G. R. Oakley1, A. Eytcheson2, D. B. Reynolds*3; 1Mississippi Sstate University, Starkville, MS, 2Mississippi State University, Mississippi State, MS, 3Mississippi State University, Starkville, MS (188)

ABSTRACT

Time of Day Effects on Barnyardgrass Control with Glufosinate

 

G. R. Oakley, A. N. Eytcheson, and D. B. Reynolds

 

Field studies were conducted to evaluate the effect of clethodim and glufosinate tank mixtures applied at differing times of day on barnyardgrass control.  Clethodim at 76 g ai ha-1, pooled over glufosinate rates provided 92 to 95% barnyardgrass control, regardless of time of day of application.  At 28 DAT, glufosinate applied alone controlled barnyardgrass 87% compared to 95% control by clethodim applied alone.  Clethodim applied alone provided greater barnyardgrass control compared to glufosinate plus clethodim.  Barnyardgrass control as affected by glufosinate rate and application time of day was significant at all rating intervals.  Barnyardgrass control with glufosinate at 594 g ai ha-1 differed significantly at the different times of application.  Applied at midnight and 6 A.M., glufosinate applications reduced barnyardgrass control compared to applications made at noon and 6 P.M.  Clethodim applied alone reduced barnyardgrass biomass greater than glufosinate plus clethodim compared the untreated check, suggesting barnyardgrass antagonism when glufosinate is tank-mixed with clethodim.  Environmental factors such as temperature, dew, relative humidity and light at the time of application are likely responsible for the time of day effects observed in this study.  These data suggest that in order to optimize barnyardgrass efficacy with tank mixtures of glufosinate and clethodim, applications should be made at noon or early evening to avoid potential time of day effects. 

 


WEED MANAGEMENT WITH BRAKE® FORMULATIONS IN TEXAS COTTON. J. Spradley*1, W. Keeling2, P. A. Dotray3, P. Baumann4, M. Matocha4; 1Texas A&M AgriLife Research, Lubbock, TX, 2Texas A&M, Lubbock, TX, 3Texas Tech University, Lubbock, TX, 4Texas A&M AgriLife Extension, College Station, TX (189)

ABSTRACT

Increasing populations of glyphosate-resistant Palmer amaranth (Amaranthus palmeri) have created new weed management challenges for Texas cotton producers.  The addition of effective soil-applied residual herbicides to weed management systems is critical.  Fluridone was evaluated for weed control in cotton during the 1980’s, but weed resistance concerns has renewed interest in this herbicide. The objectives of these studies were to evaluate cotton response and weed control comparing Brake F2 (fluridone + fomesafen) and SP1178-C2 (fluridone + fluometuron) alone or tank-mixed with S-metolachlor and followed by (fb) glyphosate or glufosinate.  Fluometuron was applied alone at two rates and fb glyphosate or glufosinate.  Field trials were conducted, Lubbock, Halfway, and College Station, TX in 2015 to evaluate Brake F2 and SP1178-C2.  Soil textures at the Lubbock, Halfway, and College Station locations were loam, clay loam, and silty clay loam, respectively.  Preemergence applications were made between June 2 and June 12 and postemergence applications were made between June 30 and July 21, depending upon location.  At Lubbock, season-long Palmer amaranth control was >80% with fluometuron fb glufosinate, Brake F2 fb glufosinate + S-metolachlor.  SP1178-C2 fb glufosinate controlled Palmer amaranth 79% at the Halfway location, while Brake F2 fb glyphosate controlled Palmer amaranth 100%.  Similar control was achieved with fluometuron fb glyphosate, SP1178-C2 fb glyphosate and Brake F2 fb glyphosate + S-metolachlor.  At College Station, Palmer amaranth control ranged from 87-99% with all treatments, which was greater control than fluometuron alone at a reduced rate.  Red sprangletop (Leptochloa chinensis) was controlled 98-100%, with all treatments.  No crop injury was observed with any treatments at Halfway or College Station, while early-season injury of 5% or less was observed at Lubbock.  While further testing is needed, results indicate that these fluridone formulations could be part of an effective glyphosate tolerant Palmer amaranth weed management system.

 

 


INTERACTION OF APPLICATIONS WITH OXYFLUORFEN (PRE) AND GRASSY HERBICIDES (POST) ON CANARYGRASS CONTROL IN WINTER WHEAT IN MéXICO. E. Lopez*; Field Scientist R&D, Guadalajara, Mexico (190)

ABSTRACT

INTERACTION OF APPLICATIONS WITH OXYFLUORFEN (-PRE) AND GRASSY HERBICIDES (-POST) ON CANARYGRASS CONTROL IN WINTER WHEAT IN MEXICO

Enrique López Romero

Field Scientist R&D at Dow AgroSiences de México. elopezromero@dow.com

 

SUMMARY

The main phytosanitary problem affecting wheat production in the Mexicali Valley is caused by the presence of weeds, especially monocotyledons. During 2013-2014 two trials were established to evaluate the interaction of pre- and post-emergent applications on the dynamics of graminaceous species in batches with a history of high weed populations. PRE treatments were composed by two Oxyfluorfen formulations (Goal Tender™) and (Goal 2XL™) at doses of 240 g i.a Ha-1 and an absolute control, were applied 1 day before planting in dry. POST treatments were: 1.- Across™@0.5 L PF Ha-1; 2.-Sigma OD™@1.25 L PF; 3.-Everest Ultra™@45g + 0.5 L PF; 4.-Axial™@1.4 L PF;  5.-Traxos™@1.4 L PF; 6.-Vigia™@45 g+0.75 L PF and 7.- absolute control, were applied 40 days after planting (DAP). The application of treatments was conducted with a CO2 backpack sprayer at a pressure of 241.32 kPa. For PRE treatments, Twin-Jet 8003VS nozzles were used, with a water expenditure of 250 L Ha-1. For POST treatments, XR8003VS nozzles were used, with a water expenditure of 300 L Ha-1, additionally, the adjuvant BreakThru® was used, at doses of 0.01% (v/v). The physical and chemical characteristics of soils were: Loam texture (18.90% sand, 49.45% clay and 31.23% silt), pH 7.98 and organic matter content of 1.2%, high salt contents. The response variables were: Control, crop damage and yield. 64 (DAP) = 65 days after the application (DAA) prior to treatment and 24 DAA after treatment, according to the variance analysis (p=0.001) significant differences were obtained on the Phalaris sp. and Lolium sp. control in the interaction of both factors (PRE and POST) by showing the best controls >88%. In the case of Hordeum sp., there are significant statistical differences only for the PRE factor, but not in the interaction, since there is only one suppression effect for Oxyfluorfen and the POST treatments showed low efficiencies. The best yield was shown by the interactions Across™+Goal Tender™ 7.2 Ton Ha-1; Sigma OD™+Goal Tender™ 7.1 Ton and Everest Ultra™+Goal Tender™ 6.9 Ton. The absolute control showed an average yield of 0.98 Ton Ha-1.  

 

Keywords: Triticum aestivum, Phalaris sp., Lolium sp., Hordeum sp.,Oxyfluorfen, Pyroxsulam, Mesosulfuron, Iodosulfuron, Flucarbazone, Clodinafop, Pinoxaden, Fenoxaprop.

 

 


EFFECT OF DIFFERENT HERBICIDES AND APPLICATION TIMINGS ON THE TOLERANCE OF SESAME. Z. E. Schaefer*1, J. Rose2, R. A. Garetson1, W. Grichar3, M. V. Bagavathiannan1; 1Texas A&M University, College Station, TX, 2Sesaco Corp, Austin, TX, 3Texas AgriLife Research, Yoakum, TX (191)

ABSTRACT

Sesame is an emerging low-input crop in the southern United States, but knowledge on effective herbicide options for weed management is limited. An experiment was conducted at the Texas A&M field laboratory in College Station to evaluate the tolerance of sesame to different herbicides and application timings. The experiment included 29 treatment combinations of different rates and timings of Zidua (pyroxasulfone), Dual (S-metolachlor), Direx (diuron), Warrant (acetochlor), Pethoxamid (chloracetamide), Treflan (trifluralin), and Prowl H­20 (pendimethalin). Application timings included a pre-emergence (PRE) application and post-emergence (POST) applications at 2, 3, and 4 weeks after crop planting (WAP). Sesame showed good tolerance to PRE applications of Zidua (1.5 oz/A), Dual (21.3 oz/A), and Pethoxamid (1 lb ai/A), while moderate stunting and leaf discoloration was observed for the tank mix of Dual + Direx (10.6 oz/A + 16 oz/A) and for Warrant (64 oz/A) at 2 weeks after treatment (WAT). However, plants greatly recovered from injury to acceptable levels at 4 WAT. Among the POST applications, injury on sesame was acceptable when Dual (21.3 oz/A), Zidua (1.5 oz/A), Treflan (24 oz/A), or Prowl (32 oz/A) was applied at 2 or 3 WAP. However, POST applications at 4 WAP, especially the higher rates of Treflan (48 and 96 fl oz/A) and Prowl H20 (64 and 128 fl oz/A), caused substantial injury to sesame, with characteristic “cap gap” symptomology, which causes a gap in capsule formation along the fruiting stem. Results from this study will guide the selection of suitable herbicide programs for effective weed management in sesame.


WEED POPULATION RESPONSE TO ROTATION AND CONSERVATION PRACTICES IN A 12-YR STUDY. R. E. Blackshaw*, F. J. Larney, N. Z. Lupwayi; Agriculture and Agri-Food Canada, Lethbridge, AB (192)

ABSTRACT

Potato, dry bean, and sugar beet production have
increased markedly in recent years on irrigated cropland in Alberta, Canada.
Concerns exist about increased soil erosion and declining soil quality when
these low residue crops are grown in sequence in short duration rotations. A
12-yr study was conducted to determine the merits of adopting various soil conservation
practices (reduced tillage, cover crops, composted cattle manure) and longer
duration rotations to develop a more sustainable production system for these
row crops. Weed density and weed seedbank data were collected as a component of
this study. Weed densities recorded prior to applying postemergence herbicides
indicated that conservation compared with conventional management treatments
had greater weed densities in 30 to 45% of the cases in 3-, 4- and 5-yr
rotations. In contrast, a 6-yr conservation rotation that included 2 years of
timothy forage resulted in similar or lower weed densities than rotations with
conventional management practices. Residual weed densities recorded 4 wk after
applying postemergence herbicides were only greater in conservation than
conventional rotations in 2 of 12 yr regardless of rotation length. Weed
seedbank densities at the conclusion of the 12-yr study were similar for 3- to
6-yr rotations under either conservation or conventional management. These
findings indicate that implementing a suite of soil conservation practices poses
little risk of increased weed populations in the long term and will facilitate
grower adoption of more sustainable practices for irrigated row crops in this
region.


EFFECTS ON CROP ROTATION ON NATURAL WEED POPULATION DENSITY. H. A. Acciaresi*, G. Picapietra; Instituto Nacional Tecnologia Agropecuaria, Pergamino, Argentina (193)

ABSTRACT

 Agricultural production in the northern region of the Buenos Aires province (Argentina) has shown steady growth in the last century, accompanied by a process of intensification of production which has significantly modified weed populations. The objective was to evaluate the change in the density of natural weed under three different agricultural rotations. Plant census were conducted in two cropping cycles (2013/2014 and 2014/2015) determining the plant density and the number of weed species.
An experiment that evaluate three crop rotations systems: a) monoculture of soybean (Mo), b) current rotation (CR: wheat/soybean and corn) and c) optimized rotation(OR: no RR soybean and popcorn) was used.
In the soybean monoculture system in June 2013 and 2014, a total of 12 and 10 species, represented by 44 and 71% relative cover where predominated by Conyza spp. and Stellaria media, respectively. In CR system, 2 and 10 species represented a 1 to 36% of relative cover, mostly by Lolium multiflorum in the first year and Conyza spp. and Gamochaeta spp. in the second ones. In OR system, 9 and 5 different species, with an average relative cover of 22 and 33% represented by Conyza spp., Lamium amplexicaule and Stellaria media in the first year and Gamochaeta spp. and Hypochaeris sp. in the second ones. Additionally, during the tested period, in the soybean monoculture an increased use of glyphosate were observed, 9.36 kg ae ha-1, while7.45 a.e.kg.ha-1 and 6.66 kg a.e. ha-1 were used in OR and CR systems, respectively. Crop rotation favored a diversification in the number of species and a lower herbicides use.

POTENTIAL USE OF CROP FERTILIZATION IN THE MANAGEMENT OF SPANISH WEEDS. J. M. Urbano*1, F. Forcella2, A. Delgado1; 1Universidad de Sevilla, Sevilla, Spain, 2USDA ARS, Morris, MN (194)

ABSTRACT


COVER CROPS: EFFECTS ON WINTER WEEDS AND THEIR RELATIONSHIP WITH PHOTOSYNTHETICALLY ACTIVE RADIATION INTERCEPTION. M. V. Buratovich1, M. E. Cena2, H. A. Acciaresi*3; 1UNNOBA-ECANA, Pergamino, Argentina, 2Comision Investigaciones Cientificas (CIC), Pergamino, Argentina, 3Instituto Nacional Tecnologia Agropecuaria, Pergamino, Argentina (195)

ABSTRACT

 
The objective of the study was to determine the effect of different cover crops on  aboveground biomass of winter weed and its relation to the interception of photosynthetically active radiation. The species used as cover crops were barley (Hordeum vulgare L.), ryegrass (Lolium multiflorum L.), oats (Avena sativa L.), vetch (Vicia sativa L.), rapeseed (Brassica campestris L.) , forage radish (Raphanus sativus L.) and bromegrass (Bromus unioloides L.) and vetch/oat consociation. A sector was left without cover crop used as negative control. In each experimental unit total aboveground biomass of cover crops and weeds in both vegetative and reproductive growing stages were quantified. The percentage of  photosynthetically active radiation interception (PARI) by cover crops was measured.
The higher cover crop aboveground biomass was obtained in vetch and vetch/oat consociation, while registering the biggest IRFA. The higher weed aboveground biomass was recorded in the cover crop rapeseed, while the lowest were in vetch,  vetch/oat consociation and ryegrass.
The use of cover crops will reduce the number of herbicide application, mitigating the emergence of new resistant weeds. It also will reduce the number of weeds present a summer crop planting.

PERSPECTIVES ON SOYBEAN YIELD LOSSES DUE TO WEEDS IN NORTH AMERICA. A. Dille*1, P. H. Sikkema2, V. M. Davis3, W. J. Everman4, I. C. Burke5; 1Kansas State University, Manhattan, KS, 2University of Guelph, Ridgetown, ON, 3BASF, Verona, WI, 4North Carolina State University, Raleigh, NC, 5Washington State University, Pullman, WA (196)

ABSTRACT

Weeds are one of the most significant threats to crop production in North America. Crop losses in yield and quality due to weed interference, as well as costs of controlling weeds, have a significant economic impact on crop production. Previous WSSA Weed Loss committee reports, as chaired by Chandler (1984) and Bridges (1992), provided snapshots of the comparative losses due to weeds across geographic regions and crops within these regions. This presentation is a second report from the WSSA Weed Loss committee on crop yield losses due to weeds, specifically in soybean [Glycine max (L.) Merr.]. Yield loss estimates were determined from comparative observations of soybean yields between the weedy control and plots with greater than 95% weed control in studies conducted from 2007 to 2013. Researchers from each state and province provided at least three and up to ten individual comparisons for each year, which were then averaged within a year, and then averaged over the seven years. These percent yield loss values were used to determine total soybean yield loss in bu/ac based on average soybean yields for each state or province as well as current commodity prices for a given year as summarized by USDA-NASS and Statistics Canada. Averaged across 2007 to 2013, weed interference in soybean caused a 49.5% yield loss. For example, in 2012, in the US and Canada soybean was grown on 76,104,780 and 4,149,400 acres with production of 2,927 million and 187 million bushels, respectively. Using an average soybean price across 2007 to 2013 of US $10.61/bu, farm gate value would be reduced by US $16,353 million annually if no weed management tactics were employed.


COMPARING TWO METHODS OF MEASURING WEED SEED RETENTION AT SOYBEAN HARVEST. L. M. Schwartz*, J. K. Norsworthy, J. K. Green, M. Bararpour; University of Arkansas, Fayetteville, AR (197)

ABSTRACT

Weed resistance to common herbicides has become an epidemic in agriculture. Specifically, in soybean (Glycine max L. Merr.) production, there are 47 herbicide-resistant weed species.  Typically when harvesting occurs the weed seed has already either shattered or has been pulled through the combine. Thus, the weed seeds are being redistributed on the soil surface causing further spread as well as increasing the soil seedbank. However, there is little research on how much seed is retained on different weed species at harvest time. Therefore, the objective of this study was to compare two methods of measuring weed seed retention of barnyardgrass (Echinochloa crus-galli (L.) P. Beauv.) and Palmer amaranth (Amaranthus palmeri S. Wats) at the time of harvest. The first method was to collect weed species within one week of soybean maturity. Plants were harvested and the loose soil and debris beneath the plants were swept into a pan with a hand broom to collect any shattered seed and seed numbers are latter quantified using an exhaustive germination technique. The second method utilized seed traps that were placed below each weed species. Seed traps were placed into soybean fields following inflorescence production by weeds and were removed a month after soybean maturity. Seed from the traps were collected weekly. Regardless of the method, there was no significant difference in the method of measuring weed seed retention for either species.  Barnyardgrass seed mostly shattered prior to soybean maturity, but did retain an average of 37 to 43% seed.  Conversely, Palmer amaranth retained an average of 98 to 99% of the seed at this time. This research shows that the one time sweep method allows for an equally accurate value of seed retention as does the artificial field experiment (Method 2) that takes multiple measurements throughout the growing season. From this research, we can easily and affordably determine the seed retention of other weed species at the time of soybean maturity. This information can then be used to better understand and utilize best management practices that center on destroying weed seed such as harvest weed seed control tactics.


A DETAILED ASSESSMENT OF REDROOT PIGWEED (AMARANTHUS RETROFLEXUS) AND COMMON RAGWEED (AMBROSIA ARTEMISIIFOLIA) SEED SHATTERING IN WHEAT, CORN AND SOYBEAN. M. Simard*1, R. E. Nurse2, E. R. Page3, G. Bourgeois4, H. J. Beckie5; 1Agriculture and Agri-Food Canada, Quebec, QC, 2Agriculture Canada, Harrow, ON, 3Agriculture and Agri-Food Canada, Harrow, ON, 4Agriculture and Agri-Food Canada, Saint-Jean-sur-Richelieu, QC, 5Agriculture and Agri-Food Canada, Saskatoon, SK (198)

ABSTRACT

New cases of herbicide resistance are reported on a regular basis. Managing newly discovered populations before seed dispersal will limit the spread of herbicide resistance. In such case, knowing to what extent seeds are already formed and shattered before any late weed control operation is envisioned is essential. Our goal was to assess the seed shattering phenology of weed species that have documented herbicide resistant biotypes in field crops. Trials were conducted in two locations in Eastern Canada (St-Jean-sur-Richelieu, QC and Harrow, ON) in 2014. At each location, three adjacent fields were planted with spring wheat, soybean or corn. Each field was divided into four blocks that included four plots (3 x 4 m-2) and a target weed density of five weeds m-2 planted on the same date as the crop or when crop plants had two leaves. Plots were seeded with redroot pigweed or common ragweed. The experiment also included up to twelve weekly weed collection dates (subplots, 1 m-2). In each subplot, four weeds were individually bagged at flowering (using mesh bags) until collection. Weather data as well as crop and weed stages were recorded during the growing season. For each weed collection date, the number of shattered and unshattered seeds per plant was recorded. The viability of the collected seeds was also tested. Later emerging redroot pigweed plants flowered later while the flowering date of ragweed plants was unaltered. The phenological development of weeds was similar in both corn and soybean. In wheat, only pigweed plants that emerged early (first seeding date) produced some seeds before harvest at one location (QC). Although seed shattering started as soon as filled seeds were observed, most pigweed seeds were on plants at harvest in any crop (around 80%). Common ragweed shattered a higher percentage of seeds as the season progressed.

 


EFFECTS OF ALTERNATIVE FORAGE CROP MIXTURES ON THE ABUNDANCE AND FUNCTIONAL COMPOSITION OF WEED COMMUNITIES. R. G. Smith*, N. D. Warren, K. Juntwait, S. Crook; University of New Hampshire, Durham, NH (199)

ABSTRACT


WEEDS AS INDICATOR OF THE AGROECOSYSTEM BIODIVERSITY IN TRADITIONAL TEA-GRASS INTEGRATED SYSTEM IN JAPAN. H. Inagaki*; Shizuoka University, Shizuoka, Japan (200)

ABSTRACT


PALMER AMARANTH IN SOUTH DAKOTA. S. A. Clay*1, M. Erazo-Barradas2, B. Van de Stroet2; 1South Dakota State University, Brookings, SD, 2SDSU, Brookings, SD (201)

ABSTRACT

Palmer amaranth (Amaranthus palmeri) is a native southern weed that has been extending its range northward.  This study’s objectives were to 1) examine areas in South Dakota to determine if Palmer amaranth is becoming a SD problem and 2) examine Palmer amaranth growth under South Dakota environmental conditions (through controlled field experiments) and compare among common pigweed species (redroot pigweed and common waterhemp).  Three planting dates were used, early, mid, and late over a 6-week span.  Unfortunately, Palmer waterhemp was found in three areas of southern South Dakota, in sunflower fields [near Martin (far west) and near Chamberlain, (central)] and in a soybean field [near Mitchell (east-central)].  The soybean infestation was thought to come from hog manure with hogs originally from Texas with the manure spread as a fertilizer.  The other infestations were not traced to source.  Plants were grown from seed taken from Mitchell plants and were found to be Round-up resistant.  Palmer amaranth grew all too well in South Dakota conditions, with early emerging plants extremely robust.  Plants all flowered about the same time.  In 2014, an early frost (Sept 7) did not allow seeds to mature.  This was not a problem in 2015.

 


PALMER AMARANTH DEMOGRAPHICS IN WIDE-ROW SOYBEAN. N. E. Korres*, J. K. Norsworthy, J. Green, J. Godwin Jr., S. Martin, Z. Lancaster; University of Arkansas, Fayetteville, AR (202)

ABSTRACT

Knowledge of Palmer amaranth (PA) biology, demographics, and population dynamics is essential for development efficient weed management systems. A two-year field experiment in a complete randomized block design was conducted at Fayetteville, AR to investigate the effects of intraspecific competition on PA demographics in wide-row soybean. A glufosinate-resistant soybean cultivar was planted in 76-cm wide, four-row plots at 260,000 seeds/ha on June 25, 2015. Pots were 3.6 m wide by 6 m long. A few days after crop planting, PA seeds were hand-spread along the middle two rows at predetermine targeted densities and slightly covered with sieved fine soil. PA targeted densities were 1, 10, 100, 1000 and 10000 plants/m2. A 1 m2 quadrat was established in the center of each plot to monitor PA emergence and survival through soybean harvest. Palmer amaranth plants within the quadrat were counted at 10 days after emergence (DAE) intervals (i.e. 20, 30, 40, 55, 65, 75 DAE). Experimental plots were routinely hand-weeded to remove unwanted broadleaf, grasses, and sedges and were irrigated when rainfall did not occur within a two-week period. Palmer amaranth plants emerged a few days earlier than soybean, but targeted densities were underachieved, in the second experiment, due to heavy rains that occurred a few days after planting. A hierarchical cluster analysis was used to group Palmer amaranth densities for further analysis. Four clusters were determined which were 700-1200, 190-400, 90-120, and 30-70 plants/m2. The age-specific mortality rates were determined using Time Tables for each Palmer amaranth cluster. All Palmer amaranth plants appear to be vulnerable in the first three age classes (20, 30 and 40 DAE) with a peak in the second age class. The higher the Palmer amaranth density the higher the mortality of the population as a result of intraspecific and interspecific competition.


LATE-SEASON SEED PRODUCTION POTENTIAL IN PALMER AMARANTH IN SOUTHERN US. V. Singh*1, J. K. Norsworthy2, P. A. Dotray3, M. V. Bagavathiannan1; 1Texas A&M University, College Station, TX, 2University of Arkansas, Fayetteville, AR, 3Texas Tech University, Lubbock, TX (203)

ABSTRACT

Palmer amaranth and waterhemp are two of the economically damaging and difficult-to-control weeds in the United States. While efforts are implemented to manage these species within crops, little emphasis is placed on managing seedlings that recruit after crop harvest. The aim of this study was to determine the post-harvest seed production potential of Palmer amaranth and waterhemp. Field experiments were conducted across three locations (College Station and Lubbock, TX, and Fayetteville, AR) and two years (2014, 2015). All the three sites included Palmer amaranth in both years, whereas waterhemp was studied at two locations (College Station and Fayetteville) in 2014 and at one location (College Station) in 2015. Seed production was determined on seedlings recruited at weekly intervals from late-summer until the first killing frost. At the termination of the experiment, seedlings pertaining to each cohort were harvested separately, dried, and thrashed to determine seed production on each cohort. Palmer amaranth and waterhemp exhibited high levels of plasticity in seed production, with greater fecundity in 2014 compared to 2015. The average Palmer amaranth seed production/plant for the first cohort was 19510 (emergence at the 33rd Julian week, Aug 13-19), 266 (36th week) and 2 (36th week) in 2014, and 210, 167 and 175 (emergence during 34th Julian week) in 2015, at College Station, Lubbock, and Fayetteville, respectively. Palmer amaranth produced mature seeds when seedlings emerged as late as the 41st week in College Station, 40th in Lubbock, and 37th week in Fayetteville, in both years (2014 and 2015). Waterhemp, when emerged at the 36th week, produced 824 seeds in College station and no seed in Fayetteville in 2014. In 2015, waterhemp produced 204 seeds in College Station and 195 seeds in Fayetteville when emerged at the 34th week.  Results demonstrate that Palmer amaranth and waterhemp seedlings that emerge after crop harvest in the southern US can add substantial amount of seed to the soil seedbank, though the level of seed addition can be variable across environments. Effective management of these species will require the management of late-season recruits.

 


DISTRIBUTION OF MULTIPLE HERBICIDE-RESISTANT KOCHIA IN MONTANA. V. Kumar*, P. Jha, C. A. Lim, A. J, S. Leland; Montana State University-Bozeman, Huntley, MT (204)

ABSTRACT

Evolution and rapid spread of herbicide-resistant (HR) kochia is an increasing concern for growers in the US Great Plains. After the confirmation of glyphosate-resistant (GR) kochia in Montana, random field surveys were conducted in 2013 through 2015 to determine the distribution, frequency, and levels of resistance to most commonly used herbicides (glyphosate, dicamba, ALS-inhibitors) in cereal production systems. Over the three years, approximately 200 kochia populations were collected from different Counties in northern Montana. Fully-matured seeds from kochia plants were sampled from chemical fallow-wheat fields, organic wheat fields, field edges/fence lines, and roadsides. The collected kochia populations also included samples sent by growers. After threshing and cleaning, seeds from each kochia population were sown in germination flats filled with a commercial potting mix under greenhouse conditions at the MSU Southern Agricultural Research Center near Huntley, MT. Discriminate dose experiments were conducted by treating 80 kochia plants from each population with glyphosate (1260 g ae ha-1), dicamba (280 g ae ha-1), or thifensulfuron + tribenuron + metsulfuron (ALS-inhibitor) (18 g ai ha-1) at the 8- to 10-cm height. The frequency of resistant or tolerant individuals in a kochia population was determined for all three herbicides at 21 DAA. The confirmed HR populations were further characterized for levels of resistance to each herbicide by using the seeds obtained from the survivors (selfed plants) from the discriminating-dose experiments. Data on percent control was recorded at 7, 14, and 21 DAA, and shoot dry weight was determined at 21 DAA. Results indicated that 24 kochia populations were resistant to glyphosate, and frequency of GR individuals ranged from 33 to 100% in a population. The selected GR kochia populations showed 3- to 15-fold levels of resistance to glyphosate compared to the susceptible population in dose-response studies. Results from qPCR assay indicated that the confirmed GR populations had 3- to 11-fold increase in EPSPS (5-enol-pyruvylshikimate-3-phosphate synthase) gene copy number compared to the susceptible population (single EPSPS gene copy). Resistance to the ALS-inhibitor was observed in >95% of the surveyed kochia populations, and frequency of ALS-inhibitor-resistant individuals varied from 67 to 100% in a population. The selected ALS-resistant populations exhibited >30-folds level of resistance. Out of the total, fifteen kochia populations exhibited 1.5- to 7.1-fold levels of tolerance to dicamba, and frequency of dicamba-tolerant individuals varied from 5 and 51% in a population. Based on these results, multiple HR kochia populations (resistant to both glyphosate and ALS-inhibitors) are confirmed in Blaine, Choteau, Hill, Glacier, Liberty, and Toole Counties. Kochia populations with multiple resistance to dicamba and ALS-inhibitors are confirmed in Choteau, Liberty, and Glacier Counties from northern Montana. Growers should utilize multiple control tactics, including chemical and non-chemical (tillage and crop rotation) to manage multiple HR kochia in this region.

 

 


DEVELOPMENT OF GLYPHOSATE-RESISTANT ARABIDOPSIS LINES TO EXAMINE FITNESS EFFECTS OF OVER-EXPRESSING EPSPS. Z. Beres, A. A. Snow*, L. Jin, D. Mackey, J. Parrish; Ohio State University, Columbus, OH (205)

ABSTRACT

More than 30 weed species have evolved resistance to glyphosate, and at least six of these species (Amaranthus palmeri, A. tuberculatus, A. spinosus, Lolium multiflorum, Kochia scoparia, and Eleusine indica) derive resistance via amplification of the EPSPS gene. Resistant biotypes with gene amplification over-produce EPSPS (5-enolpyruvylshikimate-3-phosphate synthase), which is the target for glyphosate and a key metabolic enzyme of the shikimate pathway. To date, relatively few studies have examined potential fitness effects of over-producing EPSPS in the absence of exposure to glyphosate. To better understand these effects, we developed 9 independent, single-copy, homozygous T3 Arabidopsis thaliana lines (Col-0 background) that over-express EPSPS (OX), along with 9 corresponding empty vector lines (EV).  Agrobacterium tumefaciens strain GV3101 bearing either 35S::EPSPS or the empty vector (pB2GW7 alone) was used to transform Arabidopsis Col-0 by the floral dip method.  The T3 OX and EV transgenic lines were compared in two dose response experiments that included wild-type plants.  Glyphosate dosages ranged from 0x (control) to 16x (13.44 kg ae ha-1), with 3 replicates per treatment. Visual scores from 0 (no damage) to 10 (death) were recorded at 7, 14, and 21 days after treatment and were used in regression analyses with the drc package in R. In a third experiment, we used 0x vs. 1x glyphosate to compare visual damage and biomass of 20 plants per line three weeks after spraying.  As expected, these experiments confirmed that the EPSPS over-expression conferred varying levels of resistance to the OX lines, while the EV and wild-type lines remained susceptible to glyphosate.   Two OX lines had only weak resistance, possibly due to position effects of transgene insertion. Growth of the remaining OX lines was reduced by 67-86% at 1x when compared to their 0x controls. In contrast, all of the EV and wild-type plants in this experiment died following the 1x treatment.  We conclude that over-expression has been achieved in the OX lines based on enhanced resistance to glyphosate. Further studies to compare the growth and reproduction of over-expressed lines with empty vector lines and non-transgenic controls are in progress.


VALIDATION OF THE MODEL TO SIMULATE HERBICIDE RESISTANCE EVOLUTION IN BARNYARDGRASS (ECHINOCHLOA CRUS-GALLI L.) IN RICE-SOYBEAN PRODUCTION SYSTEMS. M. V. Bagavathiannan*1, J. K. Norsworthy2, K. Smith3, P. Neve4; 1Texas A&M University, College Station, TX, 2University of Arkansas, Fayetteville, AR, 3FMC/Cheminova, Groveton, TX, 4Rothamsted Research, Harpenden, England (206)

ABSTRACT

Barnyardgrass (Echinochloa crus-galli) is the most troublesome weed in rice production and is also the most dominant grass weed in soybean in southern US. Currently, barnyardgrass is resistant to at least five different herbicide modes of action used in Midsouth rice, leaving few herbicide options for effective control. A resistance simulation model was developed to predict the evolution of resistance to ALS-and ACCase-inhibitor herbicides in barnyardgrass. A long-term field experiment was conducted in Keiser, AR from Summer 2012 to spring 2015 to determine changes to the population dynamics of an ALS-inhibitor resistant barnyardgrass in response to different crop rotation and weed management treatments. The experiment was conducted in a split-plot arrangement involving two crop rotations in the main plot (rice-rice-rice and rice-soybean-rice) and three herbicide treatments in the subplot (non-ALS herbicide program, ALS-only herbicide program, and a diversified program tested in the model). One thousand seed of a known ALS-inhibitor resistant barnyardgrass population was introduced in each plot prior to the initiation of the experiment in 2012. Total seed production (each summer) as well as soil seedbank size (each spring) were estimated from four 1 m2 quadrats. Data obtained from this experiment were used to validate the resistance simulation model. Results of this three-year experiment showed that the diversified weed management program integrated with soybean rotation was the best treatment for controlling the resistant population compared to the other treatment combinations. The general trends in population size predicted by the model closely resembled field observations for each of the treatment evaluated.


DIFFERENTIAL MOLECULAR BASIS OF ENVIRONMENTAL ADAPTIVE DIVERSITY IN ECHINOCHLOA SPECIES. D. KIM*1, G. Nah1, J. Im1, A. Fischer2; 1Seoul National University, Seoul, South Korea, 2University of California, Davis, Davis, CA (207)

ABSTRACT

Echinochloa is a major weed that grows almost everywhere in farmed land. This high prevalence results from its high adaptability to various water conditions, including upland and paddy fields, and its ability to grow in a wide range of climates, ranging from tropical to temperate regions. Three Echinochloa crus-galli accessions (EC-SNU1, EC-SNU2, and ECSNU3) collected in Korea have shown diversity in their responses to flooding, with ECSNU1 exhibiting the greatest growth among three accessions. In the search for molecular components underlying adaptive diversity among the three Echinochloa crus-galli accessions, we performed de novo assembly of leaf transcriptomes and investigated the pattern of differentially expressed genes (DEGs). Although the overall composition of the three leaf transcriptomes was well-conserved, the gene expression patterns of particular gene ontology (GO) categories were notably different among the three accessions. Under nonsubmergence growing conditions, five protein categories (serine/threonine kinase, leucinerich repeat kinase, signaling-related, glycoprotein, and glycosidase) were significantly (FDR, q < 0.05) enriched in up-regulated DEGs from EC-SNU1. These up-regulated DEGs include major components of signal transduction pathways, such as receptor-like kinase (RLK) and calcium-dependent protein kinase (CDPK) genes, as well as previously known abiotic stress-responsive genes. qRT-PCR analysis of leaf samples of Echinochloa crus-galli and Echinochloa oryzicola grown under different flooding conditions revealed candidate genes responsible for environmental adaptive diversity in Echinochloa species. Our results thus suggest that diversified gene expression regulation of upstream signaling components conferred the molecular basis of adaptive diversity in Echinochloa species.


MODELING ECHINOCHLOA COLONA EMERGENCE UNDER NO TILLAGE SYSTEM BY MEANS OF THERMAL TIME. G. Picapietra, H. A. Acciaresi*; Instituto Nacional Tecnologia Agropecuaria, Pergamino, Argentina (208)

ABSTRACT

Junglerice (Echinochloa colona) is one of the most important summer crops weed in the Northwest of the Buenos Aires province (Argentina). It can cause large yield losses, as well as achieve early reproductive stage, which reduces the efficiency of chemical control. Seedling emergence was determined under field conditions during the period from September to January. The seedling emergence was carried out in two consecutive years in soybean field cultivated under non-tillage system. Metallic frames of 0.175 m2 in fixed stations were used. Emergence was adjusted to monomolecular model (non-linear) based on thermal time, which showed a good fit to the data obtained in both years (r2 2014 = 0.95, r2 2015= 0.875). For the beginning of the thermal time it is considered a calculation of average temperatures for the last 10 days show a decline and rise in temperature that occurs in late August. Reached 200 ° d can obtain 80% of the total weed emergence, coinciding with the end of October.


JUNGLERICE (ECHINOCHLOA COLONA) GROWTH AND DEVELOPMENT IN RESPONSE TO TEMPERATURE AND SHADE. L. M. Sosnoskie*1, A. Ceseski1, S. Parry2, A. Shrestha2, B. D. Hanson1; 1University of California, Davis, Davis, CA, 2California State University, Fresno, CA (209)

ABSTRACT

Glyphosate-resistant junglerice (Echinocloa colona) in orchards and vineyards is a significant concern as there are few herbicide options registered for its control, relative to non-specialty crop systems. It is, therefore, critical to understand the biological and physiological factors driving the evolution and spread of this species in order to develop effective and economical management options. In 2015, we conducted several experiments to describe the germination, growth, and development of seven (A3, A8, C6, H5, L2, N3, SV2) junglerice accessions from California to differing temperature (15, 20, 25, 30, 35, 40°C) and light conditions (0, 30, and 60% shade) that could be encountered in tree and vine crops throughout the Central Valley.

Temperature and germination: Junglerice seed were scarified in concentrated sulfuric acid for 30 minutes; 50 seeds of each biotype were placed in Petri dishes containing 7.0mL of 0.2% Captan fungicide solution. The Petri dishes were held in nested cardboard flats to exclude intense, direct light and minimize desiccation potential.  Seed germination was monitored, daily; a seed was considered germinated when the protruded radicle was as long as the length of the seed coat. Germinated seeds were counted and then discarded at each observation point. Results showed that the rate of seed germination increased with increased temperature. All biotypes reached 50% germination 2-4 days after plating for all temperatures except 15°C, where it took 5-37 days to reach 50% germination. Maximum germination was reached by 49 days after plating for all biotypes at 15°C; by 40 days for all biotypes, but L2, at 20°C; and by 5 days for most biotypes at temperatures between 25-40°C. This study is currently in the process of being repeated.

Temperature and growth: Seedlings of each biotype were planted in 1600 cm plastic pots filled with a mixture of peat, compost, sand and perlite, grown out to the 3-tiller stage, and then placed into growth chambers programmed to constant temperatures between 20-40°C. Plant growth and development was monitored for 28 days after which each specimen was destructively harvested and the aboveground biomass separated into three, distinct tissue classes: stems, leaves, and panicles. Results from this experiment demonstrated that junglerice growth and development can occur over a wide range of temperatures (20-40°C). Maximum basal stem production occurred at 25°C and ranged from 37 stems/plant (C6) to 67 stems/plant (SV2) with an average (across accessions) of 53 stems per plant. Per plant panicle production was greatest at 30-35°C; maximum panicle production ranged from 18 panicles per plant (C6) to 45 panicles per plant (N3) with an average maximum production of 24 panicles per plant (across all accessions). This study is currently being repeated in its entirety.

Light quantity and growth: In the summer of 2015, two to three seedlings (at the three tiller stage) of each biotype were transplanted into field plots (1 m wide by 15 m long) that were exposed to either full sunlight (0% shade) or 30% and 60% shade environments. The shade treatments were established by covering the entire plots with black, plastic fabric of differing mesh size on PVC frames. Plant growth and development was monitored for four weeks after which each specimen was destructively harvested. Each shade environment was replicated three times and the entire study was conducted at two locations: UC Davis and CSU Fresno. With few exceptions, junglerice plants were largest when gown in full sunlight. In general, tissue number and biomass (stem, leaf, panicle) decreased as the amount of transmitted light decreased. For example, tiller number per plant averaged between 79 and 134 at 0% shade; at 30% shade, tiller number ranged from 62 to 88 per plant; at 60% shade, the mean number of tillers per plant did not exceed 61. Similar observances were made with respect to leaf number and panicle production. Knowledge of the growth and development of junglerice under different environmental conditions is critical for understanding the species’ invasive potential. Results from our study show that junglerice populations collected from the Central Valley of California can grow and develop under a range of temperatures and light environments. Continuing analyses will help us describe how multiple environmental variables affect the potential for junglerice invasion across a diverse array of habitats.

 


POPULATION GENETICS AND STRUCTURE OF BROMUS TECTORUM FROM WITHIN THE SMALL GRAIN PRODUCTION REGION OF THE PACIFIC NORTHWEST. I. C. Burke*, N. Lawrence, A. Hauvermale; Washington State University, Pullman, WA (210)

ABSTRACT

Despite the wealth of information regarding downy brome population genetics, previous studies have not focused on, or made comparisons of downy brome genetics as it persist in agroecosystems. The lack of downy brome population genetic studies within agroecosystems is significant given downy brome is a widely distributed and serious pest in small grains and other crops across western North America. Additionally, the yearly disturbance of tillage, planting, and herbicide applications may drive selection on downy brome genotypes differently from the forces acting in non-agronomic ecosystems. It is likely that downy brome exists as an assemblage of unique but inbreed biotypes within agronomic fields. The objectives of this study were to assess the genetic variability of downy brome sourced exclusively from within small grain production regions of the Pacific Northwest (PNW). Population genetics metrics were calculated and population structure estimated using a genotyping-by-sequencing (GBS) approach. Of particular interest is if downy brome persists within the small grain production regions of the PNW as specialist or generalist genotypes, and if downy brome genotype distribution is driven by climatic factors or grower practices. Downy brome population genetics and genetic structure from within an agronomic system indicates that the heterozygous state of downy brome is similar, if not marginally greater, to what has been reported in previous literature. Additionally, downy brome exists within the PNW small grain production region as a series of generalist genotype clusters with limited evidence of spatial adaptation. Given the apparent random spatial distribution of downy brome clusters at the spatial scale of this analysis, unique genotypes may be well mixed within small grain fields. 


VARIATION IN PHENOLOGY AND VERNALIZATION REQUIREMENTS OF BROMUS TECTORUM COLLECTED FROM THE SMALL GRAIN PRODUCTION REGION OF THE PNW. A. Hauvermale*, N. Lawrence, I. C. Burke; Washington State University, Pullman, WA (211)

ABSTRACT

Bromus tectorum (downy brome) is arguable one of the worst invasive weed species in both natural and agronomical environments in the United States. Phenological variation is a key factor in the success of the species as a competitor in small grain production regions of the inland Pacific Northwest (PWN). Prior research characterized vernalization and flowering time requirements of downy brome collected from different environments, but no previous work has focused on the connection between such phenotypic responses with the genotypic control of vernalization. A series of common garden experiments was conducted involving 85 accessions of downy brome collected from within small grain production fields of Washington, Oregon, and Idaho. Results of previous common garden experiments identified differences in time to flowering of up to 19 d and time required for mature seed production of up to 21 d among accessions with little variation among siblings. From the common garden experiments cumulative growing degree days required for mature seed production for each accession was estimated using non-linear regression. Variation in vernalization requirements of related species have been attributed in part to variation of the vernalization gene VRN1. Quantifying the expression of a downy brome VRN1 orthologue may help explain the genetic controls regulating observed differences in vernalization. A series of greenhouse experiments was conducted to characterize the vernalization requirements of downy brome accessions demonstrating differences in development and flowering time, and to determine if differences in expression of VRN1 orthologues is associated with differences in flowering time. Semi-quantitative PCR was used measure VRN1 expression in eight downy brome accessions with different vernalization requirements. Expression of a VRN1 orthologue was only observed in treatments were flowering occurred, suggesting that the molecular controls regulating vernalization and flowering in downy brome are likely conserved with those in related species.

 


INFLUENCE OF SELECTED ENVIRONMENTAL FACTORS ON THE ARID ZONE INVASIVE SPECIES NICOTIANA GLAUCA R GRAHAM (TOBACCO BUSH) SEED GERMINATION AND DECADE LONG POPULATION DYNAMICS AFTER FLOOD EVENT. S. Florentine*; Federation University Australia, Victoria, Australia (212)

ABSTRACT

Influence of selected environmental factors on the arid zone invasive species tobacco tree (Nicotiana glauca R. Graham) seed germination

S. K. Florentine, S. Weller, T. Simpson, M. E. Westbrooke, and N. Fernando

*First, second, third, fourth and fifth authors: Associate Professor, Higher Degree Student, Research Associate, Professor and Post Doctorate. Centre for Environmental Management, Faculty of Science and Technology, Federation University Australia, PO Box 663, Victoria 3350, Australia.

 

Abstract

Tobacco tree is an aggressive invader after disturbances such as high rainfall events and flooding. Previous studies focused population dynamic and allelopathic effect but little was known about the seed ecology. The objectives of this study were to investigate the threshold level of temperature for seed dormancy loss of determine the effect of temperature and photoperiod, osmotic, salt stress, heat, heat + smoke pH buffer and burial depth of tobacco tree seed and determine the fate of this invasive species seeds when over mature. Our study shows that tobacco tree was able to germinate over a broad range of temperatures with highest seed germination percentage in 30/20 OC 12 h of light and 12 h dark conditions. Tobacco tree seedling emergence was greatest (89%) when seeds were placed on the soil surface but decreased considerably as planting depth increased from 0.5 to 1.5 cm. Water stress reduced seed germination (58% germination at osmotic potentials below — 0.2 MPa and was completely inhibited at water potentials of — 0.4 to — 0.6 MPa. Similarly, increasing salinity reduced the seed germination of this invasive species, however, Tobacco tree seed can germinate in both alkaline (pH 10 – 81%) and acidic (pH 4 – 80%) conditions. Finally, our study on the effect of seed age and field burial on seed germination shows a slight decline after 140 days of burial compared with un buried seeds. Studies such as this will assist in the development of control strategies of this invasive species into arid landscapes.

Corresponding author’s E-mail: s.florentine@federation.edu.au

Nomenclature: Tobacco tree, Nicotiana glauca R. Graham

Keywords: Australia, arid zone, Germination, weed.

 


DO CHANGES IN RED/FAR-RED RATIO MODIFY SUSCEPTIBILITY TO UV-B RADIATION? L. Ma*1, C. J. Swanton2, M. K. Upadhyaya1; 1University of British Columbia, Vancouver, BC, 2University of Guelph, Guelph, ON (213)

ABSTRACT

Do Changes in Red/Far-red Ratio Modify Susceptibility to UV-B Radiation?

Li Ma*, Clarence J. Swanton** and Mahesh K. Upadhyaya*, *University of British Columbia, Vancouver and ** University of Guelph, Canada.

