Energycane (Saccharum spp.) has been proposed as a potential perennial bioenergy crop for lignocellulosic-derived fuel production in the United States. No herbicides are currently labeled for use in energycane, but herbicides used in sugarcane and other crops can potentially be used if there is acceptable crop tolerance. Container studies were conducted outside to evaluate the tolerance of energycane to 9 PRE and 19 POST herbicides. PRE application of atrazine, metribuzin, S-metolachlor, mesotrione, pendimethalin, and diuron at rates labeled for sugarcane did not injure or significantly reduce energycane aboveground and belowground biomass compared with the nontreated plants 28 and 56 d after treatment (DAT). Injury from flumioxazin (7%), hexazinone (29%), and clomazone (54%) was observed 28 DAT. Injury from flumioxazin was transient and was not observed 56 DAT. At 56 DAT, energycane injury increased to 71 and 98%, respectively for clomazone and hexazinone. Hexazinone and clomazone applied PRE reduced aboveground and belowground biomass compared with the nontreated plants. POST application of atrazine, ametryn, mesotrione, carfentrazone, 2,4-D amine, dicamba, halosulfuron, asulam, metribuzin, and trifloxysulfuron did not injure or significantly reduce energycane aboveground and belowground biomass compared with the nontreated plants 28 DAT at labeled use rate for sugarcane. Injury was observed when diuron (51%), hexazinone (100%), paraquat (66%), clomazone (51%), flumioxazin (21%), sethoxydim (100%), clethodim (99%), glyphosate (100), and glufosinate (84%) were applied POST and each of these treatments reduced both aboveground and belowground energycane biomass compared with the nontreated plants. These results show that several PRE and POST herbicides used for weed management in sugarcane may potentially be used in energycane for weed control if planted hectares increase in the future.

Dow AgroSciences has developed the Enlist™ Weed Control System, breakthrough weed control technology that advances herbicide and trait technology by building on the Roundup Ready^® system. The Enlist system will help control herbicide-resistant and hard-to-control weed populations.  Enlist traits give corn, soybeans and cotton tolerance to Enlist Duo™ herbicide in the same application window as Roundup® herbicide.  Enlist Duo herbicide is a proprietary blend of glyphosate and a new 2,4-D choline.  Just as important as the trait and herbicide, Enlist™ Ahead is a benefits-based management resource that helps growers get the best results from the Enlist system—today and in the future.  Built on a three-pillar foundation, Enlist Ahead will offer farmers, applicators and retailers management recommendations and resources, education and training, and technology advancements. Continued in 2014, Enlist 360 education and training provides growers, ag retailers and applicators with information they need to know about the Enlist™ system. Participants learned about advanced herbicide and trait technology, best management practices for applying Enlist Duo herbicide and weed resistance management. Dow AgroSciences has used the latest science and technology to address problem weeds, and Enlist will be a very effective solution.

Fenoxaprop is a selective herbicide used for postemergence (POST) control of grasses in rice, and bispyribac has been used for selective POST control of barnyardgrass and other weeds in rice. Previous research has shown that bispyribac is the most effective herbicide for control of barnyardgrass that exceeds one to two tillers in size.  Fenoxaprop is effective for control of small barnyardgrass prior to flooding. The efficacy of fenoxaprop and bispyribac for barnyardgrass control in rice has been documented. However, there are no published reports on sequential applications of fenoxaprop and bispyribac at different application timing combinations. The objective of this research was to evaluate sequential applications of fenoxaprop and bispyribac at different application timing combinations for barnyardgrass control in rice.

Research was conducted in 2014 at the Mississippi State University Delta Research and Extension Center in Stoneville, MS. Soil at Stoneville was a Sharkey clay with a pH of 8.2 and 2.1% organic matter. Individual plots were eight 8-in rows measuring 15 feet in length. All broadleaf weeds were controlled throughout the growing season. Nitrogen was applied at 180 lb/A as urea prior to flooding at the one- to two-tiller rice stage. The experimental design was a randomized complete block with four replications. Sequential applications of fenoxaprop at 0.109 lb ai /A followed by (fb) bispyribac at 0.025 lb ai/A or bispyribac fb fenoxaprop at the same rates were applied at five different application timing combinations. All bispyribac applications included a blended methylated seed oil/organosilicon/urea-ammonium nitrate adjuvant. Application timing combinations were (1) early-postemergence (EPOST) fb mid-postemergence (MPOST), (2) EPOST fb late-postemergence (LPOST), (3) MPOST fb LPOST, (4) MPOST fb 7 d after flooding (PTFLD), and (5) LPOST fb PTFLD. The EPOST, MPOST, and LPOST applications were made to rice in the two- to three-leaf, three- to four-leaf, and four-leaf to one-tiller stages, respectively. A nontreated control was included for comparison of rough rice yield.  Barnyardgrass control was visually estimated at 7, 14, and 28 days after each treatment (DAT). Rough rice yield was adjusted to 12% moisture content. Rough rice yield data were analyzed in comparison to the nontreated control. Yield of the nontreated control was averaged for each site year and then subtracted from the yield of each plot in that site year to provide a number for relative yield.  Data were subjected to ANOVA and means were separated using Duncan’s multiple range test at p=0.05.

Fenoxaprop fb bispyribac controlled more barnyardgrass 28 DAT than sequential applications of bispyribac fb fenoxaprop regardless of application timing combination. Differences in barnyardgrass control between the two sequential herbicide treatments ranged from 11% for EPOST fb MPOST to 35% for the EPOST fb LPOST application timing combination. Barnyardgrass control was ≥95% with fenoxaprop fb bispyribac at application timing combinations EPOST fb MPOST or EPOST fb LPOST. For all treatments beginning with bispyribac, the greatest barnyardgrass control was with the EPOST fb MPOST application timing combination. Barnyardgrass control with bispyribac EPOST fb fenoxaprop MPOST was similar to fenoxaprop fb bispyribac applied MPOST fb LPOST or MPOST fb PTFLD. For both sequential herbicide treatments, barnyardgrass control 28 DAT decreased as the initial treatment in each application timing combination was delayed from EPOST to MPOST or MPOST to LPOST. Barnyardgrass control was ≤ 80% when either sequential application was triggered MPOST or LPOST.  Similar to barnyardgrass control, relative rough rice yield was optimized with sequential applications of fenoxaprop fb bispyribac applied EPOST fb MPOST or EPOST fb LPOST. Barnyardgrass was one- to two-leaf at time of EPOST application, which explains the level of control with fenoxaprop fb bispyribac at EPOST fb MPOST or EPOST fb LPOST. It was expected that bispyribac fb fenoxaprop at EPOST fb MPOST or EPOST fb LPOST would provide similar control to fenoxaprop fb bispyribac at the same application timing combinations.  However, barnyardgrass had reached the tillering stage for application timing combinations initiated at MPOST. Barnyardgrass control and relative rough rice yield were reduced with sequential applications initiated after beginning of tillering in barnyardgrass.

Sequential applications of fenoxaprop fb bispyribac were more effective than bispyribac fb fenoxaprop with all application timing combinations.  Therefore, when circumstances necessitate a total POST barnyardgrass control program in rice, optimum control will be achieved when fenoxaprop is applied to one- to two-leaf barnyardgrass and then bispyribac is used to control plants that survived fenoxaprop.

The Caribbean Biogeographic Unit, comprising the Caribbean and south Florida, has been identified as the third most important global biodiversity hotspot in the world. This is based on the percentage of endemic plants and remaining primary vegetation. Guana Island, British Virgin Islands, is roughly 343 hectares of tropical forest, mountains, hills, and valleys that contain more flora and fauna than any other island similar in size. However, several non-native grass species (Digitaria spp., Setaria spp., Sporobolus spp., etc.) have been documented to exist on Guana Island. The introduction and competitive nature of several of these non-native species may result in a loss in biodiversity and the extinction of certain endemic grass populations. The previous identification of grass species on the island may not accurately depict what is currently present in the salt flats. Therefore, we conducted a systematic survey of the grasslands of Guana Island in October of 2013 in order to determine the abundance and distribution of endemic and non-endemic grass species. A total of 59 transects measuring 40 to 67 m were run northeast to southwest approximately 3 m apart from one another from the salt pond to White Bay beach. Grass or sedge species were identified and geo-referenced (Trimble GeoExplorer 6000 series gps unit) every 3 m along each transect for a total of 1,087 data points. Data were imported into ArcGIS in order to create spatial distribution maps of grass and sedge species across the salt flats. Data points for each species were counted to determine overall abundance (%). Eight grass/sedge species were identified: broadleaf panicum [Brachiaria adspersa (Trin.) Parodi], Indian bluegrass [Bothriochloa pertusa (L.) A. Camua], thin paspalum (Paspalum setaceum Michx.), goosegrass [Eleusine indica (L.) Gaertn.], common bermudagrass [Cynodon dactylon (L.) Pers.], southern sandbur (Cenchrus echinatus L.), crowfootgrass [Dactyloctenium aegyptium (L.) Beauv.], and tropical fimbry (Fimbristylis cymosa R. Br.). The most abundant species present was Indian bluegrass (76%), while all other species constituted < 10% of the total area, respectively. Indian bluegrass may have been introduced as forage for livestock during the 18th century when the island was primarily used for sugar cane production. Thin paspalum, although poorly distributed (4% abundance), is endemic to Guana and several surrounding islands within the Caribbean. Coastal sandbur (Cenchrus incertus M. A. Curtis.) is indigenous to the island; however, our surveys only revealed a small population of non-endemic southern sandbur. Land use and anthropogenic activity may have created a population of goosegrass exclusively inhabiting a utility road that traverses the salt flats from east to west. Tropical fimbry, a sedge native to several other islands in the Caribbean, had the second highest abundance (10%). Tolerance to high levels of soil moisture may increase the competitive ability of tropical fimbry present in the salt flats. Most of these plants were observed in small depressions where water runoff collects and/or depth to the water table is less. Information obtained from this survey will be used to understand the conservation significance of several of these species and determine strategies to enhance the growth and survival of endemic plants and the biodiversity of the island flora.

SESAME RESPONSE TO POST-DIRECTED HERBICIDE APPLICATIONS. W. J. Grichar, P. A. Dotray, and D. R. Langham; Texas A&M AgriLife Research and Extension Center, 10345 State Hwy 44, Corpus Christi, TX 78406; Texas A&M AgriLife Research and Extension Center, 1102 E FM 1294, Lubbock, TX 79403; Sesame Research, LLC, San Antonio, TX 78209.

                                                                                        ABSTRACT

Sesame (Sesamum indicum L.) is one of the oldest crops known to humans.  It has been planted for over 7,500 years in Asia and Africa in very poor growing conditions.  Sesame cultivars in those areas were tall, had very long internodes, and grew above the weeds.  Letters from Thomas Jefferson document his trials with sesame between 1808 and 1824.  Jefferson stated that sesame “…is among the most valuable acquisitions our country has ever made. …  I do not believe before that there existed so perfect a substitute for olive oil.”  He talks about the rule of thumb that still exists today - that sesame will do well where cotton (Gossypium hirsutum L.) does well.   

The presence of weeds can negatively influence sesame yields.  It has been reported that the major factor influencing sesame yield loss in a competitive situation between the crop and weed is the ratio between the relative leaf area of the weed and the crop at the time of crop canopy closure.  In direct combining, the weeds can be a big problem in that they are normally green and add moisture to the combine bin.  There are many cases where the sesame seeds are dry and weed seeds are not.  Thick stems can add moisture, but the major problem is weed seeds.  Since it is logistically difficult to scalp off the weed seeds at harvest, moisture from the weeds will transfer to sesame seeds.  Sesame is 50% oil and needs to be harvested at 6% moisture or below in order to be transported by trucks and stored in silos.  High moisture under these conditions can lead to heating and ruining of the seed.  A second concern is that mechanically harvested sesame moves through a series of augers from the combine screen, to the combine bin, to the truck, to the silo, to the cleaning equipment, and within the cleaning process.  Moist sesame can be damaged by this movement forming free fatty acids and leading to spoiling. 

Field studies were conducted during the 2006 and 2007 growing seasons under weed-free conditions in south Texas and the Texas High Plains to determine sesame tolerance to herbicides applied postemergence-directed to the lower 5 and 15 cm of the sesame main stem.  Sesame injury was greatest when herbicides were applied to 15 cm of the main stem compared to herbicide applications made to 5 cm of the main stem height.  Glyphosate at 0.84 kg ae/ha and pyrithiobac at 0.07 kg ai/ha resulted in the greatest sesame stunting (28 to 90%) when applied up to 15 cm main stem height.  When glyphosate was applied up to 5 cm main stem height, sesame injury was 20% or less.  Glyphosate applied up to the 15 cm stem height and pyrithiobac applied 5 and 15 cm stem height consistently reduced sesame yield when compared with the non-treated  control.  Glufosinate-ammonium and the premix of linuron plus diuron applied up to the 5 cm stem height caused the least sesame stunting and resulted in no reduction in sesame yield when compared with the non-treated control.

Virginia buttonweed (Diodia virginiana) is a difficult to control broadleaf perennial weed. Field experiments were conducted at Pine Hills Golf Club in Winder, GA to examine the control of Virginia buttonweed in a 'Tifway 419' hybrid bermudagrass fairway. The soil was an Appling sandy loam (Fine, kaolinitic, thermic Typic Kanhapludult). Research was conducted on a mature hybrid bermudagrass fairway maintained at a 1.0 cm height. Virginia buttonweed cover (25 to 35%) within each plot was determined at the time of initial herbicide application. Treatments were applied to plots (1.2 m x 1.5 m) arranged in a randomized complete block design with four replications. Treatments included a non-treated check, metsulfuron (0.021 kg ai ha^-1) alone, metsulfuron (0.021 kg ai ha^-1) + dicamba (0.14 kg ai ha^-1), metsulfuron (0.021 kg ai ha^-1) + halosulfuron (0.053 kg ai ha^-1) + dicamba (0.14 kg ai ha^-1), metsulfuron (0.021 kg ai ha^-1) + sulfentrazone (0.070 kg ai ha^-1), metsulfuron (0.021 kg ai ha^-1) + sulfentrazone (0.070 kg ai ha^-1) + dicamba (0.14 kg ai ha^-1), and thiencarbazone + iodosulfuron + dicamba [Celsius (0.17 kg ai ha^-1)]. All treatments included a non-ionic surfactant (NIS) at 0.25% v/v. Treatments were applied on 29 July 2013 using a CO₂ pressurized backpack sprayer equipped with XR8004VS nozzle tips calibrated to deliver 375 L ha^-1 at 221 kPa. Virginia buttonweed cover was visually evaluated 1, 2, 4, and 8 weeks after treatment (WAT). Percent Virginia buttonweed control for each treatment was calculated relative to initial Virginia buttonweed cover. Analysis of variance was performed in SAS and means were separated according to Fisher's protected LSD at the 0.05 significance level. No bermudagrass phytotoxicity was observed throughout the length of the trial, regardless of treatment. Virginia buttonweed control was 4 to 14% 1 WAT, regardless of treatment. At 2 WAT metsulfuron + halosulfuron + dicamba resulted in 100% Virginia buttonweed control. All other treatments resulted in 74 to 89% control 2 WAT. Metsulfuron + dicamba and metsulfuron + halosulfuron + dicamba resulted in 100% Virginia buttonweed control 4 WAT followed by (fb) metsulfuron + sulfentrazone (93%) fb metsulfuron (88%) fb Celsius (87%) fb metsulfuron + sulfentrazone + dicamba (80%). At 8 WAT significant Virginia buttonweed regrowth was observed, regardless of treatment. Metsulfuron + sulfentrazone resulted in the greatest Virginia buttonweed control (71%) 8 WAT. Metsulfuron + dicamba, metsulfuron + halosulfuron + dicamba, and metsulfuron + sulfentrazone + dicamba resulted in 65 to 68% control 8 WAT, regardless of treatment. Virginia buttonweed control in response to metsulfuron 8 WAT was reduced to 31%, while control with Celsius was reduced to only 9%. Sequential applications may have increased long-term Virginia buttonweed control in response to all treatments.

Field studies were conducted at the Plant Sciences Farm near Athens, GA to examine the feasibility of a living white clover – cotton production system. White clover was established in the Fall 2013. Four weeks prior to cotton establishment in the Spring 2014, white clover was treated with one of four treatments applied in a 20 cm band, dicamba applied at 275 g ai/ha; dicamba plus flumioxazin applied at 275 + 70 g ai/ha; and dicamba plus glyphosate applied at 275 + 840 g ai/ha. Within each of these preplant treatments, either fomesafen plus pendimethalin applied at 275 + 840 g ai/ha or glyphosate applied at 840 g ai/ha was applied PRE followed by either metolachlor plus glyphosate applied at 990 + 840 g ai/ha applied EPOST when cotton was at the 2-leaf stage followed by diuron plus glyphosate applied at 550 + 840 g ai/ha layby. PRE and EPOST treatments were applied broadcast. White clover and cotton injury were monitored throughout the season. Volumetric soil moisture was evaluated within the white clover and cotton row to determine if there was competition for water during the season.

Early season white clover ranged from 0-50% after application of PRE cotton herbicides. Glyphosate caused the most injury (50%) and the pendimethalin + fomesafen treatment caused 30% injury. White clover injury dissipated by 60 DAT. No cotton injury was observed throughout the season. Soil moisture readings indicated that white clover was competing with cotton for moisture after cotton flowering began. There were no significant differences in cotton height among the treatments or from an adjacent field of conventional cotton. It should be noted that early season thrips injury was not detected in the white clover-cotton areas. Early season thrips injury was severe in an adjacent field of conventional cotton without a soil applied insecticide.

All treatment combinations provided excellent season-long Palmer amaranth control (>95%). Tall morningglory and large crabgrass control were not as robust. Late season tall morningglory control ranged from 70 to 90%. Treatements that included fomesafen + pendimethalin provided better tall morningglory control (85-90%). No treatment provided more than 85% large crabgrass control at the end of the season.

Cotton yield reflected successful white clover competition with cotton for water during the drier parts of the season. For a white clover-cotton intercropping system, water management will be essential. This would consist of providing greater irrigation than was available in this study and killing a larger strip of white clover before cotton establishment. Future studies will examine if killing a larger strip of white clover will still provide early season thrips control and successful Palmer amaranth suppression observed in these studies.

Bioherbicidal activity
of the fungus Myrothecium verrucaria (MV) on

glyphosate-resistant
and -susceptible Palmer amaranth was examined on whole plants and in leaf
bioassays of young and mature plants. Leaf bioassays using MV mycelia (obtained
from the fermentation) indicated that excised leaves of young greenhouse-grown
(glyphosate-resistant and -susceptible) and mature field-grown (glyphosate-resistant)
plants exhibited injury. Generally, injury was directly proportional to the MV
mycelial concentration applied, and glyphosate-susceptible and -resistant plant
leaves were equally sensitive to the MV phytotoxic effects as measured by
reduction of chlorophyll content. Similar effects occurred on whole plants
challenged by MV spray applications to foliage, as substantiated by plant growth
reduction (fresh and dry weight accumulation) at termination of the time course.
MV disease progression over a 7-d period in young (2-week-old) plants increased
with time, and at 48 to 72 h after treatment, disease was severe with nearly 100%
mortality occurring and there were no significant response differences in the glyphosate-susceptible
and -resistant plants. Disease progression in 4-week-old plants was slower than
for younger seedlings, indicating more tolerance to the bioherbicide, but
injury was moderately severe at the endpoint (168 h) of treatment. Results
demonstrate that under greenhouse and laboratory conditions, MV can control
both glyphosate-resistant and -susceptible Palmer amaranth seedlings which
could make this bioherbicide a possible candidate for use against this
economically important weed.

Off-site movement of herbicides due to volatility can be a serious issue, particularly with sensitive crops.  Occasionally this is an issue in Mississippi with herbicides applied to rights of way and other noncropland areas.  The Mississippi Department of Transportation maintains 75,181 lane miles of roadside right of way, many of which are adjacent to crops sensitive to certain herbicides.  Since broadleaf weeds are problematic on roadsides, herbicides like triclopyr could be a problem if applied close to sensitive crops and during climatic conditions favorable for volatility.  This objective of this study was too evaluate the use of Vista XRT (2.8 lb ae fluroxypyr/gal) as a potential alternative to triclopyr for hemp dogbane (Apocynum cannabinum) control in sensitive areas along roadsides in Mississippi.  Two applications on 12 May and 2 June 2014 of Vista XRT were applied to hemp dogbane at early flower and full-flower growth stages on a roadside in Noxubee County, Mississippi.  Herbicide treatments were Vista XRT at 8 or 12 oz, Vista XRT at 12 oz plus Milestone (2 lb ae aminopyralid/gal) at 7 oz, Vista XRT at 12 oz plus Capstone (1 lb ae triclopyr plus 0.1 lb ae aminopyralid/gal) at 6 pts, Garlon 3A (3 lb ae/gal triclopyr) at 32 oz, and Triclopyr HL (4 lb ae/gal triclopyr) at 24 oz product per acre.  Application rates on 2 June 2014 were the same, except the addition of Capstone alone at 8 pts product per acre.  A non-ionic surfactant at 0.25 % v/v was added to each herbicide treatment.  Herbicides were applied using a CO₂ backpack sprayer at 20 PSI.  The boom was 6 ft wide with 8003 flat fan nozzles delivering 25 GPA.  Environmental conditions were recorded at the time of the applications.  Data was analyzed using ARM software’s Least Significant Difference mean separation.  AT 1.5 and 1 MAT for Application 1 and Application 2, respectively, burn down ranged from 72 to 90 percent.  At 2 MAT, burn down was higher in Application 2 treatments, ranging from 92 to 98 percent burn down compared to 72 to 92 percent for Application 1.  This pattern was the same 3 MAT.  It is possible that these treatments more effectively control hemp dogbane at later growth stage.  Still, some regrowth was observed in all treatments by 3 MAT.  Thus, sequential retreatment at a later date would be required for complete control.  No significant differences were observed between treatments made either Application timing.  Although the Vista XRT 12 oz rate showed slightly more burn down, it was not significantly better than the 8 oz rate in this study.   This research indicates Vista XRT would be an acceptable alternative to triclopyr in areas were volatility is a concern.

Studies were conducted in 2013 and 2014 to determine the effect of an insecticide seed treatment (CruiserMaxx Rice®) on conventional rice tolerance to low doses of the herbicides glyphosate and imazethapyr applied early postemergence.  Treated seed included the insecticide thiamethoxam and “untreated” seed contained only the fungicide and other components of the commercial seed treatment which was applied at a rate of 7 ounces per 100 pounds of seed.  Herbicide treatments included glyphosate applied at 1, 2 and 4 ounces per acre and imazethapyr applied at 0.25, 0.5 and 1.0 ounces per acre.  The results of the test revealed a significant decrease in crop response when thiamethoxam treated rice was exposed to any rate of either glyphosate or imazethapyr applied at the 3- to 4-leaf stage.  Additional studies revealed that this effect was true across multiple rice varieties.

Grain sorghum is one of the most important cereal crops worldwide and is the third largest grain crop grown in the United States after corn and wheat. Weed management programs are an essential component of crop production. A field study was conducted at the Agricultural Experiment Station, Fayetteville, Arkansas, in 2014 to evaluate the effectiveness of Zest^TM (liquid formulation of nicosulfuron) herbicide in tank-mix combination with either Aatrex, Huskie, Clarity, 2,4-D, and Ally or a combination of these herbicides for broadleaf and grass control in Inzen^TM grain sorghum. The experiment was designed as a randomized complete block with ten treatments and four replications. The experiment was established in a natural weed population of Palmer amaranth (Amaranthus palmeri), pitted morningglory (Ipomoea lacunosa), yellow nutsedge (Cyperus esculentus), and broadleaf signalgrass (Urochloa platyphylla). Treatments were as follows: 1) Zest at 12 oz/A + Aatrex at 13.3 fl oz/A postemergence (POST); 2) Zest + Huskie at 13 fl oz/A + Aatrex POST; 3) Zest + Clarity at 8 fl oz/A + Aatrex POST; 4) Zest + 2,4-D (Weedar) at 8 fl oz/A + Aatrex POST; 5) Zest + Ally at 0.05 oz/A + 2,4-D + Aatrex POST; 6) Cinch ATZ at 3.20 pt/A preemergence (PRE) followed by (fb) Zest + 2,4-D + Aatrex POST; 7) Cinch ATZ PRE fb Zest + Huskie + Aatrex POST; 8) Cinch ATZ PRE fb Zest + Clarity + Aatrex POST; 9) Cinch ATZ PRE; and 10) nontreated check. All POST treatments were applied to 2- to 4-inch grass and included a crop oil concentrate at 1% v/v and ammonium sulfate at 2 lb/A in the tank. There was no grain sorghum injury from Cinch ATZ applied PRE 1 week after emergence (WAE). Grain sorghum injury ranged from 8 to 18% from tank-mix applications of Zest at 1 week after POST application (WAPO) and 2 to 3% at 4 WAPO from treatments 1 through 9.  Most injury appeared to be result of the tank-mix partner or adjuvant rather than Zest (minimal ALS-type injury). There was no grain sorghum injury by 7 WAPO. Single application of Zest + Aatrex and Zest + Huskie + Aatrex provided significantly less Palmer amaranth control (87 to 88%) compared to the other treatments (Trts 3 through 9) at 1 WAPO. However, all treatments provided 96 to 100% control of Palmer amaranth by 7 WAPO. A single application of Zest + Aatrex applied at 2- to 4-inch grass and Cinch ATZ applied PRE provided the same level of Palmer amaranth control (97 to 99%). All treatments provided excellent (98 to 100%) control of pitted morningglory. Broadleaf signalgrass control was weak (78 to 84%) from a single application of Zest + Aatrex and from Zest + Huskie + Aatrex compared to the two applications (PRE fb POST; 99% control) at 1 WAPO.  However, broadleaf signalgrass control was >90% from all treatments by 7 WAPO. All treatments provided excellent control of yellow nutsedge (97 to 99% control) by 7 WAPO.

With technological developments in smartphones, tablets and applications, extension personnel are able to record, store, and analyze data efficiently. New non-traditional tools are able to collect information through normal extension operating procedures relating to turfgrass weed science.  These tools include an automated field operation application, doForms™. doForms™ is a free application that allows users to build and customize electronic forms that can be used to record detailed information. The objective of this study is to survey the non-traditional outreach tool, doForms™, for efficiency, effectiveness, and application to extension in turfgrass weed science.  doForms™ was downloaded, installed and forms were created for use during May 2013.  For duration of the survey period, extension personnel testing doForms™ spent approximately 70% of extension related activities conducting on site visits with turfgrass managers.   From conception to deployment of doForms™ approximately 3 hours was required.  Information that was able to be collected by initial form included, date and time of contact between extension personnel and turfgrass manager, category of turfgrass manager (golf course superintendent, sod producer, athletic field manager, residential/commercial landscape operator, etc.), nature of contact (telephone, email, text, social media, etc.), nature of response, subject matter (weeds, diseases, cultural practices, undetermined, etc.), specific weed species, and location.  Information that was obtained from initial testing included time allocated to data acquisition, effort to extract data, and practicality.  Extension personnel discovered that minimal effort was required to operate doForms™.  After the conclusion of extension site visit data could be recorded in less than one minute.  Ability to extract data from computer interface required negligible effort.  Extension personnel also noted that the ability for the user to record data on devices that were already in their position increased practicality.  Although, doForms™ greatly increased extension personnel in efficiency and effectiveness of data collection disadvantages were also observed.  Extension personnel were not able to alter forms previously created and must create new forms if desired. The inability to alter forms negatively impacts data extraction.  Ultimately, the use of applications such as doForms™ can allow extension personnel to obtain information efficiently and effectively.  Due to the minimal time required to record data with applications such as doForms™, Extension personnel are able to devote additional time to other activities, ultimately increasing efficiency.  Most importantly this allows issues in turfgrass weed science from extension outreach practices to become location and time stamped for the development of focused Extension programs and current research projects.  

A field experiment was conducted from March to May 2013 in Griffin, Georgia to evaluate annual bluegrass control programs from sequential applications of amicarbazone and mesotrione combinations in tall fescue. The experiment was conducted as a randomized complete block design with four replications of 1 x 3-m plots. Treatments were applied with a single flat-fan nozzle calibrated to deliver 374 L ha^-1 of spray volume on March 1, 2013. Results showed that all treatments caused minimal tall fescue injury (<5%).  Three sequential treatments of mesotrione at 175 g ai ha^-1 alone on a two-week interval provided 50 to 61% annual bluegrass control from April 4 to 25. Amicarbazone at 98 g ai ha^-1 applied twice sequentially on a two-week interval provided <40% annual bluegrass control. Sequential applications of amicarbazone at 98 g ai ha^-1 combined with mesotrione at 175 g ai^-1 significantly increased annual bluegrass control from March 27 to April 11 compared to the herbicides alone, but did not improve final control. Ethofumesate sequentially applied at 840 g ai ha^-1 provided <50% control of annual bluegrass. Increasing the amicarbazone rate from 98 to 196 g ai ha^-1 generally increased efficacy on annual bluegrass.  Results suggest that mesotrione use with amicarbazone may improve the speed of annual bluegrass control compared to amicarbazone alone in spring.  However, application rates and regimens warrant further investigation to improve annual bluegrass control in spring.  

RESIDUAL HERBICIDES FOR PALMER AMARANTH CONTROL IN SOYBEAN. J.D. Peeples, H.M. Edwards, J.A. Bond, C.B Edwards, and T.W. Eubank; Delta Research and Extension Center, Mississippi State University, Stoneville, MS 38776.

Recommended programs for control of glyphosate-resistant Palmer amaranth begin with residual preemergence (PRE) herbicides. Research suggests that the critical weed-free period for soybean is through the R1 growth stage. Herbicides applied PRE are one tool that can be utilized to minimize weed interference in soybean. The efficacy of PRE herbicide treatments is evaluated annually in Mississippi to provide producers with up-to-date information on management of glyphosate-resistant Palmer amaranth in soybean. The objective of this research was to compare the efficacy of residual herbicides applied PRE for control of Palmer amaranth in soybean.

Research to evaluate control of Palmer amaranth with residual herbicides was conducted from 2010 to 2014 at seven sites in Mississippi. Soil textures each site year ranged from very fine sandy loam to silty clay. Field preparation each site year consisted of fall disking and field cultivation. The experimental sites were left fallow during the winter. Emerged weeds were controlled prior to planting with an application of paraquat at 1 lb ai/A.  Individual plots were four 30-in rows measuring 30 or 40 feet in length. Late maturity group IV or early maturity group V soybean cultivars adapted to the local environment were planted from mid-April to mid-May each site year. Herbicide resistance technology varied across site years. The experimental design was a randomized complete block with four replications. Treatments were applied within 48 hours of planting each site year. A nontreated control was included for comparison. Palmer amaranth control was visually estimated 14, 28, and 35 days after treatment (DAT) on a scale of 0 (no control) to 100% (complete control). An arcsin-square root transformation did not improve homogeneity of variance, so nontransformed data were used in analyses.  Nontransformed data were subjected to the Mixed Procedure with site year and replication (nested within site year) as random effects. Least square means were calculated and mean separation (p ≤ 0.10) was produced using PDMIX800.

All treatments except Canopy EX controlled Palmer amaranth ≥92% 14 DAT.  Authority MTZ and Prefix, which are mixtures containing multiple herbicide modes of action, controlled more Palmer amaranth 14 DAT than Canopy EX, Prowl H2O, TriCorr, and Valor SX.  Prowl H2O, TriCorr, and Valor SX contain a single herbicide mode of action. Palmer amaranth control 28 DAT was ≥92% with Authority MTZ, Boundary, Canopy, Dual Magnum, Envive, Fierce, Gangster, Prefix, Valor SX, Valor XLT, and Zidua.  At the same evaluation, Envive, Fierce, Prefix, and Valor XLT controlled more Palmer amaranth than Canopy EX, Prowl H2O, or TriCorr. In contrast to 28 DAT, Palmer amaranth control 35 DAT was greater following Envive, Fierce, Prefix, and Valor XLT compared with Canopy, Dual Magnum, and TriCorr.  Prowl H2O and  TriCorr or Canopy EX provided <80 or 70% control, respectively, 35 DAT.

Herbicide treatments that were mixtures containing protoporphyrinogen oxidase (PPO) and/or very long chain fatty acid synthesis inhibitors (VLCFA) were among the treatments that provided approximately 90% Palmer amaranth control as late as 35 DAT. Valor SX (PPO) and Zidua (VLCFA) each contain only a single active ingredient, but these herbicides provided control similar to mixtures containing PPO and/or VLCFA. Resistance to acetolactate synthase (ALS) inhibitors is prevalent in Palmer amaranth throughout the southern U.S. Consequently, control with Canopy EX, which is a mixture of multiple ALS herbicides, was poor. Results indicate several currently labeled PRE herbicides provide early-season control of Palmer amaranth in soybean. However, even at 14 DAT, no treatment provided complete control, so additional management would be required for season-long control. In the event that a glyphosate-resistant population of Palmer amaranth evolves multiple resistance to PPO and/or VLCFA herbicides, control options will be severely limited with currently labeled herbicides.

Sicklepod and morningglory control and Seed production of surviving plants after treatment with tank mixtures of glyphosate with 2,4-D and dicamba. R.G. Leon*¹ and J.A. Ferrell². ¹University of Florida, Jay, FL 32565, ²University of Florida, Gainesville, FL 32611.

New cotton varieties with stalked tolerance to 2,4-D, dicamba, and glyphosate will likely be quickly adopted by growers to control glyphosate resistant (GR) weeds. However, due to budget constraints growers are considering the possibility of not using glyphosate tank-mixed with synthetic auxins in fields with GR weeds. Field experiments were conducted in 2013 and 2014 to determine the need to use tank mixtures of glyphosate with 2,4-D or dicamba to control sicklepod and pitted morningglory, two important weed species in cotton production in Florida. Different herbicide treatments including dicamba, 2,4-D amine, and glyphosate, alone and in combination were applied to sicklepod and pitted morningglory populations when individuals were 3 to 6 and 6 to12 inches tall. Applications at 3-6 inches provided inconsistent control, but plots treated with combinations of dicamba and glyphosate were among those exhibiting the lowest weed biomass in both years. When averaging across application timings, plots treated with tank-mixtures exhibited the highest sicklepod control (82 to 98%) in both years regardless of the rates used at 3 WAT. Herbicides applied alone at full label rates provided in many cases >80% control, these results were not consistent, especially at the low rates. Conversely, tank mixtures provided more consistent sicklepod and pitted morningglory control regardless of the rate. At 6 WAT, differences between treatments was similar to 3 WAT, but control level was at least 10% lower due to recovery of surviving plants. Overall, plants that survived herbicide applications exhibited seed production similar to the nontreated control. Also, seed viability and germinability was not affected by herbicide treatments. The results of the present study showed that dicamba or 2,4-D alone are not sufficient to ensure proper control of important broadleaved weed species such as sicklepod and pitted morningglory and tank-mixtures of glyphosate with these auxinic herbicides might still be necessary for their control.

Herbicide resistant weeds have led to a resurgence in preemergent herbicide use. Research was conducted to investigate preemergence weed control efficacy and safety to soybeans in conventional tillage.

Research was conducted at the Auburn University’s Sand Mountain Research and Extension Center near Crossville, AL in a Hartsells sandy loam (pH 6.2). The soybean variety was Pioneer 95Y70 planted 2.5 cm in depth. Soybeans were planted and treatments applied shortly thereafter on June 2, 2014. Treatments included pendimethalin at 1.39 kg ai ha^-1 (Framework 3.3EC, Winfield Solutions LLC, St. Paul, MN), flumioxazin at 0.07 kg ai ha ^-1 (Valor SX, Valent U.S.A Corp., Walnut Creek, CA), sulfentrazone at 0.14 kg ai ha^-1 + cloransulam-methyl at 0.02 kg ai ha^-1 (Sonic, Dow AgroSciences LLC, Indianapolis, IN), and pyroxasulfone at 0.12 kg ai ha^-1 (Zidua, BASF Corp., Research Triangle Park, NC), with and without metribuzin (Glory, Makhteshim Agan of North America, Inc., Raleigh, NC) at 0.28 kg ai ha^-1. A nontreated check was also included. Treatments were applied at 93 L ha^-1 using a 6-nozzle, CO₂ pressurized backpack sprayer to 3 by 6 m plots. A randomized complete block design with four replications was used. Visual weed control and crop injury data were collected 7, 15, and 28 days after treatments (DAT) using a percent scale where 0 corresponds to no control or injury and 100 corresponds to complete plant necrosis relative to the nontreated. By 7 DAT, 4.8 cm of rainfall occurred, and by 28 DAT, a total of 14.1 cm occurred. Data were subjected to ANOVA and means separated using Fisher’s protected LSD_0.05.

Treatments including metribuzin controlled broadleaf signalgrass [Urochloa platyphylla (Munro ex C. Wright) R.D. Webster] > 90% 7 and 15 DAT and > 85% 28 DAT. Pyroxasulfone and sulfentrazone + cloransulam-methyl treatments both controlled broadleaf signalgrass 35 to 65% throughout the trial, while pendimethalin resulted in < 15% control. Flumioxazin resulted 75 to 85% broadleaf signalgrass control. Only treatments including metribuzin were in the top performing statistical grouping for broadleaf signalgrass control 15 and 28 DAT.

Treatments including metribuzin resulted in > 97% goosegrass [Eleusine indica (L.) Gaertn.] control 7 DAT. Pyroxasulfone, sulfentrazone + cloransulam-methyl, flumioxazin, and pendimethalin (all without metribuzin) resulted in 17, 95, 75, and 48% goosegrass control, respectively 7 DAT. Goosegrass was completely controlled by all treatments 15 and 28 DAT.

All treatments resulted in > 99% control of carpetweed (Mollugo verticillata L.) and smooth pigweed (Amaranthus hybridus L.) throughout the trial with the exception of flumioxazin alone, which resulted in 74% control of both weeds 15 and 28 DAT.

Overall these data indicate that all treatments were effective for broadleaf weed (carpetweed and smooth pigweed) control when applied with or without metribuzin; however, metribuzin was required for adequate grass weed (broadleaf signalgrass) control.

IMPACT OF DEEP TILLAGE AND HAND REMOVAL ON PALMER AMARANTH POPULATION IN COTTON.  M. Inman*, D. Jordan, A. York, K. Jennings, D. Monks; North Carolina State University, Raleigh, NC

Glyphosate-resistant Palmer amaranth has become one of the most problematic weeds in cotton production systems throughout Southeastern United States. Overreliance of glyphosate has shifted management practices to integrate alternative control methods such as deep tillage and a zero tolerance of weed seed production system. These practices can be costly to implement, however, can be effective in situations of heavy infestations of herbicide resistant weed species. Research was conducted from 2012-2014 to determine the influence of a single deep tillage operation and hand removal on Palmer amaranth populations. This experiment was also designed to determine the economic impact of a single deep tillage operation and a zero tolerance seed production strategy on Palmer amaranth populations in following years. Treatments consisted of moldboard plow vs. no moldboard plow both with and without hand removal of Palmer amaranth.  Although not always statistically significant, moldboard plowing and hand removal reduced weed populations in subsequent years.  However, differences in weed populations did not always translate into differences in yield and economic returns.  Major differences in yield and economic return were not observed because effective herbicides were used during both years to control resistant and susceptible biotypes.

EVALUATION OF HERBICIDES FOR CONTROL OF FRINGED REDMAIDS (CALANDRINIA CILIATA) IN WINTER WHEAT.  D.O. Stephenson, IV, B.C. Woolam, R.L. Landry, A. Mészáros, and G. Colburn; Dean Lee Research and Extension Center, LSU AgCenter, Alexandria, LA, 71302 and Pest Management Enterprises, LLC, Cheneyville, LA, 71325. 

ABSTRACT 

Fringed redmaids (Calandrinia ciliata) is an annual species native to the western U.S.  It has also been identified in Massachusetts and Mississippi.  In 2013, fringed redmaids was documented in Louisiana when it emerged in a sugarcane production area in the fall of the year.  Due to its observed emergence in the fall, infestation of winter annual crops such as winter wheat could be problematic.  Therefore, research was conducted in the winter/spring of 2013/2014 at Pest Management Enterprises, LLC research farm in Cheneyville, LA to evaluate herbicides labeled for use in winter wheat for control of fringed redmaids.  A randomized complete block experimental design with four replications was utilized.  Herbicide treatments evaluated were chlorsulfuron:metsulfuron at 22:4 g ai ha^-1 preemergence (PRE), saflufenacil at 50 g ai ha^-1 PRE, metribuzin at 160 g ai ha^-1 early-postemergence (EPOST), 2,4-D at 1120 g ae ha^-1 mid-postemergence (MPOST), dicamba at 140 g ae ha^-1 MPOST, mesosulfuron at 60 g ai ha^-1, pyroxsulam at 18 g ai ha^-1, and thifensulfuron:tribenuron at 21:11 g ai ha^-1.  EPOST treatment was applied to 2 to 3 lf wheat and MPOST treatments were applied to 8 to 10 cm fringed redmaids.  Wheat injury and fringed redmaids control was visually evaluated 14, 28, and 42 d after each application timing.  Wheat yields were collected, but are not presented. 

Chlorsulfuron:metsulfuron PRE controlled fringed redmaids 89 to 97% at all evaluation intervals.  Saflufenacil PRE provided similar control to chlorsulfuron:metsulfuron PRE 14 DAT, but control decreased to 38 to 35% 28 and 42 DAT, respectively.  Metribuzin EPOST controlled fringed redmaids 95 to 99% regardless of evaluation interval.  Fringed redmaids control 14 DAT following 2,4-D and dicamba MPOST was 8 and 5%, respectively.  However, 2,4-D MPOST controlled fringed redmaids 83% 42 DAT, which was similar to chlorsulfuron:metsulfuron PRE and metribuzin EPOST.  Mesosulfuron and thifensulfuron:tribenuron MPOST controlled fringed redmaids similarly (61 to 69%) which was greater than pyroxsulam MPOST (28%) 14 DAT.  All three provided equal control 28 DAT (70 to 86%).  Thifensulfuron:tribenuron MPOST provided similar control (89%) to chlorsulfuron:metsulfuron PRE and metribuzin MPOST 42 DAT.  Mesosulfuron and pyroxsulam MPOST controlled fringed redmaids 55 and 63%, respectively, 42 DAT.  Chlorsulfuron:metsulfuron PRE and metribuzin EPOST are the only treatments to provide 89% or greater fringed redmaids control at all evaluation intervals; however 2,4-D and thifensulfuron:tribenuron MPOST provided similar fringed redmaids control 42 DAT. 

Restrictive rotational crop requirements following application of chlorsulfuron:metsulfuron PRE and differential wheat variety tolerance to metribuzin may reduce the use of these herbicides for fringed redmaids control by winter wheat producers in Louisiana.  To avoid these issues, Louisiana wheat producers should apply 2,4-D or thifensulfuron:tribenuron for fringed redmaids management with the understanding that excellent season-long control may not be achieved.  Research of fringed redmaids management programs in winter wheat will continue.

EVALUATION OF PREEMERGENCE RESIDUAL HERBICIDES FOR WEED MANAGEMENT IN LOUISIANA SOYBEAN.  R.L. Landry, D.O. Stephenson, IV and B.C. Woolam; Dean Lee Research and Extension Center, LSU AgCenter, Alexandria, LA, 71302.

ABSTRACT

Experiments were conducted at the LSU AgCenter Dean Lee Research and Extension Center near Alexandria, LA in 2012, 2013, and 2014.  These experiments evaluated soybean (Glycine max) injury and weed management following applications of PRE residual herbicides.  A randomized complete block with four replications was utilized in all experiments.  Plot size was 9 m long with four, 0.97 m rows.  Soil type was a Coushatta silt loam with pH = 8.  Treatments include flumioxazin 72 g ai ha^-1, flumioxazin:chlorimuron 63:21 g ai ha^-1, chlorimuron:tribenuron 24:7 g ai ha^-1, chlorimuron:flumioxazin:thifensulfuron 22:72:7 g ai ha^-1, chlorimuron:flumioxazin:thifensulfuron 6:71:17 g ai ha^-1, metribuzin:chlorimuron 180:30 g ai ha^-1, S-metolachlor:fomesafen 1216:267 g ai ha^-1, S-metolachlor:metribuzin 1103:262 g ai ha^-1, sulfentrazone:metribuzin 117:264 g ai ha^-1, sulfentrazone:chlorimuron 471:54 g ai ha^-1, pyroxasulfone 149 g ai ha^-1, flumioxazin:pyroxasulfone 71:90 g ai ha^-1, and pyroxasulfone:fluthiacet-methyl 146:4 g ai ha^-1.  Soybean injury and control of hophornbeam copperleaf (Acalypha ostryifolia), ivyleaf morningglory (Ipomoea hederacea), Palmer amaranth (Amaranthus palmeri), sicklepod (Senna obtusifolia), and smellmelon (Cucumis melo) were visually estimated 21 and 42 d after application (DAT).  Following final evaluation, glyphosate was applied at 870 g ae ha^-1 to all treatments and sequential applications were applied as needed.  Soybean yield was calculated by harvesting the center two rows of each plot using conventional harvesting equipment.  Yield was adjusted to 13% moisture before analysis.

Soybean injury was ≤ 23% for all treatments 21 DAT; however, injury was greater following treatments that contained chlorimuron at greater than 6 g ha^-1, which may be due to soil pH greater than 7.5 at the experiment location.  However, soybean injury was ≤ 7% for all treatments 42 DAT.  All residual PRE herbicides controlled hophornbeam copperleaf, ivyleaf morningglory, Palmer amaranth, sicklepod, and smellmelon at least 88% 21 DAT.  Furthermore, ivyleaf morningglory, Palmer amaranth, sicklepod, and smellmelon were controlled at least 78% by all residual herbicides 42 DAT.  Hophornbeam copperleaf was controlled at least 81% by all treatments except S-metolachlor:fomesafen (77%) and flumioxazin:pyroxasulfone (76%) 42 DAT.  Soybean yields averaged 4185 kg ha^-1 following all PRE residual herbicide treatments; however, only soybean treated with chlorimuron:flumioxazin:thifensulfuron, S-metolachlor:fomesafen, and pyroxasulfone:fluthiacet-methyl yielded greater than the non-residual treatment.  Data suggests that multiple PRE residual herbicide options are available for Louisiana soybean producers; however, herbicide selection should be based on weed spectrum as weed control varied between different treatments and weeds.  Furthermore, little to no difference in soybean yields among treatments indicated that early-season visual injury in these experiments did not influence soybean yield.  These data indicate that if ALS- and/or glyphosate-resistant weeds are present, producers could benefit from using PRE residual herbicides.

EVALUATION OF INSTIGATE, REALM Q, AND RESOLVE Q FOR WEED MANAGEMENT IN LOUISIANA CORN.  J.C. McKibben, D.O. Stephenson, IV, R.L. Landry and B.C. Woolam; Dean Lee Research and Extension Center, LSU AgCenter, Alexandria, LA, 71302.

ABSTRACT

Utilization of herbicides with multiple sites of action is needed for management of herbicide-resistant weeds in corn.  Instigate is a pre-formulated mixture of rimsulfuron and mesotrione (1:10 ratio) labeled for use preemergence (PRE) in corn.  Realm Q is a pre-formulated mixture of rimsulfuron and mesotrione (1:4.2 ratio) labeled for use postemergence (POST) in corn.  Both Instigate and Realm Q contain two herbicidal sites of action.  Resolve Q is a pre-formulated mixture of rimsulfuron and thifensulfuron (4.6:1 ratio) labeled for use postemergence in corn.  Research was conducted at the LSU AgCenter Dean Lee Research and Extension Center near Alexandria, LA in 2012 and 2013 to evaluate weed control programs containing Instigate, Realm Q, and/or Resolve Q.  The experimental design was a randomized complete block with four replications.  Treatments included Instigate (rimsulfuron:mesotrione) at 18:175 g ai ha^-1 alone PRE, Instigate plus Aatrex (atrazine) at 280 g ai ha^-1 PRE, and Instigate plus Cinch ATZ (atrazine:S-metolachlor) at 650:505 g ai ha^-1 PRE.  Sequential POST treatments of Realm Q (rimsulfuron:mesotrione) at 21:88 g ai ha^-1 or Resolve Q (rimsulfuron:thifensulfuron) at 16:4 g ai ha^-1 plus atrazine at 420 g ha^-1 and Roundup PowerMax (glyphosate) at 860 g ae ha^-1 were applied following each PRE treatment containing Instigate.  Lexar EZ (atrazine:S-metolachlor:mesotrione) at 1460:1460:190 g ai ha^-1 PRE followed by Roundup PowerMax POST and Halex GT (glyphosate:S-metolachlor:mesotrione) at 1050:1050:105 g ae ha^-1 plus atrazine at 420 g ha^-1 POST were comparison treatments.  All POST treatments were applied with 0.25% v/v non-ionic surfactant to 26 cm corn.  Visual evaluations for control of barnyardgrass [Echinochloa crus-galli (L.) Beauv.], browntop millet [Urochloa ramosa (L.) Nguyen), glyphosate-susceptible Palmer amaranth (Amaranthus palmeri S. Wats.), and ivyleaf morningglory (Ipomoea hederacea Jacq.) were collected 28 d after the PRE and POST treatment (DAT).  No corn injury was observed 28 DAT following the PRE or PRE followed by (fb) POST treatments.  All PRE or PRE fb POST treatments controlled all weeds 99% 28 DAT.  This data indicates that weed management programs in corn containing Instigate, Realm Q, and/or Resolve Q are viable options for Louisiana corn producers. 

TOLERANCE OF POPCORN, SWEET CORN, AND FIELD CORN INBREDS TO PRE-EMERGE AND POST-EMERGE ACURON APPLICATIONS. B. D. Black*, M. Saini, R. D. Lins, T. L. Trower, and G. D. Vail, Syngenta, Greensboro, NC, 27419-8300

ABSTRACT

Acuron is a new selective herbicide under development by Syngenta with anticipated registration allowing first sales in the 2015 growing season. Acuron contains four active ingredients with three modes of action and is formulated with liquid capsule suspension (ZC) technology.  Acuron will have a wide window of application including pre-plant, pre-emergence and post-emergence (up to 12” corn) and will provide broad-spectrum residual control of annual grass and broadleaf weeds in field corn, silage corn, and seed corn.  It will be registered for pre-emergence use only in sweet corn and yellow popcorn.

Multiple field trials were conducted across the corn growing regions of the US to determine crop safety of field corn inbreds, sweet corn, and popcorn to pre-emergence and post-emergence applications of Acuron at 2890 and 5780 g ai/ha and compare crop tolerance to Lumax EZ at 3340 g ai/ha and 6680 g ai/ha rates.  Results from these studies showed field corn inbred, sweet corn hybrid, and popcorn tolerance to Acuron were equal to or better than Lumax EZ.

Historically, barnyardgrass (Echinochloa crus-galli) has been reported as the most troublesome species impacting Arkansas rice producers. Recent research has identified three species in Arkansas rice fields: barnyardgrass, junglerice (E. colona), and rough barnyardgrass (E. muricata). To date, no research has been conducted to evaluate the growth rates of these three species in comparison to rice under field conditions. A field study was conducted in the summer of 2014 to determine if these species grow at different rates at the vegetative stage. Thirty-nine accessions (populations) representing various ecotypes of the three species from Arkansas and a rice cultivar were used in the study. Of the 39 accessions 26 were junglerice (ECO), 9 were barnyardgrass (ECR), and 4 were rough barnyardgrass (EMU). The rice used was an early line indica type Provisia® rice developed by BASF. Seed were drill-planted to a density of 200 seed per 4.6 m plots, in single-row plots, with three replicates at the Vegetable Research Station Kibler, AR. Plots were irrigated via overhead sprinkler irrigation. Three plants per accession per replication were marked for observation. At 4 WAP, tiller number and height (cm) were measured weekly until anthesis (8 WAP) of the Echinochloa. The three plants and three replications were averaged prior to analysis. Regression models were fit to the data and analysis of covariance was used to obtain a final model that best represents each species. Rice showed a different growth and was analyzed separately. The three Echinochloa sp. followed a linear growth model for both tiller number and height increment. The three species were of different stature, with ECO being the tallest, but all species exhibited linear growth within the observation period and grew at the same rate (12.78 cm per week). All species also produced 3.48 tillers every week. The rice height measurements fit a 3-parameter nonlinear logistic model and averaged 1.64 cm increment per week. The rice tiller numbers followed a linear model and averaged 2.61 tillers a week. The three Echinochloa species grew approximately 8 times faster from 4 to 8 weeks than the experimental rice line did, but contemporary commercial varieties may grow as fast as the weed. This study highlights the importance of application timing and the effect a missed application will have on the efficacy of an herbicide treatment for Echinochloa management. 

