Proceedings


PERFORMANCE OF SWEET SORGHUM UNDER DIFFERENT PLANTING DENSITIES, WATER REGIMES, AND N LEVELS. V. Singh*1, N. R. Burgos1, L. Earnest2, S. Singh1, L. Martin2, S. Abhugo1, L. Estorninos1; 1University of Arkansas, Fayetteville, AR, 2University of Arkansas, Rohwer, AR (1)

ABSTRACT

Sweet sorghum is one potential alternative biomass source for ethanol production. Expanded and successful production in Arkansas depends on optimization of crop management practices. Toward this goal, we studied the effects of plant population, water regime, and N level on sweet sorghum at the Southeast Research and Extension Center (SEREC), Rohwer, in 2013. The experiment was conducted in a Randomized Complete Block Design with plant population and N level in a factorial combination within an irrigated or non-irrigated block. Sweet sorghum 'Topper 76-6' was planted at the highest possible plant population in 4- row plots with 6.1 m row length on May 14, 2013 and thinned to the desired plant populations (204,000; 102,000; 68,000; 51,000; 41,000 plants/ha) on June 4, 2013. Plants under the 'high' N  and 'low' N levels received 168 kg N ha-1 and 84 kg N ha-1, respectively. The irrigated plots were watered four times during the cropping season. For general weed management, atrazine (Aatrex) and S-metolachlor (Dual Magnum) were applied at 1.2 kg ai ha-1 and 1.1 kg ai ha-1, respectively, preemergence (PRE). The irrigated (IR) and non-irrigated (NIR) sweet sorghum were harvested 21 d after 50% flowering on September 13 and October 3, 2013, respectively. Plant height, stem diameter, above-ground fresh biomass, and total solids in fresh juice were recorded.  Sweet sorghum plants in the irrigated plots were taller (3.2 m) compared with the non-irrigated plants (1.9 m). Plants with high N fertilizer produced more fresh biomass (77 t ha-1) than those with low N levels (69 t ha-1), averaged over planting density and irrigation regimes. Planting density did not affect the total fresh biomass production. Irrigated sweet sorghum produced more biomass (94 t ha-1) than the non-irrigated crop (54 t ha-1). Total solids content (which reflects total sugar content) was not affected by irrigation, N level, or planting density. When irrigated, plants that received less N had thin stalks, which resulted in more lodging compared with those that received more N. In conclusion, sweet sorghum has tremendous capacity to compensate for low plant population by producing more tillers. Although irrigation and high N fertilizer significantly improved biomass production, sweet sorghum could still produce a lot of biomass even without irrigation and with less N. 

 


SOYBEAN ROW WIDTH, SEEDING RATE, AND HERBICIDE STRATEGY EFFECT ON CUMULATIVE INTERCEPTED PHOTOSYNTHETICALLY ACTIVE RADIATION AND WEED CONTROL. T. R. Butts*1, J. K. Norsworthy2, G. R. Kruger3, L. Sandell4, B. G. Young5, L. E. Steckel6, M. M. Loux7, K. Bradley8, V. M. Davis1; 1University of Wisconsin, Madison, WI, 2University of Arkansas, Fayetteville, AR, 3University of Nebraska-Lincoln, North Platte, NE, 4Valent Corporation, Lincoln, NE, 5Southern Illinois University, Carbondale, IL, 6University of Tennessee, Jackson, TN, 7Ohio State University, Columbus, OH, 8University of Missouri, Columbia, MO (2)

ABSTRACT

Current soybean production recommendations place emphasis on simultaneously increasing yield and weed suppression.  These goals are achieved when soybean plasticity and competitiveness are exploited to maximize cumulative intercepted photosynthetically active radiation (CIPAR).  The objective of this research was to evaluate the effect of soybean row width, seeding rate, and herbicide strategy on CIPAR and pigweed (Amaranthus spp.) control.  A field study was conducted in cooperative effort with seven universities across 10 different locations in 2013 and 2014 representing 16 total site-years.  Locations were combined relative to their optimum adaptation zone for soybean maturity groups.  The North region was comprised of Missouri, Nebraska, Ohio, and Wisconsin, and the South region was comprised of Arkansas, Southern Illinois, and Tennessee.  Two row widths (≤38 and ≥76 cm), three seeding rates (173,000, 322,000, and 470,000 seeds ha-1), and two herbicide strategies (preemergence plus postemergence (PRE + POST) vs. a single postemergence application (POST-only)) were arranged in a randomized complete block split-plot design with row width as the main plot factor and a 3x2 factorial of seeding rate and herbicide strategies as the subplots.  Across all locations, PRE applications were made within two days of planting in 2013 and 2014.   POST-only applications were made approximately six and eight days after the V1 (DAV1) soybean growth stage in 2013 and 2014, respectively.  POST applications in the PRE + POST treatments were made approximately 22 and 12 DAV1 in 2013 and 2014, respectively.  Pigweeds were counted prior to the POST herbicide applications.  CIPAR was calculated from the V1 soybean growth stage to 50 DAV1 using light interception values determined through digital imagery analysis.  In the North region, a significant interaction between row width (narrow) and seeding rate (high) increased CIPAR (P=0.0194).  In the South region, seeding rates of 322,000 and 470,000 seeds ha-1 (P=0.0034) and the PRE + POST herbicide strategy (P=0.0356) increased CIPAR.  Similarly, soybean yield increased when seeding rates of 322,000 and 470,000 seeds ha-1 and the PRE + POST herbicide strategy were used in the North (P=0.0036 and P=0.0319, respectively) and South (P=0.0317 and P=0.0320, respectively) regions.  Soybean yield and CIPAR were positively correlated using logarithmic models in both the North (R2=0.3196) and South (R2=0.0709) regions.  Moreover, the PRE + POST herbicide strategy increased soybean yields by 565 and 267 kg ha-1 in the North and South regions, respectively.  To achieve equal yield gains, seeding rate increases of more than 297,000 and 87,000 seeds ha-1 were needed in the North and South regions, respectively.  In both the North and South regions, the PRE + POST herbicide strategy reduced pigweed density at the POST timing by 38 (P=0.0131) and 203 (P=0.0004) pigweeds m-2, respectively.  In conclusion, our research illustrates the importance of a PRE + POST herbicide strategy in soybean production systems to simultaneously increase CIPAR and seed yield, as well as to reduce selection pressure for the evolution of resistance to the POST applied herbicide.  


INFLUENCE OF PLANTING DATE ON PEANUT RESPONSE TO FLUMIOXAZIN AND FLUMIOXAZIN PLUS PYROXASULFONE. M. D. Inman*, D. L. Jordan, D. Johnson; NCSU, Raleigh, NC (3)

ABSTRACT

INFLUENCE OF PLANTING DATE ON PEANUT RESPONSE TO FLUMIOXAZIN PLUS PRYOXASULFONE M. D. Inman, D.L. Jordan, P.D. Johnson North Carolina State University, Raleigh, NC

 

Possible interactions of flumioxazin or flumioxazin plus pyroxasulfone with phorate, an insecticide commonly applied to peanut in the seed furrow at planting to control thrips (Franklienelia spp.), have not been evaluated.  Additionally, the interaction of these pesticides has not been evaluated at different planting dates in North Carolina.  Research was conducted during 2013 and 2014 to determine visible peanut injury and pod yield when flumioxazin (107 and 214 g ai/ha) and flumioxazin plus pyroxasulfone (70 plus 89 g ai/ha and 140 plus 179 g/ha) were applied immediately after planting when either no insecticide was applied at planting or phorate (1.1 kg ai/ha) was applied in the seed furrow at planting.  Peanut, cultivar Bailey, was planted May 5, May 18, or May 28 in conventionally-prepared seedbeds.  Visible estimates of percent injury were recorded 2, 3, and 4 weeks after peanut emergence.  Visible injury and pod yield was affected by the interaction of year and herbicide.  Response to herbicides and phorate was independent of one another.  Injury was affected by planting date with increased injury across all evaluations observed when rainfall occurred within 7 days after application.  During these years significant rainfall occurred shortly after planting on May 28 but was minimal following the first two planting dates.  Regardless of herbicide or herbicide rate, greater injury associated with herbicide effects and stunting from thrips feeding was noted in absence of phorate compared with phorate applied in seed furrow.  Injury varied across years for herbicide treatments but was generally greater when the higher rate of herbicide was applied.  The higher rates of herbicides reduced yield compared with the standard rate but there was no difference in yield when comparing flumioxazin or flumioxazin plus pyroxasulfone.  Although these data suggest that flumioxazin plus pyroxasulfone could be an effective alternative to flumiozaxin alone based on crop response, other research has shown elevated injury from flumioxazin plus pyroxasulfone compared with flumioxazin and may limit the possibility of use in peanut.

 


DIFFERENTIAL RESPONSE OF TEOSINTE AND FLINT, SWEET, AND DENT CORN VARIETIES TO WEED COMPETITION. S. A. Hansen*1, S. A. Clay2, D. Horvath3, S. Flint-Garcia4; 1South Dakota State University, Brookings, SD, 2SDSU, Brookings, SD, 3USDA-ARS, Fargo, ND, 4USDA ARS, Columbia, MO (4)

ABSTRACT

Weeds negatively impact crop growth and future yields. Literature suggests that sweet corn (Zea mays convar. saccharata var. rugosa) and some modern dent variants (field corn, Zea mays indentata) have varying degrees of weed tolerance (or weed suppressive ability). These variants were derived from teosinte, the ancestor to all corn varieties, which is a weedy plant that still grows wild in southern ranges. Understanding what genes are involved in weed tolerance, what mechanisms are involved in the process of yield loss, and what untapped genetic resources may exist in teosinte, are keys to reaching the goal of increasing crop tolerance of weeds. Determining which early and mid-season growth parameters correlate with minimal yield differential while under weed pressure is a first step in determining genetic mechanisms available for increasing or building upon pre-existing crop tolerance abilities in corn and other crops. Eleven corn varieties and five teosinte lines in a two year study were evaluated to determine correlations between corn or teosinte variety crop height, leaf area, stem diameter, and mid-season biomass differentials and yield differentials between weedy and non-weedy treatments. Yield differentials ranged from no significant yield gain in weedy over non-weedy to an 19% yield loss (p-value=0.00) in weedy plots when compared to weed-free controls. Height deficits of up to 34% (p-value=0.01) in weedy versus weed-free plots were observed.  Height in weedy plots did not correlate with yield loss or gain in weedy plots compared with controls. Leaf area differentials ranged from a 44% increase to a 40% decrease in leaf area in weedy plots compared to controls.  Further research is needed to determine which, if any, morphological traits in corn and teosinte are clearly related to weed tolerance and the ability to maintain yield under weedy conditions. 