In order to determine if red/far-red (R/FR) ratio influences the response of plants to UV-B radiation and if a change in anthocyanin concentration induced by exposure to lower R/FR ratio is involved in this effect, corn (Zea mays L.), lettuce (Lactuca sativa L.), amaranth (Amaranthus tricolor L.) and redroot pigweed (Amaranthus retroflexus L.) seedlings were grown under two different (0.3 and 1.1) R/FR ratios for one or two weeks in growth chambers and then transferred to three levels of UV-B radiation in a greenhouse. Different levels of UV-B radiation were achieved by filtering radiation from ten 40 W UVB-313 fluorescent tubes with 1 (high UV-B), 2 (medium UV-B) and 3 (low UV-B) layers of cellulose acetate film. Anthocyanin pigment, which is present in the leaf sheath of corn, was extracted with acidified methanol and estimated using the difference between A530 and A657. Digital image analysis (Image J software) and red/green ratio were used to estimate anthocyanin concentration in lettuce, amaranth and pigweed leaf lamina. Anthocyanin concentration in leaf sheaths of corn grown under low R/FR ratio (0.3) for seven days was 60% lower (P < 0.05) compared to high R/FR ratio (1.1). Anthocyanin concentration in leaf  lamina of lettuce, amaranth and pigweed grown under low R/FR ratio for two weeks decreased by 3%, 16%, 27% (P < 0.05) respectively, compared to those grown under high R/FR ratio. UV-B exposure influenced a variety of plant growth parameters (e.g. height, biomass, and leaf area, length, width and weight) in these species. Interestingly, R/FR treatments prior to UV-B exposure and the associated change in anthocyanin concentration did not modify the plant response to UV-B radiation. This suggests that differences in R/FR ratio, which can result from a change in planting density or shading and the associated change in anthocyanin pigment concentration do not influence the response of corn, lettuce, amaranth and pigweed seedlings to elevated levels of UV-B radiation. This finding is significant to our understanding of plant-plant interactions in ecosystems where both R/FR ratio and UV-B levels are fluctuating. 

 


GLYPHOSATE RESISTANCE IN ORCHARDS IN GREECE: CURRENT SITUATION, MECHANISM OF RESISTANCE AND FUTURE PROBLEMS. D. Chachalis*1, E. Tani2, I. S. Travlos2, D. Bilalis2; 1Benaki Phytopathological Institute, Athens, Greece, 2Agricultural University of Athens, Athens, Greece (214)

ABSTRACT


KHELLIN AND VISNAGIN, FURANOCHROMONES FROM AMMI VISNAGA (L.) LAM., AS POTENTIAL BIOHERBICIDES. M. L. Travaini*1, N. J. Corrilla1, E. A. Ceccarelli1, H. Walter2, G. Sosa3, C. L. Cantrell4, K. M. Meepagala4, S. O. Duke5; 1National University of Rosario, Rosario, Argentina, 2AgroField Consulting, Obrigheim, Germany, 3INBIOAR, Rosario, Argentina, 4USDA, Oxford, MS, 5USDA-ARS, Stoneville, MS (215)

ABSTRACT

There is an increasing demand for new molecules that serve as lead structures for the development of herbicides. Plants natural products provide an attractive alternative in finding effective and environmentally safe phytotoxic compounds with high structural diversity and novel modes of action. Considering this situation, a systematic process of searching, evaluation and selection was developed in order to find plant extracts with promising phytotoxic activity.

As a result of this screening process involving nearly 2400 plant extracts of plants from different regions of Argentina, a dichloromethane extract of toothpick weed (Ammi visnaga (L.) Lam.) was selected for further study because of its significant herbicidal activity. Phytotoxicity assay-guided fractionation yielded two furanochromones: khellin and visnagin. These compounds have been previously reported in toothpick weed, but their herbicidal activity had not been described before.

Khellin and visnagin significantly inhibited the development of lettuce (Lactuca sativa) (germination IC50 = 700 and 740 µM, repectively; growth IC50 = 110 and 170 µM, respectively) and duckweed (Lemna paucicostata) (growth IC50 = 160 and 120 µM, respectively). In laboratory bioassays in Petri dishes, both compounds at 1 mM strongly interfered with growth and germination of weeds: ryegrass (Lolium perenne), morningglory (Ipomea spp.), foxtail (Setaria italica) and millet (Panicum spp.). The natural compounds’ inhibitory effects were similar to those caused by acetochlor (0.54 mM) and glyphosate (0.75 mM) in the same bioassays.

Visnagin showed the most promising activity. It had significant contact post-emergence herbicidal activity on velvetleaf (Abutilon theophrasti) and crabgrass (Digitaria sanguinalis) during greenhouse tests at 2 kg ai ha-1. Moreover, its effects at 4 kg ai ha-1 against velvetleaf, crabgrass and barnyardgrass (Echinochloa crus-galli) were comparable to the bioherbicide pelargonic acid at the same rate. These results support visnagin’s potential as bioherbicide or lead for the development of a new herbicide.

Physiological assays suggest that the mode of action of these furanochromones involves multiple targets: membrane destabilization, photosynthetic efficiency reduction, and cell division inhibition. Although the membrane destabilization was greater after an irradiation period, the phytotoxic activity of these natural compounds was not light-dependent.

In conclusion, the plant extract screening method developed in this work enabled the identification of two natural compounds, visnagin and khellin, whose herbicidal activity is hereby reported for the first time.


CONFIRMATION OF PROTOPORPHYRINOGEN OXIDASE RESISTANCE IN AN INDIANA PALMER AMARANTH POPULATION. D. J. Spaunhorst*, W. G. Johnson; Purdue University, West Lafayette, IN (216)

ABSTRACT

A greenhouse experiment was conducted to determine if Indiana Palmer amaranth populations are resistant to protoporophyrinogen oxidase inhibiting herbicides. A total of 42 Palmer amaranth populations were collected from 18 Indiana counties over a two year period. Fomesafen was applied to Palmer amaranth at 350 or 1,052 g ae ha-1 plus 1% v/v of COC at the 6 to 8 true leaf growth stage. Fomesafen applied at 350 g ae ha-1 provided 100% control of Palmer amaranth from 50% of counties screened. Moreover, 1,052 g ae ha-1 of fomesafen controlled 100% of Palmer amaranth from 11 out of 18 counties. All Palmer amaranth populations were controlled more and had fewer alive plants after treatment of 1,052 g ae ha-1 compared to 350 g ae ha-1 of fomesafen. However, increased Palmer amaranth control was not observed with a population from Daviess County Indiana. Future research is planned to evaluate the magnitude of PPO-resistance and heritability of the resistance trait in the Daviess County population.                   

 


HERBICIDE RESISTANCE IN-SEASON QUICK ASSAY FOR ITALIAN RYEGRASS AND ANNUAL BLUEGRASS. J. C. Argenta1, R. A. Salas*1, N. R. Burgos1, J. T. Brosnan2; 1University of Arkansas, Fayetteville, AR, 2University of Tennessee-Knoxville, Knoxville, TN (217)

ABSTRACT

Italian ryegrass (Lolium perenne ssp. multiflorum) and annual bluegrass (Poa annua) are cool-season winter annuals that are troublesome in cool-season crops and turfgrass. These weeds are a concern due to the evolution of resistance to various herbicides. Italian ryegrass is a principal problem in wheat production fields and had evolved resistance to glyphosate, ACCase- and ALS-inhibiting herbicides. Simazine-resistant annual bluegrass has plagued golf courses in the southeastern US.  Resistance confirmation is usually done using seedlings grown in pots, but this method is relatively time-consuming and laborious, requires a lot of greenshouse space, and is only applicable to seeds collected post-herbicide treatment at the end of the growing season. Syngenta has developed a resistance in-season quick assay to detect pinoxaden resistance in Italian ryegrass. This research aimed to expand the quick assay for detecting resistance to ACCase (diclofop) and ALS (mesosulfuron and pyroxsulam) herbicides in Italian ryegrass and simazine in annual bluegrass. The objective of this study is to determine the discriminating herbicide rate that could distinguish a resistant from a susceptible plant. Seedlings at 1-3 leaf stage were transplanted onto Petri dishes containing agar with different concentrations of herbicides, incubated in a growth chamber under fluorescent lights at 21°C, and evaluated for mortality and injury after 10 days. Each Petri dish contained 4 seedlings with 16 plants evaluated per herbicide treatment. The experiment was conducted twice. The ranges of herbicide concentrations were 0-80 µM diclofop, 0-210 µM mesosulfuron, and 0-200 µM pyroxsulam and simazine. At 70 µM discriminating rate of diclofop, the susceptible Italian ryegrass seedlings were completely controlled, but resistant plants were actively growing. Root development was the major discriminating response between ALS-susceptible and -resistant plants. At 120 µM mesosulfuron and 40 µM pyroxsulam, ALS-resistant Italian ryegrass seedlings had healthy new roots whereas susceptible seedlings had reduced or no root growth. The discriminating rate for simazine was 80 µM. At this concentration, simazine-resistant annual bluegrass had healthy shoots and new roots whereas the susceptible plants had chlorotic leaves and inhibited root development. This herbicide resistance in-season quick assay is a  simple, space-efficient, cost-effective, and robust method that can be used in detecting herbicide resistance in Italian ryegrass and annual bluegrass early in the growing season, allowing growers to adjust weed management decision for effective weed control. 

 


MULTIPLE HERBICIDE RESISTANCE IN KANSAS  . P. W. Stahlman*, J. Jester; Kansas State University, Hays, KS (218)

ABSTRACT

Kochia (Kochia scoparia) and Palmer amaranth (Amaranthus palmeri) are among common broadleaf weeds in Kansas that have evolved resistance to one or more herbicide sites of action. Though most confirmed cases involve resistance to a single site of action, in recent years multiple site of action resistance has been confirmed in multiple states/provinces in both species.  In fall 2014, seed was collected from 40 ± 5 Palmer amaranth plants in each of 157 fields in 24 southcentral and northwestern Kansas counties and composited into one sample per field (accession) after drying and cleaning.  All seed was placed in cold storage (-0 C) for approximately 3 months and then moved to storage at room temperature.  In spring 2015, each accession was seeded into 10 by 10 cm plastic pots filled with commercial potting mix and grown in a greenhouse with 14-h photoperiod. Sunlight was supplemented with artificial illumination. When approximately 6- to 9-cm tall, plants were sprayed with a dose of 870 g ha-1 glyphosate and 1% w/v ammonium sulfate.  Each pot contained a minimum of 10 plants.  At 7 days after spraying, the number of living and dead plants were counted.  All plants in 31% of the accessions died (susceptible), whereas 69% of the accessions were either segregating or completely resistant to glyphosate. Subsequently, four accessions from each of five counties were tested further for resistance to chlorsulfuron (26 g ha-1), 2,4-D (870 g ha-1), and glyphosate (1100 g ha-1). Thirteen of the 20 accessions were resistant to glyphosate and all 20 accessions were resistant to chlorsulfuron.  2,4-D injured all plants of all accessions. However, of the 13 accessions that were resistant to both glyphosate and chlorsulfuron, more than 50% of plants in each of seven accessions survived 2,4-D treatment and began recovering after 3 wk. Additional testing is being conducted on those and other accessions.    


AN UPDATE ON MISSISSIPPI STATE-WIDE HERBICIDE RESISTANCE SCREENING IN PIGWEED (AMARANTHUS) POPULATIONS. V. K. Nandula*; USDA-ARS, Stoneville, MS (219)

ABSTRACT

Herbicide resistant pigweed (Amaranthus spp.) populations are widely distributed across Mississippi. These populations comprise of glyphosate resistant (GR) and/or acetolactate synthase (ALS)-inhibitor(s) resistant Palmer amaranth, GR tall waterhemp, and GR spiny amaranth. In 2014, tests for resistance to protoporphyrinogen oxidase (PPO)-inhibitors in approximately 200 pigweed accessions (both GR and non GR) comprising Palmer amaranth, tall waterhemp, spiny amaranth, and redroot pigweed, collected across all counties of the state, indicated variable survival of POST treatments of fomesafen and/or lactofen. None of the pigweed accessions emerged through a PRE flumioxazin treatment.  Additional resistance screening tests on 120 of the above accessions were conducted in 2015 with POST applications of atrazine (PS II inhibitor) and pyrithiobac (ALS inhibtor).  Of these, 70% (majority redroot pigweed) were resistant to atrazine, 47% (majority Palmer amaranth) were resistant to pyrithiobac, and 15% were resistant to both. In just concluded greenhouse studies (2015-16), resistance to fomesafen was detected in 76% of 50 populations collected from suspect fields across the Mississippi Delta (a 17-19 county area in the northwestern part of the state where 70% of the state’s row crop production is practiced). In a separate line of research, a Palmer amaranth X spiny amaranth hybrid was confirmed resistant to several ALS inhibitors including imazethapyr, nicosulfuron, pyrithiobac and trifloxysulfuron. Enzyme assays indicated that the ALS enzyme was insensitive to pyrithiobac and sequencing revealed the presence of a known resistance conferring point mutation Trp574Leu. Alignment of the ALS gene for Palmer amaranth, spiny amaranth, and putative hybrids revealed the presence of Palmer amaranth ALS sequence in the hybrids rather than spiny amaranth ALS sequences. In addition, sequence upstream of the ALS in the hybrids matched Palmer amaranth and not spiny amaranth. This is the first report of gene transfer for ALS inhibitor resistance documented to occur in the field without artificial/human intervention.


MOLECULAR SCREENING FOR RESISTANCE TO PPO INHIBITORS IN PALMER AMARANTH (AMARANTHUS PALMERI). P. J. Tranel*1, J. Song1, C. Riggins1, N. Burgos2, J. Martin3, L. Steckel4; 1University of Illinois, Urbana, IL, 2University of Arkansas, Fayetteville, AR, 3University of Kentucky, Lexington, KY, 4University of Tennessee, Jackson, TN (220)

ABSTRACT

Resistance to protoporphyrinogen oxidase (PPO) inhibitors was first identified in waterhemp (Amaranthus tuberculatus) in 2000, and since has been reported in only a small number of additional species. In waterhemp, resistance to PPO inhibitors is due to deletion of three nucleotides in the PPX2 gene, resulting in deletion of glycine at position 210 (G210) of the encoded PPO enzyme. To date, this is the only known mechanism of resistance to PPO inhibitors in waterhemp, and has been identified in numerous populations from numerous states. The nucleotide sequence within and adjacent to the G210 codon (specifically, tri-nucleotide repeats) likely fosters the occurrence of this unusual mutation. Because the same tri-nucleotide repeats were identified at the homologous position of Palmer amaranth PPX2, it was predicted that the same resistance-conferring mutation would arise in this species as well. Since the widespread occurrence of glyphosate resistance in Palmer amaranth, this species has undergone extensive selection for resistance to the PPO inhibitors. During the 2015 growing season, several Palmer amaranth populations were suspected of resistance to PPO inhibitors. Using a PCR-based molecular marker, the G210 deletion was identified in some of these Palmer amaranth populations. Because prior research using a transgenic approach demonstrated that the G210 deletion is sufficient to confer resistance to PPO inhibitors, its identification in Palmer amaranth populations provides strong confirmation that they are indeed resistant. Based on this approach, resistance to PPO inhibitors has now been confirmed in Palmer amaranth populations from Arkansas, Kentucky, and Tennessee. It remains unknown if the PPO G210 deletion is the predominant resistance mechanism in Palmer amaranth, as is the case with waterhemp, or if other mechanisms of resistance to PPO inhibitors are common in Palmer amaranth.


GEOGRAPHIC DISTRIBUTION OF EPSPS COPY NUMBER VARIATION IN PALMER AMARANTH (AMARANTHUS PALMERI). J. Hart*1, E. Mutegi1, M. Loux1, M. Reagon2; 1Ohio State University, Columbus, OH, 2Ohio State University, Lima, Lima, OH (221)

ABSTRACT

Palmer amaranth (Amaranthus palmeri) is an annual forb that is native to the southwestern United States and northwestern Mexico. In the past century, A. palmeri has experienced a great range expansion and has become a significant weed in many agricultural systems throughout the southeastern, central, and eastern United States. Much of this range expansion has been attributed to the evolution of glyphosate resistance due to an increase in the number of copies of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene. In this study, we compared EPSPS copy number variation using q-PCR and resistance to glyphosate in 20 populations sampled from across the current geographic range of A. palmeri. We also included historic samples that were collected prior to the widespread planting of glyphosate resistance crops and from within the original range of A. palmeri. We found considerable geographic variation both in EPSPS copy number and glyphosate resistance.  Consistent with previous studies we found a correlation between EPSPS copy number and glyphosate resistance. Interestingly, both resistant and susceptible individuals could be found within the same population in several locations. In particular, recently introduced populations in Ohio contained both glyphosate resistant and susceptible individuals. Our results suggest that factors other than glyphosate resistance may have contributed to the range expansion of A. palmeri.


INCREASED HPPD GENE AND PROTEIN EXPRESSION CONTRIBUTE SIGNIFICANTLY TO MESOTRIONE RESISTANCE IN PALMER AMARANTH (AMARANTHUS PALMERI) . S. Betha, C. R. Thompson, D. E. Peterson, M. Jugulam*; Kansas State University, Manhattan, KS (222)

ABSTRACT

Extensive genetic variability coupled with intense herbicide selection in Palmer amaranth resulted in the evolution of resistance to multiple herbicides, including hydroxyphenylpyruvate dioxygenase (HPPD)-inhibitors such as mesotrione, in US Midwestern states, KS and NE. We previously reported that the mesotrione resistance in these Palmer amaranth populations was not due to reduced absorption or translocation of mesotrione; however, at 24 hours after treatment, more than 90% of 14C-mesotrione was metabolized to polar compounds. The objective of this study was to examine if increased HPPD gene and protein expression contribute to mesotrione resistance in Palmer amaranth populations from KS (KSR) and NE (NER) using known susceptible populations from MS (MSS), KS (KSS) and NE (NES) as the control. Quantitative PCR analysis on cDNA (using β-tubulin as an endogenous control) showed at least 5-12 and 5-10 fold increase in HPPD gene expression in KSR and NER, respectively, compared to MSS, KSS and NES. Furthermore, immunoblot analyses showed increased HPPD protein levels which correlate with mRNA expression levels of HPPD gene. Overall, these results suggest that in addition to rapid metabolism, increased HPPD gene and protein expression significantly contribute to mesotrione resistance in Palmer amaranth. To our knowledge, this is the first case of field-evolved resistance to mesotrione as a result of both non-target (rapid metabolism) and target-based (increased HPPD gene expression) modifications in any weed species. Metabolism-based resistance may pose a serious threat to Palmer amaranth management as this may confer resistance to several unknown herbicides.

 


TO WHAT EXTENT DOES REPEATED USE OF DICAMBA SELECT FOR RESISTANCE IN PALMER AMARANTH? P. Tehranchian*1, J. K. Norsworthy1, S. Powles2; 1University of Arkansas, Fayetteville, AR, 2University of Western Australia, Perth, Australia (223)

ABSTRACT

Since the 1980s, Palmer amaranth (Amaranthus palmeri S. Wats.) has demonstrated a strong propensity to evolve resistance to multiple herbicide modes of action.  New tools are needed for controlling Palmer amaranth and other herbicide-resistant broadleaves in crops; hence, companies are working to bring forth soybean and cotton cultivars having resistance to soil-applied as well as over-the-top applications of dicamba in the near future.  History has shown that repeated use of any single weed control tactic can quickly lead to resistance.  Resistance can be endowed by a single or multiple genes (polygenic).  Polygenic resistance often results when sublethal doses select for the most tolerant plants within a population and when the selection agent is repeatedly employed over several generations.  Reduced sensitivity to a herbicide can quickly evolve as has been shown previously for glyphosate-resistant Palmer amaranth in the U.S.  Several scenarios exist in which low dose selection can occur under field conditions, but some of the most common means are when herbicides are applied at a recommended rate to plants that are too large to effectively control, when spray coverage is reduced, or when use rates are reduced in an attempt to minimize the amount of herbicide applied as a cost savings measure.  With the impending registration of dicamba and likely use of the herbicide across vast acres targeting glyphosate-resistant Palmer amaranth, experiments were conducted to assess the potential for sublethal doses of dicamba to select for reduced sensitivity to the herbicide over multiple generations under laboratory conditions as well as field conditions. In a greenhouse experiment, 384 seedlings of a Palmer amaranth population collected from a vegetable crop production field in Fayetteville, AR were initially treated at the four- to five-leaf stage with dicamba at 140 g ae ha-1, a rate that equates to 1/4th the anticipated rate for dicamba-resistant crops. The survivors were grown and cross-pollinated in a growth chamber to avoid pollen contamination. Subsequently, seeds were collected and the following progenies subjected to higher dicamba doses for three generations. Subsequently, experiments were conducted to determine the response of each generation (line) to dicamba over a range of doses. In a parallel field selection experiment, soil was collected from a 2-ha cotton field infested with glyphosate-resistant Palmer amaranth immediately following crop harvest in 2011 and placed in cold storage.  In the spring of 2012 to 2015, the same field was planted to grain sorghum and treated with S-metolachlor at 1060 g ai ha-1 immediately after planting to provide early-season control of Palmer amaranth while still allowing later cohorts to escape.  When most of the Palmer amaranth plants in the field were approximately 45 cm in height, dicamba at 560 g ae ha-1 was applied to the entire field.  Following harvest of the 2015 grain sorghum crop, soil samples were again collected from the field. The response of Palmer amaranth seedlings from the 2011 and 2015 soil samples was evaluated over a range of dicamba rates under greenhouse conditions. Based on the survival percentage from the greenhouse selection, significant differences were observed among selected lines and progeny from unselected parents in response to dicamba doses. Thirty percent of F3 progenies survived application of dicamba at 560 g ae/ha. Based on LD50 values, the F3 progenies were >3-fold less sensitive to dicamba than the initial parents, with survival of plants occurring at the anticipated labeled rate. Palmer amaranth is an obligate cross-pollinated species and this characteristic enables resistance-endowing gene recombination in this species. In in vitro study, we illustrated the capability of a Palmer amaranth population to respond to low dose selection with dicamba and heritability of resistance traits within three generations. Albeit to a lesser extent, as expected, the response of progeny to dicamba from the 2011 soil sample differed from the 2015 sample, indicating that the population had become 1.5-fold less sensitive to dicamba. This milder shift of dose response curves can be attributed to the field conditions. The use of S-metolaclor each year as a preemergence herbicide at crop planting also likely reduced the extent of separation in response of progenies following the 2011 and 2015 growing seasons. Additionally, wind-borne pollen of late emerging unselected individuals or of Palmer amaranth plants from adjacent fields can cause contamination and interfere with the process of selecting for resistance. Similar to that observed in other research, these data strongly suggests that there will be sizeable evolutionary consequences if dicamba is not properly stewarded in dicamba-resistant crops such as applying it repeatedly in a manner that provides less than complete control. 

 


INTERACTIONS OF AUXINIC COMPOUNDS ON CA2+ SIGNALING AND ROOT GROWTH IN ARABIDOPSIS THALIANA. N. D. Teaster1, J. A. Sparks2, E. Blancaflor2, R. E. Hoagland*3; 1USDA-ARS, Stuttgart, AR, 2Samuel Roberts Noble Foundation, Inc., Ardmore, OK, 3USDA-ARS, CPSRU, Stoneville, MS (224)

ABSTRACT

Auxinic-like compounds have been widely used as weed control agents. Over the years, the modes of action of auxinic herbicides have been elucidated, but most studies thus far have focused on their effects on later stages of plant growth. We found that some select auxins and auxinic-like herbicides trigger a rapid elevation in root cytosolic calcium levels within seconds of application. Arabidopsis thaliana plants expressing the Yellow-Cameleon (YC) 3.60 calcium reporter were treated with indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), 1-naphthalene acetic acid (NAA), and two synthetic herbicides, 2,4-dichlorophenoxyacetic acid (2,4-D) and mecoprop [2-(4-chloro-2-methylphenoxy) propanoic acid], followed by monitoring cytosolic calcium changes over a 10-min. time course. Seconds after application of compounds to roots, the Ca2+ signaling-mediated pathway was triggered, initiating the plant response to these compounds as monitored and recorded using Fluorescence Resonance Energy Transfer (FRET)-sensitized emission imaging. Each compound elicited a specific and unique cytosolic calcium signature. Also primary root development and elongation was greatly reduced or altered when exposed at two concentrations (0.10 and 1.0 μM) of each compound. Within 20 to 25 min. after triggering of the Ca2+ signal, root growth inhibition could be detected. We speculate that differences in calcium signature among the tested auxins and auxinic herbicides might correlate with their variation and potency with regard to root growth inhibition. Information such as this may also be useful in elucidating aspects of auxinic herbicide mode of action, secondary effects of herbicides in planta, and herbicide resistance mechanisms in weeds.


USING RNA-SEQ TO EXPLORE DICAMBA RESISTANCE MECHANISMS IN KOCHIA SCOPARIA. D. J. Pettinga*, E. L. Patterson, P. Westra, T. A. Gaines; Colorado State University, Fort Collins, CO (225)

ABSTRACT


BIDENS PILOSA L., CHARACTERIZATION OF THE FIRST CASE OF GLYPHOSATE RESISTANCE OF THIS SPECIES. R. Alcantara-de la Cruz1, P. T. Fernandez*1, H. E. Cruz-Hipolito2, J. A. Dominguez-Valenzuela3, D. Rafael1; 1University of Cordoba, Cordoba, Spain, 2Bayer CropScience, Mexico City, Mexico, 3Chapingo Autonomous University, Texcoco, Mexico (226)

ABSTRACT

Bidens pilosa L., first case of glyphosate resistance worldwide of this species. R. Alcántara-de la Cruz1; P.T. Fernández1*, H.E. Cruz-Hipólito2, J.A. Domínguez-Valenzuela3, R. De Prado1;

1University of Cordoba, Cordoba, Spain, 2Bayer CropScience, Col. Ampl. Granada, Mexico, 3Chapingo Autonomous University, Mexico.

 

Persian lime is the more important economical crop in Veracruz State, Mexico, so it receives more care than other citrus crops. Weed control is done from 4 to 6 times per yearly, mainly by applying glyphosate. Leptochloa virgata was reported as the first glyphosate-resistant weed species in these crops. However, glyphosate remains as being the main chemical control tool used by farmers, which has caused great changes in weed flora. Recently, Bidens pilosa L. also been identified as a new species with glyphosate resistance. B. pilosa is a native Asteraceae weed from Mexico with a wide distribution in tropical areas of the country. Characterization studies of glyphosate resistance in a sensitive population (S) and two resistant populations (R1 and R2) of this species were carried out. Dose-response assays in greenhouse indicated that the R1 and R2 populations were 24.8 and 2.5 times more resistant in comparison to the S population, respectively. In the foliar retention assays, the R2 population retained 1.6 times more herbicide solution (ml g-1 dry weight) with respect to the S and R1 populations. The S population had an accumulation of 9.4 and 3.1 times more shikimic acid to the R1 and R2 populations, respectively, at 96 h after treatment. There were significant differences in the absorption and translocation of 14C-glyphosate between populations studied. The S population moved 24.9% of the radiolabeled herbicide to roots; the R1 and R2 populations moved 12.9% and 15.5% at 96 (HAT), respectively. Phosphor imaging results of 14C-glyphosate translocation showed poor penetration and translocation to the rest of the plant and root in R1 and R2 populations compared to S population. These results showed that B. pilosa has developed glyphosate resistance. This resistance could be influenced by a poor penetration and translocation of glyphosate to its action site. However, it is necessary to carry out studies for a possible mutation in the EPSPS enzyme to confirm the resistance mechanisms involved.

 

Keywords: B. pilosa populations, dose-response, 14C-glyphosate, foliar retention, persian limes, resistance.

 

Email address: pablotomas91@hotmail.es

 


CHARACTERIZATION MOLECULAR OF GENUS CHLORIS IN CUBA TREATED AND NON TREATED WITH GLYPHOSATE. R. Alcantara-de la Cruz1, P. T. Fernandez*1, H. E. Cruz-Hipolito2, M. D. Osuna3, I. Travlos4, D. Rafael1; 1University of Cordoba, Cordoba, Spain, 2Bayer CropScience, Mexico City, Mexico, 3Finca La Orden-Valdesequera Research Centre, Badajoz, Spain, 4Agricultural University of Athens, Athens, Greece (227)

ABSTRACT

Characterization Molecular of Genus Chloris in Cuba Treated and Non Treated with Glyphosate. R. Alcantara-de la Cruz1, P.T. Fernandez*1, H.E. Cruz-Hipolito2, M.D. Osuna3, I. Travlos4, R. De Prado1; 1University of Cordoba, Cordoba, Spain, 2Bayer CropScience, Col. Ampl. Granada, Mexico, 3La Orden-Valdesequera Research Centre, Badajoz, Spain, 4Agricultural University of Athens, Athens, Greece.

 

Strategies for weed control in Cuba are primarily based on post-emergence herbicide applications, mainly using glyphosate. In citrus groves from Arimao and Cienfuegos towns have been observed glyphosate resistant populations from genus Chloris. For this reason, it is necessary to identify the species of the genus Chloris that are evolving into a glyphosate resistance, as well as the mechanisms involved. Seeds were collected from fields with glyphosate treatment history (potential R population), and neighboring fields which had not been treated with glyphosate (S). AFLP molecular marker technique showed that all populations collected belong to the species C. elata. Dose response experiments showed that the potential R population was 6 times less sensitive to glyphosate than the S one. Shikimic acid accumulation was also higher in the S compared with the R population.14C- glyphosate translocation was higher in the S than in the R population. EPSPS gene sequencing resulted in an amino acid substitution of Proline 106 Serine.

 

Keywords: Chloris, AFLP, EPSPS gene sequencing, 14C- glyphosate translocation.

Email address: pablotomas91@hotmail.es

 


WATER POTENTIAL AND SALINITY EFFECTS ON GERMINATION OF GLYPHOSATE-SUSCEPTIBLE AND -RESISTANT JUNGLERICE (ECHINOCHLOA COLONA) SEEDS. L. Larocca de Souza1, L. M. Sosnoskie2, S. Morran2, B. D. Hanson2, A. Shrestha*1; 1California State University, Fresno, CA, 2University of California, Davis, Davis, CA (229)

ABSTRACT

The control of junglerice (Echinochloa colona) in California, in recent years, is being challenged by the presence of glyphosate-resistant (GR) populations in several parts of the state. Much of the agricultural area in the San Joaquin Valley (SJV) is prone to soil moisture stress. Furthermore, the western part of the SJV also have highly saline soils. Adaptation of junglerice under these stress environments need to be determined. Therefore, a study was conducted to assess the effect of moisture or salinity stress on the germination of a GR and a glyphosate-susceptible (GS) biotype of junglerice. Polyethylene glycol was used to create solutions of different water potential (0, -0.149, -0.51, -1.09, -1.88, -2.89, -4.12, and -5.56 MPa) and sodium chloride (NaCl) was used to create a range of salinity solutions (0, 25, 50, 100, 150, 200, and 250 mM).  Experimental units consisted of 20 junglerice seeds in a petri dish with a Whatman No. 2 filter paper and 10 mL of a treatment solution.  Dishes were sealed with parafilm, and placed in a growth chamber programmed for a day/night temperature of 30/25°C with 12 h daylight. Germination was monitored up to 21 days and data were expressed as a percentage of the distilled water control. Germination of the GS and GR types was reduced by 50% at 1.45 and 2.4 MPa, respectively. Similarly, germination of the GS and GR types was reduced by 50% at 99 and 124 mM of NaCl, respectively. This study showed that the GR junglerice was more tolerant to moisture and salt stress than the GS type. However, this cannot be generalized for all GR types of junglerice. Additional research is needed to ascertain if the stress tolerance characteristics of this GR junglerice types are linked to herbicide resistance.

 


TARGET-SITE RESISTANCE TO ACCASE INHIBITORS IN A BIOTYPE OF ECHINOCHLOA SPP FROM RICE FIELDS IN SPAIN. M. D. Osuna1, Y. Romano1, I. Amaro1, F. Mendoza1, J. A. Palmerin1, R. Alcantara-de la Cruz2, D. Rafael*2; 1Finca La Orden-Valdesequera Research Centre, Badajoz, Spain, 2University of Cordoba, Cordoba, Spain (230)

ABSTRACT

The
objective of this study was to determine the resistance of an Echinochloa spp. population from rice
fields of Extremadura to penoxsulam, cihalofop and profoxidim. These herbicides,
which inhibit acetyl CoA carboxylase (profoxidim and cihalofop) and
acetolactate synthase (penoxsulam), are the commonly used in weed control of
rice in Spaim. Seed samples collected from the field site were initially
screened with the herbicides in the glasshouse, and surviving individuals were
used for subsequent dose-response studies. To confirm the mechanism of
resistance, molecular studies were carried out. Estimations of GR50 (growth
rate) showed an 82,7-fold resistance to profoxidim, 7,4-fold to cihalofop and
2,7-fold to penoxsulam. The population was found to have a mutation Ile1781Leu
in the ACCase gene whilst the same population did not show resistance in the
ALS study. The introduction of herbicides with new mechanisms of action will be
useful to manage herbicide-resistant Echinochloa.
However,
cross- and multiple resistance emphasize the need to integrate herbicide use
with nonchemical means of weed management.


EFFECT OF SHADE AND SOIL MOISTURE LEVELS ON THE EFFICACY OF POSTEMERGENCE HERBICIDES ON JUNGLERICE (ECHINOCHOLA COLONA). R. Cox, A. Shrestha*; California State University, Fresno, CA (231)

ABSTRACT

Junglerice (Echinochloa colona) is a problematic weed in California and its postemergence control is now further compromised by the presence of glyphosate-resistant (GR) populations in the Central Valley. Two postemergence alternatives that have been identified are sethoxydim and glufosinate.  However, the performance of these herbicides can be influenced by environmental conditions such as light intensity and soil moisture. A study was conducted in Fresno, CA to evaluate the effect of light intensity and soil moisture levels on the efficacy of sethoxydim, glufosinate, and glyphosate on junglerice plants grown in pots containing field soil.  Three levels of shade (70%, 50%, and 0%, i.e. no shade) and three soil moisture regimes (100%, 50%, and 25% of field capacity) were imposed.  The plants were treated with label rates of the selected herbicides and an untreated control was also included. Mortality of these plants were evaluated every 7 days after treatment and aboveground biomass was recorded at 28 days after treatment. Results indicated that plant mortality was affected differentially by light intensity, moisture level, and herbicide type. There was a significant interaction between light intensity and soil moisture level.  Interactions occurred between moisture level and herbicide type under shade but not under full sun. Among the herbicides compared, glufosinate was the best treatment under all levels of shade and moisture conditions.  Control of junglerice with sethoxydim was lower under shaded and low moisture conditions, whereas control with glyphosate was better under shaded conditions at 100% and 75% FC moisture conditions.  Therefore, both shade and soil moisture conditions should be taken into consideration when selecting postemergence herbicides for control of junglerice as these conditions can vary especially in orchards and vineyards


INVESTIGATING THE EFFECT OF HIGH TEMPERATURE AND ITS DURATION ON SEED MORTALITY OF PHALARIS MINOR. J. Gherekhloo1, M. Khadempir1, A. Nehbandani1, D. Rafael*2; 1Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran, 2University of Cordoba, Cordoba, Spain (232)

ABSTRACT

Investigating the Effect of High Temperature and its Duration on Seed Mortality of Phalaris minor. Javid Gherekhloo1, Mohammad Khadempir1, Alireza Nehbandani1, Rafael, De Prado*2; 1Department of Agronomy, Gorgan University of Agricultural Sciences and Natural Resources, Iran, 2Department of Agricultural Chemistry and Edaphology, University of Cordoba, Spain.

Due to problems caused by herbicides, there is a strong tendency to develop alternative methods for weed control. For this reason, studying non-chemical and environmentally friendly methods such as storage of manure in pile and soil solarization to control weeds is on the increase. An experiment was conducted in a completely randomized design with factorial arrangement of the samples to study the effect of high temperature (simulating storage of manure under pile and soil solarization conditions) and its duration on seed mortality of littleseed canarygrass (Phalaris minor L.) at Gorgan University of Agricultural Sciences and Natural Resources during 2015. The treatments included two biotypes of littleseed canarygrass (resistant and susceptible to ACCase inhibitor herbicides), temperature at three levels (60, 70, 80 ºC) and incubation time at 9 levels (0, 24, 48, 72, 96, 120, 144, 168 and 192 hours) and the experiment was done with three replications. Results showed that there WAS no significant difference between the seed mortality of resistant and susceptible biotypes of P. minor in response to the temperatures. The time needed to reach 50 percent seed mortality was significantly different between  60, 70 and 80 °C and it was estimated to be  89.31, 66.02 and 45.02 hours for 60, 70 and 80 °C, respectively. According to these results, it can be concluded that soil solarization and storage of manure in pile could be effective in seed mortality of little seed canarygrass and be considered as an effective method for weed control.

Keywords: Manure, pile, seed mortality, solarization, temperature.

Email address: qe1pramr@uco.es

 


PHYSIOLOGICAL AND MOLECULAR CHARACTERIZATION OF RESISTANCE TO GLYPHOSATE IN JOHNSONGRASS FROM LOUISIANA. S. E. Abugho*1, R. A. Salas1, Y. Mohammed1, H. Guo2, N. R. Burgos1, D. O. Stephenson IV3; 1University of Arkansas, Fayetteville, AR, 2Rutgers University, Rutgers, NJ, 3LSU AgCenter, Alexandria, LA (233)

ABSTRACT

Physiological and molecular characterization of resistance to glyphosate in johnsongrass from Louisiana*

S.E. Abugho1, R.A. Salas1, Y. Mohammed1, H. Guo2, N.R. Burgos1, A.L. Rauh3 and D.O. Stephenson IV4

University of Arkansas-Fayetteville1, AR, Rutgers University2, NJ and LSU AgCenter3, LA

 

Johnsongrass is one of the problematic weeds in the Southern US, having evolved resistance to glyphosate, ALS inhibitors, and ACCase inhibitors. It can propagate through seeds and rhizomes, which facilitates its spread by various vectors and processes. Glyphosate-resistant johnsongrass has been confirmed in Louisiana. This study aims to understand the basis for this resistance. Experiments were conducted at the Altheimer Laboratory complex in 2015 to investigate differential absorption and mobility of glyphosate in resistant (R) and susceptible (S) plants grown from seeds or rhizomes. Four-leaf plants at 21 days were sprayed with a commercial formulation of glyphosate and spotted with 14C glyphosate (115,000 dpm) on the uppermost fully expanded leaf.  Shoot and root tissues were harvested at 24 and 72 hours after treatment (HAT). There were 4 replicates per harvest per accession. Plants were harvested and processed following established protocols, summarized in the Research Methods for Weed Science.  The level of resistance to glyphosate is at least five-fold relative to the susceptible population. Total 14C glyphosate recovered from the resistant plant was 73%; of this, 42% was absorbed (35098 DPM); the rest (48942 DPM) was recovered in the leaf wash. Total 14C recovered from the susceptible plant was 83% wherein 51% was absorbed (49931 DPM) and 48% was recovered in the leaf wash. Among susceptible plants, only 11% of absorbed 14C glyphosate remained in the treated leaf of seedlings 72 HAT; movement to the younger leaves was minimal (<5%) and the majority was moved basipetally – about 30% below the treated leaf and 56% to the roots. In rhizome-derived plants, also very little glyphosate (6%, 72 HAT) was moved to the younger leaves as in the seedling plants, but more glyphosate (33% of absorbed) remained in the treated leaf and less (16%) reached the roots relative to seedling plants. The proportion of 14C glyphosate remaining in the treated leaf was similar between R and S plants whether from seeds or rhizomes. Glyphosate was translocated basipetally in both ecotypes.  However, more 14C glyphosate was moved to the roots of S seedlings than R seedlings 72 HAT. Similarly, more 14C glyphosate was moved to shoot tissues below the treated leaf in S rhizome-derived plants than in R plants. Therefore, basipetal movement of glyphosate was reduced in R plants and this could explain why resistant plants in the field can be desiccated with glyphosate, but eventually regrow.  

 

 

Nomenclature: johnsongrass, glyphosate, resistance, HAT

 


DEGRADATION OF MESOTRIONE IN BRAZILIAN SOILS WITH CONTRASTING TEXTURE. K. F. Mendes*1, S. A. Collegari1, R. F. Pimpinato1, V. L. Tornisielo1, K. Spokas2; 1University of So Paulo, Piracicaba, Brazil, 2University of Minnesota, St. Paul, MN (234)

ABSTRACT

The environmental behavior of herbicides is determined by the interactions occurring at herbicide-soil interfaces. The mesotrione [2-(4-methylsulfonyl-2-nitrobenzoic acid) 1,3-cyclohexanedione] herbicide is a pre-emergent and early post belonging to the family of triketones, marketed for the control of a wide range of species weeds with low dose applications. Degradation and destination routes in mesotrione environment and its metabolites are poorly understood. Therefore, the objective of this study was to evaluate the degradation of mesotrione applied in two Brazilian soils (Alfisol – Paleudult, sandy clay texture and Ultisol - Typic Hapludalf, sandy loam texture). In brief, 50 g soil (dry weight) was placed in each Bartha flask, and spiked with a mixture of mesotrione, water, and trace amounts of 14C-mesotrione yielding a final concentration of 0.125 mg mesotrione kg−1 soil and a soil moisture content of ∼75% of the Water Holding Capacity and a radioactivity of ∼1,360,000 dpm 14C-mesotrione. The flasks were kept in an incubator at 20 ± 2°C for a period of 49 days. Degradation was measured at 7, 14, 21, 28, 35, 42 and 49 days after application, in thin layer chromatography (TLC) plates, with images in radio scanners. Was elucidated the superiority of degradation in soil sandy clay against the sandy loam, resulting in DT50 (Dissipation Time) next 12 and 27 days, respectively. Occurred to rapid degradation of mesotrione in two metabolites, possibly classified as MNBA and AMBA. The soil texture influenced this dissipation process of mesotrione.


MINERALIZATION OF 14C-DIURON IN COMMERCIAL MIXTURE WITH HEXAZINONE AND SULFOMETURON-METHYL. F. C. Reis*1, V. L. Tornisielo2, K. F. Mendes3, R. F. Pompinato4, B. A. Martins4, R. Victria Filho1; 1Luiz de Queiroz College of Agriculture, Piracicaba, Brazil, 2University of So Paulo, Piracicaba, Brazil, 3Center of Nuclear Energy in Agriculture - University of São Paulo, Piracicaba, Brazil, 4Center of Nuclear Energy in Agriculture (CENA), Piracicaba, Brazil (235)

ABSTRACT

Interactions among herbicides in a mixture may be additive, synergistic or antagonist on weed control. These interactions could potentially promote changes in herbicide behavior in the soil.This study evaluated diuron mineralization applied alone and in mixture with hexazinone and sulfometuron-methyl in soils with clayey or sandy textures, up to seventy days after application (DAA). The top 10 cm layer of the soils were collected. Ten days before applying the treatments, soil moisture was adjusted to 75% of the soil water-holding capacity. Non-radiolabeled herbicide solutions were prepared. Diuron alone or in mixture was used at the recommended dose of 1,387 g a.i. ha-1. Hexazinone and sulfometuron-methyl were added to the mixture with diuron at 391 and 33 g a.i.ha-1, respectively. 14C-diuron was added to the non-radiolabeled herbicide solutions and applied on top of the soil for each treatment. Diuron mineralization was evaluated at 0, 7, 14, 21, 28, 35, 42, 63 and 70 DAA. The 14CO2 released by 14C-diuron was trapped in a 0.2 N sodium hydroxide solution, and quantified by liquid scintillation. Applying diuron alone or in mixture did not affect its mineralization. When applied alone or in mixture in the clayey and sandy soils, diuron mineralization was about 11% and 7%, respectively. Thus, greater diuron mineralization occurred in the clayey soil, compared with the sandy soil, regardless of the application mode (alone or in mixture). Our results indicate that diuron mineralization is influenced by soil texture.


OPENCV SOFTWARE INTERACTIVE TRAINING FOR WEED IMAGE RECOGNITION IN RESIDENTIAL AND AGRICULTURAL SETTINGS. C. Lowell*1, A. Erdman2, J. Jackson2; 1Central State University, Wilberforce, OH, 2Global Neighbor, Inc., Centerville, OH (236)

ABSTRACT

Automated weed control would enhance the effectiveness of both conventional and non-chemical approaches to integrated pest management.  A sensor combined with image recognition software to identify weeds from desirable plants is needed.  The objective of this research was to train existing image recognition software to distinguish weeds from desirable plants in a residential and/or agricultural setting.  OpenCV 2.4 is an open-source BSD-licensed library with more than 2500 optimized computer vision algorithms.  OpenCV 3.0 was released May 2015 and was also adapted for weed identification.  Cascade training includes training and detection, and “opencv_traincascade” application was used for this project.  OpenCV created samples were used to prepare training datasets of different species of weeds (positive samples or detected objects) and non-weeds (negative samples or non-object images).   Color photos of dandelions (Taraxacum officianale F. H. Wigg) were taken with cell phones in southwest Ohio from residential properties, parks, natural areas and commercial properties at approximately 1.1 m height with between 8 to 20 megapixels and saved as jpg files.  Negative sample pictures were taken of anything that was not a weed and not green such as bare soil, asphalt, mulch, cement and brick.  All pictures were cropped to a 1:1 aspect ratio and reduced to image size of approximately 50 x 50 pixels.  Images were placed in files with matching text files.  A set of positive samples was developed using OpenCV create samples.   When training the classifier, the number of stages or complete run through the software training process was specified.  The testing information of the first classifier was 50 positive and 50 negative images with 50x50 pixels detected 20-35 parts of a plant common to all training images and multiple false positives, although the number of false positives was less than the number of positives.  In an image without any weeds, the software gave approximately four false positives. For dandelion trials, OpenCV identified five common features in the leaf patterning and the yellow flower.  False positives on images were highest with a grass or green background similar to the color of the dandelion.  In conclusion, positive images need to be cropped as close to the image as possible while still keeping most if not all of the weed in the picture.  High image resolution with a minimum of 460:460 will increase positives.  Keeping the dimensions 1:1 increases the number of positives.  Weeds on a variety of backgrounds such as stone, dirt, streets, sidewalks, and wood increased positives.  OpenCV software does show promise in identifying weeds and larger datasets using different weeds have been added and are undergoing testing.