EVALUATION OF SONIC HERBICIDE IN LOUISIANA SOYBEAN PRODUCTION SYSTEMS, D. K. Miller, M. S. Mathews, and T. M. Batts; LSU AgCenter Northeast Research Station, St. Joseph, LA.

ABSTRACT 

A field study was conducted in 2014 at the LSU AgCenter Northeast Research Station near St. Joseph, La to evaluate PRE herbicides for effectiveness in Liberty Link soybean production systems in Louisiana.  The study was conducted in a randomized complete block design with treatments replicated four times.  Soil was a silt loam with pH 6.8.  ‘HBKLL4653” soybean was planted on April 30.  Treatments were applied via compressed air sprayer at 15 GPA on May 1.  Treatments included Sonic at 3, 4, 5, or 6 oz/A; Surveil at 2.12, 2.83, 3.53, or 4.23 oz/A; Valor XLT at 4 oz/A; Prefix at 2 pt/A; Fierce at 3 oz/A; Authority MTZ at 14 oz/A; and Valor at 2 oz/A.  All treatments excluding the non-treated received an application of Liberty at 29 oz/A on July 29 to preserve treatment effects.  Parameters measured included weed control 28 and 42 d after PRE application, crop injury 14 and 28 d after PRE application, and soybean yield. 

At 28 d after PRE application, control of barnyardgrass, crabgrass, broadleaf signalgrass, sicklepod, hemp sesbania, redroot pigweed, pitted morningglory and entireleaf morningglory was at least 98, 99, 95, 64, 63, 100, 100, and 100%, respectively, and equal among all treatments.  Surveil at 4.23 oz/A controlled yellow nutsedge 99%, which was equal to all treatments except Fierce (83%) and Valor (81%). 

At 42 d after PRE application, control of barnyardgrass, crabgrass, broadleaf signalgrass, sicklepod, redroot pigweed, pitted morningglory, entireleaf morningglory and goosegrass was at least 82, 100, 85, 56, 100, 100, 100, and 91%, respectively, and equal for all treatments.  Authority MTZ controlled hemp sesbania 75%, which was equal to all treatments except Sonic @ 3 oz/A (45%) and 5 oz/A (44%) and Prefix (29%).  Prefix resulted in 100% control of yellow nutsedge, which was equal to all treatments except Surveil at 3.5 oz/A (90%), Fierce (79%), and Valor (82%).

Soybean injury at 14 d after application was no greater than 3% for any treatment.  Soybean injury at 28 d after application was not observed for any treatments.  All treatments resulted in equal yield ranging from 32 to 40 bu/A.

In Liberty Link soybean production systems in Louisiana, residual and soil applied herbicides evaluated in this study provide an excellent PRE foundation for weed management.

EVALUATION OF Authority HERBICIDEs IN LOUISIANA SOYBEAN PRODUCTION SYSTEMS, D. K. Miller, M. S. Mathews, and T. M. Batts; LSU AgCenter Northeast Research Station, St. Joseph, LA.

ABSTRACT

A field study was conducted in 2014 at the LSU AgCenter Northeast Research Station near St. Joseph, La to evaluate PRE herbicides for effectiveness in Roundup Ready soybean production systems in Louisiana.  The study was conducted in a randomized complete block design with treatments replicated four times.  Soil was a silt loam with pH 6.8.  ‘Pioneer 94Y82 RR” soybean was planted on April 30.  Treatments were applied via compressed air sprayer at 15 GPA.  PRE treatments were applied on May 1 and POST application on May 21 to V2/V3 soybean.  Treatments included Roundup Powermax at 22 oz/A POST; Authority Elite PRE at 24 oz/A fb, Authority Maxx PRE at 5 oz/A, or Authority MTZ PRE at 14 oz/A all fb Anthem at 6.5 oz/A or Marvel at 7 oz/A POST; Anthem at 6.5 oz/A in combination with Authority Maxx at 5 oz/A or Authority MTZ at 14 oz/A PRE fb Cadet at 0.6 oz/A in combination with Accolade at 0.12 oz/A POST; and Fierce PRE at 3 oz/A, Boundary PRE at 32 oz/A, or Valor XLT PRE at 3 oz/A fb Prefix at 32 oz/A POST.  A non-treated was included for comparison.  All POST treatments included Roundup Powermax at 22 oz/A in combination with NIS at 0.25%.  All treatments excluding the non-treated received an application of Roundup Powermax at 22 oz/A at the V5/V6 growth stage.  Parameters measured included weed control 15 and 60 d after PRE application and 28 d after the POST application, crop injury 20 d after PRE application and 7 and 15 d after POST application, and soybean yield. 

At 15 d after PRE application, control of barnyardgrass, crabgrass, broadleaf signalgrass, sicklepod, hemp sesbania, redroot pigweed, entireleaf morningglory, pitted morningglory, and yellow nutsedge was at least 98, 100, 98, 99, 79, 100, 99, 100, and 84%, respectively, and equal among all treatments.

At 28 d after POST application, barnyardgrass was controlled at least 94% by all treatments except sequential application of Roundup Powermax (79%).  Crabgrass, broadleaf signalgrass, sicklepod, hemp sesbania, redroot pigweed, entireleaf morningglory, pitted morningglory, and yellow nutsedge were controlled at least 100, 94, 100, 97, 100, 100, and 94%, respectively, and equally among all treatments.

At 60 d after PRE application, the program that included Boundary PRE resulted in 100% control of barnyardgrass, which was equal to control with programs that included Authority Elite PRE fb Anthem POST (99%), Authority Maxx PRE fb Anthem POST (99%), Anthem MTZ PRE fb Anthem POST (99%),  and Fierce PRE (96%), and greater than all other treatments (73-94%).  Control of crabgrass, broadleaf signalgrass, sicklepod, hemp sesbania, redroot pigweed, entireleaf morningglory, pitted morningglory, yellow nutsedge, and browntop millet was at least 100, 100, 99, 94, 100, 100, 100, 95, and 90%, respectively, and equal among all treatments.

At 20 d after PRE application, injury was not observed from any treatment.  At 7 d after POST application, injury with POST application of Marvel following PRE application of Authority MTZ was 13%, which was equal to injury with Anthem POST following Authority Elite PRE (11%), Anthem following Authority Maxx PRE (10%), and greater than all other treatments (4  to 9%).  All treatments resulted in equal soybean yield ranging from 43 to 62 bu/A.

In Roundup Ready soybean production systems in Louisiana, residual and soil applied herbicides evaluated in this study provide an excellent PRE foundation for weed management.

EVALUATION OF ANTHEM HERBICIDE IN LOUISIANA SOYBEAN PRODUCTION SYSTEMS, T. M. Batts, D. K. Miller, and M. S. Mathews; LSU AgCenter Northeast Research Station, St. Joseph, LA.

ABSTRACT

A field study was conducted in 2014 at the LSU AgCenter Northeast Research Station near St. Joseph, La to evaluate PRE herbicides for effectiveness in Liberty Link soybean production systems in Louisiana.  The study was conducted in a randomized complete block design with treatments replicated four times.  Soil was a silt loam with pH 6.8.  ‘HBKLL4653” soybean was planted on April 30.  Treatments were applied via compressed air sprayer at 15 GPA on May 1.  At planting treatments included Authority Maxx at 5 oz/A alone or in combination with Accolade at 0.89 oz/A; Anthem at 6.5 oz/A alone or in combination with Authority Maxx at 5 oz/A, Authority MTZ at 14 oz/A, or Accolade at 0.89 oz/A; Authority MTZ at 14 oz/A alone or in combination with Accolade at 0.89 oz/A; Authority Elite at 24 oz/A; Fierce at 3 oz/A; Zidua at 2 oz/A; Valor XLT at 3 oz/A; and Prefix at 32 oz/A.  A nontreated control was included for comparison.  All treatments with the exception of the nontreated received a POST application of Liberty at 29 oz/A at the V5/V6 growth stage on June 3.  Parameters measured included weed control 30 and 60 d after PRE application, crop injury 20 and 40 d after PRE application, and soybean yield. 

At 30 d after PRE application, complete control of barnyardgrass was achieved with Anthem + Authority Maxx, Anthem + Authority MTZ, Zidua, and Prefix.  Control was equivalent to Anthem (99%), Authority Elite (99%), Authority Maxx + Accolade (99%), Anthem + Accolade (99%), Authority MTZ + Accolade (98%), and Fierce (99%), but greater than that for Authority Maxx (97%), Authority MTZ alone (92%) and Valor XLT (86%).  All treatments resulted in equivalent crabgrass control of at least 96%.  Complete control of broadleaf signalgrass was achieved with Authority Maxx, Anthem + Authority MTZ, and Anthem + Accolade.  Control was equivalent to Anthem + Authority Maxx (98%), Authority Elite (99%), Authority Maxx + Accolade (99%), Authority MTZ + Accolade (99%), Fierce (99%), and Prefix (99%), but greater that all other treatments (93 to 98%).  All treatments resulted in equivalent sicklepod control of at least 85%.  Authority MTZ alone or in combination with Anthem resulted in complete control of hemp sesbania.  Control was equal to all other treatments except Authority alone (70%), Authority Maxx + Accolade (72%), Anthem + Accolade (73%), and Prefix (82%).  All treatments resulted in at least 100, 99, and 99 percent control of redroot pigweed, entireleaf morningglory, and pitted morningglory.  Authority Elite resulted in 100% control of yellow nutsedge, which was equal to all other treatments, except Authority alone (90%), and Fierce (91%).

At 60 d after PRE application, Anthem + Authority Maxx Controlled barnyardgrass 98%, which was equal to control with Anthem alone (89%), Anthem + Authority MTZ (96%), Authority Elite (95%), Anthem + Accolade (93%), Fierce (95%), and Zidua (94%).  All other treatments controlled barnyardgrass (66 to 85%).  Control of crabgrass, broadleafsignalgrass, sicklepod, hemp sesbania, redroot pigweed, entireleaf morniongglory, pitted morningglory, and yellow nutsedge was at least 100, 100, 97, 98, 100, 100, 100, 83%, respectively, and equivalent for all treatments.

At 20 DAT, Anthem + Authority MTZ (10%) and Anthem + Accolade (10%) resulted in injury that was equal to that for Fierce (8%), Valor XLT (6%), and Prefix (5%), and greater than all other treatments (1 to 4%).  At 40 DAT, injury was not observed for any treatment.  Anthem + Authority Maxx resulted in a yield of 55 bu/A, which was equal to all other treatments (51 to 53 bu/A) and greater than yield observed following application of Anthem alone (49 bu/A).

In Liberty Link soybean production systems in Louisiana, residual soil applied herbicides evaluated in this study provide an excellent preemergence foundation for weed management and with the excpetion of Anthem alone maximized yield.

Johnsongrass (Sorghum halepense) is a perennial warm season grass, listed as a noxious weed, and a common problem on right-of-way sites. There are a number of herbicides labeled and available to control johnsongrass and most rely on translocation from the leaves to the rhizomes for greatest efficacy.  However, mowing is part of roadside management and one question is how does the timing of mowing after herbicide application affect efficacy?

This study was initiated August 14, 2014 to answer the questions asked above at an interchange near Bardstown KY.  Four herbicide treatments were applied to 10 ft x 60 ft strips at 337 L/ha.  Six time of mowing treatments were applied as 10 ft x 40 ft strips across the herbicide treatments in a split block design, replicated three times.  The herbicide treatments were Outrider (sulfosulfuron), Fusilade II (fluazifop), Acclaim Extra (fenoxaprop), and Fusilade + Acclaim.  The time of mowing treatments were as follows: no mowing, same day as herbicide application, as well as 1 day, 2 days, 1week, and 2 weeks after application.  Visual assessments of percent johnsongrass control were done 34 (9/17/2014) and 70 (10/23/2014) days after herbicide treatment (DAT).

While Outrider had the lowest visual control (70%) without mowing 34 DAT it had the greatest control (83%) (compared to the other herbicide treatments) when mowed the same day as application.  Outrider still had the greatest control (88%) when mowed the same day 70 DAT while the other herbicides ranged from 0 to 17% control.  Control in the top set of treatment combinations ranged from 88 to 100% 70 DAT.  Only the no mowing and 2 weeks after combinations with Acclaim Extra were in this top group.  Final assessments will be done in 2015.

                Palmer amaranth (Amaranthus palmeri) is one of the most problematic weed species in Mid-South soybean systems.  Lack of diversity in soybean weed management has led to almost total reliance on herbicides, particularly glyphosate for weed control, which in turn has led to glyphosate-resistant Palmer amaranth. Clearly new tools are needed for consistent weed control in this crop. Fluridone, a potentially new herbicide mode of action in soybean, has shown some promise providing residual Palmer amaranth control in cotton.

Fluridone needs at least 1.25 cm of precipitation to activate, whereas fomesafen requires very little moisture to activate.  Therefore, fomesafen was added to fluridone in a premix which, in limited cotton research, has provided more consistent Palmer amaranth control than fluridone alone.  Evaluation of the effectiveness of fluridone for residual control is necessary in order to make recommendations for its use in alternative weed management programs in soybeans.

A field study was conducted at the West Tennessee Research and Education Center in Jackson, TN and on a production field in Medina, TN in 2014.  The objective of this research was to compare preemergent applications of fluridone (alone or mixed with fomesafen) to local standard herbicides for residual weed control and crop injury in Mid-South soybean systems.  Visual evaluations were used to determine Palmer amaranth control and soybean injury 14 days after treatment (14 DAT).  Yield was taken at the Medina location.

The three higher rates of fluridone alone and the tank-mixtures of fomesafen + fluridone injured soybeans more than the other treatments 14 DAT at Jackson.  All treatments containing fluridone dramatically injured soybeans (23-70%) at Medina.  The higher rate of fomesafen, the highest rate of fluridone, all fomesafen + fluridone tank-mixtures, and the fomesafen + S – metolachlor premix provided acceptable Palmer amaranth control (>90%) across both locations.  The visual injury 14 DAT translated into yield loss for the highest rate of fluridone applied alone at Medina.  Moreover, the fomesafen + fluridone tank-mixtures reduced soybean yield 40-90% compared with the untreated at that location.

Fluridone alone and fluridone + fomesafen tank-mixtures provided residual control of Palmer amaranth similar to the fomesafen + S – metolachlor standard.  This result is similar in cotton weed control research where fluridone was found to have value.

Fluridone crop injury was minimal at Jackson and severe at Medina.  This is likely due to soil type differences where the Medina location was a silty loam and the Jackson location was a silty clay loam. 

Fluridone can have value in soybean weed control as it could add a new herbicide mode of action for preemergence control of Palmer amaranth.  However, future research would need to be conducted to determine the influence of soil type in fluridone efficacy and crop tolerance in Mid-South soybean systems before a label could be pursued.

PEANUT RESPONSE TO PYRAFLUFEN-ETHYL APPLIED POSTEMERGENCE.  P.A. Dotray*^1,2,3, W.J.Grichar⁴, T.A. Baughman⁵, T.S. Morris², R.M. Merchant¹, and M.R. Manuchehri¹; ¹Texas Tech University, Lubbock, ²Texas A&M AgriLife Research, Lubbock, ³Texas A&M AgriLife Extension Service, Lubbock, ⁴Texas A&M AgriLife Research, Corpus Christi, and ⁵Oklahoma State University, Ardmore, OK.

Pyraflufen-ethyl (ET) was labeled in 2013 for postemergence use in peanut.  The label lists over 60 weeds that are controlled or suppressed when applications are made to broadleaf weeds up to 4 inches in height or to rosettes up to 3 inches in diameter.  Previous research suggested that ET applied postemergence-topical caused significant peanut injury.  The objective of this research was to determine peanut response to postemergence-topical applications of ET when applied according to the 2013 label.  ET applications were made to peanut at the 6-leaf, 30 days after (DA) 6-leaf, 60 DA 6-leaf, and 90 DA 6-leaf in single and in all possible 2-application sequential treatments.   Trials were conducted in the Texas Southern High Plains (Halfway in 2013 and Seagraves in 2014), South Texas (Yoakum in 2013 and 2014), and in Oklahoma (Fort Cobb in 2014).  Applications were made using 10 to 20 GPA and included a non-ionic surfactant (0.25% v/v). Visual injury was recorded during the growing season with yield and grade determined at the end of the season. At Halfway, 15 to 28% peanut injury was noted following single application treatments when evaluated 14 days after treatment (DAT), whereas 35 to 45% peanut injury was noted in 2-application treatments when evaluated 14 days after the second application.  No treatment reduced peanut yield when compared to the non-treated control.  At Seagraves, ET applied at 6-leaf injured peanut 33% when evaluated 14 DAT.  Injury following other single application treatments caused 8 to 18% injury.  Injury following 2-application treatments ranged from 10 to 42%, with the greatest injury observed in the 6-leaf followed by (fb) 30 days treatment.   Peanut yield loss averaged 734 lb/A in plots that received single or 2-applications that involved treatments made at 60 days after 6-lf and 90 days after 6-lf applications, with the exception of the 60 days after 6-lf fb 90 days after 6-lf treatment, which produced the lowest yield (4975 lb/A) when compared to the non-treated control (7008 lb/A).  At Fort Cobb, stunting was observed following the last application in all treatments and ranged from 9 to 14% in single application treatments and 5 to 18% in 2-application treatments.  No yield reductions were noted at this location.  At Yoakum in 2013, no peanut injury was noted 28 days after the last application in each treatment; however, average yield decreased by 941 lbs/A relative to non-treated control for all single and 2-application treatments that involved the 60 days after 6-lf treatment.  At Yoakum in 2014, the greatest visual injury 3 DAT was noted following the 6-lf application (27%).  YIELD DATA FORTHCOMING.  The use of ET in peanut may provide postemergence control of troublesome broadleaf weeds, but visible peanut injury (leaf burn and stunt) was noted at all locations and yield loss was noted at 3 of 5 locations.

Acuron is a new selective herbicide for weed control in field corn, seed corn, popcorn and sweet corn. Acuron contains a new active herbicide ingredient Bicyclopyrone. The mode of action of Bicyclopyrone is inhibition of HPPD (4-hydroxyphenyl-pyruvate dioxygenase) enzyme which ultimately causes the destruction of chlorophyll followed by death in sensitive plants. Upon registration, Acuron will be the first bicyclopyrone containing product launched with anticipated first commercial application in the 2015 growing season.  Acuron is a multiple mode-of-action herbicide premix that provides preemergence and postemergence grass and broadleaf weed control.  Field trials were conducted to evaluate Acuron for burndown and residual weed control compared to commercial standards.  Results show that Acuron will control many difficult weeds in no-till corn and provides improved residual control and consistency compared to the commercial standards. 

Clearfield hybrid rice (Oryza sativa L.) was introduced in 2003, and is resistant to the imidazolinone family of herbicides. Newpath and Beyond are the two herbicides labeled for use on Clearfield rice in the United States. Hybrid rice seed 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 imazomox. 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 potential of Clearfield rice with red rice (Oryza 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 in 2008 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. A long term study was established in 2009 through 2012 to evaluate four different rotations to better determine the best management practices for managing weedy rice. The rotations used in this time period were: rotation 1) Roundup Ready soybean (2009)/Clearfield hybrid rice (2010)/Roundup Ready soybean (2011)/Clearfield hybrid rice (2012); rotation 2) Roundup Ready soybean (2009)/Roundup Ready soybean (2010)/ Roundup Ready soybean (2011)/Clearfield hybrid rice (2012); rotation 3) fallow (2009)/fallow (2010)/ Roundup Ready soybean (2011)/Clearfield hybrid rice (2012); rotation 4) fallow (2009)/Clearfield hybrid rice (2010)/ Roundup Ready soybean (2011)/Clearfield hybrid rice (2012). The herbicide programs and cultural practices were consistent across a given rotation.

In 2013, a second four year study was established consisting of five different rotations.  The same size blocks were established, 0.5 acre.  The second four year rotational study utilizes the use of Provisia Rice which contains a non-genetically modified trait allowing the use of Provisia herbicide, quizalofop. The study also added Liberty Link soybean which allows the use of Liberty herbicide, glufosinate. The utilization of these two herbicides in conjunction with the other herbicides further expands the flexibility of active ingredient and 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). However, rotation 4 received Roundup at 1qt/A plus Outlook at 18 oz/A plus Zidua at 2.5 oz/A at the first trifoliate leaf stage in 2013 and 2014. 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 2014, rotations 1 and 2 were planted with Provisia Rice. Rotation 1 contained 34,796/0.5 acre weedy rice plants in 2013 and only 10/0.5 acre in 2014 at the end of the growing season. Rotation 2 contained 50,777/0.5 acre weedy rice plants in 2013 and only 8/0.5 acre in 2014 at the end of the growing season. Rotation 3 was planted with CLXL 745 and contained 544/0.5 acre weedy rice plants in 2013 and planted with Liberty Link soybean in 2014 resulting in an infestation of 5,259/0.5 acre weedy rice plants at the end of the growing season. Rotation 4 was planted with Roundup Ready soybean and contained 15,779/0.5 acre weedy rice plants in 2013 and planted with Liberty Link soybean in 2014 resulting in an infestation 6,271//0.5 acre weedy rice plants at the end of the growing season. Rotation 5 was planted with Roundup Ready soybean in 2013 and contained 15,779/0.5 acre weedy rice plants in 2013 and planted with CLXL 745 in 2014 resulting in an infestation of 80,111/0.5 acre weedy rice plants at the end of the growing season. The utilization of Provisia vastly improved rotational flexibility in 2014 and will serve as an excellent rotational tool in conjunction with Clearfield Rice for weedy rice control. This research indicates that long term crop rotation, herbicide rotation, and employing different production practices can be used to manage weedy rice plants.

COMBINATIONS OF FLURIDONE AND FOMESAFEN FOR PREEMERGE WEED CONTROL IN ARKANSAS COTTON

L.M. Collie,

T.L. Barber,

A. W. Ross,

University of Arkansas

Lonoke, AR

R. C. Doherty,

University of Arkansas

Monticello, AR

Abstract

                Combinations of fluridone and fomesafen were evaluated at different rates to compare preemerge weed control to other commonly used cotton residual herbicides. These trails were conducted in 2014 on 38 in rows at Marianna and Rohwer, AR using Stoneville 4946 cultivar. The soil types for this trial were a Commerce silt loam at the Marianna AR, location and a Herbert silt loam at the Rohwer, AR site. Palmer amaranth (Amaranthus palmeri), pitted morningglory (Ipomoea lacunose), and barnyardgrass (Echinochloa crus-galli) were over seeded at planting to provide a consistent weed population. Residual herbicides were applied at planting at 12 gal/A.  Fluridone and fomesafen were applied alone and in tankmix combinations at rates 0.125, 0.2, and 0.25 lb ai/A. These applications were compared to fluometuron at 1 lb ai/A and an untreated check. No significant differences among treatments in regards to weed control were noted at the Rohwer, AR location 14 DAT.  Obvious differences in weed control were noted at 30 DAT. Fluridone applied alone at any rate, did not provide equivalent control as industry standards fluometuron or fomesafen at 1.0lb ai/A or 0.25lb ai/A, respectively. The combination of fluridone and fomesafen at 0.25lb ai/A provided the greatest control (80%) of Palmer amaranth  and barnyardgrass at 30 days after treatment, but control was not significantly different than fomesafen applied alone at 0.2lb ai/A. It was also noted that fluridone at any rate alone did not provide equivalent control of morningglories as fluometuron at 1.0lb ai/A.  At Marianna, the highest control of Palmer amaranth and barnyardgrass at 20 days after application was achieved with fluometuron 0.75lb ai/A plus fomesafen 0.2lb ai/A and combinations of fluridone plus fomesafen at 0.2 or 0.25 lb ai/A.  Morningglory control was less for fomesafen 0.125lb ai/A than any other treatment.  By 40 days after treatment, weed control decreased for all treatments, but the combination of fluridone and fomesafen at 0.25lb ai/A continued to control Palmer Amaranth and morningglory greater than 80%. 

Experiments were conducted throughout central Florida from 2010-2014 to determine if fluroxypyr or aminopyralid could effectively manage spreading pricklypear.  Aminopyralid + 2,4-D was not effective and provided only 15% control by 18 months after application (MAT).  However, fluroxypyr at 0.55 kg ha^-1, or sequential applications of 0.27 kg ha^-1, provided greater than 82% control at 18 MAT.  Reducing fluroxypyr rates to 0.32 kg ha^-1 reduced control to 40 and 71% for spring versus fall applications, respectively.  However, the addition of aminopyralid + 2,4-D to fluroxypyr at 0.32 kg ha^-1 improved pricklypear control to 92%, regardless of application timing.

Cotton Variety Response to Preemerge Application of Anthem Flex A.W. Ross, L.T. Barber, and L.M. Collie- University of Arkansas Lonoke, Arkansas, R.C. Doherty- University of Arkansas Monticello, Arkansas, D.M. Dodds- Mississippi State University 

Anthem Flex is a pre-mix combination of pyroxasulfone and carfentrazone. In previous research pyroxasulfone was found to injure cotton when applied preemerge. A trial was initiated to determine if cotton varieties respond differently to preemerge applications of Anthem Flex. This trial was conducted one year (2014)- in Starkville, MS at the R.R. Foil Plant Science Research Center on a Leeper silt loam soil and in Rohwer, AR at University of Arkansas Rohwer Research Station on a Herbert silt loam. Treatments at both locations consisted of three rates of Anthem Flex -0, 3, and 6oz/A. Ten varieties were planted on 38 inch rows at both locations. Ten varieties evaluated were Stoneville 4946 GLB2, Fiber Max 1944 GLB2, Stoneville 5289 GLT, Delta Pine 1321 B2RF,  Delta Pine 1311 B2RF, Nex-Gen 1511 B2RF, Pyhtogen 499 WRF, Pyhtogen 339 WRF, Phytogen 427 WRF and Dyna-Grow 2570 B2RF. Both studies were arranged in a randomized complete block design and data was analyzed using Fisher’s protected LSD at P ≤ 0.05 for significance. Applications were made using a tractor mounted, compressed air broadcast sprayer with Greenleaf Air-Mix nozzles on 19 in spacing at 12 gallons per acre (GPA). The main type of injury observed at 28 days after treatment (DAT) was stunting. Results show there are significant differences in stunting among the varieties at both locations. All applications of Anthem Flex caused significant injury at Rohwer. Numerically injury was greater for the 6oz/a rate with Stoneville 4946 GLB2, Stoneville 5289 GLT, and Phytogen 339 WRF at Rohwer. Delta Pine 1311 B2RF appeared to be the most sensitive variety at Rohwer, with injury above 30% for both rates of Anthem Flex. Anthem Flex injury at Starkville was highest on Phytogen 339 WRF at 14%, 28 DAT with the 6oz/a rate. All varieties were significantly injured at the 6oz/a rate over the untreated check. The 3oz/a rate of Anthem Flex did not result in significant injury for Stoneville 4946 GLB2, Phytogen 449 WRF, and Phytogen 427 WRF at Starkville. Yields at Rohwer were highest for Stoneville 4946 GLB2 and Phytogen 499 WRF regardless of Anthem Flex rate. Injury from Anthem Flex did not negatively affect yield with the exception of Stoneville 5289 GLT, where yield was significantly reduced with the 6oz/a rate. There was no difference in yield with any rate of Anthem Flex at the Starkville location.Based on the amount and consistency of injury observed in these results, Anthem Flex should not be applied as PRE in Mid-South cotton production. However, Anthem Flex provides excellent control for glyphosate-resistant pigweed in cotton and should be considered as a post-directed option, once cotton reaches the appropriate size. 

Use of winter cover crops is an integral component of conservation systems in corn. However, guidelines concerning cover residue and herbicide use intensity is needed.  Field experiments were conducted from autumn of 2010 through cash crop harvest in 2014 at the Alabama Agricultural Experiment Station’s E.V. Smith Research Center at Shorter, AL to evaluate weed management in a high-residue crimson clover system compared to a winter fallow system, both managed with conservation practices and utilizing glyphosate resistant corn.  The entire experimental area rolled with a cover crop roller crimper and then treated with glyphosate at 1.12 kg ae/ha to terminate the cover crop. The experiment involved a factorial arrangement of the following: 1) crimson clover presence and absence, 2) atrazine at 0.56 lb ai/ha applied preplant burndown (PPBD), PRE, PPBD+PRE, or none, and 3) glyphosate at 1.12 lb ae/ha plus atrazine applied POST, glyphosate applied POST alone, or none.  The POST application was applied when corn reached V-8.  Weeds evaluated included Palmer amaranth, smooth crabgrass, and a pitted and tall morningglory complex.  Results show that utilizing a high residue crimson cover crop significantly increased weed control in lower input systems while weed control was maintained in high input systems in most comparisons compared to the winter fallow system. Crimson clover alone provided 33% morninggory control, 37% pigweed control, and 60% crabgrass control.  Treatments integrating atrazine applied PPBD or PRE plus clover provided excellent weed control without additional input. Corn population was decreased without herbicide; cover crop use did not affect stand establishment.  Use of herbicides increased grain yield over non-treated controls in both clover and fallow systems.  Similar to weed control, atrazine applied PPBD or PRE protected grain yield while the glyphosate POST only systems resulted in grain loss likely due to early season weed competition.

Multiple management practices have been developed over the years to alleviate the effects of fescue toxicosis on beef cattle performance.  These practices include inter-seeding complementary forage species to improve forage quality and dilute the harmful alkaloids; and supplementing animals with grain, plant by-products, or mineral supplements to alleviate fescue toxicosis.  Another method that was studied during the 1970s and 1980s was application of plant growth regulators that suppressed the formation of tall fescue (Lolium arundinaceum (Schreb.)) seedheads, which contain a higher concentration of ergot alkaloid than leaf tissue.  This method prevents grazing of the seedheads via suppression and maintains tall fescue in a high quality vegetative state throughout the growing season.  However, these growth regulators were never registered for use in range and pasture systems despite their benefits, and grower interest in the concept diminished.  Recently, the concept was reintroduced by Dow AgroSciences, LLC with the introduction of Chaparral® specialty herbicide, which not only suppresses tall fescue seedhead formation but also provides broadleaf weed control.  Tall fescue pastures treated with Chaparral for seedhead suppression have been shown to have 16% greater crude protein, 9% greater water soluble carbohydrates, and 11% greater in vitro dry matter digestibility.  Due to increased grazing pressure by non-stressed cattle and the removal of seedheads a reduction in carrying capacity may be incurred.  However, improved cow pregnancy rates (10-18% unit increase)and average daily gain (0.11-0.23 kg/day) may compensate for this reduction in stocking rate. 

Fescue seedhead suppression can mitigate fescue toxicosis and thereby improve herd performance through increased average daily gains, weaning weights, and pregnancy rates.  Using Chaparral for tall fescue seedhead suppression and weed control requires increased management to reach optimal levels of suppression, forage yield, and forage quality improvements.  For the highest level of seedhead suppression Chaparral® should be applied at 140 g product/ha, 2 to 3 weeks prior to seedhead emergence. Forage managers should limit Chaparral application to 50% or less of their tall fescue acres in a grazing season, targeting areas that can be utilized during the summer grazing seasons (May-July). It is also recommended that grazing managers treat pastures every other year to avoid long-term reduction in tall fescue stands.

^® Trademark of The Dow Chemical Company (“DOW”) or an affiliated company of Dow

Always read and follow the label directions.

Vastlan^TM is a herbicide developed by Dow AgroSciences for the control of woody plant species and annual and perennial broadleaf weeds on industrial vegetation management, aquatic, Conservation Reserve Program (CRP), range and permanent grass pastures sties and grasses grown for hay.  Vastlan herbicide is formulated as a soluble liquid (SL) and contains 480 g ae per liter (4 lbs ae/gallon) of triclopyr choline.  This higher concentration of triclopyr and “Caution” and instead of “Danger” signal word sets Vastlan herbicide apart from its predecessor Garlon^® 3A.  Vastlan herbicide provides broad spectrum control required to manage brush and weed species complexes common to many industrial vegetation management sites.  Grass tolerance and efficacy field trials were established in 2011 – 2014.  Bermudagrass (Cynodon dactylon), tall fescue (Festuca arundinacea), orchard grass (Dactylis glomerata), timothy (Phleum pretense), smooth bromegrass (Bromus inermis) and Kentucky bluegrass (Poa pratensis) were equally tolerant to Vastlan herbicide when compared to Garlon 3A.  There was no statistical difference between Vastlan and Garlon 3A for control of sweetgum (Liquidamber styraciflua), white oak (Quercus alba), southern red oak (Quercus falcate) black cherry (Prunus serotina) and water oak (Quecus nigra) when applied as a foliar spray.  Vastlan will be commercially available in the summer of 2016.

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

Always read and follow the label directions.

INFLUENCE OF IMPACT^® BASED HERBICIDE PROGRAMS ON WEED MANAGEMENT IN FIELD CORN IN THE SOUTHERN US.  Ned M. French, Ph.D., AMVAC Chemical Corporation, Newport Beach, CA  92600

ABSTRACT

Weed interference from Palmer amaranth (Amaranthus palmeri) and other weed species limits yield in field corn, and herbicides are a key tool for minimizing weed competition.  In recent years, selection for glyphosate-resistant weeds has exacerbated the challenge of managing key broadleaf weeds in field corn. Consequently, corn growers are modifying herbicide programs.  A series of field trials was conducted to compare Impact® based herbicide programs with competitive programs.  Findings are reported here.

Nine 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 21-Mar to 14-June 2014. 

Herbicide programs of Impact® (topramezone) at 0.75 oz./A + Roundup PowerMAX® (glyphosate) at 22 oz./A + AAtrex® (atrazine) at 1 qt./A, Impact® (topramezone) at 1.0 oz./A + Roundup PowerMAX® (glyphosate) at 22 oz./A + AAtrex® (atrazine) at 1 qt./A, Impact® at 0.75 oz./A + Roundup PowerMAX® at 22 oz./A + AAtrex® at 1 qt./A + Warrant® (acetochlor) at 3 pt./A, Impact® 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, Impact® at 0.75 oz./A + Roundup PowerMAX® at 22 oz./A + AAtrex® at 1 qt./A + Zidua® (pyroxasulfone) at 2 oz./A, and Capreno® (thiencarbazone-methyl + tembotrione) at 3 oz./A + Roundup PowerMAX® at 22 oz./A + AAtrex® at 1 qt./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 adjuvant (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 V3-V4. Weeds observed were ABUTH, ACCOS, AMAPA, BRAPP, CASOB, CUMMD, CYPES, DIGSA, ECHCG,  IPOHE, IPOLA, PANRA, PANTE, and SIDSP. 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.  Eight 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 93-99% control of Palmer amaranth, morningglory spp., and velvetleaf compared with the untreated check, and results against annual grasses and yellow nutsedge were quite good. Impact® + atrazine + Sequence® and Halex® GT + atrazine offered equivalent control of Palmer amaranth, pitted and ivyleaf morningglory, annual grasses, velvetleaf, and yellow nutsedge.  The addition of a WSSA Group 15 residual herbicide (HRAC Group K3), acetochlor, s-metolachlor, or pyroxasulfone, to the weed management program tended to improve overall weed control compared with herbicide programs lacking a residual herbicide and offered an additional mode of action for resistance management.  All herbicide programs significantly increased grain yield by 53 to 63 bushels per acre above the untreated check, which averaged 108 bu./A.

Across nine 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 other commercial herbicide programs.

With increasing herbicide tolerance in the southeastern U.S., it is important for scientists to consider best management programs for herbicides on the market.  Scientists must also consider the best way in which to preserve current modes of action for which resistance has not occurred.  One way in which modes of action can be preserved is by utilizing crops with tolerance to herbicides of varying modes of action.  Field studies were conducted in 2014 at the Upper Coastal Plain Research Station near Rocky Mount, NC comparing multiple glyphosate and glufosinate tolerant soybean varieties.  These varieties were applied with herbicide programs of flumioxazin PRE, followed by a POST and late POST of S-metalochlor, fomesafen, and their respective tolerant herbicide.  The study design was a randomized complete block.    The success of these varieties with herbicide programs left minimal weeds for rating.  Preliminary results indicated yield differences between treatments. 

The Office of Pest Management Policy (OPMP) was established in September 1997 with the mandate to integrate the Department's strategic planning and activities related to pest management, coordinate the Department's role in the pesticide regulatory process and related interagency affairs, primarily with the Environmental Protection Agency (EPA), and strengthen the Department's support for agriculture by promoting the development of new pest management approaches that meet the needs of an evolving and sustainable U.S. agricultural system.  The OPMP is an administrative unit within the Agricultural Research Service (ARS); however, the OPMP reports to the Office of the Secretary of Agriculture.  Key issues before the OPMP include EPA Pesticide Registration Review, Resistance Management, Endangered Species, Invasive Species, Methyl Bromide Critical Use Exemptions (CUEs), Pollinators, Maximum Residue Limits, and the National Plant Disease Recovery System (NPDRS).  The OPMP role in all matters is to ensure that grower stakeholders are involved and informed regarding activities that affect pest management.  In addition, OPMP staff are expected to provide technical expertise throughout the interagency review and public comment process on decisions related to pest management.  Weed science colleagues are needed to provide information to help explain the diversity of weed management practices, grower needs, and issues across the southern region.

Atrazine continues to be a major component of weed management programs in corn.  However, the use of atrazine has raised environmental concerns in many areas.  The p-hydroxyphenyl pyruvate dioxygenase (HPPD)-inhibiting herbicides have been shown to be effective in controlling many grass and broadleaf weed species.  Furthermore, the effectiveness of this mode-of-action is has been shown to improve with the addition of atrazine to the tank mix.  Current label recommendations suggest applying topramezone at 18.4 g ai ha^-1 with 560 g ai ha^-1 atrazine.   The objective of this study was to determine if the recommended rates of the topramezone/atrazine tank mix could be reduced by half and maintain the same weed control efficacy.  In 2013 and 2014, field studies were established in conventional–tillage corn system at the Virginia Tech Eastern Shore Agricultural Research and Extension Center in Painter, VA.  The study was a two-way factorial with topramezone and atrazine rate as factors arranged in a randomized complete block design with 3 replications.  Treatments were applied when weeds reached 10 to15 cm in height.  The rates of 18.4 g ai ha^-1 topramezone with 560 g ai ha^-1 atrazine were chosen as standards and applied alone at 0X,1X, and ½X rates alone or in combinations of 1X + 1X, ½X + 1X, 1X + ½ X, and ½X + ½X topramezone and atrazine, respectively.  Each application also contained methylated soybean oil and urea ammonium nitrate at 1% and 1.25% v/v respectively according to label recommendations.  Plots were visually evaluated for percent control 7 and 35 days after treatment (DAT) on a scale of 0 to 100 with 0 being no control and 100 being complete weed control.  Data were analyzed using the generalized linear model in JMP Pro 11 (SAS Institute Inc., Cary, NC).  Data were combined over repetitions in time if there was no trial by treatment interaction.  Appropriate means were separated using Fisher’s least protected LSD (α = 0.05).  There were no significant trial by treatment interactions for smooth pigweed control 7 DAT (p = 0.52), ivyleaf morningglory control 35 DAT (p = 0.46), and corn yield (p = 0.69), so data was pooled over years.   All topramezone/atrazine combinations controlled common ragweed, ivyleaf morningglory, and smooth pigweed 85% or greater 7 DAT and 96% or greater 35 DAT.  This study shows that the recommended rates for the topramezone/atrazine tank mix can be reduced by half without a significant reduction in the control of certain weed species.

Palmer amaranth and waterhemp are two major herbicide-resistant weeds infesting Southern US cropping systems. While tremendous emphasis has been placed on in-crop weed management, plants that emerge after crop harvest are often ignored. The resources available after the harvest of crops such as corn and sorghum may be sufficient for some weeds to emerge and produce viable seeds prior to killing frost. Experiments were conducted in late summer/fall 2014 in College Station (CS), Lubbock (LB), Texas and Fayetteville (FY), Arkansas to understand post-harvest seed production potential of Palmer amaranth, and in CS and FY to quantify seed production in common waterhemp. Seedlings that emerged at weekly intervals were monitored from Aug 19 (Palmer amaranth) or Sep 9 (waterhemp) in CS, Sep 11 for Palmer amaranth in LB and from Sep 12 for both species in FY. The plants pertaining to each emergence time were harvested individually on Nov 11 in Texas sites and on Oct 31 in FY, following killing frosts. Average Palmer amaranth seed production/plant for the first cohort indicated above was 19,510 (max 28,260), 270 (max 450), and 2 (max 5), respectively in CS, LB and FY. Mature seed production was observed when Palmer amaranth seedlings emerged as late as Oct 14 (CS, max 22 seeds), Oct 10 (LB, max 12) or Sep 17 (FY, max 2). Waterhemp did not produce any mature seed when emerged on or after Sep 11 in FY, but mature seed production was found in the CS location, with an average of 820 seeds/plant (max 1700) when emerged on Sep 9 and continuing for as late as Oct 14 (average 8, max 17 seeds) in this location. Results strongly suggest the need for managing post-harvest recruits of Palmer amaranth and waterhemp to minimize seedbank replenishment.

Weed control has always been a major component of crop production. However, with the increased difficulties with weed resistance, the emphasis on a good herbicide foundation has increased. Several soybean weed management studies were conducted in Oklahoma to investigate different programs and herbicide modes of action to determine the most efficacious. Trials (10) were conducted at the Vegetable Research Station near Bixby, OK and the Wes Watkins Agricultural Research and Extension Center near Lane, OK.

Typical small plot research techniques were employed in all trials. Various preemergence herbicide programs were investigated including various preemergence combinations of acetochlor, chlorimuron, clomazone, cloransulam, dimethenamid, flufenacet, fomesafen, flumioxazin, imazethapyr, metolachlor, metribuzin, pendimethalin, pyroxasulfone, saflufenacil, sulfentrazone and thifensulfuron. These were followed by postemergence application of dicamba, fomesafen, glyphosate or glufosinate.

Soybean injury was less than 10% in 7 of 10 soybean herbicide trials.  Trials containing preemergence combinations of pyroxasulfone + saflufenacil alone or with metribuzin resulted in 10% or greater soybean injury at Bixby in both Roundup Ready and Liberty Link systems.  Fomesafen + metolachlor + metribuzin treatments resulted in over 10% injury at Lane in the Roundup Ready soybean system.  Injury decreased over the season in all trials. No soybean injury was observed in Roundup Ready Xtend soybean regardless of herbicide combination. 

Palmer amaranth (AMAPA) control was greater than 95% with PRE combinations of chlorimuron alone or with flumioxazin + thifensulfuron, flumioxazin + metribuzin, or metribuzin + metolachlor. Tall waterhemp (AMATU) control was 99 to 100% control with all treatment combinations. Broadleaf signalgrass (BRAPP) control was 100% late season with all herbicide combinations. In a second trial, only flumioxazin in combination with pyroxasulfone or metribuzin + sulfentrazone followed by glyphosate controlled AMAPA at least 95%.  AMATU control was 100% when flumioxazin was combined with cloransulam or chlorimuron + thifensulfuron, and followed by glyphosate POST.  BRAPP control was at least 93% when flumioxazin was combined with chlorimuron alone or with thifensulfuron, or when sulfentrazone was combined with cloransulam, metolachlor or metribuzin and followed by glyphosate POST.

Various preemergence herbicides were evaluated in both Roundup Ready and Liberty Link soybean. The only preemergence treatments that controlled AMAPA at least 95% and AMATU 99% were pyroxasulfone + saflufenacil + metribuzin, and sulfentrazone + metolachlor + metribuzin, followed by fomesafen + glyphosate POST.  BRAPP control was over 85% except when pyroxasulfone + saflufenacil and fomesafen + metolachlor + metribuzin was followed by fomesafen alone POST.  In Liberty Link soybean, the only treatment that controlled AMAPA at least 94% was fomesafen + metribuzin PRE, followed by fomesafen + glufosinate POST.  The only treatments that did not control prostrate pigweed at least 98% were flufenacet + metribuzin or pendimethalin PRE followed by fomesafen + glufosinate POST.

The final study was conducted with the Roundup Ready Xtend system.  Preemergence combinations of acetochlor, pyroxasulfone + saflufenacil alone or in combination with dimethenamid, followed by POST applications of dicamba + glyphosate applied alone or in combination with dimethenamid controlled AMAPA at least 97%.

These trials indicate that effective weed control systems can be developed with the judicious use of various preemergent herbicide combinations.

PREEMERGENCE WEED CONTROL OPTIONS IN DIRECT SEEDED LETTUCE. R.E. Strahan and K. Fontenot, LSU AgCenter, Baton Rouge, LA 70803.

ABSTRACT

Commercial lettuce producers struggle with weed control in direct-seeded fields. Preemergent herbicides with the ability to control weeds without injuring the crop would be beneficial to producers. In this study, ‘Green Salad Bowl’ leaf lettuce was seeded into plots arranged in a randomized complete block with 4 replications three days prior to pre-emergent herbicide application. Precision single row push seeders were used to direct seed the crop. Plot size was 4 rows totaling 16 ft x 20 ft. The 2 center rows were used for data collection.  Eight herbicide treatments were evaluated for weed control efficacy as well as crop safety. 

Pronamide is currently labeled for use in leaf lettuce production was used as the standard.  Treatments included:  Pronamide at 1 and 2 lbs/A rates, imazapic at 2, 4, and 6 oz/A rates and and imazethapyr at 6 oz/A rate. An untreated weed-free check was maintained by weekly cultivation and an untreated check receiving no cultivation served as a control treatment. Herbicides were sprayed at the listed rates with a CO₂ backpack sprayer delivering 15 GPA.

Throughout the 78d study, lettuce germination rates and heights were recorded. Final lettuce fresh and dry weights were collected and analyzed. Data were subjected to analysis of variance (P=0.05) and means were separated using Fisher’s LSD. Plots treated with pronamide at the 1lb/A rate and 2lb/A rate and the untreated weed-free check produced significantly more fresh and dry tissue weight than all other treatments. Although lettuce germinated and grew in the imazapic and imazethapyr treated plots, growth was severely stunted. Preliminary results suggest that imazapic and imazethapyr should not be considered for preemergent weed control in direct seeded leaf lettuce due to excessive injury and yield loss.

BROADLEAF WEED CONTROL OPTIONS IN TRANSPLANTED WATERMELON. R.E. Strahan and K. Fontenot; LSU AgCenter, Baton Rouge, LA

ABSTRACT

Managing broadleaf weeds in watermelon is very difficult due poor crop tolerance to most PRE and POST herbicides.  A field study was conducted at the Burden Research Center in Baton Rouge, LA in 2014 to evaluate preemergence herbicides for large crabgrass (Digitaria sanguinalis), redroot pigweed (Amaranthus retroflexus) and pitted morningglory (Ipomoea lacunosa) control in transplanted watermelon.

Legacy variety watermelon seed from Reimer were planted on March 1, 2014 and placed on heating pads at 85F for 24 hours then grown out in a greenhouse with a max temp of 85 and a min temperature of 60F. After seedlings had reached first true leaf stage, they were fertigated with 20-20-20 soluble fertilizer weekly prior to field transplanting at a rate of 200 ppm N.

Field areas selected had a natural population of broadleaf weeds but to insure uniform pressure, research areas were seeded with redroot pigweed, pitted morningglory, and large crabgrass 2 days prior to herbicide treatment. Three days prior to transplanting (March 29, 2014), preemergence herbicide treatments were applied to a prepared seedbed.  Treatments included a premix of Strategy (clomazone + ethalfluralin) at 5 pt/A, Command (clomazone) at 0.67 pt/A, Sinbar (turbacil) at 4 oz/A, Strategy + Sinbar at 5 pt/A and 4 oz/A, respectively, Valor (flumioxazin) @ 1 and 2 oz/A, Specticle 20 WP (indazaflam) at 5 oz/A, and an untreated check.  All plots except the untreated check received a mid-season application of sethoxydim at a rate of 1 pt/A.  Herbicides were applied with a CO₂ backpack sprayer delivering 15 GPA.  Watermelons were transplanted on April 1, 2014 in the field plots.  Plots were three rows each 10 plants per row for a total of 30 plants per plot.  There were 4 replications.  Plots were three rows with 10 plants per row for a total of 30 plants per plot.  All plots had drip irrigation with 12 inch separation between emitters.

Data collected included bi-weekly visual percent weed control (0 = no control and 100 = complete control).  The experiment was conducted as a randomized complete block with 4 replications.  Data were subjected to analysis of variance (P=0.05) and means were separated using Fisher’s LSD.

Specticle and Valor at the 2 oz rate provided the highest level of pitted morningglory control (90% and 80%) and pigweed control (80% and 70%) 45 days after treatment.  However, plant maturity was delayed with Specticle applications.  Sinbar or Sinbar + Strategy provided no greater than 40% control.  Crabgrass control for all treatments ranged from 60 to 75%. 

POSTEMERGENCE CONTROL OF LARGE CRABGRASS IN HYBRID BERMDUAGRASS HAY MEADOWS.  R. E. Strahan, E. Twidwell, LSU AgCenter, Baton Rouge, LA, 70803.

ABSTRACT

Large crabgrass (Digitaria sanguinalis) is a difficult weed to manage in hybrid bermudagrass pastures.  Crabgrass germinates early and infests hay meadows throughout the growing season.  The following research evaluates glyphosate and glyphosate combinations with Prowl H₂O for controlling large crabgrass infesting bermudagrass hay.

A field study was conducted in 2014 at the Ben Hur Research Station in Baton Rouge, LA in an established Alicia hybrid bermudagrass hay meadow with a very heavy natural population of large crabgrass (average 3 plants/foot²).  The study was initiated June 30.  Herbicides were applied 10 days after hay harvest.  Bermudagrass was approximately at 30% green up following hay harvest.  Large crabgrass was 3 to 6 inches tall at the time of treatment.  Herbicides evaluated in single application included glyphosate (Cornerstone 4 lbs. active ingredient per gallon) applied at 6, 8, 12, 16, and 24 oz/A.  These glyphosate treatments were also evaluated tank-mixed with pendimethalin (Prowl H₂O) at 4 pt/A.  Additionally, Pastora (nicosulfuron + metsulfuron) at 1 oz + glyphosate @ 8 oz/A was included as well as an untreated check.

 Herbicides were applied with a CO₂ pressurized backpack sprayer equipped with 11003 XR flat fan nozzles that delivered 15 GPA at 23 psi.  Plot size was 6 ft x 10 ft.  Visual ratings of percent weed control and  bermudagrass injury data were collected bi-weekly.  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.

By 35 days after treatment, glyphosate applied at 6 oz/A provided acceptable bermudagrass injury (10%) but the poorest level of large crabgrass control (40%).  Acceptable large crabgrass control (>75%) was obtained by glyphosate rates greater than 8 oz/A.  Glyphosate at 12 oz/A controlled 92% of the large crabgrass and casused an acceptable level of bermudagrass injury.  Glyphosate applied at 16 and 24 oz per acre provided 95% crabgrass control but caused excessive bermudagrass injury (>35%).  Pastora + glyphosate provided 85% glyphosate control and acceptable bermudagrass injury by 35 days after treatment.  Prowl H₂O appeared to antagonize glyphosate at most rates evaluated.  Only glyphosate + Prowl H₂O at 16 and 24 oz/A provided acceptable large crabgrass control.

Results of this study indicate that successful control large crabgrass with minimal bermudagrass injury can be achieved by glyphosate rates as low as 8 oz/A.  

POSTEMERGENCE CONTROL OF YELLOW FOXTAIL IN HYBRID BERMDUAGRASS HAY MEADOWS.  R. E. Strahan, E. Twidwell, LSU AgCenter, Baton Rouge, LA, 70803.

ABSTRACT

Yellow foxtail is a difficult weed to manage in hybrid bermudagrass pastures.  Yellow foxtail germinates early and infests hay meadows throughout the growing season.  The following research evaluates glyphosate and glyphosate combinations with Prowl H₂O for controlling yellow foxtail infesting bermudagrass hay meadows.