 


CORN, SOYBEAN, AND WHEAT YIELDS IN AN ORGANIC ROTATIONAL NO-TILL SYSTEM DURING THE 3-YEAR TRANSITION. C. L. Keene*1, W. S. Curran1, J. M. Wallace2, S. Mirsky3, M. J. VanGessel4, M. Ryan5, M. Barbercheck1; 1Penn State University, University Park, PA, 2Pennsylvania State University, State College, PA, 3USDA, Beltsville, MD, 4University of Delaware, Georgetown, DE, 5Cornell University, Ithaca, NY (5)

ABSTRACT

Cover crops can be used to reduce tillage in organic grain production.  Cover crop-based, organic rotational no-till is characterized by growing large amounts of cover crop biomass, terminating cover crops with a roller-crimper, and no-till planting cash crops into the resulting mulch.  This approach eliminates primary tillage and associated seed bed preparation prior to planting and in-season mechanical weed control passes.  The Reduced-tillage Organic Systems Experiment (ROSE) was conducted at three locations in the Mid-Atlantic to investigate trade-offs between delaying cover crop termination, weed suppression, and cash crop yield.  Additionally, the ROSE provided an opportunity to study cover crop management legacies within an organic rotational no-till system.  Early, Middle, and Late cover crop termination/ cash crop planting date treatments were applied to a hairy vetch-triticale cover crop preceding corn and a cereal rye cover crop preceding soybean in a corn-soybean-wheat rotation.  Corn and soybean varieties were selected so that maturities were appropriate for the planting date treatments.  It was hypothesized that the Middle planting date of both corn and soybean would minimize the trade-off between cover crop biomass accumulation for enhanced weed suppression and maximizing cash crop growing season length.  Yield stability analyses were conducted with corn and soybean yields across sites and years to determine if the Middle planting date reduced trade-offs by exhibiting the most stable yield.  Yield stability analysis regresses treatment means on environmental means which are the mean yield of all treatments within a given site year.  The means of the site years are interpreted to represent a gradient of environmental conditions.  Slope coefficients closer to 0 indicate that yield did not fluctuate greatly over the observed environmental gradient, i.e. was more stable.  In uncultivated corn treatments, slopes were 1.15, 0.78, and 1.07 for the Early, Middle, and Late planting dates, respectively, and in cultivated corn treatments, slopes were 1.06, 0.82, and 1.1 for the Early, Middle, and Late planting dates, respectively.  In uncultivated soybean, slopes were 1.12, 0.74, and 1.17 for the Early, Middle, and Late planting dates, respectively, and in cultivated soybean, slopes were 1.07, 0.87, and 1.07 for the Early, Middle, and Late planting dates, respectively.  In each crop and cultivation treatment, the test of homogeneity of slopes was not significant (P > 0.05).  The Middle planting date of corn and soybean tended to exhibit the smallest slope, but this result was not significant.  In regards to cover crop management legacies, volunteer cover crops were problematic at all sites, though in which crop and to what extent depended on site.  At Delaware volunteer hairy vetch in rye survived rye rolling and interfered with the soybean crop: at Maryland volunteer hairy vetch in wheat resulted in 11-29% wheat grain contamination; and at Pennsylvania, volunteer rye in wheat resulted in 3-11% wheat grain contamination.  Results from the ROSE suggest that manipulating cover crop termination/ cash crop planting date in an organic rotational no-till system has potential to reduce the trade-off between cover crop biomass accumulation and cash crop yield, but also that incomplete kill of cover crops with a roller-crimper can compromise the viability of the rotation over the long-term.  Optimum cover crop termination timing and cash crop establishment can increase cash crop success, but relatively small differences in geography can impact both cover crop and cash crop performance.  Predicting this outcome will continue to challenge organic rotational no-till systems.


ECHINOCHLOA COLONA SEEDLING EMERGENCE ON SOYBEAN FALLOW UNDER NO-TILLAGE SYSTEM. H. A. Acciaresi*1, G. Picapietra2; 1Instituto Nacional Tecnologia Agropecuaria, Pergamino, Argentina, 2UNNOBA-INTA, Pergamino, Argentina (6)

ABSTRACT

The phenotypic plasticity of weeds is an important attribute that determines the persistence of weeds in production systems. The aim of this study was to characterize the phenotypic plasticity of Echinochloa colona under three environments: no competition (isolated plant), intraspecific and interspecific competition (soybean). Significant differences in plant height in the ranking for interspecific  (129.67 cm),  intraspecific competition (93 cm) and isolated plant (44 cm) were observed. The plant diameter was 77.33 cm for isolated plant, 12.33 cm and 11.33 for interspecific and intraspecific competition, respectively. The same environment order for the total stem number (.plant-1) was observed (53, 20 and 8). The grain yield (.plant-1) was 2.64, 1.16 and 0.44 in the interspecific competition>isolated plant>intraspecific competition order. The grain number (.plant-1) followed the same environments order (4035 (interespecific competition), 2.312 (isolated plant) and 1.003 (intraespecific competition). The kernel weight was not significantly different between environments. The results showed a significant junglerice phenotypic plasticity which contributes to the high competitive ability of the species in the argentinean agroecosystem.


EFFECT OF RYE VERSUS WINTER ANNUAL WEEDS ON SUMMER ANNUAL WEED GROWTH AND SOYBEAN YIELD. M. L. Bernards*, B. S. Heaton; Western Illinois University, Macomb, IL (7)

ABSTRACT

Two potential benefits of cover crops are weed suppression in and increased yield of the cash crop.  Winter annual weeds occupy a similar niche to winter annual cover crops in a corn-soybean rotation and may also provide suppression of summer annual weeds, but are not generally considered to increase yield.  Delaying cover crop or winter annual weed control until the time of soybean planting maximizes winter cover biomass but may have negative effects on soybean yield.  Early-planted soybean maximizes soybean yield potential, but limits the amount of cover crop biomass that can be grown and may limit the weed suppression benefit of the cover crop. The objective of this research was to measure the effects of winter annual weeds or a rye cover crop on waterhemp suppression as affected by winter cover removal time and soybean planting date. Four experiments (two rye cover, two winter annual weed cover) were laid out side-by-side and were established at two locations (AFL and Kerr farms).  Rye (Secale cereal) was drilled on October 2, 2013 at the two study locations.  Winter annual weeds were removed at four times relative to the treatment planting date: Fall (Nov 15, 2013), 28 DBP (days before planting), 14 DBP or 0 DBP. Soybeans were planted on three different dates: early (May 8, 2013), middle (May 23, 2013) and late (June 7, 2013).  Two experiments (one rye cover, one winter annual weeds) were maintained weed free after winter cover removal.  Two experiments allowed summer annuals to emerge after winter removal. In the weedy studies weed counts and biomass were made in two 0.1 m2 quadrats per plot at planting, 5 WAP (weeks after planting), and 8 WAP. Biomass at the time of winter cover removal increased as removal time was delayed until planting. The greatest amount of biomass was accumulated in the rye cover crop for the late planting date.  Waterhemp counts at the time of planting following winter annual weed cover was greatest at the 28 DBP removal time (2.4 plants/0.1m2). Waterhemp counts following the rye cover were not consistent between locations.  At AFL counts were greatest for the Fall removal time (5.1 plants/0.1m2) and declined until 0 DBP (0.1 plants/0.1m2), but there were no differences in counts between the removal time treatments at Kerr (average of 0.8 plants/0.1m2).  Waterhemp counts at 5 WAP and 8 WAP were not affected by planting date or removal time following winter weeds or a rye cover crop. Soybean yields were greater numerically where the rye cover crop was grown than where winter annual weeds provided the groundcover. Yields were greatest for the mid-planting date, intermediate for the early planting date and least for the late planting date.  The lower than expected yields for the first planting date may have been a consequence of severe sudden death syndrome (Fusarium virguliforme) symptoms present in the plots.  For the early planting date delaying the removal of cover crop or winter annual weed cover until 14 DBP resulted in yield loss.  For the mid- and late-planting date treatments there was a linear relationship and yields declined relative to the fall removal time as cover crop or winter annual removal was delayed until planting.


IMPACT OF GLYPHOSATE-RESISTANT VOLUNTEER CORN DENSITY, CONTROL TIMING, AND LATE SEASON EMERGENCE ON SOYBEAN YIELD. P. S. Chahal*1, M. L. Bernards2, G. R. Kruger3, H. Blanco-Canqui1, A. J. Jhala4; 1University of Nebraska-Lincoln, Lincoln, NE, 2Western Illinois University, Macomb, IL, 3University of Nebraska-Lincoln, North Platte, NE, 4University of Florida, Lake Alfred, FL (8)

ABSTRACT

Glyphosate-resistant volunteer corn is a problem weed in corn (Zea mays L.)-soybean (Glycine max L.)  rotation. Most growers control volunteer corn when it is visible above the soybean canopy, but this approach could result in early season competition with soybean. Thus, we studied the impact of 1) different densities of glyphosate-resistant volunteer corn present as individual plant or clump controlled at different timings, and 2) late season volunteer corn emergence after being controlled at different soybean growth stages on soybean yields. Field experiments were conducted under irrigated conditions at the South Central Agricultural Laboratory (SCAL), University of Nebraska-Lincoln, near Clay Center, NE and under rainfed conditions at Havelock Farm, University of Nebraska-Lincoln, NE in 2013 and 2014. Individual seeds and whole ears were hand planted in each plot to maintain desired isolated volunteer corn plants (1,250, 2,500, 5,000, and 10,000 plants ha-1) and clumps densities (63, 125, 250, and 500 ha-1). Volunteer corn was controlled with application of clethodim at V4, V6, or R2 soybean growth stages. Late season volunteer corn emergence did not affect soybean yield for any volunteer corn density and control timing. During the first year of study at Clay Center, no significant effect of volunteer corn density and control timings was observed on soybean yield. Lower soybean yield was reported at clay center in 2014 and at Lincoln in 2013 and 2014 at the highest volunteer corn density (10,000 plants ha-1 plus 500 clumps ha-1) left uncontrolled or when controlled at R2 soybean growth stage. Although no yield reduction was reported with lower volunteer corn densities (≤ 5,000 plants ha-1) at all control timings, control is necessary to avoid interference of volunteer corn during harvesting operations and attraction of western corn rootworm.