 


MANUAL FOR PROPANE-FUELED FLAME WEEDING IN CORN, SOYBEAN & SUNFLOWER. A. Datta1, C. Bruening2, G. Gogos2, S. Z. Knezevic*3; 1Asian Institute of Technology, Bangkok, Thailand, 2University of Nebraska-Lincoln, Lincoln, NE, 3University of Nebraska-Lincoln, Concord, NE (237)

ABSTRACT

Flame weeding is an approved method for weed control in organic cropping systems, with the potential for use in conventional agriculture. From 2006-2012 we have conducted a series of over 40 studies, which were funded by PERC and other sources (eg. USDA). This extensive work resulted in over 20 journal and proceeding articles about crop tolerance to heat and weed control with flame weeding in field corn, popcorn, sweet corn, sunflower, soybean, sorghum and winter wheat. We compiled the above research information into a training manual that describes the proper use of propane fueled flaming as a weed control tool in six agronomic crops (field corn, popcorn, sweet corn, soybean, sorghum, and sunflower). Flame weeding manual contains 32 pages of text and color pictures. The pictures provide visuals of crop growth stages when flaming can be conducted safely without having side-effects on crop yield. Pictures of weeds provide visuals of appropriate growth stages when weeds need to be flamed to achieve good weed control. There are six chapters in the manual: (1) The need for alternative weed control methods; (2) Propane fueled-flame weeding; (3) How flame weeding works; (4) Equipment and configurations; (5) Propane dosage at different weed growth stages, and (6) Crop Tolerance to post-emergent flame weeding. We believe that our manual provides a recipe on how to use flaming procedures and it is written in a user friendly manner that can be understood by the general public. Manual is free, it can be downloaded in a pdf format from the following website:

http://www.agpropane.com/ContentPageWithLeftNav.aspx?id=1916


A NEW HOE BLADE FOR INTER-ROW WEEDING. O. Green1, L. Znova1, B. Melander*2; 1Agro Intelligence, Aarhus, Denmark, 2Aarhus University, Research Center Flakkebjerg, Slagelse, Denmark (238)

ABSTRACT

A New Hoe Blade for Inter-Row Weeding. O. Green1, L. Znova1 & B. Melander*2., 1Agro Intelligence, Aarhus, Denmark, 2Aarhus University, Slagelse, Denmark,

New camera-based systems for automatic steering of inter-row cultivators have made it possible to conduct inter-row weeding in small inter-row spaces at reasonable work rates. This has motivated organic growers to shift from full-width weed harrowing of small grain cereals to inter-row hoeing. The aim is mainly to improve weeding effectiveness against tall-growing and tap-rooted weed species. The ‘Ducksfoot’ hoe blade is commonly used for traditional inter-row weeding in row crops such as sugar beets and maize. This blade usually provides satisfactory weed control, if soils are not too wet and weeds are relatively small. The term ‘Ducksfoot’ covers a range of hoe blade configurations where all have some resemblance with the shape of a ducks foot. However, the ‘Ducksfoot’ blade is not an optimal solution for weed control in narrow inter-row spaces. Several disadvantages have been encountered, for example uncontrollable sideward soil movement causing injurious coverage of crop plants. Based on feedbacks from researchers and practioners, a new device has been designed to overcome most of the problems associated with ‘Ducksfoot’ blades. The device consists of a stiff shank mounted on a curved VCO-tine attached to the frame of an inter-row cultivator. An L-shaped blade provides the weeding action where the vertical part of the blade is mounted at the bottom end of the shank making change of blades very easy. The horizontal part of the L-blade points slantingly backward and toward the middle of the inter-row space and attacks the soil at a very flat angle. This means that the shank runs closely to the crop row. Investigations made in a test bin revealed that undesired soil movement with the L-blade is markedly less than with a ‘Ducksfoot’ blade. The L-blade did not affect the soil structure adversely and the draft forces needed to pull it were approx. half those measured for a ‘Ducksfoot’ blade. The weeding features of the new L-blade will be further studied under field conditions.                

bo.melander@agro.au.dk                  

 


INTERACTIVE EFFECTS OF HAND WEEDING, TINE AND SWEEP CULTIVATION FOR WEED CONTROL IN ORGANIC PEANUT PRODUCTION. R. S. Tubbs*1, D. Q. Wann2; 1University of Georgia, Tifton, GA, 2Algrano Peanuts, Brownfield, TX (239)

ABSTRACT

Previous research has shown that mechanical cultivation is the most effective and affordable method of weed control in organic peanut production.  However, growers are in need of more information on specific integrated cultivation regimes for effective season-long weed control with minimal hand-weeding requirements.  Therefore, field trials were conducted in 2010-2012 to evaluate the effects of various tine and sweep cultivation treatments combined with or without hand-weeding on season-long weed control, stand establishment, and yield and grade of an organically-managed peanut crop.  Tine cultivation treatments consisted of no cultivation or weekly cultivations for 5 wks after planting (WAP).  Sweep treatments consisted of no cultivation, weekly cultivations (for 5 WAP), cultivations at 2 and 5 WAP only, or cultivation at 5 WAP only.  Hand-weeding treatments were no hand-weeding or hand-weeding of the entire plot.  There were numerous significant interactions among tine and sweep treatments on weed control.  Initial weed species composition greatly affected cultivation effects on overall weed control.  Tine cultivation was most effective at controlling annual grass weeds.  Sweep cultivation was effective at reducing weeds (Amaranthus spp., southern crabgrass, and Florida pusley), but primarily when tine cultivation was absent.  Hand-weeding significantly improved weed control for every weed species every year.  Additionally, inclusion of certain cultivation regimes significantly reduced the hand-weeding time requirement over the control.  However, cultivation treatments did not improve pod yield or grade in any year.  The most significant benefit in cultivation from these data is in the reduction in hand-weeding requirements.  Based on this research, a regime consisting of weekly tine cultivations for 5 WAP, combined with two timely sweep cultivations provided the best overall balance of weed control and minimization of  hand-weeding.  Hand-weeding is the most critical weed control method, followed by tine cultivation, and finally sweep cultivation, which primarily served as an aid in the event of missed tine cultivations or failure.

 


INTEGRATED WEED MANAGEMENT FOR SNAP BEAN PRODUCTION. M. VanGessel*, B. Scott, Q. Johnson; University of Delaware, Georgetown, DE (241)

ABSTRACT

Integrated Weed Management for Snap Bean Production.  M.J. VanGessel, B.A. Scott, Q.R. Johnson, University of Delaware, Georgetown, DE.

Using cover crops has many advantages, with weed control being one of them.  In a vegetable crop such as fresh market snap beans, using an integrated approach is important to supplement herbicides as well as for resistance management.  This was a multi-disciplinary project examining use of no-till cover crops with or without pesticides for snap bean production.  The study was conducted for two seasons at the University of Delaware Research and Education Center in Georgetown, DE.  The treatments were a factorial arrangement of soil management and pesticide usage.  The three soil management strategies were conventional tillage, no-tillage Austrian winter peas (AWP) cover crop, or no-tillage with AWP plus cereal rye (AWP+rye).  The pesticide usage was with or without pesticides.  The cover crops were seeded the fall prior to the snap bean crop and either mowed with flail mower 1 day prior to planting (no pesticides) or sprayed with glyphosate 1 week before planting (pesticide).  The conventional tillage, no pesticide treatment used a stale-seedbed approach with initial soil preparation at least 3 weeks prior to planting.  The pesticide treated plots were sprayed with s-metolachlor within 1 day of planting.  All plots were cultivated twice.  Snap bean emergence was delayed 3 to 5 days with all the cover crop treatments compared to the conventionally tilled plots in both years, but final stand was similar for all treatments.  In the first year, total weed biomass after the second cultivation was significantly higher for both the no-till cover crop treatments without pesticides.  All remaining treatments had similar weed biomass.  In the second year, weed biomass was higher if no pesticide was used compared to a pesticide treatment.  There were no differences between the soil management treatments if pesticides were used.  Without pesticides, AWP had higher weed biomass than the stale-seedbed treatments, with AWP+rye not significantly different from either of them.  Snap bean yield was reduced in the first year for the cover crops without pesticide treatments.  All other treatments had similar yields.  In the second year, there were no significant differences in yields, in part due to lower weed pressure.  Cover crops can be incorporated into snap bean production without impacting yields, but additional steps may be necessary to improve weed management if no herbicides are used.

mjv@udel.edu


THE IMPORTANCE OF WEED CONTROL IN THE DEVELOPMENT OF INTEGRATED DISEASE MANAGEMENT STRATEGIES. J. E. Woodward*; Texas A&M AgriLIfe Extension Service & Texas Tech University, Lubbock, TX (242)

ABSTRACT

Diseases caused by soilborne pathogens can significantly reduce yield and quality of many crops. Diagnosis of such diseases may go unnoticed as symptoms can often occur on below ground tissues. Incidence of Sclerotinia blight of peanut (Arachis hypogaea L.), caused by Sclerotinia minor Jagger, is positively correlated with the density of surival structures in the soil. Likewise, yield losses in cotton (Gossypium hirsutum L.) are more severe in fields infested with high populations of root-knot nematodes (Meloidogyne incognita (Kofoid & White) Chitwood). Crop rotation with non-hosts in conjunction with fallow periods allows for populations of these pathogens to decline overtime. Weed management during fallow periods is important, as numerous weeds are known to be alternative hosts of these and other pathogens. In West Texas, galling similar to that caused by M. incognita has been observed on weeds such as Palmer amaranth (Amaranthus palmeri), Russian thistle (Salsola tragus L.), morningglory species (Ipomoea spp.) and other members in the Solanaceae in cotton fields. Suitability of these weeds as host for M. incognita have been determined in recent studies with nematode reproduction rates on S. tragus being 3.5 and 12.0 times greater than susceptible and partially resistant cotton varieties, respectively. Likewise, sclerotia of S. minor have been observed on 22-52% of hard to control weeds such as ivyleaf morningglory (I. hederacea Jacq.), red morningglory (I. coccinea L.) and eclipta (Eclipta prostrata L.) in fields with a history of Sclerotinia blight. A total of 19.3 and 7.4 sclerotia per cm of stem were recovered, respectively from ivyleaf and red morninglory plants artificially inoculated with S. minor isolates. Results from these studies suggest that alternative weed hosts are capable of augmenting soil inoculum of fungal and nematode pathogens, thus weed control must be considered when developing management strategies for such diseases. 

 


INFLUENCE OF PHOTOSYNTHETICALLY ACTIVE RADIATION INTERCEPTION BY WHEAT VARIETIES ON WEED SUPPRESSION. M. E. Cena1, M. V. Buratovich2, H. A. Acciaresi*3; 1Comision Investigaciones Cientificas (CIC), Pergamino, Argentina, 2UNNOBA-ECANA, Pergamino, Argentina, 3Instituto Nacional Tecnologia Agropecuaria, Pergamino, Argentina (243)

ABSTRACT

The objective of this study was to evaluate the competitive ability of wheat (Triticum aestivum) through the interception of photosynthetically active radiation and its relationship with aboveground biomass of a natural weed population.
Eight genotypes of wheat belonging to the breeding program of the Experimental Station INTA Pergamino (Buenos Aires, Argentina) were used.
The percentage of interception of photosynthetically active radiation (PARI, %) was measured. Aboveground biomass of weeds
at four crop growing stages (growing degree days from sowing date) was quantified: 1136 °D, 1429°D, 1732 °D and 2214 °D.
For the four growing stage tested,
more photosynthetically active radiation were intercepted by varieties with both greater angle and leaf area. These varieties registered the lower weed abovegroun biomass. Conversely, lower leaf angle and leaf area varieties registered a lower photosynthetically active radiation interception and recorded increased weed aboveground biomass.
The results obtained indicate that the attenuation of the IRFA during the crop cycle, due to the combination of angle and leaf area, has an inverse relationship with aboveground biomass of weeds. These traits could be useful to incorporate into the national wheat breeding programs selecting genotypes with increasing weed suppressive ability.


COVER CROP MANAGEMENT STRATEGIES FOR IMPROVING WINTER ANNUAL WEED SUPPRESSION IN MID-ATLANTIC NO-TILL CROPPING SYSTEMS. J. M. Wallace*1, W. S. Curran2, D. A. Mortensen2, M. VanGessel3; 1Pennsylvania State University, State College, PA, 2Pennsylvania State University, University Park, PA, 3University of Delaware, Georgetown, DE (244)

ABSTRACT

Glyphosate resistant horseweed (Conyza canadensis) is a significant weed management challenge for annual crop producers practicing conservation tillage in the Northeastern United States. In this region, horseweed typically behaves as a facultative winter annual, with distinct emergence periods in both fall and spring. Consequently, glyphosate-only burndown programs can become ineffective. Current management recommendations are to include multiple herbicide sites of action in burndown programs and to use soil residual herbicides if horseweed emergence is known to extend into the cash crop growing season. Looking forward, development of integrative approaches for horseweed management will be necessary to move selection pressure away from herbicides. No-till producers are increasingly integrating cover crops for soil health benefits, particularly following small grains or short season summer annual crops. This trend presents an opportunity to optimize cover cropping strategies for horseweed management. Weed suppressive cover crop strategies that also provide nutrient retention and soil erosion prevention benefits likely have the greatest potential for adoption. We conducted field experiments to evaluate cover crop strategies for horseweed management in 2014-2015 at Penn State’s Russell E. Larson Agricultural Research Center (PSU-RELARC) in central PA and at University of Delaware’s Carvel Research and Education Center (UD-CREC) near Georgetown DE.  Cover cropping treatments were evaluated following small grain production and were imposed as a RCBD with a split-plot and four replications. Main plots were cover crop treatments: no cover, cereal rye (134 kg ha-1), spring oats (134 kg ha-1), cereal rye + hairy vetch (67 + 22 kg ha-1), cereal rye + forage radish (67 + 6 kg ha-1), spring oats + hairy vetch (67 + 22 kg ha-1), and spring oats + forage radish (67 + 6 kg ha-1). Split-plots were fertility treatments: 0 or 67 kg N ac-1 using AMS.  Cover crops were planted using a no-till grain drill on 19-cm row spacing following burndown and fertilizer applications in early September. Cover crops were terminated at the cereal rye boot stage (Zadok 45) using glyphosate + 2,4-D (1.26 + 0.56 kg ha-1) and soybean was planted across the study. Prior to planting cover crops, locally-collected horseweed seed was distributed in permanently marked microplots (0.50 m2) at an average rate of 5,400 seeds m-2.

At the PA site, all treatments provided significant horseweed suppression (37 to 97%), which was measured as the percent population decrease relative to the no cover crop control, prior to spring burndown applications. Fertilization increased horseweed suppression across cover crop treatments in comparison to unfertilized plots. High levels of horseweed suppression (81 to 97%) were observed in treatments that included cereal rye. At the DE site, fertilization did not have a significant effect on horseweed suppression. Cover crop treatments that included cereal rye as well as the oats + vetch treatment resulted in significant horseweed suppression (71 to 100%) prior to burndown applications. The winter kill strategies, oats and oats + forage radish, did not differ compared to the control. In evaluations of cover crop traits and performance, we found that fall ground cover 10 weeks after planting and total spring biomass were most predictive of horseweed suppression at the PA and DE sites, respectively.  Our PA results suggest that fall fertilization of cover crops may be necessary to maximize weed suppression benefits for horseweed management.  However, this practice may increase the potential for nitrate leaching. In comparison to the unfertilized control, fall N retention in fertilized oat or oat mixture treatments increased from 23 to 39 lbs N/ac.  Total fall and spring N retention increased 53 to 61 lb N/ac across fertilized rye or rye-mixture treatments in comparison to the control. These results indicate that additional work is needed to identify fall fertilization rates that will maximize suppression of winter annual weeds without contributing to nitrate leaching potential.


NUTRIENT MANAGEMENT IMPACT ON WEEDS IN ORGANIC FIELD CORN IN THE MID-ATLANTIC REGION. V. J. Ackroyd*1, S. B. Mirsky1, J. T. Spargo2, M. A. Cavigelli1; 1USDA-ARS, Beltsville, MD, 2Pennsylvania State University, University Park, PA (245)

ABSTRACT

 

Organic production systems rely on cover crops and/or animal byproducts such as poultry litter to meet crop nutrient needs. Legume cover crops provide N, while poultry litter is a source of both N and P. When poultry litter is applied at rates sufficient to meet crop N needs, the amount of P applied is in excess of the amount of P removed by the crop, increasing the likelihood of P loss to the environment. In systems with a history of cover crop use and poultry litter application, soil nutrient reserves may serve as a considerable third source of fertility. Nutrient management techniques, including the use of cover crops and animal byproducts, can also impact weed dynamics in cropping systems. The purpose of this study was to determine if legume cover crops, in combination with a reduced rate of poultry litter application, could meet cash crop nutrient needs while minimizing weed-crop competition. Poultry litter was applied at rates of 0, 3.4, and 6.7 Mg ha-1. Three sites used winter annual legume cover crops (Austrian winter pea, crimson clover and hairy vetch) and one site used alfalfa and cereal rye. Spring cover crop and weed biomass varied by site and by year. Results were inconsistent across years and sites. In three out of seven site-years, cover crop had no impact on weed biomass in corn at silking. When differences were observed, more weed biomass at corn silking was present in legume cover crop treatments than in the no-cover crop control. In five out of seven site years, poultry litter application rate was not observed to impact weed biomass in corn. Our results suggest that at the poultry litter application rates and legume cover crop biomass present in our study, nutrient management techniques had minimal impact on weed biomass in corn.


DOES POULTRY LITTER INFLUENCE WEED DYNAMICS IN CORN AND SOYBEANS? E. Haramoto*1, E. Ritchey2, J. Gray2; 1University of Kentucky, Lexington, KY, 2University of Kentucky Research and Education Center, Princeton, KY (246)

ABSTRACT

Kentucky is the nation’s seventh largest broiler producer and poultry is a $1.2 billion industry in the state.  Poultry litter (PL) represents a nutrient source for Kentucky’s grain farmers that has the potential to influence weed dynamics.  Weed community structure and composition may be affected by changes in edaphic conditions and litter itself may also be a source of weed seeds from other areas.  We previously determined that PL increased mid-season weedy ground cover from 4.7% to 8.4% in corn and 10.1% to 14.3% in soybeans but did not affect weed height—factors that may influence growers’ POST decisions.  Research was conducted in western Kentucky to determine whether (1) the weed community changes in response to PL treatment and (2) litter is a source of viable weed seeds.  Field trials were conducted on four cooperating farms in 2013, 2014, and 2015 to address the first objective.  Each site rotated between corn and soybeans, with each crop present at two sites in a given year.  There were two treatments at each site—PL or nutrients supplied from synthetic fertilizer.  Plots were located in the same location from year to year and litter was surface broadcast each spring.  Most growers used a combination of burndown and soil residual herbicides applied PRE and foliar active herbicides applied POST for weed management.  The weed community was assessed prior to burndown and, in most cases, prior to POST applications and prior to harvest.  Percent ground cover was estimated for the major species present.  Community structure measures (species richness, Shannon-Wiener diversity index, and species evenness) were subjected to analysis of variance; treatment and crop were considered fixed factors, while replicate and site, year, or site-year were considered random factors.  Early- and mid-season community composition (measured as relative abundance) was analyzed with non-metric multidimensional scaling.  Multi-response permutation procedure (MRPP) was then used to test for differences in the ordination responses between treatments, counties, crops, and years.  Community structure measures were similar between PL and synthetic fertilizer plots at both sampling times.  Early season weed community was best described by a two dimensional ordination; these two axes explained a total of 79% of the variation in the dataset.  The ordinations did not differ between treatment, crop, or year, though the MRPP results showed that early-season communities differed between county.  Most site-years grouped together closely on the ordination biplot, with little differences between PL and synthetic fertilizer plots.  The mid-season sampling date was best described by a three dimensional ordination, with the three axes explaining 89% of the variation.  MRPP results showed that ordinations did not differ between treatment or crop, though mid-season communities differed between counties and year.  Pairwise comparisons showed that year 3 was significantly different from year 1 and year 2, suggesting that the mid-season weed community may be diverging through time.  Greenhouse trials were used to address the second objective.  PL from multiple sources was mixed with sterilized (autoclaved or fumigated) field soil, spread into flats, and placed in a greenhouse.  Flats were watered to maintain moist conditions and inspected for emerging seedlings.  No weed seedlings were observed in the PL greenhouse screenings.  Prickly lettuce seedlings were observed in the flats after they had been stored in an open area of the greenhouse for > 1 year, though these were likely from seed deposited from nearby populations.  Overall, our results suggest that PL does not influence weed community composition, at least over a three year time frame, and that PL is not a source of weed seeds from other locations. 


COVER CROP SPECIES RESPONSE TO HERBICIDE DOSE. B. S. Heaton*, M. L. Bernards; Western Illinois University, Macomb, IL (247)

ABSTRACT

The use of cover crops is increasing because of benefits they provide such as recycling nutrients, reducing soil erosion, and suppressing weeds. Maximum cover crop biomass depends on early establishment, ideally prior to the senescence of the cash crop.  In this study we use doses associated with three herbicide half-life times to estimate cover crop response at various potential establishment times relative to herbicide application time.  Ten common cover crop species response to 12 corn and soybean herbicides were measured. The cover crops were red winter wheat (53 kg ha-1), cereal rye (65 kg ha-1), winter rapeseed (3 kg ha-1), red clover (7 kg ha-1), Austrian winter pea (58 kg ha-1), hairy vetch (9.7 kg ha-1), radish (6 kg ha-1), crimson clover (2.6 kg ha-1), annual ryegrass (1.2 kg ha-1), and turnip (1.3 kg ha-1). The herbicides were applied at four doses (the first dose is the labeled rate), including: 2,4-D amine (1120, 280, 70, 17.5), atrazine (1120, 560, 280, 140), dicamba (1120, 280, 70, 17.5), isoxaflutole (48, 24, 12, 6), mesotrione (210, 105, 53, 26), chlorimuron-ethyl (17.5, 8.8, 4.4, 2.2), cloransulam methyl (35.3, 17.7, 8.8, 4.4), flumioxazin (107, 53.5, 26.8, 13.4), fomesafen (329, 165, 82, 41), pyroxasulfone (240, 120, 60, 30), sulfentrazone (420, 210, 105, and 53), and sulfentrazone + chlorimuron-ethyl (420+52.5, 210+26, 105+13, 53+6). The study was established June 2014 and September 2015.  Visual evaluations of injury on a scale of 0 (no injury) to 100 (plant death) were made 3 and 5 weeks after planting. Cover crop response was not identical to all herbicides across both years. The ratings reported below indicate crop response to herbicides at doses that would be expected approximately 3-4 months after herbicide application. Brassicacea species (turnip, radish, and rapeseed) were most injured by the ALS- (chlorimuron, cloransulam) and PPO-inhibiting (flumioxazin, fomesafen, sulfentrazone) herbicides evaluated. The legume species (red clover, crimson clover, winter pea, and hairy vetch) were less sensitive than brassicacea species, but were also most affected by the ALS-inhibiting herbicides.  There was response by some legume species to some PPO- and HPPD-inhibiting herbicides, especially the clovers.  The only species severely injured by pyroxasulfone was annual ryegrass. Neither 2,4-D or dicamba caused significant injury at doses expected to remain in the soil 7 weeks after application. The only active ingredient mixture tested (sulfentrazone + chlorimuron) was the most injurious product across the species evaluated, and negatively impacted all cover crop species. Because herbicide degradation rate is strongly influenced by environmental conditions, using a dose response analysis similar to that conducted in this study may improve the predictability of cover crop response as environmental conditions vary.

 


DIRECTED ENERGY COMMON RAGWEED CONTROL . F. Hayes*1, C. Lowell1, J. Jackson2; 1Central State University, Wilberforce, OH, 2Global Neighbor, Inc., Centerville, OH (248)

ABSTRACT

Non-chemical weed control includes such methods as mechanical, cover crops and board cover, flaming, microwaves, and directed energy.  The NatureZap DE is a commercially available, hand-held weed control device designed for residential and small commercial applications that delivers the equivalent of 48 suns (1200 joules in 10 seconds) of visible, near infrared and ultraviolet-A light.  It has been shown to control the growth of a variety of common Midwest United States weeds.  The purpose of this research was to measure the effectiveness of directed energy on common ragweed (Ambrosia artemisiifolia L.) found in Midwest residential and agricultural settings. The NatureZap DE was used to control ragweed grown under greenhouse conditions. Ragweed seeds were planted and seedlings transplanted to separate pots in a soiless mix.  Each treatment of 3 plants were exposed to a time range from 5 to 20 seconds of directed energy for 4 weeks, and compared to glyphosate and no treatment controls. One week after exposure, weeds stress indicators were observed including degreening, weakened stems and inhibited growth. The ragweed seedlings were rated from a scale of 0 (complete control), 1 (some visible damage) to 2 (no visible damage).  Results showed that directed energy provided 100% control across all plant ages tested at 20 second treatment which was comparable to 100% glyphosate control.  Trials with 5 and 10 seconds showed decreased effectiveness as the plants reached maturity.  Additional stress indicators are under investigation for quantification.  Directed energy, especially at longer exposure times, provides non-chemical weed control of common ragweed up to flowering maturity.

 


VERTICAL DISTRIBUTION OF NUTSEDGE (CYPERUS SPP. L.) AND BAHIAGRASS (PASPALUMNOTATUM L.) SEED BANK IN RICE GROWTH CYCLE. M. Yaghubi1, H. Pirdashti1, M. Mohseni-Moghadam*2, R. Roham3; 1Sari Agricultural Sciences and Natural Resources University, Sari, Iran, 2Ohio State University, Wooster, OH, 3Lorestan University, Khorram Abad, Iran (249)

ABSTRACT

Weed management in rice continues to be a major challenge to the success of rice growers in northern Iran, a major rice-producing province. The primary method of rice establishment in this region is transplanting. Field experiments were conducted at Sari Agricultural Sciences and Natural Resources University to investigate the vertical spatial distribution of weed seed bank in rice growth cycle using regression and geostatic relation in 2010 and 2011. Transplanting was done on June 6 in both years. Samples for seed bank analysis were collected 10 days before transplanting and weed density was determined on three different dates during the growing season. Results indicated that nutsedge (Cyperus spp. L.) and bahiagrass (Paspalum notatum L.) were the two most abundant weed populations. The vertical distribution of weeds seed bank decreased by depth, from 10 to 30 cm whileweed pressure was the highest at the 0-10 cm soil depth. Due to the lack of significant relationships between soil weed seed banks (at different depths) and weed populations, we concluded that weed seed bank data are not good predictors of weed seedling densities. Nevertheless, Kriging maps indicated that the spatial distribution of weed seed bank was in accordance with seedling germination pattern. Also the regression coefficient for 0-10 cm soil depth was R2=0.17 and R2=0.34 for relation between nutsedge and bahiagrass seedlings and their seed bank in 2010 and also, R2=0.18 and R2=0.05 in 2011, respectively, therefore results achieved from this depth can be used to predictthe relationship between nutsedge and bahiagrass seedlings densities and weed seed banks. The results of this study provide another option for the farmers growing rice to understand the dynamics of weed populations in a cost effective way.

 


QUAILS CONTRIBUTION TO WEED SEED BANK. J. M. Urbano*1, F. Forcella2, P. Gonzalez-Redondo1; 1Universidad de Sevilla, Sevilla, Spain, 2USDA ARS, Morris, MN (250)

ABSTRACT


CROSS- AND MULTIPLE-RESISTANCE IN BARNYARDGRASS (ECHINOCHLOA CRUS-GALLI) POPULATIONS FROM RICE FIELDS IN BRAZIL. B. A. Martins*1, J. A. Noldin2, D. Karam3, C. Mallory-Smith4; 1Center of Nuclear Energy in Agriculture (CENA), Piracicaba, Brazil, 2Santa Catarina State Agricultural Research and Rural Extension Agency, Itajai, Brazil, 3Brazilian Agricultural Research Corporation (EMBRAPA), Sete Lagoas, Brazil, 4Oregon State University, Corvallis, OR (252)

ABSTRACT

Seeds from two E. crus-galli populations (ECH73 and ECH77) that survived a quinclorac application were collected in two rice production fields from Santa Catarina State, Brazil. The rice fields had a history of quinclorac and ALS inhibitor use for more than 10 years. Quinclorac whole-plant dose-response and ALS inhibitor screening studies were conducted in the greenhouse. Treatments were applied under the same conditions in both studies, with a known susceptible population (SUS) included. The variables evaluated were percent dry weight for the dose-response study and percent visual control for the screening study, both evaluations were 21 days after treatment (DAT). Results confirmed quinclorac susceptibility in SUS and that the suspected resistant populations ECH73 and ECH77 were quinclorac-resistant. For the labeled use rate, percent dry weight for SUS was less than 35%, whereas for ECH73 and ECH77 percent dry weight was nearly 70% and 100%, respectively. For the herbicide screening experiment, SUS was controlled by all herbicides at the field rate. ECH73 and ECH77 were resistant to imazethapyr and bispiribac-sodium, but were not resistant to penoxsulam, to the formulated mixture imazapic+imazapyr or to the mixtures fenoxaprop-p-ethyl+penoxsulam or fenoxaprop-p-ethyl+bispiribac-sodium. Thus, the latter herbicides could be used to manage E. crus-galli in the sampled rice fields. Results from the dose-response and the screening experiments indicate that populations ECH73 and ECH77 possess multiple-resistance to two modes of action groups (synthetic auxins and ALS inhibitors) and have the same cross-resistance patterns to two ALS inhibitors, imazethapyr and bispiribac-sodium. Absorption, translocation and metabolism studies using radiolabeled quinclorac and ALS inhibitors are being conducted to investigate non-target-site-based mechanisms of resistance in the Echinochloa crus-galli populations.

 


COMPARATIVE GROWTH OF HENBIT (LAMIUM AMPLEXICAULE) BASED ON EMERGENCE DATE. B. C. Woolam*, D. O. Stephenson IV, S. L. Racca; LSU AgCenter, Alexandria, LA (253)

ABSTRACT

Louisiana crop producers typically apply a burndown herbicide four to six wk prior to seeding summer annual crops; however, these treatments often provide inadequate henbit (Lamium amplexicaule L.) control.  This poor control may be attributed to hardening off and senescence of fall emerged henbit that overwinter into spring.  Henbit emergence and growth patterns need to be determined to aid in the development of control strategies.  Therefore, a state-wide henbit emergence pattern survey was conducted concurrently with an evaluation of the comparative growth of henbit accessions based on emergence date.  The survey was conducted at four locations throughout Louisiana and the comparative growth study was conducted at the LSU AgCenter Dean Lee Research and Extension Center near Alexandria, LA in 2012/2013 and 2013/2014 and 2014/2015.  For the survey, six, 1 m2 plots were established at each location and total number of henbit were counted weekly, beginning in mid-September until late-March.  After each weekly count was collected, paraquat at 0.56 kg ai ha-1 plus 0.25% v/v nonionic surfactant was sprayed to remove all henbit.  A weather station was utilized at each location to record various environmental parameters to determine if correlations between emergence and these parameters existed.  Survey results indicate that henbit emerges from September thru April in Louisiana, with greatest emergence occurring from October 10 to December 12 when soil temperatures reach 8 to 20 C.  To evaluate comparative growth of henbit accessions based on emergence date, cotyledon henbit that emerged in mid-September, -October, and -November were transplanted into individual pots.  Each pot contained a single henbit plant.  Plants were arranged as a factorial in a completely randomized experimental design with individual plants constituting a single experimental unit.  Factors included henbit emergence date and harvest intervals of 2, 3, 4, 6, 8, 10, and 12 wk after emergence (WAE).  At each harvest interval, eight plants were cut at the soil surface, leaves and stems separated, and total leaf area was measured for each plant.  Leaves and stems were then dried in a forced-air drier for 7 d.  Leaf and stem weights and leaf area were utilized to calculate total aboveground plant weight, leaf area ratio (LAR), relative growth rate (RGR), and net assimilation rate (NAR) on a per-plant basis at each harvest interval.  LAR is a measure of the leafiness of a plant.  RGR is a measure of the overall growth over time relative to initial size and NAR indicates the photosynthetic efficacy of a plant.  All data were subjected to ANOVA in SAS.  Regardless of harvest interval, LAR for September (120 cm2 g-1) and October (121 cm2 g-1) emerged henbit were not significantly different; however, the LAR for November emerged henbit was 32% less than September and October.  Greater LAR of September and October emerged henbit indicates that these plants obtain greater leaf area per total dry weight, which implies that they are more competitive.   For RGR, only September differed from November emerged henbit with 0.2 and 0.14 g-1 g-1 d-1, respectively, indicating that September emerged henbit growth was greater on a per day basis compared to November emerged henbit.  NAR for October and November emerged henbit showed no change from weeks 2 thru 12.  However, NAR for September emerged henbit was similar to October and November weeks 2 through 6, but increased 455% between 8 to 10 WAE (from 1.8 to 8.2 g cm-1 d-1) and then decreased after 10 WAE (8.2 to -1.6 g cm-1 d-1).  NAR data indicate that September emerged henbit allocated more resources to leaf production and greater photosynthetic efficiency on a per day basis compared to October and November emerged henbit.  Also, the decrease in NAR after 10 WAE was due to plants beginning to senescence.  Data indicates that September and October emerged plants may mimic populations that are difficult to control with spring herbicide applications due to senescence in later weeks of growth, which reduces leaf area and may be responsible for decreased absorption of spring-applied herbicides.

 


CHINESE TALLOWTREE (TRIADICA SEBIFERA (L.) SMALL) SEED BIOLOGY: AN EVALUATION OF SEEDFILL, GERMINATION AND SEED BANK LONGEVITY. H. VanHeuveln*; University of Florida, Gainesville, FL (254)

ABSTRACT

Chinese tallow (Triadica sebifera) is a habitat transforming, invasive tree species present throughout the Southeastern United States that displays high growth rate and heavy  seed production.   Successful control can be achieved through the use of mechanical and chemical control, treated sites still are vulnerable to recolonization via seeds.  Therefore, a better understanding of seed biology of this species is needed for long-term control. The focus of this study was to characterize the physiological development of  Chinese tallow seeds and longevity under field conditions.   

Seed longevity was studied under field conditions at Paynes Prairie Preserve State Park (PPP) in Gainesville, Florida and Jay, Florida using 1 m2 seed exclusion frames.  Frames were placed over heavy deposits of seeds prior to spring germination at the PPP site in Jan. 2014 and Feb. 2015 and at the Jay site in Mar. 2015.  Each frame was monitored monthly for seedling emergence for 1-2 years.   Results from this study show that initial onset of germination at PPP occurred in March 2014 (Mean=4.1± S.E. 1.80 seedlings/m2), peaked in April (Mean=16.6 ± S.E. 9.02 seedlings/m2) then declining to ≤1 seedling/m2 until April of 2015 (Mean=3.1± S.E. 2.99 seedlings/m2) after which germination was ≤1 seedlings/m2 into December of 2015.  Frames placed at the PPP site in February 2015 showed trends comparable to the 2014 seedling emergence indicating that Chinese tallow seeds might have a longevity of 1-2 years under field conditions.  The 2015 seed frames in Jay showed a similar emergence pattern as PPP but the onset of germination occurred a month later peaking in May 2015. 

The effect of after-ripening was studied from  seed cohorts collected directly from trees at, 2 week intervals, after seed capsule split for a period 2 months using non-parametric survival analysis.  Germination was conducted in a growth chamber using moist potting soil at alternating Florida average spring temperatures of 27°C light (9 hrs.) and 15°C dark (15 hrs.) for 60 days, recording germination daily.  All non-germinated seeds were subjected to a tetrazolium viability test to calculate remaining viable seeds upon termination of the tests.  In addition, 2 cohorts of seeds from each harvest were also subjected to a 60 day germination and viability test after storage for 6 months at either 25°C or 5°C.  Results for the after ripening study showed that there was no significant difference (P-value=0.6608) in germination among harvest dates.  Storage had a significant effect on germination (P-value=0.0029) revealing a significant decline in seed germination after six months of storage when compared to freshly germinated seeds regardless of storage condition (p=0.01), but no effect of storage condition on germination at 6M.  No significant differences were detected in seed viability as a function of harvest treatment within storage treatments.  Pooling harvests within each storage treatment divulged a significant difference between seed viability components for seeds stored 6M vs fresh seeds (6M@25°C, χ2(2)= 25.38, p<0.025,0.005; 6M@5°C, χ2(2)= 21.31, p<0.025,0.005) but were not significantly different among 6M storage treatments (χ2(2)=9.29, p<0.005).  Seed fill was investigated using x-ray imaging and evaluated using visual estimates.  Results showed 37% of seeds harvested directly from the tree had <100% seed fill, which accounts for 60% of the non-viability observed.   Regardless of treatment, germination observed was about 30% of the viable seeds, indicating that the Chinese tallows seeds collected in these studies exhibit a significant degree of dormancy.  Elucidating these mechanisms will be the focus of future experiments. 


 


 


BIOLOGY AND SEED PRODUCTION OF MIMOSA PIGRA LON THE EAST OF PUERTO RICO. J. D. Arocho*1, W. Robles2, M. Lugo Torres1, R. Couto1; 1University of Puerto Rico, Mayaguez, Mayaguez, PR, 2University of Puerto Rico, Mayaguez, Dorado, PR (255)

ABSTRACT

Shrubby weeds are a problem on farms producing foragebecause weeds can affect the palatability of the grass, limit access to the premises and also decrease the quality and quantity of forage available.  A woody shrub like catclaw mimosa (Mimosa pigra) is considered a threat in the north, east and west pasture zonesof Puerto Rico. Its rapid reproduction and dispersal by seed reduce the establishment of forage and its availability. Hence,an effective weed management planshould be considered in managing pastures used for grazing.  Although the problems associated with this weed are widely known, its biology including growth and reproduction have not been studied locally. In April 2013, a field studywas conducted at theAgricultural Experiment Station in Gurabo, Puerto Rico,to determine the growth and development of catclaw mimosa as well as its reproductive capacity.  In order to carry out this research, catclaw mimosa seeds were germinated in a greenhouse. Once the plants reached an average height of 0.30 cm, they were transplanted to an area used for grazing and allowed to grow under natural conditions. Each plant was measured at 22-dayintervals to determine dry weight, height, stem diameter, and number of inflorescences, pods and seeds. The seeds were collected in a plastic 3.5 m2meshplaced around each plant. Twelve months after transplant the average plant height was 666.5 cm and maximum stem diameter was10.5 cm.Flower production started three months after transplant, and the number of inflorescence per plantfluctuated between 4 and 40. Maximum production of pods observed was 77 pods per plant, which produced a total of 300 seed per m2. Seeds collected showed up to 45% germination.


DISTRIBUTION OF HERBICIDE RESISTANCE IN PALMER AMARANTH AND WATERHEMP IN TEXAS. R. A. Garetson*1, P. A. Dotray2, J. A. McGinty3, P. Baumann4, G. D. Morgan1, W. Grichar5, R. M. Merchant2, M. V. Bagavathiannan1; 1Texas A&M University, College Station, TX, 2Texas Tech University, Lubbock, TX, 3Texas A&M AgriLife Extension, Corpus Christi, TX, 4Texas A&M AgriLife Extension, College Station, TX, 5Texas AgriLife Research, Yoakum, TX (256)

ABSTRACT


RESCUE TREATMENTS FOR PALMER AMARANTH CONTROL. D. Denton*1, D. M. Dodds1, C. A. Samples2, M. T. Plumblee2, L. X. Franca1, A. L. Catchot1, T. Irby2, J. A. Bond3, D. B. Reynolds2; 1Mississippi State University, Mississippi State, MS, 2Mississippi State University, Starkville, MS, 3Mississippi State University, Stoneville, MS (257)

ABSTRACT

Rescue Treatments for Palmer Amaranth (Amaranthus palmeri) Control.  A.B. Denton, D.M. Dodds, C.A. Samples, M.T. Plumblee, L.X. Franca, A.L. Catchot, T. Irby, J.A. Bond, D.B. Reynolds; Mississippi State University, Mississippi State, Mississippi. 

 

            An experiment was conducted at Hood Farms in Dundee, MS and at the Delta Research and Extension Center in Stoneville, MS in 2015 to determine the effect of multiple herbicide applications and timing programs on glyphosate-resistant-Palmer amaranth control.  The experiment was initiated in fields with heavy natural infestations of GR-Palmer amaranth.  Applications were initiated when Palmer amaranth plants were 20 to 25 cm in height as well postponing additional initial applications for two and four weeks after the original application timing.  Herbicide programs in which two applications were made, the second application was made two weeks or four weeks after the initial application regardless when treatments were initiated.  Herbicide programs in which three applications were made, the third application was made two weeks after the second application regardless when treatments were initiated.  Treatments utilized in this experiment included: glyphosate + dicamba at 0.8 kg ae/ha and 0.6 kg ai/ha; glufosinate + dicamba at 0.6 kg ai/ha each; glyphosate + 2, 4-D at 0.8 kg ae/ha and 1.1 kg ae/ha; glufosinate + 2, 4-D at 0.6 kg ai/ha and 1.1 kg ae/ha.  At the second application timing, the tank mix of glyphosate + 2,4-D provided significantly greater height reduction (45%) than all other tank mixes.  Two weeks after final application, tank mixes containing glufosinate provided significantly greater visual control (≥85%) than those containing glyphosate when pooled across all timing programs.  Multiple applications significantly increased visual control compared to single application programs two weeks after final application.  In multiple application programs, keeping the interval between applications to two weeks significantly increased visual control up to four weeks after final application compared to longer sequential application intervals.  Multiple applications of any of the herbicide combinations tested were needed to control GR-Palmer amaranth in a rescue application scenario.  abd93@msstate.edu

 


CHARACTERIZATION OF GENE FLOW FROM S. HALEPENSE TO S. BICOLOR UNDER FIELD CONDITIONS. M. N. Carlson*, W. Rooney, G. Hodnett, M. V. Bagavathiannan; Texas A&M University, College Station, TX (258)

ABSTRACT


CAN PLANT GROWTH REGULATORS IMPROVE RICE TOLERANCE TO PRE-FLOOD HERBICIDES? . T. M. Penka*1, C. E. Rouse2, N. R. Burgos2, J. Hardke3, R. C. Scott2; 1University of Arkansas, Amarillo, AR, 2University of Arkansas, Fayetteville, AR, 3University of Arkansas, Stuttgart, AR (259)

ABSTRACT

Herbicide use in rice production helps eliminate troublesome weeds, but one weeds that is difficult to control is volunteer rice. Volunteer rice may come from conventional varieties or from herbicide-resistant (Clearfield) rice varieties. Our past experiments show that volunteer rice problems tend to be higher following hybrid rice than following inbred rice. Planting Clearfield rice after non-Clearfield rice varieties will control volunteer rice, but there is no in-crop alternative to control volunteers from Clearfield varieties. Researchers have been investigating chloroacetamides and other root/shoot inhibitors as alternative residual grass herbicides in rice. We are exploring the utility of these types of herbicides for controlling volunteer rice and investigating if plant growth regulators (PGRs) can alleviate the physiological stress to rice from such herbicides. Both acetochlor and pyroxasulfone are known to severely stunt and injure rice, but would seed treatment with a PGR reduce rice injury from these herbicides? The PGR seed treatments tested were Falgro, Ascend, and Falgro plus Ascend. Acetochlor and pyroxasulfone were applied either preemergence (PRE) or at V2. Check plots without PGRs and herbicide treatments were included. The experiment was conducted in Stuttgart and Rohwer, Arkansas. Both locations had a “volunteer” CL111 rice seed shallowly incorporated prior to planting the rice crop CL151. The experimental units were arranged in a randomized complete block design with three factors; herbicide, application timing, and PGR seed treatment. Crop injury, crop stand, and height were recorded at 3,6, and 9 wk after planting. The number of stalks and panicles was recorded at harvest. The location effect was not significant. Without PGR seed treatment, acetochlor PRE caused 56% injury 6WAP; pyroxasulfone caused 92% injury. PGR seed treatment did not reduce the injury incurred from these herbicides applied at planting. There was no crop injury from 2-lf application of acetochlor. Pyroxasulfone applied at V2, without PGR, caused  14% injury, 6 WAP and injury increased with time. PGR seed treatment, without the root/shoot inhibitors, yielded 9,584-9,685 kg/ha. This was 5% higher than, although not significantly different from, the nontreated check (9,281 kg/ha).  Seed treatment with Ascend numerically improved the yield of rice treated with acetochlor PRE by 5%. Ascend+Falgro increased the yield of the rice treated with pyroxasulfone at V2 by 12% from 7,818 kg/ha to 9,020 kg/ha. Injury from this treatment was 27% at 6WAP. Thus, some PGRs may help overcome the yield deficit owing to moderate stress, but cannot overcome severe stress. Further research should be performed to determine how PGR and herbicide interactions could vary with year-to-year growing conditions as well as across varieties. 

 


DOES SHARPEN ADDITION TO RICE HERBICIDES LESSEN BARNYARDGRASS CONTROL? R. R. Hale*, J. K. Norsworthy, L. T. Barber, Z. Lancaster, M. L. Young, N. R. Steppig; University of Arkansas, Fayetteville, AR (260)

ABSTRACT

Barnyardgrass [Echinochloa crus-galli] is one of the most problematic weeds in Midsouth rice production.  The physiological and biochemical capability of barnyardgrass to quickly evolve resistance continues to limit herbicide options for control.  Provisia rice is a new technology being developed by BASF that will allow for the use of quizalofop, an ACCase-inhibiting herbicide, for control of grass weeds.  Sharpen is a contact herbicide labeled for broadleaf weed control in rice.  When tank-mixing systemic herbicides with contact herbicides, antagonism or a reduction in efficacy is often observed.  Hence, a field study was conducted at the Pine Tree Research Station near Colt, AR to determine whether the addition of Sharpen with grass herbicides in Provisia rice reduces barnyardgrass control.  This experiment was arranged in a randomized complete block design with three common rice herbicides applied at the 1/2X and 1X rate with and without a 1/2X and 1X rate of Sharpen.  All applications were made using a CO2-pressurized backpack sprayer at 15 GPA.  Treatments were applied when barnyardgrass reached the 3- to 4-leaf growth stage, and all treatments contained crop oil concentrate (COC) at 1% (v/v).  Treatments contained a 1/2X and 1X rate that included Sharpen at 0.5 and 1 fl oz/A, Clincher at 7.5 and 15 fl oz/A, Ricestar HT at 12 and 24 fl oz/A, and Targa (Provisia) at 10.3 and 20.7 fl oz/A, respectively, along with a nontreated check. An additive response was observed with the addition of Sharpen for barnyardgrass control at 7 and 14 days after treatment (DAT) for all combinations, except for the 1/2X rates of Clincher + Sharpen, based on Colby’s method for assessing herbicide interactions.  Rice injury did not exceed 7% across all treatments.  Overall, main effects of herbicide and the addition of Sharpen were significant at 7 DAT and a main effect of herbicide was significant at 14 DAT.  From these results, Sharpen + Clincher may not be a good tank-mix option when both broadleaf and grass weed species are present in the field.


INFLUENCE OF INSECTICIDE SEED TREATMENTS ON RICE TOLERANCE TO LOW RATES OF GLYPHOSATE AND IMAZETHAPYR. S. M. Martin*1, J. K. Norsworthy1, R. C. Scott1, G. M. Lorenz2, J. Hardke3, Z. Lancaster1; 1University of Arkansas, Fayetteville, AR, 2University of Arkansas, Lonoke, AR, 3University of Arkansas, Stuttgart, AR (261)

ABSTRACT

Every year there are multiple incidences of herbicide drift in rice.  With a large percentage of crops being glyphosate-resistant and approximately 50% of Arkansas rice being non-Clearfield (imidazolinone-resistant), the majority of drift complaints in rice are from Newpath (imazethapyr) or Roundup (glyphosate).  In 2014 and 2015, a field experiment was conducted at the Rice Research and Extension Center near Stuttgart, Arkansas and the University of Arkansas Pine Bluff Farm near Lonoke, Arkansas, to evaluate whether insecticide seed treatments could reduce injury from glyphosate or imazethapyr drift or decrease the recovery time of the rice.  ‘Roy J’ rice was planted and simulated drift events of a 1/10X rate of imazethapyr or glyphosate was applied to each plot.  Each plot had either a seed treatment of CruiserMaxx Rice, NipSit Inside, Dermacor X-100, or no insecticide seed treatment.  Seed that were not treated with an insecticide were treated with a fungicide such that all seed in the trial would be treated with a fungicide.  The simulated drift event was applied at the 2- to 3-leaf growth stage of rice.  Crop injury was assessed 2 and 5 weeks after application.  Rice water weevil samples were taken 3 weeks after flood in 2015. Sigma Scan photos and canopy heights were also taken throughout the growing season.  All insecticide seed treatments provided adequate rice water weevil control in the event of drift compared to the non-insecticide treated plots.  After initial injury ratings at 2 WAT, CruiserMaxx and NipSit significantly reduced injury compared to the fungicide-only treatment when averaged over herbicides. Five weeks after application, injury had decreased with CruiserMaxx and NipSit remaining significantly less injured than the fungicide-only treatment. CruiserMaxx and NipSit protected the yield potential of the rice when averaged across herbicides.  A drift event of imazethapyr or glyphosate however did reduce yields by 1,000 kg/ha compared to non-treated plots.  Based on these results, CruiserMaxx Rice and NipSit Inside have potential to provide some safening against imazethapyr and glyphosate drift whereas Dermacor X-100 will provide little to no safening to these herbicides.     