A field study was conducted in 2014 at the Ben Hur Research Station in Baton Rouge, LA in an established Alicia hybrid bermudagrass hay meadow with a very heavy natural population of yellow foxtail (average 4 plants/foot²).  The study was initiated June 30.  Herbicides were applied 10 days after hay harvest.  Bermudagrass was approximately at 30% green up following hay harvest.  Yellow foxtail was 3 to 6 inches tall at the time of treatment.  Herbicides evaluated in single application included glyphosate (Cornerstone 4 lbs. active ingredient per gallon) applied at 6, 8, 12, 16, and 24 oz/A.  These glyphosate treatments were also evaluated tank-mixed with pendimethalin (Prowl H₂O) at 4 pt/A.  Additionally, Pastora (nicosulfuron + metsulfuron) at 1 oz + glyphosate @ 8 oz/A was included as well as an untreated check.

 Herbicides were applied with a CO₂ pressurized backpack sprayer equipped with 11003 XR flat fan nozzles that delivered 15 GPA at 23 psi.  Plot size was 6 ft x 10 ft.  Visual ratings of percent weed control and  bermudagrass injury data were collected bi-weekly.  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.

By 35 days after treatment, glyphosate applied at 6 oz/A provided acceptable bermudagrass injury (10%) but the poorest level of yellow foxtail control (55%).  Acceptable yellow foxtail control (>75%) was obtained by glyphosate rates greater than 8 oz/A.  Glyphosate at 12 oz/A controlled 95% of the yellow foxtail and casused an acceptable level of bermudagrass injury.  Glyphosate applied at 16 and 24 oz per acre provided 97% yellow foxtail control but caused excessive bermudagrass injury (>35%).  Pastora + glyphosate provided 95% glyphosate control and acceptable bermudagrass injury by 35 days after treatment.  Prowl H₂O appeared to antagonize glyphosate at most rates evaluated.  Only glyphosate + Prowl H₂O at 16 and 24 oz/A provided acceptable yellow foxtail control.

Results of this study indicate that successful control yellow foxtail with minimal bermudagrass injury can be achieved by glyphosate rates as low as 8 oz/A.  

The effects of aminocyclopyrachlor (AMCP) uptake by crop species is not well understood, nor is the impact that uptake may have on developing crop species. Three studies were performed to better understand the effects of AMCP on key crop species.

A greenhouse study was implemented to examine root and shoot absorption of AMCP by isolation in treated layers with activated charcoal. Seven cone designs were employed to test different scenarios of absorption and corresponding controls to rule out carbon influence on seed development. AMCP was applied at 0.07 kg ai ha^-1 to cones of pure sand, to prevent soil binding, planted with Zea mays, Gossypium hirsutum, Glycine max and Sesbania herbacea. A second greenhouse study was performed to examine the soil breakdown half-life of AMCP. A dose titration bioassay was performed with 545, 272, 136, 68, 34, 17, 8.5, 4.25, and 0 µg kg^-1 on three soil types (e.g. sand, silt and clay). Crop species examined included Z. mays, G. hirsutum and G. max. Finally, a field study was performed examining carryover of AMCP on G. max. Plants showed auxinic symptomology 21 days after planting, indicating root absorption of small concentrations of AMCP applied the year before.

Results showed that Z. mays was highly tolerant to AMCP and showed minimal responses except when both root and shoot absorption occurred at the same time. However, G. hirsutum, G.max and S. herbacea were more sensitive to aminocyclopyrachlor, especially through root absorption. These results may shed light on the carryover and persistence of AMCP in soil that could be detrimental to crops like soybeans and cotton. In effect, due to the hydrophilic nature and low soil binding of aminocyclopyrachlor, proliferation deeper into the soil profile following application can occur, creating a potential belowground surplus of the chemical below the planted roots of susceptible seedlings

BARNYARDGRASS CONTROL AS AFFECTED BY APPLICATION TIMING OF TANK-MIXTURES OF CLETHODIM AND GLUFOSINATE.  A.N. Eytcheson and D.B. Reynolds; Department of Plant and Soil Sciences, Mississippi State University, Mississippi State, MS 39762.

Abstract

The development of genetically modified (GM) crops with tolerance to non-selective herbicides has been rapidly adopted in the United States.  The LibertyLink^® system utilizes the GM crop resistance to the herbicide glufosinate.  Glufosinate is a non-selective, non-residual postemergence (POST) herbicide that has the ability to control weeds considered to be difficult to control with glyphosate as well as glyphosate resistant weeds.  However, previous research has reported grass weed control with glufosinate may be inadequate and may require additional management inputs.  Clethodim, a graminicide herbicide is a POST annual and perennial grass control product that does not cause injury to dicotyledonous weeds or crops.  Producers often chose to tank mix herbicides to broaden the spectrum of weed control, improve efficacy and reduce application cost by combining applications.  However, combinations of graminicides with herbicides used to control broadleaves typically result in antagonism.  There have been conflicting reports of annual grass antagonism from graminicides applied before or after glufosinate.  This could be due to the size of the grasses at the time of glufosinate application or that the antagonism is species specific.  Barnyardgrass is considered to be one of the most troublesome grasses in soybean production systems in the Southern United States.  Therefore, field experiments were conducted at the Black Belt Research Station in 2013 and 2014 to determine if sequential applications of glufosinate either before or after clethodim will reduce or alleviate antagonism.  In 2013, the experiment was conducted in a fallow field with an average barnyardgrass population of 1,205 plants/m².  In 2014, Pioneer 95L01 soybeans were planted May 19 to evaluate the potential effect on yield, with an average barnyardgrass population of 269 plants/m². In both 2013 and 2014, the experimental design was a randomized complete block with plots 2.8 by 9.1 m in size.  Treatments included glufosinate (594 g ai/ha) applied 7, 3 or 1 day(s) before (DB) clethodim (76 g ai/ha), clethodim (76 g ai/ha) tank-mixed with or without glufosinate (594 g ai/ha), and glufosinate (594 g ai/ha) applied 1, 3 or 7 day(s) after (DA) clethodim (76 g ai/ha).  A crop oil concentrate (1% v/v) was included in all clethodim applications.  Clethodim applications were applied on day 0 to eliminate any control differences due to barnyardgrass plant size.  Data collected included barnyardgrass control 7, 14, 21, 28 and 56 DAT, barnyardgrass biomass (g/m²) collected at 56 DAT and soybean yield.

At 14 DAT, all treatments had greater barnyardgrass control compared to clethodim applied alone, except when glufosinate was applied 3 DA clethodim.  By 28 DAT, all treatments effectively controlled barnyardgrass greater than clethodim applied alone.  However, by 56 DAT, significant regrowth from the crown occurred in all treatments except when glufosinate was applied 7 DB clethodim.  When compared to the tank-mix of clethodim + glufosinate, barnyardgrass biomass was reduced 88 and 76% when glufosinate was applied 7 DB and 7 DA clethodim, respectively.  Differences in soybean yield were not significant due to time of glufosinate application in relation to the application of clethodim, with soybean yield ranging from 1,958 to 2,713 kg/ha.

Glufosinate alone may not adequately control annual grasses, thus requiring additional management inputs.  In times of less than adequate grass weed control, producers may consider tank-mixing glufosinate and clethodim.  Our data suggests that applying glufosinate 7 DB clethodim provides greater season long control of ECHCG compared to clethodim applied alone or the tank-mix of glufosinate and clethodim.  Data from previous research of glufosinate and clethodim antagonism with goosegrass and other summer annual grass species differ from our results, suggesting that the glufosinate-graminicide antagonism complex may be species specific.  

Palmer amaranth is the most troublesome herbicide-resistant weed in row-crop production in the southern United States.  Currently, PPO-inhibitor herbicides (Group 14) including fomesafen and flumioxazin are used extensively for Palmer amaranth control in the Southeastern United States across many cropping systems.  Norflurazon, a Group 12 herbicide, is currently labeled for use in cotton, but not used to a significant degree.  Currently, fluridone, a member of the same mode-of-action group as norflurazon, is being evaluated as an at-plant herbicide for Palmer amaranth control in cotton.  In an effort to broaden the modes-of-action available in the cotton herbicide portfolio and delay resistance to the PPO-inhibitor family, field experiments were conducted at the Edisto Research and Education Center in 2014 near Blackville, SC to evaluate the efficacy of at-plant norflurazon and fluridone herbicide programs on Palmer amaranth control in glufosinate-tolerant cotton.  Experimental design was a randomized complete block design with individual plot sizes of 3.8 by 12 m.  Treatments were replicated 4 times in all experiments.  Herbicides were applied in water using a tractor mounted air pressurized sprayer calibrated to deliver 240 L/ha with a pressure of 234 kPa.  Each site was naturally infested with pitted morningglory, mixed population of glyphosate-resistant and sensitive Palmer amaranth, and large crabgrass.  At-plant preemergence (PRE) treatments included norflurazon at 1.4 kg ai/ha, fluridone at 0.22 kg ai/ha plus fomesafen at 0.14 kg ai/ha, fomesafen at 0.28 kg ai/ha, and fomesafen at 0.28 kg ai/ha plus diuron at 0.28 kg ai/ha. Over-the-top postemergence treatments included glufosinate at 0.59 kg ai/ha plus s-metolachlor at 1.1 kg ai/ha (POST1) followed by glufosinate at 0.59 kg ai/ha plus acetochlor at 1.26 kg ai/ha (POST2).  The layby treatment of MSMA at   2.23 kg ai/ha plus diuron at 0.90 kg ai/ha was applied shortly before row closure.  Data collected included percent visual weed control and crop injury on a scale of 0 to 100 with 0 being no control or injury and 100 indicating complete weed control or crop death.  Cotton was machine harvested from the middle 2 rows of each plot.  Data were subjected to ANOVA and means were separated using Fisher’s Protected LSD at the p = 0.05 level.  Fluridone plus fomesafen and norflurazon at 14 days after treatment (DAT) [POST1 application] provided 100% control of Palmer amaranth.  Fomesafen and fomesafen plus diuron also provided excellent control of Palmer amaranth at 14 DAT.  At the POST2 application, Palmer amaranth control was greater than 95% except for the fomesafen PRE alone treatment (80%).  Cotton injury from the treatments was minor (less than 10%) throughout the study.  Seed cotton yields among the herbicide treatments ranged from 2828 to 3137 kg/ha.  In summary, norflurazon and fluridone PRE programs provided good to excellent control of Palmer amaranth, pitted morningglory, and large crabrass.  Aside from the cost, the addition of these two herbicides will provide a viable mode-of-action alternative for PPO-inhibitors in cotton production.  

Crested floating heart (Nyphoides cristata) has been rapidly spreading northward since it was first observed in Naples, Florida in 1996. Despite the apparent threat to our waterways, little published data on the growth characteristics of this highly invasive plant are currently available. It is widely recognized that crested floating heart can reproduce vegetatively via the production of daughter plants, much like water lettuce and water hyacinth.  In 2014 research was initiated at North Carolina State University to document reproductive potential. In particular, studies focused on the production of seed and on vegetative reproduction via leaf and stem fragmentation. On average 10 ovules were observed per crested floating heart fruit. Of mature fruit harvested, an average of 1 or 2 seeds appeared to be mature and the remaining ovules appeared to be aborted.  In cut stem fragmentation studies, 100% of the plants cut at the stem approximately one inch below the leaf produced new roots and 83% produced new daughter leaves. In leaf fragment studies in which leaves were cut from the stem and then segmented in half, 87% of the leaf fragments produced mature roots and daughter leaves and only one of the leaves died prior to the production of mature roots. These preliminary findings and their potential impacts to management strategies and concerns will be discussed. 

A thorough understanding of the emergence pattern of weeds is critical to developing effective season-long management strategies.  Research was conducted across eight states in the Midsouth and Midwest in 2013 and 2014 to characterize the emergence pattern of Amaranthus species, particularly Palmer amaranth, waterhemp, and redroot pigweed.  These experiments assessed whether one or two tillage events during the growing season would substantially change the emergence pattern at each site.   Soil moisture and temperature at a 2.5-cm depth was recorded in the plots and emergence was determined weekly beginning in early spring until the first killing frost.  Only the 2013 data will be reported here.  The first documented emergence for waterhemp occurred between April 20^th and April 26^th.  In comparison, the first emergence of Palmer amaranth was over a broader range with some sites not observing the emergence of seedlings until the second week of May.  One of the more interesting observations is that the peak emergence (date with the greatest number of emerged seedlings) for Palmer amaranth was commonly in mid- to late-May, while waterhemp peak emergence was in the early portion of June.  Thus, even though Palmer amaranth had a later start for emergence, seedling emergence peaked earlier than waterhemp.  Redroot pigweed serves as a more common and well-managed Amaranthus species for comparison to the other two problematic Amaranthus species.  First emergence and peak emergence for both waterhemp and Palmer amaranth were typically prior to redroot pigweed.  This provides further evidence, over the broad geographies encompassed in this research, that the early and persistent emergence of waterhemp and Palmer amaranth are critical aspects that contribute to the challenge in managing these species.  In addition, it highlights the importance of residual herbicides as a foundation for an effective management system.

The economic importance of wheat is worldwide because it is used for a large number of processed foods for humans and animals. The advances in genetic engineering have obtained new varieties of genetically modified crops with advantages for farmers to facilitate a better weed control. Triticum aestivum “T-590” varieties with resistance to glufosinate (genetically modified) and “Pantera” with resistance to imazamox (non-genetically modified with tolerance to imidazolinone herbicides) were hybridized and ten lines were obtained. The two best lines were resistant to the application of glufosinate + imazamox showing multiple resistance. This study examined the multiple resistance with dose-response experiments and a spray retention assay of these two lines in comparison with the sensitive variety "Gazul". A line with similar morphological characteristics to “Pantera” showed a GR₅₀ value of 128.51 g ia ha^-1 and the line with similar morphological characteristics to “T-590” showed a GR₅₀ value of 56.00 g ia ha^-1 obtaining a resistance factor (FR) of 2.29. “Gazul” showed a value of 14.15 g ia ha^-1. The “Pantera” line had a FR value of 9.08 respect to “Gazul”. No significant differences were found in spray retention with values of 0.31 and 0.24 µL spraying glyphosate g^-1 dry matter in “Pantera” and “T-590”, respectively. Spray retention values in “Gazul” were similar to the previously mentioned. These results suggest that multiple resistance is present in these lines and further study is required to achieve commercial varieties with this advantage in the future.

Repeated glyphosate application on large weed-infested areas has led to the emergence of resistant biotypes. In recent years, the Spanish citrus crop farmers have been concerned about the appearance of Eleusine indica and Paspalum distichum, grass species that are difficult to control in groves with a long history of glyphosate application. Glyphosate resistance in both species with a large distribution in Spain was examined in greenhouse, laboratory and field experiments. In vivo tests on whole plants revealed no differences between glyphosate-treated (T) and non-treated (NT) populations of P. distichum and E. indica. However, P. distichum population is more sensitive to glyphosate than the E. indica population. No differences were observed in the foliar retention of the glyphosate and shikimate accumulation acid in the T and NT populations of both species. However, the values of both parameters were greater in P. distichum compared to E. indica. No significant differences in the foliar absorption of ¹⁴C-glyphosate were found at 96 hours after treatment between species. The ¹⁴C-glyphosate translocation from the treated leaf to the rest of the plants and roots was higher in P. distichum than in E. indica.  In field experiments, chemical control alternatives were carried out for E. indica and P. distichum in two different groves for two years. Flazasulfuron and Cycloxidim provided more than 90% of the control of both species for 60 days after treatment. Glufosinate, Oxyfluorfen, Paraquat and Iodisulfuron provided 90% of the control only for E. indica. Glufosinate, Iodisulfuron, Paraquat and Glyphosate (1440 g ae ha^-1) provided a control that was less than 90%, but more than 81%, for P. distichum. These results confirmed that, despite the history of glyphosate application, E. indica and P. distichum populations have not developed resistance yet. It is recommended that different measures of the integrated weed management should be taken to prevent herbicide resistance.

Glyphosate is the main herbicide in Mexico used in perennial crop systems such as citrus. Veracruz is the main citrus producer and the largest consumer of glyphosate. In commercial citrus groves subject to weed management based on the use of herbicides, it has caused great changes in weed flora. Recently, Leptochloa virgata has been confirmed as the first resistant species in these crops. Furthermore, we have identified species with some levels of glyphosate tolerance such as Physalis sp. This genus is a widely distributed solanacea that includes wild and cultivated species. The tolerance of physalis sp. could be transferred to cultivated species susceptible to glyphosate by breeding such as P. ixocarpa. To determine the tolerance level in Physalis sp., greenhouse and laboratory assays were carried out comparing it with Physalis ixocarpa. Dose-response assays indicate that Physalys sp. was 22.24 times more tolerant to glyphosate than P. ixocarpa. The spray retention assays indicate that P. ixocarpa kept twice as much of herbicide solution (µL g^-1 dry weight) than Physalis sp. In addition, shikimic acid accumulation (mg g^-1 fresh weight) was highly significant at 96 HAT when glyphosate was applied at 150 y 300 g ae ha^-1. P. ixocarpa accumulated 15.7 and 12.4 times more shikimic acid than Physalis sp., respectively. Qualitative assays with ¹⁴C-glyphosate translocation showed poor penetration and translocation to the rest of the plant and root in Physalis sp. The observed tolerance could be utilized in crop species such as P. ixocarpa by a plant breeding program.  

Black oat (Avena strigosa) and velvet bean (Stilozobium aterrimum) are important cover species preceding the corn crop in Brazil. This study is aimed to evaluate the complementary effect of associating different levels of black oat or velvet bean straw covers with atrazine doses in weed control and maize yield. Two field experiments were conducted in a different block with a split plot design with four replications. The main plots had four random straw levels (0, 0.75, 1.5 and 3 times the amount originally produced), corresponding to 0, 3037, 6075 e 12150 kg ha^-1 of oat (Exp 1) or 0, 1387, 2775 e 5550 kg ha^-1 velvet bean (Exp 2). The subplots had four different doses of atrazine (0; 2100; 4200 and 8400 g ha^-1). The use of straw species coverage on the ground, even at higher levels, was not enough to exercise full weed control. The combination of atrazine 2100 g ha^-1 and the absence of velvet bean straw on the soil were not effective to control the weeds. However, only 1387 kg ha^-1 of straw velvet bean (a lower level than the productive potential of the species) makes it possible to get full weed control supplementing the effect of this herbicidal dose. This study shows that by using straw it is possible to reduce the atrazine levels used, which demonstrates the efficacy of the integration of these management practices.

SYN-A205: A TECHNICAL OVERVIEW.  R. Jackson*¹, S. Payne², R. D. Lins³, G. Vail⁴, M. Saini⁴; ¹Syngenta, Carrollton, MS, ²Syngenta, Slater, IA, ³Syngenta, Byron, MN, ⁴Syngenta, Greensboro, NC

ABSTRACT

SYN-A205 is a multiple mode-of-action herbicide premix that provides preemergence and early postemergence control of grass and broadleaf weeds in corn.  SYN-A205 will be labeled for preemergence and postemergence use in field corn and seed corn and for preemergence use only in sweet corn, and yellow popcorn. SYN-A205 contains mesotrione, S-metolachlor, and bicyclopyrone, a new HPPD (4-hydroxyphenyl-pyruvate dioxygenase) inhibitor, with anticipated first commercial applications in the 2016 growing season. Field trials demonstrate that SYN-A205 is safe when applied to field corn, seed corn, sweet corn and yellow popcorn.  SYN-A205 is effective on difficult-to-control weeds, including giant foxtail (Setaria faberi), common lambsquarters (Chenopodium album), common ragweed (Ambrosia artemisiifolia), giant ragweed (Ambrosia trifida), Palmer amaranth (Amaranthus palmeri) and waterhemp (Amaranthus rudis) with improved residual control and consistency compared to commercial standards.

Weed control in reduced tillage systems has been reported as a challenge in cotton production. Cost related to herbicide usage has increased tremendously due to development of herbicide-resistant weeds. The use of cover crops in conservation tillage offers many advantages such as weed suppression through physical and chemical allelopathic effects. Federal conservation payments are available for growers that want to include cover crops as a means to reduce tillage and increase weed suppression. A field study was initiated in the fall of 2013 at the Arkansas Agricultural Research and Extension Center in Fayetteville to determinate the adequate cereal rye seeding rate and planting method for optimum weed control and cotton yield. This experiment was a split-plot design with the main plot being cereal rye seeding rates at 50, 100 and 150 lb/A in absence or presence of a herbicide program.  Subplots consisted of drilled and broadcasted planting methods. Cereal rye biomass was collected at cotton planting and weed control was visually assessed at 2, 4, 6, and 8 weeks after planting. Seedcotton yield was also collected. No significant differences were observed between planting methods in any parameter evaluated. Cereal rye biomass production increased as seeding rate increased. Cereal rye by itself was more effective on Palmer amaranth suppression than barnyardgrass. When herbicides were not applied, cereal rye at 50 lb/A provided the least weed control. Cereal rye at 100 and 150 lb/A provided comparable levels of weed control. All plots treated with a standard herbicide program had weed control greater than 98% for all species, regardless of the seeding rate. Yields from plots with the standard herbicide program were significantly higher than from plots without herbicide, independent of seeding rates.  Yield improvement was observed due to use of cereal cover crop in the system compared to no cover crop. 

Herbicide-resistant weeds are a growing problem in the U.S. and around the world. To preserve the efficacy of the herbicides that are currently in use, diverse weed control tactics must be brought into current production systems. Harvest Weed Seed Control measures similar to those currently used in Australian cropping systems are being evaluated for use in U.S. soybean production at the University of Arkansas. A field experiment was conducted in 2014 at the University of Arkansas Northeast Research and Extension Center in Keiser, Arkansas to characterize the amount of heat resulting from narrow-windrow burning of soybean chaff passing through a 41-cm wide chute attached to the rear of a combine.  Additionally, the effectiveness of the burn in destroying weed seed was determined.  The amount of soybean chaff was varied by adjusting the swath width on the combine (10, 9, 8, 7, 6, & 5 rows, respectively), and chaff was collected and weighed in 1-m of chaff row near the location in which the burn took place. Small aluminum tins (5-cm diameter) each containing 100 Palmer amaranth, barnyardgrass, johnsongrass, and pitted morningglory seeds were placed inside the windrows at the soil surface and the temperature and duration of the burn near the seed was recorded with a thermocouple.  Maximum temperatures recorded during the burn, depending upon wind speed and amount of chaff present, ranged from 188 C to 680 C.  The duration in which the burn was above 100 C near the seed was generally 8 to 33 minutes.  Based on visual inspection, most of the Palmer amaranth, barnyardgrass, and johnsongrass were ash following the burn.  Pitted morningglory appeared to be the most resilient to burning. Seed germination and viability estimates of these seeds were conducted and it was concluded that none of the seeds survived any of the burning treatments. It appears that a Harvest Weed Seed Control strategy such as narrow-windrow burning has great potential for helping manage the soil seedbank in U.S. soybean production and this seed destruction practice should aid resistance management in fields in which it is practiced. 

COTTON AND WEED RESPONSE TO PYROXASULFONE APPLIED PREEMERGENCE AND POSTEMERGENCE. C.J. Webb¹, J.W. Keeling², P.A. Dotray³, ¹Texas A&M AgriLife Research, ²Texas Tech University Lubbock, TX

The most common annual broadleaf weed in Texas High Plains cotton is Palmer amaranth (Amaranthus palmeri). For many years it has been controlled successfully with a combination of soil residual herbicides, glyphosate, and cultivation. Glyphosate-resistant Palmer amaranth, first identified in this region in 2011, has increased dramatically in recent years. Pyroxasulfone, marketed alone as Zidua or in a pre-mix with carfentrazone-ethyl (Aim) and sold as Anthem Flex, has excellent activity on Palmer amaranth. Previous research suggests that there is potential for cotton injury when these products were applied preemergence, especially in coarse textured soils.

Field studies were conducted in 2014 on different soil textures to evaluate cotton response and Palmer amaranth control following Zidua and Anthem Flex applied early-preplant (EPP), preemergence (PRE), and postemergence-directed (PDIR). Early-preplant and PRE treatments of Zidua (1.5oz/a), Warrant (48oz/a), and Dual Magnum (20oz/a) were applied at Halfway (clay loam soil) and Lamesa (sandy loam soil). Preemergence treatments of Anthem Flex (1.38, 1.84, 2.75, 3.68, 5.54, 7.7oz/a) and Caparol (26, 38oz/a) were applied at Lamesa and Lubbock (loam soil). Postemergence treatments of Zidua (1.27oz/a), Warrant (48oz/a), Anthem Flex (2.76oz/a), Direx (32oz/a), Roundup (22oz/a), and Aim (1.23oz/a) were applied at Lamesa and Lubbock. Treatments were applied using a CO₂-pressurized backpack sprayer calibrated to deliver 10 gallons per acre. Plots, 4 rows by 30 feet in length, were replicated three times. Cotton injury and Palmer amaranth control was estimated visually based on a standard scale of 0 to 100%, where 0 = no injury and no weed control, and 100 = complete crop loss and complete weed control.

Cotton was injured 20 to 65% following Zidua applied EPP and PRE, and greater injury was observed on course textured soils. Cotton yield was not reduced by any Zidua treatment. Zidua applied EPP and PRE at either location controlled Palmer amaranth 88 to 92% 109 days after planting. Cotton injury from 5 to 30% was observed following Anthem Flex applied PRE at the sandy loam location and greater injury was observed with increased rates at both locations. No injury or yield reduction was observed following Zidua or Anthem Flex applied PDIR and both herbicides provided excellent residual Palmer amaranth control.

Italian Ryegrass (Lolium multiflorum) is one of the most problematic weeds in the production of winter wheat in the southeast.  As herbicide resistance issues continue to develop and expand throughout the area, our options for control post emergence continue to decline.  As a result we are looking at some cultural practices that may help to suppress the problem when combined with a variety of chemical control plans.  One method studied was to improve the crops ability to compete by changing row spacing.  We compared wheat planted in 7.5 rows with a drill to those planted in approximately 3.75 inch rows.  Each row spacing received the following treatments; non-treated check, Zidua (pyroxasulfone) at 1.25 oz/a pre, Zidua at 1.25 oz/a pre fb Zidua at 1.25 oz/a post, Zidua at 1.25 oz/a pre fb Osprey (mesosulfuron) at 4.75 oz/a and non-ionic surfactant at 0.25% v/v post, Zidua at 1.25 oz/a pre fb Axial XL (pinoxaden) at 16.4 oz/a post, Zidua at 1.25 oz/a pre fb Osprey at 4.75 oz/a and Zidua at 1.25 oz/a and non-ionic surfactant at 0.25 % v/v post, Zidua at 1.25 oz/a pre fb Zidua at 1.25 oz/a and Axial XL at 16.4 oz/a post, Osprey at 4.75 oz/a and non-ionic surfactant at 0.25% v/v post, Axial XL at 16.4 oz/a post, Osprey at 4.75 oz/a and Zidua at 1.25 oz/a and non-ionic surfactant at 0.25 % v/v post, Zidua at 1.25 oz/a and Axial XL at 16.4 oz/a post, Axiom (flufenacet and metribuzin) at 8 oz/a at spike.  Visual ratings did not show differences in control between the two planting arrangements.  One location had very little ryegrass population, but population densities were recorded in the other location.  Densities did not show differences between row spacing practices. 

Differential Tolerance of Glyphosate-Resistant Palmer amaranth to Mesotrione in Arkansas

Shilpa Singh*¹, Nilda R. Burgos¹, Vijay Singh¹ and Vinod Shivrain²

¹University of Arkansas, Fayetteville, Arkansas, ²Syngenta Crop Protection, Vero Beach, FL

Palmer amaranth is an economically troublesome and difficult-to-control weed in the United States. Rapid and widespread evolution of resistance to glyphosate and Group 2 herbicides has limited the chemical control options in infested fields. The response of Palmer amaranth populations to alternative herbicides in HR (herbicide-resistant) crops was evaluated to determine inherent variability among and within populations to aid in the proactive approach to resistance management. These populations were generally resistant to glyphosate. Bioassays were conducted in the greenhouse at the Arkansas Agricultural Research Station, Fayetteville, in 2013-14. Seeds were collected from crop fields across Arkansas between 2008 and 2012. Seedlings (7-10 cm tall) were treated with mesotrione, 1x rate (105 g ai ha^-1) with COC (1% v/v) and liquid AMS (2.5% v/v). The bioassays were conducted twice with two replications, with 50 seedlings per replication. Injury was recorded at 3 wk after treatment on a scale of 0-100% where 100% is complete death. Mesotrione killed 97% of plants in 51 of 57 populations; the remaining 7 populations had survivors with different levels of injury ranging from 67% - 90%. The populations with survivors showing lower injury levels were selected for estimation of tolerance level. Dose response assays were conducted with 4 putative tolerant populations. A mesotrione-resistant population of tall waterhemp was used as reference. In the dose-response assays, survivors were observed only at sub-lethal doses and the average predicted rate of mesotrione that would control these populations 50% (GR₅₀) was 21.5 g ai ha^-1. Mesotrione controlled the glyphosate-resistant accessions 88%-97%. It is an effective supplemental tool for managing glyphosate-resistant Palmer amaranth and should be used in combination with other herbicides to avoid escapes. 

Palmer amaranth (Amaranthus palmeri) and common waterhemp (Amaranthus tuberculatus) have become increasingly troublesome weeds throughout the United States. Both species are highly adaptable, dioecious, exhibit rapid growth, and are highly fecund, capable of producing hundreds of thousands of seeds per plant. These weedy characteristics contribute to the competitiveness of Amaranthus spp. with agronomic crops and facilitate the rapid spread of herbicide resistance.  The effectiveness of nineteen future preemergence (PRE) herbicide programs were evaluated on glyphosate-resistant Palmer amaranth in 2013 and 2014 at locations in Arkansas, Indiana, Nebraska, Illinois, and Tennessee. These same programs were also evaluated on glyphosate-resistant waterhemp at locations in Illinois, Missouri, and Nebraska. Locations evaluating the same species were analyzed together with location and year as a random effect. The PRE programs were also subjected to a regression analysis to determine how percent control for each treatment degraded over time. PRE programs for Palmer amaranth were evaluated for percent control up to 8 weeks after application and for waterhemp up to 5 weeks after application. Inverse prediction using a regression analysis was conducted on these data for each herbicide treatment to predict the amount of time each program will provide greater than 75% control. Comparing the inverse prediction means and confidence intervals for those means provides a measure of the strength and consistency of each program across environments and years. Dicamba at 0.5 lb ae/A, metribuzin at 0.375 lb ai/A, and 2,4-D at 0.5 and 1.0 lb ae/A provided less than three weeks of acceptable control (>75%) of Palmer amaranth across all site-years.  Dicamba + S-metolachlor + metribuzin, isoxaflutole + metribuzin, isoxaflutole + metribuzin + S-metolachlor, pyroxasulfone, flumioxazin + pyroxasulfone, and mesotrione + S-metolachlor all provided greater than 8 weeks of acceptable control across all site years. Results were similar for waterhemp except that locations were only rated up to 5 weeks after application. Except for dicamba at 0.5 lb/A and 2,4-D at both rates, all treatments provided at least 3 weeks of acceptable control of tall waterhemp. Isoxaflutole + S-metolachlor, isoxaflutole + metribuzin, isoxaflutole + metribuzin + S-metolachlor, pyroxasulfone, flumioxazin + pyroxasulfone, and mesotrione + S-metolachlor all provided greater than 5 weeks of acceptable control across all site-years. In both experiments, treatments providing less than three weeks of acceptable control also had significantly less control of each species according to visual ratings collected 3 to 4 weeks after application.

Barnyardgrass [Echinochloa crus-galli] is the most problematic weed in Arkansas rice production. The physiological and biochemical capability of barnyardgrass to quickly evolve resistance continues to limit herbicide options for control.  Sharpen^® is a new contact herbicide labeled for broadleaf weed control in rice.  Acetyl-CoA carboxylase (ACCase)-inhibiting herbicides, often referred to as graminicides, are systemic and provide an effective barnyardgrass control option in rice.  When tank-mixing graminicides with contact herbicides, a reduction in graminicide efficacy is often observed.  Hence, a greenhouse study was conducted at the University of Arkansas Altheimer Laboratory in Fayetteville, AR to evaluate ACCase-inhibiting herbicides alone and tank-mixed with two rates of Sharpen^® for barnyardgrass control. The two rates of Sharpen were evaluated in separate experiments, both of which were setup as a randomized complete block design with three tank-mix partners applied with and without Sharpen^® along with a nontreated control.  All treatments contained crop oil concentrate (COC) at 1% v/v. Barnyardgrass was maintained under saturated conditions in pots containing potting mix. Graminicides evaluated alone and with Sharpen^® included Clincher^® (cyhalofop) at 15 fl oz/A, Ricestar HT^® (fenoxaprop) at 24 fl oz/A, and Targa^® (quizalofop) at 20.7 fl oz/A. All herbicides were applied to 6- to 8-leaf barnyardgrass. Tank-mixing Sharpen^® with either of the three graminicides, regardless of Sharpen rate, did not reduce barnyardgrass control, and for several combinations barnyardgrass control improved with the addition of Sharpen^® over the graminicide applied alone.  Based on these results, Sharpen^® tank-mixed with graminicides labeled for use in rice should be a good option in fields where both broadleaf and grass weeds are present.

With the stress that herbicide-resistant weeds put on our current production systems, new technologies are needed to control these weeds.  BASF is currently developing a new non-GMO rice trait that will be resistant to quizalofop, an acetyl coenzyme A carboxylase (ACCase)-inhibiting herbicide. The Provisia™ rice system will provide an additional herbicide trait to be used in Midsouth rice production systems.  A field experiment was conducted in the summer of 2014 at the University of Arkansas Rice Research and Extension Center in Stuttgart, Arkansas to determine the best rate structure for sequential applications of quizalofop when the first application is made at either the 2- or 6-leaf stage of grass weeds.  The experiment was set up as a two factor, randomized complete block design with factor-A being the growth stage at first application and factor-B being the rate structure of quizalofop.  This experiment was evaluated for two different growth stages of initial herbicide application.  Herbicide rate structures were 80, 120, or 160 g ai/ha followed by 80, 120, or 160 g/ha sequential application 14 days after the initial application.  The highest total amount of quizalofop applied in a rate structure was 240 g/ha total.  Barnyardgrass and broadleaf signalgrass control were rated at 2, 4, and 6 weeks after treatment.  Greatest control of both barnyardgrass and broadleaf signalgrass was recorded with the 120/120 g/ha treatment with 99 and 98% control, respectively.  The 80/80 g/ha sequence had the least control of both barnyardgrass and broadleaf signalgrass with 89 and 90% control, respectively. Control for barnyardgrass and broadleaf signalgrass was reduced by making the first application on 6-leaf grass compared to 2-leaf grass.  The results of this experiment suggest that the most likely recommended rate structure for quizalofop will be 120 g/ha on 2-lf grasses followed by a subsequent application at the same rate approximately 14 days after the initial application.

EVALUATION OF APPLICATION DATES AND RESIDUAL HERBICIDES FOR CONTROL OF HENBIT (LAMIUM AMPLEXICAULE L.).  B.C. Woolam, D.O. Stephenson, IV, and R.L. Landry; Dean Lee Research and Extension Center, LSU AgCenter, Alexandria, LA 71302. 

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) control.  Determination of programs to effectively manage henbit are needed.  Therefore, experiments were conducted at the LSU AgCenter Dean Lee Research and Extension Center near Alexandria, LA in 2012/2013 and 2013/2014 to evaluate fall application dates for henbit control with residual herbicides.  A factorial arranged in a randomized complete block with four replications was used in all experiments. Factors consisted of five herbicide application dates and seven residual herbicides.  The five application dates were October 15, November 1, November 15, December 1, and December 15.  The seven residual herbicides were diuron 840 g ai ha^-1, flumioxazin at 72 g ai ha^-1, oxyfluorfen at 280 g ai ha^-1, pyroxsulfone at 150 g ai ha^-1, preformulated mixture of rimsulfuron:thifensulfuron at 8:18 g ai ha^-1, S-metolachlor at 1420 g ai ha^-1, and no residual herbicide.  Paraquat at 840 g ai ha^-1 plus non-ionic surfactant at 0.25% v/v was co-applied with all residual herbicide treatments to control any emerged henbit at the time of application. Visual evaluations of henbit control (0 = no control; 100 = total henbit death) were collected in late-January, mid-February, and late-March of 2013 and 2014.  Only control data collected in late-March of each year is presented.  Henbit density m^-2 and height (10 plants plot^-1) were recorded in late-March of 2013 and 2014.  Henbit density and height in the non-residual herbicide treatment averaged 13 m^-2 and 127 mm in late-March of each year.  Henbit density and height were converted to the percent of the non-residual herbicide treatment prior to analysis. 

Regardless of residual herbicide, November 1 through December 1 applications provided 69 to 84% henbit control in late-March.  Applications on October 15 controlled henbit 36% in late-March.  A lack of activating rainfall and warmer soil temperatures possibly leading to accelerated herbicide degradation may be the reason poor henbit control was observed following the October 15 application date of residual herbicides.  Averaged across application date, flumioxazin, oxyflurofen, and rimsulfuron:thifensulfuron provided 73, 86, and 84% henbit control, respectively, in late-March.  However, diuron, pyroxasulfone, and S-metolachlor controlled henbit 46, 46, and 56%, respectively, in late-March.  Regardless of residual herbicide, henbit density was 36% of the non-residual herbicide treatment following the November 1 and December 1 applications.  Similarly, henbit height was 28 and 18% of the non-residual herbicide treatment following a residual herbicide application on November 1 and December 1, respectively.  However, these data did not differ from density and height observations following the November 15 and December 15 applications.  Similar to control data, flumioxazin, oxyflurofen, and rimsulfuron:thifensulfuron reduced henbit density and height to an average of 16 and 18% of the non-residual herbicide treatment, respectively, in late-March.  Henbit density (64 to 100%) and height (52 to 61%) as a percent of the non-residual herbicide treatment following diuron, pyroxasulfone, and S-metolachlor applications was unacceptable.  Poor control in late-March following diuron and S-metolachlor application was a combination of greater henbit density and height.  However, poor control following pyroxasulfone application was a function of decreased henbit height alone in late-March.  Data indicates that flumioxazin, oxyflurofen, or rimsulfuron:thifensulfuron applied November 1 through December 1 will provide the greatest henbit control and density and height reduction prior to seeding a summer annual crop in late-March.

A study was established in a greenhouse on the Louisiana State University campus in Baton Rouge, Louisiana. The objectives were to evaluate herbicides for the control of Nealley’s sprangletop (Leptochloa nealleyi Vasey). The study was a completely randomized design with nine replications. The study was repeated. Nealley’s sprangletop seed was planted in plastic planting flats with 50 – 2.5 by 2.5 cm cells filled with potting mix until reaching one- to two-leaf growth stage. The Nealley’s sprangletop was transplanted into 6 by 10 cm cone containers filled with potting mix and placed into racks. The racks were placed in plastic containers and filled with 67 L of water for subsurface irrigation for the length of the study. Urea fertilizer, 46-0-0, was added to the water at 280 kg/ha.

Nealley’s sprangletop had one- to two-tillers with a height of 20- to 30-cm at herbicide application. Herbicides applied were: propanil at 2240 g ai/ha, propanil at 4480 g/ha, propanil plus thiobencarb at 3360 g ai/ha, propanil plus thiobencarb at 6720 g/ha, quinclorac at 420 g ai/ha, thiobencarb at 4480 g ai/ha, bispyribac at 28 g ai/ha, imazethapyr at 105 g ai/ha, imazomox at 44 g ai/ha, penoxulam at 40 g ai/ha, clethodim at 150 g ai/ha, cyhalofop at 314 g ai/ha, fenoxaprop at 122 g ai/ha, quizalofop at 185 g ai/ha, glufosinate at 450 g ai/ha, glyphosate at 840 g ai/ha. Nealley’s sprangletop control, leaf number, tiller number, and height were evaluated at 0, 5, 10, and 14 days after treatment (DAT). Fresh plant biomass was obtained at 14 DAT.

At 14 DAT, Nealley’s sprangletop treated with clethodim, fenoxaprop, and quizalofop was controlled 91 to 98%. Height and number of leaf and tillers were reduced with these herbicides compared with the nontreated. Nealley’s sprangletop treated with glyphosate and glufosinate, common burndown herbicides, controlled Nealley’s sprangletop 88 and 87%, respectively. Penoxulam and quinclorac had little to no activity on Nealley’s sprangletop. Fresh plant biomass of Nealley’s sprangletop treated with propanil or propanil plus thiobencarb at both rates, cyhalofop, fenoxaprop, clethodim, glyphosate, or glufosinate was less than 3 grams, compared with the nontreated with a fresh weight of 15 grams.

Nealley’s sprangletop is a prolific seed producer with high seed viability at maturity. It is important to correctly identify this weed in order to select the appropriate weed management program. Fenoxaprop is the best option for controlling Nealley’s sprangletop in rice production. Although not labeled in rice, Nealley’s sprangletop treated with clethodim and quizalofop was controlled 91 and 98%, respectively.

Tolerance of AVS-4002 Edamame to Sulfentrazone*

Seth Bernard Abugho, Nilda Roma Burgos, Leopoldo Estorninos Jr. and Reiofeli Salas

Department of Crop, Soil and Environmental Sciences

University of Arkansas-Fayetteville

Edamame (Glycine max L.), a vegetable soybean, is considered an emerging crop in Arkansas. However, limited herbicides are available for this crop compared to field soybean.  AVS-4002 edamame, the first commercialized variety from the University of Arkansas breeding program, was tested with different herbicides to expand herbicide options. Field studies were conducted in the summer of 2013 and 2014 at the Vegetable Research Station, Kibler, Arkansas using to determine its response to different rates  and time of application of herbicides especially sulfentrazone. The study was conducted in a randomized complete block design consisting of 11 herbicide treatments with three replications. Weedy and weed-free check plots were established for crop response and weed control evaluation reference. Stand count, crop injury, weed control, and yield were recorded. Major weeds such as red sprangletop (Leptochloa panicia Retz.), Palmer amaranth (Amaranthus palmeri L.) and barnyardgrass (Echinochloa spp.) were effectively controlled at 21 d after planting (DAP). Flexstar (0.42 kg ai ha^-1) had the highest weed control (82-100%) among the postemergence herbicides. At 21 DAP, Spartan applied preemergence (PRE) at a higher rate (0.42 kg ai ha^-1) resulted in the lowest crop stand (24% and 32%) relative to non-treated weed-free check and highest crop injury (68% and 70%) resulting in the lowest crop yield (77% lower than weed-free) in both years. Spartan Charge applied PRE caused cosmetic injury (e.g. stunting); whether applied PRE or pre-plant, this herbicide resulted in similar weed control (93-96%) and did not reduce yield. This study showed that sulfentrazone, at 0.21 kg ai ha^-1, provides good weed control and is safe for AVS-4002 edamame.

Nomenclature: preemergence, postemergence, sulfentrazone, edamame

SEQUENTIAL APPLICATIONS FOR RESCUE CONTROL OF GLYPHOSATE RESISTANT PALMER AMARANTH.  A. B. Denton, D.M. Dodds, C.A. Samples, and J. D. Copeland; Mississippi State University, Mississippi State, Mississippi 39762. 

ABSTRACT

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 and will be commercially available as Roundup Ready Xtend® crops.  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.  Substantial previous research is available regarding postemergence applications of glufosinate on GR-Palmer amaranth; however, little previous research has been conducted evaluating GR-Palmer amaranth control with dicamba.  Therefore, this research was conducted to evaluate control of GR-Palmer amaranth following sequential timings application in a rescue scenario with glyphosate + dicamba and glufosinate + dicamba.

An experiment was conducted in 2014 at Hood Farms in Dundee, MS to determine the effect of timing between sequential applications and herbicide program on GR-Palmer amaranth control.  The experiment was initiated in a grower field 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.  Applications were made with a CO₂ powered backpack sprayer at a pressure of 317 kPa and an application volume of 140 L/ha. 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.  All herbicide treatments were applied using Turbo Teejet Induction 110015 tips.  Visual estimates of weed control, the number of Palmer amaranth plants per square meter, count reduction of Palmer amaranth plants per square meter, height of Palmer amaranth plants per square meter, and height reduction of Palmer amaranth plants per square meter were collected at two and four weeks after each herbicide application.  Experiments were conducted using a factorial arrangements of treatments in a randomized complete block design with four replications.  Visual estimates of weed control, number of plants per square meter, count reduction, plant height, and plant height reduction data were subjected to analysis of variance and means were separated using Fisher’s Protected LSD at p = 0.05.

Four weeks after final applications, GR-Palmer amaranth percent height reduction was significantly greater when applications were made ≤ 3 weeks after initial treatment with height reductions ranging from 78 to 82% for plants initially treated at 20 to 25 cm in height.  Sequential applications following initial application to 20 to 25 cm Palmer amaranth made ≥ 2 weeks after initial application significantly reduced Palmer amaranth counts from 59 to 82%.  Sequential applications containing glufosinate + dicamba applied 1, 2, and 3 weeks after initial application maximized height reductions compared to other treatments when initial applications were made to 40 to 50 cm GR-Palmer amaranth.  Sequential application tank mixtures containing glufosinate + dicamba provided more consistent control of 40 to 50 cm Palmer amaranth. 

Sequential herbicide applications provided effective rescue control of Palmer amaranth.  Control was not ideal but can facilitate crop harvest.  Sequential applications should be made no later than 3 weeks after initial application regardless of Palmer amaranth size.  

Glyphosate-resistant (GR) Italian ryegrass (Lolium perenne ssp. multiflorium) has been identified in 70 counties across Mississippi.  Multiple resistance to glyphosate, acetolactate synthase- and Acetyl CoA carboxylase-inhibiting herbicides is also common in Mississippi.  Previous research in Mississippi has demonstrated that a minimum of two herbicide applications were required for >90% control of GR Italian ryegrass and that corn yield and economic returns were optimized following herbicide programs that included fall and spring herbicide applications.  Additional research is needed to identify the optimum timing for GR Italian ryegrass control and to understand the effect of GR Italian ryegrass residue on corn growth and yield.  The objective of this research was to determine the effect on corn growth and yield of GR Italian ryegrass residue present at the time of planting. 

Research was conducted in 2014 at the Mississippi State University Delta Research and Extension Center in Stoneville, MS, at a site known to be infested with GR Italian ryegrass.  Individual plots were four 40-inch rows that were 40 feet in length.  The experimental design was a randomized complete block with four replications.  Treatments were defined as intervals at which GR Italian ryegrass was controlled prior to corn planting and included 49, 28, 21, 14, 7, and 0 days before planting (DBP).  A nontreated control (NTC) was included for comparison.  At each prescribed interval, designated plots were treated with paraquat at 1 lb ai/A plus nonionic surfactant.  After reaching the prescribed interval for each treatment, complete control of GR Italian ryegrass was maintained thereafter.  All plots received at least two herbicide applications prior to planting.  Corn was planted March 20, 2014, at a rate of 26,000 seed/A.  All plots except the nontreated control were maintained weed-free after planting.  Nontreated control plots were treated with glyphosate at 0.77 lb ae/A plus atrazine at 1.5 lb ai/A to control all weed species except GR Italian ryegrass.  Corn height in each plot was recorded at weekly intervals from emergence through canopy closure.  Crop growth rate (CGR) was calculated from corn height data.  Corn yield data were adjusted to 15.5% moisture content.  Gross economic returns were calculated by multiplying the yield for each plot by average farm price for corn of $5.35 per bushel received by Mississippi producers in 2013.  All data were subjected to ANOVA with means separated by Fisher’s Protected LSD test at P≤0.05.

When GR Italian ryegrass was left uncontrolled (NTC), crop growth rate for corn was 80% lower than when GR Italian ryegrass was controlled at planting (0 DBP).  Crop growth rate was similar for control intervals of 7, 14, and 21 DBP.  However, an increase in CGR of ≥ 1 cm/day was observed when GR Italian ryegrass control was initiated >21 DBP.  No corn was present at harvest where GR Italian ryegrass was not controlled prior to planting.  Corn yield and gross economic returns increased as the interval before planting for GR Italian ryegrass control increased from 0 to 7, from 7 to 21, and from 14 to 28 DBP.  However, corn yield and gross economic returns were optimized when GR Italian ryegrass control was triggered at least 21 DBP.  Gross economic returns were $190/A greater when GR Italian ryegrass was controlled at 21 compared with 0 DBP.  

Glyphosate-resistant Italian ryegrass should be controlled ≥ 28 DBP to optimize CGR; however, corn yield and gross economic returns were optimized with control at 21 DBP.  When GR Italian ryegrass was controlled 21 DBP, corn compensated for reduced CGR observed early in the season because yield following control initiated 21 DBP was similar to when control was initiated 28 or 49 DBP.  All GR Italian ryegrass was completely controlled at planting, and plots were maintained weed-free from planting to harvest.  Therefore, reductions in CGR and yield were strictly due to interference from GR Italian ryegrass residue.  Although not evaluated in this experiment, interference was likely due to the quantity of GR Italian ryegrass residue or possible allelopathic effects.  

INFLUENCE OF SOYBEAN MATURITY GROUP ON RECOVERY FROM DICAMBA INJURY.

M.S McCown¹, L.T Barber², and J.K Norsworthy¹

¹Department of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, AR.

²Deparment of Crop, Soil, and Environmental Sciences-Extension, University of Arkansas, Little Rock, AR. 

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. This trial was conducted in 2014 at Lon Mann Cotton Research Station in Marianna, Arkansas. The purpose of this study was to determine if soybean cultivar and maturity group has an influence on recovery from dicamba injury. Four susceptible soybean cultivars were chosen based on relative maturity and included Progeny 4650, Go Soy 5111, HBK 4950, and Halo 5.45. Dicamba was applied at 1.42g ae ha^-1 (1/64x rate) at V3 and R1 soybean growth stages. 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.  During this experiment weeds were managed with a glufosinate herbicide weed control program consisting of pre-emerge herbicides and glufosinate plus metolachlor POST. Significant difference in recovery from herbicide injury was observed between maturity groups. Progeny 4650 and Go Soy 5111 cultivars reached maturity 7 days prior to the HBK 4950 and Halo 5.45 cultivars. With treatments applied at V3, 1-6% yield loss was observed for early maturing cultivars (Progeny 4650, Go Soy 5111) whereas later maturing cultivars expressed 6-12% yield loss (HBK 4950, Halo 5.45). With treatments applied at R1, yield loss of 7-23% was observed for early maturing cultivars whereas 40-42% yield loss was observed for later maturing cultivars. Early maturing cultivars had a greater amount of recovery in comparison with later maturing cultivars; however, the yield potential of each cultivar influenced yield loss. Progeny 4950 treated with dicamba averaged greater yields than untreated Go Soy 5111 cultivars. Future studies will be conducted to determine if cultivar variety in comparison with maturity group have an effect on recovery from dicamba injury.

DICAMBA-TOLERANT SOYBEAN WEED MANAGEMENT SYSTEMS.

Anthony Growe, Dennis Williamson, Tony White, Wesley  Everman, North Carolina State University, Raleigh, North Carolina.

ABSTRACT

Due to glyphosate-resistant weed biotypes becoming more common in North Carolina agricultural systems, new technologies, such as the development of dicamba tolerant soybeans, will be available to integrate into current weed management systems.  An experiment was conducted at the Upper Coastal Plain research station in Rocky Mount, NC to examine the effectiveness of weed management strategies involving experimental dicamba, dicamba premixes and flumioxazin in dicamba- tolerant soybeans.   Various weed species, including Palmer amaranth (Amaranthus palmeri), were treated with various rates and herbicide combinations to determine greatest control.  Plots were rated 23, 38 and 52 DAP. Results exhibited greater Palmer amaranth control when an effective PRE followed by a POST was utilized.  All POST systems obtained statistically similar weed control.  The experimental dicamba PRE followed by POST of dicamba/glyphosate premix had greater control than a PRE of dicamba alone.  All treatments with a PRE followed by POST exhibited more than 89% control of Palmer amaranth.