 


CLEARFIELD® RICE GENOTYPES TOLERANCE TO AERIAL APPLICATION OF IMIDAZOLINONE AS AFFECTED BY PLANT DENSITY. E. R. Camargo*, A. T. Martini, L. A. Avila, L. F. Martini, A. Pivetta, F. Schreiber; Federal University of Pelotas (UFPel), Pelotas, Brazil (9)

ABSTRACT

Aerial application of herbicides is a common operational practice in rice production of Southern Brazil. This experiment was conducted to investigate the tolerance of Clearfield® genotypes sprayed with aircraft equipped with conventional and electrostatic spraying systems at different seeding rates. The experiment was conducted at Granja 4 Irmãos in partnership with Taim Aero Agrícola, located in Rio Grande, RS, Brazil. Treatments were arranged in a factorial scheme with four replications. Fator A was composed by five-rice genotypes: Puitá Inta CL, Guri Inta CL, QM 1010, Avaxi e Inov. Fator B was the spraying systems: hydraulic conical nozzles (20 L ha-1) and electrostatic (10 L ha-1). Fator C was two-seed quantities used at crop establishment: 45 and 100 kg ha-1. Each individual plot had an untreated check that was obtained by covering the plants with a transparent plastic at the time of herbicide application. Herbicide Only® (75 + 25 g L-1 of imazethapyr and imazapic, respectively) was applied sequentially at pre and postemergence (POST) using 0.75 L ha-1 in each application. Crop conduction was performed according the Southern Brazil Rice Production Guidelines. Crop injury was estimated visually using a scale of 0 to 100% where 0 = no rice injury and 100 = rice death. Immediately after the postemergence application four plants in each replication of cultivar Puitá Inta CL were collected, placed in a vial containing 50 mL of acetonitrile, and agitated for 15 seconds. Sample were stored under refrigeration and analyzed using a UPLC/MS/MS. Rice injury evaluations conducted 9 days after POST applications (DAA) indicated an interaction between genotypes and spraying systems. For cultivars Puitá Inta CL and Guri Inta CL no injury was observed. However among the hybrids higher injury was obtained with the hydraulic systems as compared with the electrostatic. This trend persisted for the evaluation conducted until 30 DAA. It is important to point out that higher injury was expected to occur with the electrostatic system as charged droplets generally result in better spraying coverage. In all evaluation higher injury was obtained at lower seeding rates. This was in agreement with a numerically higher herbicide concentration reaching individual plants of Puitá Inta CL at 45 kg ha-1 when compared with 90 kg ha-1. Results indicated that different level of genotypes tolerance observed in the field are associated with genetic differences where the cultivars (Puitá Inta CL and Guri Inta CL) were more tolerant to Only® than the hybrids (QM 1010, Avaxi e Inov). Moreover, the lower quantity of plant per area established in the field when using a rice hybrid resulted in a higher dosage of herbicide per individual plant that contributed to intensify the crop injury.


INFLUENCE OF PREHARVEST HERBICIDES ON BLACK BEAN DESICCATION, YIELD, AND CANNING QUALITY. A. M. Goffnett*1, C. Sprague1, K. A. Cichy2; 1Michigan State University, East Lansing, MI, 2USDA-ARS, East Lansing, MI (10)

ABSTRACT

The retention of the black color in canned black beans is viewed as a key attribute in finished product quality and is very important for consumer acceptance. Changes in production practices and black bean varieties may influence canned dry bean quality.  A field trial was conducted at the Saginaw Valley Research and Extension Center near Richville, Michigan, in 2013 and 2014 to evaluate the effects of preharvest treatments on desiccation, yield and color retention of black beans after canning. Type II black bean varieties ‘Zorro’, ‘Eclipse’, and ‘Zenith’ were planted on two dates; June 13 and 26 in 2013 and June 5 and 27 in 2014 (at the beginning and end of the ideal planting time for the region). Three preharvest treatments were tested: 1) paraquat (0.56 kg ha-1) + non-ionic surfactant (0.25% v/v); 2) glyphosate (0.84 kg a.e. ha-1) + ammonium sulfate (2% w/w); and 3) saflufenacil (0.05 kg ha-1) + methylated seed oil (1% v/v) + ammonium sulfate (2% w/w). An untreated control was established for each variety. Preharvest treatments were applied at two different timings for each planting date; at 50% pod yellowing (early) and 80% pod yellowing (standard application timing). The early application was to evaluate differences in desiccation treatments and simulate green areas in a field that may be present during standard applications. Desiccation was evaluated 3, 7, and 14 days after treatment (DAT). Beans were direct harvested, adjusted to 18% moisture, and canned using a small scale protocol. Canned samples were assessed for color and appearance by 22 trained evaluators, using a scale from 1 (poor or unacceptable) to 5 (excellent). Black bean color was also evaluated by measuring the luminosity (L) value with a colorimeter, ranging from 0 (black) to 100 (white). Differences in black bean desiccation were greatest 3 DAT, with paraquat and saflufenacil showing the quickest desiccation at the early application timing. By 7 DAT, desiccation for all preharvest treatments were over 95%, except for early applications of glyphosate on ‘Zorro’ and ‘Zenith’ in the second planting of 2013 and the first planting of 2014, which took until 14 DAT to reach acceptable levels. Early applications of paraquat on ‘Zorro’ and ‘Zenith’ in the second planting of 2013 also required 14 DAT to reach acceptable levels of desiccation. Early applications of saflufenacil in the first planting had the greatest impact on yield for both years, when compared with the untreated. This may be due to the quicker speed of activity halting dry bean development. At the standard application timing, saflufenacil did not differ from other treatments compared with the untreated for both years of the first planting. The evaluation panel observed the lightest black bean color when glyphosate was applied early to ‘Zenith’ and ‘Zorro’. Luminosity measurements also indicate lighter black bean color after canning with early applications of glyphosate. ‘Eclipse’ had the lightest luminosity measurements while ‘Zenith’ had the darkest, regardless of planting date or application timing. Evaluation of appearance resulted in a variety difference, with ‘Zenith’ or ‘Zorro’ scoring higher than ‘Eclipse’. Overall, differences in desiccation, yield, and canning quality were observed between black bean varieties, preharvest herbicide treatment, and application timing.

 


EVALUATION OF PRE HERBICIDE AND SEED TREATMENT ON THRIPS INFESTATION AND COTTON GROWTH, DEVELOPMENT, AND YIELD. J. Copeland*1, D. M. Dodds1, A. Catchot1, D. Reynolds1, J. Gore2, D. Wilson3, D. Denton1, C. A. Samples4; 1Mississippi State University, Mississippi State, MS, 2Mississippi State University, Stoneville, MS, 3Monsanto, St. Louis, MO, 4Mississippi State University, Starkville, MS (11)

ABSTRACT

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.

 


COMPARISON OF RESIDUAL HERBICIDE SYSTEMS FOR PALMER AMARANTH MANAGEMENT IN WEST TEXAS. R. M. Merchant*1, P. A. Dotray2, J. Keeling3, M. R. Manuchehri4; 1University of Georgia, Tifton, GA, 2Texas Tech University, Texas A&M AgriLife Research and Extension Service, Lubbock, TX, 3Texas A&M AgriLife Extension Service, Lubbock, TX, 4Washington State University, Pullman, WA (12)

ABSTRACT

Comparison of residual herbicide systems for Palmer amaranth management in West Texas: Rand M. Merchant*1; Peter A. Dotray1,2; Wayne K. Keeling2, Misha R. Manuchehri1. 1Texas Tech University, Lubbock, and 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. Trials were conducted at Lubbock and Halfway, Texas in 2013, and at Lubbock in 2014, in order to better understand the effectiveness of currently available residual herbicide options in cotton. The Lubbock and Halfway locations were rain-fed and pivot irrigated, respectively. Treatments included 32 residual herbicide options in varying combinations, applied at rates appropriate for these soil types and conditions. Palmer amaranth control was recorded following postemergence and late post-directed applications. The best seven treatments for each location were identified. At the Lubbock location in 2013, best control following the postemergence (POST) application was achieved by trifluralin preplant incorporated (PPI) followed by (fb) prometryn plus s-metolachlor preemergence (PRE) (99%), s-metolachlor plus prometryn PRE fb s-metolachlor POST (96%), trifluralin PPI fb prometryn plus s-metolachlor PRE fb diuron late-POST (98%), s-metolachlor plus prometryn PRE fb pyrithiobac POST (94%), trifluralin PPI fb prometryn PRE fb s-metolachlor POST fb diuron late-POST(96%), s-metolachlor plus prometryn PRE (98%), and trifluralin PPI (78%). At the Lubbock location in 2014, best control following the postemergence application was achieved by trifluralin PPI fb prometryn PRE fb s-metolachlor POST (99%), s-metolachlor plus prometryn PRE fb pyrithiobac POST (99%), s-metolachlor plus prometryn PRE fb s-metolachlor POST fb diuron late-POST (99%), s-metolachlor plus prometryn PRE (96%), s-metolachlor plus prometryn PRE fb s-metolachlor POST (93%), trifluralin PPI fb prometryn PRE fb s-metolachlor POST fb diuron late-POST (88%), and trifluralin PPI fb prometryn PRE (85%). At the Halfway location best control following the late post-directed application was achieved by s-metolachlor plus prometryn PRE fb s-metolachlor POST fb diuron late-POST(95%), s-metolachlor plus prometryn PRE fb s-metolachlor POST (88%), trifluralin PPI fb prometryn PRE fb s-metolachlor POST fb diuron late-POST(95%), trifluralin PPI fb prometryn plus s-metolachlor PRE (87%), s-metolachlor plus prometryn PRE fb pyrithiobac POST (85%), trifluralin PPI fb prometryn PRE (60%), and s-metolachlor plus prometryn PRE (68%). In summary, several residual-based weed management programs are available that will reduce the selection pressure following the use of postemergence herbicides.