 

 


WEEDY RICE CONTROL WITH BENZOBICYCLON IN RICE: IS THIS POSSIBLE? M. L. Young*1, J. K. Norsworthy1, C. A. Sandoski2, M. Palhano1, S. Martin1; 1University of Arkansas, Fayetteville, AR, 2Gowan, Collierville, TN (262)

ABSTRACT

Resistance has evolved to multiple herbicide modes of action in rice. With increasing stress on our current chemistries, a new mode of action is needed in rice production. A new post-flood herbicide, benzobicyclon, is being developed by Gowan Company. Benzobicyclon, a Group 27 herbicide, controls a broad-spectrum of grasses, aquatics, broadleaves, and sedges, including those currently resistant to Group 2 herbicides.  Benzobicyclon will most likely be premixed with halosulfuron and marketed under the tradename Rogue.  This will be the first 4-hydroxyphenylpyruvate dioxygenase (HPPD) herbicide commercially available in U.S. rice production. In 2015, an unexpected observation was made from a field study conducted at the Rice Research and Extension Center near Stuttgart and at the Pine Tree Research Station near Colt, Arkansas.  At both locations, bays treated post-flood with benzobicyclon at 247 or 494 g ai/ha had a high level of weedy rice control relative to bays not containing benzobicyclon. This observation prompted a greenhouse evaluation of the efficacy of benzobicyclon on weedy rice accessions collected across Arkansas, Mississippi, and southeast Missouri. Grain from these weedy rice accession had a tremendous amount of variability in awn presence, hull color, grain shape, and grain color. More than 120 accessions are currently being evaluated for resistance to imazethapyr and sensitivity to benzobicyclon.  Although the screening results are not yet complete, it appears that benzobicyclon at 371 g ai/ha will provide control of many of the weedy rice accessions included in this study.  Efforts are currently underway to better understand if morphological characteristics correlate with sensitivity of weedy rice to benzobicyclon.

 


EFFICACY OF PREPARE FOR RESCUEGRASS (BROMUS CATHARTICUS) CONTROL IN WINTER WHEAT. L. Roberts*1, A. R. Post1, G. Strickland2, C. Effertz3; 1Oklahoma State University, Stillwater, OK, 2Oklahoma State University, Altus, OK, 3Arysta LifeScience, Velva, ND (263)

ABSTRACT

Winter wheat is Oklahoma’s number one commodity. For producers who sell their wheat at local markets grain quality is very important and producers work hard to minimize the potential dockage due to weed seed and foreign material. Grass weeds still present in wheat fields at harvest are the most common cause of weed seed and foreign material dockage. One grass in particular, rescuegrass (Bromus catharticus), has become increasingly problematic in winter wheat in the southern great plains over the last ten years. As effective products have come on the market to control other Bromus species such as cheat, and downy brome producers notice rescuegrass escaping most of these treatments and continuing to cause competition, yield reduction, and price discounts at the elevator. Effective early season management with a residual will be essential for rescuegrass control since it may germinate from November through March in the region and actively grows during wheat’s dormant period. PrePare a residual herbicide from Arysta LifeSciences is labeled for Rescuegrass suppression, but has not been widely marketed in the southern Great Plains region. Field experiments were conducted to determine the efficacy of preemergent PrePare applications in winter wheat production compared to other products currently on the market.

Two field trials were conducted in Oklahoma during the 2014-2015 growing season, both in Altus, OK, one at Howard Farms and one at Butchee Farms. All trials were randomized complete block designs with four replications. Both locations were evaluated for visual percent rescuegrass control, visual percent phytotoxicity to wheat, and visual percent stand reduction of wheat each week for six weeks after treatment (WAT) and monthly thereafter until harvest.

Experiment one in Altus, OK included the following 15 treatments:  1) nontreated; 2) 30 g ai ha-1 flucarbazone sodium (as Everest 2.0); 3) 30 g ai ha-1 flucarbazone sodium + 21 g ai ha-1 chlorsulfuron/metsulfuron methyl (Finesse); 4) 30 g ai ha-1 flucarbazone sodium + 4.2 g ai ha-1 metsulfuron methyl (Ally); 5) 30 g ai ha-1 flucarbazone sodium + 15.8 g ai ha-1ARY-0922-001; 6) 18.5 g ai ha-1 pyroxsulam (PowerFlex HL); 7) 30 g ai ha-1 flucarbazone sodium; 8) 30 g ai ha-1 flucarbazone sodium + 14 g ai ha-1 ARY-547-102; 9) 30 g ai ha-1 flucarbazone sodium + 21 g ai ha-1 chlorsulfuron/metsulfuron methyl; 10) 30 g ai ha-1 flucarbazone sodium + 15.8 g ai ha-1 ARY-0922-002; 11) 30 g ai ha-1 flucarbazone sodium + 4.2 g ai ha-1 metsulfuron methyl; 12) 18.5 g ai ha-1 pyroxsulam; 13) 30 g ai ha-1 flucarbazone sodium; 14) 30 g ai ha-1 flucarbazone sodium + 21 g ai/ha-1 chlorsulfuron/metsulfuron methyl + 30 g ai/ha-1 flucarbazone-sodium (as Everest 2.0) + 4.2 g ai ha-1 metsulfuron methyl; 15) 18.5 g ai ha-1 pyroxsulam. All treatments included 0.25% v/v NIS + 1.12 kg ha-1 sprayable ammonium sulfate.

Treatments including Finesse as part of the tank-mixture significantly reduced stands by 3.8%; however, this would be acceptable to any winter wheat grower in the Southern Great Plains and the reduction was no longer noticeable by 6 weeks after treatment (WAT). In this study all products tested provided excellent control of rescuegrass though weed populations were very low.

Experiment two in Altus, OK  included a fall burndown application of 870 g ae ha-1glyphosate + 1.12 kg ha-1 sprayable ammonium sulfate in addition to tank-mixtures (treatments 3-7) or a follow up application in spring (treatments 8-11):  1) nontreated; 2) burndown only; 3) + 15 g ai ha-1 flucarbazone-sodium (PrePare); 4) + 15 g ai ha-1 flucarbazone-sodium + 15.8 g ai ha-1 ARY-0922-001; 5) + 15 g ai ha-1 flucarbazone-sodium + 10.5 g ai ha-1 ARY-0922-001; 6) + 15 g ai ha-1 flucarbazone-sodium + 21 g ai ha-1 chlorsulfuron/metsulfuron methyl (Finesse); 7) + 15 g ai ha-1 flucarbazone-sodium + 4.2 g ai ha-1 metsulfuron methyl; 8) + 15 g ai ha-1 flucarbazone-sodium + 4.2 g ai ha-1 metsulfuron methyl; 9) + 15 g ai ha-1 flucarbazone-sodium + 18.5 g ai ha-1 pyroxsulam (PowerFlex HL); 10) +18.5 g ai ha-1 pyroxsulam; 11) + 15 g ai ha-1 flucarbazone-sodium + 4.2 g ai ha-1 metsulfuron methyl + 15.3 g ai ha-1 flucarbazone-sodium (as Everest 2.0) + 21 g ai ha-1 chlorsulfuron/metsulfuron methyl.

Again treatments containing PrePare + Finesse no matter what else was included in the tank mixture significantly reduced wheat stands by 7.5%; however, this did not translate to a significantly reduced yield. All treatments except glyphosate alone and treatment number 5 controlled rescuegrass greater than 90% by 4 weeks after spring follow-up treatments (WASP). Treatment 5 controlled rescuegrass only 75% 4 WASP.

PrePare is an effective product for rescuegrass control when included as part of a burndown application prior to planting winter wheat or as part of a follow-up spring weed control operation.  In these studies rescuegrass was effectively controlled with all tank-mix partners.

 


S-METOLACHLOR INTERACTIONS WITH SESAME ESTABLISHMENT. B. P. Sperry*1, J. A. Ferrell1, R. Leon2, M. J. Mulvaney3, D. L. Rowland1; 1University of Florida, Gainesville, FL, 2University of Florida, Jay, FL, 3University of Florida, Jay, FL, FL (264)

ABSTRACT

Early season weed control is essential for successful production of sesame (Sesamum indicum L.).  S-metolachlor (7.62 lbs ai/gallon) is registered for use in the state of Florida on sesame as a PRE only.  However, severe injury can occur from the application, but the reason for this injury is currently unknown. Two field studies were conducted at the Plant Science Research Unit at Citra, FL in the summer of 2015. The two sites were chosen with different soil types and planting dates, to assess the role of application timing on sesame emergence, growth and yield.  Four application timings were tested: 3 days before planting (3 DBP), day of planting (0 DBP), 3 days after planting (3 DAP), and 6 days after planting (6 DAP). S-metolachlor was applied at 4 rates at each timing: 0, 0.65 pts/A, 1.33 pts/A, 2.6 pts/A.  The experiment was conducted as a randomized complete block design with a factorial arrangement.  Injury was evaluated by stand counts and plant heights at 21 DAP and seed yield was collected.  Data were analyzed using a two-way ANOVA and means were separated using Fisher’s LSD.  In location A, no interaction between main effects was observed, but main effects were significant, so data are presented by main effects.  The 2.6 pts/A treatment caused reductions of 62% in emergence and 60% in plant height.  Also, the 1.33 pts/A treatment caused 47% reduction in plant height.  0 DBP application timing resulted in a 60% reduction in emergence while plant height was reduced 40-50% by all timing treatments.  The main effect of application timing was not significant for yield.  However, the 2.6 pts/A rate affected yield though no significant difference was present between the 0.65 pts/A and 1.33 pts/A rates.  In location B, there was an interaction between main effects for emergence only.  Regardless or rate, the delayed PRE applications (3 and 6 DAP) showed higher emergence than the 3 DBP and 0 DBP application timings.  Both the 1.33 pts/A and 2.6 pts/A rates caused ~30% reductions in plant height. On the contrary, rate was not significant for yield.  The 3 DBP application timing reduced plant height and yield by 56% and 65% respectively.  The results of these studies indicate that delayed PRE applications (3 and 6 DAP) of S-metolachlor provide more safety to sesame emergence, growth and yield. Despite reductions in emergence and plant heights early in the growing season, as an indeterminate crop, sesame is able to compensate in yield by branching.  Regardless, the current practice by growers of applying S-metolachlor the day of planting may not be optimal for preventing injury.  

 


GENETIC DIVERSITY, POPULATION STRUCTURE AND MARKER-HERBICIDE TOLERANCE TRAIT ASSOCIATION OF A DIVERSE TOMATO GERMPLASM. G. Sharma*, T. Tseng; Mississippi State University, Starkville, MS (265)

ABSTRACT


Genetic Diversity, Population Structure and Marker-herbicide Tolerance Trait Association of a Diverse Tomato Germplasm. G. Sharma*1, T.M. Tseng 1 ,1 Mississippi State University, Starkville, MS

 Tomato (Solanum lycopersicum) originated from South America, in Andes Mountains of Peru, Ecuador and Chile. Botanically, it is a fruit and horticulturally it is a vegetable. Both fresh and processed tomatoes are good source of vitamin A and C. In Mississippi it is grown on over 444 acres across 627 farms. Even though the crop is primarily grown in a plasticulture system, weeds are still a major problem in tomato production. Diverse germplasm is vital for crop improvement and understanding genetics of complex traits (particularly, herbicide tolerance). A total of 63 tomato lines (including wild and abiotic stress tolerant lines) used in this study was obtained from the Tomato Genetic Resource Center at UC Davis. The cultivars were grown up to 4-leaf stage and then sprayed with 2, 4-D at two different concentrations 0.5 % (0.0056 kg ai/ha) and 1 % (0.0112 kg ai/ha) of the recommended rate in soybean, in a spray chamber. Injury, stunting, and mortality, were recorded at 12 days after treatment (DAT). Thirty (17 wild, and 13 abiotic stress tolerant), and eleven (7 wild, and 4 abiotic stress tolerant) accessions showed no sign of injury and stunting at 0.5 and 1 % concentration of 2, 4-D, respectively.  The genetic diversity of 11 tomato lines which were tolerant at 1 % 2,4-D was analyzed using 30 SSR markers commonly used in tomato genetic diversity studies. All 11 lines was clustered based on the estimated genetic distance, and the genetic diversity analysis was carried out based on the unweighted pair-group method using arithmetic average clustering and principal component analysis method. Findings from this study will help understand the level of diversity within and among herbicide-tolerant populations. A highly diverse population of tomato will be a preferred candidate for tolerance screening with additional herbicides, as they will have higher degree of adaptability to herbicide and abiotic stress.


SWEETPOTATO (IPOMOEA BATATAS) TOLERANCE TO LINURON POST. S. C. Beam*, K. M. Jennings, D. W. Monks, J. R. Schultheis, S. J. McGowen, N. T. Basinger, M. B. Bertucci; North Carolina State University, Raleigh, NC (266)

ABSTRACT

Sweetpotato (Ipomoea batatas) Tolerance to Linuron POST. S.C. Beam*, K.M. Jennings, D.W. Monks, J.R. Schultheis, S.J. McGowen, N.T. Basinger and M.B. Bertucci; North Carolina State University, Raleigh, NC. 

Field studies were conducted in 2015 on grower fields in Faison, North Carolina to determine tolerance of ‘Covington’ and ‘Murasaki’ sweetpotato to linuron POST.  Flumioxazin at 107 g ai ha-1 was applied PREPLANT to all plots.  Fields were mechanically transplanted on May 19 using a tractor pulled transplanter.  Treatments were applied 7 or 14 d after transplanting (DAP) and included linuron alone or tank mixed with S-metolachlor.  Linuron was applied at 0, 420, 560, 841, and 1121 g ai ha-1; S-metolachlor was applied at 803 g ai ha-1.  Visual injury ratings were recorded at 0, 1, 2, 4, 8, 10 and 12 wk after treatment (WAT).  Storage roots of Covington and Murasaki were harvested at 105 and 142 DAP, respectively, using a single row disk turn plow.  Sweetpotato storage roots were hand-graded (jumbo, no. 1, and canner grades) and then weighed.  Visual injury from linuron applied 7 DAP was less (9 to 75%) than when applied at 14 DAP (71 to 93%) all season long.  Visual injury to treated sweetpotato was transient and was not present at 8 WAT.  Marketable yield was greater when linuron was applied 7 DAP (Covington ranged from 25,627 to 36,312 kg ha-1 and Murasaki ranged from 16,316 to 24,289 kg ha-1).  However, yield from linuron applied 14 DAP was 17,424 to 25,606 kg ha-1 and 3,959 to 17,563 kg ha-1 for Covington and Murasaki, respectively.  Differences in visual injury and yield of sweetpotato were not observed between linuron alone and linuron plus S-metolachlor.

 

scbeam@ncsu.edu

 


IMPACT OF REDUCED RATES OF HORMONAL HERBICIDES ON SWEETPOTATO (IPOMOEA BATATAS LAM.) GROWTH AND DEVELOPMENT. T. M. Batts*1, D. K. Miller1, T. P. Smith2, A. Villordon2, J. L. Griffin3, D. O. Stephenson IV4; 1LSU AgCenter, St Joseph, LA, 2LSU AgCenter, Chase, LA, 3LSU AgCenter, Baton Rouge, LA, 4LSU AgCenter, Alexandria, LA (267)

ABSTRACT

Two field studies were conducted in 2014 and repeated in 2015 at the Sweet Potato Research Station near Chase, La with the objective to evaluate impacts of hormonal herbicides on growth and development of sweetpotato.  ‘Beauregard’ cultivar was used in both studies.  Treatments were applied at 10 d after transplant (6/20/14 and 6/12/15) to 3 x 7.62 m plots.  A four replication factorial arrangement of treatments was used and included glyphosate, DGA salt of dicamba, or glyphosate + DGA salt of dicamba (Factor A; 1.0 lb ae/A, 0.5 lb ae/A, and 1.0 + 0.5 lb ae/A use rates, respectively) at 1/10, 1/100, 1/250, 1/500, 1/750, or 1/1000 of use rate (Factor B) in one study and glyphosate, Choline salt of 2,4-D, or glyphosate +  Choline salt of 2,4-D (1.0 lb ae/A, 0.75 lb ae/A, or 1.0 + 0.75 lb ae/A use rates, respectively) at similar reduced rates in the second study.  Parameter measurements included visual crop injury (chlorosis, stunting, twisting, leaf crinkling) 7 and 28 d after application, storage root number 10 and 30 d after application, and yield.  A non-treated control was included to aid in making visual assessments and also used to calculate percent reduction with respect to quantitative measurements for statistical analysis.  A non-treated control was not included in the statistical analysis, which consisted of the MIXED procedure in SAS. The fixed effects for the model for yield data were treatment (product and rate). The fixed effects for the model for injury and root data were treatment and repeated measures effects for DAT. The random effects for all models were year, replications, and plots.

In the dicamba study, at 7 DAT greatest injury of 48% and 55% was observed for dicamba alone and glyphosate + dicamba applied at the highest rate, respectively.  Results were similar at 28 d after application with these respective treatments resulting in greatest injury of 30 and 41%.  Percent reduction calculations from the non-treated control for root number at 10 and 30 d, jumbo, no. 1, canner grade and total yield indicated no deleterious effects from the herbicide applications.

In the 2,4-D study, averaged across application rates, at 7 DAT greatest visual injury of 28%  was observed with 2,4-D applied alone in comparison to glyphosate (22%) and the combination (23%) which resulted in equivalent injury. Averaged across herbicides, greatest injury of 37% was observed at the highest fractional rate applied.  Minor differences were noted among lower rates resulting in injury ranging from 19 to 27%.  At 28 DAT, averaged across herbicides, greatest injury of 21% was observed for the highest fractional rate applied.  With the exception of the 1/100 fractional rate (11%), no other rate resulted in greater than 8% injury.  Storage root number at 10 and 30 d after application, as well as jumbo, and #1 grade yields were not significantly reduced by any herbicide application.  When averaged across herbicides, canner grade and total potato yield were significantly reduced (26% and 19%, respectively) at the highest rate.  Off target application of reduced rates of dicamba has the potential to result in visual injury, but plants appear to recover where no yield reductions are observed.  Off target application of 2,4-D can cause deleterious visual symptoms as well as yield reductions. Therefore, based on cumulative results, producers with multi-crop farming operations are cautioned to thoroughly follow all labeled sprayer cleanout procedures when previously spraying one of the combination herbicides evaluated or to devote separate equipment to spraying Xtend® and Enlist® crops.

 


WEED CONTROL IN INZEN GRAIN SORGHUM. N. R. Steppig*, J. K. Norsworthy, M. Bararpour, J. K. Green, C. J. Meyer; University of Arkansas, Fayetteville, AR (268)

ABSTRACT

In 2015, grain sorghum was the fifth-largest agricultural crop produced in the United States, accounting for nearly 8 million acres of production. As a result of increased demand for American grain sorghum in China, coupled with low returns from cotton, there is likely to be continued interest in grain sorghum. As such, growers are looking for progressive ways to manage the crop and maintain high yields.  One of the primary yield-reducing factors for any crop is competition from weeds. Grain sorghum is no different, and grassy weeds are particularly difficult to control in grain sorghum cropping systems. However, DuPont Pioneer will soon introduce Inzen™ grain sorghum, a hybrid exhibiting resistance to nicosulfuron. The Inzen™ trait allows for the use of DuPont’s nicosulfuron-based Zest™ herbicide, which provides control of a number of grasses, including johnsongrass (Sorghum halepense). As with any new herbicide being brought to market, the need exists for research to assess crop tolerance and spectrum of weed control. A field study was conducted in 2015 at the Lon Mann Cotton Research Station in Marianna, Arkansas to evaluate control programs for johnsongrass and other grass weeds in grain sorghum. Of particular interest in this study was an evaluation of weed control with a preemergence (PRE) application of LeadOff® herbicide followed by a postemergence (POST) application of Zest™ plus atrazine, a DuPont recommendation for season-long weed control. Results demonstrate that by incorporating herbicide programs examined in this study, both broadleaf and grass weeds can controlled throughout the growing season. The most successful weed control in this particular study was a result of utilizing any of the PRE applications coupled with a POST application of Zest™ plus atrazine. These programs displayed >90% control of grass weeds such as johnsongrass, large crabgrass (Digitaria sanguinalis), and barnyardgrass (Echinochloa crus-galli), and >85% control of Palmer amaranth (Amaranthus palmeri) throughout the growing season.  Additionally, crop injury after Zest™ application was negligible, suggesting that current weed control programs that incorporate the Inzen™ trait and utilize Zest™ herbicide are both safe and effective for season-long weed control. These results are promising for American growers and suggest that adoption of Inzen™ grain sorghum may be a highly beneficial tool for helping producers contend with POST control of grasses as grain sorghum competes for more acreage nationwide.


POSTEMERGENCE CONTROL OF LARGE CRABGRASS (DIGITARIA SANGUINALIS) WITH NON-SYNTHETIC HERBICIDES. M. E. Babb-Hartman*1, C. Waltz1, G. Henry2; 1University of Georgia, Griffin, GA, 2University of Georgia, Athens, GA (269)

ABSTRACT

There is growing public interest in non-synthetic/organic weed management strategies; however, relatively little research has been performed on this type of weed control in warm-season turfgrass systems. The objectives of this research were to evaluate the efficacy of commercially available organic products for postemergence weed control in turfgrass. Greenhouse experiments were conducted at the Crop and Soil Sciences greenhouse complex in Athens, GA during the spring/summer of 2015. Large crabgrass [Digitaria sanguinalis (L.) Scop.] was seeded at 1.12  kg ha-1 into pots (15.24 cm diameter) containing an Appling sandy loam (Fine, kaolinitic, thermic Typic Kanhapludult) soil  on May 6, 2015 in two separate greenhouses. Temperatures were maintained at 33/29 and 29/24 C (day/night). Pots were maintained at 2.5 cm throughout the length of the trial to simulate management conditions present on a home lawn, athletic field, or golf course rough. Prior to treatment application, pots were thinned to 10 plants pot-1 to increase trial uniformity. Following treatment, crabgrass was allowed to grow without mowing until harvest. Pots were arranged in a 3 x 7 factorial with four replications. The main factor was large crabgrass growth stage (1-2 leaf, 1-2 tiller, and 3-5 tiller) and the sub-factor was treatment. Treatments included Avenger (d-limonene oil), Espoma corn gluten meal, WeedZap (cinnamon/clove oil), WeedPharm (acetic acid), and Scythe (pelargonic acid). Non-selective treatments, Roundup PRO Max (glyphosate) and Finale (glufosinate), were included as industry standard comparisons. Liquid treatments were applied with a CO2 backpack sprayer equipped with XR8004VS nozzles calibrated to deliver 375 L ha-1 at 221 kPa. Corn gluten meal was applied by hand with a shaker jar to the crabgrass canopy. Visual ratings of % large crabgrass control were recorded 1, 7, 14, 28, and 56 days after treatment (DAT) on a scale of 0 (no control) to 100% (complete control). Above-ground biomass was harvested 1 and 2 months after treatment (MAT), dried, and weighed (g). Percent large crabgrass control and above-ground biomass were subjected to ANOVA using error partitioning appropriate to a split block analysis in the general linear models procedure. Means were separated using Tukey’s HSD test at the 0.05 significance level. Field trials were established during fall of 2015 on the University of Georgia Griffin campus. Field plots (1.5 x 1.5 m) were seeded with large crabgrass at a rate of 2.24 kg ha-1 on September 2, 2015. The site was maintained at a 3.81 cm height with a rotary mower throughout the trial duration. Plots were arranged in a 2 x 6 factorial within a randomized complete block design with four replications. The main factor was application timing (single or sequential) and the sub-factor was treatment. Applications were made at the 1-2 tiller stage on Set 18, 2015. Half the plot received a single treatment, while the other half received sequential treatments applied two weeks apart. The same treatments were examined as described in the greenhouse trial except for Espoma corn gluten meal. Visual ratings of % large crabgrass control and % cover were recorded 0, 14, 28, and 56 days after initial treatment (DAIT). Percent large crabgrass cover was determined using a 1 x 1 m grid with 25 intersecting points that was randomly placed into each plot. Statistics were analyzed by 2-way ANOVA in JMP software, and means were separated using Tukey’s HSD test at the 0.05 significance level.  In the greenhouse trials, the growth stages showed significant differences in injury up to 28 DAT, after which 1-2 leaf and 1-2 tiller stages were significantly higher than the 3+ tiller stage (p<0.0003). Plants treated with Scythe, Avenger, and WeedPharm had significantly more injury than other treatments at 1 DAT, but Finale, Roundup PRO Max, and Scythe maintained significantly  higher injury than other treatments from 7 DAT to 56 DAT (p<0.0001). The Finale, Roundup PRO Max, and Scythe treated plants also yielded significantly less biomass than all other treatments at both the 28 DAT harvest and the 56 DAT harvest (p<0.0001).  The Espoma corn gluten meal treated plants had significantly more biomass than all other treatments, including the non-treated control (p<0.0001).  For this reason, it was excluded from the field trial.  In the field trial, over 80% weed cover was measured in all plots prior to initial application, and differences between plots were not significant.  WeedPharm and Avenger injured the plants significantly more than the other treatments at 1 DAIT (p<0.0001). However, Finale, Roundup PRO Max,  Avenger, and Scythe led in significant injury levels from 7 DAIT to 56 DAIT with 99.4, 97.5, 87.5, and 78.8 % injury, respectively, at 7 DAIT.  Roundup PRO Max and Finale provided significantly more crabgrass control in terms of % cover than all other treatments (p<0.0001).  There was no significant difference between applying one treatment and two sequential treatments.  Finale and Roundup PRO Max remain the efficient industry standards for non-selective control of large crabgrass, however, Avenger and Scythe performed similar to these popular herbicides.  Avenger and Scythe are the best options from those tested here for organic/non-synthetic control of large crabgrass in warm-season turfgrass systems.

 

 


SANDBUR (CENCHRUS ECHINATUS) HEAD DEFORMATION USING POSTEMERGENCE HERBICIDES. E. Jenkins*, A. R. Post, J. Q. Moss; Oklahoma State University, Stillwater, OK (270)

ABSTRACT

Several sandbur species affect residential and recreational turfgrass in the Southern Great Plains (SGP) including southern sandbur (Cenchrus echinatus), field sandbur (Cenchrus spinifex), and longspine sandbur (Cenchrus longispinis).  Sandburs typically behave as summer annuals or weak perennials but the biology of sandbur is not well understood.  Since the loss of MSMA, there are no postemergent herbicides which effectively control sandburs in bermudagrass (Cynodon dactylon (L.) Pers.) turf. After preliminary evidence suggests certain postemergence herbicides will sufficiently deform the bur of sandbur florets so that they do not cause physical harm to people or livestock.  We also hypothesize that these deformities decrease seed fill and viability.

Five experiments were initiated in the greenhouse in Stillwater, Oklahoma in 2014 to evaluate the efficacy of postemergent herbicide products to deform sandbur florets at different growth stages. Three of the experiments were a 5 by 4 factorial treatment design, factor one being timing of application and factor two being herbicide treatment with four replications. Southern sandbur were germinated 7 days apart for 5 weeks and treated one week after the last set germinated. Plants were maintained at a 16 hour photoperiod with 82/75 F day/night temperatures.  The studies included  application timings from one to five week old plants and 3 postemergent treatments:  1)770 g ae ha-1 2,4-D, 2) 1010 g ai ha-1 aminopyralid + 2,4-D (GrazonNext), 3) 70g ai ha-1 aminopyralid (Milestone), and 4) non-treated check. Percent injury, plant quality on a scale from 0-10, and number of florets produced were recorded weekly for 8 weeks after treatment (WAT). Data were managed in ARM 9.2 and subject to ANOVA. Means were separated using Fisher’s protected LSD at α=0.05. Milestone applied to one week old sandbur and GrazonNext applied to two week old sandbur were the two treatments which exhibited the most severe head deformities based on plant quality ratings. GrazonNext applied to 1 or 2 week old sandbur and Milestone applied to one week old sandbur limited floret production to an average of less than one floret per plant compared to an average of 6 per plant on the nontreated by 8WAT. All 2,4-D alone treatments applied at four and five week old sandbur increased floret production to as many as 12.8 florets per plant by 8 WAT

Two other experiments were established as a 5 by 9 factorial, factor one being application timing and factor two being treatment.  Herbicides evaluated included:  1) 840 g ae ha-1 dicamba, 2) 840 g ai ha-1 triclopyr (Garlon), 3) 70 g ai ha-1 imazapic (Plateau), 4) 530 g ae ha-1 glyphosate, 5) 89 g ai ha-1 pyroxasulfone (Zidua), 6) 70 g ai ha-1 nicosulfuron + metsulfuron methyl (Pastora), and 7) 93 g ai ha-1 aminocyclopyrachlor (Method), 8) 70 g ai ha-1 aminopyralid (Milestone) and 9) non-treated check.

Method, Milestone and Pastora applied through to sandbur plants up to four weeks old severely deformed heads and prevented them from forming burs strong enough to penetrate skin.  . Our data suggests applications of Milestone or GrazonNext to pastures soon after sandbur germination may deform heads enough to prevent livestock injury and will also decrease seed production.  Additional studies are planned to evaluate seed viability for florets collected from these studies.  

 


INCREASING WINTER SURVIVABILITY OF WINTER CANOLA WITH PLANT GROWTH REGULATORS. K. McCauley*, J. Matz, A. R. Post; Oklahoma State University, Stillwater, OK (271)

ABSTRACT

Canola (Brassica napus L.) was introduced to Oklahoma in the early 2000’s as a rotational crop with winter wheat as a tool to control resistant biotypes of the grassy weeds that infest Oklahoma wheat fields. However, canola production in the Southern Great Plains is limited by the crop’s overwintering capability. The planting window for canola crop insurance spans only 30 days, from September 10th to October 10th each year.  This narrow planting window severely limits flexibility for producers trying to plant winter crops each fall. In addition, canola planted early in this window is subject to develop over-sized top-growth making it more sensitive to winterkill and canola planted late in the window is subject to freezing before a good stand can be established. A wider planting window and options for managing fall top-growth would increase flexibility for producers in this cropping system. Though there are currently only two labeled products, plant growth regulators (PGRs) are a good option for reducing top-growth when canola is planted early to prevent excessive winter kill. In this research, early planting dates and PGRs were evaluated in winter canola to control fall growth and promote optimum plant conditions moving into the winter season.

A preliminary study was conducted in Stillwater, Oklahoma during the 2014-2015 cropping season to evaluate the impact of earlier planting dates and the use of plant growth regulators (PGR) on fall stand establishment, winter hardiness, and yield for winter canola. The study used a randomized complete block design with a factorial treatment structure; factor 1 being planting date and factor 2 being PGR treatment. Planting dates began on August 28 and were repeated weekly for five weeks.  Treatments for this site included: 1) control plot for each planting date that received no PGR treatment; 2) 63.07 g ai ha-1 tebuconazole; 3) 126.15 g ai ha-1 tebuconazole; 4) 12.27 g ai ha-1 mepiquat chloride; 5) 24.53 g ai ha-1 mepiquat chloride; 6) 57.47 g ai ha-1 mepiquat pentaborate; 7) 139.75 g ai ha-1 prohexadione-calcium; and  8) 52.56 g ai ha-1 metconazole. The following year in the 2015-2016 cropping season, more in-depth field experiments were conducted at six sites across Oklahoma.  Experiments were conducted in a strip block design with a factorial treatment arrangement of planting date by PGR application.  Treatments included 1) a control plot for each planting date that received no PGR treatment, 2) 63.07 g ai ha-1 tebuconazole; 3) 126.15 g ai ha-1 tebuconazole; 4) 12.27 g ai ha-1 mepiquat chloride; 5) 24.53 g ai ha-1 mepiquat chloride; 6) 57.47 g ai ha-1 mepiquat pentaborate; 7) 139.75 g ai ha-1 prohexadione-calcium; 8) 52.56 g ai ha-1 metconazole and 9) 2.25 g ai ha-1 + 0.841 g ai ha-1 + 1.12g ai ha-1 kinetin + gibberellic acid + indole butyric acid.  The first planting date was August 25th (hereafter, Planting date A) followed by a sequential planting date every week for five weeks: September 1st (B), Septmeber 8th (C), September 15th (D), and September 22nd (E).  PGR applications were made with a CO2 propelled sprayer at 280 L ha-1 at the four to six leaf growth stage.  Stand counts were measured at the time of application as a reference rating.  Subsequently, stand count, height, and above ground biomass of 3 random plants were taken 4 weeks after treatment (WAT).

Prohexadione-calcium significant decreased yield across all planting dates in the 2014-2015 season compared to the control. During the 2015-2016 field season metconazole applied to planting date E significantly decreased plant height compared to mepiquat pentaborate applied to planting date A, prohexadione calcium applied to planting date A or D, and the kinetin premix applied on planting date D or E. Stand counts 4 WAT were significantly higher in planting dates D and E across all treatments. Although data to date indicate few measurable differences over the fall season, the true differences in winter survivability will be stand counts after spring green-up in addition to 2016 yield. Current data indicate metconazole applied to canola planted in the 2nd week of the normal window benefits the crop most for decreased top-growth. Plant growth regulators may not be the answer to decreased top-growth and increased winter survivability, but may still assist in preserving yield potential. This work has been funded by the Oklahoma Oilseed Commission and USDA-NIFA-SACC.  

 


DETERMINING NOZZLE TYPE EFFECTS ON PEANUT WEED CONTROL SYSTEMS. O. W. Carter*, E. P. Prostko; University of Georgia, Tifton, GA (272)

ABSTRACT

The increase in herbicide resistant weeds over the past decade has led to the introduction of crops that are tolerant to auxin herbicides.  Strict application procedures will be required with auxin resistant crops.  One requirement for application is the use of nozzles that will minimize drift by producing larger droplet sizes.  Generally, an increase in droplet size can lead to a reduction in coverage and efficacy depending upon the herbicide and weed species.   In studies conducted in 2015, two of the potential required auxin nozzle types (AIXR11002 and TTI02) were compared to a conventional drift guard nozzle (11002DG) for weed control in peanut herbicide systems on bare ground and in-crop.  In the bare ground test, the following POST herbicide treatments were evaluated: paraquat + acifluorfen + bentazon + S- metolochlor;  imazapic + 2,4-DB + S-metolochlor;  lactofen + 2,4-DB + S-metolochlor; and acifluorfen + 2,4-DB + S-metolochlor.   Herbicide systems evaluated for the in-crop study included the following: pendimethalin + flumioxazin + diclosulam (PRE) followed by either lactofen or imazapic + 2,4-DB + S-metolochlor (POST); or pendimethalin (PRE) followed by paraquat + acifluorfen + S-metolochlor (EPOST) followed by lactofen or imazapic + 2,4-DB + S-metolochlor (POST).  All treatments were applied using 141 L/ha at 262 kPa and 4.83km/h.   Palmer amaranth control, annual grass control and yield were not affected when using the AIXR 11002 and the TTI02 nozzles in peanut weed control systems when compared to the conventional DG nozzle.


COGONGRASS MANAGEMENT USING CHEMICAL CONTROL AND COVER CROPPING SYSTEMS. M. M. Zaccaro*, J. D. Byrd, Jr.; Mississippi State University, Mississippi State, MS (273)

ABSTRACT

Cogongrass (Imperata cylindrica (L.) Beauv.) is a noxious weed that invaded the Southeast region of the United States many decades ago. There are a few management options that provide highly effective, long-term control of cogongrass. The purpose of this experiment was to assess cogongrass control using RR ‘Big Fellow’ forage soybeans (Glycine max (L.) Merr.) with multiple glyphosate applications. The experimental design each year was a 2 x 3 factorial arrangement of treatments in randomized complete block design with four replications. The factors were presence or absence of soybean cover crop, and number of glyphosate applications. In the first season, the soil was tilled and the ‘Big Fellow’ forage soybean cover crop was planted July 2014 with a no-till drill calibrated to deliver 84.1 kg seed ha-1. Sequential herbicide applications of 1.1 kg ae ha-1 of Roundup PowerMax 4.5L (glyphosate) plus 0.25% v/v of non-ionic surfactant were made August, September and October as needed based on cogongrass recovery. Visual percent control data were taken periodically after the first herbicide application, until after spring transition the following year. Soybeans and cogongrass biomass samples were collected in October 2014, and dry weight measured. The experiment was replicated in 2015 at the same location. However, due to more favorable weather, soybean was planted in June. Herbicide applications at of the same rate were made in June and August, again based on cogongrass recovery. Biomass samples were harvested in September. Data analysis were performed using PROC GLIMMIX in SAS 9.4 with α value of 0.05. Data for the two years were not combined for analysis. In the 2014 season, number of herbicide applications was the independent factor that significantly affected mean cogongrass control regardless of cover crop use. Increasing from single to a double Roundup application more than doubled visual cogongrass control. Increasing from two to three Roundup applications did not significantly affect cogongrass control. Similarly, the increase from a single to double herbicide application reduced mean cogongrass biomass weight by 85%. In the 2015 season, cover crop was the independent factor that significantly affected mean cogongrass control regardless of number of herbicide applications. The use of soybean cover crop significantly increased mean cogongrass control up to 99% at September, independent of the number of herbicide applications. When comparing none to cover crop only, the increase from a single application to double resulted in a significant increase of mean cogongrass control. So after two years of research, we conclude that established cogongrass cannot be controlled with only a single year of this management system. Generally, two glyphosate applications are recommended during one growing season to control cogongrass, but a reduction to a single application could be made if the soybean cover crop is well established.


TIMING OF HERBICIDE APPLICATION FOR COVER CROP TERMINATION OF SUNN HEMP (CROTALARIA JUNCEA) AND SORGHUM. B. Farrow, C. Hofegartner, V. R. Bodnar*, J. Warren, A. R. Post; Oklahoma State University, Stillwater, OK (274)

ABSTRACT

Cover crops can be an excellent rotational choice in no-till cropping systems compared to a fallow period.  The offer many benefits including but not limited to erosion control, nitrogen fixation (some species), biological tillage (some species), increased soil organic matter content and weed suppression. However, cover crops need to be chosen carefully for each system so they do not disrupt the overall goals of crop production. Two species we examined have the potential to cause problems in no-till systems, sunn hemp (Crotalaria juncea L.), and forage sorghum (Sorghum spp.).  Sunn hemp is an annual legume which fixes nitrogen and creates large amounts of biomass in a short time. This species can grow over 2 m in height and is difficult to terminate with herbicides above 30 cm in height. It is also expected that sunn hemp can make viable seed in some warmer climates like that of Oklahoma, depending on when it is planted in the spring. Viable seed production may lead to the species becoming weedy in this system. Forage sorghum is another species capable of adding organic matter to the soil through copious biomass production.  This species also offers grazing capacity for livestock and shading for weed control. But chemical termination of forage sorghum can be a challenge when preparing fields for the next crop. 

Two greenhouse studies were implemented in 2015 to evaluate the efficacy of several herbicides for cover crop termination of sunn hemp and forage sorghum, respectively.  Each study was designed with a 3 by 13 factorial treatment arrangement and four replications, factor one being plant height and factor two being herbicide. Greenhouses were located in Stillwater, Oklahoma at the Oklahoma State University Ridge Road Greenhouse Facility. Conditions were maintained at 85/78 F day/night temperatures and a 16 hour photoperiod. Sunn hemp and sorghum plants were separated into three size classes for treatment: 30-90cm, 91-150cm, 151-215cm. In the sunn hemp study herbicide treatments included: glyphosate (Roundup Powermax) at three rates 1540, 3850, or 7700 g ai ha-1; 2,4D (LV400) at three rates 766, 1150, or 1530 g ai ha-1; carfentrazone + 2,4-D (Rage D-Tech) at three rates 390, 780, or 1570 g ai ha-1; and saflufenacil (Sharpen) at three rates 25, 37.4, or 50 g ai ha-1; as well as a nontreated check. In the sorghum study herbicide treatments included: glyphosate (Roundup Powermax) at three rates 1540, 3850, or 7700 g ai ha-1 + 3360 g ai ha-1 AMS; glufosinate (Liberty) at three rates 450, 1390, or 1730 g ai ha-1 + 3360 g ai ha-1 AMS; sethoxydim (Poast) at three rates 210, 315, or 420 g ai ha-1 + 2800 g ai ha-1 AMS + 1% v/v COC; and saflufenacil (Sharpen) at three rates 25, 37.4, or 50 g ai ha-1+ 9500 g ai ha-1 AMS+ 1% v/v MSO; as well as a nontreated check.

Plants in each study were visually evaluated for percent control every seven days for four weeks following treatment. This would be appropriate since most burn-down applications occur two to four weeks prior to planting the next crop and full termination of a cover crop would be required before planting. As expected, for both species, plant size played a role in herbicide efficacy.  The larger the plants the more difficult they were to control with chemical applications.

For sunn hemp, saflufenacil at all three rates controlled 30-90cm plants 95 to 100% at all rating dates. Glyphosate controlled 30-90cm plants and 91-150cm plants at the highest rate 70 to 95%. However, all other plant size and rate combinations were less than 70% controlled. Additionally, in all size classes, regrowth occurred after initial herbicide injury and about three weeks after treatment. For forage sorghum, saflufenacil and glyphosate at all rates controlled sorghum 83 to 100% for plants 30-90 cm. The two larger size classes for both species were not fully terminated with any evaluated herbicide treatment. Therefore, it is recommended that characteristics of sunn hemp and forage sorghum be weighed carefully before planting for a full season cover crop ahead of winter crops in Oklahoma.  These two species are not effectively terminated after reaching 90cm in height and most herbicide labels do not recommend an effective rate for target plants larger than 30cm in height. 

 


EVALUATION OF CHEMICAL TERMINATION OPTIONS FOR COVER CROPS. M. G. Palhano*, J. K. Norsworthy, M. L. Young, R. R. Hale, J. K. Green; University of Arkansas, Fayetteville, AR (275)

ABSTRACT

Cover crop acreage has substantially increased over the last few years due to the intent of growers to capitalize on federal conservation payments and incorporate sustainable practices into agricultural systems. Despite all the known benefits, widespread adoption of cover crops still remains limited due to their potential cost and management requirements. Cover crop termination is crucial for the success of management strategy since a poorly terminated cover crop can became a weed and lessen the yield potential of the current cash crop. A field study was conducted in the fall of 2015 at the Arkansas Agricultural Research and Extension Center in Fayetteville to evaluate burndown options for cover crops. This experiment was organized as a randomized completely block with a strip-plot, where the herbicide treatments was the main plot and cover crops the strip-plot. Treatments were composed of 25 termination options. Visual assessment of control was evaluated at 2 and 4 weeks after application. Biomass was collected at 4 weeks after application. Fresh biomass was measured immediately after biomass collection and dry biomass production was determined. Cereal cover crops, such as wheat and cereal rye, were effectively terminated by glyphosate, and all the containing glyphosate treatments. The legume cover crops hairy vetch, Austrian winterpea and crimson clover were poorly controlled by glyphosate alone. However, better control was observed when auxin herbicides and saflufenacil were present in the tank mixture with glyphosate. Paraquat plus metribuzin demonstrated to be a worthy option for both cereal and legumes cover crops. Rapeseed was not well controlled by any of the termination options. Earlier application of burndown herbicides might enhance the control of this cover crop or maybe growers should consider other easier to terminate cover crops. 

 


WEED CONTROL IN SOYBEAN WITH MIXTURES OF HERBICIDES AND FOLIAR NUTRITION PRODUCTS. H. T. Hydrick*, J. A. Bond, B. R. Golden, B. Lawrence, J. D. Peeples, H. M. Edwards, T. L. Phillips; Mississippi State University, Stoneville, MS (276)

ABSTRACT

To reduce expenses, growers often include foliar nutrition products with in postemergence herbicides applications.  Research was conducted in 2015 at the Delta Research and Extension Center in Stoneville, MS, to evaluate weed control and crop response to common soybean herbicides applied in mixtures with a foliar nutrition product.  Two weedy sites assessing weed control and two weed-free sites evaluating soybean response were utilized in the study.  Treatments were arranged as a two-factor factorial in a randomized complete block design with four replications.  Factor A was herbicide treatments and included no herbicide, glyphosate at 1.12 kg ae ha-1, glyphosate plus s-metolachlor at 1.42 kg ai ha-1, glyphosate plus fomesafen at 0.395 kg ai ha-1, and glyphosate plus lactofen at 0.218 kg ai ha-1.  Factor B was Brandt Smart Trio (4-3-3-3-0.25% N-S-Mn-Zn-B) applied at 0, 0.390, and 0.778 kg ai ha-1.  Treatments were applied when soybean reached the V3 growth stage.  Visual estimates of soybean injury were recorded 3, 7, 14, 21, and 28 days after treatment (DAT), while control of Palmer amaranth and barnyardgrass were visually estimated 7, 14, 21, and 28 DAT.  Soybean biomass and tissue samples were collected 14 DAT in the weed-free study.  Soybean heights were recorded 14 DAT and prior to harvest.  Yield was converted to 13% moisture content.  All data were subjected to ANOVA and estimates of the least square means were used for mean separation with P = 0.05.  In the weed-free experiment, no effect due to Brandt Smart Trio rate was detected for soybean injury at any evaluation.  Additionally, Brandt Smart Trio rate did not influence soybean dry weight, nutrient content, mature height, or yield.  In the weedy experiment, soybean injury was not reduced when Brandt Smart Trio was added to herbicide treatments.  Soybean injury was greatest with glyphosate plus lactofen 3, 7, and 14 DAT.  At 14 DAT, Palmer amaranth control was reduced when either rate of Brandt Smart Trio was mixed with glyphosate, glyphosate plus s-metolachlor, or glyphosate plus lactofen.  Barnyardgrass control 14 DAT with all herbicide treatments was lower when Brandt Smart Trio was included.  Including Brandt Smart Trio in postemergence herbicide applications reduced weed control and had no effect on soybean injury and agronomic performance.  

 


EVALUATION OF PETHOXAMID IN COTTON AND SOYBEAN. J. S. Rose*, L. T. Barber, J. K. Norsworthy, M. S. McCown; University of Arkansas, Fayetteville, AR (277)

ABSTRACT

Evaluation of Pethoxamid in Cotton and Soybean. J.S. Rose*, L.T. Barber, J.K. Norsworthy, M.S. McCown.