Every year there are multiple reports of drift occurrences in rice.  With a large percentage of other crops being Roundup Ready (glyphosate-resistant) and approximately 50% of Arkansas rice being non-Clearfield (imidazolinone-tolerant), the majority of drift complaints in rice are from Newpath (imazethapyr) and Roundup (glyphosate).  In 2014, a field experiment was conducted at the Rice Research and Extension Center in Stuttgart, Arkansas and at the University of Arkansas Pine Bluff Farm in Lonoke, Arkansas to evaluate whether or not insecticide seed treatments could reduce injury from Roundup or Newpath drift or decrease the recovery time of the rice.  Roy J rice was planted and simulated drift events of a 1/10X rate of Newpath or Roundup was applied to each plot.  Each plot had either a seed treatment of CruiserMaxx Rice, NipSit Inside, Dermacor X-100, or no seed treatment.  The simulated drift event was applied at the 2- to 3-leaf growth stage.  Crop injury was assessed immediately prior to establishing the permanent flood (preflood) and two and four weeks after flooding. At preflood, all insecticide seed-treated rice showed reduced injury from low rates of Roundup, and rice treated with NipSit Inside or CruiserMaxx Rice showed reduced injury from Newpath. At Stuttgart, CruiserMaxx Rice and NipSit reduced injury from Newpath initially while NipSit Inside also provided reduced injury from Roundup.  Eight weeks after application, the rice treated with CruiserMaxx Rice had recovered significantly from both Newpath and Roundup drift at both locations based on visual estimates of injury.  The rice treated with NipSit Inside had recovered from Roundup drift at both locations and Newpath drift at one location.  CruiserMaxx Rice protected the yield potential of the rice after Roundup and Newpath drift at both locations.  NipSit Inside protected rice against yield loss from Roundup drift at both locations.  Based on these results, CruiserMaxx Rice and NipSit Inside have potential to provide some safening against Newpath and Roundup drift whereas Dermacor X-100 will provide marginal of no safening to these herbicides.   

Evaluation of PRE Herbicide and Seed Treatment on Thrips Infestation and Cotton Growth, Development, and Yield. J. Drake Copeland¹, D.M. Dodds¹, A.B. Denton¹, C.A. Samples¹, A.L. Catchot¹, J. Gore², D. Wilson³; ¹Mississippi State University; ²Delta Research and Extension Center; ³Monsanto Company

ABSTRACT

Since 2011, foliar treatments for thrips in cotton in Mississippi have increased to nearly two applications per acre on 80% of total acres in spite of these acres being planted with seed treated with an insecticidal seed treatment. Additionally, glyphosate-resistant Palmer amaranth has become problematic for Mississippi producers.  As a result, the use of preemergence (PRE) herbicides has increased dramatically since 2008. From 2008 to 2012 the number of cotton bales lost due to thrips damage increased from 152 bales lost in 2008 to 5,057 bales lost in 2012. In cotton, both thrips damage and PRE herbicides can interfere with emergence and early season growth. Previous research on thiamethoxam and imidacloprid has shown both to be effective in controlling thrips in cotton. Given the increased use of PRE herbicides in Mississippi cotton production, it has been suggested that PRE herbicides may be contributing to the increase in damage from thrips observed over the past several growing seasons.  Therefore, the objective of this research was to evaluate the use of PRE herbicides and seed treatments on thrips populations as well as cotton development and yield.

Studies were conducted at three locations in Mississippi which included the Black Belt Branch Experiment Station near Brooksville, the R.R. Foil Plant Science Research Center near Starkville, and the Delta Research and Extension Center in Stoneville in 2013 & 2014. Seed treatments included thiamethoxam + fungicide, imidacloprid + fungicide, and fungicide only. Preemergence herbicides included fluometuron at 1.12 kg ai/ha, diuron at 1.12 kg ai/ha, fomesafen ay 0.28 kg ai/ha, S-metolachlor at 1.07 kg ai/ha, S-metolachlor at 1.07 kg ai/ha + fluometuron at 1.12 kg ai/ha, as well as an untreated check. Experiments were conducted using a factorial arrangement of treatments in a randomized complete block design, with the two factors being PRE herbicide and seed treatment.  All data were subjected to analysis of variance and means were separated using Fishers Protected LSD at p = 0.05.

Cotton seed treated with imidacloprid had significantly less injury from thrips than cotton seed treated with thiamethoxam and fungicide only treatments. Thrips counts at the four leaf stage indicated significantly greater infestation on cotton treated with thiamethoxam compared to cotton treated with imidacloprid. Cotton seed treated with imidacloprid resulted in significantly taller cotton plants throughout the season than those grown from thiamethoxam treated seed. Averaged across seed treatments, cotton treated with with fluometuron and fomesafen was significantly shorter at first bloom; however, heights were not significantly different than cotton treated with s-metolachlor alone. Cotton seed receiving treatment of fungicide only as a seed treatment had significantly increased nodes above cracked boll when compared to cotton seed treated with imidacloprid and thiamethoxam, indicating a delay in maturity. Cotton treated with imidacloprid produced the highest yields. No significant differences in seed cotton yield were present due to PRE herbicide. Cotton seed treatments had a significant effect on yield when averaged over PRE herbicides. Treatments that include imidacloprid produced seed cotton yields of 6017 kg/ha whereas cotton seed treated with thiamethoxam produced seed cotton yields of 5858 kg/ha. Trends in reduced thrips control with seed treatments are present, specifically with cotton treated with thiamethoxam. Even if seed treatments are applied, it is still critical to scout and treat thrips according to threshold.

Currently, the major corn hybrid companies (i.e. Pioneer and Dekalb) screen their hybrids using unsafened  ALS formulations.  Therefore, research was conducted in 2014 to  determine if  ALS herbicides that contain isoxadifen could be used  on field corn hybrids with reported ALS sensitivity.

A small plot field trial was conducted in 2014 near Tifton, GA to investigate the potential effects of a various ALS herbicides on field corn growth and yield.  Two popular corn hybrids with reported  ALS sensitivity (DKC 62-08, DKC 64-69) were planted on March 24.  Accent 75WG, Steadfast Q 37.7WG, and Capreno 3.45SC were applied at 1X and 2X labeled use rates in combination with Aatrex 4L (64 oz/A) and COC (1% v/v).   Both Steadfast Q and Capreno formulations include a crop safener (isoxadifen). Treatments were applied 18 DAP to corn in the V3 stage of growth. The plot area was maintained weed-free.  

Treatments were arranged in a split-plot design [whole plot = corn hybrid (2), sub-plot = herbicides (7)] with 4 replications.  Herbicides were applied using a CO₂ -propelled backpack sprayer calibrated to deliver 15 GPA using 11002DG nozzles.  Data collected included above-ground biomass,  plant height, and grain yield. 

DKC 62-08 produced less above-ground biomass than DKC 64-69.  All herbicides caused significant reductions in biomass.All herbicides caused significant plant height reductions at 28 DAT. However, plants recovered  by 61 DAT and at this point DKC 64-69 was taller than DKC 62-08.  There was no difference in yield between DKC 62-08 and DKC 64-69.  The only herbicide treatment that caused a significant yield reduction was the 2X rate of Capreno. Although these corn hybrids were reported to be sensitive to ALS herbicides, these data suggest that they are sufficiently tolerant of the formulations used in this test at 1x rates.

Creating a fit for grain sorghum in North Carolina cropping systems has proven a difficult challenge for several reasons, particularly in achieving effective weed management.  However, DuPont Pioneer has introduced the Inzen-Z sorghum system to provide relief for sorghum growers. Inzen is an ALS-herbicide resistant grain sorghum variety created from traditional breeding methods and is paired with their proprietary herbicide, Zest.  The proprietary herbicide Zest is a re-formulated liquid nicosulfuron product, the same active ingredient as Accent typically used for post emergence grass control in corn.  The product is awaiting final approval from the Environmental Protection Agency (EPA) and the system as a whole is expected to be available for the 2015 growing season. Thus far, Zest has been said to control foxtail species, barnyardgrass, crabgrass, witchgrass, and non-ALS resistant shattercane. However, experimentation conducted this year expanded that weed control spectrum.

From summer 2014 field experimentation results; Zest has proven to provide excellent post emergence control of grass weeds in grain sorghum.  In the 10 treatment protocol, four plots of each replication received a pre emergence application of s-metolachlor + atrazine. Of those four plots, Zest at a rate of 5 oz ai/A was combined with 2, 4-D + atrazine, pyrasulfotole + bromoxynil + atrazine, and dicamba + atrazine.  The other five plots did not receive a pre emergence herbicide application and only received a MPOST herbicide application.  Zest was applied at MPOST with atrazine, pyrasulfotole + bromoxynil + atrazine, clarity + atrazine, 2, 4-D + atrazine, and 2, 4-D + atrazine + metsulfuron. Regardless of timing, each plot received crop oil concentrate at 1% v/v and ammonium sulfate at a rate of 2 lb/A.  The final plot of each replication was a non-treated check.  

Based on herbicide efficacy ratings taken 7, 14, and 28 days after treatment (DAT) evaluating three different herbicide application timings; pre emergence (PRE), mid-post emergence (MPOST), and post emergence (POST); results were clear that including a pre emergence component is essential to staying weed-free. In every plot, texas panicum, yellow nutsedge, goosegrass, broadleaf signalgrass, and large crabgrass were better controlled in applications which contained a pre emergence herbicide application versus those which did not.  At the alpha = 0.05 level, the PRE only herbicide application provided statistically significant better control of texas panicum and large crabgrass.  In addition, the treatment tank mix of Zest + atrazine + pyrasulfotole + bromoxynil which received a PRE, proved to be a statistically significant leader in control of tough to tackle weeds such as texas panicum, goosegrass and compared to the same tank mix which did not receive a PRE. Finally, when comparing the Zest + 2,4-D + atrazine treatment which received a PRE and the treatment which did not, results are clear that including the PRE component provides a significant difference.

Broomsedge control in perennial ryegrass turf

J. R. Brewer, S. D. Askew

Broomsedge(Andropogon virginicus)(BS) is a native, perennial grassy weed that is found throughout the eastern United States. Common in pastures, cleared timber areas, rights of way, and other uncultivated areas, BS is a bunch-forming grass that can grow 2 to 4 feet tall.  Broomsedge is often associated with low fertility and low pH areas but can also be problematic in fertile pastures and lawns. Research has been conducted to evaluate methods that can efficiently control BS in pasture areas using chemicals and cultural practices. The chemical control methods include treatments of certain herbicides like glyphosate, substituted ureas (diuron), and organic arsenicals (MSMA). The cultural practices mainly focus on annual fertilizer programs that can increase desired grass competition and lower the BS percentage in the pasture over multiple years. Currently available cultural practices and herbicides are unacceptable for BS control in lawn turf because previously reported herbicides are not available or not selective in lawn turf and homeowners require immediate results and a higher degree of turf quality than typically associated with pastures.  Since few studies have evaluated lawn herbicides for BS control, our objective was to evaluate several lawn herbicides for BS in a lawn setting.

The study was conducted in Blacksburg, VA on a residential perennial ryegrass lawn mown at 6.4 cm.  The trial was initiated on August 15, 2014. The following treatments were applied twice at a 3-week interval:  mesotrione at 186 g ai/ha^-1 plus triclopyr at 1120 g ai/ha^-1, topramezone at 70 g ai/ha^-1 plus triclopyr at 1120 g ai/ha^-1, quinclorac at 1.12 kg ai/ha^-1, fenoxaprop at 140 g ai/ha^-1, fluazifop at 88 g ai/ha^-1, and metamifop at 400 g ai/ha^-1 and 1600 g ai/ha^-1.  These treatments were compared to MSMA at 2250 g ai/ha^-1 applied twice at one week interval and a nontreated check.  All mesotrione treatments included NIS, while treatments containing topramezone and quinclorac included MSO. These treatments were applied with a hooded sprayer at 280 L/ha^-1 and a speed of 4.8 km/h, and the sprayer had a 71.12 cm spray width.

Initial BS cover in the lawn plots ranged from 10 to 70%. At 3 WAIT, MSMA had completely controlled BS.  Metamifop at 1600 g/ha controlled BS 82% and more than all other herbicides except MSMA.  Fenoxaprop, fluazifop, and metamifop at 400 g/ha controlled BS 48-65%.  Quinclorac, mesotrione, and topramezone programs did not control BS more than 22%.  At 5 WAIT, MSMA controlled BS 100% and more than all other treatments.  Metamifop at 1600 g/ha controlled BS 72% and equivalent to metamifop at 400 g/ha (60%).  All other herbicides controlled BS 40% or less, and metamifop and fluazifop had controlled BS greater than 50%. All other treatments had less than 50% control of BS. At 5 WAIT, MSMA was the only treatment that completely controlled BS, and all other treatments had controlled BS 60% or less.  Only MSMA significantly injured turf in this study.  Injury was expressed as necrotic tissue and stunting and varied between 30 and 50% depending on rating date.  These data suggest metamifop, if registered, could have some utility for BS control in lawn turf while currently-registered herbicides are ineffective.

Evaluation of Interval Required for Seedling Miscanthus to Become Perennial and Effects of Cutting on Rhizome Development

D.N. Barksdale, J.D. Byrd, M.L. Zaccaro, and D.P. Russell;

Department of Plant and Soil Sciences

Mississippi State University, Mississippi State, MS.

 ABSTRACT

            In 2014, greenhouse experiments were conducted at the Plant Science Research Center, Mississippi State University, Mississippi State, MS with two objectives in mind: 1) evaluate the time interval required for Miscanthus to become perennial after germination and 2) determine if cutting seedling Miscanthus stimulates rhizome production. A variety of Miscanthus seed, ‘Powercane’ TM, was germinated in 6” x 5.5” size pots that were filled with Miracle Grow potting mix, then transplanted into 24” x 2” x 12” plexiglass sided rhizotrons after reaching an average height of 35 cm. Plexiglass sides were covered with foam board insulation to exclude sunlight. When plants reached an average height of 52 cm, half of the plants were cut to a height of 4 inches to simulate mowing. All plants were monitored weekly for rhizome initiation. The number of shoots and plant height was also recorded weekly. Rhizomes were visible on uncut plants 15 weeks after germination (WAG). Miscanthus that had the terminal removed by cutting produced visible rhizomes at 19 WAG. Cutting young Miscanthus plants delayed rhizome development up to 4 weeks. Data collected on the number of shoots and rhizomes produced, shoot height, total aboveground biomass, and rhizome biomass, revealed a significant difference (P < 0.05) in these biomass measurements between uncut and cut plants. A 65.4% decrease in the number of rhizomes produced was noted in Miscanthus plants with terminals removed compared to plants with intact terminals, respectively. However, plants with terminals removed produced 25.7% more aboveground shoots than their counterparts, respectively. This corresponded to a 45.3% increase in aboveground biomass and 11.1% increase in height for Miscanthus plants that had been cut once. Terminal removal in Miscanthus that has not been established appeared to impede rhizome development, but stimulated shoot number and height. The implications for control of escaped seedling Miscanthus is mowing seedlings will retard rhizome development, but will stimulate lateral shoot development which increases aboveground biomass and results in a thicker and denser Miscanthus stand which may be more difficult to eradicate.

TOLERANCE OF SEVERAL LEGUMES TO SOIL APPLIED IMAZAPYR. M.L. Zaccaro*, J.D. Byrd, D. Russell and D.N. Barksdale; Mississippi State University, Mississippi State – MS 

ABSTRACT

The use of nitrogen-fixing plants in pastures is an important element to provide valuable nutrients to the animal diet and contribute nitrogen to the forage system. The objective of this experiment was to evaluate the residual effects of imazapyr on the early development of several legume crops. Herbicide treatments were applied August 8, 2014 through a spray chamber that delivered 25 GPA to greenhouse containers filled with a mixture of 2:1 sand and silty clay loam soil. The design of the experiment was a complete randomized design with a factorial arrangement of treatments with 4 repetitions, which the factors were legume species, herbicide rates and planting dates. The herbicide treatments were Arsenal 2L (imazapyr) at 0, 4, 8 and 16 fl oz/A.  White clover (Trifolium repens L.) 'Durana', crimson clover (T. incarnatum L.), lespedeza (Kummerowia stipulacea (Maxim.) Makino) 'Kobe' and 'AG4934' RR/STS soybean (Glycine max (L.) Merr.) were planted 0, 1 and 3 MAT to produce 48 treatment combinations. Average fresh weight measurements were taken six weeks after each planting. Data were analyzed in PROC GLM of SAS v. 9.3, to test interactions and main effects, then means were separated by the LSMEANS with α=0.05. The interaction between plant species, imazapyr rates and planting dates was significant. Of the species tested, soybean presented superior tolerance to imazapyr, followed by lespedeza and the clovers had similar lower tolerance, with respect to mean fresh weight reduction. When considering only lespedeza, crimson and white clover, the treatment combinations with 4, 8 and 16 fl oz of imazapyr and seeding date 0 MAT, injury occurred as failed emergence or early death just as seedlings were emerging. The same treatment combinations resulted on tolerance for soybean, although the fresh weight of the plants was significantly lower when compared to 1 MAT combinations. The treatment combinations 8 fl oz and 16 fl oz of imazapyr, with soybean planted 1 MAT are the best treatments, but similar to 0 fl oz of imazapyr and 0 MAT combination. For lespedeza, crimson and white clover, the treatment combinations of 4, 8 and 16 fl oz of imazapyr applications, seeding date delayed to 1 MAT and 3 MAT, reduced the negative impact fresh weight. Therefore, for better early development of white clover, crimson clover, soybean and lespedeza in forage systems, it is recommended to delay planting at least 1 month after imazapyr applications between 4 and 16 fl oz/A to avoid significant injury to the seedlings that could affect the stand establishment.

Bollgard II^® XtendFlex™ Cotton* is an innovative technology with tolerance to dicamba, glyphosate and glufosinate herbicides (pending regulatory approval). This technology—while still offering insect protection—has been designed to help maximize weed control by encompassing three unique modes of action allowing farmers the choice and flexibility to apply multiple combinations of herbicides before, during and after planting. In 2014 studies were conducted at three locations in the Texas High Plains to evaluate crop response and yield potential following single and sequential post emergence topical (POST) applications of MON76832, an enhanced dicamba/glyphosate premix. This was compared with a single application of Liberty^® 280 SL plus MON119096 at different timings. The objective of these studies was to determine the possible impact application timing and potential crop response of glyphosate and dicamba premix products and glufosinate and dicamba tank mix products have on the yield potential of a candidate Bollgard II® XtendFlex™ variety. Small plot field trials were conducted in Halfway (Hale County), Lorenzo (Crosby County), and Seminole (Gaines County), Texas to evaluate crop injury and growth rate following application of glyphosate, dicamba and glufosinate  at 4, 8, 12 and 16 node (A, B, C and D timings, respectively) growth stages. Applications included four (A+B+C+D timings) sequential applications of MON76832 at 64 oz/A, a single 128 oz/A application of MON76832 to individual plots at each timing, sequential applications of 128 oz/A at both A+C and B+D timings, as well as a tank mix of Liberty + MON119096 applied at the B timing at rates of 32 oz/A + 22 oz/A or 32 oz/A + 44 oz/A, respectively. Crop response ratings were collected 3-, 7- and 14-days after application and recorded as percent injury and percent growth reduction. Yield (lbs/A) was also recorded for each plot at each location. All treatments were applied at 10 GPA using TTI 11015 nozzles at 30 psi. Experimental design at each location was RCBD with four replications.  Across the three locations significant crop response was observed following the application at the C timing, for the 64 and 128 oz/A application rates. Crop response ratings for this timing were 20, 21.3 and 11.3% from Lorenzo, Seminole and Halfway, respectively. Following a sequential application of MON76832 at 128 oz/A, the greatest crop response were observed at Lorenzo (A+C timing, 16.3 and 23.8%, respectively) and Seminole (B+D timing, 11.3 and 22.6%, respectively). Crop response levels declined within two weeks following application. No significant yield differences were observed across locations with any treatment. Results from these experiments indicate that some crop response may be observed with MON76832 applied POST, but no effect on cotton growth or yield should occur. 

Palmer amaranth (Amaranthus palmeri S Watson) is an economically troublesome weed threatening the sustainability of crop production in the US. The rapid increase in glyphosate-resistant weeds prompted a shift in weed management strategies. Glufosinate, in glufosinate-resistant crops, is an alternative tool for controlling glyphosate-resistant weeds. A study was conducted to examine the tolerance profile of 61 Amaranthus populations and to investigate the tolerance mechanism to glufosinate in PA-AR08-Lee-C Palmer amaranth population from Arkansas. Whole-plant bioassays were conducted in the greenhouse to screen for tolerance to glufosinate in 59 Palmer amaranth and 2 tall waterhemp populations from Arkansas collected between 2008 and 2013. One-hundred offsprings were grown in cellular trays, at 1 plant/cell, and sprayed with 0.16 and 0.49 lb ai/A glufosinate when seedlings were three- to four-inches tall. Differential response of Amaranthus populations to glufosinate was observed. Nine Palmer amaranth populations were controlled 88 to 97% with 0.49 lb ai/A glufosinate. The frequency of tolerant plants was relatively low, but the majority of survivors showed 31-80% injury, indicating potential for reproduction. The progenies of PA-AR08-Lee-C (F1) glufosinate survivors were used for tolerance mechanism experiments. Six confirmed susceptible plants from the original population and six confirmed tolerant plants from the F1 population were used for ammonia accumulation assay and copy number determination of glutamine synthetase 2 (GS2) gene. The susceptible plants accumulated two times more ammonia than the tolerant ones indicating that tolerant plants have mechanism(s) that slows or hinders glutamine synthetase inhibition. GS2 copy number did not differ between tolerant and susceptible plants, ranging from 1 to 3 in all plants. Therefore, the tolerance mechanism to glufosinate in PA-AR08-Lee-C population is not due to target gene amplification. Other potential mechanisms will be investigated. For now, we know that some individuals in this population, or other similar populations, can escape glufosinate treatment when application conditions or plant growth stage is suboptimal. The survivors should be prevented from producing seeds using supplemental weed control practices and best management strategies should be practiced to delay the evolution of a resistant population and conserve the utility of glufosinate.

Tall fescue (Lolium arundinaceum) is the predominant grass species in pastures in the mid-South. Most tall fescue is infected with a fungal endophyte, Neotyphodium coenophialum, which imparts certain advantages to the plant such as drought tolerance, insect feeding deterrence, and enhanced mineral uptake. However, the endophyte also produces ergot alkaloids that are detrimental to livestock and contribute to fescue toxicosis. Common symptoms of fescue toxicosis include increased body temperature, rough hair coats, nervousness, and reduced average daily gain (ADG). Since the alkaloids are highly concentrated in seeds and stems, a potential way to reduce the likelihood of fescue toxicosis is by suppressing seed heads with herbicides. Metsulfuron is an acetolactate synthase (ALS) inhibitor and is well documented to limit seed head formation, but also injures tall fescue. Aminocyclopyrachlor, hereafter abbreviated MAT28, a new synthetic auxin herbicide, has been registered for use in non-cropland and right-of-way applications; registration in pastures is expected in 2015. The first pasture herbicide product to be registered is anticipated to be a premixture of MAT28 and metsulfuron.

Research was conducted in 2012 and 2013 using metsulfuron applied alone and in combination with other herbicides to determine the growth response of tall fescue, effects on forage quality, and potential to reduce the impact of fescue toxicosis by reducing ergot alkaloid concentration. Trials were conducted on endophyte-infected tall fescue pastures in Alcoa and Crossville, Tennessee. Experimental design was a randomized complete block with four replications and all herbicide treatments included non-ionic surfactant at 0.25%. In addition to the anticipated use rates of MAT28 plus metsulfuron, other treatments were metsulfuron alone, aminopyralid plus metsulfuron, and MAT28 plus 2,4-D. Clipping at early boot stage was also included to compare effects of herbicide applications versus mechanical removal. Visual ratings were performed monthly to evaluate fescue discoloration and stunting on a 0-99% scale. Plots were harvested in late spring and summer to determine yield, seed head density, fescue leaf proportion, and fescue stem proportion. Forage quality measurements were determined using NIRS. Alkaloid concentrations were determined by ELISA.

MAT28 plus metsulfuron (78 + 12 g ai/ha), metsulfuron alone (12 g ai/ha), and aminopyralid plus metsulfuron (65 + 12 g ai/ha) stunted tall fescue more than 50% at four weeks after treatment (WAT).  At 8WAT, tall fescue was stunted 24 to 28% by those same treatments.  Clipping or metsulfuron applied alone or in combination with MAT28 or aminopyralid reduced seed head density by 36% or more compared to the untreated control. Clipping, metsulfuron alone (12 g ai/ha), MAT28 plus metsulfuron (78 + 12 g ai/ha) and aminopyralid plus metsulfuron (65 + 12 g ai/ha) reduced tall fescue stem proportions by 8.4 to 15.6% at first harvest. Yields from the spring harvest ranged from 49 to 65% of untreated for all treatments containing metsulfuron. No differences in yield were observed in the summer harvest.  Tiller densities for all treatments containing metsulfuron ranged from 80 to 94% of untreated after spring harvest and 99 to 121% of untreated after summer harvest, further indicating tall fescue had recovered by the summer. Forage quality was improved in treatments containing metsulfuron applied alone or in combination with MAT28 or aminopyralid, as shown by increased crude protein and total digestible nutrients (TDN) and decreased acid detergent fiber (ADF). Metsulfuron applied alone or in combination with MAT28 or aminopyralid reduced total ergot alkaloid concentration 26 to 34% from untreated forage in the spring harvest.

When applied alone or in combination with MAT28 or aminopyralid, metsulfuron reduced seed heads and improved forage quality in tall fescue, but also caused injury and reduced spring yield. Also, metsulfuron applied alone or in combination with MAT28 or aminopyralid reduced total ergot alkaloid concentration and therefore can potentially reduce the severity of fescue toxicosis. Additional research includes determining effects of application timing on tall fescue growth and yield. 

GREEN ASH AND MULTIFLORA ROSE: CONTROLLING WOODY BRUSH IN BLACK BELT PASTURES. D.P. Russell and J. Byrd; Department of Plant and Soil Sciences, Mississippi State University, Mississippi State, MS.

ABSTRACT

Woody brush species has potential to severely reduce pasture production if left unmanaged. In the Black Belt Prairie region of Mississippi, green ash (Fraxinus pennsylvanica) and multiflora rose (Rosa multiflora) are two woody perennial species that infests the fine-textured clay soils in unimproved pastures. Our purpose was to evaluate several pasture herbicides based on their effective, seasonal control.

A randomized complete block design was conducted on each species population in pastures used for cattle production. Both locations had a history of weed pressure and was maintained by mowing. The population of multiflora rose was somewhat sparse with approximately one established plant per 60 m² plot, while green ash was more heavily populated with 8-10 established stems per m². Two rates of Remedy Ultra (60.45% triclopyr), Arsenal (27.8% imazapyr), Invora (7.3% aminocyclopyrachlor + 14.6% triclopyr), Cimarron (60% metsulfuron), and Tordon 22K (24.4% picloram) were applied to green ash in May 2014 at a 14 inch height. Mature plants of multiflora rose were treated with Remedy Ultra, Arsenal, and Invora in October 2013.

Cimarron at two and four oz/A exhibited the most significant green ash control nearly three months after treatment. Remedy at 48 fl oz/A was the next, most significant, treatment after 81 days. No difference in control was observed between the two rates of Cimarron, therefore, a single low rate application would provide season-long control without causing damage to bermudagrass forage.

Multiflora rose visually exhibited the greatest response from 12 and 24 fl oz of Arsenal with 75 and 100% control, respectively, at 264 DAT. Remedy Ultra applied at 48 fl oz/A provided 63% control, followed by 53% control from 24 fl oz/A of Invora. However, there was no significant difference between any herbicide treatments nearly nine months after application. Arsenal hindered all pasture forage growth through spring, but forage species recovered by late summer. Therefore, if Arsenal is applied for multiflora rose control, only individual plants should be treated. Neither Remedy Ultra nor Invora had a negative effect on pasture grasses.

The kudzu bug, Megacopta cribraria F. is an Old World pest of soybeans in Japan, China, India and several other far eastern countries. In 2009 adult M. cribraria were discovered in Northeast Georgia aggregating on homes near patches of kudzu. Kudzu is an invasive vine introduced into North America from China in 1876 for erosion control and as an ornamental. Today kudzu covers over two million acres of forest land in the Southeastern United States. Kudzu and soybean are the primary hosts of kudzu bug in the U.S. In this study the role kudzu plays as a source of kudzu bug infestations in soybean fields in GA was investigated. Flight intercept traps were placed near kudzu patches and soybean fields within proximity of kudzu patches. Adults collected in flight intercept traps at soybean and kudzu locations were counted weekly from 2012 to 2014. Traps were put out from late spring when overwintering adults became active to late fall when overwintering adults began to enter diapause. Adults and nymphs were counted from sweep samples and egg masses from kudzu shoot tips. As adults become active in the spring they disburse to the first available host and readily lay eggs. When kudzu is available populations build to high numbers. Early planted soybeans may be more heavily infested than later planted soybeans, though high infestations may build on soybeans planted later in the year. Two generations occur on kudzu and one to two generations on soybean depending on planting date. Kudzu is critical as a source of infestation for adults dispersing to soybean but it is not understood if populations could survive in its absence.

Indaziflam is a cellulose biosynthesis inhibitor herbicide reportedly more effective than isoxaben and quinoxyphen for annual bluegrass (Poa annua L.) control, representing an alternative for managing annual bluegrass resistance. Annual bluegrass can be controlled via PRE and early POST indaziflam applications, however, information on sensitivity of other annual grass species to indaziflam is limited. It is important to understand a species’ baseline sensitivity for proper rate recommendation, and for resistance screening in the future. The objective of this study was to develop baseline sensitivity curves for annual grasses to indaziflam.

 A greenhouse study was conducted from June to October 2013 at Auburn University in Auburn, AL to determine baseline sensitivity of annual grasses to indaziflam. Eight annual bluegrass, 4 goosegrass (Eleusine indica (L.) Gaertn.), 1 large crabgrass (Digitaria sanguinalis (L.) Scop.), and 1 smooth crabgrass (Digitaria ischaemum (Schreb.) Schreb. ex Muhl.) populations were treated with indaziflam as in Specticle Flo (Bayer Environmental Sciences; Research Triangle Park, NC) PRE seeding. Pots containing a screened, native Wickham Sandy Loam (fine-loamy, mixed, semiactive, thermic Typuc Hapludult) with pH 6.3 and organic matter 1.7%, were sprayed at 0.25, 0.5, 1, 2, 4, 8, 16, 32, and 48 g ai ha^-1 in a spray chamber at 280 L ha^-1 spray volume. Sprayed pots were seeded with 100 seeds of the desired weed population, lightly topdressed with sand, covered with germination cloth for 2 weeks, and mist irrigation was applied frequently to encourage germination. Seeds were lightly scarified by rubbing between sand paper just before sowing into pots. Fertility was applied every two weeks with Miracle-Gro (The Scotts Miracle-Gro Company; Marysville, OH) soluble plant food. Data was collected every two weeks for eight weeks and included seedling counts and visual estimation of percent cover. At eight weeks, aboveground biomass was harvested, and dried in an air forced, mechanical convection oven (VWR International; Radnor, PA) at 80Ëš F until constant weight was reached. Dried biomass for each population was then weighed. Data were analyzed in SAS 9.2 (SAS Institute; Carry, NC) using non-linear regression analysis with PROC NLIN with α level = 0.05. I₅₀ values were also obtained, using 95% confidence intervals in PROC GLIMMIX. Results were plotted in SigmaPlot 11.2 (Systat Software Inc.; San Jose, CA).

Overall, grass species differed in sensitivity to indaziflam. Annual bluegrass was the most sensitive species, followed by goosegrass and crabgrass. Goosegrass and crabgrass did not differ amongst each other for indaziflam sensitivity. The most sensitive goosegrass population to indaziflam was ‘W’, whereas large crabgrass was more sensitive than smooth crabgrass. Despite greater sensitivity of annual bluegrass to indaziflam, little differences between species were found. All species tested were controlled by indaziflam rates lower than label recommendations. Future research should investigate early POST indaziflam activity, as well as herbicide and soil interactions that might interfere on herbicide availability to target plants.

Chemical applicators need to consider numerous factors including nozzle size and nozzle type in order to make an effective herbicide application. In the near future, auxin-resistant crops will be introduced into the marketplace and herbicide programs may utilize auxin-type herbicides tank-mixed with other postemergence herbicides such as Liberty. While decreasing droplet size has been known to increase efficacy of contact herbicides like Liberty, influence of droplet size on efficacy of systemic herbicides such as auxin herbicides has been variable. Therefore trials were conducted in the summer of 2014 to determine the influence of nozzle selection and efficacy of Liberty and low volatility diglycolamine (DGA) formulations of dicamba, containing a proprietary Monsanto product, alone and in mixture with Liberty. Field trials were conducted at the Northeast Research and Extension Center in Keiser, Arkansas as well as complimentary droplet spectra analysis using laser diffraction at the University of Nebraska-Lincoln West Central Research and Extension Center in North Platte, Nebraska using the same nozzles from the field trial. The experimental design for the field trial was a randomized complete block with a two-factor factorial treatment structure. Factors included herbicide treatment: Liberty at 29 fl oz/A, a low volatility DGA dicamba formulation (hereafter referred to as MON 119096) at 22 fl oz/A, Roundup PowerMax at 32 fl oz/A, a low volatility DGA dicamba + glyphosate premix formulation (hereafter referred to as MON 76832) at 64 fl oz/A, Liberty + MON 119096 at 29 and 22 fl oz/A, and Liberty + MON 76832 at 29 + 64 fl oz/A across three nozzle types: TTI 11004, TDXL-D 11004, and ULD 11004.  Palmer amaranth and barnyardgrass were the weeds present in the trial, and these weeds were larger than what would be recommended for a typical application of these products.  Median droplet size decreased and percent fines increased for the MON 119096 or MON 76832 when Liberty was added.  Nozzle selection had a significant impact on droplet size over the products tested and significantly impacted barnyardgrass control.  However, nozzle selection did not impact glyphosate-resistant Palmer amaranth control possibly due to the narrow range of droplet sizes evaluated.  The MON 76832 alone or tank-mixed with Liberty provided suppression of Palmer amaranth and barnyardgrass, but effective control was not achieved in this trial as a result of the large weed sizes at application.  There appears to be no negative effect of tank-mixing Liberty with either of the dicamba-containing products evaluated in this research.    

Effect of Formulation and Cleanout Procedure on Dicamba Equipment Cleanout. Gary T. Cundiff*¹, Daniel B. Reynolds¹, Walter Thomas², Brad Guice² and Chad Brommer², ¹Mississippi State University, Mississippi State, MS, ²BASF Corporation, Research Triangle Park, NC.

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. Tank contamination can occur by the ability of a molecule to either adsorb or absorb within the spray system. Due to this sorption factor, dilution along with chemical means may be needed to completely ensure proper cleanout of the system.

Two studies were conducted to assess a new dicamba formulation known as Engenia. One study focused on determining if Engenia persistence would differ among two different cleanouts on one type of hose, flushed four separate times with each flush applied to soybean used as a bio-indicator to assess cleanout efficiency. While the second study focused on determining if Engenia persistence would differ with four different cleanouts on one type of hose flushed four separate times with each flush applied to soybean used as a bio-indicator to assess cleanout efficiency.

For the first study, two cleanout procedures of water and ammonia were used to clean a manifold system. Each cleanout method was incubated with the same treatment of Engenia at 120 ml and 266 ml of Roundup PowerMax for 12 hours. A total of eleven treatments were run in a randomized complete block, three treatments were a known working solution of Engenia at 0.0, 0.56 and 0.056 g ai/ha; while eight of those treatments constituted the lines of each cleanout method run as a factorial arrangement of treatments with cleanout and wash timing as the factors. Samples were collected for analytical analysis before incubation, after incubation and after each flush of cleanout method. Solutions of 500 ml were retained after each flush for field applications on Roundup Ready soybean at the V2 growth stage with each hose from each cleanout method representing a rep, and the process was repeated four times. Field applications were made with a non-ionic surfactant at 0.25% v/v and a two row boom with TTI 80015. Weekly visual ratings were taken 7, 14, 21 and 28 DAT with height and height reductions at 14, 21, and 28 DAT and yield and percent yield reductions.

For the second study, four cleanout procedures of BUC 328, BUC 349, BUC 690, and BUC 760 were used to clean a manifold system. Each cleanout method was incubated with the same treatment of Engenia at 120 ml and 266 ml of Roundup PowerMax for 12 hours. A total of sixteen treatments were run in a randomized complete block, four treatments were a known working solution of Engenia at 0.0, 0.56 and 0.056 g ai/ha and no cleanout; while twelve of those treatments constituted the lines of each cleanout method run as a factorial arrangement of treatments with cleanout and wash timing as the factors. Samples were collected for analytical analysis before incubation, after incubation and after each flush of cleanout method. Solutions of 500 ml were retained after each flush for field applications on Roundup Ready soybean at the V2 growth stage with each hose from each cleanout method representing a rep, and the process was repeated four times. Field applications were made with a non-ionic surfactant at 0.25% v/v and a two row boom with TTI 80015. Weekly visual ratings were taken 7, 14, 21 and 28 DAT and yield and percent yield reductions.

Results show that cleanout procedures did significantly differ with respect to water and ammonia in experiment one. Data showed water significantly increased percent soybean visual injury 28 DAT when compared to ammonia in experiment one. Cleanout with BUC 690 significantly increased visual injury when compared to other procedures in experiment two. Cleanout timings differed with respect to soybean percent visual injury 28 DAT in both experiments, but no differences were observed with respect to height reduction, yield or percent yield reduction. Results show that the known concentrations of Engenia significantly differed with respect to percent injury at 7, 14, 21, 28 DAT, percent height reductions, and yield in both experiments. In experiment one the parts per million (PPM) of Engenia analytes significantly increased in the second wash when compared to other washes. Analytical work for experiment two is still pending. Results indicate a decrease in injury with subsequent cleanings of Engenia. This research would indicate more than two rinses of any cleanout procedure would be necessary to alleviate injury to subsequent crops that are sensitive to dicamba.  

Sugarcane (Saccharum spp. interspecific hybrids) is cultivated on 165,000 ha on organic soils of the Everglades Agricultural Area (EAA) and minerals soils of the surrounding region in south Florida. Weed management is the main production cost associated with sugarcane cultivation in Florida. Although several herbicides are labeled on sugarcane, growers commonly use atrazine, metribuzin or pendimethalin as PRE herbicides and mainly depend on POST application of asulam to manage grasses later in the season. Field studies were conducted in 2014 on organic and mineral soils in Belle Glade, FL and near Loxahatchee, FL, respectively to evaluate sugarcane tolerance and weed control using a commercial premix of atrazine, mesotrione, and s-metolachlor. The premix was applied PRE or early POST at 850 + 220 + 2200 g ai ha^-1, 1,700 + 440 + 4,400 g ai ha^-1, and 3,400 + 880 + 8,800 g ai ha^-1 of atrazine + mesotrione + s-metolachlor, respectively (equivalent to 1×, 2×, and 4× rates) and compared with commercial standards used by growers. The commercial PRE standard included 4490 g ai ha^-1 of atrazine + 4270 g ai h^-1 of pendimethalin and the commercial early POST standard included 730 g ae ha^-1 of 2,4-D amine + 4490g ai ha^-1 of atrazine + 560 g ai ha^-1 of ametryn. Sugarcane varieties ‘CPCL02-0926’ and ‘CC97-2730’ were used on organic and mineral soils, respectively. Fall panicum (Panicum dichotomiflorum Michx.) was the predominant weed species on both soils while spiny amaranth (Amaranthus spinosus L.) and common ragweed (Ambrosia artemisiifolia L.) were present at the organic and mineral soil locations, respectively. There was no difference in sugarcane population on organic soils at 56 days after PRE treatment application (equivalent to 27 days after early POST application).  Also, there was no phytotoxicity from all the herbicides on sugarcane. Fall panicum control was 73% at 56 DAT following PRE application of the 1× rate of atrazine + mesotrione + s-metolachlor compared to 89% control provided by the PRE commercial standard. The 2× and 4× rates of atrazine + mesotrione + s-metolachlor applied PRE provided 85 and 94% fall panicum control, respectively 56 DAT. All the PRE treatments provided >96% spiny amaranth control at 56 DAT. Fall panicum control was 68, 89, and 100%, respectively at the 1×, 2×, and 3× rate of early POST atrazine + mesotrione + s-metolachlor compared to 96% provided by the commercial standard. All early POST treatments provided complete spiny amaranth control. On mineral soil, herbicide treatments resulted in significantly higher sugarcane population compared to the nontreated control. Similar to organic soil, there was no phytotoxicity of the treatments on sugarcane on mineral soil. On mineral soil, all rates of PRE atrazine + mesotrione + s-metolachlor and the commercial standard provided >95% fall panicum control 70 DAT. The PRE atrazine + mesotrione + s-metolachlor provided significantly higher common ragweed control (90 to 100%) compared to the commercial standard (43%). Fall panicum control on mineral soil with early POST atrazine + mesotrione + s-metolachlor at  1× rate (58%) was significantly lower than the control provided by the  2× rate (85%), 4× rate (100%), and the commercial standard (78%). These results show that atrazine + mesotrione + s-metolachlor provided variable weed control on sugarcane depending on use rate and soil type. Studies are currently ongoing to corroborate these results. 

CORN WEED MANAGEMENT PROGRAMS FOR TROUBLESOME WEEDS IN NORTH CAROLINA.  B. W. Schrage, W. J. Everman, North Carolina State University, Raleigh, North Carolina

ABSTRACT

The increase in corn acreage in North Carolina has proven to be a beneficial rotational crop in production systems determined to limit the presence of troublesome and herbicide-resistant weed species.  To explore methods of optimizing control strategies, a study was conducted in Rocky Mount and Kinston, NC in 2014 evaluating certain residual overlapping residuals in maize.  11 WAP, amaranthus palmeri control was similar among all treatments ranging from 80-98%.  Additional weed species were similarly managed by all treatments except for cases which experienced lesser control when applied with treatment 4 [atrazine + pyroxasulfone (Anthem ATZ) fb glyphosate (Roundup Powermax)] or 6 [thiencarbazone-methyl (Corvus) + atrazine (Aatrex 4L) fb tembotrione (Laudis) + atrazine + glyphosate].  In Rocky Mount, NC treatments 4 and 6 provided 21-47% less control of Ipomoea hereacea.  There was no evidence of yield differences; however, treatment 4 resulted in 16-20% less control of Ipomoea lacunosa 37 DAP in Kinston, NC.  Sublevel control of digitaria sanguinalis was also achieved by treatments 4 and 6 72 DAP.

One of the indirect adverse effects of weeds is the possibility of serving as alternative hosts of pests and diseases, including plant-parasitic nematodes. Showy crotalaria is designated as a noxious weed in many states within the southern region of the United States, where its presence is undesirable particularly because of its toxicity to livestock. It is noteworthy that, in other countries, showy crotalaria has been used as a cover crop due to its potential to suppress some species of plant parasitic nematodes. Belonolaimus longicaudatus (sting nematode) is one of the most important plant-parasitic nematodes in Florida, infesting fields that are used to growth a wide variety of crops. The first step of the present work was to evaluate the host status of showy crotalaria to the sting nematode. Nine different accessions (2 from Australia, 3 from Brazil, 3 from India and 1 from South Africa) of showy crotalaria the USDA-ARS Plant Genetic Resources Conservation Unit (Griffin, GA), were evaluated for suppression of nematode reproduction in comparison with corn, which is a good host for the sting nematode. The greenhouse experiment was conducted using potted plants arranged in a randomized complete block design (RCBD), with five replications. Among the nine accessions evaluated, two showed numbers of nematode similar to corn (PI 316945 and PI 337081 from Brazil), indicating susceptibility to B. longicaudatus. The other accessions effectively suppressed sting nematode populations in the soil, particularly PI 244597 and PI 217908 , from South Africa and India, respectively. The second aim of this study was to evaluate the chemical control of showy crotalaria at two stages of development with postemergence herbicide applications. This field experiment was conducted, using an RCBD, with a factorial arrangement of treatment, and four replications. The first factor corresponded to the herbicides flumioxazin (25 g ha^-1), fomesafen (250 g ha^-1), lactofen (150 g ha^-1), saflufenacil (35 g ha^-1), atrazine (2500 g ha^-1), diuron (2000 g ha^-1), glufosinate-ammonium (500 g ha^-1) and glyphosate (1944 g ha^-1). The second factor consisted of herbicide rates: 1X and 0.75X and a nontreated check. The variable analyzed was the percentage of showy crotalaria control at different periods after application. Except for diuron at the 0.75X, all the other treatments effectively controlled showy crotalaria plants when applications were performed at Stage I (2 to 4 leaves). For Stage II (6 to 8 leaves) applications, only diuron (both rates) and fomesafen at the 0.75X rate failed to control showy crotalaria.

Weed control remains a major challenge for economically viable sorghum production in North Carolina due to sorghum sensitivity to weed competition during early growth stages. Palmer amaranth (Amaranthus palmeri) is one of the broadleaf weeds that may be the most problematic in sorghum production (Moore et al. 2004). 2,4-D is the most common and inexpensive herbicides used POST to control Palmer amaranth. However, recent studies have reported toxic effects of 2,4-D applied POST on sorghum plants (Dan et al. 2010, Petter et al. 2011). No research data on grain sorghum response to growth regulator herbicides exists in North Carolina. Consequently, this study was conducted to investigate the effects on sorghum growth and yield of 2,4-D and Dicamba POST applications over-the-top beyond the recommended height (15 to 20 cm). Field experiments were conducted from 2012 to 2014 at the Upper Coastal Plain Research Station (Rocky Mount, NC), Caswell Research Farm (Kinston, NC), and Central Crops Research Station (Clayton, NC). Experiments were conducted as a factorial arrangement of 2 factors in a randomized complete block design. Main factors consisted of different rates of growth regulators applied POST (2,4-D amine at 100, 217 and 333 g ai.ha^-1, Dicamba at 280 g ai.ha^-1) and different stages of sorghum growth at application (25, 35, 45, 55, 65, and 75 cm). Crop height at harvest, yield, test weight, and grain moisture were measured. No interaction was observed between herbicide treatments and stage of application. Growth regulator applications on 35 to 75 cm tall sorghum resulted in taller plants compared to earlier treatments. Consequently, an important lodging effect was observed later in the season. Yield was negatively affected by growth regulator applications where sorghum was planted on sandy soils with a low field capacity, resulting in increased crop sensitivity to herbicides due to environmental stress. By contrast, sorghum grown on a fine sandy loam soil was more tolerant to hydric stress with higher yield and decreased sensitivity to growth regulator applications. Our results confirm previous reported data on the negative impact on sorghum yield of growth regulators applied beyond the actual recommended height. Nevertheless, when planted in favorable soils, sorghum can tolerate growth regulators applied over-the-top up to 50 cm crop height at application without significant yield reduction.

Exploring the influence of zoysiagrass breeding lines quality on fluazifop-P injury. W. Liu*¹, R.G. Leon¹, K.E. Kenworthy², J.B. Unruh¹, L. Xing², and P.R. Munoz². ¹University of Florida, Jay, FL 32565, ²University of Florida, Gainesville, FL 32611

Fluazifop-P-butyl is a postemergence herbicide that can be used for selective control of grass weeds in zoysiagrass. Two field experiments were conducted to compare the response of 80 zoysiagrass cultivars to fluazifop-P-butyl. In the first experiment cultivars were treated with 88 g ai ha^-1 (1X label rate) and in the second experiment with 264 g ai ha^-1 (3X label rate). Injury was determined at 2 and 5 weeks after treatment (WAT). Quality data of these zoysiagrass breeding lines were also collected to examine its influence on fluazifop-P-butyl injury. Moderate correlations were found between quality and percentage injury at 2 WAT with both application rates (Spearman's correlation coefficient <0.5). Correlation values were higher at 2 than 5 WAT due to recovery of most zoysiagrass breeding lines. There was a clear trend that cultivars with higher quality also exhibited higher tolerance to fluazifop-P-butyl, but exceptions were observed in which high quality lines exhibited similar injury to that of low quality lines. Additionally, among the most tolerant lines at 88 g ha^-1 (<10% injury) there were clear differences when treated with 264 g ha^-1, and several lines reached >65% injury while others had <35%. The results of the present study indicated that high quality will likely contribute to fluazifop-P-butyl tolerance, but quality should not be used as a surrogate marker to select for fluazifop-P-butyl tolerance.

The SWSS Endowment scholarship was set up in 2013 to provide an opportunity to graduate students to gain practical experience and exposure to Industry, Academia, or Extension Service. An educational visit to Syngenta Crop Protection (SCP) was organized by the SWSS Endowment Board in collaboration with SCP in May, 2014. The educational visit included exposure to Syngenta's Advanced Crop laboratory at Research Triangle Park, Raleigh; Syngenta Research complex, Greensboro, NC, and Syngenta Research Center, Vero Beach, FL. The company was founded on November 13, 2000 after merging two formerly large agrochemical companies - Novartis and AstraZeneca, and is headquartered in Basel, Switzerland. Syngenta is one of the world's leading industry with more than 28,000 employees in some 90 countries dedicated to research and business objectives. Syngenta AG is engaged in the manufacture, development, and distribution of crop protection products and seeds. The Crop Protection business includes herbicides, insecticides, fungicides, and seed treatments. The seed business operates in the high value commercial sector of field crops and vegetables. The Lawn and Garden business provides flowers, turf, and landscape products. Research facilities at RTP and Greensboro provide insight into advance crop technologies, innovation centers, advanced genetic and molecular breeding laboratories. The newly established crop research facility in RTP, a $72- million worth “Advanced Crop Laboratory”, allows researchers to simulate any climatic conditions and precisely measure plants' response to abiotic and biotic factors. Syngenta Research center, Vero Beach, FL provided hands-on training on some of the bioassays and personal experience on increasing efficiency by use of highly skilled manpower, and cohesive team networks. Interaction with skilled staff and workers gave new perspective to understand the company's talent acquisition and employment opportunities.

The widespread use of herbicide tolerant-traits technology formed the basis for identifying such fields to help growers prevent drift and misapplication of herbicides. In response to this need, the University of Arkansas Cooperative Extension Service launched a statewide program named Flag the Technology in 2011. This program uses color-coded flags as a visual alert of the herbicide trait technology within a farm field. This program has been endorsed by Southern Weed Science Society of America and is attracting interest from across the USA, Canada, and Australia. However, flags have risk of misplacement or disappearance due to mischief or severe windstorms/thunderstorms, respectively. This presentation will discuss the design and development of a cloud-based, free application utilizing open-source technologies, called Flag the Technology Cloud (FTTCloud), for allowing agricultural stakeholders to color code their farm fields for indicating herbicide resistant technologies. The developed software utilizes modern web development practices, widely used design technologies, and basic geographic information system (GIS) based interactive interfaces for representing, color-coding, searching, and visualizing fields. This program has also been made compatible for a wider usability on different size devices- smartphones, tablets, desktops and laptops.

A survey of cotton weed management systems in West Texas: 2014. R.M. Merchant¹, P.A. Dotray^1,2, W.K. Keeling², R. Ritz¹, M.R. Manuchehri¹. ¹Texas Tech University, Lubbock; ²Texas A&M Agrilife Extension Service, Lubbock.