EFFICACY OF FLURIDONE-BASED HERBICIDE PROGRAMS IN COTTON AND PEANUT. M. W. Marshall*; Clemson University, Blackville, SC (13)

ABSTRACT

Glyphosate and ALS-resistant weeds, including Palmer amaranth, have growers and industry searching for additional herbicide mode-of-action alternatives for use in cotton and peanut. Previous studies have shown fluridone is highly efficacious on glyphosate-resistant Palmer amaranth and other economically important weed species.  Fluridone typically provides up to 8 weeks of residual activity when properly activated.  Therefore, the objective of this study was to examine at-plant fluridone combinations on weed control and crop response in cotton and peanuts.  Field studies were conducted at Edisto Research and Education Center near Blackville, SC in 2014. Experimental design was a randomized complete block with 4 replications with individual plot sizes of 3.9 by 12 m.  Phytogen Widestrike 499 cotton was seeded at 9.7 seeds/cm on May 26, 2014.  Virginia type peanut ‘Bailey’ was seeded at 15.2 seeds/cm on May 30, 2014.  In the cotton study, preemergence (PRE) herbicides were applied in water on May 26, 2014, followed by POST1 at 2-4 leaf and POST2 at 6-7 leaf growth stage at a carrier volume of 15 GPA.  At-plant preemergence (PRE) treatments were fluridone at 0.06, 0.11, 0.14, 0.17 kg/ha in combination with fomesafen at 0.14 kg/ha and fomesafen at 0.28 kg/ha + diuron at 0.28 kg/ha.  The PRE treatments were followed by two postemergence (POST) applications of glufosinate at 0.59 kg/ha plus acetochlor at 1.26 kg/ha.  Percent weed control and crop injury ratings were collected at POST1, POST2, and LAYBY timings on a 0 to 100% scale with 0 indicating no control and 100% equal to complete control.  In the peanut study, PRE herbicides were applied in water on May 30, 2014 followed by early POST at 2-3 trifoliate stage and mid-POST at 30 days after planting.  Soil residual treatment included fluridone at 0.11 and 0.17 kg/ha + flumioxazin at 0.11 kg/ha, fluridone at 0.17 kg/ha + fomesafen at 0.14 kg/ha, and flumioxazin alone at 0.11 kg/ha.  Early POST treatment was paraquat at 0.18 kg/ha + bentazon at 0.56 kg/ha + acifluorfen at 0.28 kg/ha + s-metolachlor at 1.06 kg/ha followed by a mid-POST treatment was imazapic at 0.07 kg/ha + acetochlor at 1.26 kg/ha across all plots except the untreated. Percent weed control and crop injury ratings were collected at early POST and mid-POST timings.  Weed control data and cotton and peanut crop injury were analyzed using ANOVA and means separated at the P = 0.05 level.  Overall, no significant crop response to fluridone was observed in peanut or cotton.  The fluridone plus fomsafen combinations provided excellent Palmer amaranth, large crabgrass, and pitted morningglory control at the POST1 evaluation.  Any weed escapes were controlled by the glufosinate plus acetochlor POST applications.  At 10 weeks after planting, all treatments provided 100% or greater control of Palmer amaranth, pitted morningglory, and large crabgrass.  No differences in weed control performance was noted among the different rates of fluridone in cotton.  Similar to the cotton data, fluridone plus flumioxazin and fluridone plus fomesafen provided 90% or better control at 30 days after planting (mid-POST application timing) in peanuts.  At the use rates tested, the Virginia type peanuts seemed to tolerate fluridone; however, previous studies have shown crop response in the runner type peanuts.  Overall, fluridone as part of a robust management program provided good to excellent control of Palmer amaranth, pitted morningglory, and large crabgrass in cotton and peanuts.  Fluridone, as part of an integrated program, would reduce the selection pressure on the PPO inhibitors, fomesafen and flumioxazin, in both production systems.


HERBICIDE PROGRAMS IN OKLAHOMA SOYBEAN. T. A. Baughman*1, R. Peterson2; 1Oklahoma State University, Lone Grove, OK, 2Oklahoma State University, Ardmore, OK (14)

ABSTRACT

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.

 


EVALUATION OF GLYPHOSATE-RESISTANT PALMER AMARANTH CONTROL IN HPPD-TOLERANT SOYBEAN SYSTEMS. B. W. Schrage*1, W. J. Everman1, M. W. Marshall2; 1NCSU, Raleigh, NC, 2Clemson University, Blackville, SC (15)

ABSTRACT

EVALUATION OF GLYPHOSATE-RESISTANT PALMER AMARANTH CONTROL IN HPPD-TOLERANT SOYBEAN SYSTEMS.  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.

 


MODELING THE EVOLUTION OF SHATTERCANE RESISTANCE TO ALS-INHIBITING HERBICIDES IN AN ALS-TOLERANT SORGHUM CROPPING SYSTEM. R. Werle*, B. Tenhumberg, J. Lindquist; University of Nebraska-Lincoln, Lincoln, NE (16)

ABSTRACT

Traditional breeding technology is currently being used to develop grain sorghum germplasm that will be tolerant to acetolactate synthase (ALS)-inhibiting herbicides. This technology (Inzen Z, DuPont) has the potential to improve sorghum production by allowing for the postemergence control of traditionally hard-to-control grasses. However, grain sorghum and shattercane can interbreed and introduced traits such as herbicide tolerance could increase the invasiveness of the weedy relative. Moreover, ALS-resistance in shattercane populations has been reported, indicating that over-reliance on ALS-chemistry may also select for resistant biotypes. The objective of this research was to develop a simulation model to assess management options to mitigate risks of ALS-resistance evolution in shattercane populations in US sorghum production areas. Assuming a single major gene confers resistance and gene frequencies change according to the Hardy-Weinberg ratios we constructed a stage-structured (seedbank, plants) matrix model with annual time steps. The model explicitly considered gene flow from Inzen Z plants to shattercane populations. The management strategies considered in the model were: a) continuous sorghum, b) sorghum fb soybeans and c) sorghum fb fallow fb wheat, where postemergence ALS-herbicides were only used in Inzen Z years. During sorghum years, two options were tested: continuous Inzen Z and Inzen Z fb conventional sorghum. The parameter values used in the model were obtained from our research, the literature, and expert opinion. Our model predicted that gene flow from Inzen Z plants only has a noticeable effect on resistance evolution if the resistance trait in the weedy population is absent or low (<0.001). Evolution of resistance was predicted to occur rapidly if Inzen Z sorghum is planted continuously because of high selection pressure (ALS-herbicide application) and gene flow (especially when the resistant trait was originally absent or low in the weedy population). The time for resistance evolution was predicted to decrease with increased cropping system complexity (more crop diversity than continuous production of Inzen Z). Crop and herbicide rotation will be key strategies to postpone the evolution of ALS-resistance in shattercane.


WEED CONTROL IN SOYBEAN WITH IMAZETHAPYR APPLIED ALONE OR IN TANK-MIX WITH SAFLUFENACIL PLUS DIMETHENAMID-P. N. Soltani*, K. D. Walsh, C. Shropshire, P. H. Sikkema; University of Guelph, Ridgetown, ON (17)

ABSTRACT

Saflufenacil plus dimethenamid-P is a relatively new pre-packaged herbicide mixture that has the potential to provide enhanced weed control in soybean when tank-mixed with reduced doses of imazethapyr. Six field experiments were conducted over a 3-yr period (2011, 2012, and 2013) near Ridgetown and Exeter, Ontario, Canada, to determine the dose of imazethapyr, applied PRE, that must be added to saflufenacil/dimethenamid-P (245 g ai ha-1) to provide effective weed control in soybean. The predicted dose of imazethapyr PRE for 80% control of common lambsquarters, common ragweed, green foxtail, and velvetleaf 8 weeks after soybean emergence (WAE) was 66, 180, 137, and 48 g ai ha-1, respectively. In contrast, when tank-mixed with saflufenacil/dimethenamid-P (245 g ai ha-1), the dose of imazethapyr PRE needed for 80% control of common lambsquarters, common ragweed, green foxtail and velvetleaf was reduced to 11, 80, 48, and 18 g ai ha-1, respectively. The control of common lambsquarters, common ragweed, green foxtail, and velvetleaf was improved by 21, 23, 34, and 27%, respectively when saflufenacil/dimethenamid-P (245 g ai ha-1) was added to imazethapyr PRE. Imazethapyr at 104 g ai ha-1 resulted in soybean yield that was 95% of the weed-free control, however, when tank-mixed with saflufenacil/dimethenamid-P (245 g ai ha-1) only 54 g ai ha-1 of imazethapyr was required for the same yield level. Based on this study, PRE application of saflufenacil/dimethenamid-P with reduced doses of imazethapyr has the potential to improve soybean yield and provide acceptable weed control (≥80%), however, the extent that imazethapyr dose may be reduced is dependent upon weed community composition.


TANK-MIXING GROWTH REGULATOR HERBICIDES WITH GLUFOSINATE FOR CONTROL OF GLYPHOSATE-RESISTANT GIANT RAGWEED IN CORN. Z. A. Ganie*1, L. Sandell2, A. J. Jhala3; 1University of Nebraska-Lincoln, Lincoln, NE, 2Valent Corporation, Lincoln, NE, 3University of Florida, Lake Alfred, FL (18)

ABSTRACT

Glyphosate-Resistant giant ragweed is a problematic and difficult to control weed in corn and soybean production fields. Currently, limited POST herbicide options are available for effective control of glyphosate-resistant giant ragweed. Glufosinate is an alternate POST herbicide option for controlling glyphosate-resistant weeds, including giant ragweed in glufosinate-resistant crops. The objective of this study was to evaluate efficacy of tank-mixing glufosinate with growth regulator herbicides for control of glyphosate-resistant giant ragweed in glufosinate-resistant corn. Field experiment was conducted at Clay Centre (40.52° N, 98.05° W), NE in 2013 and at David City (41.25° N, 97.12° W), NE in 2014 in a grower’s field infested with glyphosate-resistant giant ragweed. The treatments included POST application of glufosinate, 2,4-D, and dicamba alone and in tank-mixes at varying rates. The results revealed glufosinate applied in tank-mix with 2,4-D and/ or dicamba provided ≥ 90% control of glyphosate-resistant giant ragweed at 10 d after treatment (DAT) compared to dicamba (<70%) or 2,4-D (<66%) applied alone. Control of glyphosate-resistant giant ragweed was consistently ≥ 90% with either two-way tank-mixture of glufosinate and dicamba or three-way tank-mixture of glufosinate, dicamba, and 2,4-D. Control of glyphosate-resistant giant ragweed with glufosinate was ≤ 84% irrespective of application rate, whereas control improved with dicamba to ≥ 95%. Control of glyphosate-resistant giant ragweed with glufosinate and 2,4-D tank-mix at all rates was in the range of 81% to 90%, however 2,4-D alone provided an unacceptable control (≤ 77%). All herbicide treatments reduced glyphosate-resistant giant ragweed density and –biomass compared to nontreated control, except 2,4-D at 0.28 kg ae ha-1. Results suggested that efficacy of growth regulator herbicides for control of glyphosate-resistant giant ragweed enhanced when tank mixed with glufosinate compared with applied alone. All the tank-mixes, glufosinate + dicamba, glufosinate + 2,4-D, dicamba + 2,4-D and glufosinate + dicamba + 2,4-D provided better control of glyphosate-resistant giant ragweed (≥87%) compared with alone applications of 2,4-D (≤ 77%) and glufosiante (≤84% except at 10 DAT).