FMC is currently developing pethoxamid, a new Group 15 residual herbicide, for use as a preemergence herbicide and tank-mix option with postemergence herbicides in numerous crops. Experiments were conducted in 2014 and 2015 at the Southeast Research and Extension Center in Rohwer, Arkansas, to evaluate the performance of pethoxamid in comparison to other common preemergence weed control treatments. This experiment was conducted in both LibertyLink and Roundup Ready soybean and cotton systems and was arranged using a randomized complete block design. The rate comparison trial consisted of 8 treatments that evaluated the efficacy and selectivity of pethoxamid alone in comparison to S-metolachlor (Dual Magnum) and acetochlor (Warrant) for residual weed control. Both trials consisted of 7 treatments that included pethoxamid applied at multiple timings and in combination with other broad-spectrum herbicides. Pethoxamid applied preemergence (PRE) at 1.0 lb ai/acre performed similar to 1.0 lb ai/acre of S-metolachlor and superior to acetochlor at 0.94 lb ai/acre and 1.25 lb ai/acre on Palmer amaranth and barnyardgrass. Pethoxamid when applied PRE caused less injury to cotton than did diuron, and the level of injury was similar to acetochlor. When applied POST in combination with glyphosate or glufosinate in cotton, a high level of residual barnyardgrass control, greater than 95%, was observed. In soybean, pethoxamid provided 84% control of Palmer amaranth which was statistically similar to the 89% control provided by S-metolachlor at 3 weeks after application (WAA). The application of pethoxamid + fomesafen + glyphosate provided similar control to fomesafen + S-metolachlor + glyphsoate. Based on this research, pethoxamid will provide Midsouth cotton and soybean producers another very long chain fatty acid inhibitor for use in cotton and soybean for control of small-seeded broadleaves and grasses.


THE EFFECT OF COTTON (GOSSYPIUM HIRSUTUM L.) GROWTH STAGE ON INJURY AND YIELD WHEN SUBJECTED TO A SUB-LETHAL CONCENTRATION OF 2,4-D. J. Buol*1, D. B. Reynolds2; 1Mississippi State University, Mississippi State, MS, 2Mississippi State University, Starkville, MS (278)

ABSTRACT

THE EFFECT OF COTTON (Gossypium hirsutum L) GROWTH STAGE ON INJURY AND YIELD WHEN SUBJECTED TO A SUB-LETHAL CONCENTRATION OF 2,4-D. J. Buol and D.B. Reynolds. Department of Plant and Soil Sciences, Mississippi State University, Mississippi State, MS 39762.

ABSTRACT

The pending registration and commercialization of novel auxin-herbicide-tolerant crop biotechnologies may hold great promise in helping address the compounding issue of herbicide-resistance. New weed management systems such as the Enlist™ and Extend™ platforms will allow producers of the major row crops to enjoy an additional herbicide mode-of-action (MOA) in their weed control arsenals. These systems will also allow more flexible herbicide application logistics, hopefully culminating in a more integrated and robust approach to herbicide-resistance stewardship. However, because implementation of these weed-control systems will likely promote an increased use of the auxin-mimic herbicides 2,4-D (2,4-dichlorophenoxyacetic acid) and dicamba (3,6-dichloro-2-methoxybenzoic acid), a corresponding increase in the risks associated with these herbicides will likely ensue. Due to their effects on plant hormone physiology, 2,4-D and dicamba are capable of negatively affecting susceptible species even if exposure is to low, sub-lethal concentrations. Thus, off-target exposure to the auxin-herbicides such as would manifest with herbicide drift, volatility, or spray-tank contamination events are important when considering the production of auxin-sensitive crops such as non-transgenic cotton cultivars.

Previous research has characterized a complex relationship between cotton and the auxin-herbicides. It has been shown that 2,4-D is generally more injurious to cotton than dicamba. However, growth stage at the time of exposure appears to have an effect on cotton response to sub-lethal rates of auxin-herbicides. Current research shows that exposure to sub-lethal concentrations of 2,4-D is more injurious to cotton early in its growth and development. Conversely, exposure to sub-lethal concentrations of dicamba appears to result in the most severe injury and yield loss when it occurs in the middle of cotton’s growth and development.

Upland cotton (Gossypium hirsutum L) remains an economically important crop in the United States as over 3.5 million hectares of land in the United States were planted in 2015. Thus, an experiment was conducted to assess the effect of cotton growth stage on susceptibility to injury and yield effects from a sub-lethal concentration of 2,4-D. Research was conducted in 2014 and 2015 at the R.R. Foil Plant Research Facility in Starkville, MS and the Black Belt Research Station in Brooksville, MS, where the experimental layout was a randomized complete block design with four replications with an untreated check. The dimethylamine salt formulation of 2,4-D (Weedar 64™) was applied at a rate of 0.0083 kg ae ha-1 to the center two rows of four-row plots measuring 3.9m by 12.2 m. One preemergence (PRE) application was included in the experiment, with the rest of the applications occurring weekly from 1 to 14 weeks after emergence (WAE). Crop growth stage and height were recorded at each application timing along with environmental data. Data collection included visual injury assessment ratings taken 7, 14, 21, and 28 days after treatment (DAT); plant heights; nodes above cracked boll (NACB) and nodes above white flower (NAWF) measurements; and both hand and machine-harvested seed cotton yield. Hand-harvested yield data were analyzed on the basis of Position (horizontal location of a boll on each branch relative to the main stem), Zone (vertical node of the branch on which a boll is found), and maturity cohort (combination of Position and Zone), with all yield found on monopodial (vegetative) branches or aborted terminals treated as discrete Positions. All data were analyzed in SAS 9.4 PROC MIXED, and means were separated using Fisher’s Protected LSD at the α = 0.05 level of significance.

Cotton injury 28 DAT was greatest when 2,4-D was applied 1 to 5 WAE, with a significant increase in plant height from applications made 5 to 8 WAE. Machine-harvested yield reductions occurred from exposure to 2,4-D at 1 and 5 to 7 WAE. Seed cotton yield partitioned in Position 1 and 2 bolls decreased as yield partitioned on monopodial branches and aborted terminals increased from applications of 2,4-D made 1 to 7 WAE. Similarly, yield partitioned in Zone 1 (nodes 5 to 8) and Zone 2 (nodes 9 to 12) decreased as yield partitioned in Zone 3 (nodes > 12) increased from applications of 2,4-D made 1 to 7 WAE. Thus, our data suggest that cotton growth stage is a significant factor in relation to yield reduction and partitioning in response to exposure to sub-lethal concentrations of 2,4-D. Furthermore, cotton appears to be most susceptible to injury, yield reduction, and yield partitioning effects when it is exposed to sub-lethal concentrations of 2,4-D early in its growth and development.

 


INJURY CRITERIA ASSOCIATED WITH SOYBEAN EXPOSURE TO DICAMBA AND POTENTIAL FOR YIELD LOSS PREDICTION. M. R. Foster*1, J. L. Griffin2; 1Louisiana State University, Baton Rouge, LA, 2LSU AgCenter, Baton Rouge, LA (279)

ABSTRACT

INJURY CRITERIA ASSOCIATED WITH SOYBEAN EXPOSURE TO DICAMBA AND POTENTIAL FOR YIELD LOSS PREDICTION. M.R. Foster and J.L. Griffin; School of Plant, Environmental, and Soil Sciences, Louisiana State University Agricultural Center, Baton Rouge, LA 70803.

 

ABSTRACT

 

Availability of soybean with dicamba-resistance will provide an alternative weed management option, but risk of dicamba off-target movement to sensitive crops is of concern. Indeterminate MG 4.8 to 5.1 soybean cultivars at V3/V4 (third/fourth node with 2/3 fully expanded trifoliates) or at R1/R2 (open flower at any node on main stem/open flower at one of the two uppermost nodes on main stem) were treated with dicamba (Clarity diglycolamine salt) at 0.6, 1.1, 2.2, 4.4, 8.8, 17.5, 35, 70, 140, and 280 g ae/ha corresponding to 1/1034 to ½ of the use rate of 560 g/ha.  Nonionic surfactant at 0.25% v/v was added to all treatments and a nontreated was included for comparison. A randomized complete block design with a factorial arrangement of treatments was used and the experiment was conducted three years.

In most weed science research, crop injury assessments are based on a scale of 0 (no injury) to 100% (all plants dead). To assign a single overall injury rating would require that specific injury criteria be identified and assigned a level of injury and that the criteria be ranked in regard to their contribution to total injury. When multiple criteria are considered in making a single overall rating, the rating system becomes subjective and would be expected to vary considerably among individuals. In the present research, fourteen injury criteria associated with soybean exposure to dicamba were identified to include: upper canopy leaf cupping, terminal leaf cupping, upper canopy leaf surface crinkling, upper canopy pale leaf margins, upper canopy leaf rollover/inversion, lower leaf soil contact, leaf petiole droop, leaf petiole base swelling, terminal leaf chlorosis, terminal leaf necrosis, terminal leaf epinasty, stem epinasty, lower stem base swelling, and lower stem lesions/cracking . Each criterion was visually rated 7 and 15 d after dicamba application (DAA) using a scale of 0 to 5 with 0= no injury; 1= slight; 2= slight to moderate (producer concern); 3= moderate; 4= moderate to severe; and 5= severe.  In addition, an overall visual assessment of percent soybean injury and plant height reduction using a scale of 0 to 100% with 0= none and 100%= plants dead and a soybean canopy height measurement were made 7, 15, and 30 DAA. The objectives of the research were to 1) quantify the severity of injury for the fourteen injury criteria as influenced by dicamba rate and soybean growth stage, 2) determine relationship between severity of injury for each criterion and yield, and 3) develop a procedure for use in field diagnosis of injury and yield loss prediction.

In respect to soybean injury criteria and growth stage, upper canopy leaf cupping, upper canopy pale leaf margins, lower leaf soil contact, and lower stem base swelling were observed for the V3/V4 application but not for R1/R2. Terminal leaf cupping and upper canopy leaf rollover/inversion were observed for the reproductive application but not for the vegetative.  Soybean yield was determined and a quadratic response was observed for the rates of dicamba applied at both growth stages.  When dicamba was applied at 0.56 g/ha, 1/1000th of the use rate and typical of volatility exposure, yield reduction was no more than 1% for both growth stages. Dicamba applied at 1.4 to 11.2 g/ha, typical of spray tank contamination rates of 0.25 to 2%, reduced yield 2 to 14% for V3/V4 application and 2 to 15% for R1/R2 application. For a typical spray particle drift rate of 1 to 10%, which corresponds to dicamba rates of 5.6 to 56 g/ha, soybean yield was reduced 7 to 61% for V3/V4 application and 8 to 67% for R1/R2 application.

Further analysis of the data using multiple regression models is currently underway. It is anticipated that these models will delineate which criteria and severity levels are most associated with yield based on growth stage at dicamba exposure and days after application.  A field diagnostic procedure will be discussed that includes selective injury criteria and severity level to predict soybean yield response. The ability to forecast the effect of dicamba exposure on crop growth and yield loss could be very helpful in decisions regarding replanting, additional crop inputs, crop insurance claims, and liability issues. 

 


SOYBEAN RESPONSE TO OFF-TARGET MOVEMENT OF DGA AND BAPMA DICAMBA. G. T. Jones*, J. K. Norsworthy, L. T. Barber, M. S. McCown; University of Arkansas, Fayetteville, AR (280)

ABSTRACT

With current interest in labeling diglycolamine (DGA) dicamba for use in dicamba-resistant crops, it is of great importance to examine possible differences from the technologically advanced N, N-Bis-(aminopropyl) methylamine (BAPMA) dicamba that is expected to be released in 2016 by BASF. The new BAPMA form of dicamba will be branded Engenia and is expected to exhibit decreased volatility over previous forms of dicamba. A study was conducted in 2015 at the Northeast Research and Extension Center (NREC) in Keiser, AR to examine possible differences that these two forms of dicamba may display. Glufosinate-resistant soybean was planted in two side-by-side 8 ha fields. In the center of each field, either DGA or BAPMA dicamba was applied simultaneously at V6/V7 growth stage at a rate of 560 g ae/ha to a 38 x 38 m area. Bowman Mudmaster high-clearance sprayers were used, each having a 7.6 m swath and traveling at 15.1 kph using 11003 TTI nozzles with an output of 94 L/ha. Prior to application, three subplots were established by marking 5 to 6 soybean plants per subplot at prescribed distances radiating along eight transects from the treated plot. Subplot sets were arranged approximately every 3 m up to 12 m, every 6 m up to 36 m, and every 9 m to the edge of the field (approximately 72 m). The subplots consisted of soybean plants that were exposed to a) combined primary (physical) drift plus secondary (vapor) drift, b) primary drift only, and c) secondary drift only. Prior to application, 19-L buckets were placed over the soybean plants that were only exposed to secondary drift. Applications were made in mid-afternoon and the buckets were removed 30 minutes later and immediately placed over the plants that were to be only exposed to primary drift. The buckets remained in place for 24 hours and then were removed. Visible injury ratings were taken at 7, 14, and 21 days after application (DAA) for all primary, secondary, and combined subplots. The same glufosinate-resistant soybean cultivar as that planted in the large drift trial was also planted in a smaller field located 1.6 km away for use as a DGA and BAPMA dicamba rate titration experiment on the same day as the two 8 ha fields were planted. Applications of nine dicamba doses ranging from 1/10 to 1/100,000 of a 1X rate (560 g ae/ha) were made on the same day as larger drift experiment. A CO2-pressurized backpack sprayer with a spray boom equipped with four 11003 TTI nozzles with an output of 141 L/ha was used to treat the center two rows of each four row plot. Injury ratings were taken at 7, 14, and 21 DAA and used to estimate the amount of dicamba reaching subplots in the larger experiment. Tissue samples were also collected from both the rate titration and larger drift experiment (DGA formulation only) at 7 DAA and the concentration of dicamba in the tissue determined.  Wind speed ranged from 5 to 10 kph during the six sprayer passes needed to cover the 38 x 38 m area. Approximately 6 hours after application, a 3 cm rainfall event occurred at the test site. Primary drift from DGA and BAPMA result in an estimated 5% injury at 30 m and 24 m, respectively. Distance to secondary drift injury of 5% decreased to 12 m for each form of dicamba. However, secondary injury was seen at further distances with DGA dicamba; albeit, injury was very minor. Analytical quantification of the concentration of dicamba in the plant tissue was a weaker indicator of dicamba drift than visible estimates of injury and the presence of dicama-like symptoms.  Even in plots having 25 to 40% leaf malformation the presence of dicamba could not always be detected in the soybean tissue.  For the conditions under which dicamba was applied in this study, there were few differences in DGA and BAPMA formulations.  It is likely the rainfall event after applying dicamba contributed to the inability to detect strong differences in secondary movement between the two dicamba formulations.   


SUB-LETHAL DICAMBA DOSE IMPACT ON GROUP V SOYBEAN GROWTH AND YIELD. A. M. Growe*1, M. K. Bansal1, T. E. Besancon1, D. Copeland2, J. T. Sanders1, B. W. Schrage1, L. Vincent1, W. J. Everman1; 1North Carolina State University, Raleigh, NC, 2North Carolina State University, Cary, NC (281)

ABSTRACT

Abstract

With the spread of glyphosate resistant weed species throughout North Carolina, there has been a renewed interest of using auxin herbicides for weed control options in the state. As dicamba, a common auxin herbicide, is being incorporated back into herbicide programs, there is concern of off target movement to sensitive crops in adjacent fields.  To date, there has been little information reported on soybean varietal responses to dicamba drift.

The objective of this study was to evaluate the effects of sub-lethal rates of dicamba on various group V soybean cultivars at vegetative and reproductive growth stages.  Effects of dicamba were determined by collecting visual injury ratings, height reductions and yield.  Experiments were conducted in Upper Coastal Research Station (Rocky Mount, NC) and Caswell Research Station (Kinston, NC) during 2015.  Five soybean varieties were treated with dicamba at 1.1, 2.2, 4.4, 8.8, 17.5, 35, and 70 g ae ha -1 (1/512 to 1/8 of the labeled use rate for weed control in corn) during V4 and R2 growth stages. Experiments were conducted using a factorial arrangement of treatments in a randomized complete block design, with three factors being soybean variety, dicamba rate, and growth stage. All data were subjected to analysis of variance and means were separated using Fisher’s Protected LSD at p= 0.05.

A wide range of visual injury was recorded at 1, 2 and 4 WAT for all 5 varieties and both timings. Increasing levels of injury were associated with increasing dicamba rates for all varieties.  The V4 injury ratings ranged from 17-69% 1 WAT. Significant differences in height reductions to the non-treated check were also observed.  Height reductions were more severe at the V4 timing than R2 for all varieties.  Height reduction 4 WAT, for all varieties, ranged from 35-39% at the V4 timing and 13-26% for the R2 timing. For the Kinston trial, soybean yield reduction was greater for V4 timing compared to R2 timing.  Rocky Mount yield resulted in greater yield reduction for the R2 timing compared to V4.  It is evident that environment plays a large role in soybean yield response to sub-lethal doses of dicamba. Conclusions from this study reveal the importance of making responsible dicamba applications so that risk of drift and volatility is minimized.     


DOES POD LOCATION ON SOYBEAN INFLUENCE THE DEGREE OF DICAMBA-LIKE SYMPTOMS OBSERVED ON PROGENY? M. S. McCown*1, L. T. Barber1, J. K. Norsworthy1, M. G. Palhano1, R. R. Hale1, Z. Lancaster1, R. C. Doherty2; 1University of Arkansas, Fayetteville, AR, 2University of Arkansas, Monticello, AR (282)

ABSTRACT

Commercial introduction of soybean cultivars genetically modified with resistance to dicamba will provide growers an alternative weed management option, but may expose susceptible soybean cultivars to non-target herbicide movement and tank contamination. A study was conducted to determine the effects on soybean progeny following dicamba injury. The progeny were evaluated in the greenhouse at the Altheimer Laboratory in Fayetteville, Arkansas following exposure of soybean plants to low rates of dicamba in the 2014 growing season. The purpose of this study was to determine if pod location influenced progeny growth and vigor.

In 2014, a field trial was conducted to determine the effect of soybean maturity on recovery from dicamba injury on a susceptible determinate cultivar. Two low rates of dicamba (1/64X and 1/256X) rate were applied at several growth stages (V3-R6). Ten random plants were harvested in a meter of row from each plot and each plant was then divided into thirds. Data were gathered on the number of total pods on the plant and the number of malformed pods in each third of the plant. Soybean seeds were collected for-grow-out in the greenhouse.  Fifteen random seeds from each section of the plant were chosen. Injury resulting from the field application of dicamba was visually evaluated at second trifoliate and average heights were gathered using three randomly chosen plants from each pot. Significant difference in progeny vigor and emergence was observed between soybean growth stages. A significant decrease in progeny emergence was observed when dicamba was applied at R4 and R5 compared to all other growth stages. (α=0.05) Visual estimates of injury to soybean progeny increased as dicamba was applied at later reproductive stages (R4-R6); however, injury varied depending on the location of where seeds were collected on the plants.  When averaged across all growth stages, seeds collected from the bottom portion of the plants expressed a statistically greater percentage of injury when compared to seeds collected from the top and middle of the plant. However, when averaging both rates across all growth stages, the injury across pod positions only ranged from 9-14%. When progeny seed was collected, information was also recorded on the number of malformed pods at each location. Averaging across the two rates, the largest percentages of malformed pods were collected from the middle of the plant. With this being said, a statistical difference between location was only observed when dicamba was applied at R1, R2, R4, and R5. (α=0.05) At these critical application timings, 28-40% of the malformed pods were collected from the middle of the plant, and 10-22% of malformed pods were collected from the bottom and 15-18% of malformed pods were collected from the top portion of the plant.  From these results we can conclude that pod location does have an influence on dicamba-like symptoms observed on progeny; however, there does not appear to be a strong correlation between pod malformation and injury to progeny. Future analysis will need to examine if pod malformation is directly correlated with injury to progeny.

 


IMPACT OF WEED MANAGEMENT SYSTEMS ON NITROUS OXIDE EMISSIONS. A. M. Knight*, W. J. Everman, S. C. Reberg-Horton, S. Hu, D. L. Jordan, N. Creamer; North Carolina State University, Raleigh, NC (283)

ABSTRACT

Agriculture accounts for a large portion of land use worldwide.  In the U.S. specifically, the World Bank indicated that agriculture accounts for roughly 45% of land use.  Agriculture is estimated to contribute greatly to the output of one of the main greenhouse gases, nitrous oxide (N2O), which is suspected of contributing to climate change, contributing an estimated 59 percent to emissions. These large percentages are suspected to partially be due to one-third of nitrogen applied to cropping systems being utilized by the system while the additional two-thirds are lost to the environment.  With different agricultural practices contributing to these greenhouse gas emissions, finding how various production practices contribute to greenhouse gas emissions will help in the recommendation of best management practices to minimize gas emissions by agriculture in the southeastern U.S.  Field studies were conducted in 2013, 2014, and 2015 at the Center for Environmental Farming Systems at the Cherry Research Farm in Goldsboro, NC.  Long-term plots of conventional no-till, conventional-tillage, conventional crop-hay, organic tillage, organic minimal tillage, and organic crop-hay systems were used to measure the flux of the greenhouse gases CO2, CH4, and N2O, 24 to 48 hours after ~1.25 cm or more of rainfall, following USDA-ARS GRACEnet Project Protocols. Results indicated weed-free areas in conventional managment emit more nitrous oxide than weedy areas (0.5-10 mg N m2-1day-1 more) while weedy areas emit more nitrous oxide in organic systems (0.5-10 mg N m2-1day-1 more).  In addition, tillage plays a significant role in gas emissions across cropping systems.  Full tillage systems were emitting upwards of 12 mg N m2-1day-1 while no-till or minimum tillage systems were emitting roughly 3 mg N m2-1day-1 on the same dates. 


EMERGENCE PATTERNS OF WATERHEMP AND PALMER AMARANTH UNDER NO-TILL AND TILLAGE CONDITIONS IN SOUTHERN ILLINOIS. L. X. Franca*1, B. G. Young2, J. Matthews3, D. M. Dodds4; 1Mississippi State University, Starkville, MS, 2Purdue University, West Lafayette, IN, 3Southern Illinois University, Carbondale, IL, 4Mississippi State University, Mississippi State, MS (284)

ABSTRACT

Emergence Patterns of Waterhemp (Amaranthus tuberculatus) and Palmer amaranth (Amaranthus palmeri) under No-Till and Tillage Conditions in Southern Illinois. L. X. Franca*1, B. G. Young1, J. Matthews1, D. M. Dodds2; 1Southern Illinois University, Carbondale, IL, 1Purdue University, Lafayette, IN, 2Mississippi State University, Mississippi State, MS.

ABSTRACT

A thorough understanding of weed biology is fundamental for developing effective weed management strategies. The continued spread of glyphosate-resistant waterhemp [Amaranthus tuberculatus (Moq.) Sauer (syn. rudis)] and Palmer amaranth (Amaranthus palmeri S. Wats.) has complicated weed management efforts in soybean and corn production in Illinois. The determination of emergence patterns and the influence of tillage on weed emergence will allow control strategies to be implemented at the most effective timing.

The objective of this research was to characterize the emergence patterns of waterhemp and Palmer amaranth based on weather factors as influenced by tillage. Field experiments were initiated in southern Illinois in the spring of 2013 and 2014 on fields infested with waterhemp and Palmer amaranth at the Southern Illinois University Belleville Research Center in Belleville, IL. Two tillage treatments (May 1st and June 1st) and a control (no-tillage) were evaluated. Amaranthus seedlings were identified and enumerated in the center 1-m2 quadrat every seven days from April through November or first frost. All weed seedlings were removed following each enumeration. Soil temperature and moisture were recorded hourly throughout the experiment using data loggers.

Waterhemp emerged earlier in the season than did Palmer amaranth. In 2013, the initial waterhemp and Palmer amaranth emergence were observed the first and second week of May, respectively, regardless of tillage. In 2014, initial waterhemp emergence was two weeks earlier than in 2013 while initial Palmer amaranth emergence was similar to the previous year. Palmer amaranth emerged over a longer period of time compared to waterhemp. By the end of June, 90% of the waterhemp had emerged regardless of tillage or year. The time for Palmer amaranth to reach 90% cumulative emergence was extended to the third week of July and the second week of August in 2013 and 2014, respectively. No differences were observed on waterhemp and Palmer amaranth total cumulative emergence across treatments in 2013; however, in 2014 total cumulative emergence of waterhemp and Palmer amaranth were significantly lower on early tillage and late tillage, respectively.

Spikes in soil moisture (weekly highs) were the single best predictor of Palmer amaranth emergence followed by soil temperature. For waterhemp, the single best predictor for emergence was soil temperature (weekly highs and lows) followed by soil moisture. Highest soil temperatures and lowest soil moisture were observed immediately after tillage and were correlated to low emergence of Palmer amaranth and waterhemp, but only until the next rainfall event. In 2013, spikes in soil moisture observed 11 days prior and weekly high soil temperatures 2 weeks prior to emergence were positively and negatively correlated, respectively to Palmer amaranth emergence (R2 = 0.30). In 2014, spikes in soil moisture observed 2 weeks prior and weekly high soil temperatures 8 days prior to emergence were the best predictors of Palmer amaranth emergence (R2 = 0.37). In 2013, waterhemp emergence was initially positively and later negatively correlated to maximum soil temperature 13 days prior to emergence, with temperatures above 30ºC correlated to lower emergence (R2 =0.35). In 2014, waterhemp emerged in April and had a positive correlation to high soil temperatures 10 days prior followed by a positive correlation to minimum soil temperatures 8 days prior emergence later in the season (R2 =0.55). The pattern of emergence for waterhemp was more correlated to high soil temperatures in the spring and to low soil temperatures throughout the summer in both years. Conversely, high soil moisture associated with adequate soil temperature had a greater correlation to the emergence pattern of Palmer amaranth. Monitoring soil moisture and temperature may assist in Palmer amaranth and waterhemp management in terms of field scouting or implementing control measures. 

 


RNA-SEQ ANALYSIS OF EARLY RESPONSE OF SUSCEPTIBLE AND RESISTANT ECHINOCHLOA COLONA POPULATIONS TO IMAZAMOX TREATMENT. A. A. Wright*1, K. C. Showmaker2, V. K. Nandula3, J. A. Bond1, D. G. Peterson2, J. D. Ray3, D. R. Shaw2; 1Mississippi State University, Stoneville, MS, 2Mississippi State University, Mississippi State, MS, 3USDA-ARS, Stoneville, MS (285)

ABSTRACT

Weeds with resistance to multiple herbicides are increasing in incidence.  MS1, a field population of Echinohcloa colona with resistance to imazamox, fenoxaprop, quinclorac, and propanil, was reported in Sunflower County, MS.  Treatment of MS1 with cytochrome P450 inhibitors in the presence of imazamox reduced the level of resistance, indicating involvement of herbicide metabolism in the resistance mechanism.  Due to the complexity of herbicide metabolism and the lack of sequence data for this species, a RNA-seq approach was taken to explore the mechanism.  RNA was isolated from untreated and imazamox treated plants for MS1 and a susceptible population, Bond2.  This was done in triplicate.  MiSeq SE165 and HiSeq PE100 runs were performed.  Preliminary transcriptomes assembled in Trinity generated approximately 143,803 transcripts for MS1 and 155,347 for Bond2.  Differential gene expression analysis for untreated and treated samples revealed that 368 transcripts were downregulated and 576 upregulated in Bond2, while only 30 were downregulated and 427 upregulated in MS1.  Several of these transcripts are known to be associated with stress responses, including transcripts involved in calcium signaling, ubiquitination, defense responses, cell wall modifications, and metabolism.  Future work includes generating final transcriptomes for each population and repeating the differential gene expression analysis.  An ortholog analysis will compare untreated MS1 and Bond2 samples to identify constitutive differences in gene expression.  Transcripts of interest will be examined in other populations and at other time points following herbicide treatment.  This will generate a list of candidate resistance genes for further study.

 


HERBICIDE RESISTANCE MECHANISMS OF MULTIPLE-RESISTANT JUNGLERICE (ECHINOCHLOA COLONA) FROM ARKANSAS. C. E. Rouse*1, N. Burgos1, A. Lawton- Rauh2, R. A. Salas1; 1University of Arkansas, Fayetteville, AR, 2Clemson University, Clemson, SC (286)

ABSTRACT

Echinochloa spp. pose a significant threat to upland and lowland cropping systems throughout the world, especially in flooded rice culture. Sustained use of herbicides as a primary method of controlling Echinochloa spp. has led to a rise in herbicide-resistant populations. While resistance to a single mode of action (MOA) is a concern, recent evidence suggests that multiple resistance to herbicides of different MOA is a larger threat to agriculture. This evolved resistance pattern is typically due to non-target-site (NTS) alleles endowing resistance via concerted genetic and biochemical interactions having broad implications for herbicide efficacy. Investigation into the resistance mechanisms evolved in this species is of utmost concern for researches and producers to ensure prolonged viability of rice culture. From 2010 to 2014, 254 accessions of Echinochloa spp. were collected from rice fields in Arkansas. These populations were evaluated to determine the distribution of species, characterize their morphology, and to screen for herbicide resistance. Following this initial description, it was determined that 69% of the populations were junglerice (Echinochloa colona), with resistance to propanil (52%) and quinclorac (40%) being rampant, resistance to imazethapyr and cyhalofop increased through the years; multiple resistance was also detected. A junglerice population classified as multiple resistance to 4 herbicides (ECO-45), and a susceptible standard (ECO-SS), were selected for evaluation of the mechanisms endowing resistance. A dose response assay was used to evaluate the resistance level to the four herbicides of interest: cyhalofop (8 rates up to 16x), glufosinate (8 rates up to 16x), propanil (8 rates up to 32x), and quinclorac (9 rates up to 32x). Following the dose response analysis, a series of studies investigated the mechanisms of resistance were conducted: ACCase cross-resistance assay, 14C-cyhalofop/ propanil absorption and translocation assay, and detoxifying enzyme assay. The multiple-resistant accession (ECO-45) had LD­50 values of: 0.072 kg ha-1 for cyhalofop (2x ECO-SS), 0.38 kg ha-1 for glufosinate (3x ECO-SS), 72 kg ha-1 for propanil (7x ECO-SS), and >18 kg ha-1 for quinclorac (>64x ECO-SS). ECO-45 was not cross-resistant to clethodim, fenoxaprop, fluazifop, or quizalofop. The absorption and translocation of cyhalofop and propanil were the same in resistant and susceptible plants, 72 HAT. Herbicide detoxification was evaluated, indirectly, using 3 known enzyme inhibitors- carbaryl, malathion, and piperonyl butoxide (PBO). Carbaryl enhanced the activity of cyhalofop, propanil, and glufosinate, resulting in elevated control of the population (>90%); malathion only enhanced propanil and glufosinate activity (>95%). The enzyme inhibitors did not reverse the resistance to quinclorac. ECO-45 exhibited a high level of resistance to propanil and quinclorac with moderate resistance to cyhalofop and glufosinate. These results indicate NTS resistance through a combination of genetic and physiological mechanisms. The accumulation of various NTS mechanisms can convey broader resistance than is traditionally observed with target site mutations.


ENVIRONMENTAL INFLUENCES AND TIME OF DAY EFFECTS ON PPO-INHIBITING HERBICIDES. G. B. Montgomery*1, L. Steckel1, B. Lawrence2, H. M. Edwards2, J. A. Bond2; 1University of Tennessee, Jackson, TN, 2Mississippi State University, Stoneville, MS (287)

ABSTRACT

Protoporphyrinogen oxidase (PPO) inhibiting herbicides are widely used for controlling Palmer amaranth (Amaranthus palmeri) across the Mid-South.  Efficacy from contact herbicides (such as PPO inhibitors) can be influenced by factors such as temperature, humidity, and application time of day.  As the number of herbicide resistant weed species increases, maximizing control of difficult weed species such as Palmer amaranth is imperative for successful soybean production.  The focus of this research was to examine how application time of day effects the efficacy of aciflurofen, fomesafen, and lactofen on Palmer amaranth.

The study was initiated in the summer of 2015 at the West Tennessee Research and Education Center in Jackson, TN.  The study was conducted on a uniform Palmer amaranth population ranging from 5-15 cm in height.  Treatments were arranged as a two factor factorial within a randomized complete block design with four replications.  The first factor level was herbicide and included aciflurofen applied at 280 g ha-1, fomesafen applied at 263 g ha-1, and lactofen applied at 175 g ha-1.  The second factor level was application time of day and included applications at 15 minutes prior to sunrise, 1 hour past noon, and 15 minutes prior to sunset.  Palmer amaranth control was visually assessed at 7, 14, 21, and 28 days after treatment (DAT).  Air temperature, soil temperature, relative humidity, and cloud cover were recorded at each application.  Palmer control data were subjected to an analysis of variance by herbicide using appropriate mean separation techniques and α=0.05.  14 DAT control data was regressed against air and soil temperature (ºF), relative humidity (%), and cloud cover (percent).

Application time of day effect was highly significant for each herbicide.  Control from acifluorfen was greatest (89%) from the noon application followed by the sunset application (80%), and was lowest from the sunrise application (63%) 28 DAT.  Injury from acifluorfen was not significantly affected 28 DAT.  No significant differences for control or injury were detected 28 DAT for lactofen.  Fomesafen efficacy was greatest at the noon application (94%), followed by the sunset application (87%), and lowest at the sunrise application (73%) 28 DAT; however, no differences were detected in injury at this time.  Soil temperature was good predictor (r2=0.73) of Palmer amaranth control 14 DAT and was positively correlated with an intercept of -654.96 and a slope of 10.376.  No variables accounted for greater than 45% of the variability in control of Palmer amaranth with lactofen 14 DAT.  Cloud cover, air temperature, and soil temperature were all good predictors (r2=0.88, 0.82, and 0.87, respectively) of acifluorfen efficacy 14 DAT.  A positive slope of 0.38, 2.33, and 15.25 with intercepts of 55, -88-92, and -1003.17 were observed for cloud cover, air temperature, and soil temperature, respectively.  Combinations of each of the variables for acifluorfen efficacy did not improve the regression model over that of each variable alone based upon visual observation of the r2.  

Application time of day effected each herbicide.  Two of the three PPO-inhibiting herbicides produced the greatest efficacy when applied in the middle of the day 28 DAT.  More research is needed to determine how consistent across locations environment and application time of day effects efficacy of PPO-inhibiting herbicides on Palmer amaranth.  

 


CONFIRMATION AND CHARACTERIZATION OF PPO-INHIBITOR-RESISTANT PALMER AMARANTH ACCESSION IN ARKANSAS. R. A. Salas*1, N. R. Burgos1, P. J. Tranel2, J. Song2, R. C. Scott1, R. L. Nichols3; 1University of Arkansas, Fayetteville, AR, 2University of Illinois, Urbana, IL, 3Cotton Incorporated, Cary, NC (288)

ABSTRACT

Palmer amaranth (Amaranthus palmeri S Watson) is one of the most common, troublesome, and economically damaging agronomic weeds throughout the southern US.  The widespread occurrence of ALS and glyphosate-resistant weeds has led to increasing use of protoporphyrinogen oxidase (PPO)-inhibiting herbicides. The objectives of this research were to confirm resistance to fomesafen, determine the resistance frequency, examine the resistance profile to other foliar-applied herbicides, and investigate the resistance mechanism in suspected Palmer amaranth population collected in 2011 (AR11-LAW-B) and its progenies from two cycles of fomesafen selection (C1 and C2). One-hundred plants of AR11-LAW-B were grown in cellular trays, at 1 plant/cell, and sprayed with 264 g ha-1 fomesafen when seedlings were 3-4 inches tall. Survivors were grown to generate C1 and C2 populations and the progenies sprayed with fomesafen. The frequency of fomesafen-resistant plants increased from 5% in the original AR11-LAW-B to 17% in the C2 population. The level of resistance to fomesafen is at least three-fold relative to the sensitive ecotype. The estimated doses of fomesafen required to obtain 50% biomass reduction were 81, 168, and 265 g ha-1 in AR11-LAW-B, C1, and C2 populations. The AR11-LAW-B population was sensitive to atrazine, dicamba, glyphosate, glufosinate, and mesotrione but resistant to ALS-inhibiting herbicides pyrithiobac and trifloxysulfuron. Leaf tissues from the suspected samples were tested for the presence of an indel mutation that confers PPO resistance. Fomesafen survivors from C1 and C2 populations tested positive for the PPO glycine 210 deletion previously reported in waterhemp (Amaranthus tuberculatus). Several PPO-resistant populations were confirmed in follow-up surveys in 2014 and 2015. This calls for attention as soybean and cotton farmers need to combat resistance to PPO herbicides on top of resistance to glyphosate and ALS inhibitors. PPO herbicides are the pillars of Palmer resistance management programs. Such programs need immediate adjustments.

 


EVALUATION OF RATE AND TIMING OF INDAZIFLAM HERBICIDE IN MUSCADINE AND BUNCH GRAPES . N. T. Basinger*, K. M. Jennings, D. W. Monks, S. J. McGowen, S. C. Beam, M. B. Bertucci; North Carolina State University, Raleigh, NC (289)

ABSTRACT

Expanding interest in grape production in the southeastern United States has led to increased acreage of table, muscadine, and wine grapes. However, there are a limited number of herbicides registered in muscadine and bunch grapes, especially herbicides that have long residual activity. Indaziflam herbicide was recently registered for application in grape and tree fruit. Indaziflam can provide season-long weed control and is an additional mode of action for use in vineyards. However, vineyards in the southeast are not compliant with many of the restrictions on the indaziflam label. Studies were conducted at six locations across North Carolina in mature (>5 yr old) fresh market muscadine (FMM), muscadine processed for wine/juice/jelly (PM), and processing/table grape (SUN) to assess crop tolerance and weed control efficacy. Treatments included indaziflam at 0, 50 g ai ha-1, 73 g ai ha-1 or flumioxazin  at 213 g ai ha-1 (grower standard) alone in April, and sequential applications of 36, 50, 73 g ai ha-1 or flumioxazin at 213 g ai ha-1 were applied in both in April and June. Weedy and weed-free checks were included to aid in assessment for crop tolerance and weed control. No injury was observed for any treatment, and vine phenological stage was not affected by treatments. Preliminary results indicate that indaziflam at 36 g ai ha-1 provided the greatest control within label restrictions of 73 g ai ha-1. However, 36 g ai ha-1 does not promote herbicide resistance management as it is not a full recommended rate.  Late season application of indaziflam at 50 and 73 g ai ha-1 provided >95% weed control at 16 weeks after April application. Indaziflam at 73 g ai ha-1 applied early season (first application) controlled horsenettle (Solanum carolinense) and large crabgrass (Digitaria sanguinalis) (>90%) season-long when activated, and showed similar results to flumioxazin at 203 g ai ha-1.  Sequential applications of indaziflam and flumioxazin were needed to control pitted morningglory (Ipomoea lacunosa) and sicklepod (Senna obtusifolia) season-long.

 

 


EMERGENCE, GROWTH AND DEVELOPMENT OF BLACK MEDIC IN FLORIDA STRAWBERRY FIELDS. S. M. Sharpe*1, N. Boyd2, P. J. Dittmar1; 1University of Florida, Gainesville, FL, 2University of Florida, Wimauma, FL (290)

ABSTRACT

Black medic is a troublesome weed in Florida strawberry production.  It emerges from the crop planting holes and competes with strawberry and impedes harvest.  Clopyralid is a viable post-emergence control option though growers typically report suppression only.   Field studies were established to model growing degree day based models of emergence, growth and development of black medic.  Four field sites were established in Hillsborough County, Florida to model medic emergence.  Plot size was 15.2 m x 66 cm, replicated four times per field.  Emergence was monitored weekly over the course of the growing season from November 21, 2014 to March 4, 2015.  Cumulative emergence was calculated and modelled using a Weibull equation as a function of growing degree days (GDD), using a Tbase = 0°C for the Florida population.  Growth and development data was taken within the established plots by randomly selecting 12 emerged plants per site, marking, and repeatedly measuring leaf number, stem length, and flower number.  Cumulative emergence was adequately modelled using a Weibull equation (R2=0.6399).  Black medic peak emergence (90%) occurred between 1284 and 1858 GDD after piercing of the plastic for planting of strawberries.  For the sampled emerged black medic chosen to monitor growth and development, the population reaching the two to five leaf stage varied greatly between sites, with peaks between 42 to 92% of the sampled plants reaching the two to five leaf stage between 945 and 1149 GDD.  For the six to ten leaf stage, which correlates to 0.5 to 1 cm stem lengths, peaks were between 33 to 50% of the sampled population between 945 and 1787 GDD.  The initial development of flowers occurred between 1517 and 1788 GDD representing approximately 10% of the population, though one site had 58% of the studied plants flowering at 1200 GDD.   Overall, the wide range in GDD for peak emergence combined with the high variability in growth rates makes controlling black medic with a single post emergence herbicide application difficult when considering plant size, later emerging escapes and differences in tolerance based on plant size.


EVALUATION OF PLASTIC MULCHES ON FOMESAFEN DISSIPATION. T. V. Reed*1, N. Boyd2; 1University of Florida, Riverview, FL, 2University of Florida, Wimauma, FL (291)

ABSTRACT

Fomesafen is a preemergence herbicide used for broadleaf weed control and suppression of nutsedge and grass species in Florida plasticulture production of pepper (Capsicum spp.) and tomato (Solanum lycopersicum L.). Fomesafen, a protoporphyrinogen oxidase inhibitor, has potential for use in other small fruit and vegetable crops in Florida plasticulture if tolerance can be established. Fomesafen may persist at a high concentration under plastic that may dissuade producers from using the herbicide to avoid limitations on which fruit or vegetable crops can be planted back into beds without fear of injury. A field experiment was conducted at the University of Florida Gulf Coast Research and Education Center, Wimauma, FL from August to December 2015 to evaluate the effect of plastic mulches on fomesafen persistence, squash (Cucurbita pepo L.) tolerance, and efficacy on purple nutsedge (Cyperus rotundus L.). Treatments included fomesafen at 0.42 kg ai ha-1 without mulch, under low density polyethylene (LDPE), clear, virtually impermeable film (VIF), and totally impermeable film (TIF) mulches. Fomesafen was detected in soil of all treatments through the duration of the experiment. Soil temperature was greater with plastic mulch than without from August through October, and clear mulch had >3 C soil temperature increase over other plastic mulches during the same time period. Treatments had similar soil moisture throughout the experiment. Fomesafen caused ≤10% at two weeks after transplant (WATr), and no injury was observed at 8 WATr. Similar squash yields were observed with LDPE, VIF, and TIF mulches. Fomesafen application with TIF reduced nutsedge >80% than LDPE treatment.

 


EVALUATION OF AQAUTIC HERBICIDES FOR BRAZILIAN PEPPER TREE (SCHINUS TEREBINFOLIUS) CONTROL. C. A. Lastinger*1, S. F. Enloe2; 1University of Florida, Lakeland, FL, 2University of Florida, Gainesville, FL (292)

ABSTRACT

Effects of aquatic herbicides on Brazilian pepper tree (Schinus terebinthifolius).

Cody A. Lastinger and Stephen F. Enloe

                Brazilian pepper tree (Schinus terebinthifolius) is an invasive species that was brought to Florida from Brazil and Argentina in the late 1800’s as an ornamental tree. It has since become an extremely troublesome plant to control and has invaded many ecosystems in Florida, including mangrove communities. Mangroves are vital to Florida’s coastal regions, and they provide both critical habitat for wildlife and soil stabilization along the coast. A major issue that plagues Brazilian pepper tree control in mangrove stands is that no selective treatments have been identified. This has made selective aerial treatment of peppertree infested mangrove islands virtually impossible.

                Over the last decade, several new herbicides have been registered for aquatic use in Florida. However, their effectiveness on Brazilian peppertree has not been tested. Therefore, our initial objective was to examine the response of Brazilian peppertree to all of the newer herbicides that are labeled for use in or around water bodies in the state of Florida. Brazilian pepper tree was grown in one gallon pots from seed in a greenhouse for six months to an average height of 30 inches. Herbicide treatments included carfentrazone (0.036 kg ai/ha), imazamox (0.138 kg ai/ha), bispyribac (0.073 kg ai/ha), penoxsulam (0.016 kg ai/ha), flumioxazin (0.07 kg ai/ha), and Topramezone (0.064 kg ai/ha). We also included all older aquatically labeled herbicides including endothall (2.48 kg ai/ha), glyphosate (0.55 kg ai/ha), 2,4-D (0.367 kg ai/ha), diquat (0.73 kg ai/ha), fluridone (0.04 kg ai/ha), triclopyr (0.55 kg ai/ha), and imazapyr (0.18 kg ai/ha). All herbicides were foliar applied with non-ionic surfactant (0.25% v/v). Injury was visually assessed at 90 days after treatment (DAT), on a scale of 0 to 100 with zero being no injury and 100 be complete loss of leaves and dead woody stems. Height of tallest living growth, and above ground biomass was also collected 90 DAT. Data were subjected to analysis of variance in Systat 9.0 and multiple comparisons were done using Fisher’s protected LSD at p=0.05. Glyphosate, imazapyr, and imazamox resulted in greater than 50% injury visually at 90 DAT compared to the untreated controls. Triclopyr, diquat, glyphosate, and imazapyr reduced growth height by more than 70% when compared to the untreated controls. Triclopyr, imazapyr, glyphosate, and diquat resulted in biomass reductions of 99, 92, 88, and 83% respectively compared to biomass from the untreated controls.

                These results indicate limited potential from most of the newer aquatically registered herbicides for Brazilian peppertree control.  Future work will include screening all herbicides which resulted in efficacy on Brazilian pepper tree on the four mangrove species native to Florida to determine if there is any selectivity among these herbicides.

 


INDAZIFLAM AND NON-SELECTIVE HERBICIDE COMBINATIONS FOR NATIVE WARM SEASON GRASS SAFETY. M. P. Richard*; Mississippi State University, Starkville, MS (293)

ABSTRACT

Native Warm Season Grasses (NWSG) are a popular choice for low maintenance roughs on golf courses.  They require minimal inputs to maintain and provide wildlife habitat.  NWSG are slow to establish, thus weed competition can impede stand density.  Specticle (active ingredient indaziflam) is a pre-emergent herbicide with known control of many grass and broadleaf weeds, yet minimal research has been conducted on NWSG safety.  In 2015, a multi-site research study was established at The Preserve Golf Club near Vancleave, MS and at the R.R. Foil Plant Science Research Center near Starkville, MS to evaluate the safety of indaziflam and non-selective herbicide combinations on wiregrass (Aristida virgata) and indiangrass (Sorghastrum nutans), respectively.  Study sites were arranged in a randomized complete block design with 4 replicants.  Treatments include Specticle FLO (49 g indaziflam/ha) + Round-up Pro (3.8 kg glyphosate/ha), Specticle G (49 g indaziflam/ha) + Round-up Pro (3.8 kg glyphosate/ha), Specticle FLO (49 g indaziflam/ha), and Specticle Total (109 kg ai/A) and a non-treated.  Treatments were applied to individual plots at dormancy, spring transition, and during summer.  Plots were harvested in August and dry matter yield reductions were calculated relative to the non-treated check. 

A significant timing by herbicide interaction was present in both species.  In general dormant applications of Specticle alone and combinations with glyphosate were safe on wiregrass and indiangrass.  With the exception of dormant applied treatments, Specticle + glyphosate reduced wiregrass and indiangrass dry weight yield ≥ 38% and up to 100%. 

Results indicate Specticle utility in NWSG maintenance as a stand-alone product.  When in combination with glyphosate, Specticle applications should be made during dormancy. 

Future research will evaluate weed control within NWSG swards. 