Cotton (Gossypium hirsutum) is the major agronomic crop of West Texas with over 2 million ha planted in 2014. Glyphosate-resistant Palmer amaranth (Amaranthus palmeri) is a relatively new and significant threat to cotton production in the Southern High Plains. A survey of cotton producers was conducted in the spring of 2014 in order to better understand current weed management practices of the region. The survey was published online using the Qualtrics® survey system and announced by email using County Extension Agent and the Plains Cotton Growers list servers. Ninety-five completed surveys were recorded over the period of 8 weeks. Of the respondents, 59% were producers, 13% consultants, 18% dealer/distributor, and 19% from extension/education. Fifty-five percent of respondents reported an operation larger than 800 ha, 79% of whom also planted cotton. Of the acreage reported, 60% was under some form of irrigation. Roundup Ready Flex and Roundup Ready/BGII were the most commonly used transgenic traits. Sixty-five percent received trifluralin and 36% received pendimethalin preplant incorporated. The most commonly used at-plant herbicides were s-metolachlor and pendimethalin, 30% and 22% respectively. Residual herbicides tank-mixed with postemergence applications were reported, with the most widely used being s-metolachlor (50%) and acetochlor (26%). The most widely used residual herbicides postemergence-directed were diuron (39%), MSMA (24%), and prometryn (24%). Tillage was widely used, with at least 47% of the cotton acreage receiving deep-plowing, rod-weeding, or between-row cultivation. Seventy-two percent of respondents suspect glyphosate-resistant weeds on their operation while 80% suspect glyphosate-resistance has occurred on a neighboring farm. Ninety-one percent indicated that the presence or threat of glyphosate-resistance has affected their decisions regarding crop rotation, variety selection, and tillage practices. This survey has been used to guide field research regarding glyphosate-resistant Palmer amaranth in West Texas, and will be published annually to track changes in weed management practices for the area.

Palmer amaranth (Amaranthus palmeri) is the most predominant herbicide-resistant weed threatening row-crop production in the southern US. Given the impact of seedbank size on species persistence and the risk of resistance evolution, a core focus on soil seedbank management is vital. This is particularly true for weeds such as Palmer amaranth that can produce tremendous amounts of seeds. Emphasis on minimizing seedbank size serves as a valuable proactive resistance management strategy, which is more economical in long-run compared to reactive management tactics that are deployed after the fact. However, demonstrating the biological and economic benefits of proactive, integrated management strategies remains a challenge. To this effect, a user-friendly software is being developed to educate the stakeholders of the benefits of adopting and the penalties of not adopting given resistance management strategies. This model is based on the ryegrass integrated management (RIM) model developed at the Australian Herbicide Resistance Initiative (AHRI) and implemented in Microsoft Excel® platform. The integration of Visual Basics Applications (VBA) interface provide a software-like appearance and experience. This tool allows the growers to select a range of crop production and weed management strategies (chemical and non-chemical options) and make parallel comparisons. This model will serve as an excellent decision-support tool for making rational weed management decisions based on long-term seedbank dynamics and economics.

In 2005, the University of Georgia’s Center for Invasive Species and Ecosystem Health (The Center) developed and launched EDDMapS, a web-based Early Detection and Distribution Mapping System, to accurately map distribution of invasive plants across the United States. More recently, smartphone technology has made it possible for citizen scientists and other casual reporters to submit observations of invasive species while away from their computer. The first app, IveGot1, was created in cooperation with the National Park Service, Florida Fish and Wildlife Commission and the University of Florida for reporting non-native plants and animals in Florida. As more programs have displayed interest in developing apps for identification and reporting in their region, more apps have been launched.  The Southeast Early Detection Network is an app for identifying and reporting invasive plants, and a few insects and wildlife, in the southeastern US.  The list of species has been tailored to common and emerging invasive species threats so that both casual and expert observers can effectively use the tool.  The first version of the app was very streamlined for ease of use: identification information and images, current distribution maps, and a pared down reporting page for mapping point records in the field.  New features for the app will include the ability to draw and map polygons and to map negative survey data. Polygons will be useful in showing the shape and scope of an infestation and negative data will document areas that have been evaluated for invasive species.

USING THE VIRGINIA WEED IDENTIFICATION LAB AS A MEANS TO TRACK WEED DEMOGRAPHICS AND DISTRIBUTION OVER TIME.  K. A. Venner, S. D. Askew and A. R. Post; Virginia Tech, Blacksburg VA, 24061, and Oklahoma State University, Stillwater OK, 74078. 

 The Virginia Weed Clinic is a free extension service provided by Virginia Tech through the department of Plant Pathology, Physiology & Weed Science.  The Weed Clinic has been receiving and processing weed identifications and control recommendations for over 30 years.  In a single year, the clinic can receive up to 400 weed samples from different commodities grown in Virginia including those submitted by private parties.  Spatial and demographic data for the Weed Clinic has been collected every year including weed common and botanical name, commodity of origin, county, and date received.  This information will be useful to horticultural and agronomy extension agents and to any commodity grower where an abundance of data has been collected for their crop. 

 Data from 2002-2012 has been analyzed to illustrate demographic and spatial data for weeds submitted to the Weed Clinic by both private growers and extension agents in the state of Virginia.  Submissions represent 147 plant families, 428 genera and 729 unique species.  The largest families represented, based on number of individual submissions, are Poaceae, Asteraceae, Fabaceae, Brassicaceae, Lamiaceae, Polygonaceae, and Caryophyllaceae.  Of 428 genera, 399 contained 3 unique species submitted or less, 15 genera had 4 unique species submitted, 9 genera had 5 unique species, and 3 genera had 6 unique species.  The genera Veronica and Bromus had the largest number of unique species containing 8 and 7, respectively. 

 Most samples are submitted between the months of May and September accounting for 35% of all submissions.  Only 6 different commodities account for the majority of Weed Clinic samples, including: 28% from residential turfgrass, 21% from pasture, 10% aquatic, 7% each from fallow areas and ornamental beds, and 4% from gardens.  Up to 7% of growers submit samples without specifying their crop. The remaining 16% come from various commercial crops and forested areas.   The most commonly submitted weed to the Weed Clinic over the last 10 years is Japanese stiltgrass (Microstegium vimineum).  This is a weed of growing concern in forest understories, roadsides, pastures, and other non-cropland as it creates a monoculture, crowding out native or desired vegetation.  The “top ten” weeds identified by the Virginia Weed Clinic included: Japanese stiltgrass (Microsegium vimineum), Japanese clover (Kummerowia striata), nimblewill (Muhlenbergia schreberi), tall fescue (Lolium arundinaceum), roughstalk bluegrass (Poa trivialis), bermudagrass (Cynodon dactylon), common chickweed (Stellaria media), sericea lespedeza (Lespedeza cuneata), yellow nutsedge (Cyperus esculentus), and smooth crabgrass (Digitaria sanguinalis).   As turfgrass accounts for the largest percentage of submissions, many of the weeds listed in the “top ten” are problematic weeds in turfgrass.

Flag the Technology was a program developed by the University of Arkansas in 2010 and first implemented in one county to test the feasibility of using a simple colored flag system to identify fields according to their herbicide tolerant technology.  The initial program consisted of white flags for glyphosate tolerant crops, yellow for STS and Clearfield crops, red for conventional and green for Liberty Link.  As new technology is being introduced this program must be adapted to fit all possible combinations of herbicide technology now or soon to be available to growers.  For example: black will now represent Xtend or dicamba crops and a checkered flag will indicate tolerance to both glyphosate and dicamba and the color teal will be used for Enlist or 2,4-D tolerant crops.  To date almost $250,000 worth of flags have been used in Arkansas alone to mark fields since 2011-12.  This program is being adapted with a web based version and app under development.

The volume of herbicides used in the U.S. greatly exceeds that of other pesticides. Evolution of resistance to currently use herbicides has increased the need for herbicides with new modes of action (MOAs), yet almost 30 years has passed since a genuinely new MOA was introduced.   Herbicide resistance is increasing herbicide use and the need for new MOAs.  Natural products offer potentially new herbicides MOAs.  Additionally, there are no efficacious and economical weed management chemicals (biochemical bioherbicides) available for organic agriculture.  The available products, such as organic acids, fats, and oils, have to be used in large amounts at great expense.   As are result, weed management is generally the most costly pest problem in organic farming. Experts have said that a cost-effective biochemical bioherbicide is the “holy grail” of biopesticides.  Current organic products do not act at enzymatic sites as synthetic herbicides do, but instead cause rapid plant tissue desiccation by direct effects no plant cuticles and membranes. Examples of natural compounds with new MOAs involving enzymatic sites will be discussed. New biochemical bioherbicides have the potential for greatly improving weed management in organic agriculture and providing new MOAs for conventional agriculture.

Palmer amaranth has become a significant weed problem throughout the Southern U.S., in part, due to the ability of the populations to develop resistance to various herbicide mechanisms of action.  One potential means of reducing the impact of Palmer amaranth in cropping systems is to minimize the population of these seeds in the soil seedbank.  Previous studies have documented that Palmer amaranth seed viability ranged from 9 to 22% after 36 months of burial.  Preliminary research indicated that fields with high Palmer amaranth seed densities near the soil surface could benefit from a single deep turning with a moldboard plow to invert the soil and bury the surface seed to depths from which they cannot emerge; this will bring soil to the surface with minimal populations of Palmer amaranth, providing growers with a more manageable seedbank.  The objective of this research was to determine the influence of a single deep tillage event and zero seed-return policy on Palmer amaranth soil seedbank densities.  Field studies were initiated in the autumn of 2011 and 2012 at the USDA-ARS Jones Research Farm, near Chula, GA.  The soil seedbank was sampled prior to study initiation and then each subsequent autumn.  Treatments were a factorial with two levels of tillage (single deep tillage and not disturbed) and two levels of weed control (zero seed return and no weed control).  A high-residue rye cover crop was planted each autumn, rolled in the spring, and cotton planted using a strip-tillage/planting unit that formed an 18 cm disturbance and left 73 cm of rolled rye undisturbed.  The pretreatment soil seedbank averaged approximately 11,000 seeds/m².  Zero-seed-return treatments had <6,900 seeds/m² after the first year, while the no weed control treatments increased to >19,000 seeds/m².  Prior to treatments, 48% of Palmer amaranth in the soil seedbank was in the top 5 cm.  After the first year, only 17% of the total Palmer amaranth seedbank was in the top 5 cm for the zero-seed-return and deep tillage treatment; surface seed were redistributed throughout the profile by tillage.  The zero-seed-return without deep tillage treatment had 42% of the seed remaining in the top 5 cm, representing the annual rate of attrition.  In the no weed control treatments, Palmer amaranth seedling populations were 4.4 to 6.8-fold higher in the cotton row where the strip tillage occurred, relative to the undisturbed row middles that were covered in the rolled rye mulch.  In conclusion, tillage will effectively bury Palmer amaranth seeds, and used in conjunction with zero-seed-return, reduce the soil seedbank in the top 5 cm by 80% after one year.  However, the soil seedbank is saturated with Palmer amaranth seed, allowing little differences in established seedling populations based on tillage treatments.  In addition, based on estimates of seed return by Palmer amaranth and soil seedbank sampling, the fate of over 80% of Palmer amaranth seeds produced is unknown.  Future research should focus on determining what processes regulate seed return and persistence in the soil seedbank.

Winter canola (Brassica napus L.) is becoming an important crop in Oklahoma in rotation with winter wheat (Triticum aestivum L.) as a tool to clean up weedy fields.  However, establishing this crop in no-till systems is challenging and winter survival is much lower than in conventionally tilled systems following wheat.  It is known that wheat can be allelopathic to itself and here we hypothesize that certain wheat varieties exert an allelopathic effect on winter canola survival in no-till systems where crop stubble is not removed.   

Wheat straw samples were collected from 2 locations of Oklahoma State University’s 2014 wheat variety trials, Chickasha, OK and Lahoma, OK.  Experiments were set as a complete 2 x 42 factorial with factor one being canola variety and factor two being wheat variety.  Straw was chopped to a 5 cm or smaller length as if it had been harvested with a straw chopper in place and a “tea” was made from the straw simulating a 35 bushel wheat crop and 2.5 cm of rainfall between wheat harvest and subsequent fall canola planting. The wheat straw was “brewed” for  48 hours and then vacuum-filtered. Three mLs of tea were added to each Petri dish containing 10 canola seeds. Canola was watered as needed with distilled water after initial treatment and images were taken at 3, 5, and 7 days after treatment (DAT). At 7 DAT fresh weight was taken for each plot, samples were dried at 60°C, and dry weights were taken again for each sample.  Digital images were cropped and color-inverted in Adobe Photoshop 9.  Sigma Scan Pro 5 was set to evaluate images for blue identified as plant biomass in the color-inverted images.  Data were subject to ANOVA and means separated by fishers protected LSD (p=0.05).

Of 42 varieties tested across two locations one third significantly decreased fresh weight 7 DAT.  Wheat straws sampled from Chickasha, OK had greater allelopathic affects than wheat straws sampled from Lahoma, OK.  ‘Endurance’, ‘Pete’, ‘Armour’, ‘OK Rising’, ‘WB-Grainfield’, and ‘Doublestop CL+’ sampled from both locations affected canola germination and biomass accumulation for both conventional and Roundup-Ready (RR) varieties as much as 50%.  ‘Deliver’, ‘OK Bullet’, ‘CJ’, ‘WB-Redhook’, ‘LCS Mint’, and ‘Centerfield’ sampled from Chickasha, OK significantly reduced biomass accumulation for both canola varieties; however, samples of the same varieties from Lahoma, OK did not reduce canola germination and biomass.  ‘Doans’ was the only wheat straw to significantly reduce canola biomass accumulation collected from Lahoma, while Chickasha samples of the same variety had no effect. 

It is important to further investigate the capacity for wheat straw from particular varieties to impact canola germination and biomass accumulation in the fall, as this is vital to establishment and winter survival. Remaining wheat straw samples from this experiment which had an effect on canola germination will used to investigate effects in the field in Fall 2015.  

Treatments utilizing various percent concentrations of both 3-lb. and 2-lb. AI liquid formulations of MAT-28 in basal oil were applied to fresly cut surfaces of hardwoods and pines. Stump diameters ranged from the 1-inch size class to the 5-inch size class with the majority of all stumps in the 1-inch and 2-inch size classes. Treatments included 1.67, 3.33, 6.68 and 10% v/v of the 3-lb material and 10% v/v of the 2-lb. material in addition to a 25% v/v solution of Garlon 4. The 1.67% v/v solution had significantly less control than the other treatments, and while increasing the amount of MAT-28 increased control slightly, there were no significnt differences between the other 3-lb formulation treatments. The 3-lb material produced significantly better resuslts than the 2-lb material and the MAT-28 performed overall better than the Garlon 4 treatment.

Tank mixtures of glyphosate, imazapyr and aminopyralid were compared to a tank mix of glyphosate, imazapyr and triclopyr with a timing comparison of July vs. August application. Treatments were applied using a CO2- powered backpack sprayer to simulate aerial broadcast application. Results indicated that all treatments were highly effective in controlling the hardwoods present on the site. The addition of triclopyr or aminopyralid generated no significant additional benefit in this study due to species present on the study site and the level of other active ingredients in the mixtures. Glyphosate and imazapyr combintionswere very effective on controlling all principal species on the site.

MAT28 was tested for unwanted hardwood control in Drew County, AR and in Oktabbeha County, MS. Herbicides were applied near Florence, AR on September 21, 2013 to unwanted hardwoods growing in a loblolly pine pantation recently receiving its 2nd thinning.  Hardwoods were mixed oak (southern red, cherrybark, water > white and post), winged elm, red maple, and hickory (black > mockernut). Hardwoods occupied the leave strip between down rows.  Ten stems in each of the 1-inch, 2-inch, and 3-inch groundline diameter classes received a basal application of bark oil blue and herbicide to the the bottom 14-inch of the stem using a small hand-pump sprayer. Herbicide treatments were:  (1) MAT28+oil 3%+97%, (2) MAT28+oil 7%+93%, (3) MAT28+oil 10%+90%, (4) MAT28+oil 13%+87%, (5) MAT28+oil 10%+90%, (6) MAT28+Garlon+oil 7%+5%+88%, (7) MAT28+Garlon+oil 7%+10%+83%, (8) MAT28+Stalker+oil 7%+1%+92%, (9) Garlon 25%+75%, and (10) untreated check. Treatments 1-4 and mixtures contained a 360SL MAT28 formulation while treatment 7 contained a 2.0SL MAT28 formulation.  Treatments were visually evaluated on November 7, 2014 for percent control. For all species, as rate of MAT28 in treatments 1-4 increased, percent control increased. However, treatments 3 and 4 developed a mayonnaise consistency making uniform application difficult but with little impact on results. Control using the 2.0SL was better than the untreated check. Treatments containg the higher rate of Garlon and MAT28+oil (13%+87%) provided similar control that was below the best treatment, Garlon+oil (25%+75%). In Starr Memorial Forest, MS, treatments were applied on September 23, 2014 in a clearcut. Plots were 10-ft x 100-ft with sprouts within 5-ft of either side of a center line treated and then evaluated on August 14, 2014. Thirty-one species were assessed for control.  For all species best control was achieved with treatments MAT28+oil (13%+87) and MAT28+Garlon.

Palmer amaranth (Amaranthus palmeri S. Watson), pitted morningglory [Ipomoea lacunosa (L.)] and large crabgrass [Digitaria sanguinalis (L.) Scop.] are common and troublesome weeds present in South Carolina soybean production fields. The recent evolution of herbicide resistant Palmer amaranth, control has become more difficult and expensive. In response, the Monsanto Company will be releasing Roundup^® Xtend, a new crop technology which will introduce soybean with tolerance to dicamba and glyphosate. A new low volatility formulation of dicamba premixed with glyphosate will accompany the new crop technology. In 2012 and 2013 field experiments were conducted at Edisto Research and Education Center located near Blackville, SC to evaluate preemergence (PRE) and postemergence (POST) herbicide programs for weed control in dicamba tolerant soybean. Experimental design was a randomized complete block design with individual plot sizes of 3.8 by 12 m.  Treatments were replicated 4 times in all experiments.  Herbicides were applied in water using a CO2 pressurized backpack sprayer calibrated to deliver 240 L/ha with a pressure of 234 kPa.  Each site was naturally infested with pitted morningglory, large crabgrass, and mixed population of glyphosate-resistant and sensitive Palmer amaranth.  Data collected included percent visual weed control and crop injury on a scale of 0 to 100 with 0 being no control or injury and 100 indicating complete weed control or crop death.  Data were subjected to ANOVA and means were separated using Fisher’s Protected LSD at the p = 0.05 level.  Dicamba PRE followed by glyphosate plus dicamba POST1 provided excellent control in all 3 weed species (>97%) at 2 weeks after first post emergence (2 WAP1). In general, dicamba alone PRE was not as effective as flumioxazin alone PRE when rated 2 weeks after second post emergence (2 WAP2). There were no significant differences in treatments containing three application timings than two. All treatments with at least one POST treatment effectively controlled all three weed species. Results showed flumioxazin PRE followed by glyphosate and dicamba POST1 and POST2 were the most effective treatment in Palmer amaranth and large crabgrass with 100% and 99% control respectively, 2 WAP2.  Overall, dicamba plus glyphosate POST provided excellent control for all 3 weeds species.

In data presentation, tables or bar charts are normally utilized to present the mean of a given treatment accompanied by mean separation procedures such as Fisher’s Protected LSD.  In such a comparison, treatment separation is based on the mean.  While statistically sound, end-users are only given partial information in such a scenario to base their herbicide choices. In turfgrass management, end-users are specifically interested in the consistency of products on a year after year basis, thus, the treatment variability that is also of interest. Box-and-whisker plots, also referred to as box plots, are ideal for visualizing and comparing variability of treatments when trials are conducted over multiple years or locations. Research was initiated to evaluate preemergence weed control in turfgrass for four consecutive years with the goal of identifying possible yearly variability in treatments. 

A preemergence herbicide evaluation trial was initiated in Fall 2009 to evaluate annual bluegrass control and Spring 2010 to evaluate smooth crabgrass control. Each trial was repeated yearly in a different location until 2014, with trial initiation occurring in early March for preemergence smooth crabgrass (Digitaria ischaemum (Schreb.) Schreb. Ex Muhl.) control (four trials total) and mid-September for annual bluegrass (Poa annua L.) control (four trials total).  Treatments included (in kg ai/ha):  atrazine (1.12), prodiamine (1.12), prodiamine (0.76) plus sulfentrazone (0.36) dithiopyr (0.56), pendimethalin (2.2), pendimethalin (2.2) plus dimethenamid-p (1.68), simazine (1.12), oxadiazon (3.36), indaziflam (0.027), indaziflam (0.054), and dimethenamid-p (1.68).  Data were rated for percent weed control on a 0 to 100% scale monthly, however we present data from the conclusion of experiments, which was early-April for annual bluegrass trials and late-August for smooth crabgrass control trials.  Treatments were applied with a CO₂ pressurized backpack sprayer at 280 L ha^-1. No adjuvants were included with any treatment.  Data subjected to analysis of variance using PROC GLIMMIX using SAS 9.2 (SAS Institute, Cary NC).  Box and whisker plots were generated using PROC BOXPLOT. 

First in evaluating annual bluegrass control, only prodiamine and indaziflam at 0.046 lower quartile range remained above 80% control.  Quartile range of oxadiazon and indaziflam at 0.027 was 60 to 85% and 76 to 95%, respectively. For smooth crabgrass, only indaziflam (0.054) lower quartile exceeded 90%. Minimum lower quartiles for pendimethalin, pendimethalin plus dimethenamid-p, prodiamine plus sulfentrazone, dithyopyr, and prodiamine was 70% control or greater. Lower quartiles for atrazine, oxidiazon and indaziflam (0.027) failed to reach 60% control. Based on this results, prodiamine and indaziflam (0.054) can used to consistently and efficiently control annual bluegrass yearly.  For smooth crabgrass, efficient and consistent control was only achieved with indaziflam (0.046), yet several herbicides resulted in moderate-to-high control. 

Evaluation of Harvest Aid Systems

in Mid-South Soybean Production

A. Brown*

B.W. Thomason

 J.T. Irby

Mississippi State University

 Starkville, Mississippi 39759

ABSTRACT

Indeterminate soybean varieties have become common for many mid-south soybean producers and along with that has come an increased use of harvest aids to desiccate plants at the end of the growing season. Whether due to delayed senescence under certain environmental conditions or the desire to deliver a crop sooner to achieve premium commodity prices, harvest aids provide an option to expedite the entry into a harvest season. Products such as paraquat, saflufenacil, carfentrazone and sodium chlorate can be applied to desiccate plant material. By label, harvest aid applications are to be made at 65% mature pods for the three herbicides or 7-10 days before harvest for sodium chlorate. Previous studies have shown that harvest aids do not cause significant yield reductions when applied at as high as 50% seed moisture. Conversely, if applied at 60% seed moisture a 15.4% yield reduction occurred. During the 2014 growing season, an experiment at the R.R. Foil Plant Science Research Center in Starkville, MS was conducted to evaluate paraquat, saflufenacil, and sodium chlorate applied at timings designated by the R6 and R6.5 growth stage and at 65% mature pods. Results show no significant yield reduction for any of the three application timings. However, although not statistically significant, an average of 3 bu/A reduction occurred under the R6 timing treatments. Observations recorded 7 DAA and beyond indicate no significant differences between harvest aid treatments. All treatment combinations required 14-15 DAA to facilitate harvest. Harvest was expedited 18 days under the R6 application, 11 Days at R6.5, and 4 days for the 65% mature pod application compared to the untreated check.

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, J.D. Copeland¹, 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 oberseved 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^® on the horizon, 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 3 mph. 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 Orthene 97 (SP) @ 0.84 kg ai/ha and Karate (EC) at a rate of 0.05kg ai/ha. Insecticides were applied alone or in combination with Liberty @ 0.6 kg ai/ha, Roundup Powermax @ 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 dye was added to each treatment at a rate of 0.2% v/v. Metal stands 24” 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, Roundup Powermax, or Liberty with all three having a negative impact on total deposition in the canopy. However, when analyzing the front stand, treatments containing Roundup Powermax, 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 Orthene + 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 Orthene with no additive. However, when analyzing the same interaction for the front stand treatments containing Orthene + Roundup Powermax had significantly greater deposition compared to all other treatments with deposition being 525 percent greater than that of treatments containing only Orthene. Data suggest that Roundup could be minimizing droplet size allowing for further canopy penetration at position 4 due to less surface area per droplet. 

Maximized and sustainable soybean (Glycine max) yields are the ultimate goal of producers. However, environmental conditions which expose soybean to weather extremes such as heat and drought sometimes limit a producer’s ability to achieve this goal. The Early Soybean Production System (ESPS) consists of planting early-maturing, indeterminate soybean varieties in mid-April to mid-May to reduce late-season environmental stresses.  Anecdotal evidence suggests that lactofen applied to soybean during vegetative growth stages improves yield by altering branching and height. Lactofen is a recommended herbicide for broadleaf weed control in specific situations in Mississippi soybean. Soybean injury with lactofen can be severe; however, it is unknown if this injury has a positive or negative effect on soybean growth and yield. 

A field study was conducted in 2013 and 2014 at the Mississippi State University Delta Research and Extension Center in Stoneville, MS, to determine if lactofen influences soybean growth and yield when applied to early-maturing, indeterminate soybean across multiple planting dates. The experimental design was a split plot with four replications. The whole plots were soybean planting dates of April 15, May 1, May 15, and June 1. The subplots were herbicide treatments and consisted of a control that received no postemergence treatment, crop oil concentrate (COC) at 1% (v/v), and lactofen at 0.22 kg ai/ha plus COC at 1% (v/v). All treatments were applied at V2 soybean growth stage. Soybean necrosis and soybean biomass reduction were visually estimated 7, 14, 21, and 28 days after treatment (DAT). Photosynthetically active radiation under the soybean canopy and soybean height was determined 21 and 28 DAT. Soybean height, number of nodes, and yield were determined at maturity. All data were subjected to ANOVA and estimates of the least square means were used for mean separation with α = 0.05. Pooled across planting dates, soybean necrosis from lactofen was 35% 7 DAT. However, necrosis 14 DAT with lactofen was no worse than in control plots or those treated with COC only. Pooled across planting dates, soybean height 28 DAT was 10% lower in plots treated with lactofen compared with control plots. Pooled across herbicide treatments, soybean heights were 23 and 47% greater with June 1 planting date compared with earlier plantings. The number of nodes at maturity was similar in plots treated with lactofen at all planting dates, but soybean plants in control plots produced more nodes with May 15 and June 1 plantings than April 15 or May 1.

A field study was conducted at two sites in 2014 to compare the soybean response to lactofen applied over a range of soybean growth stages. The experimental design was a randomized complete block with four replications. Lactofen at 0.22 kg/ha plus COC at 1% (v/v) was applied at weekly intervals beginning when soybean reached the V2 growth stage. Data collection and analysis were as previously described. Soybean necrosis with lactofen was 5 to 28% 7 DAT and 5 to 23% 14 DAT. At 7 DAT, soybean necrosis with lactofen applied at V3 and R1 was greater than those ≥ R2. The same trend was less apparent 14 DAT; however, necrosis was greater with V3 applications than those ≥ R3. Soybean height 14 days after last lactofen application, mature soybean height, number of nodes, and soybean yield were not affected by lactofen applied from V2 to R5.

Lactofen at V2 reduced soybean height early in the season; therefore, plant growth was altered by lactofen application. Differences in number of nodes at maturity resulted more from planting date than lactofen applications.  Soybean yield was not influenced by lactofen at different planting dates or application timings. Early-season soybean growth can be altered with lactofen; however, it has little utility as a plant growth regulator to improve yields.

Glyphosate-resistant (GR) Palmer amaranth (AMAPA) remains troublesome throughout the southern United States.  To aid in the control of this weed, Monsanto has developed cotton cultivars with tolerance to glufosinate, glyphosate, and dicamba.  Dicamba offers wide spectrum broadleaf control and will be an additional postemergence (POST) over-the-top and preemergence (PRE) option for weed control in cotton.  An experiment was conducted at North Carolina during 2013 and 2014 and Georgia during 2013 to evaluate AMAPA control in BollGard II^® XtendFlex^™ cotton with herbicide systems including dicamba.  Soil at the field site was loamy sand with 0.46 to 1.9% organic matter and greater than 100 AMAPA/m².  The experiment consisted of a factorial treatment arrangement of two base herbicide systems and seven timings of dicamba.  All plots received acetochlor (1260 g ai/ha) immediately following planting (PRE).  The two base herbicide systems were glyphosate potassium salt (1260 g ae/ha) and glufosinate-ammonium (654 g ai/ha).  These herbicides were applied to 2- to 3-leaf cotton 18 to 23 days after planting (POST 1) and 18 to 22 days later to 8- to 10-leaf cotton (POST 2).  Timing of dicamba applications included no dicamba, PRE, POST 1, POST 2, PRE and POST 1, PRE and POST 2, and POST 1 and POST 2.  All plots, except the non-treated control, received a directed lay-by application of diuron (1120 g ai/ha) plus monosodium acid methanearsonate (2240 g ai/ha) plus nonionic surfactant (1% v/v) when cotton was 41 to 58 cm tall (Lay-by).  Data for cotton injury, AMAPA control, and seed cotton yield were subjected to ANOVA using the PROC GLIMMIX procedure in SAS and means separated using Fisher’s Protected LSD at p =0.05.  Very little cotton injury was observed 7 days after POST 1 and 7 days after POST 2 (< 8%) following applications of glufosinate, glyphosate, and dicamba.  Cotton injury was transitory and 14 days after POST 3 no injury was observed by any herbicide treatment.  No cotton injury was observed following applications of PRE herbicides.  Acetochlor alone PRE controlled AMAPA 59 to 83% prior to POST 1.  At all locations, AMAPA control by acetochlor plus dicamba was greater than acetochlor alone (78 to 99%).  Dicamba benefited both the glyphosate and glufosinate system.  However, because of the significant amount of GR AMAPA at the location, the increase in control was more dramatic in the glyphosate system.  Late in the season, glufosinate and glyphosate applied alone POST 1 and POST 2 controlled AMAPA 76 and 32%, respectively.  Adding dicamba PRE or POST 1 in the glufosinate system did not improve AMAPA control compared to glufosinate alone.  The addition of dicamba at POST 2 to glufosinate increased AMAPA control 15%.  Likewise, two applications of dicamba in the glufosinate system improved AMAPA control 19 to 23%.  In the glyphosate based system, dicamba added PRE, POST 1, or POST 2 increased AMAPA control 19, 47, and 50%, respectively.  Dicamba applied PRE and either POST 1 or POST 2 also improve AMAPA control.  However, in the glyphosate system, the greatest increase in control of AMAPA was observed following dicamba applied twice POST.  When AMAPA were large (20 to 25 cm), dicamba applied POST improved AMAPA control by glufosinate and glyphosate alone 27 and 70%, respectively.  Trends in seed cotton yield were similar to AMAPA control.  Seed cotton yield was greater in plot that received acetochlor + dicamba compared to acetochlor alone.  Also, in the glufosinate system, seed cotton yield was improved by the addition of dicamba at POST 2, PRE and POST 1, PRE and POST 2, and POST 1 and POST 2.  In the glyphosate system, dicamba applied at any timing improved yield compared to plot receiving glyphosate only.  However, dicamba applied twice POST increased yield 2130 kg/ha compared to glyphosate only.  In general, including dicamba with glufosinate or glyphosate increased AMAPA control.  However, increases in AMAPA control were much more noticeable when dicamba was added to glyphosate.  Furthermore, glufosinate alone controlled AMAPA greater than glyphosate alone.  This was to be expected with the high level of GR AMAPA.  However, when dicamba was included with each of these herbicides, differences in weed control by glufosinate and glyphosate were only minor.  Therefore, in cotton tolerant to glufosinate, glyphosate, and dicamba and where GR weeds are present, glyphosate plus dicamba may prove to be a useful weed control option.  Furthermore, dicamba combined with glufosinate greatly increased AMAPA control when applied to AMAPA greater than 10 cm in height.  Growers will find utility in adding dicamba to glufosinate when weeds are larger than desired for glufosinate alone to control.  Additionally, tank mixes of dicamba plus glufosinate include two modes of action, reducing the chances of weed resistance developing to either herbicide. 

INFLUENCE OF HERBICIDE ON DEVELOPMENT OF INTERNAL NECROSIS IN ‘COVINGTON’ SWEETPOTATO. S. Beam, S. Chaudhari, N.T. Basinger, S. McGowen, K.M. Jennings and D.W. Monks; Department of Horticultural Science, North Carolina State University, Raleigh, NC, 27695.

Field studies were conducted in 2014 at the Horticultural Crops Research Station near Clinton NC to determine the influence of herbicides on the development of internal necrosis (IN) in Covington sweetpotato.  IN appears to be a postharvest disorder expressed as dark necrotic regions inside the sweetpotato storage root.  Symptoms begin from the proximal end of the storage root and proceed through the root with no external symptoms.  In study one herbicides were applied to the slip (sweetpotato plant) propagation bed after sweetpotato roots were planted and covered with soil but prior to slip emergence.  Treatments for the propagation bed study included PRE flumioxazin (1.53, 3.06 oz ai/A), S-metolachlor (0.71, 1.43 lb ai/A), linuron (0.5, 1 lb ai/A), fomesafen (0.25, 0.5 lb ai/A), napropamide (1, 2 lb ai/A) and clomazone (0.375, 0.75 lb ai/A).  Additional treatments included seperate POST treatments of paraquat (0.125, 0.25 lb ai/A) and ethephon (0.75, 1.125 lb ai/A) and nontreated checks (weedy, weed-free).  Slips were cut from the beds just above the soil and then transplanted to a production field with no additional herbicide treatments applied except for clethodim POST for grass control in late season.  Study two included herbicides applied to sweetpotato slips (nonrooted) transplanted in the production field.  Treatments in the second study included PREPLANT flumioxazin (1.53, 3.06 oz/A), linuron (0.5, 1 lb/A), fomesafen (0.25, 0.5 lb/A), and paraquat (0.5, 1 lb/A). PRE herbicide treatments included S-metolachlor (0.71, 1.43 lb/A), clomazone (0.375, 0.75 lb/A), and napropamide (1, 2 lb/A) applied 4 d after transplanting.  Additional treatments included of ethephon (0.75, 1.125 lb/A) applied 2 wk prior to harvest and nontreated checks (weedy and weed-free).  Sweetpotato storage roots in both studies were harvested 108 (+ 5) d after planting using a tractor mounted chain digger.  Internal necrosis evaluations were measured the day of harvest, 30, and 60 d after curing (cured at 85 F and 95% relative humidity for 7 d and stored at 58 F and 85% relative humidity).   Although internal necrosis occurred in sweetpotato storage roots it does not appear that herbicides greatly affect the incidence of internal necrosis.

HPPD-TOLERANT SOYBEAN SYSTEMS FOR MANAGEMENT OF GLYPHOSATE-RESISTANT PALMER AMARANTH.  B. W. Schrage, M. Rosemond, J. Allen, M. Marshall, and W. Everman, North Carolina State University, Raleigh, North Carolina

ABSTRACT

The carbon efficiency of Palmer amaranth contributes to its rapid growth, prolific reproduction, and overall competitiveness in North Carolina soybean systems.  With the growing presence of glyphosate-resistant biotypes; alternative weed management strategies such as HPPD-tolerant soybeans are being evaluated.  An experiment was conducted in Clayton, NC and Blackville, SC in 2014 to assess the efficacy of isoxaflutole and yield in HPPD-tolerant soybeans.  Several combinations of isoxaflutole (Balance Pro), flumioxazin (Valor SX), pyroxasulfone (Zidua), and flumioxazin and pyroxasulfone (Fierce) were applied PRE.  Similar POST applications of glyphosate and fomesafen (Flexstar GT) followed at 4 WAP.  Plots were rated for percent control of Palmer amaranth at 2, 4, and 7 WAP in South Carolina and 4 and 5 WAP in North Carolina.  All plots were harvested upon reproductive maturity.  All treatments exhibited greater than 95% control and without phytotoxic symptomology observed on the soybeans; there was no significant difference in yield among treatments in the study conducted in Blackville.  In Clayton, treatments failed to display significant differences.  This research might suggest the overall effectiveness of proactive weed management efforts to control glyphosate-resistant Palmer amaranth; albeit little difference was noticed among treatments.

CHANGE IN PALMER AMARANTH POPULATIONS IN COTTON FOLLOWING FOUR YEARS OF GLYPHOSATE AND DICAMBA M. Inman*, D. Jordan, A. York, K. Jennings, W. Everman, D. Monks; North Carolina State University, Raleigh, NC

Herbicide resistance has changed weed management programs considerably over the past decade. Glyphosate-resistant Palmer amaranth has been one of the most burdensome and economically challenging weed species in cotton production throughout Southeastern United States.  GR Palmer amaranth now drives weed management programs and the adoption of new strategies and tools to integrate with existing methods are needed.

Research was conducted from 2011-2014 to determine weed population dynamics and frequency of resistance of glyphosate-resistant Palmer amaranth with herbicide combinations consisting of glyphosate, dicamba, and residual herbicides in dicamba-tolerant cotton. Eight herbicide treatments were established in the experiment. Five treatments were maintained in the same plots over the duration of the experiment that consisted of glyphosate only postemergence with and without residual herbicides, glyphosate plus dicamba only postemergence with and without residual herbicides, and glyphosate plus dicamba plus acetochlor only postemergence.  Remaining treatments alternated years with glyphosate only and glyphosate plus dicamba only postemergence; with and without residual herbicides. In spring of each year and winter of 2014, ten soil cores (approximately 4 L) were collected at random in each plot after planting and prior to any herbicide application. Soil cores were placed in greenhouse containers. After seedling emergence, weed diversity and density were recorded. An application of glyphosate at 946 g/ae ha was applied to all soil cores and based on surviving weed population frequency of resistance was determined for each treatment. Density of Palmer amaranth in the field was determined in August of each year after all herbicides were applied. Comparable trends were noted between field and greenhouse data. Treatments with glyphosate only postemergence had the highest population of Palmer amaranth regardless of residual herbicide use or not. The lowest populations were observed in treatments where dicamba was applied. Treatments with alternating postemergence herbicide programs, Palmer amaranth populations were central between glyphosate only and glyphosate plus dicamba postemergence treatments. By the end of the experiment frequency of glyphosate resistance was similar regardless of herbicide program.

As the occurrence of herbicide resistant Italian Ryegrass (Lolium multiflorum) continues to spread, control options are continuing to decline.  Cultural practices may become an option to help suppress ryegrass populations and increase control effectiveness when combine with a sound herbicide program.  One practice that may have a significant impact on Italian Ryegrass population is tillage.  To test this theory, wheat was grown in both tilled and in no-till conditions and received the following herbicide treatments; non-treated check, Zidua (pyroxasulfone) at 1.25, and 1.5 oz/a pre, Fierce (flumioxazin and pyroxasulfone) at 3 oz/a pre, Zidua at 1.25 oz/a and Sharpen (saflufenacil) at 2 fl oz/a pre, Prowl H2O (pendimethalin) at 2 pt/a at spike, Axiom (flufenacet and metribuzin) at 8 oz/a at spike, Axiom at 10 oz/a at spike, Zidua at 1.25 oz/a pre fb Osprey (mesosulfuron) at 4.75 oz/a and non-ionic surfactant at 1qt/100gal post, Zidua at 1.25 oz/a pre fb Powerflex (pyroxsulam) 3.5 oz/a post, Zidua at 1.25 oz/a pre fb Axial XL (pinoxaden) at 16.4 oz/a post, Osprey at 4.75 oz/a and Zidua at 1 oz/a and non-ionic surfactant at 1 qt/100gal post, Powerflex at 3.5 oz/a and Zidua at 1 oz/a post, Axial XL at 16.4 oz/a and Zidua at 1 oz/a post .  In 2013, weed control and yield were both improved in the tilled system compared to the no-till system.  Improved control in a tilled system was again seen in two locations in 2014, and yield was improved in one location, while in the other there were no yield differences seen between tillage systems.  

Italian ryegrass is a troublesome weed in wheat production fields, which also carries over to corn, cotton, and soybean. Glyphosate-resistant Italian ryegrass in Arkansas was first detected in 2007. In 2014, 45 populations were confirmed resistant to glyphosate in eight counties across the state. This research is conducted to determine the level of resistance to glyphosate in 6 Italian ryegrass populations from Arkansas and to elucidate the resistance mechanism to glyphosate across multiple populations. The resistance level was determined by dose-response bioassay in the greenhouse.  The absorption and mobility of glyphosate was evaluated using radiolabeled glyphosate. The herbicide target gene, EPSPS, was sequenced and gene amplification was determined by quantitative real-time PCR. The dose causing 50% growth reduction (GR₅₀) was 7 to 19 times higher for the resistant than the susceptible population. Uptake and translocation of ¹⁴C-glyphosate was similar in resistant and susceptible plants. Target-site mutation associated with resistance to glyphosate was not detected. Resistant plants contained 11-fold to 151-fold more copies of the EPSPS gene than the susceptible plants, while the susceptible plants had only one copy of EPSPS. Plants surviving the recommended dose of glyphosate contained at least 11 copies. The EPSPS copy number was positively correlated to glyphosate resistance level (r=80). Therefore, resistance to glyphosate in these populations is due to multiplication of the EPSPS gene. Suppressing the mechanism of gene amplification may overcome resistance. The occurrence of EPSPS gene amplification was first reported in Palmer amaranth and now is also observed in Italian ryegrass, kochia, spiny amaranth, and tall waterhemp. Weeds are evolving ways to survive glyphosate application. Best management strategies should be implemented to curtail resistance evolution and to conserve the utility of glyphosate.

Clopyralid is the only available herbicide for post emergence weed control in Florida strawberry production.  Previous research has suggested that low rates of clopyralid may produce a hormesis effect.  Furthermore, the range of tolerance for strawberry to clopyralid is not well understood.  The objective of the study was to identify any hormesis effect by low doses of clopyralid and test the range of clopyralid tolerance for strawberry.  A dose response study was established in Citra, Florida using a randomized complete block design.  Strawberries were planted on November 12, 2013 and clopyralid applied on February 28, 2014 at rates of 0, 35, 70, 140, 280, 560, 1120 and 2240 g ae/ha.  Growth measurements were taken weekly from March 7, 2014 thru April 19, 2014.  Response variables include plant height, plant width, leaf number, flower number and damage rating.  Harvest was taken biweekly between the 19^th March and the 17^th of April.  A destructive plant harvest for dry biomass partitioned into above and below ground portions was taken at 47 days after treatment (DAT).  Hormesis was tested with nonlinear regression using the Brian-Cousens log-logistic dose response model hormesis parameter’s confidence interval.  Analysis of variance and means separation were used to determine treatment effects.  There was no significant hormesis effect on either fruit number or harvested fruit weight.  Rates up to 280 g ae/ha caused no significant visual damage at 33 DAT.  Rates above 280 g ae/ha caused significant decreases in plant height and width compared to the control at 33 DAT.   Above ground biomass was significantly reduced at 1120 g ae/ha versus the control and the 35 g ae/ha treatment was significantly higher than treatments from 280 g ae/ha and higher.  Leaf number was significant reduced by rates of 1120 g ae/ha and higher at 47 DAT.  Rates of 560 g ae/ha and higher significantly reduced below ground biomass.  Both berry number and harvested weight were significantly reduced at 1120 g ae/ha rates compared to the control though both weight and number were significantly higher at 35 g ae/ha than any other clopyralid treatment.  Vegetatively, strawberries tolerated applications of clopyralid up to 560 g ae/ha above ground and up to 240 g ae/ha below ground without any significant damage.  Reproductively, strawberries tolerated up to 560 g ae/ha without significant reductions in both berry number and harvested weight.  Low doses of clopyralid produced no significant hormesis effect on strawberry yield.

With the evolution of weeds that have resistance to multiple herbicide modes of action, a new technology is needed to control many of these troublesome weeds. BASF is currently developing a new rice that will be resistant to quizalofop, an acetyl coenzyme A carboxylase (ACCase)-inhibiting herbicide.  A field experiment was conducted in the summer of 2014 at the University of Arkansas Agricultural Research and Extension Center in Fayetteville, Arkansas to evaluate the residual activity of quizalofop relative to other graminicides for crop injury and grass weed control.  The experiment was set up as a split-split plot design assigning overhead-irrigation activation as the whole plot factor, with plant-back date as the sub-plot, and herbicide treatments as the sub-subplot.  This experiment was evaluated for four different crops (conventional rice, quizalofop-resistant rice, grain sorghum, and corn).  Herbicide treatments were the anticipated labeled (120 g ai/ha) and 2X rates of quizalofop (Targa) and the currently labeled and 2X rates of fenoxaprop (Ricestar HT), cyhalofop (Clincher), fluazifop (Fusilade DX), clethodim (SelectMax), and sethoxydim (Poast).  The irrigation event was applied with a traveling gun sprinkler system, and the plant-backs were made at 0, 7, and 14 days after treatment.  On all crops, injury increased with herbicide activation over no activation.  At 14 to 21 days after treatment, corn and grain sorghum both had the highest injury of 19% and 20%, respectively, from the high rate of sethoxydim with activation.  Conventional rice and quizalofop-resistant rice had the highest injury of 13% and 4%, respectively, from fluazifop at the 2X rate.  Herbicides effectively controlled emerged grasses at the time of application, but provided little residual grass control.  The highest level of grass control occurred at 14 days after treatment, with control for all treatments declining at later assessments.  Barnyardgrass (Echinochloa crus-galli) and broadleaf signalgrass (Urochloa platyphylla) were best controlled with the high rate of fluazifop at 98% and 96%, respectively.  The results of this experiment suggest that caution will need to be taken for the plant-back period and immediate plant-back is not likely.  Rainfall or irrigation appear to influence the activity of the evaluated graminicides and some crops exhibited greater tolerance, or less risk for injury, than others.

In Tennessee the majority of field crops are grown in the western region of the state.  Because of soil type, annual rainfall, and low elevation, flooding occurs in the counties along the Mississippi River.  Similarly in other states with regions prone to flooding, producers are faced with the question of should they replant and whether to replant corn (Zea mays) or soybean (Glycine max).  Therefore the purpose of this research was to evaluate how flooding would affect atrazine dissipation in the soil and subsequent yield.  This study was conducted at the University of Tennessee Plant Science Farm in Knoxville, TN.  Plots were arranged in a factorial split-plot design with 2 tratment levels for 2012 and 2014.  Because of above average rainfall in 2013, data was not collected.  The first level of treatment consisted of flooded (F) and non-flooded plots (NF).  The second level of treatment was atrazine with dosages of 0, 2.2, and 4.5 kg ai ha^-1.  Soil samples, soybean injury at approximately 30 days after planting (DAP), and soybean yield data were collected.  Soil samples were analyzed for atrazine concentration using a LC-MS according to laboratory standard operating procedures (SOPs).  Data was analyzed using ARM (version 9.0) for mean separations that were tested with a protected LSD (P < 0.05).  In 2012, data indicated that atrazine concentrations were higher at planting in NF plots compared to F plots.  Yield was observed to be higher in NF plots, which would be expected since atrazine was readily available for possible plant activity and soybean injury.  In 2014, although atrazine concentration was significantly higher in NF plots, there were no differences in yield among treatments.

Biochar reduces preemergence herbicide availability and weed control when used as a soil amendment. N. Soni*¹, R.G. Leon¹, J.E. Erickson², J.A. Ferrell², and Maria Silveira³. ¹University of Florida, Jay, FL 32565, ²University of Florida, Gainesville, FL 32611, ³University of Florida, Ona, FL 33865.

Biochar is a by-product of biofuel production and is currently used as a soil amendment to favor soil fertility and moisture and reduce leaching of nutrients. Despite its benefits to soil health and productivity, because biochar has high adsorption capacity its addition to the soil might affect preemergence herbicide activity. However, there is limited information available about the effect of biochar on weed control especially under field conditions. The present study evaluated how adding biochar to the soil modified atrazine and pendimethalin availability and their herbicidal activity under in vitro and field conditions. A sorption experiment showed that biochar reduced atrazine and pendimethalin concentration in the soil solution due to high levels of adsorption at all herbicide concentrations evaluated. Soil with biochar exhibited 16 and 4 times higher adsorption than soil alone. Under field conditions, atrazine and pendimethalin weed control in biochar treated plots was reduced in 75% and 60%, respectively compared to plots without biochar. Doubling the label rate did not compensate for the biochar negative effect on herbicide availability, and weed control was <50%. These results suggested that the use of biochar as a soil amendment in cropping system could decrease preemergence herbicide efficacy. Therefore, additional weed control practices such as the use of higher rates or more intensive use of postemergence herbicides and cultivation might be necessary to achieve adequate weed control levels.

Glyphosate is the cheapest and most commonly used herbicide for annual bluegrass (Poa annua L.) control in dormant bermudagrass (Cynodon dactylon L.) turf.  In 2013, field manager at the Frank Liske Park in Concord, NC reported an annual bluegrass population not controlled by glyphosate after six years of continuous applications.  Plugs of suspected glyphosate-resistant annual bluegrass plants were collected from the Frank Liske Park and screened for glyphosate resistance.  The annual bluegrass population was found resistant to glyphosate at 0.42 kg ai ha^-1, the labeled rate for annual bluegrass control in dormant bermudagrass turf.  The annual bluegrass population with glyphosate resistance was grown in a greenhouse at the Glade Road Research Facility in Blacksburg, VA to produce seeds.  Two greenhouse studies were conducted with an objective to compare locally-collected glyphosate-susceptible annual bluegrass to the suspected resistant population for response to glyphosate.  Additional greenhouse studies were conducted to determine if resistance to glyphosate in suspected glyphosate-resistant annual bluegrass population confers resistance to other herbicides.  All studies were arranged in a randomized complete block design with four replications.  Data were collected for annual bluegrass visual injury and height reduction at weekly intervals, and reduction in annual bluegrass biomass at three and seven weeks after treatment (WAT).  Replicate data were converted to percentage reductions compared to untreated plants and regressed against glyphosate rate using hyperbolic function via SAS 9.2.  Estimated GR₅₀ values were then calculated and subjected to analysis of variance to test for trial and biotype effects and interactions.  Significant effects were separated using Fisher’s Protected LSD test at the 5% level of significance.  The suspected resistant population of annual bluegrass was found to be resistant based on significantly different GR₅₀ values from height and biomass data at 3 and 7 WAT.  Resistance factors ranged between 2 and 18 depending on measured response variable and trial.  This study confirms the first report of glyphosate-resistant annual bluegrass developed on athletic field turf.  Research is currently underway to determine the mechanism of resistance in this annual bluegrass population.

CONFIRMING RESISTANCE TO PRODIAMINE AND GLYPHOSATE IN A SINGLE

ANNUAL BLUEGRASS (POA ANNUA L.) BIOTYPE FROM TENNESSEE

S.M. Breeden, J.T. Brosnan, T.C. Mueller, B.J. Horvath, D.A. Kopsell, S.A. Senseman, G.K. Breeden, and J. J. Vargas; University of Tennessee, Knoxville, TN.  

ABSTRACT

Annual bluegrass (POAAN) is a cool-season weed that commonly infests warm-season turfgrasses during winter dormancy. Cases of POAAN developing resistance to both PRE and POST herbicides in managed turfgrass systems have been reported throughout the southeastern United States; however, instances of POAAN developing multiple-resistance are limited. Poor POAAN control was reported in golf course roughs in Alcoa, TN following treatment with a tank mixture of prodiamine (1120 g ha^-1) and glyphosate (840 g ae ha^-1) during bermudagrass dormancy in 2013. POAAN had received this treatment for over ten consecutive years without chemical rotation. We hypothesized that this POAAN population had evolved multiple-resistance to both glyphosate and prodiamine and conducted research to determine the sensitivity of this POAAN biotype to applications of these herbicides.

Non-treated POAAN was harvested from field plots (1.5 x 10 m) at this location on 18 March 2014. A total of 100 plants were removed from three plots using a 1-m² grid. Each plant was distinguished by a number, then dissected into single tillers and transplanted into 164-cm³ cone-tainers filled with a peat moss growing medium. Each tiller was given an alphabetical identifier associated with the number assigned during field harvesting. Plants were grown in a glasshouse with average low and high temperatures of 19 and 29 °C respectively. Tillers were irrigated thrice daily and maintained at a 4-cm height using scissors. In total, this process produced 890 tillers for experimentation.

To evaluate glyphosate sensitivity, 100 tillers were randomly selected from all plants harvested from the field and treated with glyphosate at 840 g ha^-1 in an enclosed spray chamber (Generation III Research Sprayer, DeVries Manufacturing, Hollandale, MN) calibrated to deliver 281 L ha^-1 on 29 April 2014. Visual control was assessed 21 days after treatment (DAT) on a 0 (no control) to 100% (complete kill) scale relative to a non-treated check. Plants controlled ≤ 30% were deemed glyphosate resistant (GR), while those controlled ≥ 70% were deemed susceptible. Moreover, 100 additional tillers from the GR group were analyzed for shikimic acid accumulation compared to a known susceptible POAAN population established from seed. These 100 tillers were treated with glyphosate at 420 g ha^-1 on 13 May 2014 and destructively sampled 0, 1, 2, 3, and 6 DAT. This experiment was repeated on 20 May 2014. Each study was replicated four times and incorporated 5 sub-samples per biotype on each sampling date. Shikimic acid accumulation was quantified via high performance liquid chromatography with biotype responses compared using non-linear regression analyses.