 


RESPONSES OF GLYPHOSATE-RESISTANT AND CONVENTIONAL CANOLA (BRASSICA NAPUS L.) TO GLYPHOSATE AND AMPA TREATMENT. E. Alves Correa*1, S. O. Duke2, F. E. Dayan3, A. Rimando2; 1UNESP - Campus de Registro, Registro, Brazil, 2USDA, ARS, Oxford, MS, 3USDA-ARS, University, MS (19)

ABSTRACT

Responses of Glyphosate-Resistant and Conventional Canola (Brassica napus L.) to Glyphosate and AMPA Treatment. Alves Correa, Elza1*; Duke, Stephen O2; Dayan, Franck E2; Rimando, Agnes2. (1 UNESP-Universidade Estadual Paulista, Registro, São Paulo, Brazil; 2 USDA/ARS, Oxford, MS).

Glyphosate is the most widely used herbicide in the world. It has high specificity for the plant enzyme EPSPS that leads to the biosynthesis of aromatic amino acids in the shikimate pathway. GR canola expresses the microbial GOX gene (glyphosate oxidase) and metabolizes glyphosate to aminomethylphosphonic acid (AMPA). Injury from glyphosate in resistant plants (GR) was hypothesized to be caused by AMPA formed from glyphosate degradation. The objective of this research was to determine the response of GR and conventional canola to glyphosate and AMPA. Greenhouse experiment was conduced at the National Center for Natural Products Research. Glyphosate and AMPA effects on five-six leaf stage (34 days old) GR and not GR canola were examined. Glyphosate-potassium was applied at 0.33 and 1.0 Kg ae ha-1, and AMPA at 0.25, 0.5 and 1.0 Kg ha-1.  Controls received the same amount of surfactant. Plant height, number of leaves, fresh and dry weights of stems, leaves and plants , as well as chlorophyll content, were determined at 3, 7 and 14 days after treatment (DAT). The application of AMPA caused significant reductions in the number of leaves of GR-canola plants at 3 DAT. When comparing the AMPA treatments to nontreated control, it was found out that for Non-GR plants a percentual reduction occurred in the formation of leaves, among the three doses tested. Applications of AMPA caused significant reductions in percentage compared to control in the formation of leaves in plants of Non-GR canola at 14 DAT. Plant height was negatively impacted for the applications of AMPA performed in non-GR canola and positively to AMPA applications at GR-canola. For the fresh weight and dry weight in non-GR and GR-canola plants was observed that for applications which AMPA at all dosages used, there was a decrease in percentages relative to the untreated plants. For all variables considered there was an increase of percentages as compared to nontreated control. As for the applications of AMPA in non-GR canola yielded percentual reduction when compared to treatments without applications for all variables considered. Just a dose of 0.25 kg ha-1 resulted in increased plant height with values below 7%. It is found out the chlorophyll content was changed by the treatments. GR-canola plants had lower chlorophyll content when compared to non-GR. The resistant variety of canola used in this study was highly resistant to glyphosate application than as used to AMPA.


PEANUT RESPONSE TO GLYPHOSATE + DICAMBA DRIFT AT DIFFERENT GROWTH STAGES. P. A. Dotray*1, W. Grichar2, T. A. Baughman3, M. R. Manuchehri4, R. M. Merchant5, T. Morris2; 1Texas Tech University, Texas A&M AgriLife Research and Extension Service, Lubbock, TX, 2Texas A&M AgriLife Research, Lubbock, TX, 3Oklahoma State University, Lone Grove, OK, 4Texas Tech University, Lubbock, TX, 5University of Georgia, Tifton, GA (20)

ABSTRACT

Peanut Response to Glyphosate Plus Dicamba Drift at Different Growth Stages.  P.A. Dotray*1, W.J. Grichar2, T.A. Baughman3, M.R. Manuchehri4, R.M. Merchant4, T.S. Morris5; 1Texas Tech University, Texas A&M AgriLife Research, and Texas A&M AgriLife Extension Service, Lubbock, TX, 2Texas A&M AgriLife Research, Corpus Christi, TX, 3Oklahoma State University, Ardmore, OK, 4Texas Tech University, Lubbock, TX, 5Texas A&M AgriLife Research, Lubbock, TX.  With the anticipated release of cotton tolerance to glyphosate and dicamba in 2015, there is concern about the potential for physical drift onto non-target crops such as peanut (Arachis hypogaea).  Field studies were conducted in the Texas Southern High Plains (Seagraves), South Texas (Yoakum), and in Oklahoma (Fort Cobb) to evaluate peanut response to glyphosate plus dicamba when applied at three peanut growth stages (30, 60, and 90 days after planting (DAP)).  Glyphosate plus dicamba at 1.12 + 0.56 kg ae/ha (1X), 0.5X, 0.25X, 0.125X, and 0.0625X was applied at 10 to 20 GPA.  Visible injury was recorded throughout the growing season and peanut yield and grade determined. At Seagraves 28 days after each application timing, both time of application and herbicide rate influenced peanut injury. Injury decreased as applications were made further from planting and with decreasing herbicide rate. Across herbicide rates, approximately 79% injury was observed 28 days after the 30 DAP treatments, whereas approximately 60 and 16% injury was recorded following the 60 and 90 DAP applications, respectively.  Both application timing and herbicide rate influenced peanut yield. Across herbicide rates, the greatest peanut yield (6432 kg/ha) was observed in plots that received treatments at 90 DAP while yield was less but similar for treatments made at 30 and 60 DAP (4955 kg/ha).  At Yoakum 28 days after each application timing, both time of application and herbicide rate influenced peanut injury. Across herbicide rates, the greatest level of injury (60%) was noted following the 30 DAP treatments while injury was similar following the 60 and 90 DAP treatments (26%). Peanut injury increased as herbicide rate increased.  Herbicide rate influenced peanut yield at Yoakum. Yield from plots treated with the 0.0625X and 0.125X rates were similar to the non-treated plot yield; however, yields decreased following the 0.25X rate and continued to decrease following the 0.5X and 1X rates.  An application timing and herbicide rate interaction was observed for peanut injury at Fort Cobb 28 days after each application timing. The greatest level of injury (78%) was observed following the 1X rate applied at 30 DAP and the second greatest level of injury (10%) was observed following the 0.5X rate at this application timing.  Peanut injury was minimal and similar for all other rate by timing interactions.  Herbicide rate influenced peanut yield at Fort Cobb. Yields decreased following all herbicide rates relative to the non-treated control plots. Yield was similar in plots treated with the 0.0625X and 0.125X rates; however, yield decreased starting with the 0.25X rate.


OILSEED CUPHEA TOLERANCE TO BICYCLOPYRONE AND BROMOXYNIL. F. Forcella*; USDA, Morris, MN (21)

ABSTRACT

Weed management is a critical feature of all crop production, but especially for new and alternative crops with which growers have little experience. Oilseed cuphea is a new crop for temperate regions and, at present, it is known to tolerate only a very narrow spectrum of herbicides. Additional herbicides would be useful to encourage growers to examine this crop, particularly those products with broad activity against dicotyledonous weeds. Accordingly, cuphea tolerance to bromoxynil and bycyclopyrone was tested in both greenhouse and field settings. Oilseed cuphea tolerated postemergence applications of bromoxynil up to 210 g ae/ha, which is a common label rate for this herbicide for traditional crops, but only if the plants had reached the 4- to 5-leaf stage of development at the time of application. Earlier applications, or applications at higher rates, could damage plants or cause loss of stands. Thus, postemergence applications of bromoxynil at or beyond the 5-leaf stage appear safe for cuphea. Cuphea also tolerated preemergence applications of bicyclopyrone up to 50 g ai/ha, a commonly used experimental rate of this new herbicide. When applied at the 2-leaf stage of growth, cuphea tolerated up to 37 g ai/ha for postemergence applications (but only in the absence of NIS). These results broaden the spectrum of herbicides that can be used safely on oilseed cuphea and potentially enhance the opportunities for growers to raise cuphea successfully.


IMPACT OF GROWTH REGULATOR RATE AND APPLICATION TIMING ON SORGHUM GROWTH AND YIELD. T. E. Besancon*, W. J. Vincent, W. J. Everman; NCSU, Raleigh, NC (22)

ABSTRACT

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.

 


SEQUENTIAL APPLICATIONS FOR RESCUE CONTROL OF GLYPHOSATE RESISTANT PALMER AMARANTH. D. Denton*1, D. M. Dodds1, D. Reynolds1, A. Mills2, J. Copeland1, C. A. Samples3; 1Mississippi State University, Mississippi State, MS, 2Monsanto, Collierville, TN, 3Mississippi State University, Starkville, MS (23)

ABSTRACT

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.  