 


AN INTEGRATED SYSTEM FOR TOXIC, ENDOPHYTE-INFECTED TALL FESCUE ERADICATION. D. P. Russell*, J. D. Byrd, Jr.; Mississippi State University, Mississippi State, MS (294)

ABSTRACT

Tall fescue (Schedonorus arundinaceus) is the dominate cool-season perennial forage species found throughout the mid-South. A mutualistic association with the fungal endophyte, Neotyphodium coenophialum, imparts desirable traits such as increased root and shoot mass, drought and pest resistance, and herbivory protection. However, ergot alkaloid production from the endophyte frequently causes bovine and equine toxicosis. Diluting the consumption of the toxic alkaloids with legumes or other cool-season forage species, chemical suppression of the seedhead where alkaloids are concentrated, or total renovation with cover crops, tillage, and herbicides are currently accepted management practices to mitigate the harmful effects associated with endophyte-infected tall fescue. The spray-smother-spray method used with seedhead suppression is currently the most widely recommended process of tall fescue eradication, but complete removal with only a one year treatment strategy is unsuccessful. The systematic approach of this project is to determine the length of time necessary to completely eliminate the threat of fescue-associated toxicity though seed and underground rhizome eradication.

Research was conducted at two locations, Mississippi State University’s Prairie Research and Experiment Station (PRU) and Town Creek Farm (TC) to measure management effects on tall fescue removal. Year-round management included spring or spring and fall glyphosate applications at 1.68 kg ae ha-1 and treatments with or without fall tillage. Wheat and Roundup Ready Eagle forage soybean were planted as winter and summer forage cover crops, respectively. Percent recovery, or coverage, of tall fescue was measured in March, May, and December following the initial year of treatments. At PRU, spring and fall glyphosate applications used with fall tillage significantly reduced the percentage of tall fescue through the following March. However, by May, this treatment reduced tall fescue only when compared to the untreated check. By December, tall fescue had recovered from all treatment combinations to 74% cover on average. At TC, spring and fall glyphosate applications used with fall tillage resulted in less tall fescue recovery than with a spring only glyphosate application or the untreated check. Chemical seedhead suppression at TC prior to the initiation of this study in the spring of 2014 could be the cause of variation in percent tall fescue recovery by location. By December, each treatment reduced tall fescue equally and to at least 5% cover compared to the untreated check.  The most successful treatment at initially reducing tall fescue coverage is a spring and fall glyphosate application with fall tillage. However, management is required for more than one year to limit the amount of toxic tall fescue recovery. Forage soybeans produced over 8,000 kg ha-1 at each location by the second year and are a viable feed option to make up for fescue forage losses during renovation.

 


MAXIMIZING WINTER WHEAT YIELD FOLLOWING SORGHUM USING PRE-PLANT NITROGEN. M. K. Bansal*; North Carolina State University, Raleigh, NC (295)

ABSTRACT

Sorghum production has gained interest in recent years as regional grain demands increased which lead swine producer to offer a competitive sorghum grain price. Sorghum can be a good alternative for corn in rotation with wheat. Sorghum has ability to tolerate hot dry weather, a condition that can be challenging for corn in drought season. However, with the advantages, sorghum has some disadvantages as well when used in rotation. Grain sorghum is known to have has negative impact on the following crop. Sorghum residue when incorporated in soil can make N immobilize making it less available to following wheat.

Experiments were conducted in 2013-14 at Rocky Mount and 2014-15 at Rocky Mount and Kinston (two locations), North Carolina to evaluate the effect of different rates of pre-plant nitrogen (15, 30, 45, and 60 lbs per acre) applied to wheat following different hybrids either sorghum (DKS 53-67, P83P17) or corn (DKC 60-67) on wheat yield. In 2013-14, there was no significant effect of pre-plant nitrogen on wheat yield. There was significant effect of hybrids on wheat yield. Wheat yield was not significantly different when planted after either DKC 60-67 or DKS 53-67. Yield was significantly different when planted after DKC 60-67 and P83P17. In 2014-15, there was no significant effect of different hybrids on wheat yield at all three locations. Pre-plant nitrogen had significant effect only at one location in Kinston. Results suggests that wheat yield is not affected when planted after sorghum (DKS 53-67) compared to corn (DKC 60-67). There was no significant effect of pre-plant nitrogen at Rocky Mount in both years.

 


FALL MANAGMENT OF FIELD BINDWEED (CONVOLVULUS ARVENSIS) BEFORE AND AFTER FROST. E. B. Duell*, A. R. Post; Oklahoma State University, Stillwater, OK (296)

ABSTRACT

Field bindweed (Convolvulus arvensis) is a perennial member of the morningglory family (Convolvulaceae), native to parts of Europe and western Asia. First introduced to North America along the east coast in the mid-1700’s, field bindweed is now found across much of the continent, though the worst problems seem to be concentrated in the semiarid central and west-central United States. Field bindweed has an extensive perennial root system and vining growth habit making it extremely difficult to eradicate from cropland. In addition, thick epicuticular and cuticular waxes developed on field bindweed in semiarid and arid regions make management of under these conditions exceedingly difficult. Environmental conditions such as temperature, light, and humidity may play a role in herbicide efficacy for field bindweed. We investigated the relationship between temperature and herbicide efficacy evaluating herbicide treatments both before and after the first hard freeze of fall.

Two field trials were established in the fall of 2014, evaluating herbicide efficacy. One trial was located at the Oklahoma State University North Stillwater Farm, Stillwater, OK. The other was located at the Oklahoma State University North Central Research Station, outside of Lahoma, OK. Each trial was laid out as a randomized complete block design, with four replications and seventeen treatments. The studies consisted of sixteen post-emergent applications, eight applied prior to the first frost, and eight identical treatments applied immediately after the first frost of the fall. Post-emergence herbicide applications were as follows:  210 g ai ha-1 aminocyclopyrachlor + 0.25% v/v NIS; 4.2 g ai ha-1 metsulfuron + 0.25% v/v NIS ; 70 g ai ha-1 imazethapyr + 0.25% v/v NIS, 139 g ai ha-1 clopyralid + 0.25% v/v NIS, 2120 g ai ha-1  glyphosate + 770 g ai ha-1 2, 4-D LV 400, 100 g ai ha-1 saflufenacil + 1% v/v MSO, 69.6 g ai ha-1 quinclorac + 770 g ai ha-1 2, 4-D LV 400, and picloram + 1170 g ai ha-1 2, 4-D LV 400 and a non-treated check. Visual ratings of percent field bindweed cover and control were assessed at 1, 2, 3, and 4 weeks after treatment (WAT) and 7 and 12 months after treatment (MAT).

For treatments applied in early fall before the first freeze event glyphosate + 2,4-D and picloram + 2,4-D controlled field bindweed 100% by 4 WAT.  Quinclorac + 2,4-D and aminocyclopyrachlor controlled field bindweed 75% by 4 WAT but no additional improvement was noted as the season progressed. Salufenacil was initially very effective controlling bindweed 75% by 3 WAT but regrowth occurred from that point forward. 

Post-freeze applications performed similarly with glyphosate + 2,4-D, picloram + 2,4-D, quinclorac + 2,4-D and aminocyclopyrachlor all controlling field bindweed 100% by 4 WAT.  The difference was in the length of control. A post-freeze treatments with 100% control at 4 WAT remained at 98.8% or more through 7 MAT while for pre-freeze treatments only glyphosate + 2,4-D remained above 95% control.  Saflufenacil, imazethapyr, clopyralid, and metsulfuron did not control field bindweed well at either timing and are not recommended for bindweed control. The cheapest and most effective treatment is 2120 g ai ha-1  glyphosate + 770 g ai ha-1 2, 4-D LV 400 for pre and post freeze applications. While it is challenging for producers to leave their wheat fields fallow for a season, where field bindweed is a major problem, it pays to wait until after frost to make herbicide applications for more effective, long-term control of this perennial weed.

 


GREENHOUSE EVALUATION OF SPRAY ADJUVANTS AND FERTILIZER ADDITIVES FOR GRASS WEED MANAGEMENT WITH FACET L. L. Vincent, W. J. Everman, J. Copeland*; North Carolina State University, Raleigh, NC (297)

ABSTRACT

GREENHOUSE EVALUATION OF SPRAY ADJUVANTS AND FERTILIZER ADDITIVES FOR GRASS WEED MANAGEMENT WITH FACET L

J. Drake Copeland

W.J. Vincent

W.J. Everman

North Carolina State University

Raleigh, North Carolina

 

Abstract

 

Historically, postemergence grass weed management in grain sorghum (Sorghum bicolor) has been difficult because of limited options. In 2013, BASF introduced Facet L (quinclorac), which provides grass weed control in grain sorghum. Additionally, activity of quinclorac has been documented to require a spray adjuvant for maximum weed control. The Facet L label requires use of crop oil concentrate (COC), methylated seed oil (MSO), or a nonionic surfactant (NIS) while the addition of fertilizer additives, urea ammonium nitrate (UAN) or ammonium sulfate (AMS), are optional. Given that grass weed control is critical for grain sorghum production, effective tank-mixes of quinclorac and spray additives should be evaluated to inform producers of tank-mix options that are most valuable for grass weed management. Therefore, the objective of this study was to evaluate spray adjuvants and fertilizer additives for grass weed management using quinclorac.

 

Studies were conducted at the Method Greenhouse Facility in Raleigh, North Carolina in 2015 to evaluate the impact of various combinations of spray adjuvants and fertilizer additives on six common grass weed species in grain sorghum production in North Carolina. Grass weed species included large crabgrass (Digitaria sanguinalis), goosegrass (Eleusine indica), broadleaf signalgrass (Urochloa platyphylla), fall panicum (Panicum dichotomiflorum), Texas millet (Urochloa texana), and crowfootgrass (Dactyloctenium aegytium). Quinclorac was applied at 0.29 kg ae ha-1 alone and in combination with adjuvant treatments and fertilizer additives that included COC at 2.34 L ha-1, MSO at 2.34 L ha-1, NIS at 0.35 L ha-1, UAN at 2.34 L ha-1, and AMS at 1.43 kg ha-1, respectively as well as an untreated check. Experiments were conducted using a factorial arrangement of treatments within a randomized complete block design, with three factors being species, adjuvant, and fertilizer additive. All data were subjected to analysis of variance and means were separated using Fisher’s Protected LSD at p= 0.05.

 

Broadleaf signalgrass treated with quinclorac, regardless of adjuvant, resulted in ≥ 95% visual control 14 DAT. Quinclorac + MSO treatments resulted in significantly greater visual control for broadleaf signalgrass, large crabgrass, and fall panicum when compared to quinclorac + COC and quinclorac + NIS.  Visual control 7 and 14 DAT was minimal for Texas millet (<5%), crowfootgrass (0%), and goosegrass (0%) regardless of adjuvant and quinclorac combination. Height reductions at 14 DAT indicated that the combination of quinclorac and NIS resulted in a significantly smaller height reduction for weed species fall panicum (56%) and large crabgrass (72%) when compared to MSO (92-98%) or COC (90%). Dry weight reduction was significantly affected by weed species. Dry weight reductions were significantly greater for broadleaf signalgrass (97%) and large crabgrass (88%) when compared to fall panicum (75%) and Texas millet (44%). Dry weight reductions for crowfootgrass (0%) and goosegrass (0%) were significantly less than all other weed species. Trends in Texas millet, crowfootgrass and goosegrass control provide that these species may be tolerant to quinclorac. When using quinclorac to control susceptible weed species, choice of adjuvants will affect control of target weed species.

 


EFFECT OF FLOODING ON THE GERMINATION AND GROWTH OF PROMINENT RICE WEEDS. R. Liu*1, V. Singh2, X. Zhou3, M. V. Bagavathiannan1; 1Texas A&M University, College Station, TX, 2Texas A&M Universtiy, College Station, TX, 3Texas A&M University, Beaumont, TX (298)

ABSTRACT

Flooding can serve as an important non-chemical weed management tool in rice production. Although flooding has long been considered as a common cultural practice for weed control, the knowledge about the effects of flooding on weed biology is limited. In this study, two separate experiments were conducted in the greenhouse to document the influence of flooding conditions on (1) the germination and (2) growth and development of eight weed species dominant in Texas rice fields. These weed species were weedy rice (Oryza sativa), hemp sesbania (Sesbania herbacea), barnyardgrass (Echinochloa crus-galli), amazon sprangletop (Leptochloa panicoides), nealley’s sprangletop (Leptochloa nealleyi), Palmer amaranth (Amaranthus palmeri), common waterhemp (Amaranthus rudis), and johnsongrass (Sorghum halepense). For the germination experiment, 100 seeds of each species were planted in plastic containers filled with soil at an optimum depth for emergence of each species and subjected to three flooding treatments: periodic flushing, and 2.5 and 6.5 cm depth levels of flooding. Seedling emergence was recorded every three days, for up to 30 days after sowing, as an indication of actual germination. For the plant growth and development experiment weed seedlings were grown in plastic cups and permanent flooding (6.5 cm depth) was established when plant height reached at different growth stages viz. just emerged, 2, 5 and 10 cm tall. Non-flooded, but periodically flushed plants served as the standard controls for comparison purpose. At maturity, plant height, aboveground biomass, seed number and root volume were recorded. Preliminary results show that weedy rice and hemp sesbania had an excellent ability to germinate under both levels (2.5 and 6.5 cm depths) of flooding. However, the germination potential of barnyardgrass, amazon sprangletop and nealley’s sprangletop were reduced by flooding. Palmer amaranth, waterhemp, and johnsongrass did not germinate under either of the flooding treatments. Flooding had a tremendous impact on the continued growth and development of emerged weed seedlings and the effects were highly variable across the weed species studied. Weedy rice was the only species that continued to survive when flooding was established prior to the 2 cm seedling stage. Results of this study will be helpful in developing an effective irrigation strategy for integrated weed management in rice.

 

 


INFLUENCE OF PETROLEUM-DERIVED SPRAY OIL ON SILVERY-THREAD MOSS SUPPRESSION WITH FUNGICIDE AND HERBICIDE PROGRAMS. J. R. Brewer*, D. McCall, S. Askew; Virginia Tech, Blacksburg, VA (299)

ABSTRACT

Influence of Petroleum-derived Spray Oil on Silvery-Thread Moss Suppression with Fungicide and Herbicide Programs

J. R. Brewer, D. McCall, S. D. Askew

Every year golf course superintendents push their putting green height lower due to a need for faster ball roll. This necessity is causing an increased amount of stress on the turfgrass. The increase in overall turf stress causes poor vigor and loss in canopy closure, which in turn causes an increase in weed pressure. One of these weeds is silvery thread moss (STM) (Bryum argenteum Hedw.), which can tolerate low mowing heights and persist through wet and dry periods. As traditional treatments of carfentrazone become less effective, superintendents begin to use a plethora of different chemical and cultural methods to control STM including treatments like chlorothalonil, Fe-containing fertilizers, and topdressing. These programs typically have inconsistent results and STM can rapidly recover following treatments. Superintendents need an effective STM program which will have year-long control. We initiated two studies on May 26, 2015 at the Turfgrass Research Center in Blacksburg, VA on two creeping bentgrass putting greens (A4 & L-93). The studies were established as a randomized complete block design with 3 replications and 1 replication per block, and treatments were arranged as a factorial with 7 levels of herbicide and 2 levels of Civitas or petroleum-derived spray oil (PTSO). The 7 herbicide levels included: no herbicide, carfentrazone at 111.6 g ai ha-1, potassium phosphite at 9.4 kg ai ha-1, chlorothalonil at 8.2 kg ai ha-1, potassium phosphite + chlorothalonil, FeSO4 at 2.44 kg ai ha-1, and sulfentrazone at 35.1 g ai ha-1. Each herbicide was applied with and without PTSO at 25.5 L ha-1 All treatments were reapplied every 2 weeks until the end of the summer. The trial concluded on August 20, 2015 with 7 applications. Applications were made with a CO2 powered hooded sprayer calibrated to deliver 840 L ha-1 at a speed of 1.6 km h-1. Visual turf and moss cover, turf injury, moss control, and turf quality were assessed at application timing, 1 week after treatment (WAT), 2 WAT, and that schedule was repeated every month until the trial was completed.  Multispectral NDVI and hyperspectral NDVI readings were taken in conjunction with visual ratings to assess turf and moss health.

To control for variance structure in repeated measures over time, all data were converted to the area under the progress curve (AUPC). Effects of location, PTSO, and their interactions were insignificant. The herbicide main effect was significant for all measured responses except turf quality. Except for chlorothalonil, carfentrazone and potassium phosphite + chlorothalonil maintained higher creeping bentgrass cover than all other herbicides with an AUPC of 10716 and 10120, respectively. Moss cover appeared to be inversely correlated to bentgrass cover as the herbicides that had higher turf cover had lower moss cover and vice versa. Carfentrazone, potassium phosphite + chlorothalonil, chlorothalonil, and sulfentrazone contain lower moss cover then the other three herbicides based on area under the progress curve for visually-estimated moss cover. The above four herbicides have less than 1600 AUPC, and carfentrazone has less than 930 AUPC. Moss control follows a similar trend as the moss cover since the herbicides with the lowest moss cover also have the highest evaluated control. Carfentrazone controlled moss more than all other herbicides with 10216 AUPC. Chlorothalonil, potassium phosphite + chlorothalonil, and sulfentrazone controlled moss less than carfentrazone but greater than FeSO4, potassium phosphite, and no herbicide. Only sulfentrazone injured creeping bentgrass significantly during the trials with an AUPC of 1535. Multispectral NDVI ratings and turf quality were similar as they both had no significant herbicide effects, which is possibly due to the variability of environmental stress throughout the trial area. Hyperspectral NDVI showed a similar trend as the control data, but became more difficult to statistically differentiate the herbicides as the moss population decreased during the duration of the two studies. No herbicide and FeSO4 had higher moss disease than any other herbicides, which was partly due to higher moss population in those plot areas. 

 


MEASURING THE IMPACT OF ANNUAL BLUEGRASS ON BALL ROLL TRAJECTORY FROM A GOLF PUTT. S. S. Rana*, S. Askew, J. R. Brewer; Virginia Tech, Blacksburg, VA (300)

ABSTRACT

Annual bluegrass (Poa annua) has long been presumed to impact ball roll direction and distance.  However, there is no peer-reviewed research that evaluates the impact of annual bluegrass on ball roll trajectory from a golf putt.  A separate presentation explains sources of error and experimental procedures that were necessary to detect subtle influences of greens canopy anomalies on ball roll directional imprecision.  While minimizing potential error sources, research was conducted in spring and summer 2015 on a total of 8 different putting greens at The Tuckahoe Golf Course and The Highland Golf Course at Wintergreen and Primland Resorts, respectively in Virginia.  The objectives of the field experiments were to evaluate two ball roll devices – Putt Robot (PR) and Greenstester (GT) for measuring the influence of annual bluegrass on golf ball directional imprecision and bounce following a golf putt.  Titleist Pro V1® golf ball was used for this study.  The experiment was a randomized complete block with a split-plot arrangement of treatments.  Five blocks were spatially separated at the two above-mentioned golf courses.  Within each block, one replicate of the PR and GT (2 ball roll device main plots) were tested on two adjacent transects (2 greens canopy surface interface sub-plots); one with an isolated patch of annual bluegrass on an otherwise pure creeping bentgrass (Agrostis stolonifera) and an adjacent transect with only creeping bentgrass.  Data were collected for ball roll lateral imprecision, measured as deviation from the median ball strike position on pressure-sensitive paper placed at the 122-cm position along a 152-cm putt.  Ball bounce was assessed by recording a side view of the ball rolling across each transect at 1000 frames per second and tracking the balls position using video tracking software.  The influence of annual bluegrass on ball directional imprecision could not be detected when using the GT, presumably due to inherent error caused by the device.  Balls rolled by the GT had directional imprecision of 10 to 15 mm regardless of the presence or absence of annual bluegrass.  When using the PR, balls rolled over pure creeping bentgrass had directional imprecision of 4 to 5 mm depending on location while balls rolled over small patches of annual bluegrass increased lateral imprecision of ball roll direction to 9 to 12 mm.  Despite a rigorous quality control while adjusting the PR and studies to confirm that ball launch characteristics matched the putter manufacturers specified loft, we were able to detect a 1 to 3 mm repeating bounce that appeared to be caused by the putt.  Although several manufacturers of golf equipment claim that balls should achieve "true roll" in less than 10% of putt distance using a PR, we measured anomalies in ball behaviour in our study at beyond 20% of the total putt distance.  No peer-reviewed research was available with which to compare our results of ball bounce on putting greens.  Using our techniques to measure how greens canopy anomalies influence ball lateral imprecision, future efforts will aim to evaluate possible correlations between data obtained via ParryMeter and Sphero Turf Research App techniques and ball directional imprecision.  

 


ALTERNATIVE USES OF AMETRYN IN COTTON. M. T. Plumblee*1, D. M. Dodds2, T. Barber3, J. A. Ferrell4, C. A. Samples1, D. Denton2, L. X. Franca1; 1Mississippi State University, Starkville, MS, 2Mississippi State University, Mississippi State, MS, 3University of Arkansas, Little Rock, AR, 4University of Florida, Gainesville, FL (301)

ABSTRACT

Alternative Uses of Ametryn in Cotton. Michael T. Plumblee*1, Darrin M. Dodds1, Tom Barber2, Jason A. Ferrell3, Chase A. Samples1, Andrew B. Denton1, and Lucas X. Franca1; 1Mississippi State University, Mississippi State, MS, 2University of Arkansas, Little Rock, AR, 3University of Florida, Gainesville, FL.

 

ABSTRACT

                                                                                         

Cotton yield losses due to weed competition can be substantial. Palmer amaranth (Amaranthus palmeri) has become one of the most prolific weed species in cotton production in the United States due to increased incidence of herbicide-resistant biotypes. In 2005, glyphosate-resistant Palmer amaranth was confirmed in Georgia and since has spread throughout the cotton belt causing farmers to rely heavily on older herbicidal chemistries, multiple modes of action, and herbicides with long residual activity. Ametryn is not labeled for use in cotton but is a herbicide that has good residual activity and different mode of action than typical cotton herbicides. Thus the objective of this research is to evaluate Ametryn in a cotton production system for crop injury as well as for Palmer amaranth control.

 

An experiment was conducted in 2015 in Starkville, MS and Gainesville, FL to evaluate Palmer amaranth control and another experiment conducted in 2015 in Dundee, MS and Marianna, AR to evaluate crop injury. All plots were planted with Phytogen 499 WRF in 2-row plots 3.04 m wide x 7.62 m long using a randomized complete block with four replications. Post emergence applications were made to 20, 35, and 51 cm cotton and on 5, 10, and 15 cm Palmer amaranth. Herbicide applications consisted of Ametryn (Evik) + NIS, Ametryn (Evik) + COC, and Flumioxazin (Valor) + MSMA + NIS. Data collection consisted of visual cotton injury percentage 7 and 14 days after treatment, plant heights, Palmer amaranth control 14 and 28 days after treatment, and cottonseed yield. Data were subjected to analysis of variance using PROC Mixed procedure in SAS 9.4 and means were separated using Fishers protected LSD at p = 0.05.

 

Visual crop injury was 6% greater when applications of Evik + NIS or Valor + MSMA + NIS were made on 20 cm tall cotton in Starkville. No cotton injury was observed on cotton 51 cm tall at the time of application regardless of treatment at 7 or 14 days after treatment in Starkville, but injury was highest in Marianna at 14 days after treatment. No significant differences in cotton height were observed due to treatment or application timing. Applications of Valor + MSMA + NIS resulted in 7% less seed cotton yield compared to Evik + NIS when applied to 35 cm cotton. No significant differences between herbicide treatments were observed on Palmer amaranth control in Dundee, MS. In Gainesville, FL, applications of Valor + MSMA + NIS provided the highest percentages of Palmer amaranth control regardless of application timing at 14 and 28 days after treatment.


CORN RESPONSE TO LOW RATES OF PARAQUAT AND FOMESAFEN. B. H. Lawrence*1, J. A. Bond1, H. M. Edwards1, J. D. Peeples1, H. T. Hydrick1, D. B. Reynolds2, T. L. Phillips1; 1Mississippi State University, Stoneville, MS, 2Mississippi State University, Starkville, MS (302)

ABSTRACT

Corn (Zea mays L.) grown in the Mississippi Delta is typically planted between March 15 and April 20.  Preplant herbicide applications for soybean (Glycine max [L.] Merr.) and cotton (Gossypium hirsutum L.) are also common during this time.  Research was conducted from 2013 to 2015 at Mississippi State University to evaluate corn agronomic performance and yield following exposure to sub-lethal rates of paraquat and fomesafen applied at different growth stages.  The experimental design was a randomized complete block with four replications.  Paraquat and fomesafen were applied in separate experiments at 10% of the labeled use rates prior to corn emergence (PRE) and when corn reached the V1, V3, V5, V7, and V9 growth stages.  A nontreated control was included for comparison.  Visual estimates of corn injury were recorded 3, 7, 14, 21, and 28 d after (DAA), and corn height was recorded 14 DAA.  Ear length, number of kernel rows per ear, and yield were determined at maturity and converted to a percent of the nontreated control.  Data were regressed against days after emergence (DAE) allowing for both linear and quadratic terms with coefficients depending on application timing, and non-significant model terms were removed sequentially until a satisfactory model was obtained.  Parameters which did not exhibit linear or quadratic trends were subjected to ANOVA.  Least square means were calculated and mean separation (p ≤ 0.05) was produced using estimates of the least square means.  No trend was detected for paraquat injury 3, 7, 14, 21 or 28 DAA; however, a quadratic trend was detected for yield and height.  Corn yield was reduced 0.5% daily if paraquat application occurred anytime during vegetative growth.  Corn height was most negatively affected when paraquat was applied from V1 and V3.  A quadratic trend was detected for corn injury with fomesafen 7, 14, and 28 DAA; however, no linear or quadratic trend was observed for corn height, ear length, number of kernel rows, or yield following applications of fomesafen at 10% of the labeled rate.  Corn injury was greatest 7, 14, and 28 DAA when fomesafen was applied to V5 and V7 corn.  Applications of paraquat and fomesafen to fields near to corn should be avoided if conditions are conducive for off-target movement.


IMPACT OF IRRIGATION RATE ON PRE-EMERGENCE HERBICIDE ACTIVITY. H. C. Smith*1, J. A. Ferrell1, T. M. Webster2, P. Munoz1; 1University of Florida, Gainesville, FL, 2USDA-ARS, Tifton, GA (303)

ABSTRACT

Impact of Irrigation Rate on Pre-emergence Herbicide Activity. H. C. Smith*1, J. A. Ferrell1, T. M. Webster2, J. V. Fernandez1, P. J. Dittmar1, and P. R. Munoz1. 1University of Florida, Gainesville, FL. 2United States Department of Agriculture – Agricultural Research Service, Tifton, GA. 

The importance of preemergence herbicide applications in cotton has increased since the evolution of glyphosate-resistant Palmer amaranth (Amaranthus palmeri). Cotton producers are relying on residual herbicides for control of Palmer amaranth, as postemergence options are limited or ineffective. S-metolachlor, acetochlor, fomesafen, and dicamba all provide preemergence activity on Palmer amaranth, but little is known about the effect of irrigation rate on incorporation and herbicidal efficacy. In 2015, an experiment was conducted on fine sand and loamy sand soils to evaluate the influence of irrigation rate on preemergence herbicide control of Palmer amaranth. Irrigation rate was significant for the incorporation of both s-metolachlor and acetochlor. Herbicidal efficacy of s-metolachlor was greatest in plots receiving 6.4 and 12.7 mm of irrigation where Palmer amaranth biomass was reduced to 4.0 and 2.1% of UTC, respectively, compared to 61.3% in plots that did not receive incorporating irrigation. Acetochlor incorporated at 3.2-12.7 mm irrigation rates were not significantly different but did significantly reduce Palmer amaranth biomass compared to the 1.6 mm irrigation rate. Irrigation rate was not significant for the incorporation of fomesafen or dicamba. Across all herbicides, fomesafen treated plots provided the most consistent control of Palmer amaranth, reducing its biomass to < 2.5% of UTC at all irrigation rates. Dicamba provided the least and most inconsistent control of Palmer amaranth producing 16.6-51.4% of UTC biomass.

 


PALMER AMARANTH (AMARANTHUS PALMERI) CONTROL WITH SONIC AND SURESTART II IN AGRONOMIC CROPS. A. Umphres-Lopez*1, B. Haygood2, A. Weiss3, Z. Lopez4, T. C. Mueller1; 1University of Tennessee, Knoxville, TN, 2Dow AgroSciences, Jackson, TN, 3Dow AgroSciences, Raleigh, NC, 4Dow AgroSciences, Bishop, TX (304)

ABSTRACT

Palmer Amaranth (Amaranthus palmeri) Control with Sonic and SureStart II in Agronomic Crops

A.M. Umphres-Lopez1, T. Weiss2, Z. Lopez2, and T.C. Mueller1.  1University of Tennessee, Knoxville, TN., 2Dow AgroSciences LLC, Indianapolis, IN

Since the introduction of glyphosate resistant (GR) crops, producers have gained several advantages with this technology.  Some advantages include broad-spectrum weed control of various grass and broadleaf species, alternating to conservative tillage practices, and having a flexible window of herbicide application.  However over the years with repeated herbicide applications at higher rates combined with increased selection pressure has resulted in GR weeds.  With the discovery of GR Palmer amaranth (Amaranthus palmeri), control has become increasingly challenging and economically important for producers throughout the United States.  Palmer amaranth along with the growing list of resistant weeds, forces producers to incorporate diverse mode of actions (MOAs) in order to control weeds and prevent their survival.  Therefore the purpose of this study was to further evaluate weed control in the southeast with SureStart II and Sonic as a PRE in corn (Zea mays) and soybeans (Glycine max), respectively.  This study was conducted at the University of Tennessee Plant Science Farm-Holston Unit in Knoxville, TN.  Plots were arranged in a randomized complete block design (RCBD) with 4 replications during the 2015 crop season.  In corn, treatments consisted of a full rate of SureStart II at 1.5 kg ai ha-1 at planting and a split application of 0.9 kg ai ha-1 as a PRE and POST.  Treatments for soybeans at planting consisted of 147, 221, and 294 g ai ha-1, respectively.  Weeds identified in the plots were primarily GR-Palmer amaranth followed by pitted morningglory (Ipomea lacunosa) and broadleaf signalgrass (Urochloa platyphylla).  A soybean Liberty-Link system and sequential application of Liberty in-season was utilized   Data was collected on visual assessments of weed control and yield once crops reached maturity.  At 30 DAT, weed control in corn showed 96% and 98% control of GR Palmer amaranth for the full and split application of SureStart II, respectively.  In soybeans, plots with the 221 and 294 g ai ha-1 were observed to have the greatest Palmer amaranth control at 98% and yielded 3900 and 4200 kg ha-1, respectively.  Data from this study suggests that the use of PRE residual herbicides gives producers the advantage of reducing competition from weeds with longer weed control.

 


DRIFT POTENTIAL OF RINSKORTM ACTIVE: ASSESSMENT OF OFF-TARGET MOVEMENT TO SOYBEAN. M. R. Miller*1, J. K. Norsworthy1, M. R. Weimer2, M. L. Young1, J. K. Green1, G. T. Jones1; 1University of Arkansas, Fayetteville, AR, 2Dow AgroSciences, Indianapolis, IN (305)

ABSTRACT

Dow AgroSciences has announced a new herbicide, LoyantTM with RinskorTM Active , which is the second herbicide in a new structural class of synthetic auxins in the arylpicolinate family. This new herbicide provides an alternative mode of action for rice (Oryza sativa). It is not uncommon for soybean (Glycine max) to be planted adjacent to rice resulting in concerns for drift. Historically, the use of synthetic auxin herbicides, such as dicamba, in fields adjacent to soybean plots has concerned growers due to the high level of soybean sensitivity to this type of herbicide.  Adverse effects on growth and yield have been observed in cases where drift occurs.  Concerns about synthetic auxin herbicide drift have only increased as new dicamba-tolerant crops near commercialization. To address these concerns, a study was developed to understand the susceptibility of common row crops, such as soybean, to Rinskor and dicamba.  A field study was conducted during the summers of 2014 and 2015 to: (1) evaluate the sensitivity of soybean to low concentrations of Rinskor active and (2) compare soybean injury and yield following applications of Rinskor and dicamba at two soybean growth stages and concentrations.  Soybean were treated with 1/10, 1/20, 1/40, 1/80, 1/160, 1/320, or 1/640 of the 1X rate of Rinskor Active (30 g ai/ha) or dicamba (560 g ae/ha) at the V3 or R1 growth stage.  Rinskor applied at a rate of 1/10 to 1/40X caused significant foliar injury and subsequent height reduction. In comparison, dicamba applied at the same rates caused similar injury and growth reductions. As drift rate of Rinskor active decreased from 1/10 to 1/640X the level of soybean injury dissipated rather quickly.  Dicamba caused substantial injury at rates as low as 1/640X.  Soybean yield reduction was greatest when highest concentrations of the two herbicides were applied. Results from this study provide a starting point for understanding soybean sensitivity to low rates of Rinskor and dicamba. Based on this research and additional trials, it is believed that the weed control benefit of Rinskor active will outweigh the slight risk for off-target movement to soybean. 

 

TMTrademark of the Dow Chemical Company (“Dow”) or an affiliated company of Dow. LoyantTM is not registered with the US EPA at the time of this presentation. The information presented is intended to provide technical information only.

 


EVALUATION OF DICAMBA SEQUESTRATION IN VARIOUS TYPES OF SPRAYER HOSES. G. T. Cundiff*1, D. B. Reynolds1, T. C. Mueller2; 1Mississippi State University, Starkville, MS, 2University of Tennessee, Knoxville, TN (306)

ABSTRACT

Evaluation of Dicamba Sequestration in Various Types of Sprayer Hoses. G.T. Cundiff*1, D.B. Reynolds1, and T.C. Mueller2, 1Mississippi State University, Mississippi State, MS., 2University of Tennessee, Knoxville, TN.

ABSTRACT

The introduction of new herbicide tolerant crops may provide many benefits for producers such as alternative control options for resistant weed species, decreased costs, and different modes of action.  Along with these benefits, the use of auxin containing herbicides may also increase concern for issues such as herbicide drift, volatilization, and tank contamination.  The adjuvant and solvent system utilized in several commercial herbicides often result in the release of herbicides which have been sequestered within the spray system thus resulting in injury to sensitive crops.  Roundup WeatherMax and PowerMax (glyphosate) are two such products that have been observed to have this effect.  Synthetic rubbers, synthetic plastic polymers (Polyvinyl chlorides (PVC)), polyurethane blends and polyethylene blends comprise modern day agricultural spray hoses.  The objective of this study was to determine if agricultural hose types would differ with respect to dicamba sequestration.

Field and greenhouse studies were conducted in 2013, 2014 and 2015 in Brooksville, MS and Starkville, MS on a new dicamba formulation known as Engenia.  This study focused on determining if Engenia persistence would differ among five various hose types, three cleanout procedures and applied to soybean used as a bio-indicator to assess cleanout efficiency. Samples were collected and analyzed on High Performance Liquid Chromatography (HPLC) to the mass spec to determine Engenia persistence with respect to hose by cleanout treatments.  The use of scanning electron microscopy was utilized to give visual representation of new hoses versus used hoses.

Five different types of agricultural spray hoses were evaluated.  Each hose measured 3 m and had an inside diameter of 1.2 cm.  All spray lines were filled with Engenia at 0.56 kg ae/ha and left to incubate for 48 hours.  The dicamba spray solution was then flushed out of the lines and cleaned with either water, ammonia or no cleanout and then left to incubate in their designated cleaning solution for 24 hours.  After their final flush, all lines were left empty for 48 hours.  The spray lines were then filled with Roundup WeatherMax (glyphosate) at 1.1 kg ae/ha and incubated for 48 hours to aid in the release of any sequestered auxin herbicides before spraying to a sensitive crop.  The glyphosate solution was applied to Roundup Ready soybean at the R2 growth stage while delivering 140 liters per hectare.  A known rate titration of Engenia (0.56, 0.14, 0.00875, and 0.00219 kg ae/ha) was applied separately as comparison treatments.  Samples were collected from each hose by cleanout treatment and the titration.

Differences among hose types and cleanout procedures exist with observations including visual estimations of injury (VEOI), height reduction, dry matter, yield reduction, and ppm analyte retained.  The makeup of PVC polyurethane blend and synthetic rubber blend hoses increased retention of the dicamba analyte when compared to the polyethylene blend hose. No differences were observed by the addition of ammonia to the cleanout solution when compared to water alone. Differences in a hose type’s ability to sequester the dicamba analyte may have more to do with the hoses internal chemical composition and the manufacturing process.  Scanning electron microscopy revealed imperfections in new PVC polyurethane and synthetic rubber hoses, which eventually lead to inner wall depletion of these hose types.  This is in contrast to what was found in the polyethylene blend hose type, in which the inner wall is smooth and free of imperfections leading to less retention of the dicamba analyte.

 


VOLATILITY COMPARISON OF 2,4-D FORMULATIONS IN SOYBEANS. E. T. Parker*, T. C. Mueller; University of Tennessee, Knoxville, TN (307)

ABSTRACT

As herbicide resistance continues to be at the forefront of herbicide research, old herbicide technologies are seeing a resurgence in use. New 2,4-D formulations are being developed in an effort to reduce off-target movement via volatilization. Studies were performed to develop a method to quantify volatility of 2,4-D low-volatile ester and 2,4-D amine salt formulations for future comparison with new 2,4-D formulations.

 

No-till soybean plots measuring 15 by 15 m at V3-V5 stage were treated with either Weedar 64® (2,4-D amine) or 2,4-D ester formulations at 1120 g ae ha-1. Plots were sprayed in early morning and no wind conditions. Approximately 15 min after application, high volume (283 L m-1) air samplers were placed into each plot, and one in a non-treated plot at least 300 m from those receiving treatment. Each sampler was equipped with both polyurethane foam (PUF) collectors and filter paper to recover any volatile material. PUFs and filters were changed at 6, 12, 24, and 36 hours after treatment (HAT). Each sample was placed in bags within coolers and transported immediately to a freezer until extraction. Assay was done using chemical extraction followed by liquid chromatography mass spectroscopy. Data were subjected to ANOVA and means were separated using Fisher’s Protected LSD (P < 0.05).

 

The study was conducted twice, with 2 samplers collecting each respective 2,4-D formulation.  Environmental conditions, especially temperature, affected the results observed.  Recovery of volatile 2,4-D for all formulations was highest during the 6-12 h interval, followed by the 24-36 h interval, which were both during the warmest parts of the day. Considering the relative volatility of ester to amine formulations in the published literature, the recovery of 2,4-D ester was greater than amine over all time periods. The methods utilized for the detection of volatility of 2,4-D formulations are adequate and will be used in future research.

 


WEED MANAGEMENT WITH ENLIST™ IN TEXAS HIGH PLAINS COTTON. M. R. Manuchehri*1, P. A. Dotray1, W. Keeling2, R. M. Merchant1, S. L. Taylor1; 1Texas Tech University, Lubbock, TX, 2Texas A&M, Lubbock, TX (308)

ABSTRACT

WEED MANAGEMENT WITH ENLIST™ IN TEXAS HIGH PLAINS COTTON. M. R. Manuchehri*1, P. A. Dotray1,2, J. W. Keeling2 , R. M. Merchant1, and S. L. Taylor2; 1Texas Tech University, Lubbock, TX, 2Texas A&M AgriLife Research and Extension Center, Lubbock, TX.

Enlist™ cotton technology, utilizing 2,4-D choline + glyphosate (Enlist Duo™) and glufosinate  tolerance, has the potential to effectively manage Palmer amaranth (Amaranthus palmeri S. Wats.), Russian-thistle (Salsola tragus L.), and other difficult-to-control weeds in the Texas High Plains. Weed management systems and application timing trials assessed the effectiveness of Enlist Duo™ alone and in combination with glufosinate and several soil-residual herbicides for postemergence control of Palmer amaranth. Systems trials consisted of a preplant incorporated (PPI) application followed by (fb) an early postemergence (EPOST) application fb a mid-postemergence (MPOST) application. Application timing trials consisted of one application that was made at a specific Palmer amaranth growth stage (3 to 5 cm, 10 to 15 cm, and 20 to 30 cm). Visual control of Palmer amaranth was recorded at 14, 21, and 28 days after treatment (DAT). For the 2013 systems trial evaluated 28 days after the MPOST application, Palmer amaranth was controlled approximately 97% in all herbicide systems with the exception of systems that included a MPOST application of glufosinate alone. Combined across 2014 and 2015, Palmer amaranth control was similar across herbicide systems (approximately 98%) with the exception of trifluralin PPI fb glufosinate (with or without acetochlor) EPOST fb glufosinate MPOST. In the 2013 application timing trial evaluated 21 DAT, Palmer amaranth was controlled at least 90% at the 3 to 5 cm timing with the exception of any treatment that included glufosinate alone or in tank mix or glyphosate alone. Control never reached above 90 and 80% following applications made to 10 to 15 and 20 to 30 cm Palmer amaranth, respectively. In 2014, control never exceeded 90% following applications made to 10 to 15 cm and 20 to 30 cm Palmer amaranth. In 2015, 3 to 5 cm Palmer amaranth was controlled at least 90% with the exception of Enlist Duo alone, Enlist Duo + glufosinate, and glyphosate alone. In the same year, 10 to 15 and 20 to 30 cm Palmer amaranth control never reached above 90%. Overall, several effective treatments were identified; however, the most sustainable treatments were a result of a systems approach that involved multiple application timings, multiple herbicide modes of action, and the addition of soil residual herbicides.

 


DIFFERENTIAL SENSITIVITY OF FALL PANICUM (PANICUM DICHOTOMIFLORUM MICHX.) POPULATIONS TO ASULAM. J. V. Fernandez*1, D. C. Odero1, G. MacDonald2, J. A. Ferrell2, B. A. Sellers3, P. C. Wilson2; 1University of Florida, Belle Glade, FL, 2University of Florida, Gainesville, FL, 3University of Florida, Ona, FL (309)

ABSTRACT

Fall panicum is a troublesome annual grass weed associated with sugarcane production in Florida. Sugarcane growers in Florida depend on asulam as their best POST herbicide option for control of fall panicum. Recently, many growers have observed lack of control of fall panicum with asulam. Greenhouse dose response studies were conducted in 2015 in Gainesville, Florida to determine sensitivity of fall panicum populations to asulam. Seeds from four fall panicum populations from Florida sugarcane fields (EREC, Okeelanta, PPI, and Tecan) and a population from Leland, MS were planted and treated with asulam. Asulam was applied at 0, 231, 462, 925, 1850, 3700, and 7400 kg ha-1 on 30 cm tall fall panicum.  A four parameter log-logistic model was used to determine the rate of asulam required to cause 90% aboveground dry biomass reduction (ED90) of fall panicum at 28 days after treatment. The ED90 values were 513, 711, 857, 877, and 3,797 g ai ha-1 of asulam for EREC, PPI, Okeelanta, Azlin, and Tecan populations, respectively.  There was a minimum of 0.6 fold to a maximum of 7.4 fold difference between the sensitivity of fall panicum populations to asulam. The results of this study show that there was differential sensitivity of the fall panicum populations to asulam.

 


TOLERANCE OF XTENDFLEXTM COTTON TO VARIOUS HERBICIDE TANK MIX COMBINATIONS. C. A. Samples*1, D. M. Dodds2, A. L. Catchot2, T. Irby1, D. B. Reynolds1, G. R. Kruger3, D. Denton2, L. X. Franca1, M. T. Plumblee1, J. T. Fowler4; 1Mississippi State University, Starkville, MS, 2Mississippi State University, Mississippi State, MS, 3University of Nebraska-Lincoln, North Platte, NE, 4Monsanto Company, St. Louis, MO (310)

ABSTRACT

Injury Potential With Herbicide Tank Mixes In XtendFlex® Cotton. C.A. Samples1, D.M. Dodds1, A.L. Catchot1, A.B. Denton1, G. Kruger2, J.T. Fowler3. 1Mississippi State Univ., Mississippi State, MS, 2Univ. of Nebraska, North Platte, NE. 3Monsanto Company, St. Louis, MO.

 

 

Abstract

 

Due to the continued spread of glyphosate resistant Palmer amaranth (Amaranthus palmeri), technologies have been developed allowing growers to apply auxin-type herbicides post emergence. The XtendFlex® technology from Monsanto will allow growers to apply glufosinate, and dicamba over the top of cotton (Gossypium hirsutum L.).  Dicamba applied at 1.1 kg ae ha-1 provided up to 90 percent Palmer amaranth control. Dicamba tank mixed with glufosinate increased Palmer amaranth control over dicamba alone. Dicamba has also been observed to control other glyphosate resistant species 79 to 100 percent 14 days after application. Glufosinate is a helpful tool for controlling glyphosate resistant Palmer amaranth. Glufosinate has shown to increase control from 9 to 19 percent over glyphosate, also two POST applications of glufosinate have been shown to provide 96 percent Palmer amaranth control. Since the development of glyhosate resistance, early POST applications with several modes of actions have become common. XtendFlex® technology will allow growers to apply several different modes of action at once. However, the crop injury potential from these applications need to be further examined.

 

Experiments were conducted in Starkville, MS at the R. R. Foil Plant Science Research Center and in Brooksville, MS at the Black Belt Branch Experiment Station. Plots consisted of 4-1 m spaced rows that where 12.2 m in length. Each plot was replicated four times. DP 1522 B2XF was planted in Starkville and Brooksville. ST 4946 GLB2 was planted in a separate experiment in Starkville for comparison purposes. Applications were made on 2-4 leaf cotton with a CO2-powered backpack sprayer calibrated to apply 140 L ha-1 @ 317 kpa while walking 4.8 kph. Treatments applied to DP 1522 B2XF included glyphosate @ 1.1 kg ae ha-1, glufosinate @ 0.6 kg ai ha-1, S-metolachlor @ 1.07 kg ai ha-1, dicamba (Engenia) @ 0.6 kg ae ha-1, dicamba (Clarity) @ 0.6 kg ae ha-1, and dicamba (MON 119096) @ 0.6 kg ae ha-1 either alone or in combination. Treatments except those containing dicamba were applied to ST 4946 GLB2 for comparison purposes. Visual injury ratings were made 3, 7, 14, 21, and 28 days after applications. Other data collected included height at 1st bloom as well as the end of the season and lint yield. Data were analyzed using the PROC MIXED procedure in SAS version 9.4 and means were separated using Fisher’s protected LSD at p=0.05.