Prodiamine sensitivity was evaluated in hydroponic culture using polyethylene containers filled with 10 L of full strength Hoagland nutrient solution connected to air stones to ensure oxygenation and agitation. Ten POAAN plants were washed free of growing media and cut to a uniform root length of 5 cm. Plants were inserted into pre-dilled holes in the lid of each container such that root tissues were submerged in the nutrient solution on 29 April 2014. In total, 100 tillers were randomly selected from all harvested plants. Immediately after insertion, prodiamine was added to the hydroponic solution at 0.04 mM, a concentration known to inhibit root growth of prodiamine-resistant POAAN from our field site by 50%. At 10 DAT, root length was measured with a ruler for all plants. Plants with root length > 5 cm were deemed prodiamine resistant while those with root length ≤ 5 cm were deemed susceptible.

In total, 96 of the 100 plants studied were deemed to be GR. These plants were controlled ≤ 30% 21 DAT and accumulated 50% less shikimic acid 6 DAT than a susceptible population. A total of 84 plants were deemed resistant to prodiamine, yielding 0.1 to 3 cm of root growth during the 10-day evaluation period. Across the entire 100 plant population, 81 plants were resistant to both herbicides while only a single plant was susceptible to both chemistries.

Future research is needed to confirm these resistance traits from seed and to determine if the ratios of resistant-to-susceptible plants observed in these greenhouse studies are present after treatment with glyphosate and prodiamine in the field.

Glyphosate resistant Palmer amaranth is an economically troublesome weed too many southeastern U.S. growers.  Palmer amaranth is notable mainly due to its competitiveness, prolific seed production, and herbicide resistance.  Long-term management of Palmer amaranth requires a multi-faceted approach that includes rotating crops and herbicides, diversifying in-season herbicides, and closely monitoring fields for Palmer amaranth.  Cultural practices such as altered row spacing combined with a PRE herbicide can aid in Palmer amaranth control.  Flumioxazin plus pyroxasulfone is widely used in Mississippi as a PRE herbicide targeting Palmer amaranth.  Additionally, most soybean in Mississippi are grown on wide rows, but interest in narrow row production to aid in Palmer amaranth management has increased recently.  Therefore, research was conducted to determine the effectiveness of soybean row spacing as a tool for reducing the emergence of Palmer amaranth and to evaluate the effect of soybean row spacing on canopy light interception and soybean performance.

Two separate field studies were conducted at the Mississippi State University Delta Research and Extension Center in Stoneville, MS, in 2013 and 2014.  Both studies were in a randomized complete block design with four replications.  The first study, Palmer amaranth emergence study, evaluated three soybean row spacings (19, 38, and 76 cm) for their influence on emergence of Palmer amaranth throughout the growing season.  The second study, soybean light interception study, compared the same three soybean row spacings for their effect on canopy light interception and soybean yield.  Plots in the Palmer amaranth emergence study received no herbicide treatment and new emergence was recorded as plant/m² at 30, 60, and 90 days after planting (DAP).  Plots in the soybean light interception study were treated immediately after planting with flumioxazin plus pyroxasulfone at 0.0681 and 0.922 kg ai/ha and photosynthetic active radiation (PAR) values were recorded below the soybean canopy at 30, 60, and 90 DAP.  All data from both studies were subjected to ANOVA and estimates of the least square means were used for mean separation with α = 0.05.  Data from the Palmer amaranth emergence study were analyzed as a factorial of three soybean row spacings and three evaluation intervals.  In the soybean light interception study, PAR data were analyzed similar to data in the Palmer amaranth emergence study; however, soybean yields were analyzed as the original randomized complete block. 

Pooled over soybean row spacing, Palmer amaranth emergence was reduced 72% at 60 compared with the 30 DAP evaluation interval.  However, Palmer amaranth emergence was similar between the 60 and 90 DAP evaluation intervals. By 90 DAP, emergence of Palmer amaranth was Ë‚ 1 plant/m² regardless of row spacing.  Soybean achieved maximum observed light interception at 60 DAP at row spacings of 19 and 38 cm, but not until 90 DAP at the 76-cm spacing.  Light interception from soybean in 19-cm rows was greater at 30 DAP than soybean in wider rows.  By 60 DAP, soybean in 19- and 38-cm rows intercepted more light than in 76-cm rows. Soybean yields were increased 23 and 27% when row spacing decreased from 76 cm to 38 and 19 cm respectively.

Palmer amaranth emergence reached a minimum and soybean light interception reached a maximum at 60 DAP.  Although soybean row spacing did not affect Palmer amaranth emergence, soybean light interception at 30 and 60 DAP and soybean yield were greater with 19- and 38- compared with 76-cm row spacings.  Data indicated that a soybean row spacing of 38 cm should be utilized to optimize soybean light interception and yield while offering some suppression of Palmer amaranth emergence.

THE EFFECTS OF GLUFOSINATE AND GRAMINICIDE TANK-MIX RATES ON BARNYARDGRASS CONTROL.  A.N. Eytcheson and D.B. Reynolds; Department of Plant and Soil Sciences, Mississippi State University, Mississippi State, MS 39762.

Abstract

The rapid adoption of genetically modified (GM) crops resistant to non-selective herbicides, especially the glyphosate resistant cropping system has led to the development of glyphosate resistant weeds.  As an alternative to the glyphosate based system, the LibertyLink^® system utilizes the GM crop resistance to the herbicide glufosinate.  Glufosinate is a non-selective, non-residual postemergence (POST) herbicide that has the ability to control weeds that are considered to be difficult to control with glyphosate as well as glyphosate resistant weeds.  However, previous research has reported grass weed control with glufosinate may be inadequate and may require additional management inputs.  Producers often chose to tank mix herbicides to broaden the spectrum of weed control, improve efficacy and reduce application cost by combining applications.  However, combinations of graminicides with herbicides used to control broadleaves typically result in antagonism.  Previous research has evaluated glufosinate-graminicide antagonism in annual grass species; however, very little literature is available regarding barnyardgrass antagonism.  Therefore, field and greenhouse experiments were conducted to determine barnyardgrass control with an increasing rate titration of quizalofop-P and clethodim when tank-mixed with glufosinate

Both field and greenhouse experiments were arranged as a factorial arrangement of treatments in a randomized complete block design  Factor level A consisted of quizalofop-P (0, 28, 56 or 84g ai/ha) and clethodim (0, 38, 76 or 114 g ai/ha).  Quizalofop-P and clethodim rates represented 0, 0.5X. 1X, or 1.5X labeled rates.  Factor B consisted of glufosinate applied at 0 or 564 g ai/h.  A crop oil concentrate (1% v/v) was included in all graminicide applications.  Field data collected included barnyardgrass control 7, 14, 21, 28 and 56 DAT, barnyardgrass biomass (g/m²) collected at 56 DAT and soybean yield.  Greenhouse data collected included barnyardgrass control 7, 14, 21 and 28 DAT, as well as barnyardgrass biomass (g/m²) collected at 28 DAT.

There was not an interaction of field data due to year, therefore all data were analyzed across years.  Quizalofop-P applied at 0.5X, 1X or 1.5X applied with or without glufosinate were not significantly different at 28 DAT, with control ranging from 87 to 94%.  Clethodim applied at 1X alone controlled barnyardgrass better than when tank-mixed with glufosinate.  However, by 56 DAT regrowth occurred from the crown with all treatments.  Clethodim applied alone or tank-mixed with glufosinate significantly reduced barnyardgrass biomass compared to the untreated check.  However, quizalofop-P 1.5X + glufosinate reduced barnyardgrass biomass by 54% compared to quizalofop-P 1.5X alone.  Soybean yield increased by 54% when glufosinate was tank-mixed with either graminicide.  Data from the Greenhouse experiments at the 28 DAT evaluate was similar to the field data.  Barnyardgrass control did not differ between quizalofop-P applied alone or tank-mixed with glufosinate.  However, barnyardgrass control was antagonized when clethodim at 0.5X was tank-mixed with glufosinate. 

Glufosinate alone may not adequately control annual grasses, thus requiring additional management inputs.  In times of less than adequate grass weed control, producers may consider tank-mixing glufosinate and clethodim.  Our data suggests glufosinate alone had difficulty adequately controlling barnyardgrass; however, clethodim is more sensitive to tank-mixing with glufosinate compared to quizalofop-P.  Significant regrowth from the crown after application will require additional management inputs.  Further research needs to be conducted to further pinpoint rates which could lead to antagonism. 

Evaluation of Herbicide Efficacy and Application Timing for Miscanthus

D.N. Barksdale, J.D. Byrd, M.L. Zaccaro, and D.P. Russell;

Department of Plant and Soil Sciences

Mississippi State University, Mississippi State, MS.

 ABSTRACT

Miscanthus species and hybrids have been a main focal point in the biofuels industry because of their capability to produce massive amounts of aboveground biomass. Limited research has been conducted on the control and eradication of these grasses. In 2013, field experiments were conducted on Miscanthus in Louisville, MS with two objectives in mind: (1) determine the efficacy of different herbicide treatments and (2) determine the effect of application timing. Experiments consisted of two application timings, summer and fall, and 21 herbicide treatments: glyphosate at 2, 4, 6.5 lb ae/A, 2% (v/v), imazapyr at 0.25, 0.5 lb ae/A, 1% (v/v), clethodim at 0.25 lb ai/A, 0.25% (v/v), fluaziflop at 0.38 lb ai/A, metsulfuron at 0.075 lb ai/A, 1 oz/100 gallons, imazapic at 0.18 lb ai/A, hexazinone at 0.5, 1 lb ai/A, MSMA at 3.3 lb ai/A , diuron at 2 lb ai/A, sulfosulfuron at 0.07 lb ai/A, sulfometuron at 0.09 lb ai/A, nicosulfuron + metsulfuron at 0.05 + 0.01 lb ai/A, and quinclorac at 0.75 lb ai/A. Statistical analysis of visual control data as well as aboveground biomass samples taken 12 months after treatment (MAT) revealed significant differences (P < 0.05) among treatments. According to statistical analysis on shoot mass, glyphosate applied at 4, 2, and 6 lb ae/A and 2% (v/v) in June achieved 100, 94, 85, 90% control, respectively. While some treatments applied in June provided partial Miscanthus visual control, shoot biomass weight measured 12 months after application revealed no significant differences among any other treatments compared to the untreated control. Metsulfuron applied at 1 oz/100 gallons achieved the greatest amount of control at 49% among September applications. For fall applications, glyphosate applied at 4 lb ae/A reduced Miscanthus shoot biomass 40%, compared to a 43% reduction by quinclorac at 0.75 lb ai/A or 0.07 lb ai/A sulfosulfuron. According to both visual and biomass data, Miscanthus control is highest when an application of glyphosate at 2 or more lb ae/A or as a 2% solution is applied in the summer time; whereas, fall applications were inadequate for long term control.

Weed control remains a major challenge for economically viable sorghum production in North Carolina due to sorghum’s inability to efficiently compete with weeds during early growth stages. Moreover, herbicides capable of suppressing grasses are extremely limited due to sorghum sensitivity. In addition to Palmer amaranth (Amaranthus palmeri), grasses are extremely problematic in sorghum production. Previous studies have shown it was possible to improve weed control in sorghum by narrowing row spacing and increasing planting density. Field studies were conducted at the Central Crops Research Station (Clayton, NC) in 2013 and at the Upper Coastal Plain Research Station (Rocky Mount, NC) in 2014 to determine which association of row spacing, plant populations and herbicide program would increase crop competitiveness with grasses and eventually reduce the need for POST applications. The experiment was conducted as a factorial arrangement of 3 treatments in a randomized complete block design. Main factors consisted of different row spacings (19, 38, and 76 cm), planting density (40,000, 80,000, 120,000, and 160,000 plants per acre), and herbicide programs (non-treated, PRE application of S-metolachlor + atrazine, and PRE application of S-metolachlor + atrazine followed by POST application of acetochlor alone in 2013 or mixed with quinclorac in 2014). Weed control was visually estimated 4 weeks after PRE, 2 and 4 weeks after POST for Large crabgrass (Digitaria sanguinalis), Crowfootgrass (Dactyloctenium aegyptium), Broadleaf signalgrass (Urochloa platyphylla), and Yellow foxtail (Setaria glauca). Weed density and biomass were evaluated before harvest as well as grain yield at harvest. Data collected stressed the importance of an efficient post-emergence herbicide application to successfully control grass species and prevent sorghum yield loss.

In a situation of low weed infestation, grass biomass decreased significantly in the non-treated plots at every row spacing associated with plant density ranging from 120 to 160,000 plants per acre. Application of acetochlor as a POST herbicide didn’t improve grass control and the highest yields were associated with the combination of narrow rows and high plant densities independently of the herbicide application timing. 

 Under heavy grass infestation, the POST application significantly improved grass control compared to a single PRE application. Higher planting density significantly improved Large crabgrass control at every row spacing and similar results were observed at a lesser extent for Broadleaf signalgrass and Yellow foxtail. Differences in weed biomass according to row spacing and planting density were only recorded for the PRE application. Significant lower cumulative grass biomass and density was recorded for the narrow row spacing (7.5 cm) associated with planting density ranging from 80 to 160,000 plants per acre. At wider row spacing (15 or 30 cm), significant decrease only occurred at the highest planting density (160,000 plants per acre). Grass infestation and bad sorghum growing conditions due to partial flooding of the field prevented the observation of any significant yield difference according to row spacing or plant population in the non-treated plots. 

EVALUATION OF ROUNDUP READY SOYBEANS FOR COGONGRASS CONTROL. M.L. Zaccaro*, J.D. Byrd, D. Russell and D.N. Barksdale; Mississippi State University, Mississippi State – MS 

ABSTRACT

The control of cogongrass (Imperata cylindrica (L.) Beauv.) has proven to be difficult as few herbicide provide adequate efficiency for an extended period. An approach using cover cropping systems is under investigation, because not only can it be used to improve soil fertility and compete with the weed, but the farmer produces a usable commodity which can help pay for control. The objective of this experiment was to evaluate cogongrass control using RR 'Big Fellow' forage soybeans (Glycine max (L.) Merr.) and multiple glyphosate applications. The experiment was conducted in south Mississippi in July, where six treatments were established in a complete randomized design with 4 repetitions:  single herbicide application (1), double application (2), triple application (3), soybean cover and single application (4), soybean cover and double application (5) and soybean cover with triple application (6). After the cogongrass was mowed and the soil tilled, 75 lbs soybeans seed per acre was planted to the treatments 4, 5 and 6, with a no-till drill on 7/21/14. The initial herbicide application was made 8/13/14 with 1 lb ae per acre of Roundup PowerMax 4.5L with 0.25 % V/V of non-ionic surfactant. Second application of PowerMax at the same rate was applied 9/11/14 and the last application was 10/21/14. Roundup PowerMax was applied at 20 GPA using a 2-liter CO₂ backpack sprayer with flat fan nozzles 8002VS and 20 PSI. Visual control ratings (%) were taken monthly. Cogongrass and soybean biomass were harvested from 10.8 sq. ft area on 10/21/14, separated, dried and weighted. Data were analyzed in PROC GLM in SAS v. 9.3, then means were separated by the LSD with α=0.05. On average, the treatments 2, 3, 4, 5 and 6 were better than treatment 1 with respect to cogongrass control and biomass dry weight. Cogongrass control was improved by treatments 6 and 5, although these weren’t significantly different from each other and from 2 and 3. The treatments 2 and 3 also provided good visual control, not significantly different from each other and from 4, 5 and 6. The treatment 4 provided 60 % cogongrass control, while not significantly different from 2 and 3. With respect to cogongrass biomass, the treatments 2, 3, 4, 5 and 6 resulted in a significant decrease on average biomass dry weight compared to the treatment 1, however not significantly different from each other. Cogongrass control will be evaluated again after the 2015 spring transition. In conclusion, it’s recommended to use RR forage soybeans as a cover crop and two applications of glyphosate during the growing season to economically maximize cogongrass control.

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 and 2014 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. Incubation studies regarding the impact of herbicides on these emissions were conducted in fall of 2014.  In these combined experiments it was investigated how weeds and weed control played a role in greenhouse gas emissions. Results indicated weed-free areas in conventional managment emit more nitrous oxide than weedy areas (0.5-10 mg N m^2-1day^-1 more) while weedy areas emit more nitrous oxide in organic systems (0.5-10 mg N m^2-1day^-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 m^2-1day^-1 while no-till or minimum tillage systems were emitting roughly 3 mg N m^2-1day^-1 on the same dates.   

EVALUATING THE EFFICACY AND FIT OF QUINCLORAC TO CONTROL GRASS WEEDS IN GRAIN SORGHUM IN NORTH CAROLINA. L.J. Vincent, W.J. Everman, T.E. BesanÒ«on, Z.R. Taylor, A.M. Knight, and A.M. Growe; Department of Crop Science, North Carolina State University, Raleigh, NC 27607.

Grain sorghum production in North Carolina has been greatly inhibited by the lack of postemergence annual grass weed control herbicide options.  Selective grass weed control after the crop has emerged has not been possible until recently.  However, quinclorac has a history in rice and turf weed management as a broad spectrum herbicide and has been labeled for postemergence sorghum weed management. The objective of the study was four fold: determine sorghum phytotoxicity with quinclorac, evaluate its efficacy as a tank mix partner with common sorghum herbicides, examine its spectrum of weed control, and any impacts it may have on yield. 

The experiment was organized as a randomized complete block design with a factorial arrangement in four replications established at two locations Rocky Mount and Lewiston-Woodville, NC.  The factorial was twofold; factor A being herbicide timing (PRE fb POST and POST) and factor B was POST herbicide treatment. The PRE herbicide application was s-metolachlor + atrazine at 3.7 L/ha. All POST herbicide applications included quinclorac at a rate of 1.6 L/ha as well as crop oil concentrate at a rate of 1% v/v. In addition to quinclorac and crop oil concentrate at the aforementioned rates; the following herbicides were added as different tank mixes; atrazine, pyrasulfotole + bromoxynil, pyrasulfotole + bromoxynil + atrazine, prosulfuron, prosulfuron + atrazine, 2, 4-D, dicamba, and a nontreated check. Data collected includes; crop tolerance and weed control ratings at 7, 14, and 28 days after treatment (DAT), yield, and weed biomass weights and counts (data not presented).

End of the year data collection revealed some expected as well as unexpected conclusions.  At both locations where atrazine was included in the tank mix, crop stunting was observed particularly in treatments which received atrazine at PRE and POST timings.  Weed control ratings demonstrated the necessity of a preemergence herbicide in sorghum production.  Although there were no significant differences amongst PRE fb POST treatments themselves, drastic improvements in control of large crabgrass and broadleaf signalgrass were achieve with the addition of a PRE.  Significant differences were noted amongst treatments which only received a POST application.  Treatments including atrazine at the PRE fb POST timing again proved to be important as in some cases, weed control was significantly improved compared to the similar treatment without atrazine.  In both locations, across annual grass species, treatments including pyrasulfotole + bromoxynil with and without atrazine in some cases significantly increased weed control. Finally, average yield at Rocky Mount was 0.8 MT/ha due to above average rainfall and high weed pressure.  Lewiston-Woodville yielded on average 4.8 MT/ha.  In both locations, the PRE fb POST treatments which included atrazine decreased yield, sometimes significantly.

Goosegrass (Eleusine indica (L.) Gaertn.) is problematic summer annual weed in both cool season and warm season turfgrass. Recently, flumioxazin was registered for use in dormant bermudagrass (Cynodon dactylon (L.) Pers).  Flumioxazin inhibits protoporphyrinogen oxidase enzyme and it can be utilized for pre- and post-emergence weed control. Dormant turf application of flumioxazin has exhibited efficacy for post-emergence winter annual weed control and pre-emergence summer annual weed control.  The objective of this study was to evaluate flumioxazin for its pre-emergent control of goosegrass in common bermudagrass.  This study was conducted at Cimarron Trails Golf Course in Perkins, OK.  Seven herbicide treatments, including flumioxazin, indaziflam, prodiamine, and oxadiazon, were applied to dormant common bermudagrass.  All treatments included a non-ionic surfactant as 0.25 % V/V. Applications were applied using a CO₂ pressurized R&D Brand bicycle sprayer. The sprayer utilized a 1.5 m wide boom with three Spraying System TeeJet 8002 VS nozzles and 1.5 m x 3 m plots were assigned in a randomized complete block design with 4 replications. Treatment applied to this study did not delay bermudagrass green-up in spring 2013 and there was no significant herbicide injury observed in all plots.  On the first rating date (26 weeks after initial treatment), all flumioxazin treatments showed significantly less goosegrasses on the plots. There was no significant difference between sequential flumioxazin treatments and indaziflam on all rating dates. Compared with prodiamine and oxadiazon, flumioxazin treatments maintained greater goosegrass control throughout this study.

INFLUENCE OF GROUND-COVER COMPETITION ON GROWTH, YIELD, AND BERRY QUALITY IN CABERNET FRANC GRAPE.  Nicholas T. Basinger, Katie M. Jennings, David W. Monks, Sara E. Spayed, Wayne E. Mitchem and Sushila Chaudhari. Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695 (nabasing@ncsu.edu)

ABSTRACT

Viticulture in the Southeastern United States is limited by excessive vigor, high humidity and a challenging growing environment, all contributing to lower quality fruit.  The objective of this study was to determine effects of 5 vegetation-free in-row strip widths (VFSW) on vine growth, berry quality, and yield of wine grapes.  The study was conducted on Cabernet Franc cl. 312 on 101-14 MGT rootstock, in the Yadkin Valley region of North Carolina from 2011 to 2014.  The vineyard floor was sown to ‘Kentucky 31’ fescue after grape harvest in 2010.  In Spring 2011, vegetation-free in-row strip widths of 0, 0.3, 0.6, 1.2 and 2.4 m were established beneath the vines with paraquat and glufosinate and maintained throughout the growing season all four years. At the onset of fruit ripening (veraison), maintenance in half of each treatment ceased and the plot was allowed to grow up in native vegetation to determine the effect of late season weeds on vine growth, berry quality and yield.  In 2011, 2013, and 2014 oBrix decreased with increasing VFSW.  Titratable acidity increased with increasing VFSW in all four years. Winter pruning weight and lateral shoot number increased as VFSW increased in 2011 through 2014.   Summer fresh pruning weight was greater for wider VFSW in 2012.Yield increased as VFSW increased all years except 2014.  

Palmer amaranth (Amaranthus palmeri S. Watson) is a problematic weed species in summer row-cropping systems and has the capability to cause high economic losses.  The introduction of Roundup Ready (RR) crops in the mid-1990’s improved Palmer amaranth control significantly; however, the continuous use of this system without herbicide or crop-trait rotation has led to the development of glyphosate-resistant (GR) Palmer amaranth populations.  The first case of GR Palmer amaranth was confirmed in Georgia in 2005 and has since spread throughout the Southern and Midwestern regions of the United States.   Increases in the spread of GR Palmer amaranth are decreasing the utility of RR systems. While GR weed populations have been well documented in nearby states such as Arkansas, Kansas, and Missouri, there is a lack of data for Oklahoma, though producers often report suspected GR weed populations.  The objective of this study was to formally document suspected GR Palmer amaranth populations in Oklahoma and determine the level of glyphosate resistance. 

The cross pollination of a GR Palmer amaranth plant can easily spread the resistance gene through a population.  The genetic plasticity of Palmer amaranth as well as the selection pressure of applying glyphosate, has contributed to the rise in GR weed species.  The mechanism most often reported for GR Palmer amaranth is overexpression of 5-enolpyruvyshikimate-3-phosphate synthase (EPSP) where shikimate is not accumulated in the leaf tissue.  Altered enzyme has also been reported as a potential mechanism in this species. 

In this study, two populations of suspected GR Palmer amaranth were screened for glyphosate resistance against a glyphosate susceptible (GS) reference population.  One was collected from Hennessey, OK and the other from Payne County OK.  Each population was evaluated using a glyphosate rate titration and the level of resistance was estimated using a shikimate leaf disk assay.  The suspected resistant populations were obtained from producers in Oklahoma and had escaped at least one application of glyphosate. Seed were chemically scarified to break dormancy using H₂SO₄.  Seed were planted in the greenhouse with a 16h day length at 29/25°C day/night temperatures.  All plants were 5-10 cm in height at time of treatment.  Treatments included glyphosate at 0.65, 1.25, 2.5, 5.0, 9.9, 19.9, and 39.9 kg ae ha^-1 plus a nontreated check.  Treatments were replicated ten times and each study was repeated in space.  A DeVries Series II spray chamber was used apply treatments.  Plant height, visual percent control, and images were taken weekly for four weeks after treatment. At the conclusion above ground biomass was harvested and fresh and dry weight was recorded.   

The shikimate leaf disc assay was performed as follows: leaf disks were excised from the newest leaf of eight different plants for eight replications. Two to three leaf disks were immediately placed in a 10 mM ammonium sulfate solution plus 0.1 % Tween 80 and various glyphosate concentrations from 8 to 1000 uM. After the completion of the shikimate leaf disk assay, optical density was determined at 380 nm using a spectrophotometer.

Both the Hennessey (HEN) and the Payne county (BF) populations were resistant to glyphosate based on greenhouse trial data and differential accumulation of shikimate between GR and GS populations. This confirms glyphosate resistant Palmer amaranth populations for Kingfisher and Payne counties in Oklahoma.  Additional herbicide and crop-trait rotation strategies are necessary to manage these populations in our state and the surrounding region.  

Herbicide efficacy is a critical component of effective weed control and herbicide resistance management in cropping systems. Factors that influence herbicide efficacy include the environmental conditions before, during, and after application. A greenhouse study was conducted in the fall of 2014 to evaluate the effects of soil moisture and light on the control of junglerice (Echinochloa colona) and weedy rice following quizalofop application. Three environmental conditions were evaluated: shade, dry down prior to application, and rainfall following application; a fourth factor- ecotype of weedy species was also included. Shade conditions were: shade for 2 days before application, shade for 2 days after application, and no shade. Within each shade condition the experiment was organized as a split-plot design where the main plot was a randomized complete block of rainfall following application, the blocking factor was dry down, and the split-plot level was ecotype. Three timings of dry down were evaluated- 10 days before, 5 days before, and saturated soil up to application. The rainfall timings were 1 hour after application, 5 days after application (DAA), and 10 DAA. A susceptible and graminicide-tolerant ecotype of junglerice and weedy rice were used.  Seeds were planted in pots (1,618 cm³) containing field soil, with three replicates and maintained at 5 plants per pot. Quizalofop (60 g ha^-1) was applied once to 2-leaf plants. Plants without herbicide stress were used as reference.  Herbicide activity was evaluated visually three weeks after application and fresh biomass (g) was measured. For proper partitioning of variance, each shade treatment was analyzed separately; within the shade treatment data were analyzed using an ANOVA, with blocking factor (dry down) as random effect and all other factors fixed. Lower biomass was observed when rainfall was applied longer after application (10 DAA). Without shade, Echinochloa control was <85% with lesser activity (69%) on the tolerant ecotype. Shade for two days prior to herbicide application resulted in 88% or greater weed control, which could result in greater crop injury. The weedy rice ecotypes responded similarly to quizalofop regardless of environmental conditions. The impact of soil moisture was not clear and will be verified in follow-up experiments. The results of this study indicate that soil moisture levels have less impact on herbicide activity than low light levels prior to application; this has the potential to cause greater crop injury. 

Herbicide-resistance is a major problem in global agriculture as a result of the immense selection pressure being placed on herbicides today. Alternative weed control tactics are needed to help preserve the efficacy of our current herbicides. Harvest Weed Seed Control measures similar to those currently used in Australian cropping systems are being evaluated for use in U.S. soybean production at the University of Arkansas. Complete kill of pitted morningglory, Palmer amaranth, barnyardgrass, and johnsongrass has been observed when using narrow-windrow burning in soybean. An experiment was conducted at the University of Arkansas Altheimer Laboratory in Fayetteville, Arkansas to determine the amount of heat needed to kill seeds of various weeds. Pitted morningglory and sicklepod seeds were evaluated since these are two weeds that are likely to be most resilient to heat.  Additional species are also being evaluated including Palmer amaranth, johnsongrass, barnyardgrass, giant ragweed, hemp sesbania, prickly sida, velvetleaf, broadleaf signalgrass, giant foxtail, and common lambsquarters.  Four replications of 100 seeds of both species were placed in ceramic crucibles and subjected to a high fire kiln for various temperatures (200, 400, 600 C) and times (20, 40, 60, 80 s). Seeds were then evaluated for viability using a 1% w/v tetrazolium chloride solution. Viability estimates were recorded and data were normalized relative the viability of the nontreated control.  Data were subjected to regression analysis using JMP Pro 11.2. Heat index as defined by number of seconds of exposure times the temperature of the exposure was linearly related to seed viability.  Sicklepod was more resilient to heat than pitted morningglory.  All pitted morningglory seed were killed when 600 C was for 40 s or longer whereas the only treatment that completely killed sicklepod was 600 C for 80 s.  The heat indices need to kill these two weeds were much less than the heat indices produced under field conditions when soybean chaff was narrow windrowed and burned.  This experiment serves to validate our findings from narrow-windrow burning of soybean chaff, which is that complete kill of all weed seed should be achieved during the burn. 

Cyperus difformis L.(smallflower umbrella sedge or variable flatsedge; CYPDI) is a troublesome annual weed (Cyperaceae) commonly found in rice fields worldwide. In CA, CYPDI management was complicated by the evolution of resistance to acetolactate-synthase (ALS)-inhibiting herbicides in 1993; ALS-resistant (R) CYPDI populations are now widespread throughout CA rice fields. In the wake of resistance to ALS inhibitors, the post emergent photosystem II (PSII)-inhibiting herbicide propanil (3,4-dichlopropionanilide) has been extensively used to control ALS-R CYPDI and other weeds of rice. Lack of proper control following propanil spraying was detected in 2012 suggesting resistance to this herbicide might have also evolved in rice fields. The objectives of this research were to confirm resistance to propanil, ascertain resistance levels, and establish the underlying mechanisms of resistance in CYPDI biotypes collected in rice fields of California. Our results indicate that a number of CYPDI populations collected in CA rice fields displayed a high level of resistance to propanil (R/S ratio equaled 14). When rice cv. M-206 and propanil-susceptible (S) and –R CYPDI were sprayed with propanil jointly with the insecticide carbaryl (a known propanil synergist that inhibits propanil degradation in plants), all plant species except propanil-R CYPDI experienced significant growth suppression, suggesting propanil metabolism is not the mechanism of resistance in the R biotypes used. Interestingly, propanil-R CYPDI biotypes are also cross-resistant to other PSII-inhibiting herbicides (diuron, atrazine, bromoxynil, and metribuzin), although resistance to atrazine is weak. These results suggested propanil resistance might involve the PSII-inhibitor binding site at the target protein D1 of PSII. Therefore, we sequenced the herbicide-binding region of the chloroplast psbA gene, which codes for propanil’s target site (e.g. the D1 protein), where a valine to isoleucine substitution at amino acid residue 219 was identified. This mutation had already been identified in Poa annua biotypes resistant to diuron and metribuzin and is not associated with resistance to atrazine in agreement with our results. Therefore, unlike resistance in grasses and selectivity in rice - at which resistance is attributed to enhanced propanil degradation, resistance to propanil in CYPDI from CA is endowed by a single mutation at the D1 protein, which affects binding of propanil at its target-site. For control of propanil-R CYPDI (and given the widespread resistance to ALS inhibitors in CA rice fields), it is thus necessary to switch herbicide modes of action away from PSII and ALS inhibitors, and prevent spread of resistant populations by preventing seed contamination by performing proper cleaning of tillage and harvest machinery. Further research has also indicated that other herbicides used in rice are effective against propanil-R CYPDI, such as carfentrazone, benzobicyclon, and thiobencarb. Experiments aiming at elucidating the role of P450 monooxigenases and esterases are ongoing.

In 2015, auxin-type herbicide-resistant crops will be available in the marketplace; therefore, nozzle selection will become a highly important variable in maintaining efficacy of herbicide solutions while minimizing off-target movement. A field experiment was conducted in 2013 and 2014 at the Northeast Research and Extension Center in Keiser, Arkansas to evaluate interactions between dicamba formulated as Engenia, glyphosate (Roundup PowerMAX), and glufosinate (Liberty) applied with three different nozzle types. To supplement the field data, droplet spectra for each nozzle and tank-mix combination were determined at the West Central Research and Extension Center in North Platte, Nebraska. This experiment was arranged as a randomized complete block design with a factorial arrangement of two factors: nozzle type and herbicide treatment. TeeJet 11004 TT, AIXR, and TTI nozzles, designated by the manufacturer as coarse, extremely coarse, and ultra coarse droplets, respectively, were used to apply the herbicide treatments. Applications were made with a tractor-mounted research sprayer at 276 kPa, 140 L ha^-1, and 13.4 km hr^-1 to actively growing weeds. Herbicide treatments were labeled rates of Liberty, Roundup PowerMAX, Engenia, Liberty + Engenia, Roundup PowerMAX + Engenia, and Liberty + Roundup PowerMAX + Engenia. Percent weed control was evaluated four weeks after application for Palmer amaranth and barnyardgrass. For most treatment and nozzle combinations, Palmer amaranth control was greater than 95% in both years. In 2013, TT nozzles provided significantly greater control of barnyardgrass than with the TTI nozzle for Liberty alone, Roundup PowerMAX alone, Roundup PowerMAX + Engenia, and Liberty + Roundup PowerMAX + Engenia. In 2014, the interaction between herbicide and nozzle type was not significant; therefore, the TT nozzle provided three percentage points more control of barnyardgrass than the TT nozzle, averaged across all herbicide treatments except for Engenia alone (control of barnyardgrass by Engenia alone was 0%). When treatments were applied to 20- to 30-cm tall barnyardgrass in 2014, compared to 8- to 15-cm tall plants in 2013, an antagonistic effect was observed when Engenia was added to Roundup PowerMAX. The weed control data correlated with the droplet spectra analysis in that as volume median diameter (D_v50) increased from TT nozzles to the TTI nozzles, efficacy tended to decrease. Changing nozzle size or mixing herbicides in solution can have a dramatic effect on the droplet spectrum and volume median diameter. For example, Liberty alone tends to decrease D_v50 relative to water alone, but when tank-mixed with Engenia or Roundup PowerMAX, a reduction in droplet size is not observed. These results suggest that nozzle selection will play a key role in maximizing efficacy of postemergence applications in dicamba-resistant crops. Additionally, evaluating droplet spectra of potential dicamba-containing tank-mixtures is critical for producing the desired droplet size to minimize off-target movement.

Field experiments were conducted in Citra, FL and Tifton, GA to evaluate simulated drift of dicamba and 2,4-D on cotton at three growth stages. Citra plots were planted with Deltapine 1050 on April 29^th, 2014 and Tifton plots were planted with Phytogen 499 on May 8^th, 2014. Applications were made at the 1^st-leaf, 6^th-leaf, and 1^st square growth stages of cotton. Drift rates were applied at 0.25, 0.5, and 1 gallon per acre (GPA) using a controlled droplet applicator (CDA) sprayer with each droplet measuring approximately 125 microns. Drift rates were based off of the standard rate (0.5 lb ae/A) and carrier volume (15 GPA) for each herbicide and reduced proportionally to simulate a real-world drift situation.  This means that if the intended drift rate was 1/15^th the standard herbicide rate (0.033 lb/A) the carrier volume was also reduced by a factor of 15 (1 GPA). This allows the herbicide concentration of the drift to remain consistent with a normal herbicide application rate. The main effect and interactions for herbicide rate (i.e. the 0.25, 0.5, and 1 GPA application volumes) were not significant so data were averaged across rates. However, the main effect of application timing was significant.  All drift applications significantly reduced yield compared to the untreated control (UTC), but cotton was more tolerant to dicamba than 2,4-D. Yield was significantly reduced in the 2,4-D applications (-42.9, -70.2, and -80.3%) at the 1^st-leaf, 6^th-leaf, and 1^st-square growth stages, respectively, when compared to dicamba (-25.3, -23.0, and -37.3%). This was due to a reduction in overall boll formation as initiation of flowering was delayed to higher node positions in the plant. The first harvestable boll positions were delayed an average of 2.1 nodes by dicamba and 5.4 nodes by 2,4-D for applications made at the 1^st-square stage. Application of 2,4-D resulted in the average number of harvestable bolls being significantly reduced at the 6^th-leaf (-71.6% Citra and -64.7% Tifton) and 1^st-square (-93.8% Citra and -81.3% Tifton) applications, where dicamba only significantly reduced bolls (-47.4%) at the 1^st-square application in Tifton, GA. In conclusion, cotton was significantly more tolerant to dicamba drift than 2,4-D at all growth stages. Cotton sensitivity to both herbicides increased as plants progressed to the squaring growth stage. Yield reductions were the result of boll formation being delayed to higher nodes in the cotton plant. 

Limpograss is a warm-season C4 perennial that is well adapted to the poorly drained soils of south Florida. There have been four cultivars released but the only one that remains in production is ‘Floralta’. Past research suggested that limpograss tolerance to 2,4-D amine is the result of the regrowth height at the time of herbicide application. Dicamba has been the industry standard for weed control in limpograss, but it is relatively expensive. It is important, therefore, to investigate the effects of other herbicides on limpograss tolerance. This project examined the effects of fertilizer timing and regrowth height on limpograss tolerance to herbicides. Experiments were conducted in July, 2013 and repeated in July, 2014 at the Range Cattle Research and Education Center near Ona, FL. A split-plot design with four replications was used for these two experiments with herbicide treatment representing the whole plot and either fertilizer timing or regrowth height representing the sub-plot.  Whole plots were 3 by 12 m and the subplots were 3 by 3 m.  Ten herbicide treatments were applied on the same day to whole plots: dicamba at 840 g/ha, 2,4-D amine at 2,130 g/ha, dicamba + 2,4-D amine at 430 + 1,250 g/ha, aminopyralid + 2,4-D at 86 + 699 g/ha, metsulfuron at 13 g/ha, fluroxypyr + triclopyr at 210 + 630 g/ha, aminopyralid + metsulfuron at 130 + 20 g/ha, hexazinone at 560 and 1,120 g/ha, and aminoclopyrachlor at 70 g/ha. Dicamba is considered the industry standard for weed control in limpograss and was used as the check. In the fertilizer timing experiment  56, 28, and 56 kg/ha of nitrogen, phosphorous, and potassium were applied to sub-plots two weeks before, the same day as, and two weeks after  herbicide application. In the regrowth height experiment herbicides were applied on the same day to sub-plots with 15, 30, 60, and 90 cm of regrowth, which were obtained by clean-mowing each sub-plot at three week intervals. Limpograss tolerance was evaluated by visual injury at 30 days after treatment (DAT), with 0 equaling no injury and 100 being complete death, and by harvesting the center 1 by 2 m of each sub plot 90 DAT. Dry weight was recorded after seven days of drying in a forced-air dryer at 60 C. Data were analyzed using PROC MIXED and means separated using Fisher’s Protected LSD at P= 0.05 where appropriate. Herbicide treatment by fertilizer timing was not significant, and only the main effect of herbicide treatment was significant for both visual response and biomass data. Hexazinone resulted in at least 2-times greater visual injury than all other treatments 30 DAT and the high rate resulted in at least 51% less biomass compared to all other treatments 90 DAT. Injury from fluroxypyr + triclopyr and aminocyclopyrachlor was approximately 2-times greater than all other treatments except for hexazinone, but only aminocyclopyrachlor resulted in a significant reduction (32%) in biomass compared to dicamba (5,412 kg/ha).  All other treatments were similar to dicamba with regards to biomass production.  As in the fertilizer experiment, only the main effect of herbicide treatment was significant for the regrowth experiment.  Injury following application of the high rate of hexazinone was at least 2.5-times greater than all other treatments 30 DAT. At 90 DAT, hexazinone at 560 and 1,120 kg/ha resulted in at least 38 and 81% less biomass, respectively, compared to all other treatments. Biomass of 2,4-D amine-treated plots was approximately 36% less than dicamba-treated plots (2,108 kg/ha). Limpograss biomass in all other treatments was similar to dicamba-treated plots.  This research indicates that fertilizer application may have more of an influence on limpograss biomass following herbicide treatment than regrowth height.  Additionally hexazinone causes significant injury to limpograss, which may be of concern to ranchers who need to control smutgrass. 

Acuron is a new corn herbicide from Syngenta that could be available to producers in the 2015 growing season.  Acuron contains four active ingredients with three modes of action.  The active ingredients are bicyclopyrone, mesotrione, S-metolachlor, and atrazine.  Bicyclopyrone is a new active ingredient that will only be available as a premix component of Acuron.  Bicyclopyrone is a 4-hydroxyphenyl pyruvate dioxygenase (HPPD)-inhibiting herbicide that can provide residual or postemergence weed control.  The application window for Acuron will range from 28 d prior to planting until corn has reached 12 inches in height.  It is anticipated that combination of herbicides in Acuron will provide consistent, broad spectrum weed control in corn.  Research was conducted to compare Acuron to currently available herbicide premixes in corn.

A study to compare residual control from Acuron to other corn herbicides was conducted in 2014 at the West Tennessee Research and Education Center in Jackson, TN.  In 2013, a study to evaluate weed control from Acuron in a program approach was conducted at the Research and Education Center in Milan, TN.  At each location, treatments were arranged within a randomized complete block design with four replications in Jackson and three replications in Milan.  Treatments in Jackson included Acuron (bicyclopyrone: 0.037, mesotrione: 0.150, S-metolachlor: 1.337, and atrazine: 0.625 lb ai/A), Acuron + atrazine (bicyclopyrone: 0.037, mesotrione: 0.150, S-metolachlor: 1.337, and atrazine: 0.625 + atrazine: 0.75 lb ai/A), Anthem ATZ (atrazine: 1.00, pyroxasulfone: 0.121, and fluthiacet-methyl: 0.004 lb ai/A), Corvus (thiencarbazone-methyl: 0.033 and isoxaflutol: 0.082 lb ai/A), SureStart (acetochlor: 0.938, clopyralid: 0.095, and flumetsulam: 0.030 lb ai/A), and Verdict (saflufenacil: 0.045 and dimenthenamid-P: 0.391 lb ai/A).  Treatments at Milan were Acuron (bicyclopyrone: 0.019, mesotrione: 0.075, S-metolachlor: 0.669, and atrazine: 0.313 lb ai/A) fb Halex GT (glyphosate: 0.941, mesotrione: 0.094, and S-metolachlor: 0.941), Acuron (bicyclopyrone: 0.037, mesotrione: 0.150, S-metolachlor: 1.337, and atrazine: 0.625 lb ai/A) alone, and fb Touchdown (glyphosate: 1.00 lb ae/A) or Touchdown + Status (glyphosate: 1.00 lb ae/A + dicamba: 0.138 and diflufenzopyr: 0.053), Acuron + atrazine (bicyclopyrone: 0.037, mesotrione: 0.150, S-metolachlor: 1.337, and atrazine: 0.625 + atrazine: 0.75 lb ai/A), Corvus (thiencarbazone-methyl: 0.033 and isoxaflutol: 0.082 lb ai/A), Degree (acetochlor: 1.947 lb ai/A) fb Roundup Powermax (glyphosate: 0.773 lb ae/A), Lexar (atrazine: 1.305, mesotrione: 0.168, and S-metolachlor: 1.305 lb ai/A) and Verdict (saflufenacil: 0.045 and dimenthenamid-P: 0.391 lb ai/A) fb Roundup Powermax (glyphosate: 0.773 lb ae/A).  PRE treatments were applied immediately after planting and follow-up treatments were made 42 d after planting. Crop injury and weed control were visually estimated at weekly intervals after the PRE application throughout the growing season.  For brevity, control of all weed species present at each location, were combined and presented as overall weed control.  Weed species present at Jackson included annual grasses, Amaranthus palmeri, and Ipomoea lacunosa, and weed species at Milan included annual grasses, Amaranthus hybridus, and Abultion theophrasti. All data were subjected to ANOVA and estimates of the least square means were used for mean separation with α = 0.05.

No injury was observed from any treatment at either location (data not presented).  In Jackson, weed control was similar for all treatments 42 and 56 DAT.  However, 56 DAT all treatments provided < 80% weed control.  A main effect of herbicide was detected 70 DAT.  Verdict provided greater control than that of Anthem ATZ and SureStart.  Control from Acuron, Acuron+atrazine and Verdict was similar and greater than that of SureSart.  In Milan, there were no significant main effects 14 or 42 DA-A.  There was a significant effect of herbicide 7 and 42 DA-B.  At the 7 DA-B rating interval, Acuron fb Status + Touchdown provided the greatest control, but was similar to that of all treatments that included a follow-up application and greater than all PRE only treatments.  42 DA-B Acuron fb Halex GT provided the greatest control and was similar to that of Acuron fb Touchdown and Acuron fb Touchdown + Status.  At this interval Acuron fb Halex GT provided greater control than all treatments that only received PRE herbicides.

Acuron, as a PRE, provided improved or similar overall weed control to that of currently labeled premix herbicides for corn.  However, at each location overall weed control from any PRE only treatment was not sufficient for season long weed control.  The study from Milan indicates that Acuron can be included into corn weed control programs to sufficiently provide season long weed control in combination with other herbcides.

New control strategies are needed to optimize weed control and crop performance from the increasing prevalence of glyphosate resistant (GR) Palmer amaranth. A field study was conducted in 2012 and 2013 at the West Tennessee Research and Education Center in Jackson, TN and in 2013, there was an additional location at the East Tennessee Research and Education Center in Knoxville, TN. The objective of this research is to evaluate POST-harvest weed management programs for the prevention of seed production of glyphosate resistant (GR) Palmer amaranth, and to evaluate herbicide carryover into winter wheat.  Herbicides consisted of paraquat alone or tank-mixed with a residual herbicide of metribuzin, s-metolachlor, pyroxasulfone, saflufenacil, flumioxazin, pyroxasulfone plus flumioxazin, or pyroxasulfone plus fluthiacet-methyl. Three applications were followed by a preemergence herbicide applied at wheat planting. Paraquat alone controlled 91% of Palmer amaranth 14 DAA; however there was no control of plant regrowth or new germination. Palmer amaranth control from all residual herbicide treatments was the same.  All treatments prevented seed production of GR Palmer amaranth. Through implementation of such POST-harvest strategies, 1200 seed per m² or approximately 12 million seed ha^-1 were prevented from replenishing the soil seedbank. Overall, the addition of a residual herbicide increased Palmer amaranth control only 4 to 7% over paraquat alone.  Preemergence herbicides injured wheat in 2012 (<10%), but not in 2013. Wheat yield was not affected by any herbicide application. 

Evaluation of soil texture and pre herbicide on cotton growth, development, and yield. J. Drake Copeland¹, D.M. Dodds¹, A.B. Denton¹, C.A. Samples¹, A.L. Catchot¹, J. Gore², D. Wilson³

¹Mississippi State University; ²Delta Research and Extension Center; ³Monsanto Company

ABSTRACT

Since 1997, cotton growers have depended heavily on glyphosate for weed control. Unfortunately, growers transitioned away from the use of soil- applied residual herbicides and glyphosate-resistant (GR) weed species have become a concerning matter for cotton growers. Due to the prolific growth habit of GR Palmer amaranth, it has become the most troublesome weed pest in cotton production. Therefore, the use of preemergence (PRE) herbicides has become a necessity for cotton producers across the Cotton Belt.

Early season cotton growth is naturally slow and can be disrupted by factors such as herbicide injury. Cotton injury can occur during emergence from PRE herbicides if environmental conditions are not favorable. More specifically, soil texture and PRE herbicide choice can have an effect on early cotton development and can potentially reduce yields. Previous research indicates that soil texture, environmental conditions, and PRE herbicide use can affect crop development. With the extensive use of PRE herbicides cotton weed management programs, it is critical to determine cotton response to commonly used PRE herbicides and how crop injury may be associated with different soil textures.

Two greenhouse studies were conducted to determine the impact of PRE herbicides and soil textures on early cotton growth and development. Trials were conducted at the R.R. Foil Plant Science Research Center in Starkville, Mississippi. Deltapine 0912 B2RF seed (treated with metalaxyl [0.014 mg ai/seed] + pyraclostrobin [0.04 mg ai/seed] + ipconazole[0.002 mg ai/seed] + fluxapyroxad [0.018 mg ai/seed] + thiamethoxam [0.375 mg ai/seed] + abamectin [0.15 mg ai/seed])  was planted in two distinct soil textures, both collected from on-farm locations in Mississippi. Cotton seed were planted in a Bosket very fine sandy loam soil (49.7% silt, 27.8% sand, 22.7% clay, and 1.9% organic matter) and a Griffith silty clay soil (56.2 % clay, 29.2 % silt, 14.6 % sand, and 3.7% organic matter). Individual pots were 16.5 cm in diameter and 2600 g od air-dried soil was placed in each pot.

PRE herbicides included fluometuron at 1.12 kg ai/ha, diuron at 1.12 kg ai/ha, fomesafen ai 0.28 kg ai/ha, S-metolachlor at 1.07 kg ai/ha, S-metolachlor at 1.07 kg ai/ha + fluometuron at 1.12 kg ai/ha, as well as an untreated check. Experiments were conducted using a factorial arrangement of treatments in a repeated measurements design, with the three factors being soil texture, PRE herbicide and time (weeks after planting). Treatments were replicated 10 times. All data were subjected to analysis of variance and means were separated using Fishers Protected LSD at p = 0.05.

At three weeks after planting (WAP), cotton grown in sandy loam soil had significantly more true leaves than cotton grown in silty clay soils. However at 5 WAP, cotton grown in silty clay soils had significantly more true leaves. At two, three, and four WAP, cotton grown in sandy loam soil was significantly taller than cotton grown in silty clay loam soil. Percent height reductions due to PRE herbicide were significant at one WAP for cotton grown in sandy loam soils when compared to the untreated. There were no differences in cotton growth due to PRE herbicide in subsequent weeks. Cotton grown in sandy loam soil had significantly more biomass than cotton grown in silty clay soil. A height reduction was only observed when s- metolachlor + fluometuron was applied when compared to untreated. Fomesafen had significantly less fresh weight biomass than cotton treated with diuron or fluometuron. However, no differences were observed in cotton fresh weight biomass due to application of fomesafen and the untreated check. Application of fomesafen and s-metolachlor + fluometuron resulted in dry weight biomass reduction compared to other treatments; however, dry weight biomass from this treatment was not different than untreated check. Weed control from preemergence herbicides is critical for early season cotton growth. These data highlight the importance of abiding by the label restrictions for herbicide use across various soil textures.

Evaluation of Sequestration of Dicamba in Sprayer Hoses. Gary T. Cundiff*¹, Daniel B. Reynolds¹, Walter Thomas², Thomas Mueller³, ¹Mississippi State University, Mississippi State, MS., ²BASF Corporation, Research Triangle Park, NC., ³University 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.

Two studies were conducted to assess different formulations of dicamba persistence in sprayer hoses with different cleanout procedures. One study focused on determining if Clarity (diglycolamine salt of dicamba) persistence would differ among five various hose types, two cleanout procedures and applied to soybean used as a bio-indicator to assess cleanout efficiency in field. While the second study focused 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 in a greenhouse setting. Samples were collected and analyzed to determine Engenia persistence with respect to hose by cleanout treatments.

For the first study, five different types of agricultural spray hoses were evaluated. Each hose measured 3 m and had an inside diameter of 1.2 cm, which is enough carrying capacity to deliver sufficient volume to treat the two center rows of a four row plot with a length of 12 m. All spray lines were filled with dicamba 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 or ammonia 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 R2 with a two row spray boom using TeeJet XR 80015 spray tips delivering 140 liters per hectare. This study was conducted at two different sites (Starkville, MS and Brooksville, MS) in July and August of 2013. Weekly visual ratings were taken 7, 14, 21 and 28 days after treatment (DAT) with yield and percent yield reductions taken.