 


PUTATIVE GENES INVOLVED IN THE NON-TARGET-SITE-BASED HERBICIDE RESISTANCE IN ECHINOCHLOA CRUS-GALLI. G. Dalazen1, A. J. Fischer2, A. Merotto Junior*1; 1Federal University of Rio Grande do Sul - UFRGS, Porto Alegre, RS, Brazil, 2University of California, Davis, Davis, CA (24)

ABSTRACT

Barnyardgrass (Echinochloa crus-galli) is one of the major weeds of irrigated rice worldwide. The problems caused by this weed are increasing due to the occurrence of populations with multiple herbicide resistance, mainly caused by herbicide enhanced detoxification. Knowledge about the mechanism of herbicide resistance is important for correctly designing management practices to prevent resistance evolution and to control herbicide-resistant barnyardgrass plants. The objective of this study was to evaluate the expression of genes associated with the enhanced herbicide degradation in barnyardgrass populations resistant to ALS inhibitors and quinclorac.  The expression of genes encoding P450 enzymes was evaluated in a susceptible and in an ALS-inhibitor- resistant population with non-targert site resistance that was reversed with P450 inhibitors. Plants were grown in greenhouse and imazethapyr (106 g ha-1 plus 0,5% v/v non-ionic surfactant) was sprayed at the three to four-leaf stage. Twenty-four hours later plant material was collected for RNA extraction. Six candidate genes encoding P450 enzymes were evaluated.  Two genes were differentially expressed in imazethapyr-resistant and –susceptible barnyardgrass plants. The CYP81A6 gene was expressed only in the resistant population, both in treated and in untreated plants. The LrGSTF1 gene was expressed in treated and untreated resistant population and in the treated susceptible population. The expression of the LrGSTF1 gene was higher in the resistant than in the susceptible population. The other evaluated genes were not differentially expressed.  Further studies are been carried out in order to evaluate the expression of these genes in a dose-dependent herbicide treatment and of additional putative genes associated with herbicide resistance. The knowledge about the gene regulation of the degradation enhancement herbicide resistance is important for the understanding of the herbicide resistant evolution in barnyardgrass.


EVALUATION OF INZEN GRAIN SORGHUM IN LOUISIANA. D. Stephenson*, R. Landry, B. Woolam; LSU AgCenter, Alexandria, LA (25)

ABSTRACT

EVALUATION OF INZEN GRAIN SORGHUM IN LOUISIANA.  DO Stephenson, IV*1, R. L. Landry1, B. C. Woolam1; 1Louisiana State University Agricultural Center, Alexandria, LA. 

Weedy grass and broadleaf control is difficult in Louisiana grain sorghum.  Specifically, no options are available for control of johnsongrass.  As a consequence, determination of a program to manage annual weedy grass, johnsongrass, and broadleaf weeds is needed.  Research was conducted at the Louisiana State University Dean Lee Research and Extension Center near Alexandria, LA in 2013 and 2014 to evaluate nicosulfuron-based treatments in Inzen grain sorghum as an option for control of these weeds.  Treatments were arranged in a randomized complete block with four replications.  Different treatments were evaluated in each year.  In 2013, nicosulfuron alone at 35 and 53 g ai ha-1, nicosulfuron at 26 g ha-1 plus rimsulfuron at 13 g ai ha-1, nicosulfuron at 35 g ha-1 plus rimsulfuron at 18 g ha-1, and both nicosulfuron plus rimsulfuron treatments co-applied with atrazine at 504 g ai ha-1 plus pyrasulfotole:bromoxynil at 35:200 g ai ha-1 were evaluated.  In 2014, treatments evaluated were nicosulfuron at 35 g ha-1 was applied alone or in combination with atrazine at 840 g ha-1 plus pyrasulfotole:bromoxynil, atrazine plus dicamba at 280 g ae ha-1, and atrazine plus 2,4-D at 280 g ae ha-1.  Crop oil concentrate at 1% v/v was applied with all treatments in both years.  All treatments were applied to 5 to 10 cm weeds regardless of the grain sorghum growth stage in 2013 and 2014.  Data collected included visual control evaluation of hophornbeam copperleaf (Acalypha ostryifolia) in 2013, barnyardgrass (Echinochloa crus-galli) and browntop millet (Urochloa ramosa) in 2014, and johnsongrass (Sorghum halepense) and Palmer amaranth (Amaranthus palmeri) in 2013 and 2014.  Visual evaluation data recorded 28 d after treatment (DAT) is presented. 

Nicosulfuron at 35 and 53 g ha-1 controlled hophornbeam copperleaf 70 to 73%; however, co-applying rimsulfuron at 18 g ha-1 with nicosulfuron at 35 g ha-1 increased control to 95% 28 DAT.  The addition of atrazine plus pyrasulfotole:bromoxynil to nicosulfuron plus rimsulfuron (35 plus 18 g ha-1) also provided excellent (98%) hophornbeam copperleaf control.  Palmer amaranth control in 2013 was similar to hophornbeam copperleaf control with both rates of nicosulfuron providing 67 to 72% control 28 DAT.  All treatments controlled Palmer amaranth 99% 28 DAT in 2014.  Johnsongrass control 28 DAT following application of nicosulfuron at 35 and 53 g ha-1 was 73 and 70%, respectively, in 2013.  However, nicosulfuron at 35 g ha-1 plus atrazine provided 91% johnsongrass control 28 DAT in 2014.  Treatments were applied 4 d and 14 d after planting in 2013 and 2014, respectively.  Herbicide efficacy on johnsongrass combined with shading by the grain sorghum following application may be the reason control was greater in 2014.  Treatments containing nicosulfuron at 35 g ha-1 plus rimsulfuron at 18 g ha-1, with and without atrazine plus pyrasulfotole:bromoxynil, controlled johnsongrass greater than 90% 28 DAT.  All treatments controlled barnyardgrass and browntop millet 83 to 94% 28 DAT in 2014.  Results indicate that nicosulfuron-based treatments in Inzen grain sorghum have utility for Louisiana producers.  However, questions remain concerning Inzen grain sorghum tolerance to multiple nicosulfuron applications, co-applications with insecticides and fungicides, etc.  These topics will be investigated in the coming years.

 


BIOLOGICALLY EFFECTIVE RATE OF SULFENTRAZONE APPLIED PRE-EMERGENCE IN SOYBEAN. N. Soltani*1, K. D. Walsh1, R. E. Nurse2, D. C. Hooker1, P. H. Sikkema1; 1University of Guelph, Ridgetown, ON, 2Agriculture and Agri-Food Canada, Harrow, ON (26)

ABSTRACT

Sulfentrazone is a protoporphyrinogen (PPO)-inhibiting herbicide under evaluation for use in soybean in Ontario, Canada. The primary objective of this study was to determine the dose of sulfentrazone applied pre-emergence (PRE) that provides 50 and 90% control of redroot pigweed, common ragweed, common lambsquarters and green foxtail. Seven field trials were conducted over a three-year period (2007, 2008 and 2009) in southwestern Ontario to evaluate the efficacy of sulfentrazone applied PRE at doses ranging from 26 to 1120 g a.i. ha-1. The doses of sulfentrazone applied PRE to reduce redroot pigweed, common ragweed, common lambsquarters and green foxtail dry weight by 50% were 104, 139, 15 and 65 g a.i. ha-1; doses of 241, 514, 133 and 721 g a.i. ha-1 of sulfentrazone were required for 90% reduction in aboveground biomass of those weed species, respectively. Sulfentrazone applied PRE caused soybean injury only at 560 and 1120 g a.i. ha-1, with 6 and 13% soybean injury at four weeks after herbicide treatment (WAT), respectively. Weed control provided by sulfentrazone applied PRE at a dose of 600 g a.i. ha-1 was sufficient to maintain 90% of the soybean yield compared to the weed-free control. Therefore, PRE application of sulfentrazone has the potential to provide excellent (>90%) control of selected weeds with minimal to no crop injury; however, weed control varied by species, and thus broad spectrum weed control is not feasible using sulfentrazone alone.


EXTENT AND IMPACT OF SYNTHETIC AUXIN RESISTANT WEEDS. I. M. Heap*; WeedSmart, Corvallis, OR (27)

ABSTRACT

Synthetic auxin herbicides, introduced in the 1945, were the first widely adopted modern herbicides. Over the years synthetic auxins have been used on a greater area than any other herbicide group and are still widely used. Thirty weed species have evolved resistance to synthetic auxin herbicides, 26 of them being dicots, and four Echinochloa species that have evolved resistance to quinclorac.  This poster will focus on synthetic auxin resistance in dicots.  Despite extensive use of synthetic auxins over the last 70 years, few synthetic auxin resistant weeds have become widespread major economic problems.  Kochia scoparia in the USA, Raphanus raphanistrum in Australia, and Papaver rhoeas in Europe are the most widespread and economically important cases of synthetic auxin resistance in dicots.  Not surprisingly these cases have been found in cereal production where synthetic auxins have been extensively used for broadleaf weed control.  The introduction of synthetic auxin resistant crops in the mid-west will undoubtedly result in an increase in the number and area of synthetic auxin resistant weeds, however these traits will be of great benefit in the management of glyphosate-resistant weeds.  For those growers without glyphosate-resistant weeds, synthetic auxin resistant crops will enable them to use another herbicide site of action in conjunction with glyphosate to reduce the appearance of broadleaf weeds with resistance to either herbicide group.  Ideally periodic rotation away from synthetic auxins and glyphosate to other herbicide sites of action, in conjunction with non-herbicide weed control methods, should be employed to delay resistance.  However on fields where dicots have already evolved glyphosate resistance the application of synthetic auxins without inclusion of any other herbicide mode of action or weed control method is likely to result in multiple resistance.  In the mid-west Kochia and pigweed species are the most likely to present widespread multiple resistance to synthetic auxins and glyphosate.  Non-herbicidal control strategies, in conjunction with the use of alternate herbicide sites of action in mixtures or rotation will slow the development of multiple resistance.

 


CONTROL OF FRINGED REDMAIDS (CALANDRIAIA CILIATA) IN WINTER WHEAT. B. Woolam*1, D. Stephenson1, R. Landry1, A. Meszaros2, G. Coburn2; 1LSU AgCenter, Alexandria, LA, 2Pest Management Enterprises, LLC, Cheneyville, LA (28)

ABSTRACT

CONTROL OF FRINGED REDMAIDS (CALANDRINIA CILIATA) IN WINTER WHEAT.  BC Woolam*1, DO Stephenson, IV1, R. L. Landry1, A Mészáros2, and G. Colburn2; 1Louisiana State University Agricultural Center, Alexandria, LA; 2Pest Management Enterprises, LLC, Cheneyville, LA. 

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.

 


ADDRESSING THE CHALLENGE OF GLYPHOSATE-RESISTANT CONYZA SPECIES ACROSS THE AMERICAS. M. A. Peterson*1, D. M. Simpson2, R. Frene3, F. Lucio4; 1Dow AgroSciences, West Lafayette, IN, 2Dow AgroSciences, Indianapolis, IN, 3Dow AgroSciences, Buenos Aires, Argentina, 4Dow AgroSciences, Sao Paulo, Brazil (29)

ABSTRACT

Weed species  in the genera Conyza are commonly found around the world.  Glyphosate-resistant (GR) biotypes of these species are especially problematic for crop production in key grain producing areas of the Americas.  In North America GR Conyza canadensis has spread across many areas of the U.S. Midwest, South, and Canada.  Likewise GR Conyza sumatrensis and GR Conyza boneriensis are problem weeds across Argentina, Brazil, Paraguay, and Uruguay.  Additionally, biotypes with resistance to both glyphosate and ALS herbicides leave many farmers with limited control options, especially in soybean.