 

Five of the seven highest injury levels 3 days after application on DP 1522 B2XF were from treatments containing glufosinate and S-metolachlor in which injury ranged from 33-43 percent. The highest level of injury came from treatments containing dicamba (Engenia) + glyphosate + glufosinate + S-metolachlor.  There were no differences among treatments applied to ST 4946 3 days after applications with crop injury ranging from 3 to 10 percent depending on the treatment. Similar to 3 days after application, five of the seven treatments with the highest level of injury seven days after application contained glufosinate and S-metolachlor. There were no differences in injury to ST 4946 GLB2 with crop injury ranging from 3 to 7 percent. At 14 days after application injury to DP 1522 B2XF had dissipated and ranged from 1 - 8 percent depending on the treatment no differences due to herbicide treatment were observed. Injury to ST 4946 GLB2 due to herbicide treatment was not significantly different 14 days after application and ranged from 0- 2 percent. Cotton height of DP 1522 B2XF was found to be significantly affected by the herbicide(s) applied at 2-4 leaf cotton. Treatments that caused the greatest injury 3 and 7 days after application resulted in shorter cotton compared to the untreated control. However, no yield differences were in DP 1522 B2XF due to herbicide treatment with yields ranging from 1900-2150 kg lint ha-1. There were no differences in yielddue to herbicide treatments applied to ST 4946 GLB2 with yields ranging from 1800-2000 kg lint ha-1

 


WHAT DOES INTEGRATED PEST MANAGEMENT MEAN FOR AQUATIC WEEDS? J. D. Madsen*; USDA ARS, Davis, CA (311)

ABSTRACT

Integrated Pest Management (IPM) has been the leading paradigm for government pest management programs over several decades.  As with many broad-based approaches, its application to a specific sector or group of pests may not be well understood.  The five defining elements of an IPM approach are to 1) prevent pest problems, 2) monitor for the presence of pests and pest damage, 3) establish the density at which impacts may be tolerated, 4) treat pest problems to reduce populations below these levels, and 5) evaluate the effects and efficacy of the treatment program.  While IPM programs for insect and agricultural weed pests are fairly common, their explicit application to aquatic weeds is less obvious.  In many states, management programs follow the guidelines of IPM without necessarily invoking the title.  Common practices include 1) developing lake-wide or site-based management plans, 2) developing a prevention strategy, 3) monitoring pest populations, 4) selecting management alternatives to fit the specific site characteristics, 5) explicitly considering alternative management approaches, and 6) evaluating the effectiveness of management activities and impacts on native plant communities.  With inclusion of aquatic herbicide treatments within a generic NPDES permit, lake-wide plans including assessments are required for most significant management programs.  In practice, the management of invasive aquatic plants has more in common with the management of rangeland weeds and natural area weeds, rather than agronomic sites.  Management should consider the strong propagule pressure from incoming water-borne dispersal, and the benefits of native vegetation for ecosystem services.


APPROACHES AND PROGRESS IN WEED BIOLOGICAL CONTROL PROGRAMS IN FLORIDA. P. W. Tipping*; USDA-ARS, Davie, FL (312)

ABSTRACT

Invasive, exotic plants threaten and disrupt natural and managed ecosystems throughout the United States.  Natural systems, including wetlands, are some of the most valued and yet threatened habitats in the world.  They provide many ecological, economic, and social benefits, including flood abatement, improved water quality, recreation, and support for biodiversity.  One explanation for the success of invasive plants is the lack of potentially coevolved natural enemies in the invaded range.  Classical biological control reunites weeds with natural enemies from their native range and can result in landscape-level, permanent suppressions of exotic weeds.  Research conducted by the USDA Invasive Plant Research Laboratory in Ft. Lauderdale focuses on the development of biological control for invasive weeds and, to date, 25 insects have been introduced against nine weed species.  Of these, air potato, alligatorweed, giant salvinia, melaleuca, and waterhyacinth are under complete or increasing levels of biological control while others like Brazilian peppertree, Chinese tallowtree, lygodium, and waterlettuce require additional research and development. The process of classical biological control involves consulting with collaborators to identify weeds of concern, prioritizing targets, conducting literature reviews, examining genetic comparisons to direct foreign exploration, investigating weed life history characteristics to direct exploration efforts, and obtaining natural enemies for testing from the native range.  Intensive host range evaluations are conducted using predictive bioassays to determine environmental safety of imported natural enemies.  Studies investigate the predictability of pre-release efficacy tests for potential biological candidates.  Release, establishment, and evaluation of the permitted agents are conducted to quantify their influence on plant performance.  Effective agents and techniques are transferred to user groups to speed the deployment and adoption of biological control.  Landscape level post-release monitoring, integration of control methods, and ecosystem restoration are the final steps in a protracted effort to reduce the impact of problematic weeds in natural systems.  Biological control of weeds has an enviable biosafety record in terms of unintended impact on non-target plants.  Worldwide, of the nearly 400 insects, mites, and fungal species released for control of exotic weeds only two have caused significant damage to non-target plants and both were predictable from host range assessments.  Outcomes in classical weed biological control programs can range from complete control of the weed to the point where no more management is required, to little or no control of the weed population.  In most cases, biological control provides an intermediate degree of control whereby management may still be necessary, but to a lesser extent.  These intermediate outcomes may provide opportunities for additive integration with other control approaches.  Despite the evidence that biological control integrates well with other control methods, the development of actively integrated weed management programs that have biological control as a component are rare.


DEVELOPING AQUATIC HERBICIDE USE PATTERNS: RECENT PROGRESS, CHALLENGES, AND ESTABLISHING PRIORITIES. M. D. Netherland*; US Army ERDC, Gainesville, FL (313)

ABSTRACT

In 2007, approximately 50 scientists gathered in San Diego to discuss future research directions and priorities for aquatic plant management. Revisiting this publication from a meeting nearly a decade ago allows us to look back and think ahead as we consider the future use of aquatic herbicides. A key factor when considering “future directions” revolves around the likelihood of a major new weed introduction changing the status quo. This has been experienced at a regional level (e.g. Salvinia molesta in LA/TX, Nymphoides cristata in the SE, Lygodium microphyllum in S. Florida); however, most known serious aquatic weeds are already established in the US.  Range expansions of established plants (e.g. monoecious hydrilla Hydrilla verticillata) and changes in plant biology (e.g. hybridity) have been noted over the last decade with resultant impacts on herbicide use patterns.  We must also look at older intractable problems with fresh insight. In 2007 we identified improving herbicide performance in irrigation canals as a key challenge. With significant research and regulatory focus, the product endothall (first registered in 1960) was registered and widely adopted in 2010 on a large scale in Western irrigation. This example suggests that identifying a key problem and bringing the appropriate resources to bear can change long-term herbicide use patterns in aquatics.  In 2007, we also identified development of new strategies for control of harmful algal blooms (HAB) as a key challenge.  While research in the prevention and monitoring of HAB remains vigorous and well-funded, there has been limited progress in developing new tools or novel strategies for HAB control. From a regulatory perspective, state resource agencies typically have a major influence on how herbicides are used and whether new compounds are integrated into a program. This is unlikely to change, and it presents both a challenge and an opportunity. Given the sensitivity of treating public waters, high levels of support and professionalism are required when applying herbicides. Project costs can be orders of magnitude greater in the aquatic plant management market when compared to controlling weeds in commodity markets. Issues such as non-target impacts, T&E species, restoration of vegetation, and concerns over herbicide fate will continue to challenge both established and new management programs. Maintaining a skilled work force capable of managing multiple high-profile projects is important for future growth.  Unfortunately, ongoing attrition (often without replacement) continues to reduce both the experienced and early career scientists needed to produce innovation in this area. Dispersal of future talent between academia, government, and industry is necessary to defend current and new technical strategies in a highly regulated market. Aquatic herbicides are widely used in multiple private markets, yet the transfer of this technology (i.e. “trade secrets”) for broader public use is minimal. In the near future, we will likely see high profile projects drive innovation in the use of both old and new herbicides registered for aquatic plant management. New registrations in aquatics are likely to be limited, so each new product must receive proper stewardship from private and public interests.


REMOTE SENSING AND MODELING FOR IMPROVING OPERATIONAL AQUATIC PLANT MANAGEMENT. D. Bubenheim*; NASA - Ames Research Center, Moffett Field, CA (314)

ABSTRACT

Management of aquatic weeds in complex watersheds and river systems present many challenges to assessment, planning and implementation of management practices.  Remote sensing technologies and associated image analysis offer an opportunity to gain a comprehensive view of the problem provided: the species of interest can be identified (many aquatic weeds are submerged or in mixed communities if floating), the images are available on a time scale supportive of operational decision making and implementation, the costs of image acquisition and processing are not prohibitively expensive.  Other tools available to aide in developing management strategies include modeling at local through watershed scales to understand the ecology of the system.  We are applying both remote sensing and modeling technologies in the California San Joaquin-Sacramento Delta River system as part of a USDA sponsored area-wide project.  We will discuss remote sensing tools developed for mapping of floating and submerged aquatic weeds and how these capabilities enhance planning and operational efficiency.  Modeling efforts to define the complex interaction of land-use types, water management, and climate and drought induced impacts on water quality (at watershed and local scales) and how these affect invasive and native aquatic plant ecology will be presented.  These tools individually affect weed management operations but potentially most important is the synthesis and ability to inform science-based, decision-making.  These techniques provide for quantitative assessment, strategic planning informed by ecological understanding of the system, consideration of alternative management practices, monitoring of management practice effectiveness, and refinement of decision support systems.

 


ENVIRONMENTAL ISSUES FOR LARGE OPERATIONAL PROGRAMS IN NORTH AMERICA. J. H. Rodgers*1, A. Calomeni1, K. Iwinski1, R. Wersal2, W. Ratajczyk3; 1Clemson University, Clemson, SC, 2Lonza, Atlanta, GA, 3Lonza, Germantown, WI (315)

ABSTRACT

Large operational programs in North American water resources are those that address vascular and nonvascular weeds in aquatic systems that are thousands of hectares or span multiple jurisdictions (e.g. boundaries between states and nations). Noxious and invasive species of vascular plants and algae can impact water resources causes loss of uses of those resources as well as economic and health impacts. These weed species are moving at unprecedented rates and colonizing previously unaffected aquatic systems.  Simply stated, the problem for large scale operations is the risks of adverse effects posed by the noxious or invasive species versus the risks and costs of potential or actual remedies. Historically, large-scale operational programs were the purview or responsibility of federal or multi-state agencies that had resources to accomplish them. Currently, management options are considered in an adaptive context since support for many large scale programs have diminished.  As the problems grow, the ability of “bottom up” strategies to intervene successfully will be more apparent. Droughts and other natural disturbances such as floods will likely focus attention on critical water resources in the near future and force us to allocated resources to protect or remediate them. Weeds in critical water resources such as drinking water supplies adversely impacting the use of that water provide good examples of adaptive management and environmental issues.

 


THE USDA AREA-WIDE PROJECTS: INTEGRATED SCIENCE AND OPERATIONS FOR ADAPTIVE MANAGMENT. A. S. Llaban*; California State Parks, Sacramento, CA (316)

ABSTRACT

The USDA Area-Wide Projects: Integrated Science and Operations for Adaptive Management

California State Parks Division of Boating and Waterways

The California State Parks Division of Boating and Waterways (DBW) is designated as the lead State agency for cooperating with agencies of the United States and other public agencies in controlling invasive aquatic plants in the Sacramento-San Joaquin Delta and its tributaries. By using an integrated pest management approach, DBW currently implements control measures for water hyacinth (Eichhornia crassipes), Brazilian waterweed (Egeria densa), South American spongeplant (Limnobium laevigatum), and curly leaf pondweed (Potamogeton crispus).  Other aquatic plant species such as water primrose (Ludwigia spp.), Eurasian watermilfoil (Myriophyllum spicatum), fanwort (Cabomba caroliniana), and coontail (Ceratophyllum demersum) are identified as candidate species for future management. The Aquatic Invasive Species Program’s objectives are to keep waterways safe and navigable by controlling the growth and spread of invasive plant species and to minimize negative impacts on the environment, public health, and economy. Faced with challenges of invasive aquatic plant management in the Delta, DBW recognizes an opportunity to strengthen its scientific and holistic approach through research and interagency collaboration.


DESSICATION OF WINTER CANOLA WITH HERBICIDES TO PROTECT YIELD. E. Jenkins*, J. Matz, A. R. Post; Oklahoma State University, Stillwater, OK (317)

ABSTRACT

Since the introduction of winter canola to the southern Great Plains producers have been challenged with how to harvest the crop. It is in the mustard family (Brassicaceae) and the siliques shatter easily at pod ripening leaving producers vulnerable to yield loss while the crop stands in the field near harvest. Most producers in the region resort to swathing the crop into a wind-row a few days before ripening and allowing it to dry for several days before combines go through the field to harvest. Others have tried pod-sealant technologies. All of these harvest-aid activities require multiple passes through the field and swathing requires an additional piece of equipment. In order to more efficiently manage the winter canola harvest, we evaluated chemical harvest-aid treatments that would allow a producer to directly cut their canola while standing in the field. Currently diquat (Reglone) is the only harvest aid registered for use in winter canola.

Two studies were initiated in Roundup Ready® canola in Stillwater, Oklahoma, one at the Stillwater Agronomy Farm and one at the EFAW satellite of the Stillwater Agronomy Farm. Trials were set as randomized complete block designs with eight treatments and four replications. Treatments included: 280 g ai ha -1 diquat, 420 g ai ha -1 diquat, 50 g ai ha -1 saflufenacil, 1060 g ai ha -1 glyphosate + 50 g ai ha -1 saflufenacil, 71.5 g ai ha -1 flumioxazin, 594 g ai ha -1 glufosinate, swathing at appropriate time, and a direct cut nontreated check. Percent dessication was rated every day for seven days after treatment.  The study was harvested at 7 days after treatment and yield, % moisture, test weight and % oil content were recorded. Data were managed in ARM 9 and analyzed in SAS 9.2.  Means were separated with ANOVA using fishers protected LSD at α=0.05.

At both sites swathing at the appropriate time resulted in the greatest yield loss due to canola plants laying in a wind-row and shattering before being picked up for harvest. At the Stillwater site all treatments except flumioxazin yielded significantly greater than the crop swathed at the appropriate time. At the EFAW site, the low rate of diquat, saflufenacil alone, and flumioxazin yielded significantly more than swathed plots. No treatment impacted test weight or % oil content at either site. At Stillwater oil content ranged between 36.4 and 37.5%. At EFAW oil content was greater and ranged between 39.5 and 41.2%. These data suggest that a harvest aid followed by direct cutting of winter canola can improve yield compared to swathing the crop. The preserved yield through the use of these treatments is also cost effective compared to swathing the crop. 

 


IMPACT OF LATE GLYPHOSATE APPLICATION ON CANOLA FLOWERING AND YIELD. J. Bushong, A. R. Post*, J. Lofton; Oklahoma State University, Stillwater, OK (318)

ABSTRACT

Roundup is labeled for use in Roundup Ready winter canola up to 2 applications of  1060 g ae ha-1 per growing season. The application window for the most effective weed control is at the 4 to 6 leaf stage of growth.  This is very early in the fall and often growers do not get applications out in time due to the narrow planting window of canola, the planting of other crops, or the weather. Many winter canola producers also apply glyphosate for spring weed control even though this is outside of the labeled application window. While no visible crop injury results from these late season applications, glyphosate has been known to affect flowering and pod fill. In this experiment we investigated the effects of late season herbicide applications on flowering and canola yield. 

A trial was established at the Cimarron Valley Research station near Perkins Oklahoma in the 2014-15 field season. It was established as a 6 by 3 factorial with four replications and 19 treatments. There were six herbicide treatments each applied at 3 different application timings. Treatments included 770 g ae ha-1 glyphosate, 1060 g ae ha-1 glyphosate, 53.9 g ai ha-1 quizalofop, 92.5 g ai ha-1 quizalofop, 70 g ai ha-1 sethoxydim, and 105 g ai ha-1 sethoxydim, and a nontreated check. These are the most commonly postemergent herbicides in winter canola. Application timings were early bolt, 10% flowering and full bloom. Yield, % moisture, and % germination were measured. Data were managed in ARM 9 and analyzed in SAS 9.2.

The highest canola yield was the nontreated check at 2734.9 kg ha-1.No glyphosate treatment at any rate of application timing caused a significant decrease in canola seed yield.  However, 92.5 g ai ha-1  quizalofop applied at 10% flowering significantly reduced seed yield to 2196 kg ha-1. While no clear significant differences were noted, aside from the high rate of quizalofop, seed yields were numerically lower for all other herbicide treatments applied late. Decreases in seed yield averaged between 121.3 and 410.9 kg ha-1, or 4.4 and 15% of the nontreated yield. Producers should avoid making late applications unless weed competition will reduce yields more than the projected loss from a late herbicide application.

 


ALLELOPATHIC EFFECTS OF WINTER WHEAT RESIDUE ON WINTER CANOLA GERMINATION AND ESTABLISHMENT IN OKLAHOMA. A. R. Post*, P. Curl, J. Belvin; Oklahoma State University, Stillwater, OK (319)

ABSTRACT

Winter canola (Brassica napus L.) is growing in importance as a rotational crop for no-till winter wheat (Triticum aestivum L.) in Oklahoma. However, stand establishment has been a problem over the last 5 years for this system.  It is unclear whether residue depth, soil temperature or moisture status, or another phenomenon interferes with canola germination, growth and winter survival.Wheat and many relatives have allelopathic compounds which may interfere with germination of other species. We suspect that some wheat varieties inhibit winter canola germination and survival by exuding allelopathic compounds, particularly into no-till systems where crop residue is left in place.

Straw samples were collected from two wheat variety trials in Oklahoma at Chickasha, OK and Lahoma, OK. The experimental design was a complete 2 x 42 factorial, factor one being canola variety and factor two being wheat variety. Wheat straw samples were cut to 5 cm lengths to simulate a straw chopper on the back of a combine.  A water extraction was made from each wheat variety using a straw sample equivalent to the residue left after harvesting a 35 bushel wheat crop.  The volume simulated 2.5 cm of rainfall from harvest to canola planting and the extraction was left for 48 hours and then vacuum filtered. Three mLs of each extraction was used as the wheat variety factor and used to treat 10 canola seed. Subsequent to treatment canola seed were watered with distilled water until germination. Digital images were taken at 3, 5, and 7 days after treatment (DAT). Fresh and dry weights were taken at 7 DAT. Scan Pro 5 was used to evaluate images for pixel counts.  Data were subject to ANOVA and means separated by Fisher’s protected LSD (p=0.05).

About 30% of varieties tested significantly decreased winter canola biomass 7 DAT.  Wheat straw collected from Chickasha, OK had greater inhibitory effects than those sampled from Lahoma, OK.  Several wheat varieties decreased canola germination and biomass accumulation, regardless of location, by 50% or greater including: ‘Endurance’, ‘Pete’, ‘Armour’, ‘OK Rising’, ‘WB-Grainfield’, and ‘Doublestop CL+’.  It is not recommended that canola be seeded into wheat stubble of these varieties. 

Canola germination and biomass accumulation in the fall is vital to stand establishment and winter survival. We are currently investigating wheat stubble of these varieties in the field to determine if the same effects occur when trying to establish canola in native soils. These studies will allow producers to make more informed decisions when rotating between winter wheat and winter canola to minimize stand loss due to allelopathic effects from wheat stubble remaining in no-till systems.  

 


EVALUATION OF PRE- AND POST-EMERGENCE HERBICIDES FOR WEED CONTROL IN CASSAVA (MANIHOT ESCULENTA) IN AFRICA. F. Ekeleme*1, A. Dixon1, S. Hauser1, S. O. Lagoke2, H. Usman3, A. O. Olojede4, G. Atser1, S. Weller5; 1International Institute of Tropical Agriculture, Ibadan, Nigeria, 2Federal University of Agriculture, Abeokuta, Abeokuta, Nigeria, 3University of Agriculture, Makurdi, Makudi, Nigeria, 4National Root Crops Research Institute, Umudike, Umuahia, Nigeria, 5University of Purdue, Indiana, IN (320)

ABSTRACT

Cassava is an important crop in sub-Saharan Africa where it serves as a major staple food for more than 200 million people. It is the second most important staple food crop after maize, in term of calories consumed. Over the years, cassava has played important role in food economy of many African countries where it remains a strategic crop for both food security and poverty alleviation. It is fast becoming an important source of industrial raw material in Nigeria. Weed competition especially in the early growth stages of cassava constitutes a major production constraint. In West Africa, manual weeding is the major form of weed control in smallholder farms. Weeding takes 50 to 80% of the total labor budget of cassava growers and women contribute > 90% of the hand weeding labor. The use of PRE herbicide supplemented with hoe weeding or a POST herbicide in the later growth stages of cassava is also practiced by smallholder farmers. This later method of weed control is becoming popular in the region due to either labor shortages or high cost of labor. Field studies were conducted in the two cropping seasons of 2014 and 2015 in four contrasting agro-ecologies in Nigeria to evaluate selected PRE and POST herbicides for weed control cassava. In 2014, 43 herbicides consisting of 23 PRE and 20 POST herbicides were evaluated in an RCBD replicated three times. In 2015 the herbicides were thinned down to 12 PRE and 5 POST and evaluated in a split plot design with Sulfentrazone, Prometryn + S-metolachlor, Flumioxazin + pyroxasulfone , S-metolachlor + terbuthylazine, Oxyfluorfen 4F, Aclonifen + isoxaflutole, Indaziflam+ isoxaflutole, Diflufenican + flufenacet + flurtamone, S-metolachlor + atrazine, Indaziflam+ metribuzin, Clomazone + pendimethaline as PRE in the main plot and the following POST: Clethodim + Lactofen, Trifloysulfuron-Sodium, Foramsulfuron-sodium + iodosulfuron-methly-sodium + thiencarbazone-methly and Foramsulfuron + iodosulfuron-methly-sodium + isoxadifen-ethly in the subplot. A zero POST and hoe weeded treatments were included. Herbicides were evaluated in sole cassava and cassava intercropped with maize. Data on weed control efficacy, crop injury, height and yield were taken. PRE did not affect plant population. However, Indaziflam+ isoxaflutole and Indaziflam+ metribuzin delayed sprouting of cassava. Sulfentrazone caused leaf cupping but recovered 2 to 3 weeks after treatment (WAT). Indaziflam+ isoxaflutole, Indaziflam+ metribuzin and Flumioxazin + pyroxasulfone provided > 90 % control of broadleaf and grass weeds. Over 11.5 % to 21.4 % increase in cassava root yield was obtained from plots treated with Indaziflam+ isoxaflutole, Indaziflam+ metribuzin and Flumioxazin + pyroxasulfone compared to the hoe-weeded treatment. With the information gained in this study herbicides with potential for weed control in cassava may be identified.


WEED MANAGEMENT IN ENERGY BEET PRODUCTION IN THE SOUTHEASTERN U. S.: THE UNKNOWN OF CONTROLLING COOL-SEASON WEEDS. W. C. Johnson III*1, T. M. Webster1, T. L. Grey2; 1USDA-ARS, Tifton, GA, 2University of Georgia, Tifton, GA (322)

ABSTRACT

Sugar beet, grown for biofuel as energy beet, is being considered as an alternate cool-season crop in the southeastern U. S. coastal plain.  Typically, the crop would be seeded in the autumn and harvested early summer.  Common cool season weeds in the region are cutleaf eveningprimrose, wild radish, and swinecress.  Labels for herbicides registered for use on sugar beet grown as a warm-season crop in the traditional sugar beet production regions do not list cool-season weeds of the southeastern U. S.  In 2013, field trials were initiated in Tifton, GA to evaluate combinations of ethofumesate PRE, phenmedipham + desmedipham EPOST, clopyralid EPOST, and triflusulfuron EPOST for cool-season weed control in energy beet.  Rates chosen for each were on the lower-end of the established rate range due to the soil type; Tifton loamy sand with 88% sand, 6% silt, 6% clay with 1.0% organic matter.  Phenmedipham + desmedipham effectively controlled cutleaf eveningprimrose and swinecress when applied to seedling weeds.  Ethofumesate alone was not as effective in controlling cool-season weeds compared to phenmedipham + desmedipham and sequential applications did not improve control over phenmedipham + desmedipham alone.  Clopyralid and triflusulfuron did not control cutleaf eveningprimrose and swinecress.  Triflusulfuron alone effectively control wild radish.  None of the herbicides injured energy beet applied alone, in combination, or sequentially.  Energy beet yield reflected the degree of weed control.  Each of the herbicides evaluated in these trials are priced according to use on a high value specialty crop, sugar beet.  To make energy beet a profitable alternative crop in the southeastern U. S., weed control must be cost-effective.  Ongoing research is developing cost-effective weed management systems in energy beet based on reduced rates of phenmedipham + desmedipham and cultivation.


LUMAX EZ:  A NEW HERBICIDE FOR PREEMERGENCE AND POSTEMERGENCE WEED CONTROL IN SUGARCANE. E. K. Rawls*1, G. D. Vail2, M. Saini2, S. R. Moore3, E. Palmer2; 1Syngenta Crop Protection, Vero Beach, FL, 2Syngenta Crop Protection, Greensboro, NC, 3Syngenta Crop Protection, Monroe, LA (324)

ABSTRACT

Today there are limited herbicide options for weed control in US sugarcane production. Lumax® EZ was registered in 2012 for use in corn and registration in sugarcane is expected in 2017.  Lumax® EZ is a three way mixture of S-metolachlor, mesotrione, and atrazine and formulated as a  3.67 ZC.  It is systemic and has both pre-emergence and post-emergence weed control.  This product delivers three unique modes-of-action and controls a wide range of broadleaf and grass weeds.  The active ingredient mesotrione, an HPPD inhibitor, is an excellent choice for controlling weed biotypes resistant to ALS-inhibiting and triazine herbicides.  Other benefits of Lumax® EZ include:  flexible pre and post emergence application timing and excellent crop tolerance.  The use rates range from 2.7 to 3.25 qts / A applied preemergence or postemergence.  A maximum of two applications are allowed per year with a total season load up to 3.25 qts / A.  Lumax®  EZ is a premier herbicide with significant broadleaf and grass activity along with activity on several sedges.  Sugarcane field trials have been conducted in Florida, Louisiana, and Texas since 2010 and results indicate that Lumax®  EZ  effectively controls many broadleaf and grass weed species common to sugarcane production  like pigweeds (Amaranthus sp.), common lambsquarters (Chenopodium album), nightshade (Solanum sp.), ragweed (Ambrosia sp.), mornigglory (Ipomoea sp.), large crabgrass (Digitaria sanguinalis), broadleaf signalgrass (Brachiaria platyphylla), fall panicum (Panicum repens), and yellow nutsedge (Cyperus esculentas).  Lumax® EZ will provide US sugarcane growers an effective management tool for controlling some of their most problematic weeds.

 


DEVELOPING AN IMPROVED WEED CONTROL PROGRAM IN LIBERTY LINK SOYBEAN: IS THIS POSSIBLE? J. K. Norsworthy*1, A. Cotie2, C. Starkey3, J. Allen4, B. Philbrook4, K. Price4; 1University of Arkansas, Fayetteville, AR, 2Bayer CropScience, Research Triangle Park, NC, 3Bayer CropScience, DeWitt, AR, 4Bayer CropScience, Raleigh, NC (325)

ABSTRACT

With multiple-resistant Palmer amaranth (PPO, ALS, and EPSPS) now being documented in the Midsouth, even a greater number of growers are likely to migrate toward glufosinate-resistant (Liberty Link®) soybean because glufosinate is the only effective in-crop postemergence option for this weed.  There needs to be continued efforts to protect glufosinate against resistance because many of the stacked traits that may soon become available rely heavily on glufosinate for their long-term success.  Glufosinate is a unique mechanism of action that provides broad-spectrum weed control, but it does lack residual control, efficacy is dependent upon weed size and environmental conditions at application, and grass weeds can be challenging to completely control if applications are not timely.  Thiencarbazone-methyl (TCM), currently labeled as a premixture with several HPPD herbicides in corn, is known to lengthen and broaden the spectrum of weed control compared to HPPD herbicides alone.  TCM is currently not labeled for use in soybean, but in a trial conducted in 2015, soybean varieties with STS® or Bolt®-resistance traits were not injured by an over-the-top application of TCM, and the level of tolerance was as good as or better than that to other ALS-inhibiting herbicides evaluated in the same trial.  Conversely, TCM caused severe injury to non-STS soybean.  In other trials, TCM provided effective preemergence (PRE) and postemergence (POST) control of ALS-susceptible Palmer amaranth but was not effective against an ALS-resistant biotype.  In several trials, TCM applied PRE or POST was effective in controlling goosegrass, large crabgrass, broadleaf signalgrass, barnyardgrass, and johnsongrass, of which many of these weeds can be challenging to completely control with glufosinate alone.  The residual activity of TCM was as good as or better than most PRE or POST residual herbicides that are currently labeled for use in soybean.  POST weed control with TCM was superior to imazethapyr – once a standard in soybean production prior to Roundup Ready.  In bareground experiments, tank-mixing TCM with glufosinate appeared to broaden the spectrum of control and provide residual control in addition to serving as an additional mechanism of action for protection against weeds evolving resistance to glufosinate.  In the future, research efforts will aim at further understanding the value of TCM when used in soybean in combination with glufosinate as well as other potential herbicide combinations that could be used to preserve the utility of glufosinate.            

 


EFFECT OF HARVEST AID APPLICATION TIMING ON SOYBEAN (GLYCINE MAX) YIELD. S. G. Flint*1, J. Irby2, J. M. Orlowski3, A. B. Scholtes1, S. M. Carver1; 1Mississippi State University, Starkville, MS, 2Mississippi State University, Mississippi State, MS, 3Mississippi State University, Stoneville, MS (326)

ABSTRACT

With the increased plantings of indeterminate soybean varieties in the Mid-South, the use of harvest aids have become more important for timely crop removal.  Harvest aids are used to achieve senescence of green plant material in order to expedite a more timely harvest that may lead to premium commodity prices.  Delayed senescence may be a result of environmental conditions or certain agronomic practices that occurred during the growing season.  Products such as paraquat, saflufenacil, and sodium chlorate can be applied to desiccate plant material.  By label, harvest aid applications are to be made at 65% mature pods for paraquat and saflufenacil or 7-10 days before harvest for sodium chlorate.  Previous research has shown that applications made at moisture levels as high as 50% do not cause a yield reduction. 

Studies were conducted at the R. R. Foil Plant Science Research Center near Starkville, MS, during the 2014 and 2015 growing seasons to evaluate harvest aid efficacy and soybean yield following various application timings.  Applications of paraquat at 0.28 kilograms active ingredient per hectare (kg ai/ha), saflufenacil at 0.05 kg ai/ha, and sodium chlorate at 3.37 kg ai/ha were applied at three application timings. These timings were targeted for the R6 and R6.5 soybean growth stages and when the crop had reached 65% mature pods. An untreated check was included with each application timing for comparison purposes.  All treatments contained adjuvant systems as recommended by each product label. Visual ratings for green stems and green pods were recorded 7 and 15 days after treatment (DAT). Machine harvested yield was recorded from the two center rows of each four row plot.

With respect to soybean yield, no differences were observed between the various application timings. Within each application timing, no differences in yield were observed between any harvest aid treatment and the untreated control. When compared to the earliest application (R6), desiccation levels were greater for harvest aids applied at the R6.5 and 65% brown pod application timings with levels of 66, 98, and 93% observed 7 DAT, respectively. No differences in desiccation were observed between the different harvest aid products with all harvest aids resulting in greater desiccation compared to the untreated. Evaluations for green stems indicate that more green plant material remained following the earlier application timing (R6) with estimates of 71 and 7% remaining green stems when evaluated 7 and 15 DAT, respectively. Similar observations were noted for green pods with 69 and 5% remaining green pods when evaluated 7 and 15 DAT. These data indicate that harvest ready levels of desiccation are better achieved through application timings targeted at the R6.5 growth stage or later.


THE EFFECT OF HARVEST AIDS AND HARVEST DATES ON SEED SHATTERING AND YIELD OF SOYBEAN. J. M. Orlowski*1, T. Irby2, S. M. Carver2, A. B. Scholtes2, S. G. Flint2; 1Mississippi State University, Stoneville, MS, 2Mississippi State University, Starkville, MS (327)

ABSTRACT

The application of herbicides to desiccate and defoliate soybean [Glycine max (L.) Merr.] prior to harvest is a production practices that increasingly common in Mississippi and across much of the midsouthern United States.  The purpose of this study was to evaluate harvest losses associated with multiple herbicides used as harvest aids in Mississippi.  Paraquat, saflufenacil, and sodium chlorate were applied alone and in combination to soybean prior at the labeled application rate and timing prior to harvest.  Soybean were then harvested with a commercial combine at 7, 15, and 30 days after application.  Seed yield, seed moisture, seed mass, harvest seed loss, and germination were measured.  Harvest date affected seed moisture and seed yield, but harvest aid did not.  Harvest seed loss, seed mass, and germination were did not respond to either harvest timing or harvest date.  Regression analysis indicated that moisture decreased at a rate of 0.2% day-1 and yield decreased at a rate of 5 kg ha-1 day-1 between 7 and 30 days after application.  Harvest seed loss was similar across harvest aids and harvest dates indicating that seed yield decreases were likely the result of decreased seed moisture.  The study location received no precipitation in 2015 which is uncharacteristic of normal conditions in Mississippi.  This study will be repeated to assess harvest loss under more typical environmental conditions.


EFFECT OF ROW SPACING, SEEDING RATE, AND PLANT ARCHITECTURE ON WEED SUPPRESSION IN ARKANSAS SOYBEAN. W. J. Ross*1, R. C. Scott2, N. D. Pearrow3, C. D. Bokker4; 1University of Arkansas Division of Agriculture, Little Rock, AR, 2University of Arkansas, Fayetteville, AR, 3University of Arkansas, Newport, AR, 4University of Arkansas Division of Agriculture, Lonoke, AR (328)

ABSTRACT

Weed control is a concerning factor in soybean production [Glycine max (L.) Merr.] in Arkansas.  With the increasing number of herbicide resistant weeds, a review of agronomic best management practices to reduce weed competition is essential.  The objective of this study was to determine the interaction of weed pressure with a variety of agronomic practices including seeding rate, row spacing, and plant architecture. From 2013 to 2015, studies were located at the Newport Research Station in Newport, Arkansas.  Two studies evaluated the treatment combination on maturity group (MG) IV and V soybean varieties.  The studies were blocked according to row spacing and seeding rate and randomized for weed control and plant architecture. Treatment combination consisted of three seeding rates ranged from 110,000 to 190,000 seeds/ac, three row-spacings of 15 in, 30 in and 36 in, and a variety for each maturity group designated as either having an erect or bushy plant architecture.  For both the MG IV and V studies, the 15 in row-spacing statistically had higher grain yields than the wider spacings.  When the row-spacing by seeding rate interaction was evaluated, the 15 in row-spacing statistically had higher grain yields for all three seeding rates compared to the wider row-spacings.  All weed free treatments consistently had greater grain yields than the weedy treatments.  Because of the increase in herbicide-resistant weeds, more emphasis on agronomic practices to decrease weed competition will be required for soybean producers in Arkansas stay in business.


EFFICACY AND CROP (GLYCINE MAX) RESPONSE OF ENCAPSULATED ACETOCHLOR AND FOMESAFEN FORMULATED AS A PREMIX: WARRANT(R) ULTRA. R. F. Montgomery*1, A. Mills2, J. B. Willis3, R. C. Scott4, E. P. Prostko5, P. Baumann6, H. J. Beckie7, J. A. Bond8, B. Kirksey9, H. James10, T. Irby11, E. Wesley12, J. Martin13; 1Monsanto, Union City, TN, 2Monsanto, Collierville, TN, 3Monsanto, Saint Louis, MO, 4University of Arkansas, Fayetteville, AR, 5University of Georgia, Tifton, GA, 6Texas A&M AgriLife Extension, College Station, TX, 7Agriculture and Agri-Food Canada, Saskatoon, SK, 8Mississippi State University, Stoneville, MS, 9AgriCenter International, Memphis, TN, 10University of Missouri, Portageville, MO, 11Mississippi State University, Starkville, MS, 12North Carolina State University, Raleigh, NC, 13University of Kentucky, Lexington, KY (329)

ABSTRACT


EVALUATION OF A NEW ARYLEXTM ACTIVE HERBICIDE FOR BURNDOWN OF GLYPHOSATE-RESISTANT HORSEWEED IN NO-TILL SOYBEAN. L. Steckel*1, R. A. Haygood2, J. M. Ellis3, M. A. Peterson4, C. J. Voglewede4; 1University of Tennessee, Jackson, TN, 2Dow AgroSciences, Germantown, TN, 3Dow AgroSciences, Sterlington, LA, 4Dow AgroSciences, Indianapolis, IN (330)

ABSTRACT

Herbicides with new modes of action are needed to help manage glyphosate-resistant horseweed [Conyza canadensis (L.) Cronq] and other problematic broadleaf weeds.  Field research was conducted at 3 locations in west Tennessee in 2015 to evaluate Dow AgroSciences’  ArylexTM active (halauxifen-methyl), a novel synthetic auxin (WSSA group 4) herbicide from the new “arylpicolinate” chemical class.  Arylex efficacy was compared to competitive standards when applied with glyphosate or in tank mixes with glyphosate + 2,4-D LVE herbicides.  Arylex applied at 5.0 g ae/ha + glyphosate at 1120 g ae/ha demonstrated similar or better control of horseweed compared to Liberty (glufosinate) at 542 g ae/ha, 2,4-D LV at 560 g ae/ha + glyphosate at 1120 g ae/ha, Sharpen (saflufenacil) at 37.5 g ai/ha + glyphosate at 1120 g ae/ha, and Sharpen at 37.5 g ai/ha + 2,4-D LV at 560 g ae/ha + glyphosate at 1120 g ae/ha.

Soybean can be planted 14 days after application of Arylex without concerns of crop response.  Arylex will provide growers an alternative mode of action for horseweed and many other difficult to control pre-plant burndown broadleaf weeds like henbit (Lamium amplexicaule L).

®Trademark of The Dow Chemical Company ("DOW") or an affiliated company of Dow.

 


UTILITY OF ARYLEXTM ACTIVE HERBICIDE FOR PRE-PLANT BURNDOWN APPLICATIONS. J. M. Ellis*1, L. L. Granke2, L. A. Campbell3, D. M. Simpson4, R. A. Haygood5, M. A. Peterson4; 1Dow AgroSciences, Smithville, MO, 2Dow AgroSciences, Columbus, OH, 3Dow AgroSciences, Carbondale, IL, 4Dow AgroSciences, Indianapolis, IN, 5Dow AgroSciences, Germantown, TN (331)

ABSTRACT

Utility of ArylexTM Active Herbicide For Pre-plant Burndown Applications.  J. M. Ellis1, M. A. Peterson2, C. J. Voglewede3, D. H. Perry4, B. B. Haygood5, L. L. Walton6, J. Q. Armstrong7, Leah L. Granke8, L. A. Campbell9, K. K. Rosenbaum10 and D. M. Simpson11. 1Dow AgroSciences, Sterlington, LA, 2Dow AgroSciences, Indianapolis, IN, 3Dow AgroSciences, Indianapolis, IN, 4Dow AgroSciences, Greenville, MS, 5Dow AgroSciences, Collierville, TN, 6Dow AgroSciences, Tupelo, MS, 7Dow AgroSciences, Fresno, CA, 8Dow AgroSciences, Columbus, MS, 9Dow AgroSciences, Carbondale, IL, 10Dow AgroSciences, Crete, NE, 11Dow AgroSciences, Indianapolis, IN.

ArylexTM active (halauxifen-methyl), a new active ingredient from Dow AgroSciences, is a novel synthetic auxin (WSSA group 4) herbicide from the new “arylpicolinate” chemical class. It is being developed for the U.S. pre-plant burndown market segment for control of horsweed [Conyza canadensis(L.) Cronq] and other problematic broadleaf weeds.  The first U.S. burndown product will be an SC formulation, with a use rate of 1.0 fl oz product/acre [Arylex (halauxifen-methyl 5.0 g ae/ha)] and will be labeled for use prior to soybean and corn planting.  Initial labeling will allow application up to 14 days prior to planting of soybean and corn.  Field research was conducted from 2013 to 2015 at 15 locations across the U.S. to determine the efficacy of Arylex applied in the spring to horseweed, including glyphosate resistant biotypes, and other common weeds prior to planting soybean and corn.  Arylex was compared to competitive standards when applied with glyphosaste and in tank mixes with glyphosate + 2,4-D LVE herbicide.  Arylex applied at 5.0 g ae/ha + glyphosate at 1120 g ae/ha demonstrated similar to or better control of marestail when compared to Liberty (glufosinate) at 542 g ae/ha, Clarity (dicamba) at 280 g ae/ha + glyphosate 1120 g ae/ha, and Sharpen (saflufenacil) at 37.5 g ai/ha + glyphosate at 1120 g ae/ha.

Crop injury was evaluated in efficacy trials as well as dedicated weed-free crop tolerance trials. Results indicated that soybean and corn can be planted 14 days after application of Arylex without significant injury.  Arylex will provide growers with an alternative mode of action for many difficult to control pre-plant burndown broadleaf weeds such as horseweed and henbit (Lamium amplexicaule L)

 

 

®Trademark of The Dow Chemical Company ("DOW") or an affiliated company of Dow.

 


EVALUATION OF METRIBUZIN COMBINATIONS IN SOYBEAN WEED CONTROL SYSTEMS. D. L. Teeter*1, T. A. Baughman1, T. L. Grey2, R. W. Peterson1; 1Oklahoma State University, Ardmore, OK, 2University of Georgia, Tifton, GA (332)

ABSTRACT

Evaluation of Metribuzin Combinations for Soybean Weed Control Systems. D. L. Teeter*1, T. A. Baughman1, T. L. Grey2, and R.W. Peterson1; 1Oklahoma State University, Ardmore, OK, 2University of Georgia, Tifton, GA

ABSTRACT

The continued rise of weed resistance has made controlling weeds in all commodities more difficult. Soybean studies were established to evaluate the use of metribuzin in combination with other preemergence herbicide in Liberty-Link soybean during the 2015 growing season.  Other PRE herbicides applied alone or in various combinations included acetochlor, chlorimuron, dimethenamid, flumioxazin, fomesafen, imazethapyr, metolachlor, pendimethalin, saflufenacil, sulfentrazone, and thifensulfuron.  These studies were conducted at the Wes Watkins Agricultural Research and Extension Center near Lane, OK; the Vegetable Research Station, near Bixby, OK; and the Southwest Georgia Research and Education Center near Plains, GA.  Heavy rainfall prior and after planting effected soybean stand establishment and weed control at both locations in Oklahoma.  Trials at Bixby had to be replanted due to this excessive rainfall and stands were still not adequate to harvest.  Soybean injury in the first study at Bixby 2 WAP (second planting) was at least 10% with flumioxazin + pyroxasulfone with and without chlorimuron applied alone PRE or with metribuzin.  All subsequent soybean injury was less than 5% except flumioxazin + pyroxasulfone + chlorimuron with metribuzin 4 WAP.  Amaranthus palmeri (AMAPA) control was at least 99% with all treatments except metribuzin alone, and pyroxasulfone + saflufenacil with and without dimethenamid.  Metribuzin + fomesafen PRE was the only treatment in the second study at Bixby that injured soybean 10% 2 WAP.    Injury was less than 5% with all treatments for the remainder of the season.   All treatments controlled AMAPA 100% 2 WAP except pendimethalin applied alone.  All metribuzin combinations followed by 2 POST applications of glufosinate controlled AMAPA 100% late season except metribuzin alone or in combination with pendimethalin.  Soybean injury was less than 10% 2 and 4 WAP at Lane except with flumioxazin + pyroxasulfone + chlorimuron and sulfentrazon + chlorimuron both applied with metribuzin.   Amaranthus tuberculatus (AMATU) and Mollugo verticillata (MOLVE) control was 100% season long with all treatments applied.  Soybean yield was increased over the untreated control with all treatments except sulfentrazon + chlorimuron + metribuzin PRE.   Soybean injury 2 WAP was less than 10% in the second study at Lane except with metribuzin applied in combination with flumioxazin or pyroxasulfone.  Soybean injury was less than 10% with all treatments for the remainder of the season.  AMATU and MOLVE control was greater than 95% season long with all treatments applied.  Soybean yields were increased with all treatments applied.  No soybean injury was observed with any treatment at Plains.  AMAPA control was 99% season long regardless of PRE herbicide applied. Senna obtusifolia (CASOB) and Ipomoea hederacea (IPOHE) control was at least 97% season long except with fomesafen alone and pendimethalin + metribuzin PRE early season.  When these treatments were followed by a POST application of glufosinate control was 99%.  All treatments increased yields with both Liberty-Link cultivars (5947LL and 7007LL).  No yield differences were observed between herbicide treatments applied.  

 


METRIBUZIN PROVIDES COST-EFFECTIVE RESIDUAL CONTROL OF RESISTANT AMARANTHUS AND OTHER PROBLEM WEEDS IN SOYBEANS. N. Rana*1, K. Kretzmer1, J. Gilsinger2, A. Perez-Jones1, P. Feng1, J. Travers1; 1Monsanto Company, Chesterfield, MO, 2Monsanto Company, Mt. Olive, NC (333)

ABSTRACT

Glyphosate resistant Palmer amaranth was detected in the mid 2000’s and since then growers have relied upon PPO herbicides for weed control in soybean and cotton. Unfortunately, but not surprisingly, PPO-resistance in Palmer amaranth to POST applications was recently detected. Metribuzin is a low-cost herbicide that provides an additional mechanism of action that will be a useful tool to control herbicide resistant weeds. With the heavy reliance upon PPO chemistry and glufosinate in soybean weed control systems, weed scientists are advocating the addition of metribuzin (162 to 280 g ai/ha) to boost the level of control of glyphosate resistant Amaranthus species. Soybeans exhibit varietal sensitivity to metribuzin and our research in molecular breeding led to the identification of a marker for metribuzin sensitivity. These studies show that the combination of the marker screen with a high throughput lab screen could potentially replace the greenhouse and field screens which produce inconsistent data from variations in soil, water, and environmental conditions. Field experiments were conducted in 2014 to validate the marker and lab high throughput assays. There were two objectives - to evaluate crop safety of selected soybean genotypes to field use rates of metribuzin and examine weed efficacy of metribuzin with tank mix combinations of dicamba, acetochlor, and/or fomesafen herbicides. Results indicated that under normal field conditions genotypes selected by marker and lab screens showed little to no injury at 280 g ai/ha rate of metribuzin and furthermore, addition of metribuzin provided a significant increase in the level of weed control of glyphosate resistant palmer amaranth and common waterhemp, as well as other broadleaf and narrowleaf weed species. 


EVALUATION OF SONIC AND SURVEIL FOR PALMER AMARANTH (AMARANTHUS PALMERI) MANAGEMENT IN MISSISSIPPI SOYBEAN. S. M. Carver*1, J. Irby2, L. C. Walton3, A. B. Scholtes1, S. G. Flint1; 1Mississippi State University, Starkville, MS, 2Mississippi State University, Mississippi State, MS, 3Dow AgroSciences, Tupelo, MS (334)

ABSTRACT

With herbicide resistant Palmer amaranth continuing to be problematic in current Mid-South cropping systems, it is vital to achieve early control of this weed to avoid detrimental yield losses.  One component of a complete herbicide resistant Palmer amaranth management program contains early pre-plant (EPP) or pre-emergence (PRE) herbicide applications consisting of long lasting residual products. Sonic® and Surveil® are available for use EPP or PRE in soybean and can be used in combination with burndown herbicides such as paraquat or glyphosate for control of emerged weeds at the time of application.

The objective of this research was to evaluate the effectiveness of Sonic and Surveil for management of Palmer Amaranth.  Applications were made at 14 and 7 days EPP as well as PRE at planting.  Treatments applied 14 or 7 days EPP or PRE consisted of Sonic at a rate of 3 ounces per acre (oz/A), Sonic at 4.5 oz/A, Surveil at 2.8 oz/A, and Valor® SX at 1.8 oz/A plus Classic® at 1.2 oz/A. Additional treatments included Gramoxone® SL applied at 32 fluid ounces per acre (fl oz/A) 14 and 7 days EPP and PRE as well as a split application of Surveil at 1.4 oz/A 14 days EPP and PRE. An untreated check was included for comparison purposes.  The experimental design was a randomized complete block with each treatment being replicated 4 times.  Experimental units were 30 feet in length by 6.3 feet in width. The plots were crop destruct before podset resulting in no data collected for yield.  