For the second study, 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 V3 growth stage in a spray chamber 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. These samples were run on an HPLC to determine residual concentration from each treatment. This study was conducted twice in a greenhouse setting (Starkville, MS) in October 2014. Visual ratings were taken 3, 5, 7 and 14 days after treatment (DAT) with dry matter taken at 21 DAT.

Initial results of the dicamba hose study showed significant differences with soybean injury based on hose type four weeks after treatment. There were no differences based on cleanout method, and no differences in yield or percent yield reduction based on hose, cleanout or hose x cleanout. Results of the Engenia trial show significant differences due to hose type by cleanout procedure 14 DAT with respect to injury. Dry matter showed significant differences based on hose type when compared to the untreated check. Analytical data showed significant differences based on hose type by cleanout procedure. Results indicate that the use of a polyethylene hose type shows significantly less injury and less retention of the dicamba analyte than other agricultural hoses.

CRITICAL WEED-FREE PERIOD IN PICKLING CUCUMBER. S. McGowen, S. Chaudhari, N. Basinger, S. Beam, K.M. Jennings, D.W. Monks; Department of Horticultural Science, North Carolina State University, Raleigh, NC.

ABSTRACT

Field studies were conducted at the Horticultural Crops Research Station in Clinton, North Carolina in 2014 to determine the critical weed-free period for Palmer amaranth (Amaranthus palmeri) in pickling cucumber. A naturally occurring population of Palmer amaranth was present at the study site. Palmer amaranth emergence at different time points throughout the season was simulated by allowing Palmer amaranth to establish at 0, 2, 3, 4, and 5 wk after crop seeding. Palmer amaranth control was simulated by allowing Palmer amaranth to emerge with crop and then removing Palmer amaranth at 0, 2, 3, 4 and 5 wk after crop seeding and preventing further establishment of Palmer amaranth after the removal date. Assuming an acceptable yield loss of 5%, the critical weed-free period for Palmer amaranth in pickling cucumber was 17 to 33 d after seeding.

Interspecific grafting using rootstock and scion from different species is common practice in solanaceous crop production to address many abiotic and biotic stresses, including drought/waterlogging, insects, and diseases. Tomato rootstocks have been successfully used for eggplant production. However, the safety of tomato herbicides has not been tested on grafted eggplant which is combination of two plants, tomato rootstock and eggplant scion. Greenhouse and field studies were conducted in 2012 through 2014 to determine the response of grafted eggplant to napropamide, metribuzin, halosulfuron, trifluralin, S-metolachlor and fomesafen herbicides which are registered in tomato. The greenhouse study had treatments of metribuzin pre-transplant (PRE) or post-transplant (POST) at 0.14 and 0.28 kg ai/ha, S-metolachlor PRE at 0.4, and 0.8 kg ai/ha, and halosulfuron POST at 0.018, and 0.036 kg ai/ha. The field study was conducted at Mountain Research Station, Waynesville, NC and at Horticultural Crops Research Station, Clinton, NC. Herbicide treatments in the field study included PRE S-metolachlor (0.8 and 1.06 kg ai/ha), fomesafen (0.28 and 0.42 kg ai/ha), metribuzin (0.28 and 0.55 kg ai/ha), napropamide (1.12 and 2.24 kg ai/ha), halosulfuron (0.039 and 0.052 kg ai/ha), and trifluralin (0.56 and 0.84 kg ai/ha). The eggplant cultivar ‘Santana’ was used as scion and non-grafted control, while two hybrid tomatoes ‘DP106’ and ‘Maxifort’ were used as rootstocks for grafted plants. No differences were observed in grafted and non-grafted eggplant for herbicide injury in greenhouse and field studies. Injury from metribuzin POST at 0.14 and 0.28 kg/ha 4 WAT was 94 and 100% injury for grafted and non-grafted eggplant, respectively. In field studies, PRE napropamide, S-metolachlor, fomesafen and trifluralin appeared to be safe and did not cause any injury and yield reduction in grafted and non-grafted eggplant. However metribuzin caused severe injury and yield reduction in both grafted and non-grafted eggplant. Metribuzin at 0.55 kg/ha caused 60 and 81% plant stand loss in 2013 and 2014, respectively. Halosulfuron PRE caused 24% yield reduction in grafted and non-grafted eggplant compared to nontreated control during 2013 but was not injurious in 2014. PRE napropamide, S-metolachlor, fomesafen and trifluralin can be considered safe for weed control in grafted eggplant on tomato rootstock.

GLYPHOSATE RESISTANT PALMER AMARANTH MANAGEMENT IN GLYPHOSATE TOLERANT SOYBEANS Anthony Growe, Wesley Everman, North Carolina State University, Raleigh, North Carolina.

ABSTRACT

The over-exploitation of glyphosate tolerant technology has resulted in increased resistance of troublesome weed biotypes, such as Palmer amaranth (Amaranthus palmeri).  As this resistance becomes more common in agricultural systems throughout the southern and mid-western United States, integrated herbicide systems should be practiced to suppress its impact on crop production. Field trials were conducted in Caswell Research station in Kinston, NC and Upper Coastal Plain near Rocky Mount, NC to evaluate the control of glyphosate resistant Palmer amaranth (Amaranthus palmeri) with overlapping residual herbicides.  Herbicide systems applied PRE were pyroxasulfone, saflufenacil with and without metribuzin, a premix of saflufenacil and imazethapyr with pyroxasulfone, a premix of sulfentrazone and cloransulam alone, and a premix of sulfentrazone and metribuzin alone. These treatments were compared when a POST of Dimethenamid-P was added, with the exception of a sulfentrazone and cloransulam premix.  Treatments with Dimethenamid-P as a POST generally were more effective in controlling Palmer amaranth than those without. Between both locations, the PRE only and PRE followed by POST treatments controlled 78 and 87 percent of Palmer amaranth respectively.  Control of Palmer amaranth was variable between the two locations.  All treatments achieved over 95 percent control at the Caswell station. PRE application of  saflufenacil and imazethapyr premix with pyroxasulfone was most effective with 86 percent control of Palmer amaranth (Amaranthus Palmeri) at the Upper Coastal Plain location.  

Influence of Water Quality and Conditioning Agents on Glyphosate Efficacy. M. R. Manuchehri*¹, P. A. Dotray^1,2, J. W. Keeling³, T. S. Morris³. ¹Texas Tech University, Lubbock, TX, ²Texas A&M AgriLife Research and Extension Service, Lubbock, TX, ³Texas A&M AgriLife Research, Lubbock, TX.

Water is the main carrier used in most herbicide applications. The quality of water may play an important role in herbicide efficacy, especially for weak acid herbicides such as imidazolinones, 2,4-D, and glyphosate. Growers in the Texas High Plains are considering the use of reverse osmosis (RO) water to offset potential antagonism of herbicides due to poor water quality. Defining the role of water quality on glyphosate efficacy is important due to its increased use over the past 15 years. The effects of water quality and water conditioning agents on glyphosate efficacy were assessed in eight field trials established near Lubbock, TX over three growing seasons. The objectives of these studies were to 1) determine if glyphosate efficacy is affected by water carrier source, 2) determine if there is a benefit in using RO water, and 3) determine if the addition of ammonium sulfate or other water conditioning agents will improve glyphosate control when water quality is poor.  Test plants included volunteer winter wheat (Triticum aestivum L.) and Palmer amaranth (Amaranthus palmeri S. Wats.). All trials were organized in a randomized complete block design with four replications. Five water sources, ranging in cation concentrations of 519 to 1,046 ppm, were selected from 23 wells throughout the Texas High Plains in the fall of 2011. In 2012 and 2013, five water sources plus a RO water source were used as carriers for the following four herbicide treatments: glyphosate applied alone at 0.43 and 0.86 kg ae/ha, and glyphosate applied at 0.43 and 0.86 kg ae/ha plus dry ammonium sulfate (AMS) at 2.04 kg/100 L. Injury was recorded at 14, 21, and 28 days after treatment. In 2014, two of the five water sources were selected (202 PPM and 1,028 PPM) plus a RO water source as carriers for the following eight herbicide treatments: glyphosate applied alone at 0.86 or 1.27 kg ae/ha, glyphosate applied alone at 0.86 or 1.27 kg ae/ha plus AMS at 2.04 kg/100 L, Interactive® at 1 L/100 L, Quest® at 0.625 L/100L, Choice® at 0.5 L/100 L, Weather Gard™ at 0.5 L/100 L, Bronc® Max at 1L/100 L, or Bronc® Total at 1 L/100 L. In 2012 and 2013, water source did not affect glyphosate performance in any of the trials; however, an increase in glyphosate rate and addition of AMS improved efficacy in three out of six trials while a rate by AMS interaction was observed in the other three studies. Glyphosate applied at 0.86 kg ae/ha plus AMS was most effective at controlling volunteer wheat. Similar control was achieved for glyphosate applied alone at 0.86 kg ae/ha and glyphosate applied at 0.43 kg ae/ha plus AMS. Glyphosate applied alone at 0.43 kg ae/ha was the least effective treatment. Treatments were similar for control of Palmer amaranth with the exception of glyphosate applied alone at 0.43 kg ae/ha, which was the least effective treatment. In 2014, RO water increased control of volunteer wheat while AMS was the only water conditioner that improved efficacy compared to glyphosate applied alone.  Greater Palmer amaranth control was observed using RO and the 202 PPM water source compared to the 1,028 PPM water source.  The addition of a water conditioner did not improve glyphosate performance.

GRAIN SORGHUM AND SOYBEAN AS REPLACEMENT CROPS FOLLOWING A FAILED COTTON STAND.  Lewis R. Braswell, Alan C. York, David L. Jordan, Charles W. Cahoon Jr.; Department of Crop Science, North Carolina State University, Raleigh, NC, 27695. 

ABSTRACT

Cotton growers have resumed use of preemergence herbicides in an effort to better control glyphosate-resistant weeds.  This has complicated replanting decisions when cotton stands fail and it is too late to replant to cotton. Soybean and grain sorghum are the most likely replacement crops for a failed cotton stand in the southeastern United States.  Soybean and grain sorghum response to most commonly used preemergence cotton herbicides is well understood.  Less understood is the response of soybean and grain sorghum to fluometuron and diuron. Labels for fluometuron and diuron specify 9- and 12-month rotational restrictions, respectively, for both crops.  Research conducted in the 1970’s and 1980’s on fine-textured soils in Arkansas and Tennessee indicated it was possible to replant to grain sorghum 6 weeks after fluometuron application to cotton whereas at least a 9-week waiting interval was needed for soybean.  Grain sorghum was less sensitive to both herbicides than soybean.  Similar research has not been conducted on coarse-textured, low organic matter soils typical of cotton production in the southeastern United States. 

Experiments were conducted in North Carolina in 2013 and 2014 at four locations for grain sorghum and three locations for soybean on soils ranging in texture from sand to sandy loam and humic matter ranging from 0.3 to 0.9%.  Treatments were a factorial arrangement of herbicides, planting delays after herbicide application, and tillage in a split-strip-strip design with four replications.  Herbicides were none, fluometuron at 1120 g ai/ha, and diuron at 840 g ai/ha.  Planting delays were 3, 6, and 9 weeks after fluometuron and diuron application.  Tillage options included none or disking prior to planting the replacement crops.  Data recorded included replacement crop injury at 3 and 6 weeks after planting, crop stand, and grain yield. 

Little to no soybean injury was observed with the 6- or 9-week planting delays.  Injury by fluometuron and diuron ranged from 6 to 33% and 1 to 15%, respectively, when soybean planting was delayed 3 weeks.  Injury was generally greater when disking occurred before replanting.  Fluometuron and diuron reduced soybean stand at 2 of 3 and 1 of 3 locations, respectively, regardless of tillage.  Diuron did not reduce soybean yield regardless of planting delay or tillage.  Fluometuron reduced soybean yield at 2 of 3 locations with the 3-week planting delay.  However, because of a strong effect of planting delay on yield, soybean yield was still greater when planted 3 weeks after fluometuron compared with later plantings.

Little to no effect of herbicides was noted for sorghum injury or stand regardless of tillage or length of planting delays.  Herbicides did not affect sorghum yield regardless of planting delay or tillage.  The main effect of planting delay was significant, with a 24% reduction in sorghum yield due to the 9-week delay.  

Weedy red rice (Oryza sativa) competes aggressively with rice, reducing yields and grain quality. Clearfield^TM rice, a nontransgenic, herbicide-resistant (HR) rice introduced in 2002 to control weedy rice has resulted in ALS-resistant weedy rice due to gene flow. Studies were conducted to determine the occurrence of resistance in fields with history of Clearfield^TM rice and verify the resistance-conferring mutations in the ALS gene. Weedy rice collected from 11 counties in Arkansas, USA were tested for resistance in a field experiment consisting of 89 weedy rice accessions and 3 Clearfield^TM rice cultivars in Stuttgart, AR (2011). Sequential application of imazethapyr was made at 0.5x and 1x dose (0.071 kg ai ha^-1). Injury and mortality were recorded 21 days after the second application. Two-to-five HR plants per accession per replication (727 plants) were marked based on plant type and characterized for 14 morphological traits. Allele-specific PCR-based genotyping was used to detect point mutations in the ALS gene, S₆₅₃N and G₆₅₄E in resistant plants. The ALS gene of 10 selected accessions was sequenced using Automated DNA Sequencing and aligned (Bioedit®) with those of Clearfield^TM cultivars to verify the mutation. S₆₅₃N mutation was detected in all of the resistant red rice accessions which is one of the mutations in Clearfield^TM rice that confer resistance to imidazolinone herbicides.  Outcrossing between weedy rice and Clearfield^TM rice will be verified using micro-satellite markers.

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 effective postemergent herbicides which effectively control sandburs in bermudagrass (Cynodon dactylon (L.) Pers.) turf. 

Two experiments were initiated at Perkins Park in Perkins, OK in 2014 to evaluate the safety and efficacy of several pre- and postemergent products to control sandbur.  Experiments were set as randomized complete block designs with four replications.  The preemergence study included 10 treatments and the postemergence study included 11 treatments.  Preemergent treatments were pendimethalin at 4.34 L ha^-1 as a single application and a split application spaced 3 weeks apart, indaziflam at 0.35 L ha^-1, oxadiazon at 8.1 kg ha^-1, dithiopyr at 1.06 kg ha^-1, prodiamine at 2.1 L ha^-1, oryzalin at 4.2 L ha^-1, simazine at 2.8 L ha^-1, thiencarbazone-methyl + foramsulfuron + halosulfuron +0.25% v/v NIS at 0.224 L ha^-1, and a nontreated check.  In the postemergence study treatments included quinclorac at 7.39 L ha^-1, metsulfuron-methyl at 0.070 L ha^-1, iodosulfuron-methyl + dicamba at 0.26 Kg ha^-1, foramsulfuron at 1.4 L ha^-1, trifloxysulfuron-sodium at 0.037 kg ha^-1, amicarbazone at 0.35 L ha^-1, topramezone at 0.070 L ha^-1, mesotrione at 0.28 L ha^-1, topramezone + triclopyr at 0.070 L ha^-1 + 2.24 L ha^-1, mesotrione + triclopyr at 0.28 L ha^-1 +  2.24 L ha^-1,  and a nontreated check.  Percent bermudagrass injury, percent sandbur control and # sandbur plants per plot were taken 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. 

The majority of treatments in the postemergence experiment caused greater than 30% and unacceptable injury to bermudagrass for up to 8 WAT and did not effectively control sandbur.  In the preemergence study no treatment caused unacceptable injury at any evaluation timing.  Pendimethalin in a single application, dithiopyr and simazine controlled sandbur at 63, 77, and 70% respectively 16 WAT.  The split pendimethalin application did not improve the length of residual control or the level of sandbur control as expected.  Data suggest a single application of pendimethalin, dithiopyr or simazine would be most effective at managing sandbur in residential or recreational bermudagrass turf where activating rainfall or irrigation can be expected.  No effective postemergence treatment was identified to replace MSMA as a tool for sandbur control in bermudagrass turf.  Additional work is needed to improve postemergence sandbur control options in this system.

Purple nutsedge (Cyperus rotundus L.) is a problematic weed in Florida small fruit and vegetable production. EPTC and fomesafen are potential preemergence herbicides for control of purple nutsedge in Florida plasticulture, but field application has shown control to be erratic. Greenhouse experiments were conducted in Gainesville, FL from May to August 2014 to investigate susceptibility of various purple nutsedge tuber growth stages to EPTC and fomesafen applications. Treatments included EPTC at 2.94 kg ai ha^-1 and fomesafen at 0.42 kg ai ha^-1 at 0, 3, 6, 9, 12, and 15 days after planting (DAP) tubers, plus a nontreated check. Purple nutsedge emergence, shoot height, leaf number, and dry shoot weight decreased with a reduction in time between application and planting. At 28 DAP, across all application timings, EPTC had lower values of 5.6 cm and 2.2 for average shoot height and leaf number, respectively, and greater reduction in dry shoot mass versus the nontreated, compared to fomesafen with values of 9.3 cm, 3.6, and, 51% for average shoot height, leaf number, and dry shoot mass compared to the nontreated control, respectively.

Response of Edamame Varieties to PRE and POST Herbicides*

Seth Bernard Abugho, Nilda Roma Burgos, Leopoldo Estorninos Jr., Vijay Singh, Reiofeli Salas, S. Singh and C. E. Rouse

Department of Crop, Soil and Environmental Sciences

University of Arkansas-Fayetteville

Edamame consumption is projected to increase annually in the US due to its potential health benefits. However, few herbicides are labeled for growing edamame in Arkansas along with the continuous development of new varieties to meet this demand. A field study was conducted at the Vegetable Research Station on Kibler, Arkansas and at the Arkansas Agricultural Research Station in the summer of 2013 and 2014 to determine the effect of PRE herbicides [sulfentrazone (0.21 kg ai ha^-1), flumioxazin (0.07 kg ai ha^-1), pyroxasulfone (0.12 kg ai ha^-1) and metribuzin (0.56 kg ai ha^-1)] and POST application of fomesafen (0.26 kg ai ha^-1) on edamame varieties and advanced soybean lines. The experiment was conducted in a split-plot design (herbicides as whole plot and varieties as subplot) with four replications. A broadcast PRE application of S-metolachlor (1.12 kg ai ha^-1) was done to maintain the plots weed-free. Crop stand count, injury rating (21 DAP for PRE and 35 DAP rating for fomesafen) and yield were recorded. In 2013, crop stand in nontreated plots was higher in Fayetteville (18 plants m^-1) than in Kibler (14 plants m^-1). Metribuzin and sulfentrazone caused the highest injury (33-35%) on all varieties in Kibler; in Fayetteville, UA-4913, UA-5612 and UA-5213 C showed stunting at 21 DAP. Fomesafen caused 14% and 18% cosmetic injury, respectively, in Fayetteville and Kibler. In 2014, crop stand in the nontreated plots was higher in Kibler (15 plants m^-1) than in Fayetteville (12 plants ha^-1).Metribuzin caused the highest injury (77%) in Kibler while flumioxazin, metribuzin, and sulfentrazone caused the highest injury in Fayetteville (22-26%). Injury from fomesafen at both locations was minimal (7-8%). UA-5612 had the highest yield in 2013 (3.3 mt ha^-1) in Kibler as well as in 2014 (2.58-3.13 mt ha^-1) in both locations. This study demonstrates differential response of edamame varieties to soil-applied herbicides and that metribuzin could not be used on these varieties because of high risk of yield loss. Fomesafen, applied POST, is safe on all varieties tested.

Nomenclature: edamame, varieties, preemergence, postemergence

INFLUENCE OF SIMULATED 2,4-D DRIFT ON REPRODUCTIVE DEVELOPMENT AND MATURITY OF COTTON.  S.A. byrd¹, A.S. Culpepper¹, D.M. Dodds², A. Jones³, K.L. Edmisten⁴, D.L. Wright⁵, G.D. Morgan⁶, P.A. Baumann⁶, P.A. Dotray⁷, M.R. Manuchehri⁷, J.L. Snider¹, J.R. Whitaker⁸, D.R. Chastain¹, and G.D. Collins⁹.  ¹Department of Crop and Soil Science, University of Georgia, Tifton, GA 31793, ²Department of Plant and Soil Science, Mississippi State University, Starkville, MS 39762, ³Department of Plant Science, University of Missouri, Portageville, MO 63873, ⁴Department of Crop Science, North Carolina State University, Raleigh, NC 27695, ⁵Agronomy Department, University of Florida, Quincy, FL 32351, ⁶Department of Soil and Crop Sciences, Texas A&M University, College Station, TX 77843, ⁷Department of Plant and Soil Science, Texas Tech University, Lubbock, TX 79409, ⁸Department of Crop and Soil Science, University of Georgia, Statesboro, GA 30460, ⁹Department of Crop Science, North Carolina State University, Rocky Mount, NC 27801.

ABSTRACT

Since its release in the 1940s, 2,4-D has been a broadly used agricultural herbicide.  With the impending release of 2,4-D resistant cotton cultivars, an increase is expected in the use of this herbicide, as well as an increase in the interface between resistant and nonresistant cotton cultivars, likely raising the potential for drift injury on cotton.  It has been reported that 2,4-D is very prone to drift, up to distances ofseveral kilometers, and cotton is regarded as one of the most sensitive crops to injury from 2,4-D. Injury to terminal growing points, reproductive structures, delays in maturity, and reduced yield have been observed from cotton exposed to drift of 2,4-D.  The vegetative stage is regarded as the most sensitive in terms of yield loss from 2,4-D exposure.  The objectives of this study were to determine the yield effects of 2,4-D as well as the impacts on fruiting and maturity characteristics on cotton.  The study took place in two locations in Georgia in 2013, and in Georgia, Mississippi and Missouri in 2014.  The study consisted of single applications of two simulated drift rates of 2,4-D, 0.002 kg a.i. ha^-1(low rate) and 0.04 kg a.i. ha^-1(high rate) at the four leaf (4 leaf), nine leaf (9 leaf), first bloom (FB), two weeks after FB (FB + 2 wks.), four weeks after first bloom (FB + 4 wks.), and six weeks after FB (FB + 6 wks.) growth stages.  A non-treated control (NTC) treatment receiving no 2,4-D applications was also included.   The cultivar PhytoGen 499 was utilized at all study locations.  Reproductive and maturity data was collected in both years at the Georiga sites, and at Mississippi and Missouri in 2014.  When significant, yield loss at all locations typically resulted from the high rate of simulated 2,4-D drift, though the low rate also resulted in yield loss in three of the five locations.  Applications made at growth stages nearer to bloom, specifically at the 9 leaf, FB, and FB + 2 wks. stages led to the most severe instances of yield loss.  Across all locations, plant maturity characteristics corresponded with treatments which resulted in yield loss more so than total boll measurements taken at 0.3 meter increments of the plant.  In 17 out of the 27 treatments that resulted in significant yield loss, either the percent of open bolls, or the total number of bolls measured on the whole plant were significantly reduced compared to the NTC values.  The yield results of this study provide evidence that later growth stages of cotton, around and after first bloom are sensitive to 2,4-D in terms of yield loss, and that maturity and reproductive development could provide some explanation for the mechanism behind the yield loss.  The authors would like to acknowledge the Georgia Cotton Commission for their support and funding of cotton agronomic research at the University of Georgia.

                Hairy Indigo (Indigofera hirsuta) is an aggressive annual that can grow to be several feet in height. It is a problem weed in peanut and can be difficult to manage since it is challenging to manage a legume weed in a legume crop. Growers in Florida have had trouble in recent years achieving adequate control of this weed. To this end, the objective of this project was to evaluate different herbicide treatments for the control of hairy indigo in peanut and to investigate the impact of different application timings on control. Plots were established in a factorial arrangement in a randomized compete block design in 2014. The five herbicide treatments consisted of imazapic (0.07gal/ha), imazapic + 2,4-DB (0.07gal/ha+0.31gal/ha), lactofen + 2,4-DB (0.23gal/ha + 0.31gal/ha), imazapic + lactofen + 2,4-DB (0.07gal/ha + 0.23gal/ha + 0.31gal/ha), and bentazon + acifluorfen + 2,4-DB (0.62gal/ha + 0.31gal/ha). All herbicide treatments were applied with crop oil concentrate at 1% v/v. Herbicides were applied at three different timings based on the height of the hairy indigo: 2.5-5cm, 5-10cm, or 10-15cm. When applied to hairy indigo at 2.5-5cm in height, all herbicide combinations provided greater than 85% control at 2 weeks after treatment (WAT).  By 4 WAT, all treatments provided greater than 87% control, except imazapic alone (77%).  The lactofen containing treatments performed exceedingly well with 97-99% control at 4 WAT.  When hairy indigo reached 5-10 cm, control with imazapic and imazapic plus 2,4-DB decreased to approximately 50% at 2 and 4 WAT.  Lactofen containing treatments provided between 82 and 87% control, with no differences detected between these treatments.  Acifluorfen + bentazon + 2,4-DB was less effective, providing 85% control at 2 WAT and decreasing to 70% by 4 WAT.  Control of plants between 10-15cm was similar to those treated at 5-10 cm.  Control of 10-15 cm hairy indigo with imazapic or imazapic + 2,4-DB was unacceptable, ranging between 52 and 28% at 4 WAT.  The lactofen treatments continued to provide 84 to 90% control, while acifluorfen + bentazon + 2,4-DB was less effective at 70% control.  These data demonstrate that if the herbicide is applied when the weed is 2.5-5 cm in height, there are many effective options. However, if application is delayed to after 5 cm, including lactofen will likely be necessary to achieve acceptable control.  

OFF-TYPE GRASSES OF ULTRADWARF BERMUAGRASS PUTTING GREENS:  A NEW WEED MANAGEMENT ISSUE?  E. H. Reasor¹, J. T. Brosnan¹, R.N. Trigiano¹, G. M. Henry², J. C. Sorochan¹, and B. M. Schwartz³

¹ University of Tennessee – Knoxville, Knoxville, TN

² University of Georgia, Athens, GA

³ University of Georgia, Tifton, GA

ABSTRACT

Ultradwarf bermudagrass (Cynodon dactylon (L.) Pers. x Cynodon transvaalensis Burtt Davy) putting green use is rapidly increasing in the southeastern United States.  Many golf course superintendents managing these surfaces have noticed off-type grasses in their ultradwarf bermudagrass greens. Anecdotal observations suggest that these off-types vary in texture, color, growth rate, and susceptibility to plant growth regulators compared to commercial ultradwarf cultivars such as ‘TifEagle’, ‘MiniVerde’, and ‘Champion’. 

Research was initiated in 2013 with an objective of morphologically and cytogenetically characterizing bermudagrass selections from ultradwarf putting greens. Fifty-two different selections (off-types and desirable cultivars) were collected from golf course putting greens in the southeastern United States.  Off-type selections were identified by visual differences in texture and color compared to the desirable cultivar.  Selections were cultured from single stolon transplants in a greenhouse at the University of Tennessee (Knoxville, TN) for two months prior to morphological characterization.  Plants received 25 kg N ha^-1 wk^-1, 1 cm^-1 day^-1, and 30°C average temperature.  Morphology was characterized by measuring internode length, stolon diameter, leaf length, leaf width, and leaf length-to-width ratio.

Morphological variability was evident across the 52 selections. Internode length ranged from 16 to 39 mm, stolon diameter ranged from 0.6 to 0.9 mm, leaf length ranged from 6 to 34 mm, leaf width ranged from 1.7 to 2.4 mm, and leaf length:width ranged from 3:1 to 15:1.  Considering the number of response variables and range of recorded measurements, a cluster analysis using a K-means algorithm was performed using SAS Enterprise Guide 6.1.  A maximum of three clusters were defined by cubic clustering criterion and frequency of observations.  Cluster means for all variables were significantly different (p < 0.0001).  Selections for future research will be made using a Mantel-Haenszel Chi-Square test for cluster association.       

Ploidy levels of all 52 selections were determined using flow cytometry comparing a tetraploid bermudagrass and two triploid bermudagrasses (TifEagle and Tifway).  All 52 selections were determined to be triploid and had higher DNA frequency than Tifway. This response suggests that all selections were within the Tifgreen-derived cultivar family.  Moreover, selections collected in this study are not tetrapoloid or Tifway contaminants from collars, fairways or roughs. 

Future research will evaluate how the selections identified in this initial research compare to authentic cultivars such as Tifgreen, Tifdwarf, TifEagle, MiniVerde, and Champion when subjected to varying plant growth regulator, nitrogen, and cold temperature regimes.  Genotype-by-sequencing techniques will also be used to develop a DNA fingerprint of authentic cultivars to help identify the presence of off-type grasses in the field.

ABSTRACT

INFLUENCE OF TILLAGE METHODS ON MANAGEMENT OF AMARANTHUS SPECIES IN SOYBEAN. A.G. Scott¹, M.A. McClure¹, L.E. Steckel¹, V.M. Davis², W.G. Johnson³, M.M. Loux⁴, J.K. Norsworthy⁵, J. Farmer⁶, K.W. Bradley⁶. ¹ University of Tennessee, Jackson, TN, ²  University of Wisconsin-Madison, Madison, WI, ³ Purdue University, West Lafayette, IN, ⁴ University of Ohio, Columbus, OH, ⁵ University of Arkansas, Fayetteville, AR, ⁶ University of Missouri, Columbia, MO.

Glyphosate resistant (GR) weeds have brought a sense of urgency to weed scientists to find alternative means to control herbicide resistant weeds. GR Amaranthus is considered one of the top 3 most troublesome weeds in the Southern United States.  Since producers have a history of terminating weeds mechanically through tillage this prompted weed scientists to explore different tillage systems to try and manage GR Amaranthus in Glycine max.

Research was conducted in 2014 in Jackson, TN, Fayetteville, AR, Lafayette, IN, Arlington, WI, South Charleston, OH, Belleville, IL, Moberly, MO, and Columbia, MO. Treatments were arranged within a split plot design with 4 replications at each location. Whole plots were set as tillage types and sub plots were set as herbicide treatments. Whole plot treatments included deep tillage with a moldboard plow in the fall followed by a field cultivator in the spring, conventional tillage with a chisel plow in the fall followed by a field cultivator in the spring, minimum tillage in the spring with a turbo-till, and a no-till plot. Each tillage treatment also received two herbicide treatments: 1) Residual Program of flumioxazin preemergence at 0.087 kg ai/ha^-1 followed by a post application of glufosinate at 0.59 kg ai/ha^-1 and s-metolachlor at 1.42 kg ai/ha^-1. 2) Post applications of glufosinate 0.59 kg ai/ha^-1 throughout the season. Glycine max planting dates and varieties were reflective of those typically utilized by producers at each location. Glycine max varieties were glufosinate tolerant. Six soil cores per treatment were taken up to a depth of 25 cm. Soil cores were cut in to 6 sections based on depths of 0-1, 1-5, 5-10, 10-15, 15-20, 20-25 cm, then pulverized and spread over potting soil and grown in a green house. Emerged weeds were counted and identified to species every two weeks and then removed by hand for a span of 3 months. Weeds species in field plots were counted and identified in two m² quadrants per treatment every two weeks following planting, until soybeans reached R6. Weeds were hand removed from quadrants then the entire plot received an application of glufosinate at 0.59 kg ai/ha^-1, applied at 140 L/ha^-1.

Tillage decreased Amaranthus emergence when a tillage method was utilized verse the no-till treatments in the Tennessee location. There was a similar trend that showed in the other locations that had significant Amaranthus populations. The deep tillage treatment showed the greatest variety of seed being distributed throughout the soil profile, with the largest portion of the seed being buried in the 5-15 cm range. As could be expected, besides the no-till treatment, the minimum tillage treatment showed the least variation of seed distribution through the soil profile, with most of the seed being buried in the 0-5 cm range.

Mechanical suppression of herbicide resistant weeds through tillage could be a viable option for some producers in the future. However, due to issues with soil erosion, especially in Tennessee, deep tillage is not a sustainable solution. Other options to control GR weeds in the future will still be needed to maintain control of row crops in agricultural fields.

EXPLORING INHIBITION OF TYROSINE AMINOTRANSFERASE AS A PUTATIVE MODE OF ACTION OF METHIOZOLIN.  K.A. Venner, S.D. Askew and S.J. Koo; Virginia Tech, Blacksburg, VA, 24061 and Moghu Research Center, Daejeon, Korea 305-333.

Methiozolin is a new herbicide under evaluation in the US for the selective removal of annual bluegrass in creeping bentgrass putting greens.  This herbicide is a member of the isoxazoline class of chemistry, but the primary mode of action is currently disputed.  Experiments performed in Korea have suggested that methiozolin may act as a cell wall biosynthesis inhibitor but the data were inconclusive as to whether the inhibition was a primary or secondary effect.  Research performed at Virginia Tech in 2014 found that incorporation of 13C-glucose was inhibited by methiozolin, and lends some support to this statement.  In Germany, Dr. Klaus Grossmann's lab concluded that methiozolin acts as a putative inhibitor of tyrosine aminotransferase, thus grouping this herbicide with other inhibitors of plant carotenoids, like cinmethylin, a product used in rice for the selective control of grassy weeds.  Tyrosine aminotransferase is an important enzyme in the conversion of L-tyrosine to 4-hydroxyphenylpyruvate (4-HPP).  In support of the TAT-inhibitor conclusion, Grossman et al. reported increased levels of tyrosine and L-DOPA and an apparent safening of Lemna paucicostata when 4-HPP was added to methiozolin-containing solution.  An Arabodopsis TAT isoenzyme, TAT7, was also inhibited by methiozolin but the required rate was over 1000 times typical field rates of methiozolin.  Commercial products containing methiozolin are used to target two primary weeds, Poa annua and P. trivialis, yet neither of these weeds have been used in previous attempts to determine the mode of action.  The objective of this research is to determine whether or not tyrosine aminotransferase inhibition is a primary mode of action for methiozolin in annual bluegrass and several desirable turfgrass species.  

Laboratory experiments were conducted in an attempt to duplicate the reported safening of L. paucicostata to methiozolin by addition of 4-HPP.  Our goal was to test several turfgrass species and annual bluegrass along with duckweed, L. paucicostata.   Seeds of annual bluegrass (Poa annua), creeping bentgrass (Agrostis stolonifera), Kentucky bluegrass (Poa pratensis), and perennial ryegrass (Lolium perenne) were cultured aseptically in 0.25x Hoaglands solution in order to germinate seed for use in the study.  L. paucicostata was cultured in 1.0x Schenk and Hildebrant media.  All plants were transferred to 0.25x Hoaglands solution containing the following treatments: methiozolin at 0.2 uM, methiozolin at 0.2 uM + 10uM 4-HPP, no methiozolin, and no methiozolin + 10 uM 4-HPP.  All treatments contained 1.0% DMSO as a solvent for methiozolin.  Digital images were taken regularly in order to ascertain whether or not 4-HPP had an effect on plant response to methiozolin via comparison between green pixel counts throughout the duration of the study.  In previous studies, 4-HPP has not altered methiozolin activity on: annual bluegrass, creeping bentgrass, Kentucky bluegrass, perennial ryegrass, and Lemna minor.  In one of four studies, 4-HPP improved L. paucicostata growth in the presence of methiozolin.   These effects were visible as regrowth six days after addition to media containing methiozolin plus 4-HPP.  In two additional studies, addition of 4-HPP to methiozolin-containing solution did not affect the incorporation of 13C-glucose into plant cell wall sugars versus methiozolin alone.  Our preliminary conclusion to date is that the three turfgrasses and annual bluegrass respond similarly to methiozolin and 4-HPP does not influence response of these species to methiozolin under conditions similar to previous studies.

Influence of Drift-Reduction Nozzle Technology on Efficacy of Contact and Systemic Tank-Mixed Herbicides. S.A. Butler; Department of Entomology and Plant Pathology, University of Tennessee, Jackson, TN. L.E. Steckel, Department of Plant Sciences, University of Tennessee, Jackson, TN.

Abstract. Weed management has become a challenge in soybean and cotton production because of the steady increase in number of glyphosate-resistant (GR) weed species. In the Mid-south, GR Palmer amaranth (Amaranthus palmeri) is one of the most problematic weeds to control. Palmer amaranth is highly competitive to soybeans and cotton due to its quick adaptability, lengthy germination window, aggressive competition, and ability to produce large quantities of seed. As of 2014, GR Palmer amaranth has spread to 21 states in the U.S. In order to consistently control weeds and slow the development of further herbicide resistance, diverse herbicide chemistries should be applied. Future soybean and cotton crops tolerant to synthetic auxins, such as dicamba and 2,4-D, and inhibitors of 4-hydroxyphenylpyruvate dioxygenase (HPPD), such as mesotrione, give growers another post emergence (POST) option to control problematic GR Palmer amaranth (Amaranthus palmeri). With multiple non-selective herbicides being used POST in crops, the need for drift management will increase. Also, synthetic auxins possess high rates of drift potential and volatility. Drift-reducing nozzle technology should be utilized in order to manage weeds POST in crops with crop-tolerant herbicides. Application stewardship practices will be required with future herbicide tolerant crops, including the use of spray nozzles that produce reduced quantities of driftable fines (<140 micron volume median diameter). Nozzles designed for minimizing drift manipulate spray mixtures to be applied in coarse droplets (>400 micron volume median diameter). Coarse droplets typically reduce coverage thus decreasing efficacy of contact herbicides, such as glufosinate. Contact herbicides work most effectively through nozzles producing fine to medium droplets (between 150 and 400 micron volume median diameter). Dual orifice nozzles historically increase coverage. Alternate spray application methods should be considered to improve efficacy of contact and systemic herbicides tank-mixed.

A field experiment was conducted at the West Tennessee Research and Education Center in Jackson, Tennessee in 2013 and 2014 to evaluate efficacy of contact and systemic herbicides tank-mixed through drift-reduction spray nozzles in single and dual orifices and in angled, vertical, and combination of angled and vertical fan arrangements. This study was performed in corn (Zea mays) comparing efficacy of glufosinate, glufosinate plus mesotrione, glufosinate plus 2,4-D, and glufosinate plus dicamba on Palmer amaranth. Each herbicide treatment was applied through 5 spray nozzles including: Teejet AIXR11002 (single orifice, vertical), Teejet TTI11002 (single orifice, angled), Teejet AITTJ60-11002VP (dual orifice, angled), simulated Wilger Combo-Rate with Greenleaf Airmix11002 (dual orifice, vertical), and Greenleaf TADF02 (dual orifice, combination of angle and vertical). Applications were made POST on 15 to 21 cm Palmer amaranth. Assessments were made of Palmer amaranth visual control 7, 14, and 21 days after application (DAA). Fresh weight biomass samples were collected 14 DAA and corn was harvested for yield at maturity and adjusted to 15.5% moisture. Atomization analysis of droplet size was evaluated using Helos KR laser diffraction at the West Central Research and Extension Center in North Platte, Nebraska. Droplet size had greatest effect on visual control ratings across spray nozzle parameters, significantly increasing control up to 6% when decreasing droplet size from 649 microns to 292 microns. Fans arranged vertically or in combination of vertical and angled significantly increased control up to 3.5% in comparison to angled fan arrangements. Dual orifice nozzles showed up to 3% higher control of Palmer amaranth at 14 DAA than a single orifice nozzle, however, no significant differences were found between the number of orifices based on visual control ratings at 21 DAA. Tank-mixing a systemic herbicide with glufosinate significantly increased Palmer amaranth control up to 12%. Palmer amaranth fresh weight biomass was significantly reduced 128 g m^-2 when tank-mixing a systemic herbicide. Thus, the ability to apply alternate herbicide chemistries tank-mixed with glufosinate has the potential to improve Palmer amaranth control in future herbicide-tolerant soybean and cotton crops and promote protection of herbicide chemistries from resistance. Also, when applying contact herbicides tank-mixed with systemic herbicides in future tolerant crops, using an approved spray nozzle that creates the finest droplets will provide the greatest control of Palmer amaranth

AMINOCYCLOPYRACHLOR COMBINATIONS FOR WOODY PLANT CONTROL IN PASTURES.  D.E. Sanders*; LSU AgCenter, Clinton, LA 70722

                                                                                                ABSTRACT

Interest in pasture woody plant control in Louisiana and other Gulf Coast states has increased in the past several years for several reasons.  Long term neglect of woody plant encroachment from wood lines and pasture margins due to low cattle prices has been replaced with renewed interest in reclaiming pasture margins due to increased cattle prices.  In addition, throughout south Louisiana downed trees in pastures due to four hurricanes in eight years has resulted in an increase in woody plant infestations increasing throughout pastures. Invasive species such as Chinese tallow (Sapium sebiferum) and Chinese privet (Ligustrum sinense) continue to increase.   Since 2008, sixteen replicated trials using amincyclopyrachlor alone or in combination with registered pasture herbicides have been conducted targeting nine woody species commonly occurring in pastures in south Louisiana.  Seven bermudagrass (Cynodon dactylon) tolerance trials were conducted with six harvested for yield analysis.  Three Pensacola bahiagrass (Paspalum notatum) tolerance trials were conducted with two harvested for yield analysis.  Trials were conducted at the Bob R. Jones-Idlewild Research Station at Clinton, LA or the Reproductive Biology Center at St. Gabriel, LA.

Three trials targeting Chinese Tallow (Sapium sebiferum) were conducted using MAT 28 (aminocyclopyrachlor) at rates from 0.94-2.0 oz ai/a in combination with Escort at .60 oz ai/a, Telar at .75 oz ai/a, triclopyr at 0.5 lb ai/a, 2,4-D at 1.0 lb ai/a or imazapyr at 1.0 lb ai/a.  MAT 28 treatments were compared to either triclopyr at 1.0 lb ai/a, Milestone at 1.73 oz ai/a + Escort at 0.31 oz ai/a or Grazon P+D at .95 lb ai/a.  All MAT 28 combinations provided 100% control of Chinese tallow one year after application.  One trial targeting Chinese privet (Ligustrum sinense) and two trials targeting yaupon (Ilex vomitoria) were conducted using MAT 28 at rates from 2-10 oz ai/a in combination with Escort at 2-4 oz ai/a, Triclopyr at 2.0 lb ai/a or imazapyr at 1.0 lb ai/a.  All MAT 28 combinations provided 95% or better control of Chinese privet and 99% or better control of Yaupon one year after treatment  Standard treatments of Escort at 2-3 oz provided 80% control and Triclopyr at 2 lb ai/a provided 60% control one year after treatment.  Three trials targeting dewberry (Rubus sp.) were conducted using MAT 28 at rates from 0.94-2.0 oz ai/a in combination with either Escort at 0.60 oz ai/a, Telar at 0.75 oz ai/a or triclopyr at 1.0 lb ai/a.  MAT 28 plus triclopyr provided 99% or better control one year after treatment.  MAT 28 plus either Escort or Telar provided 80% control one year after treatment.  The standard treatment of Grazon P+D at 1.0 lb ai/a provided less than 50% control one year after treatment.  Additional target species: box elder (Acer negundo), water oak (Quercus nigra), sugarberry (Celtis laevigata) and wax myrtle (Myrica cerifera) were evaluated over the past eight years.  Most MAT 28 combinations provided greater than 90% control of box elder and water oak one year after application.  MAT 28 combinations provided 50% or less control of sugarberry and wax myrtle one year after application.

Between 2009 and 2012 seven bermudagrass tolerance trials were conducted to evaluate phytoxicity and yield effects from MAT 28 alone or in combination with Escort, Telar, 2,4-D or triclopyr.  MAT 28 rates ranged from 0.667 to 2.0 oz ai/a alone or in combination with one of the following: Telar from 0.56 to 0.75 oz ai/a, Escort from 0.10-0.30 oz ai/a, 2,4-D from 5.3-10.6 oz ai/a or triclopyr at 2.0-3.0 oz ai/a.  All MAT 28 treatments at 1.0 oz ai/a or greater alone or in combination showed transient yellowing for 7-10 days with the exception of combinations containing 2,4-D which showed little or no discoloration.  Yield results from these trials showed no significant differences between treatments and weed free checks.  Three phtotoxicity trials with Pensacola bahia grass were conducted using the same above rates.  No discoloration or yield reduction was noted except with MAT combinations containing Escort at any rate.  MAT 28 plus Escort reduced Pensacola bahiagrass yields greater than 50%.

Further work in determining effects of MAT 28 combinations on pasture shade trees needs to be conducted.  In all but the wax myrtle trial one or more of the combination treatments controlled the target species as well or better than the standard.  The residual control provide by MAT 28 would be advantageous in pastures. 

Chinese tallowtree is an invasive tree found throughout the southeastern United States.  Its negative impacts can be seen in numerous natural and managed ecosystems including bottomland hardwood forests, pastures, pine plantations, and along lakes, ponds, streams, and rivers.  Despite its troublesome presence for many decades, relatively few effective control strategies are available. Root sprouting following management efforts is a major impediment to successful control. Studies were conducted in Alabama and Louisiana at three locations to test several herbicides for cut stump, basal bark, and foliar individual plant treatment methods. Herbicide treatments included triclopyr amine and ester formulations, imazamox, aminopyralid, aminocyclopyrachlor, and fluroxypyr. Data were collected just before leaf senescence one and two growing seasons after treatment, and included Chinese tallowtree foliar cover, number of stump or root collar sprouts and number of sprouts originating from lateral roots within a one meter radius of each tree. For the cut stump and basal bark studies, most herbicide treatments prevented sprouting from the stump or root collar region better than from lateral roots. Aminopyralid reduced total sprouting better than all other treatments in the cut stump study. The high rates of aminocyclopyrachlor and fluroxypyr resulted in the highest mortality in the basal bark study. Aminocyclopyrachlor reduced total sprouting better than all other herbicides in the foliar treatment study. Triclopyr amine and ester formulations, which are commercial standards, did not consistently control Chinese tallowtree across these IPT studies. These studies provide some promising treatments to increase the number of effective tools that can be used to manage Chinese tallowtree. Additional research is needed to address the prolific nature of lateral root sprouting following any of these treatment methods.    

BUSH-TYPE BLACKBERRY CONTROL AFTER 2 ANNUALLY APPLIED TREATMENT PROGRAMS UTILIZING HERBICIDE MIXTURES VERSUS MECHANICAL MOWING.

W.N. Kline*¹, E. G. Lowe², P.L. Burch³; ¹William N Kline, LLC, Ball Ground, GA,²University of Georgia, Arnoldsville, ³Dow AgroSciences, Christiansburg, VA (166)

ABSTRACT

The objective of this field research was to evaluate currently labeled herbicides and herbicide mixtures for long term blackberry control and compare to mechanical mowing for pasture renovation.  This experiment was initiated in Oct 2012 in an abandoned fescue pasture near Crawford, GA.  All plots were sprayed 2 years in a row – “sequential applications” in Oct 2012 and again in Oct 2013.  Sprayed plots are 24 ft X 50 ft with 16 ft untreated buffers between plots arranged in a randomized complete block design with 3 replications per treatment.  

Treatments were: Chaparral^® 3.3 Oz/A; Chaparral 2 Oz + PastureGard^® HL 1 Pt/A; GrazonNext^® HL 2 Pt + Remedy^® Ultra 2 Pt/A; GrazonNext HL 2 Pt + PastureGard HL 1 Pt/A; PastureGard HL 2 Pt/A; ACP 1.11 Oz + Metsulfuron 0.17 Oz (Ai/Ac); ACP 2.22 Oz + Metsulfuron 0.34 Oz  (Ai/Ac); Metsulfuron 0.34 Oz (Ai/A); and Mechanical Mowing.  (note: ACP = Aminocyclopyraclor)

Total sprayed volume was 30 GPA applied with ATV boom sprayer.  All treatments included non-ionic surfactant (0.25% v/v).  Mechanical mowing was completed at the same time as spray treatments with a “bush hog” mower attached to a farm tractor.  All plots were visually rated for % blackberry control and fescue cover in fall 2013 (365 DAT) and fall 2014 (705 DAT).

Conclusions:  Blackberry briars take a long time to “take over” a pasture.   Getting rid of them takes several years – a multi-year herbicide program is necessary.  After 2 annual “sequential applications” to a blackberry infested fescue pasture, results suggest that treatments containing metsulfuron are less efficacious for blackberry control than non-metsulfuron treatments. Our observations suggest that sequential applications of metsulfuron containing herbicides (2 years in a row) cause significant fescue injury.  This injury results in bare ground areas that promote re-invasion by blackberry, weedy grasses and other broadleaf weeds.  In general the lack of fescue canopy provides opportunity for weeds (including blackberry) to re-establish.  Herbicides and herbicide mixtures that did not contain metsulfuron improved the fescue canopy following each of the sequential applications.  This outcome is different from the results that were presented in 2014 (Kline et al SWSS 2014).  The best treatments at the end of 2 years (705 DAT) were GrazonNext HL 2 Pt + Remedy Ultra 2 Pt/A providing 94% blackberry control followed by GrazonNext HL 2 Pt + PastureGard HL 1 Pt/A with 91% control followed by PastureGard HL 2 Pt/A with 80% control. Chaparral treatments provided marginal control, ranging from 70 to 75% control.  All other treatments were less than 70% control and should be considered not commercially acceptable.  The net result is the combination of blackberry control provided by non-metsulfuron herbicides, plus the thick fescue canopy that develops following these treatments, results in excellent pasture renovation and near complete blackberry eradication.

Recommendations:

Based upon these results, recommendations are for sequential annual spray treatments (at least 2 years) using one of the following:

GrazonNext HL 2 pts/acre + Remedy Ultra 2 pts/acre

GrazonNext HL 2 pts/acre + PastureGard HL 1 pt/acre

Chaparral (or other metsulfuron containing herbicide mixture) as a first year treatment on thick canopy blackberry stands, then switch to non-metsulfuron mixtures such as GrazonNext HL + Remedy Ultra or GrazonNext HL + PastureGard HL as the second year treatment.

Also, PastureGard HL was evaluated in this trial at 2 pts/acre; 3 pts/acre has been shown to be efficacious on blackberry in operational programs.  Sequential annual applications of Pasturegard HL at 3 pts/acre need to be evaluated in field experiments and compared to the recommended rates above.

Mowing blackberry is a waste of time and money.

^® Trademarks of Dow AgroSciences LLC

Pawpaw (Asimina  spp.) is in the custard family, and ten species are known to occur in Florida.  While these species are native, edible, and serve as a host of the zebra swallowtail butterfly, they can become problematic in grazing systems.  Experiments were conducted in 2011 through 2014 in pastures naturally infested with pawpaw.  Experiment one treatments included broadcast applications of triclopyr ester at 1.12 kg/ha, triclopyr + fluroxypyr at 0.84 + 0.28 kg/ha, aminocyclopyrachlor (ACP) + chlorsulfuron at 0.111 + 0.044 kg/ha, and ACP + chlorsulfuron at 0.222 + 0.088 kg/ha; sequential applications of these herbicides were also applied six months following the first application as separate treatments.  This experiment was conducted two times beginning in May, 2011 (sequential application in December)  and repeated in December, 2011 (with sequential application in May 2012).  A second experiment was conducted that included the following treatments: ACP alone at 0.035, 0.070, and 0.140 kg/ha, ACP + chlorsulfuron at 0.069 + 0.027 and 0.138 + 0.054 kg/ha, ACP + 2,4-D amine at 0.070 + 0.533 and 0.140 + 1.066 kg/ha, ACP + triclopyr-ester at 0.070 + 0.140 and 0.140 + 0.280 kg/ha, and ACP + metsulfuron at 0.046 + 0.007, 0.078 + 0.012, and 0.168 + 0.026 kg/ha.  Experiment two was conducted in December 2011 and repeated in May, 2013, using single, rather than sequential, applications.  The number of pawpaw stems were counted in each plot prior to herbicide application and at six and twelve months after treatment (MAT).  To account for differences among stem densities within each plot, stem counts at application were used as a covariate in the data analysis.  There was a timing by treatment interaction for the first experiment at 6 MAT.  All treatments following the May application resulted in at least 68% less pawpaw stems compared to the untreated, but no differences among treatments were detected.  Following the December application, however, a single application of triclopyr at 1.12 or triclopyr + fluroxypyr resulted in at least 84% fewer pawpaw stems at 6 MAT; sequential applications of these herbicides at a six month interval did not improve control with these herbicides at 6 months after the sequential application. At 12 MAT only the main effects of treatment and timing were significant.  A May application of herbicide treatment resulted in approximately 50% fewer pawpaw stems as compared to the December application.  Except for a single application of triclopyr + fluroxypyr and the low rate of ACP + chlorsulfuron, all treatments resulted in at least 42% less pawpaw stems than the untreated control.  The highest level of stem reduction was observed following a single (70%) or sequential (81%) application of  the high rate of ACP + chlorsulfuron. In the second experiment, only treatment was significant at 6 MAT and ACP at 0.140 kg/ha plus either 2,4-D amine, triclopyr, or metsulfuron resulted in at least 68% fewer pawpaw stems compared to the untreated control.  At 12 MAT there was a timing by treatment interaction and pawpaw stem density averaged across all treatments was approximately 75% less when treatments were applied in May versus December.  Pawpaw stem density following the December application of all treatments ranged from 40 to 153 stems per plot, which was at least 31% lower than the untreated control; ACP at 0.140 kg/ha alone and ACP plus either 2,4-D amine or triclopyr resulted in at least 60% fewer pawpaw stems.  No pawpaw stems were recorded in plots following the May applications of ACP at 0.140 plus 2,4-D amine, triclopyr, chlorsulfuron, or metsulfuron.  Pawpaw stem density was 76% lower when treated with ACP at 0.070 and 0.140 kg/ha.  All other treatments had similar stem densities as the untreated control.  These data suggest that ACP may be a good alternative to pawpaw management in pastures, but timing of application may be critical as control was typically higher following a spring versus late fall application. 