New tools enabled by herbicide tolerance traits can provide a means to improve control of these difficult to control weeds.  The EnlistTM Weed Control System is composed of new herbicide-tolerant traits and new 2,4-D choline-based herbicide solutions such as Enlist Duo™ herbicide(2,4-D choline + glyphosate DMA).   Additional modes of action, such as glufosinate, are also enabled by Enlist™ traits and Enlist E3TM soybean.   Field trials in North and South America in 2012-14 have tested various programs combining 2,4-D choline, glyphosate, glufosinate, and various PPO inhibitor and/or ALS inhibitor products.  Results indicate that burndown treatments containing multiple modes of action followed by postemergence applications of 2,4-D choline + glyphosate or glufosinate can provide high levels of control of GR Conyza biotypes.  In the U.S., C. canadensis control of >95% can be achieved by a burndown application of cloransulam + sulfentrazone tank mixed with combinations of 2,4-D choline + either glyphosate or glufosinate followed by a postemergence application of 2,4-D choline + glyphosate.   Control of C. sumatrensis in Argentina was >90% with programs containing burndown applications of glyphosate + 2,4-D choline + diclosulam followed by postemergence treatments of 2,4-D choline + glyphosate.

mapeterson@dow.com  

™®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. Enlist Duo herbicide is not registered for sale or use in all states or countries. 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.


GLUFOSINATE- AND GLYPHOSATE- RESISTANT ITALIAN RYEGRASS (LOLIUM MULTIFLORUM) IN CALIFORNIA ORCHARDS AND VINEYARDS. E. Karn*, M. Jasieniuk; University of California-Davis, Davis, CA (30)

ABSTRACT

Resistance to glyphosate has become widespread in Italian ryegrass (Lolium multiflorum) in areas of northern California and resistance to glufosinate has recently been found in some of these same areas. The objective of this study is to characterize resistance to glufosinate and glyphosate in selected ryegrass populations from orchards and vineyards of Sonoma and Lake Counties.  Seeds were collected from >30 parents in each of 14 populations and pooled.  A random sample was planted in the greenhouse and 100-150 individuals per population clonally propagated to test genetically identical individuals for resistance. Percentage of plants surviving 1681 g ae ha­-1 (1.5 lbs/acre) glyphosate ranged from 9 to 89% among populations, while 0 to 38% survived treatment with 2242 g ai ha-1 (2 lbs/acre) glufosinate.  Twenty-two percent of individuals survived treatment with both herbicides based on the response of clones.  A dose-response experiment with selected populations and a susceptible control showed that a population from a pear orchard in Lake County exhibits an LD50 of 3550 g ae ha-1 for glyphosate and a selectivity index (R:S ratio) of 16.1 compared to the susceptible control.  DNA sequencing surrounding site 106 of the EPSPS gene revealed that resistant plants from this population do not contain a target-site mutation conferring glyphosate resistance.  In contrast, resistant plants from a vineyard population do have a proline to serine mutation at site 106.  The mechanism of resistance responsible for the high level of glyphosate resistance observed in the pear orchard population is currently unknown.

 


EMPLOYING LEAF MULTISPECTRAL REFLECTANCE DATA AND RANDOM FOREST METHOD TO DIFFERENTIATE BETWEEN SOYBEAN AND THREE BROADLEAF WEED SPECIES. R. S. Fletcher*, K. N. Reddy, S. J. Thomson; USDA, Stoneville, MS (31)

ABSTRACT

Accurate weed identification is a requirement prior to implementing site specific management of herbicides in agricultural fields. The objective of this study was to evaluate leaf multispectral reflectance data as input into the random forest machine learning algorithm to differentiate soybean (Glycine max L., ‘Progeny 4928’) from three broadleaf weeds commonly found in agricultural fields.  The three weed species were Palmer amaranth (Amaranthus palmeri S. Wats.), redroot pigweed (Amaranthus retroflexus L.), and velvetleaf (Abutilon theophrasti Medik).  Reflectance measurements were collected from the most recently matured leaf of soybean, Palmer amaranth, redroot pigweed, and velvetleaf plants grown in a greenhouse.  Data were obtained at the vegetative growth stage of the plants on two dates, June 30, 2014 and September 17, 2014.  A plant probe attached to a hyperspectral spectroradiometer was employed to collect the spectral data.  The hyperspectral data were aggregated to sixteen multispectral bands mimicking those recorded by the WorldView 3 satellite sensor, including cyan, blue, green, yellow, red, red-edge, near-infrared 1 and 2, and shortwave-infrared 1thru 8.   

The June 30, 2014 dataset was used as the training dataset; and the September 17, 2014 dataset was employed as the test dataset.  Three datasets were developed for the training and the test datasets:  (1) soybean and Palmer amaranth, (2) soybean and redroot pigweed, and (3) soybean and velvetleaf.  Ten-fold cross validation was repeated ten times to derive the model for differentiating soybean from the weed of interest for the training datasets.  The best model was chosen using overall accuracy and the kappa statistic.  Finally, the best model selected for the training datasets was evaluated on the corresponding test datasets.  Overall classification accuracies of the soybean versus Palmer amaranth, soybean versus redroot pigweed, and soybean versus velvetleaf on the test datasets were 98.3%, 93.3%, and 65.0%, respectively.  Kappa values obtained from the soybean versus Palmer amaranth and soybean versus redroot pigweed were 0.97 and 0.87, respectively, indicating very good agreement between the reference data and the predicted data.  Fair agreement (Kappa value = 0.30) was observed between the reference data and the predicted data for soybean versus velvetleaf classification.  Velvetleaf was often misclassified as soybean. The results of this study indicate that using multispectral data as input into the random forest algorithm has good potential to differentiate soybean from broadleaf weed species. 


PROCESSING TOMATO (SOLANUM LYCOPERSICUM) VARIETY TOLERANCE TO THIFENSULFURON-METHYL. M. Mohseni-Moghadam, K. J. Linder*, R. J. Edwards, D. Doohan; Ohio State University, Wooster, OH (32)

ABSTRACT

Field experiments were conducted at the Ohio Agricultural Research and Development Center in Wooster, OH in 2005, 2006 and 2007 to evaluate the tolerance of tomato to thifensulfuron-methyl, a sulfonylurea herbicide used for post-emergence control of broadleaf weeds. The experimental design was a randomized complete block with 4 replications. The split plot treatment design included 3 rates of herbicide (main plots) and 8 tomato varieties (subplots). Herbicide treatments included thifensulfuron-methyl at 0, 6 and 12 g ai ha-1, and were applied using a CO2 sprayer with 8002VS flat fan nozzle tips operated at 241 kPa to deliver 234 L ha-1. The crop was machine-transplanted on June 2, 2005, and June 15 in 2006 and 2007. Treatments were applied on June 21, 2005, July 11, 2006, and July 7, 2007. Crop injury was assessed visually using a 0-100 linear scale in which 0 indicated no crop injury, and 100 indicated death of the crop. Plots were evaluated at 1, 3, and 6 weeks after treatment (WAT), and the crop was harvested on September 26 in 2005 and 2006, and September 13, 2007. When averaged over variety, initial crop injury (plant stunting) for both rates of thifensulfuron-methyl at 1 and 3 WAT was low, ranging between 3% and 7% in all three years. However, crop injury among the tested tomato varieties differed in 2005, with the highest crop injury (38%) observed for variety TR122244 at 1 WAT. Thifensulfuron-methyl had a conflicting effect on crop yield in 2005 and 2006. In 2005, variety TR122244, which had the highest crop injury, produced at least 50% higher yield with both rates of herbicide compared to the weed free control. However, in 2006 the high rate of thifensulfuron-methyl had no effect on the yield of TR122244, but 97045116 produced 48% less yield compared to the weed free control. Registration of thifensulfuron-methyl herbicide is not recommended at this time due to the potential for crop stunting and yield reduction in certain tomato varieties.


RESPONSE OF TOMATO (SOLANUM LYCOPERSICUM) AND SOYBEAN (GLYCINE MAX L.) TO SUB-LETHAL DOSES OF 2,4-D OR DICAMBA, WITH/WITHOUT GLYPHOSATE. A. S. Leiva Soto*, M. Mohseni-Moghadam, L. Fleuridor, R. J. Edwards, D. Doohan; Ohio State University, Wooster, OH (33)

ABSTRACT

Greenhouse experiments were conducted at the Ohio Agricultural Research and Development Center in Wooster, OH in 2014 to evaluate the response of tomato (Solanum lycopersicum) to simulated drift rates of 2,4-D, glyphosate, and mixtures of 2,4-D plus glyphosate and soybean (Glycine max) to simulated drift rates of dicamba, glyphosate, and mixtures of dicamba plus glyphosate. Tomato and soybean seedlings were transplanted on July 24 and November 3, 2014, into 7.5 and 1 L pots, respectively. Experimental design was a randomized complete block with 4 replications. Herbicide doses for tomato included three rates of 2,4-D (1/30X, 1/100X, and 1/300X of the recommended field rate of 840 g ae ha-1) , three rates of glyphosate (1/30X, 100X, and 1/300X of the recommended field rate of 840 g ae ha-1), and three rates of 2,4-D plus glyphosate mix (1/100X plus 1/30x, 1/100X and 1/300X of the recommended field rates).  Herbicide doses for soybean included three rates of dicamba (1/30X, 1/100X, and 1/300X of the recommended field rate of 560 g ae ha-1), three rates of glyphosate (1/30X, 1/100X, and 1/300X), and three rates of dicamba plus glyphosate (1/100X plus 1/30x, 1/100X and 1/300X). Herbicide doses were applied with a laboratory track-sprayer using a three nozzle hydraulic boom fitted with TTJ60-11002 nozzle tips. Nozzle spacing was set at 46 cm, liquid pressure was set at 276 kPa and boom travel speed was 6.5 km h-1 delivering 140 L ha-1. Applications were made on August 15, 2014 for tomato plants at the three leaf stage and on November 28, 2014 for soybean when they were approximately 28 cm tall and at growth stage V3. Crop injury was assessed visually using a 0-100 linear scale in which 0 indicated no crop injury and 100 indicated death of the crop. Crop injury and plant height was evaluated at 1, 2, 7, and 9 weeks after treatment (WAT) for tomato and 1, 2, 3, 4, and 5 WAT for soybean. Tomatoes were harvested on October 13 and soybeans on December 22, 2014. Yield and dry weight for each plant was also determined. The data show that when tomato plants were treated with the 2,4-D plus glyphosate mix at the rate of 1/100X + 1/30X, plant height, main stem dry weight, total plant fresh weight, and yield was reduced compared to when the 2,4-D 1/100X rate was applied alone but not compared to when the glyphosate 1/30X rate was applied alone. However, tomato crop injury ratings and total plant dry weight were not different when herbicide mixtures were applied, compared to when they were applied separately. Soybean injury, plant height, yield, and dry weight were not different when herbicide mixtures were applied, compared to when dicamba was applied alone. These data indicate that risk of drift damage to tomatoes from mixtures containing 2,4-D plus glyphosate is potentially greater than when these herbicides are applied alone. However, the risk of drift damage to soybeans from dicamba is not increased by the addition of glyphosate.