Visual evaluations for crop injury and Palmer amaranth control were collected at 7, 14, 28, and 42 days after planting (DAP).  There was no crop injury from the herbicide applications observed 7, 28 and 42 DAP. However, evaluations 14 DAP indicated minimal, but significant, injury from applications of Sonic at 4.5 oz/A and the tankmix of Valor SX plus Classic when applied 14 days EPP, Surveil when applied 7 days EPP, and the split application of Surveil applied 14 days EPP and PRE with injury levels of 5, 8, 5, and 8%, respectively.  Visual evaluations for control of Palmer amaranth were also collected at 7, 14, 28, and 42 DAP. At all evaluation timings, Palmer amaranth control was found to be greater for all herbicide treatments when compared to the untreated.  At 14 and 28 DAP, treatments of Surveil and the tankmix of Valor SX plus Classic applied both 14 and 7 days EPP, Sonic at 4.5 oz/A applied 7 days EPP and PRE, along with the split application of Surveil at 14 days EPP and PRE resulted in greater Palmer amaranth control when compared to the stand alone Gramoxone SL treatment. However, by 28 DAP, control levels decrease numerically between 3 and 20% for these same treatments. These data indicate that in order to maintain adequate control of this weed species, a post-emergence herbicide application may be required between 14 and 28 DAP. These data also demonstrate the value of adding a residual herbicide component, such as Sonic, Surveil, or Valor SX plus Classic, to a Palmer amaranth management program in order to prolong control of this problematic weed species.


INTRODUCTION OF SURVEIL™ HERBICIDE FROM DOW AGROSCIENCES FOR PREPLANT AND PREEMERGENCE WEED CONTROL IN SOYBEANS. L. C. Walton*1, J. A. Armstrong2, L. B. Braxton3, J. M. Ellis4, R. A. Haygood5, R. M. Huckaba6, M. A. Peterson7, J. S. Richburg8, C. J. Voglewede7; 1Dow AgroSciences, Tupelo, MS, 2Dow AgroSciences, Fresno, CA, 3Dow AgroSciences, Travelers Rest, SC, 4Dow AgroSciences, Sterlington, LA, 5Dow AgroSciences, Germantown, TN, 6Dow AgroSciences, Wake Forrest, NC, 7Dow AgroSciences, Indianapolis, IN, 8Dow AgroSciences, Dothan, AL (335)

ABSTRACT

Introduction of Surveil®  Herbicide for Preplant and Preemergence Weed Control in Soybeans - L.C. Walton, J.Q. Armstrong, L.B. Braxton, J.M. Ellis, R.A. Haygood, R.M. Huckaba, M.A. Peterson, J.S. Richburg, C.J. Voglewede; Dow AgroSciences, Indianapolis, IN.

ABSTRACT

Surveil® herbicide is a new premix of cloransulam-methyl and flumioxazin (48% water dispersible granule formulation; 1:3 ratio) for weed control in soybean from Dow AgroSciences. Comprised of active ingredients from two different modes of action (WSSA Group 2 and Group 14), Surveil provides long lasting, broad-spectrum residual control of many herbicide-resistant and hard-to-control weeds. This new formulation also has excellent handling and mixing properties, such as rapid dispersion and mixing when added to water. Surveil offers flexible application timings for  preplant burndown and premergence weed control, as well as allowing favorable rotation intervals to many crops with no soil pH restrictions. 

From 2013 through 2015 Dow AgroSciences conducted 42 field research trials with key cooperators in the Southern and MidWestern U.S. In these trials, Surveil was applied preplant or pre-emergence timing at use rates ranging from  71 to 142 g ai/ha.  

Data from these trials demonstrated >90% control of several key weeds at 4 weeks after application including tall waterhemp (Amaranthus tuberculatus), palmer pigweed (Amaranthus palmeri), velvetleaf (Abutilon theophrasti), and morningglory species (Ipomoea spp.) with a minimum use rate of 71 g ai/ha.

Surveil herbicide provides excellent residual control of many herbicide-resistant and hard-to-control weeds in herbicide-tolerant and conventional soybean, crop tolerance similar to other industry herbicide standards, and has excellent handling and mixing properties. Surveil received federal registration in May 2015 and will be available for use for the 2016 growing season.

 ® Surveil is a trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dow. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions


INTRODUCING BOLT™ TECHNOLOGY: A NEW HERBICIDE SYSTEM FOR CLEANER FIELDS AND GREATER MANAGEMENT FLEXIBILITY IN SOYBEANS. D. Johnson*1, H. Flanigan2, J. Carpenter3, S. Strachan3, S. Mitchell4, A. Trepanier4, M. Vogt4, S. Sebastian4; 1DuPont Crop Protection, Des Moines, IA, 2DuPont Crop Protection, Greenwood, IN, 3DuPont Crop Protection, Johnston, IA, 4DuPont Pioneer, Johnston, IA (336)

ABSTRACT


NEW ZERO-DAY PLANT-BACK OPTIONS FOR DUPONT™ LEADOFF® AND BASIS® BLEND HERBICIDES IN BOLT™ TECHNOLOGY SOYBEANS. K. A. Backscheider*1, P. T. Marquardt2, K. L. Hahn3, M. D. Meyer4, L. H. Hageman5, K. A. Diedrick6, K. D. Johnson7, S. E. Swanson5, J. T. Krumm8, D. Edmund9, D. H. Johnson2; 1DuPont Crop Protection, Shelbyville, IN, 2DuPont Crop Protection, Johnston, IA, 3DuPont Crop Protection, Bloomington, IL, 4DuPont Crop Protection, Norwalk, IA, 5DuPont Crop Protection, Rochelle, IL, 6DuPont Crop Protection, Rio, WI, 7DuPont Crop Protection, Grand Forks, ND, 8DuPont Crop Protection, Hastings, NE, 9DuPont Crop Protection, Little Rock, AR (337)

ABSTRACT


PALMER AMARANTH CONTROL AND SOYBEAN TOLERANCE TO BALANCE BEAN HERBICIDE. B. W. Schrage*, W. J. Everman; North Carolina State University, Raleigh, NC (338)

ABSTRACT

Palmer amaranth Control and Soybean Tolerance to Balance® Bean Herbicide.  B.W. Schrage*, W.J. Everman; North Carolina State University, Raleigh, NC; J. Allen and M. Rosemond; Bayer CropScience, RTP, NC

ABSTRACT

The integration of new technologies and management strategies is becoming increasingly necessary to control Palmer amaranth in Southeastern soybean production.  The anticipated release of the isoxaflutole-based product Balance Bean by Bayer CropScience and the anticipated deregulation of HPPD-tolerant soybean varieties, pending regulatory approvals, could serve as a new-era rotational tool enabling applications of isoxaflutole, glufosinate, and glyphosate.  Best management practices dictate that rotating herbicide mechanisms of action can reduce weed seed bank densities—prompting further investigation of stacked traits.

 In 2015, experiments were conducted in Clayton, South Mills and Sunbury, North Carolina to evaluate the impact of various herbicide programs including Balance Bean on Palmer amaranth and HPPD-tolerant soybeans. In Clayton, all herbicide treatments exceeded 90% control of Palmer amaranth for the entire growing season.  In Sunbury and South Mills, eight application rates, ranging from 20 to 160 g ai ha-1 were applied to non-crop plots.  Control of Palmer amaranth exceeded 90% in both locations at higher rates.  Results suggest that pending the introduction of HPPD-tolerant soybean varieties bred for Southeastern soybean producers, Balance® Bean could become an influential aspect of herbicide programs that embrace rotational technology.

 


PREEMERGENCE WEED CONTROL IN SOYBEAN USING FLUMIOXAZIN, METRIBUZIN, AND PYROXASULFONE. K. M. Vollmer*1, M. VanGessel1, C. W. Cahoon2, T. Hines2, Q. Johnson1, B. Scott1; 1University of Delaware, Georgetown, DE, 2Virginia Tech, Painter, VA (339)

ABSTRACT

The use of herbicides applied preemergence are an integral part of most herbicide programs.  Preemergence herbicides can play an important role in resistance management by incorporating multiple herbicide mechanisms-of-action.  Flumioxazin, metribuzin, and pyroxasulfone are herbicides that are registered for preemergence weed control in soybean, each with a different mechanism-of-action.  The objective of this experiment was to determine the effectiveness of each of these herbicides individually or in combination.  In 2015, the study was performed at Kiptopeake, VA and Georgetown, DE.  The study was of factorial arrangement of flumioxazin, metribuzin, and pyroxasulfone applied at 0.071, 0.21, and 0.125 kg ai ha-1 arranged in a randomized complete block design.  The entire site was sprayed with a POST treatment of fomesafen + glyphosate at 0.416 kg ai ha-1 and 1.66 kg ae ha-1 14 days after treatment (DAT) at the VA site and 32 DAT at the Delaware site.  At the VA site, all treatments controlled Palmer amaranth 90% or greater 14 DAT.  At the DE site at 32 DAT, all tank-mix treatments controlled Palmer amaranth 98% or greater, while individual herbicides controlled Palmer amaranth 67 to 80%. All treatments at the DE site provided less than 70% morningglory control when evaluated 32 DAT.  The broadcast treatment of fomesafen + glyphosate in VA provided >95% control, since weeds were small and susceptible at time of application.  At DE, the POST application improved Palmer amaranth control, however, treatments with PRE combinations were significantly better than single active ingredients.  These results show that flumioxazin, metribuzin, and pyroxasulfone combinations can provide excellent preemergence control of certain weeds; however, a timely postemergence control option is still needed for season-long control.  Furthermore, incorporating effective PRE herbicides with alternative mechanism of action, can help in alleviating further development of herbicide resistance.    

 


POST EMERGENT GOOSEGRASS CONTROL IN BENTGRASS GREENS. P. J. Brown*, P. O. Signoretti, B. McCarty; Clemson University, Clemson, SC (340)

ABSTRACT

Postemergent goosegrass control in bentgrass greens. P.J. Brown*, P. Signoretti, and L.B. McCarty.  Clemson University, Clemson, SC 29634-0310.

 

ABSTRACT

 

Bentgrass (Agrostis spp.) is a common cool-season grass species used on golf course putting greens, unfortunately environmental and cultural stresses placed on the grass maintained in the Southern USA can lead to infestations by weeds such as goosegrass (Eleusine indica).  Currently no herbicides are labeled for postemergence control of goosegrass in bentgrass, therefore, a study was conducted in the upstate of South Carolina to investigate the control of goosegrass (Eleusine indica) in a bentgrass research green.  Treatments were applied with a CO2 backpack sprayer calibrated at 40 GPA, using 8004 flat fan spray nozzles. Treatments were replicated four times. Data was analyzed using ANOVA with means separated by LSD (α=0.05).

 

Treatments included: Acclaim Extra at 4 oz/A; Pylex at 0.25 oz/A; Speedzone at 64 oz/A; Dismiss at 6 oz/A; Dismiss at 4 oz/A; Speedzone at 64 oz/A + Pylex at 0.25 oz/A; Pylex at 0.25 oz/A + Acclaim at 2 oz/A; Pylex at 0.25 oz/A + Velocity at 2 oz/A applied August 14, 2015 followed by August 29, 2015.  A single Pylex treatment at 0.5 oz/A was applied August 14, 2015.  All treatments included a non-ionic surfactant at 5% V/V.

 

Visual ratings were taken throughout the study. Percent goosegrass control was rated on a 0 to 100% scale with 100% representing complete control.  In addition, percent bentgrass phytotoxicity was measured on a 0 to 100% scale, with 0% representing no bentgrass phytotoxicity and 100% representing complete bentgrass death.

 

Acclaim Extra at 4 oz/A (61% control, 31.5% phytotoxicity);

Pylex at 0.25 oz/A (79.3% control, 40.0% phytotoxicity);

Speedzone at 64 oz/A (60.3% control, 31.5% phytotoxicity);

Dismiss at 6 oz/A (54.5% control, 68.3% phytotoxicity);

Dismiss at 4 oz/A (49% control, 55.5% phytotoxicity);

Speedzone at 64 oz/A + Pylex at 0.25 oz/A (60.8% control, 22.5% phytotoxicity);

Pylex at 0.25 oz/A + Acclaim at 2 oz/A (78.3% control, 62.0% phytotoxicity);

Pylex at 0.25 oz/A + Velocity at 2 oz/A (65.3% control, 31.5% phytotoxicity);

Single Pylex treatment at 0.5 oz/A (85.5% control,7.3% phytotoxicity). 

 

In conclusion, all treatments including Pylex provided >60% control of goosegrass by study’s end. A single application of Pylex provided the greatest control of goosegrass at 85.5% control, with the split applications of Pylex providing second greatest control at 79.3%.  In addition, the single application of Pylex had the lowest phytotoxicity in the bentgrass at 7.3%. 

 

Future research will continue with herbicides used in this study, evaluating different combinations and timings.

 


MSMA ENVIRONMENTAL FATE: WHAT WE KNOW AND EXISTING KNOWLEDGE GAPS. T. Gannon*, M. Polizzotto; North Carolina State University, Raleigh, NC (341)

ABSTRACT

Monosodium methylarsenate (MSMA) is an organic arsenical postemergence herbicide currently registered for use with imposed restrictions in the United States for sites including golf courses, sod farms, highway rights of way and cotton.  Monosodium methylarsenate is valuable from an agronomic perspective because it controls many common and troublesome weed species, is economical and offers an alternative mode of action that aid producers and land managers with herbicide resistance management.  In 2006, the United States Environmental Protection Agency enacted a phaseout of all organic arsenical pesticides including MSMA.  The concern and resulting phaseout was based on the premise that organic arsenical pesticides convert to more toxic inorganic arsenic (As) species and may contaminate drinking water. Currently, a registration review which includes a scientific peer review of the carcinogenic mode of action of inorganic As is underway and is scheduled to be completed in 2019.  While much research has been completed assessing the environmental fate and behavior of As from MSMA in various agronomic systems, many questions pertaining to the environmental fate and behavior remain unanswered. Much of our prior knowledge about the fate of As in the environment following MSMA applications has largely been gleaned from controlled laboratory systems, which have used excessive MSMA loading rates and low soil-solution ratios, or field experiments, where environmental factors limited the ability to quantify As mass balance and speciation across the plant-soil-water system.  However, controlled research in established turfgrass systems indicates 1%, 29%, 64% and 13% of As from MSMA applications is sequestered in clippings, remaining aboveground vegetation, soil and roots, respectively, at 2 weeks after treatment, with > 90% of the As sequestered in soil by 8 weeks after treatment.  Whereas previous research has also concluded organic As species may convert to more toxic inorganic species, the extent of this conversion has ranged widely.  Further, factors that may influence the extent and rate of the conversion remain largely unanswered.

 


POSTEMERGE GOOSEGRASS CONTROL IN BERMUDAGRASS TURF. N. J. Gambrell*, R. B. Cross, B. McCarty; Clemson University, Clemson, SC (342)

ABSTRACT

POSTEMERGE GOOSEGRASS [ELEUSINE INDICA (L.) GAERTN.] CONTROL IN BERMUDAGRASS TURF.  N.J. Gambrell, R.B. Cross, and L.B. McCarty. Clemson University, Clemson, SC 29634.

ABSTRACT

The purpose of this study was to determine the efficacy of various herbicides and combinations for postemergence control of goosegrass in bermudagrass turf.  Goosegrass is a clumped summer annual, easily characterized with a white or silverish coloration in the plant’s crown.  Goosegrass reproduces by seed and possesses a short-toothed, membranous ligule at base of leaf blade.  Due to its ability to withstand various mowing heights, competitive growth in compacted, wet, or dry soils, goosegrass disrupts the appearance and uniformity of a turf stand.  Lack of persistent aerification, and chemical control options, goosegrass is a very troublesome grassy weed, in most turf situations.      

A study with ten treatments was initiated in Pickens, South Carolina on August 11, 2015, with rating dates on August 19, August 26, September 4, and September 29 which corresponded to 8, 15, 24, and 49 days after initial treatment (DAIT), respectively.  Treatments included: Tenacity 4 L @ 0.25 lb ai/a + Princep 4 L @ 0.78 lb ai/a fb Tenacity 4 L @ 0.25 lb ai/a + Princep 4 L @ 0.78 lb ai/a; Pylex 2.8 SC @ 0.22 lb ai/a + Princep 4 L @ 0.78 lb ai/a fb Pylex 2.8 SC @ 0.22 lb ai/a + Princep 4 L @ 0.78 lb ai/a; Dismiss 4 L @ 0.1875 la ai/a + Tenacity 4 L @ 0.25 lb ai/a fb Dismiss 4 L @ 0.1875 la ai/a + Tenacity 4 L @ 0.25 lb ai/a; Dismiss 4 L @ 0.1875 lb ai/a + Pylex 2.8 SC @ 0.22 lb ai/a fb Dismiss 4 L @ 0.1875 lb ai/a + Pylex 2.8 SC @ 0.22 lb ai/a; Revolver 0.19 L @ 0.038 lb ai/a fb Revolver 0.19 L @ 0.038 lb ai/a; Revolver 0.19 L @ 0.025 lb ai/a + Dismiss 4 L @ 0.1875 lb ai/a fb Revolver 0.19 L @ 0.025 lb ai/a + Dismiss 4 L @ 0.1875 lb ai/a; MSMA 6 L @ 1.5 lb ai/a + Sencor 75 DF @ 0.33 lb ai/a; Dismiss 4 L @ 0.1875 lb ai/a + Sencor 75 DF @ 0.33 lb ai/a fb Dismiss 4 L @ 0.1875 lb ai/a + Sencor 75 DF @ 0.33 lb ai/a; Pylex 2.8 SC @ 0.22 lb ai/a + Xonerate 70 WDG; and Speedzone @ 4 pt/a+ Sencor 75 DF @ 0.33 lb ai/a fb Speedzone @ 4pt/a+ Sencor 75 DF @ 0.33 lb ai/a.  A sequential application was made on September 4, 2015, 3 weeks after initial treatment (3 WAIT), for all treatments, expect MSMA 6 L @ 1.5 lb ai/a + Sencor 75 DF @ 0.33 lb ai/a, and Pylex 2.8 SC @ 0.22 lb ai/a + Xonerate 70 WDG.  A second study with twelve treatments was initiated in Orlando, Florida on August 18, 2015, with rating dates on September 2, September 16, and October 5 which corresponded to 15, 29, and 48 days after treatment (DAT), respectively.  Treatments included: Roundup 4 L @ 0.156 lb ai/a fb Roundup 4 L @ 0.156 lb ai/a; Tenacity 4 L @ 0.156 lb ai/a + Princep 4 L @ 0.469 lb ai/a fb Tenacity 4 L @ 0.156 lb ai/a + Princep 4 L @ 0.469 lb ai/a; and previously mentioned ten treatments from initial trial in Pickens, South Carolina.  A sequential application was made on September 2, 2015, 2 weeks after initial treatment (2 WAIT), for all treatments.  Both studies were conducted in common bermudagrass maintained as golf course rough, with no irrigation, and heavily infested with goosegrass.  Applications were made using a CO₂ powered sprayer calibrated at 20 GPA.  Three treatment replications were applied on 1x1.5 meter plots, using a randomized complete block design.  Visual ratings evaluated percentage control of goosegrass and turf injury.  Ratings were based on a 0-100% scale.  0% indicating no control and 100% indicating complete control.  ANOVA was evaluated with alpha at 0.05.

On the September 29, 2015 rating date, in Pickens, South Carolina, five treatments provided excellent control (≥ 90%): Pylex 2.8 SC @ 0.22 lb ai/a + Princep 4 L @ 0.78 lb ai/a fb Pylex 2.8 SC @ 0.22 lb ai/a + Princep 4 L @ 0.78 lb ai/a; Dismiss 4 L @ 0.1875 lb ai/a + Pylex 2.8 SC @ 0.22 lb ai/a fb Dismiss 4 L @ 0.1875 lb ai/a + Pylex 2.8 SC @ 0.22 lb ai/a; MSMA 6 L @ 1.5 lb ai/a + Sencor 75 DF @ 0.33 lb ai/a; Pylex 2.8 SC @ 0.22 lb ai/a + Xonerate 70 WDG; and Speedzone @ 4 pt/a+ Sencor 75 DF @ 0.33 lb ai/a fb Speedzone @ 4pt/a+ Sencor 75 DF @ 0.33 lb ai/a, at 49 DAT.  On the October 5, 2015 rating date, in Orlando, Florida, six treatments provided excellent control (≥ 90%): Tenacity 4 L @ 0.25 lb ai/a + Princep 4 L @ 0.78 lb ai/a fb Tenacity 4 L @ 0.25 lb ai/a + Princep 4 L @ 0.78 lb ai/a; Pylex 2.8 SC @ 0.22 lb ai/a + Princep 4 L @ 0.78 lb ai/a fb Pylex 2.8 SC @ 0.22 lb ai/a + Princep 4 L @ 0.78 lb ai/a; Dismiss 4 L @ 0.1875 lb ai/a + Pylex 2.8 SC @ 0.22 lb ai/a fb Dismiss 4 L @ 0.1875 lb ai/a + Pylex 2.8 SC @ 0.22 lb ai/a; Pylex 2.8 SC @ 0.22 lb ai/a + Xonerate 70 WDG; Speedzone @ 4 pt/a+ Sencor 75 DF @ 0.33 lb ai/a fb Speedzone @ 4pt/a+ Sencor 75 DF @ 0.33 lb ai/a; and Tenacity 4 L @ 0.156 lb ai/a + Princep 4 L @ 0.469 lb ai/a fb Tenacity 4 L @ 0.156 lb ai/a + Princep 4 L @ 0.469 lb ai/a, at 48 DAT.

Repeat applications and screening of products will be continued in the future for timing, turf safety, and control of goosegrass in burmudagrass turf.  

 


INTEGRATING TRICLOPYR AND QUINCLORAC IN TOPRAMEZONE PROGRAMS FOR CRABGRASS AND GOOSEGRASS CONTROL IN BERMUDAGRASS TURF. J. R. Brewer*1, J. McCurdy2, M. Elmore3, S. Askew1, M. P. Richard2; 1Virginia Tech, Blacksburg, VA, 2Mississippi State University, Starkville, MS, 3Texas A & M University, Dallas, TX (343)

ABSTRACT

Integrating Triclopyr and Quinclorac in Topramezone Programs for Crabgrass and Goosegrass Control in Bermudagrass Turf

J.R. Brewer, J. McCurdy, M. Elmore, S.D. Askew, and M. P. Richard

Goosegrass (Eleusine indica) and smooth crabgrass (Digitaria sanguinalis) are troublesome weeds of bermudagrass (Cynodon dactylon) turf throughout the Southeastern U.S.  Topramezone is an HPPD-inhibiting herbicide that controls crabgrass and goosegrass but severely injures bermudagrass.  When combined with other herbicides and used at appropriate rates, topramezone could help control goosegrass and crabgrass while ensuring minimal bermudagrass injury.  In the summer of 2015, studies at Virginia Tech (VT) and Mississippi State University (MSU) were conducted to evaluate multiple topramezone programs for effective annual grass control and to reduce bermudagrass injury. All studies used the same treatment protocol which included: a non-treated check, topramezone at 6.14 g ha-1 (LR-low rate), topramezone at 12.3 g ha-1 (HR-high rate), quinclorac at 420.7 g ha-1 (LR), quinclorac at 841.4 g ha-1 (HR), topramezone LR + quinclorac LR, topramezone HR + quinclorac at LR, topramezone at LR + quinclorac at HR, topramezone at HR + quinclorac at HR, topramezone LR + triclopyr at 17. 5 g ha-1, topramezone HR + triclopyr, topramezone LR + quinclorac HR + triclopyr, topramezone HR + quinclorac HR + triclopyr, MSMA at 2271.7 g ha-1 (all treatments applied with 0.5% V/V methylated seed oil except MSMA).  At the VT Turfgrass Research Center in Blacksburg, VA, two studies were initiated on July 29, 2015 which included one area of 'Tifway 419' bermudagrass to evaluate turf tolerance and an adjacent fallow area that was heavily infested with crabgrass and goosegrass to evaluate weed control.  All treatments were applied a second time 4 weeks later on August 13, 2015. These treatments were applied with a hooded sprayer at 280 L ha-1 and 4.8 km h-1, and the sprayer had a 71-cm spray width provided by two TeeJet 11002XR flat fan nozzles.  At the MSU R.R. Foil Plant Science Research Center near Starkville, MS, separate sites were also used to assess weed control and turf tolerance.  These studies were initiated on June 18, 2015, and July 27, 2015, with follow-up applications on July 16, 2015, and August 21, 2015, respectively.  Treatments at MSU were applied at 280 L ha-1 with a CO2-pressurized (276 kPa) backpack sprayer equipped with four TeeJet XR8002 flat fan nozzles that delivered a 1-m spray width at 4.8 km h-1.  

The interaction of location by treatment was significant for all measured responses and data are presented separately by VT and MSU for bermudagrass tolerance and crabgrass control, while goosegrass was only evaluated at VT.  At 2 weeks after initial treatment (WAIT), all treatments at VT except quinclorac alone (both rates) and MSMA injured bermudagrass greater than 50%, while topramezone HR and topramezone HR + quinclorac LR or triclopyr injured bermudagrass 87 to 93%.  At MSU, no treatment injured bermudagrass greater than 44%.  Only 3 treatments at MSU injured bermudagrass more than 30% and all included topramezone HR.  At 6 WAIT, the disparity in bermudagrass response between VT and MSU continued as all topramezone-containing treatments injured bermudagrass 70% or more at VT and 10% or less at MSU.  Weed control trends between VT and MSU were also divergent.  At VT 2 WAIT, all quinclorac-containing treatments, except quinclorac LR alone (87%), controlled smooth crabgrass greater than 95%.  At MSU 3 WAIT, quinclorac alone did not control crabgrass greater than 15% regardless of rate and no treatment controlled crabgrass more than 65%.  The crabgrass population at MSU is suspected to be quinclorac-resistant based on earlier studies.  By 8 WAIT at VT, all quinclorac-containing treatments completely controlled crabgrass and topramezone alone controlled crabgrass 83 to 94%.  At MSU 7 WAIT, only 5 treatments controlled crabgrass greater than 50% and no treatment controlled crabgrass greater than MSMA alone (78%).  At VT 2 WAIT, all topramezone treatments controlled goosegrass greater than 77% while treatments containing the high rate of topramezone controlled goosegrass greater than 85%. MSMA controlled goosegrass less than 60% while quinclorac alone (both rates) had relatively no control. At 8 WAIT, all topramezone-containing treatments completely controlled goosegrass while MSMA controlled goosegrass less than 60%.  The reasons for differences in turf and weed response between locations is not known but better bermudagrass growing conditions and a longer growing season may have helped decrease injury responses at MSU and a herbicide-resistant crabgrass population may have reduced weed response at MSU.

 


EFFICACY OF TOPRAMEZONE TO REMOVE BERMUDAGRASS FROM COOL-SEASON TURFGRASSES. K. Umeda*; University of Arizona, Phoenix, AZ (344)

ABSTRACT

During 2013-15, several small plot field experiments were conducted in Arizona on golf courses where cool-season turfgrasses were invaded by bermudagrass. Initially, in the higher elevation region where a mix of Kentucky bluegrass and perennial ryegrass are typically used on fairways, topramezone at 25 g/ha applied 3 times at 3-week intervals during August-September 2013 showed 96% reduction of bermudagrass with no observable injury to the cool-season turf.  During spring 2014 when bermudagrass emerged from winter dormancy in and around a bentgrass green cv. SR 1020, topramezone showed a rate response with 37 g/ha applied 2 times exhibiting more activity against bermudagrass than 25 or 12 g/ha applied 3 times.  At another location, 2 spring applications of topramezone at 37 g/ha was more effective than 25 g/ha and perennial ryegrass was minimally injured while creeping bentgrass blend cv. Dominant X-treme 7 showed no visible injury.  During October-November 2014, three applications of topramezone after overseeding of perennial ryegrass in the collar areas around a bentgrass green cv. SR-1020 caused severe bleaching of bermudagrass and chlorosis of the ryegrass.  Two weeks after the third application of all rates, ryegrass stand was thinned 40% while the bentgrass green showed no evidence of injury. Similar perennial ryegrass injury was observed at a second location where the overseeding was completed 10 days before and the grass was treated when it was emerging at the 1 to 2-leaf stage. The creeping bentgrass green cv. Dominant Plus was not injured while the encroaching bermudagrass was bleached white. Late spring, April to June, applications of topramezone showed effective bermudagrass removal at better than 81% in late July with safety to Dominant X-treme 7.  


EFFECT OF SPRAY CARRIER VOLUME AND NOZZLE TYPE ON DISLODGEABLE 2,4-D RESIDUES FROM HYBRID BERMUDAGRASS TURF. T. Gannon*1, M. D. Jeffries1, K. Ahmed1, J. T. Brosnan2, G. K. Breeden3; 1North Carolina State University, Raleigh, NC, 2University of Tennessee-Knoxville, Knoxville, TN, 3University of Tennessee, Knoxville, TN (345)

ABSTRACT

Research to date has confirmed 2,4–dimethylamine salt (2,4–D) can dislodge from hybrid bermudagrass (Cynodon dactylon x Cynodon transvaalensis), the most common athletic field turfgrass in adapted zones; however, efforts have focused on site conditions and post–application management practices.  Field research was conducted to evaluate application parameters to reduce dislodgeable 2,4-D residues.  More specifically, research evaluated 2,4-D residues dislodged via soccer ball roll (3.7 m) following spray applications at varying carrier volumes (187, 374 or 748 L ha-1) and nozzles with varying droplet size spectrums [fine = extended range (XR), coarse = drift guard (DG) or extra coarse = air induction extended range (AIXR)].  Data suggest 2,4–D dislodgeability decreased as spray carrier volume and droplet size increased.  Across experimental runs at 2 DAT, 2,4–D dislodged was 48 to 55% greater when spraying at 748 compared to 187 L ha-1.  At 1 DAT, 2,4–D dislodged was greater from XR nozzles (3% of the applied) than DG (2.3%) or AIXR (2.0%).  Numerical trends persisted through 6 DAT; however, statistical significance was not detected.  Findings from this research will improve turfgrass management practices to minimize human pesticide exposure.

 


DIAMOND ZOYSIAGRASS POSTEMERGENT HERBICIDE TOLERANCE. P. O. Signoretti*; Clemson University, Clemson, SC (346)

ABSTRACT


NATURAL MANAGEMENT WITH SPECTICLE FORMULATIONS AND PROGRAMS. S. Wells*1, D. Myers2, J. Michel2, B. Monke3; 1Bayer CropScience, High Springs, FL, 2Bayer CropScience, RTP, NC, 3Bayer CropScience, Kansas City, MO (347)

ABSTRACT

Golf course managers are implementing or enhancing natural areas on golf courses to reduce maintenance inputs such as labor, mowing, pesticide and fertility applications and irrigation.  The objective of research conducted in 2014-2015 was to evaluate the use of indaziflam formulations for plant tolerance in natural areas at spring, summer and winter timings. Overall weed management was a secondary objective.  Trials were conducted throughout the United States on diverse plant material.  Treatments included Specticle G at 50.2 g ai/ha, Specticle FLO at 48 g ai/ha applied over the top of the plant material or directly to the soil surface.   Prairie grasses that showed excellent tolerance to FLO and G formulations of indaziflam included: switchgrass (Panicum virgatum L.), big bluestem (Andropogon gerardii), little bluestem (Andropogon scoparius), yellow Indian grass (Sorghastrum nutans), prairie cordgrass (Spartina pectinata), Basin wildrye (Elymus cinereus), prarie sandreed (Calamovifa longifolia), tall wheatgrass (Thinopyrum  porticum).  Hottentot fig also known as ice plant (Carpobrotus edulis) and gazania (Gazania hybrids) were tolerant of Specticle Flo when seasonal applications were made in June.   Sericia lespedeza (Lespedeza cuneata) showed unacceptable injury to Specticle FLO at the spring and fall timings and the winter application reduced the stand of lespedeza at spring greenup.  Sericia lespedeza was tolerant to Specticle G at spring and summer applications, but not at the winter or dormant timing. Overall weed infestation in a stand of little bluestem at 153 days after the spring application was 13% with Specticle FLO applied directly, 20% with Specticle G applied over the top, 37% with Specticle FLO applied over the top compared to 65% infestation in the control.  The results of these trials conclude that several plant species used in golf course natural areas are tolerant of Specticle G and Specticle FLO at labeled rates.


EFFECT OF EDAPHIC CONDITIONS AND MANAGEMENT INPUTS ON INDAZIFLAM-SOIL BIOAVAILABILITY. M. D. Jeffries*, T. Gannon; North Carolina State University, Raleigh, NC (348)

ABSTRACT

Indaziflam is a cellulose biosynthesis–inhibiting herbicide for annual weed control in various agricultural systems.  Sporadic cases of unacceptable injury to desirable plants have been reported following indaziflam application, which may have been due to conditions favoring increased indaziflam–soil bioavailability.  Research was conducted from 2013 to 2015 on a sandy soil to elucidate the effects of soil organic matter content (SOMC) and soil volumetric water content (SVWC) on indaziflam–soil bioavailability.  Indaziflam was applied (50 or 100 g ai ha-1) at fall–only, fall–plus–spring and spring–only timings to plots comprising a factorial arrangement of SOMC, pre–application (PRE) SVWC and post–application (POST) SVWC.  Following application, field soil cores were collected for a subsequent greenhouse bioassay experiment, where foliage mass reduction of perennial ryegrass (Lolium perenne L.) seeded from 0 to 15 cm soil depth was used as an indicator of indaziflam–soil bioavailability throughout the profile.  Significant edaphic effects were observed at 0 to 2.5, 2.5 to 5 and 5 to 7.5 cm depths, with increased bioavailability at low compared to high SOMC.  Pre–indaziflam application SVWC did not affect bioavailability, while POST high SVWC increased indaziflam–soil bioavailability at 2.5 to 7.5 cm depth compared to POST low.  Low SOMC–POST high SVWC decreased perennial ryegrass foliage mass 40 and 37% at 5 to 7.5 cm depth from cores collected 10 and 14 wk after treatment, respectively, while reductions from all other SOMC–POST SVWC combinations were < 12% and did not vary from each other.  Data from this research will aid land managers to effectively use indaziflam without adversely affecting growth of desirable species.

 


THREE WAY INTERACTIONS INVOLVING TRIFLOXYSULFURON, CULTURAL PRACTICE, AND NITROGEN FERTILIZATION ENABLE MATURE TROPICAL SIGNALGRASS UROCHLOA SUBQUADRIPARA CONTROL. N. G. Young*1, R. G. Leon2, J. T. Brosnan3, J. R. James4; 1Turfgrass Environmental Research Inc., Fort Lauderdale, FL, 2University of Florida, Jay, FL, 3University of Tennessee-Knoxville, Knoxville, TN, 4Syngenta Crop Protection LLC, Greensboro, NC (349)

ABSTRACT

Stringent regulatory policy in Florida has reduced chemical options for grassy weed control in turfgrass. Assessment of integrated weed management approaches are necessary to increase efficacy of existing herbicides, particularly for troublesome weed species such as tropical signalgrass (BRASU). The objectives were to (1) determine whether light vertical mowing (LVM) or ammonium sulfate fertilization (ASF) interacted with trifloxysulfuron sodium salt (TSS) and influenced BRASU or bermudagrass (CYNDA) coverage and (2) assess which of these factors had most impact on herbicide response. A 2 by 2 by 2 split-split-plot experiment investigated the effect of factors (A) with and without TSS (0.028 kg ai ha-1), (B) with and without LVM (depth 0.32 cm), and (C) with and without soil-applied ASF (49 kg N ha-1) on BRASU and CYNDA coverage. Integrated management practices were implemented three times on 14 d intervals as part of experiments, repeated over space and time in south-west Florida during summer and fall in 2014 and 2015. Repeated measures analysis of consolidated data indicated BRASU coverage was influenced by the three-way interaction of TSS, LVM, and ASF (p=0.001). Integrated treatments TSS+LVM+ASF, TSS+LVM, TSS+ASF, and TSS reduced BRASU coverage by 95, 60, 73, and 21 %, respectively. Pooled across LVM treatment, TSS+ASF and TSS-ASF increased CYNDA coverage by 781 and 340%, respectively, when initial cover were compared to final coverage. Data suggest the capacity of CYNDA to fill voids following weed removal was influenced more by ASF than LVM, although both factors were required for near complete BRASU reduction. Findings suggest that integrated programs incorporating TSS, LVM, and ASF can selectively reduce BRASU cover in managed turf. This information could benefit turf managers and the environment in Florida by enabling effective BRASU management with low active ingredient loading in a situation with limited herbicide alternatives. 

 


POSTEMERGENCE TROPICAL SIGNALGRASS CONTROL IN FLORIDA. R. B. Cross*, B. McCarty; Clemson University, Clemson, SC (350)

ABSTRACT

Tropical signalgrass (Urochloa subquadripara) has become a serious weed problem in Florida in recent years in association with the ban of organic arsenical herbicide use in turf. The purpose of this research was to identify alternative POST herbicides which control tropical signalgrass. Two field experiments were conducted on common bermudagrass fairways in Florida in fall 2014 and 2015 as previous research suggested tropical signalgrass control is greater with fall applications. Several non-organic arsenical herbicide treatments controlled tropical signalgrass. Initial treatments were applied on October 6, 2014 and September 16, 2015 with sequential applications made two weeks after initial (WAIT). In the first experiment, treatments containing Xonerate (amicarbazone) alone and in combination with other herbicides provided >97% tropical signalgrass control 12 WAIT in 2014 and 2015. These included a single application of Xonerate 4 SC at 14 oz/acre, or sequential applications of Xonerate at 7.25 oz/acre in combination with Revolver 0.19 L (foramsulfuron) at 26 oz/acre, Dismiss South 4 F (sulfentrazone + imazethapyr) at 7.25 oz/acre, Tribute Total 61 WDG (thiencarbazone + foramsulfuron + halosulfuron) at 3.2 oz/acre, or Celsius 68 WDG (thiencarbazone + iodosulfuron + dicamba) at 3.7 oz/acre. In the second experiment, sequential applications of Tribute Total at 3.2 oz/acre in combination with either Drive XLR8 1.5 L (quinclorac) at 64 oz/acre or Sencor 75 DF (metribuzin) at 4 oz/acre provided >85% tropical signalgrass control 12 WAIT in 2014 and 2015. Appropriately-timed POST applications of several non-organic arsenical herbicides provide excellent tropical signalgrass control. Control was most effective when two herbicides were tank-mixed which is also a sound practice for managing herbicide resistance. Research will continue investigating tropical signalgrass control and other grassy weeds to determine potential alternatives for organic arsenical herbicides, including expanding research into St. Augustinegrass.

 


TROPICAL SIGNALGRASS UROCHLOA SUBQUADRIPARA CONTROL IS INFLUENCED BY DIFFERENTIAL RESPONSE OF ACETOLACTATE SYNTHASE INHIBITOR CLASS TO EXOGENOUS GIBBERELLIC ACID (GA3) AND CONTROLLED-RELEASE UREA. N. G. Young*1, R. G. Leon2, J. T. Brosnan3, J. R. James4; 1Turfgrass Environmental Research Inc., Fort Lauderdale, FL, 2University of Florida, Jay, FL, 3University of Tennessee-Knoxville, Knoxville, TN, 4Syngenta Crop Protection LLC, Greensboro, NC (351)

ABSTRACT

Monosodium arsenate (MSMA) deregistration in Florida reduced Tropical signalgrass (BRASU) control options in bermudagrass (CYNDA), and recent herbicide introductions to replace MSMA are cost-prohibitive. Reevaluation of older, low-cost chemistries within integrated weed management (IWM) approaches is necessary in efforts to mitigate factors that prevented historic adoption. A factorial field experiment was conducted in the summer of 2015 in south-west Florida to determine the effects of controlled-release nitrogen (CRN), acetolactate synthase (ALS) inhibitors, and gibberellic acid-3 (GA3) on BRASU control and CYNDA injury.  Treatments were: with and without CRN (122.5 kg N ha-1) applied at study initiation; imazapic (0.052 kg ai ha-1), trifloxysulfuron sodium (0.028 kg ai ha-1), and a nontreated control; and with and without GA3 (0.007 kg ai ha-1). Herbicides and GA3 were applied three times on 14 d intervals. Imazapic+CRN+GA3 produced 95 and 79% BRASU control at 42 and 84 days after initial application (DAIA), respectively, and imazapic+CRN without GA3 exhibited similar control. Pooled across GA3 treatment, CRN significantly increased control with imazapic by 34 and 41% compared to imazapic without CRN at 56 and 84 DAIA, respectively. For trifloxysulfuron sodium, negligible benefits were associated with CRN application. Across assessments with CRN, imazapic produced significantly higher control (54%) than trifloxysufluron sodium with differences apparent 14 DAIA. Without CRN, differences between herbicides were slower to manifest and had subsided by study completion. Bermudagrass injury was assessed 7 d after each application. Compared to trifloxysufluron sodium, imazapic caused higher injury. Without CRN, the maximum injury (19%) occurred after the first application with imazapic, but diminished with successive treatments. For imazapic+CRN, injury peaked 21 DAIA (27%), indicating a link between injury and nitrogen release characteristics. Overall, GA3 applications increased herbicide injury. Data suggest imazapic may offer a low cost option for BRASU management if applied with CRN and temporary injury can be tolerated. 

 


PREEMERGENCE AND POSTEMERGENCE CONTROL OF LONGSPINE SANDBUR (CENCHRUS LONGISPINUS). J. F. Derr*; Virginia Tech, Virginia Beach, VA (352)

ABSTRACT

Longspine sandbur [Cenchrus longispinus (Hack.) Fern] is a summer annual grass with sharp spines on the burs.  These spines make it a troublesome weed in turf sites and other locations where children play.  Experiments were conducted to determine the effectiveness of preemergence and postemergence herbicides for controlling this weed.  Preemergence experiments were conducted in the greenhouse in flats using a pine bark plus peat plus compost growing medium.  Seed was removed from burs and planted into the flats.  Flats were irrigated immediately after treatment.   Plant stand and shoot fresh weight were recorded 1 MAT and the trial was repeated.  In both trials, dithiopyr at 0.56 kg ai ha-1 and prodiamine at 0.84 kg ha-1 gave greater than 90% control based on both stand and shoot weight reduction. Pendimethalin at 3.4 kg ha-1, indaziflam at 0.05 kg ha-1, and oxadiazon at 2.24 kg ha-1 reduced sandbur shoot weight by 78, 71, and 69%, respectively.  Mesotrione at 0.28 kg ha-1 reduced sandbur shoot weight by 41%.  Longspine sandbur was grown in 10 cm diameter pots for postemergence trials.  Fenoxaprop at 0.14 kg ha-1 applied once, or two applications of topramezone at 0.025 kg ha-1 or MSMA at 2.24 kg ha-1 gave excellent postemergence control of longspine sandbur.  Applications of trifloxysulfuron at 0.028 kg ha-1, mesotrione at 0.28 kg ha-1 and imazaquin at 0.42 kg ha-1 suppressed longspine sandbur growth, while quinclorac at 0.84 kg ha-1 did not control this weed.

 


FALL APPLICATIONS OF ALS INHIBITING HERBICIDES FOR ANNUAL BLUEGRASS (POA ANNUA) CONTROL. E. H. Reasor*1, J. T. Brosnan1, G. K. Breeden2; 1University of Tennessee-Knoxville, Knoxville, TN, 2University of Tennessee, Knoxville, TN (353)

ABSTRACT

Annual bluegrass (Poa annua) is a problematic weed of golf course turf.  Acetolactate synthase (ALS) inhibiting herbicides are traditionally applied in spring to control mature annual bluegrass plants postemergence.  Limited information is available regarding the efficacy of fall applications of ALS inhibitors for annual bluegrass control throughout winter and early spring.  Therefore, our objective was to evaluate the efficacy of fall applications of ALS inhibiting herbicides for annual bluegrass control compared to standard pre- and postemergence herbicide treatments.

Research trials were conducted in Knoxville and Memphis, TN in hybrid bermudagrass (Cynodon dactylon x C. transvaalensis) golf course roughs infested with annual bluegrass.  Fall ALS inhibiting herbicide treatments were applied in November 2014 and included the following:  thiencarbazone + foramsulfuron + halosulfuron (TT) at 135.7 g ai ha-1, trifloxysulfuron at 27.9 g ai ha-1, and foramsulfuron at 29 g ai ha-1.  Efficacy of these treatments was compared to oxadiazon (3364 g ai ha-1), indaziflam (32.7 g ai ha-1), simazine (2243 g ai ha-1), and pronamide (1682 g ai ha-1) applied at pre- or early-postemergence timings during fall of 2014, as well as trifloxysulfuron, trifloxysulfuron + mesotrione (175 g ai ha-1), and trifloxysulfuron + triclopyr (561 g ai ha-1) applied in March 2015.  Foramsulfuron and TT were also applied during March 2015 at the Memphis, TN location only.  All treatments except oxadiazon were applied with a CO2 pressurized boom sprayer calibrated to deliver 280 L ha-1 with four, 8002 flat-fan nozzles at 124 kPa.  Oxadiazon was a granular (2G) formulation applied using a shaker jar.  Adjuvants were also included with treatments according to the label recommendations.  Experimental design at each location was a randomized complete block design with three replications.  Annual bluegrass control was visually assessed during April 2015 at both locations using a 0 (i.e., no weed control) to 100% (i.e., complete weed control) scale relative to non-treated check plots.  Data were subjected to analysis of variance with means separated using Fisher’s Protected LSD using the ‘ExpDes' package in R version 3.2.2.        

Annual bluegrass control in Memphis, TN ranged from 33 to 99%.  Fall applications of ALS inhibiting herbicides were not significantly different from those applied in spring.   In Knoxville, annual bluegrass control ranged from 80 to 100% with no statistical differences detected among treatments.  Across both locations, annual bluegrass control using fall applications of ALS inhibiting herbicides ranged from 97 to 100%, whereas spring applications controlled annual bluegrass control 87 to 100%. 

Data suggest that fall applications of ALS inhibiting herbicides provide similar annual bluegrass control compared to treatments applied in spring.  Fall applications may allow turf managers a wider range of favorable environmental conditions to apply treatments.  Moreover, fall applications of ALS inhibitors can provide alternative rotational options to mitotic and photosystem II inhibiting herbicides typically applied in fall for annual bluegrass control.  However, caution must be exercised to not solely rely on ALS inhibiting herbicides for annual bluegrass control as resistance to this mechanism of action has been regularly documented in annual bluegrass. 

 


APPLYING ETHEPHON IN FALL OR SPRING TO IMPROVE ANNUAL BLUEGRASS SEEDHEAD SUPPRESSION. S. S. Rana*, S. Askew, J. R. Brewer; Virginia Tech, Blacksburg, VA (354)

ABSTRACT

Annual bluegrass (Poa annua L., AB) seedheads in spring deteriorate aesthetic beauty and playability of putting greens whether it is present as the desired turf or a wanton weed on creeping bentgrass