Several sandbur species affect forage production in the Southern Great Plains (SGP) including southern sandbur (Cenchrus echinatus L.), field sandbur (Cenchrus spinifex Cav.), and longspine sandbur (Cenchrus longispinis (Hack.) Fernald).  Taken together they are detrimental to forage production, decreasing the quality and value of improved bermudagrass (Cynodon dactylon (L.) Pers.) pasture and hay.  Livestock may be harmed when stocked on infested sites or fed infested hay.  Injured animals require veterinary care and increase the cost of production. In-season management is necessary but few practices have proven effective.

Improved management strategies for sandburs in the SGP will increase the quality and value of bermudagrass pasture and hay produced in this region.  It will also decrease veterinary costs to livestock producers and ultimately increase farm revenues for livestock and hay enterprises.  Currently only four products are labeled for sandbur control in improved bermudagrass systems.  They are pendimethalin, imazapic, nicosulfuron, and low-rate glyphosate.  Pendimethalin is a preemergence product and the other three are postemergence.  All of the post products are known to cause severe reductions in forage quantity and quality in the season of application.  The objective of this research was to evaluate management practices including several pre-, split pre- and postemergent herbicides compared to industry standards to improve herbicide options for bermudagrass hay and pasture operations.  The study was initiated on a producer site in Hennessey, OK as a split plot design with 9 treatments and four replications.  The main plot was herbicide treatment and the subplots were 100% bermudagrass and 100% sandbur.  Treatments included pendimethalin at 5.6 L ha-1 and 11.8 L ha-1, nicosulfuron at 0.105 kg ha-1, quinclorac at 1.12 kg ha-1, imazapic at 0.28 kg ha-1, aminopyralid at 0.28 kg ha-1, glyphosate at 0.77 kg ha-1, and pendimethalin PRE fb nicosulfuron POST at 5.6 L ha-1 fb 0.105 kg ha-1 and a nontreated control.  Percent sandbur control, percent bermudagrass injury were evaluated visually 1, 2, 4, 6 , 8, 12, 15, and 16 WAT.  Percent sandbur seedhead suppression was evaluated at 15 WAT and height and standing forage samples were taken for fresh and dry biomass.   Data were managed in ARM 9.2 and subject to ANOVA.  Means were separated using Fishers protected LSD at p=0.05.

Nicosulfuron, imazapic, and glyphosate significantly injured bermudagrass season-long at 25, 58, and 36% respectively even 16 weeks after the last treatment.  Imazapic and glyphosate were also the only treatments to provide season-long control of sandbur at 93 and 84% respectively 16 WAT.  Though nicosulfuron did not provide season long control, it did provide significant seedhead suppression, preventing sandbur from producing burs and leaving edible forage for livestock.  New products investigated including quinclorac and aminopyralid did not effectively control sandbur or provide seedhead suppression.  However, aminopyralid had a growth stimulating effect on bermudagrass and a significantly improved forage fresh weight compared to the nontreated.  Additional products will need to be investigated to develop new tools for sandbur management in improved bermudagrass.  This work suggests currently registered products are too detrimental to forage yields to be a feasible strategy unless a grower has significant ground to rotate livestock in a given season and leave land ungrazed or minimally grazed while managing for sandbur.  

Although bermudagrass (Cynodon dactylon (L.) Pers.) currently comprises only 5 percent of Tennessee’s grass forage base, interest in growing this warm season perennial grass for hay has increased in recent years.  In particular, the strong demand for bermudagrass hay in small bales has prompted a number of growers, particularly in West Tennessee, to establish fields for hay production.  To successfully compete in this high value market, producers must be in a position to produce virtually weed-free bermudagrass hay for their customers, many of whom are horse owners. Horse owners are willing to pay a premium for clean hay and they are becoming increasingly selective buyers.  The registration of Pastora (nicosulfuron + metsulfuron) has greatly improved the ability of producers to effectively manage many grass and broadleaved weeds in bermudagrass hay fields. In particular, it has proven effective on troublesome annual grass weeds such as barnyardgrass (Echinochloa crus-galli (L.) Beauv.), fall panicum (Panicum dichotomiflorum Michx.), and annual foxtails (Setaria spp.).  Foxtail control is particularly important in production of horse hay in that the seed head bristles can cause serious problems with mouth ulcers in horses.  Horse owners are becoming increasingly aware of this problem and many refuse to purchase hay that contains foxtail seed heads.

Reports of Pastora failures on foxtail have increased in Tennessee over the past few years.  Upon investigation of these reports, we learned that the majority of cases of insufficient foxtail control were in hay fields infested with knotroot foxtail (Setaria parviflora (Poir.) Kerguélen), a perennial species.  Research was conducted in 2013 and 2014 to identify an effective herbicide option for management of knotroot foxtail in bermudagrass hay fields.  While no effective control option was identified, the most effective option for suppression of knotroot foxtail  (reduction or elimination of seed heads in harvested hay) was Pastora plus glyphosate (1.5 oz + 8 oz of a 3 lb ae/gal formulation) at first cutting followed by a second application of Pastora (1 oz/A), 2 to 3 weeks later. Fall applications of Pastora, glyphosate, Pastora + glyphosate, and other herbicides were found to be ineffective when evaluated the following year at green-up.

While on farm visits in 2013 and 2014 we observed that there appeared to be a relationship between management of N and K, and severity of knotroot foxtail infestations.  Fields fertilized with recommended N and K rates and timings appeared to be less severely infested than those that were receiving less N and K.  Accordingly, we conducted research in 2014 to investigate this apparent relationship and a possible interaction of fertility management and Pastora + glyphosate applications on knotroot foxtail biomass and seed head production. High N and K rates (100 lb/A N and K20) resulted in a lower  knotroot foxtail seed head density at the second harvest as compared to  low N and K rates (50 lb/A N and K20).  No herbicde by fertility interaction was observed.  As expected, the effect of herbicide was stronger than that of fertility.

PRE-EMERGENT WEED CONTROL WITH SPRING AND EARLY SUMMER PASTURE HERBICIDES.  W.N. Kline*¹, E. G. Lowe², P.L. Burch³; ¹William N Kline, LLC, Ball Ground, GA,²University of Georgia, Arnoldsville, ³Dow AgroSciences, Christiansburg, VA (170)

ABSTRACT

There were 3 key objectives for this experiment.  1) Quantify the level and duration of pre-emergent weed control provided by pasture weed control herbicides. 2) Document herbicide response and length of control when sprayed at 2 timings (timing varied by location - early was April/May; late was June/July).  3) Identify key weed species controlled or suppressed by herbicide treatments during the growing season.  

This project was initiated at 8 field trial locations across the Southeast (GA,FL,AL,KY) during the spring of 2014.  Sprayed plots were 10 ft X 30 ft; with 5 ft untreated buffers between plots arranged in a randomized complete block design - 4 replications per treatment. Total sprayed volume was 20 GPA applied with CO2 “T” wand.  All treatments included a non-ionic surfactant (0.25% v/v).  Plots were visually rated for % weed control throughout the duration of the growing season.

Treatments included 2 rates of GrazonNext^® HL at 1.2 & 1.5 pints/A, Chaparral^® at 2.5 oz product/A, Grazon^® P+D at 2 pints/A, 2,4-D (DMA 4) at 2.1 pints/A, and Weedmaster at 2 pints/A.  Each of the 6 treatments was applied at 2 timings in each trial - total of 12 treatments.  Timing varied by location: Early was April/May; Late was June/July

Conclusions:  Results demonstrated large and significant differences between treatments applied at the early timing (April/May) on key target weeds in these trials.  Early timings demonstrated excellent burn-down followed by pre-emerge control of horsenettle and spiny amaranth with both rates of GrazonNext HL & Chaparral through the end of the growing season.  Grazon P+D provided moderate control and 2,4-D & Weedmaster gave poor control of these weeds.  This was particularly true at later rating dates.  Sicklepod pre-emerge control was excellent with GrazonNext HL (April application) providing ~ 85% pre-emerge sicklepod control at 27 DAT and ~50% pre-emerge sicklepod control out to 83 DAT on an abandoned ag field with no grass competition.

In general, across trials where these weeds were present, small differences between treatments were observed on common ragweed, Canada horseweed and annual marshelder.

Smaller and generally non-significant differences resulted from the late timing - June/July.  Initial control ranged from ~60 to 95% control across all weeds evaluated.  Percent weed control ranking from the late timing - June/July was: GrazonNext>Chaparral>GrazonP+D>Weedmaster>2,4-D.  By end-of-season (Sept/Oct), there were small numerical differences between treatments due to the limited number of sites rated and natural senescence of weeds.

Recomendations:  Based on results from these trials, GrazonNext HL and Chaparral herbicides provide superior initial (burn-down) and residual (pre-emerge) weed control of many problematic weeds in the Southeast.  These products produce the best results when applied early in the growing season.  Residual soil activity of the herbicide followed by early season pasture grass response after spraying herbicides, heavily influences the potential for season long weed control. This is especially true on healthy and dense coastal bermuda pastures at the time of spraying.  If weeds are eliminated during the early part of the growing season, grass response can prevent weed germination for most of the rest of the growing season.  Also, the importance of proper pasture management is critical.  Weed control with herbicides is only part of successful forage production.  Fertilization, cattle rotation and grass recovery after heavy grazing are as important as proper weed control.  Over grazing can reduce or nullify weed control efforts, particularly with spring applied herbicides.

^® Trademarks of Dow AgroSciences LLC

Buttercups (Ranunculus spp.) are some the most common weeds found in the mid-South and over 20 species are found in Tennessee. Hairy buttercup (R. sardous Crantz) and bulbous buttercup (R. bulbosus L.) are of particular concern in pastures and hay fields. Both species mature in spring and reduce pasture and hay field quality and productivity. Hairy buttercup can be controlled with 2,4-D at 2 pt/A applied in late fall or late winter to early spring. Application prior to bloom stage is critical for managing buttercups because herbicides are more effective and it prevents plants from going to seed. In the past 5 years, several producers have experienced poor control of buttercup with 2,4-D, even while following recommended guidelines. Further investigation has revealed that these areas have become heavily infested with bulbous buttercup in addition to hairy buttercup.

Bulbous buttercup is a perennial that is strikingly similar to hairy buttercup. Virtually, the only difference is that bulbous buttercup has an enlarged corm or bulb-like base. Bulbous buttercup has spread in Tennessee and is thought to be more tolerant to 2,4-D. The purpose of our research is to determine control levels of hairy and bulbous buttercup using 2,4-D and some newer chemistry. Aminocyclopyrachlor (AMCP) is a new synthetic auxin herbicide and is anticipated to be registered for pasture use as premixtures: AMCP + 2,4-D (Kindra), AMCP  + metsulfuron (Rejuvra), and AMCP + triclopyr (Invora).

Research was conducted in 2010, 2013, and 2014 on naturally occurring hairy and bulbous buttercup populations in eastern Tennessee. Experimental design was a randomized complete block with three replications. All treatments included non-ionic surfactant at 0.25%. Visual control ratings were evaluated monthly on a 0-99% scale. Spring-applied 2,4-D ester at 2 pt/A, Kindra at 16 oz/A, and Rejuvra at 1.5 oz/A controlled hairy buttercup >85%. Spring-applied GrazonNext HL at 1.6 pt/A, Rejuvra at 1.5 oz/A, and Kindra + Cimarron Plus at 24 + 0.2 oz/A controlled bulbous buttercup >87%. Fall-applied Rejuvra at 1.5 oz/A and Kindra + Cimarron Plus at 24 + 0.2 oz/A controlled bulbous buttercup >91%. Neither fall-applied nor spring-applied 2,4-D ester at 8 pt/A adequately controlled bulbous buttercup. The results indicate that while 2,4-D is still effective on hairy buttercup, other active ingredients should be utilized when managing bulbous buttercup.

Despite decades of research on broadleaf weed control in forage systems, there are still very few herbicide options that are safe on forage legumes. In the southeastern United States, winter annual weeds such as hairy buttercup are a significant problem for forage legumes including white and crimson clovers. To address this issue, two separate studies were conducted at pasture sites in Lamison and Russellville, Alabama from December 2013 to May 2014. The first was a dose response study using six rates of carfentrazone. The second study compared tank mixes of carfentrazone and imazethapyr or 2,4-D to each product alone. Treatments were applied in either December 2013 or March 2014 to mixed stands of hairy buttercup and either white clover or crimson clover. Visual evaluations of buttercup control and forage injury were collected during the spring of 2014. In the dose response study, carfentrazone was not effective for hairy buttercup control at any rate at either location. In the tank mix study at Lamison, carfentrazone increased buttercup control when applied with either 2,4-D or imazethapyr at 41 DAT compared to either product alone. However, this result was not found at later evaluation dates. Carfentrazone severely injured crimson clover at the Russellville site but was safened when tank mixed with imazethapyr. These results indicate that carfentrazone may be limited in its utility when controlling hairy buttercup in white or crimson clover forages. More research is needed to determine its fit for other forage legume/weed complexes.    

PERILLA MINT CONTROL: AVOIDING TOXICITY TO GRAZING LIVESTOCK. D.P. Russell and J. Byrd; Department of Plant and Soil Sciences, Mississippi State University, Mississippi State, MS.

ABSTRACT

Perilla mint (Perilla frutescens) is an erect, herbaceous annual known to cause respiratory toxicity in livestock. Perilla mint may reach an average height of 2 feet and is predominately found in areas of partial shade, low-lying areas, and woodland edges.  Elevated toxicity levels are believed to occur as the plant enters the reproductive stage during late summer.  The goal of these studies was to evaluate efficacy of several preemergence and postemergence herbicide treatments in randomized complete block design experiments.

A field experiment to evaluate postemergence treatments was initiated in August 2014 in east-central Mississippi. Plants were at the late vegetative/early reproductive stage at the time of application. Per-acre herbicide treatments included Perspective (39.5% aminocyclopyrachlor + 15.8% chlorsulfuron) at 16 fl 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.

Results from the postemergence field experiment indicated Roundup Powermax exhibited the quickest response with 100% perilla mint control 14 days after treatment (DAT). Complete control was achieved by every treatment except Remedy Ultra and Cimarron 42 DAT.

Inflorescences from perilla mint plants outside the postemergence field study were collected October 14, 2014 and later cleaned and stored for future testing.  Prior to seed harvest, a preemergence greenhouse study was initiated using older seed with a germination percentage of 69% pure live seed.  Preemergence herbicides were applied through a controlled environment spray chamber with a CO₂ pressurized sprayer that delivered 23 GPA one day after perilla mint seed was planted into commercial potting mix.  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.

Evaluation of the preemergence greenhouse study indicated all treatments except Prowl H₂0 provided acceptable control, and were not significantly different through 49 DAT. Perspective, Grazon P+D, and Weedmaster provided complete control, inhibiting germination of all seed. Evaluation of control through 49 DAT indicated Prowl H₂0 provided visually less perilla mint control compared to all other treatments. However, there were no significant differences among preemergence treatments based on plant green weight. 

PALMER AMARANTH MANAGEMENT WITH ENGENIA IN BOLLGARD II XTENDFLEX COTTON.  A.C. York*¹, C.W. Cahoon¹, G.W. Oliver²; ¹North Carolina State University, Raleigh, NC, ²BASF Corporation, Research Triangle Park, NC (174)

ABSTRACT

An experiment was conducted on a loamy sand soil in 2013 and 2014 to evaluate Palmer amaranth (AMAPA) control in Bollgard II XtendFlex cotton with systems utilizing Engenia (BAPMA salt of dicamba; pending EPA approval) herbicide.  Treatments included a factorial arrangement of two base systems and seven Engenia options.  Base systems in 2013 included Prowl H2O (pendimethalin, 924 g ai/ha) applied PRE, either Roundup PowerMax (glyphosate, 1120 g ae/ha) plus Dual Magnum (S-metolachlor, 1090 g ai/ha) or Liberty (glufosinate-ammonium, 594 g ai/ha) plus Dual Magnum at first POST, and Roundup PowerMax plus Dual Magnum at second POST.  These are referred to as the Roundup system and the Liberty/Roundup system.  Base systems were the same in 2014 except that Outlook (dimethenamid-P, 630 g ai/ha) replaced Dual Magnum in the first POST and Warrant (acetochlor, 1260 g ai/ha) replaced Dual Magnum in the second POST.   Engenia (560 g ae/ha) options included none, PRE, first POST, second POST, first and second POST, PRE and first POST, and PRE and second POST.  The first POST was applied to 1- to 2-leaf cotton and 6- to 8-cm weeds.  The second POST was applied to 5- to 7-leaf cotton.  AMAPA at the second POST ranged from 5 to 18 cm, depending upon previous treatments.   Data were averaged over years.  An additional treatment was Roundup first and second POST with no residual herbicide PRE or POST.  This treatment indicated 40 to 50% of the AMAPA was glyphosate-resistant.

No cotton injury was observed with Engenia PRE or POST.  Dual Magnum, Outlook, and Warrant caused minor (5% or less), transient foliar necrosis. 

Residual activity from Engenia applied PRE was observed.  At 14 days after PRE application and prior to POST application, AMAPA was controlled 31 and 75% by Prowl and Prowl plus Engenia PRE, respectively.  Following POST application, a base herbicide system by Engenia interaction was noted for AMAPA control.  In the absence of Engenia, greater control was noted throughout the season with the Liberty/Roundup system compared to the Roundup system.  For example, at 14 days after second POST, AMAPA was controlled 89% by the Liberty/Roundup system without Engenia compared with 40% by the Roundup system. 

Engenia was of greater benefit in the Roundup system than in the Liberty/Roundup system.  In the Roundup system, at 14 days after second POST, AMAPA was controlled 40, 61, 96, and 86% with no Engenia, Engenia PRE, Engenia first POST, and Engenia second POST, respectively.  Engenia applied PRE and POST was no more effective than Engenia POST only.  In the Liberty/Roundup system, AMAPA was controlled 89% in the absence of Engenia.  Control was not improved when Engenia was included PRE, first POST, or PRE plus first POST.  AMAPA was controlled 100% when Engenia was included with the second POST.

Although residual control from Engenia applied PRE was observed, POST application was more effective than PRE application.  With a single POST application, Engenia was more effective in the first POST application in the Roundup system and more effective in the second POST application in the Liberty/Roundup system.  When Engenia was included with both POST applications, complete AMAPA control was noted in both systems.

ABSTRACT

Crop Response of Bollgard II^® XtendFlex™ Cotton to Applications of Dicamba and Dicamba Premix Formulations. J.T. Fowler; Technology Development and Agronomy, Monsanto Company, St. Louis, MO, 63167

Bollgard II® XtendFlex™ cotton is expected to be introduced in 2015, pending deregulation by USDA of the trait.  Testing of the trait in 2012 revealed that a potential crop response in the form of necrosis can result from applications of dicamba + glyphosate, either tankmixed or applied as a premix.  To evaluate the potential for response and the factors that contribute to it, three separate studies were conducted in 2013 and 2014 across the US cotton belt.  In 2013, a study to examine the influence of nozzle droplet size, herbicide, and application volume was conducted at 3 locations.  Teejet AIXR 11002, Green Leaf Air Mix AM110-02, and Teejet TTI 11002 nozzles with very coarse, extremely coarse, and ultra coarse droplet sizes, respectively, were used to apply either 0.5 lbs ae/A dicamba or 0.5 lbs ae/A dicamba + 1.0 lbs ae/A glyphosate at 10, 15, and 20 gallons per acre application volumes.  Also, in 2013, a study to determine the effect of application rate and timing was established at 11 locations.  In this study, increasing rates of dicamba + glyphosate at a 1:2 ratio (0.5, 1.0, 1.5, 2.0, 3.0, and 4.0 lbs ae/A dicamba plus 1.0, 2.0, 3.0, 4.0, 6.0, 8.0 lbs ae/A glyphosate) were applied sequentially to 4-, 8-, and 12-node cotton.  In 2014, an additional study evaluating the influence of nozzle droplet size, herbicide, and application volume was conducted at 10 locations.  Treatments consisted of Teejet AIXR 11002 and Teejet TTI 11002 nozzles with very coarse and ultra coarse droplet sizes, respectively, used to apply either 0.5 lbs ae/A dicamba or 0.5 lbs ae/A dicamba + 1.0 lbs ae/A glyphosate at 5, 10, 15, and 20 gallons per acre application volumes.

The premix of dicamba + glyphosate in both 2013 and 2014 caused a greater crop response than the dicamba alone treatments (11.2 and 7.3% necrosis in 2013 and 2014, respectively, compared to 5.2 and 3.9%).  In both years, the effect of nozzle droplet size was significant, with the Teejet TTI 11002 causing greater necrosis than the treatments using nozzles with smaller droplet sizes.  In 2013, application volume was not significant with similar crop response across 10, 15, and 20 gallons per acre.  However, in 2014, the 5 gallons per acre application volume did significantly increase necrosis compared to 10 and 15 gallons per acre.  Cumulatively, treatments across both years of the dicamba + glyphosate premix applied with Teejet TTI 11002 nozzles at the lowest application volumes caused significantly greater crop response than dicamba alone applied at greater volume with smaller droplet size nozzles.  In the 2013 study to examine a rate and timing response, crop response in the form of necrosis increased significantly between rates but there was no effect due to application timing.  Location did effect the level of response, but did not interact significantly with the rate treatment response.  Applications of 0.5 lbs ae/A dicamba + 1.0 lbs ae/A glyphosate through 4.0 lbs ae/A dicamba + 8.0 lbs ae/A glyphosate caused a necrosis response of 4.6 to 40.7%, respectively, across application timings.  Final plant height was significantly reduced by applications of 1.5 lbs ae/A dicamba + 3.0 lbs ae/A glyphosate and higher compared to the untreated check.  The two highest rates also caused a delay in the node of first fruiting branch (6.7 and 6.6 for the 6X and 8X rates, respectively) compared to the untreated check (6.1).  Total nodes trended higher with increasing rates, but only the 3.0 lbs ae/A dicamba + 6.0 lbs ae/A glyphosate differed significantly from the untreated check.  Seed cotton yield was similar for the untreated check (3358 lbs/A) and the sequential treatments of 0.5 lbs ae/A dicamba + 1.0 lbs ae/A glyphosate (3398 lbs/A) and 1.0 lbs ae/A dicamba + 2.0 lbs ae/A glyphosate (3102 lbs/A).  All other treatments reduced seed cotton yield significantly compared to the untreated check.

Field trials were conducted in 2013 and 2014 at various locations across the Texas High Plains to evaluate Engenia™ herbicide in
Bollgard II^® XtendFlex™ cotton, which is genetically modified for tolerance to dicamba, glufosinate, and glyphosate. The use of glyphosate in Roundup Ready cotton has effectively controlled many annual weeds that were problems in cotton prior to commercialization of this technology. However, some weeds including Russian-thistle (Salsola tragus), Kochia (Kochia scoparia), horseweed (Conyza canadensis) and perennials such as Texas blueweed, woollyleaf bursage, and field bindweed (Convolvulus arvensis) are not always effectively controlled with glyphosate, especially under cool or dry conditions. Additionally, glyphosate-resistant Palmer amaranth (Amaranthus palmeri), first identified in this region in 2011, has significantly increased in subsequent years and presents a major challenge to cotton producers. The objective of these studies was to evaluate Engenia™ herbicide, a new dicamba formulation specifically developed by BASF Corporation, as part of an overall weed management system in cotton for the Texas High Plains. Small plot field trials were conducted in Lubbock, Hale and Gaines Counties in 2013 and 2014 to evaluate Palmer amaranth, Russian-thistle, and field bindweed control in a system with residual herbicides including Prowl® H2O and Outlook^®. All treatments were applied at 20 GPA using TTI 11002 nozzles at 50 psi.

Russian-thistle control ranged from 40-50% with Prowl^® H2O PRE followed by (fb) glyphosate POST. The addition of Engenia™ POST at 12.8 floz/A improved Russian-thistle control to 100%. Late-season palmer amaranth control with Prowl^® H2O PRE or glyphosate POST alone was less than 50%, while Prowl^® H2O PRE fb glyphosate POST controlled Palmer amaranth 80%. When Engenia™ was added to glyphosate POST, Palmer amaranth control increased to 98-100%. When Prowl^® H2O was not applied, the addition of Outlook^® to Engenia™ + glyphosate improved control compared to Engenia™ + glyphosate POST alone.

Prowl^® H2O PRE fb glyphosate POST controlled field bindweed less than 30%. While control improved to 50% with Engenia™ PRE, Engenia™ + Roundup POST controlled this weed 90% or greater. Cotton yields were increased 50-75% where field bindweed was controlled by 90-95% with Engenia™ treatments compared to glyphosate only treatments.

The results of these studies showed excellent crop safety with Engenia™ applied PRE or POST in Bollgard II^® XtendFlex™ cotton, with improved control of problem annual and perennial weeds. For resistance management, Engenia™ still needs to be combined with residual herbicides for maximum weed control.

New weed control options are needed to manage herbicide resistant weeds that are limiting control tactics
and cropping options in some areas.  Dicamba tolerant soybean and cotton will enable the postemergence in crop use of
dicamba to manage problematic weeds with an additional herbicide site-of-action.  In addition, dicamba tolerant cropping
systems will allow for dicamba application preemergence without a planting interval restriction.  Engenia^™ herbicide, currently not registered by the US EPA, is an advanced formulation based on BAPMA (N, N-Bis-(aminopropyl) methylamine) dicamba salt that minimizes secondary loss of dicamba.  Combined with this formulation innovation, a comprehensive stewardship strategy will be
implemented to focus on effective weed control, weed resistance management, and maximizing on-target application. 

Engenia herbicide should be integrated as a component of a grower’s weed control program along with other cultural, mechanical, and chemical control methods.  A robust herbicide program uses sequential and/or tank mixtures of herbicides that have multiple effective sites of action on target weeds.  Likewise, Engenia should complement current programs adding an additional effective site of action for broadleaf weed control.  Over several years of testing, the most effective soybean weed control programs have utilized preemergence followed by postemergence applications of herbicides like Optill^® PRO followed Engenia plus glyphosate. 

Many parameters related to equipment setup and environmental conditions during application should be considered to maximize on-target deposition.  Nozzle selection offers the opportunity to dramatically reduce the potential for spray drift.  Research shows that venturi-type nozzle technology can significantly reduce drift potential.  Other application parameters that should be considered include travel speed, boom height, application volume, use of a deposition aid, and proximity to sensitive crops.  BASF has initiated the ‘On Target Spray Academy’ training program to educate applicators on best application practices.  The combination of Engenia and dicamba tolerant crops plus stewardship will provide growers with an effective system to control increasingly difficult and herbicide-resistant broadleaf weeds. 

Cotton with multiple herbicide resistance will be utilized as a means to help mitigate herbicide resistant weeds.  One herbicide-triple-stack resistant cotton (Xtend from Monsanto) will be tolerant to glyphosate, glufosinate, and dicamba. Engenia from BASF will be a dicamba product that will be available to growers of these cotton cultivars, where dicamba is formulated with a drift control agent: N,N-bis-(amiopropyl)methylamine (BAMPA).  Research was conducted in 2012, 2013, and 2014 in Plains GA to evaluate Xtend cotton tolerance and weed control to Engenia when applied PRE, EPOST, or POST emergence in combination with contact and residual herbicides. When PRE applied, there was no injury or stand reduction from Engenia and Engenia plus Prowl H₂O.  Combinations of Engenia with Outlook, Warrant, or Dual Magnum EPOST applied resulted in injury in the form of chlorosis (10-20%), but this was transient and not visible 10 days later.  Injury was confounded in 2014 when Engenia and Outlook were combined with Roundup or Liberty, primarily due to excessive thrip feeding.  However, this injury was transient and cotton recovered with minor stand reduction.  POST applications of Engenia with Roundup, Liberty, or residual herbicides did not significantly injure cotton.  Palmer amaranth with multiple-resistance (glyphosate/ALS) was effectively controlled (>90%) each year by the combination of Engenia with other PRE, EPOST, and POST herbicide treatment.  When Engenia was not included as part of the postemergence (EPOST or POST) treatment program, Palmer amaranth escapes were evident with control decreasing during the season which would have prevented cotton harvest.  When no residual herbicides were used, EPOST or POST treatments did not provide season long Palmer amaranth control.  Sicklepod, morningglory species (smallflower and pitted), and wild poinsettia were controlled (>95%) by the EPOST and POST sequential applications of Engenia in combination with other contact and residual herbicides.  Engenia will be an effective tool for controlling weeds in cotton when used in combination with other herbicides.

New weed control options are needed to manage herbicide resistant weeds that are limiting control tactics and in some areas cropping options.  Dicamba glufosinate tolerant (DGT) cotton and dicamba tolerant (DT) soybeans will enable the use of dicamba to manage these problematic weeds with an additional herbicide mechanism-of-action.  In addition to being a new control tactic, DGT cotton and DT soybeans will allow for application of dicamba as a preplant burndown without a planting interval and postemergence over the top of the crop.  Engenia™ herbicide is an advanced formulation (EPA approval pending) based on the BAPMA (N, N-Bis-(aminopropyl) methylamine) form of dicamba.  In addition to formulation innovation, a comprehensive stewardship strategy will be implemented to focus on weed management and effective control, weed resistance management, and maximizing on-target application.    Engenia herbicide should be used as a complimentary tool in a grower’s weed control program where it is integrated into a comprehensive strategy that includes cultural, mechanical, and chemical control.  A robust herbicide program uses sequential and/or tank mixtures of herbicides that have multiple effective sites of action on a single weed.  Likewise, Engenia should complement current programs to add an additional effective site of action for broadleaf weed control. Over several years of testing, the most effective cotton weed control programs have utilized sequential POST applications of glufosinate and dicamba tank mixed with residual herbicides following application of PRE residual herbicides. BASF field trials in DT soybeans have also demonstrated that postemergence use of dicamba with glyphosate and other effective herbicides following a preemergence or preplant residual herbicide program often provides the most consistent and effective control. 

Residual herbicides are a major component of most resistance management programs; however, these herbicides are dependent upon rainfall or irrigation for activation.  Furthermore, for Palmer amaranth alone, the occurrence of resistance to glyphosate and acetolactate synthase-inhibiting herbicides is common place on most farmers throughout the Midsouth.  With no new mechanisms of herbicide action in the foreseeable future, there is tremendous need for new weed management technologies.  Two new technologies will soon be available to growers to combat herbicide-resistant Palmer amaranth and other difficult-to-control weeds.  Monsanto is developing the Roundup Xtend Crop System which will provide growers the option of making over-the-top applications of dicamba, glyphosate, and glufosinate in cotton and similar applications in soybean, except for the exclusion of glufosinate.  Of most significance from Dow AgroSciences is the anticipated commercialization of the Enlist^TM Weed Control System, which allow a proprietary formulation of glyphosate and 2,4-D choline (Enlist Duo^TM) to be applied over-the-top of soybean and cotton as well as the use of glufosinate in these crops.   Unlike in the late 1990’s when only one technology was available that widely swept Midsouth cotton and soybean production, growers will have several options for weed management.  With a divergence in technologies and number of effective weed control options growing, the likelihood for crop injury from tank-contamination and off-target movement of these herbicides increases immensely.  Dicamba and 2,4-D, both auxinic herbicides, are prone to causing damage to soybean and cotton, respectively.  While recent improvements in dicamba volatility have been made with development of the Bis(3-amonopropyl)methylamine salt of dicamba through the formulated product Engenia^TM, availability and use of a more volatile diglycolamine formulation of dicamba in the Roundup Xtend Crop System is anticipated.  In the Enlist Weed Control System, only the lower volatility formulation, 2,4-D choline (Enlist Duo), will be permitted.  In 2014, research was conducted at the Northeast Research and Extension Center in Keiser, AR to understand the distance that Clarity (diglycolamine formulation of dicamba) would cause injury to soybean when applications were made using those being promoted as forthcoming recommendations for dicamba use in the Roundup Xtend Crop System.  A single spray swath 28 ft in width was made using a Bowman Mudmaster traveling at 9.4 mph and equipped with 11003 AIXR nozzles calibrated to deliver 10 gal/A at 40 PSI.  Applications were made at the R1 or R3 growth stage of soybean.  A similar trial was conducted at Jackson, TN with the dicamba application made at the R1 stage of double-cropped soybean.  Assessments for crop injury and height, pod malformation, and grain yield were made downwind as well as either perpendicular or upwind from the spray application.  Wind speeds were recorded during each spray application.  For the nine trials conducted, the greatest distance to which 5% soybean injury was observed was 420 ft downwind at a wind speed of 9.8 mph.  Fields where drift occurred at the R1 stage generally had symptoms present for longer downwind distances than when drift occurred at the R3 growth stage.  However, progeny originated from plants that were exposed to drift at the R3 growth stage exhibited greater dicamba-like systems soon after emergence than did progeny from seeds collected following the R1 drift events.  In regards to upwind or perpendicular movement from the spray application, it is most likely that this damage to soybean was the result of both volatility and physical drift.  Soybean injury (5%) from dicamba was observed up to 51 ft upwind at a 96 degree direction from the downwind drift plume in one trial. As the day for introduction of these technologies draws nearer, there is continued need to understand the risks associated with off-target movement of dicamba and 2,4-D, and steps must be taken to protect against these technologies being introduced in a manner that causes undue risk to non-traited cultivars or other sensitive crops.           

Dow AgroSciences has developed the Enlist^™ Weed Control System, breakthrough weed control technology that advances herbicide and trait technology by building on the Roundup Ready^® system. The Enlist system will help control herbicide-resistant
and hard-to-control weed populations. Enlist traits give corn, soybeans and cotton tolerance to Enlist Duo^™ herbicide in the same application window as Roundup^® herbicide. Enlist Duo herbicide is a proprietary blend of glyphosate and a new 2,4-D choline. Just as important as the trait and herbicide, Enlist™ Ahead is a benefits-based management resource that helps growers get the best results from the Enlist system—today and in the future. Built on a three-pillar foundation, Enlist Ahead will offer farmers, applicators and retailers management recommendations and resources, education and training, and technology advancements. As part of the Enlist Ahead program, Dow AgroSciences has developed the Enlist Ahead App. The app, designed for use with the Enlist Weed Control System, is a precision agriculture tool for maximizing weed control performance, managing weed resistance and making responsible applications of Enlist Duo^™ herbicide with Colex-D^™ Technology. In addition to the label, it offers growers and applicators practical herbicide application information from a single source that they can take with them from field to field. An example of the specific features found within the Enlist Ahead app are an application planner, mode of action calculator and a nozzle selection tool. The app’s herbicide application planner combines real-time, localized weather data, capabilities to map crop fields and trait technologies, and other important considerations for growers and applicators to review before making a responsible herbicide application. Dow AgroSciences has used the latest science and technology to address problem weeds, and Enlist will be a very effective solution. 

^®™Colex-D, Enlist and Enlist Duo are trademarks of The Dow Chemical Company (“Dow”) or an affiliated company of Dow. ^®Roundup Ready and Roundup are registered trademarks of Monsanto Technology LLC. Regulatory approval is pending for Enlist cotton. Enlist Duo herbicide is not registered for sale or use in all states. 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.©2014 Dow AgroSciences LLC

Dicamba-resistant cotton and soybean developed by Monsanto have recently been deregulated by the USDA and may be available to plant on a small scale in 2015.  Dicamba herbicide will offer producers another mode of action to manage broadleaf weeds postemergence in these crops. Concerns with off-target movement and spray tank contamination of dicamba have resulted in an increase of field research devoted to potential effects on non-tolerant soybean and cotton.  Soybean is especially sensitive to dicamba and previous research has demonstrated significant yield losses with dicamba at rates as low as 0.23 g ai/A when applied at sensitive (R1) stages of growth.  The purpose of this research was to determine if low rate applications of dicamba to soybean in reproductive stages will have any effect on progeny produced by affected plants.  A study was conducted with an indeterminate (maturity group IV) and determinate (maturity group V) soybean cultivar at Marianna, AR. Dicamba was applied at V3, V6, R1, R2, R3, R4, R5 and R6 growth stages at 3.5 g ai/A and 0.89 g ai/A at each stage of growth.  Additional studies were conducted with multiple soybean varieties at Fayetteville, AR, Brooksville, MS, Starkville, MS and Stoneville, MS with equivalent rates, but only at V3, V6, R1 and R2 growth stages.  Soybean plants were rated for injury and plant heights were recorded during the season as well as yield at harvest.  During harvest, a 454 g sub-sample of progeny seed was taken from each plot.  Seed from all studies were collected and 15 seed from each representative plot at each location was returned to the principal investigator at each location.  Each plot of 15 seed was then planted in the greenhouse to determine if any effects from dicamba applications during the season were apparent in the progeny.  Yield was decreased in both maturity group IV and V cultivars.  The most sensitive timing for yield loss from low rates of dicamba was R1 and R2 for the group IV cultivar at either dicamba rate.  Yield loss appeared to be more severe in the determinate (group V) soybean cultivar with significant yield loss occurring at each growth stage.  Dicamba applications at R1 provided the greatest yield loss in both soybean cultivars at 20% and 44%, respectively. Progeny produced by injured plants during vegetative growth stages (V3) did not result in significant visual injury or have reduced vigor when planted in the greenhouse.  However, progeny from plants treated at R1-R6 growth stages revealed significant injury or dicamba symptomology at 14 days after planting (DAP).  Injury to progeny increased significantly, when dicamba applications were made at each additional reproductive stage, with R5 and R6 displaying the greatest symptomology.  Once again progeny from the determinate (group 5) cultivar displayed the most injury, up to 50% when dicamba was applied at the R5 and R6 soybean growth stages.  Seedling vigor was also greatly reduced when dicamba was applied to plants later in reproductive growth stages.  Data from the multiple location and variety study revealed a similar trend. Plants treated with low rates of dicamba at R1 and R2 growth stages produced progeny that had reduced germination, vigor and increased injury or dicamba symptomology.  These results indicate that yield loss can be significant, depending on growth stage with off-target applications of dicamba to non-tolerant soybean.  However, if non-tolerant soybean plants are affected with dicamba later in the growing season at the R3 to R5 growth stages, yield loss probably will not occur, but seed produced or progeny will be affected and will display symptoms when planted the following season. The ending result will be a poor soybean stand that exhibits dicamba-like symptoms and significantly reduced seedling vigor. This research will continue and affected progeny seed will be planted in the spring to determine stand reduction and yield loss under field conditions. 

Studies were conducted in 2012 (22 trials), 2013 (22 trials) and 2014 (14 trials) in the U.S. to evaluate the weed control delivered by a systems approach composed of PRE followed by POST herbicide applications in Enlist E3 soybeans. PRE herbicide treatments consisted of cloransulam + sulfentrazone, flumioxazin + cloransulam, flumioxazin + chlorimuron ethyl or S-metolachlor + fomesafen herbicide products. Postemergence treatments of Enlist Duo (2,4-D choline + glyphosate DMA) at 1640 and 2185 g ae/ha, glufosinate at 542 g ae/ha, 2,4-D choline + glufosinate at 800 + 542 and 1065 + 542 g ae/ha, and glyphosate at 1120 g ae/ha were applied approximately 28 days after planting.  PRE applications of cloransulam + sulfentrazone or flumioxazin + cloransulam followed by Enlist Duo at 1640 or 2185 g ae/ha or 2,4-D choline + glufosinate at 800 + 542 or 1065 + 542 g ae/ha provided greater than 95% control of glyphosate-resistant AMAPA (Amaranthus palmeri S. Wats), AMATA (Amaranthus rudis Sauer),  AMBEL (Ambrosia artemisiifolia L.), and AMBTR (Ambrosia trifida L.) at 28 days after application.

Due to continuous germination of Palmer amaranth through the growing season, studies were conducted in 2013 (5 trials) and 2014 (6 trials) in the U.S. to evaluate the weed control delivered by a systems approach composed of pre-emergence (PRE) followed by a single POST herbicide application or two sequential POST applications in Enlist E3 soybeans. PRE herbicide treatments consisted of flumioxazin + cloransulam (71.5 + 23.5 g ai/ha), or flumioxazin + chlorimuron ethyl (62.7 + 21.6 g ae/ha) herbicide products. The POST treatments were single applications made to less than 4 inch tall Palmer amaranth or sequential POST applications made to less than 4 inch Palmer amaranth followed by a second application 14 to 21 days later. Single POST herbicide treatments were Enlist Duo at 1640 or 2185 g ae/ha, glufosinate at 542 g ae/ha, 2,4-D choline + glufosinate at 1065 + 542 g ae/ha, Enlist Duo + metolachlor at 2185 + 1070 g ae/ha or Enlist Duo + fomesafen + metolachlor at 2185 + 266 + 1214 g ae/ha.  Sequential applications of Enlist Duo followed by Enlist Duo at 1640 fb 1640 or 2185 fb 2185 g ae/ha or glufosinate at 542 g ae/ha followed by glufosinate at 542 g ae/ha, or Enlist Duo at 2185 g ae/ha or 2,4-D choline +glufosinate at 1065 + 542 g ae/ha were applied approximately 18 days after POST application.  At 14 to 21 days after sequential applications, Enlist Duo at 1640 and 2185 g ae/ha provided 92% control with sequential applications of Enlist Duo at 2185 g ae/ha provided 99% control.  Addition of metolachlor or metolachlor + fomesafen to Enlist Duo at 2185 g ae/ha did not significantly improve control compared to Enlist Duo alone.  Sequential applications of glufosinate followed by (fb) glufosinate, glufosinate fb Enlist Duo, Enlist Duo fb glufosinate or 2,4-D+glufosinate fb 2,4-D+glufosinate provided >97% control of AMAPA compared to 89% with a single application of glufosinate. 

With germination of ERICA (Conyza canadensis L.) extending into May and June, effective control options of glyphosate-resistant ERICA is needed prior to planting and in crop.   A total of 19 studies were conducted between 2013 and 2014 to evaluate the ERICA control delivered by a systems approach composed of burndown followed by post-emergence (POST) herbicide applications in Enlist E3™ soybeans.  Burndown applications consisted of glyphosate at 1120 g ae/ha, Enlist Duo™ at 1640 or 2185 g ae/ha, glufosinate at 542 g ae/ha, 2,4-D choline + glufosinate at 1065 + 542 g ae/ha and glyphosate + dicamba at 1120 + 560 g ae/ha applied with and without cloransulam + sulfentrazone at 25 + 195 g ae/ha.  POST herbicide treatments consisting of Enlist Duo at 1640 and 2185 g ae/ha, glufosinate at 542 g ae/ha, 2,4-D choline + glufosinate at 1065 + 542 g ae/ha, glyphosate at 1120 g ae/ha or glyphosate + dicamba at 1120 + 560 g ae/ha were applied to V3 soybeans.   At 4 weeks after the POST application, sequential applications of Enlist Duo, 2,4-D + glufosinate or glyphosate + dicamba provided >95% control of glyphosate resistant ERICA.  Addition of cloransulam + sulfentrazone improved glyphosate-resistant ERICA control to >98% for all post treatments except glyphosate alone.

Controlling glyphosate-resistant weeds requires an integrated systems approach which will vary based on weed biology, particularly germination intervals.  Glyphosate resistant AMBEL, AMBTR and AMATA can be effectively controlled with PRE herbicide followed by Enlist Duo.  Glyphosate resistant AMAPA will likely require a PRE herbicide followed by single POST application of Enlist Duo plus metolachlor or metolachlor + fomesafen or two sequential POST applications of Enlist Duo.  Glyphosate-resistant ERICA will require a systems approach of Enlist Duo + cloransulam + sulfentrazone applied as a burndown application followed by a V3 application of Enlist Duo. Enlist Duo used as a component in a weed management program provides a sustainable solution to control herbicide-resistant and herbicide –susceptible weeds.

™®Enlist, Enlist Duo and Enlist E3 are trademarks of The Dow Chemical Company ("Dow") or an affiliated company of Dow. Enlist E3 soybeans are jointly developed by M.S. Technologies and Dow AgroSciences. Regulatory approval is pending for Enlist cotton. Enlist Duo herbicide is not registered for sale or use in all states. 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.

Dow AgroSciences has developed the Enlist™ Weed Control System, a novel weed control technology to combat herbicide-resistant and hard-to-control weed populations that will improve upon the proven benefits of the glyphosate-tolerant cropping system.  The Enlist Weed Control System is enabled through the cultivation of Enlist crops which contain multiple herbicide tolerance traits that allow for the post emergence application of Enlist Duo™ herbicide, a proprietary blend of glyphosate and 2,4-D choline.  Just as important as the trait and herbicide solution, Enlist™ Ahead is a management resource designed to help growers succeed while promoting responsible use of the system. Built on a three-pillar foundation, Enlist Ahead will offer farmers, applicators and ag retailers technology advancements, management recommendations and resources, and education and training.  The Enlist Duo label details specific requirements for the application of the product onto Enlist-traited crops.  These requirements represent several years of research aimed at reducing the potential of off-target movement of Enlist Duo herbicide.  The key requirements focus on making applications with the correct application equipment setup, making applications in environmental conditions that are consistent with minimal off-target movement potential and the proper identification and protection of sensitive areas around the treatment area. Dow AgroSciences is committed to responsibly commercializing the Enlist Weed Control System and to sustain its longevity.

The Enlist™ Weed Control System by Dow AgroSciences is a new weed control tool incorporating unique herbicide tolerance traits, a new herbicide featuring a 2,4-D choline based formulation and the Enlist Ahead management resource.  The primary objective of this multi-year research was tolerance characterization of Enlist cotton to 2,4-D, glyphosate and glufosinate.  Data collected included visual percent injury, droop/epinasty, necrosis, chlorosis , growth inhibition and cotton yield at harvest.  Since 2010, Dow AgroSciences and university researchers have conducted 233 trials throughout the cotton-growing regions of the southern U.S.  This research included characterization of dose response to the enabled herbicides as well as the effects of tank mixtures, multiple applications, and crop growth stage.   Results demonstrated Enlist cotton tolerance to 2,4-D, glyphosate and glufosinate with no negative impacts on yield.  Enlist cotton weed management programs utilizing these herbicide modes of action will provide growers an additional tool to achieve greater control of economically-important and herbicide-resistant weed biotypes. 

^TMEnlist and Enlist Duo are trademarks of The Dow Chemical Company (“Dow”) or an affiliated company of Dow.  Regulatory approval is pending for Enlist cotton.  Enlist Duo herbicide is not registered for sale or use in all states.  Contact your state regulatory agency to determine if a product is registered for sale or use in your state.  Always read and follow label directions.

The Enlist Weed Control System by Dow AgroSciences is a new weed control technology incorporating unique herbicide tolerance traits, a new herbicide featuring a 2,4-D choline formulation, and the Enlist Ahead management resource.  The primary objective of this multi-year research was to collect key weed efficacy data on glyphosate-resistant biotypes such as Palmer amaranth (Amaranthus palmeri) and marestail (Conyza canadensis), as well as other economically-important weed species.  Since 2007, Dow AgroSciences and university researchers have conducted 218 trials throughout the cotton-growing regions of the southern U.S. evaluating Enlist Duo^TM herbicide (a proprietary blend of 2,4-D choline + glyphosate) or 2,4-D choline within weed control programs for controlling herbicide-resistant and -susceptible weeds in Enlist™ cotton. Herbicide efficacy research ranged from standard characterization trials to full-season weed control systems.  Characterization trials evaluated Enlist Duo and other 2,4-D choline-based treatments compared to other commercially-available herbicides.  Herbicide programs evaluated consisted of a preemergence herbicide followed by sequential postemergence applications of Enlist Duo, 2,4-D choline +  glufosinate and glufosinate applied alone and in tank mixture with other herbicide modes of action (MOA). All programs containing Enlist Duo or 2,4-D choline + glufosinate controlled glyphosate-resistant Palmer amaranth more than 90%. Programs containing Enlist Duo or 2,4-D choline + glufosinate provided greater levels of glyphosate-resistant Palmer amaranth control than glufosinate-only programs and also incorporate two additional modes of action (MOA). While sequential applications of glufosinate provided greater than 85% Palmer amaranth control, these single MOA programs are not sustainable. Research results demonstrate a full-season, Enlist-enabled approach utilizing multiple herbicide MOAs applied preemergence and postemergence will allow growers to achieve greater control of economically-important and herbicide-resistant weed biotypes in the U.S. mid-South.

 ™® Enlist™ and Enlist Duo™ are trademarks of The Dow Chemical Company ("Dow") or an affiliated company of Dow. Regulatory approval is pending for Enlist cotton. Enlist Duo herbicide is not registered for sale or use in all states. 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.

Southernpea producers in Arkansas lack diverse and viable weed control programs for season-long management. Two studies were conducted in the summer of 2014 at the Arkansas Agricultural Research and Extension Center (AAREC), Fayetteville, AR, and at the Vegetable Research Center (VRS), Kibler, AR to evaluate various herbicides in different combinations for use in a season-long weed control program in southernpea. In total, 19 herbicide programs were evaluated which included fomesafen, halosulfuron (54 g ha^-1), imazethapyr (70 g ha^-1), S-metolachlor (1120 g ha^-1), sulfentrazone (210 g ha^-1), a premix of sulfentrazone + carfentrazone (160 g ha^-1), trifluralin (840 g ha^-1), bentazon (1120 g ha^-1), fluthiacet-methyl (6.7 g ha^-1), or sethoxydim (320 g ha^-1) applied in various combinations and timings; both a weedy and weed- free control were also included. Herbicides were applied preplant-1 week before planting (PPL), preplant incorporated (PPI), preemergence (PRE), or postemergence (3 to 4 trifoliate). The experiments were arranged in a randomized complete block design with 4 replications.  ‘Top Pink’ southern pea were drill-seeded into beds spaced 91 cm apart and 6.1 m long. Each plot had 2 treated rows where data were collected and border rows on each side. Stand count (21 DAP), crop injury (%), weed count (1 sq m^-1), weed control by species (%), total weed control (%), and dry yield were evaluated throughout the season.  Data were analyzed using an ANOVA; locations were analyzed separately. None of the herbicide treatments had an affect on the crop stop stand at either location. Low levels of injury were observed at AAREC (<25%), overall injury at the VRS location was higher early in the season (<55%) but greatly reduced (<20%) by the end of the season. The premix of sulfentrazone + carfentrazone (PPL or PRE) fb fluthiacet with other herbicides exhibited the greatest injury (13%-25%), mid-season, at both locations. None of the treatments reduced yield at the AAREC location; the crop at VRS was lost to sudden death at pod-filling stage . Weed pressure was low at the AAREC location while Palmer amaranth infestation was very high at the VRS location. At the VRS, trifluralin (PPI) was least effective, while treatments containing fomesafen, the premix of sulfentrazone + carfentrazone, and flumioxazin were most effective (>90%) 2 WAP and were consistent throughout the season. All programs evaluated were deemed safe on southernpea. This study indicated that the premix of sulfentrazone + carfentrazone applied preplant or preemergence provides excellent, broad spectrum, residual weed control and that a tailored POST treatment should be used to control the remaining species season-long weed control.