WEED CONTROL, AND TOLERANCE OF PROCESSING TOMATO (SOLANUM LYCOPERSICUM) TO FOMESAFEN. M. Mohseni-Moghadam*, D. Doohan; Ohio State University, Wooster, OH (34)

ABSTRACT

Weed management in tomato (Solanum lycopersicum Mill.) continues to be a challenge for vegetable growers in Ohio as well as elsewhere. Field experiments were conducted at the North Central Agricultural Research Station in Fremont, OH in 2009 and 2010 to evaluate efficacy and tolerance of tomato to fomesafen. The crop was machine-transplanted in June 5, 2009 and June 3, 2010, with a 0.6 m spacing between rows. Plots were 3.1 m wide and 7.6 m long. The experimental design was a randomized complete block with 4 replications. Herbicide treatments were applied using a CO2 pressurized (276 kPa) backpack sprayer with 8002VS nozzle tips delivering 234 L ha-1. Pre-transplant (PRETP) treatments were applied on June 4, 2009, and May 27, 2010. Treatments included fomesafen at 280, 350, 420, 560, and 840 g ai ha-1. Crop injury and weed control were assessed visually using a 0-100 linear scale in which 0 indicated no crop injury or weed control, and 100 indicated death of crop or total weed control. Plots were evaluated at 7, 14, 28, and 42 day after treatment. The crop was harvested on September 16, 2009 and September 30, 2010 and total yield per plot was determined. Symptoms of fomesafen injury at the 840 g ai ha-1 were observed at 7 and 14 DAT. However the crop recovered by 28 DAT and by 42 DAT no foliar symptoms were observed either year. Fomesafen at the highest rate provided acceptable annual grass, common purslane, and redroot pigweed control 42 DAT. Tomato yield was not different in plots treated with fomesafen in comparison to the weed free control plots. Registration of fomesafen herbicide would provide tomato growers an opportunity to control weeds caused by late emergence or poor initial control following a burndown herbicide application in tomato.


IMPACT OF GRAFTING ON TOMATO WEED MANAGEMENT. S. Chaudhari*, K. Jennings, D. W. Monks, F. Louws; NCSU, Raleigh, NC (35)

ABSTRACT

Field studies were conducted in 2012 and 2013 to determine the effect of herbicides on grafted tomato. Grafting treatments included non-grafted ‘Amelia’ and Amelia scion grafted onto ‘AnchorT’, ‘Beaufort’, or ‘Maxifort’ tomato rootstocks. Herbicide treatments included nontreated, and soil-applied S-metolachlor (0.8 and 1.06 kg/ha), fomesafen (0.28 and 0.42 kg/ha), metribuzin (0.28 and 0.55 kg/ha), napropamide (1.12 and 2.24 kg/ha), halosulfuron (0.039 and 0.052 kg/ha), and trifluralin (0.56 and 0.84 kg/ha). In 2012, at 1 and 2 wk after treatment (WAT) injury was greater in grafted plants regardless of rootstock type (AnchorT, Beaufort, Maxifort) than in non-grafted for halosulfuron, metribuzin, and fomesafen. However, by 4 WAT no injury was observed in grafted or non-grafted plants. In 2013, no injury was reported regardless of rootstock and herbicide treatment. Herbicide treatment had no effect on total and marketable fruit yield. Thus, growers can use the same herbicides for weed control in grafted tomato that is registered in non-grafted tomato. In 2013 and 2014, removal and establishment studies were conducted to determine critical period for weed control (CPWC) of grafted and non-grafted tomato. Grafting treatments included non-grafted Amelia and Amelia grafted onto Maxifort rootstock. In the establishment study, weeds were transplanted at 1, 2, 3, 4, 5, 6, and 12 wk after tomato transplanting (WAT) and remained until final tomato harvest. In the removal study, weeds were transplanted on the same day of tomato transplanting and removed at 2, 3, 4, 5, 6, 8, and 12 WAT. Each planting hole contained one grafted or non-grafted tomato plant and six weed seedlings including 2 yellow nutsedge, 2 common purslane and 2 large crabgrass. In grafted and non-grafted treatments, tomato plant biomass increased as establishment of weeds was delayed and tomato plant biomass decreased when removal of weeds was delayed. The delay in establishment and removal of weeds resulted in weed biomass decrease and increase of the same magnitude in grafting treatments, respectively. The predicted CPWC to avoid ≥ 5% yield reduction of marketable fruit in the presence of a mixed population of weeds was from 2.2 to 4.5 WAT in grafted tomato and from 3.3 to 5.8 WAT in non-grafted tomato. The length (2.3 or 2.5 wk) of CPWC in fresh market tomato was not affected by grafting, however, the CPWC begins and ends one week earlier in grafted tomato than non-grafted tomato.

 

 


IMPACTS OF LATE-SEASON TALL MORNINGGLORY INFESTATIONS ON CHILE PEPPER PRODUCTION. B. J. Schutte*; New Mexico State University, Las Cruces, NM (36)

ABSTRACT

Previous research indicated that pendimethalin control failures on tall morningglory generally increased in response to increasing population density in tall morningglory seedbanks.  Although these results suggest that pendimethalin control outcomes in chile pepper production can be improved by reducing the number of tall morningglory seeds in soil, farmer adoption of a novel seedbank reduction strategy is likely to require more specific information on the consequences of changes in soil seedbank density.  The overall objective of this study was to develop functional relationships for the intrinsic connections between tall morningglory seedbank density and time requirements for both hoeing and hand harvesting.  To accomplish this objective, chile pepper was grown at a university research farm near Las Cruces, NM using irrigation, soil management and pest management practices typical for the region.  At the time of crop thinning (9.5 weeks after planting), tall morningglory infestations were seeded and sections of the study area were sprayed with pendimethalin at 1.6 kg ai ha-1.  Consistent with previous research at this site, 3 to 5% of the added tall morningglory seeds produced seedlings in the presence of pendimethalin.  Hoe efforts to remove the emerged tall morningglory plants were not influenced by pendimethalin.  Each additional tall morningglory plant increased the time required to hoe 10 m of row by 3.6 s and decreased the amount of chile pepper harvested in 1 min by 11 g (fresh weight). Pendimethalin did not influence the effects of tall morningglory on harvest time.  Combined with knowledge of the percentage of buried seeds that produce seedlings that escape control, the results of this study can be used to communicate specific consequences of changes in population density in tall morningglory seedbanks.


NATURAL WEED CONTROL PRODUCTS FOR ORGANICALLY GROWN VEGETABLES. J. O'Sullivan*1, R. C. Van Acker2, R. D. Grohs1; 1University of Guelph, Simcoe, ON, 2University of Guelph, Guelph, ON (37)

ABSTRACT

Demand for organic food has grown tremendously throughout the developed world. Weed control remains the most significant agronomic problem associated with organic crop production. There is a need for more effective weed management in organic crop production. Developing new natural weed control products with superior weed management properties to control or effectively suppress weeds will help the organic crop production industry remain competitive and sustainable into the future. The objective of this research was to evaluate the weed control potential of bioactive, non-synthetic, natural products for the management of weeds in organic crop production and to provide weed control efficacy, synergy and crop safety data on improved, lower-risk herbicides that are appropriate for use by organic growers. Field experiments were conducted at the Simcoe Research Station, Simcoe, Ontario, in 2014. Plots were arranged in a randomized complete block design with 4 replications. Plot size was 1.5m X 15m. Herbicides were applied at 1000 L ha-1 with CO2-pressurized back-pack sprayer @ 240 k pa. There was no crop injury from any treatment. POST treatments of manuka oil, at 1 and 2% v/v, gave 29 and 69% weed control, respectively. Weed control with manuka oil, tank mixed with Weed Zap or Weed Pharm gave about 85% control and gave a level of weed control that was comparable to the weed-free control. This was a 6 to 20% improvement in weed control, compared to each product used alone. Finalsan at 8.4 and 16.6% v/v gave 73 and 93% weed control, respectively. All treatments gave significantly improved pepper and sweet corn yields, compared to the weedy control.The synergy associated with tank-mix applications of manuka oil with currently approved essential oils and acetic acid was demonstrated. Manuka oil is the first natural product herbicide that has soil activity, systemic and, when mixed with other approved products, enhances their weed control activity. This synergy has the potential to significantly improve weed management and will help growers to find solutions to the long standing issue of managing weeds in organic crop production. This will help address the limitations of currently-approved organic herbicides and will provide organic growers with environmentally and economically sustainable alternatives to synthetic chemical herbicides. 

 

 


EFFECT OF GREEN MANURE AND COVER CROPS FOR WEED AND DISEASE MANAGEMENT IN TULIP. Y. Duan*1, G. A. Chastagner2, A. Debauw2, T. W. Miller3; 1Washington State University, Pullman, WA, 2Washington State University, Puyallup, WA, 3Washington State University, Mount Vernon, WA (38)

ABSTRACT

Tulip is grown on over 400 acres in western Washington, representing 76% of U.S. tulip production. Growers currently rely primarily on pesticides for weed and disease management. However, pesticide applications are sometimes limited by proximity to sensitive areas and products are sometimes inadequate. To better control weeds and diseases in tulip production as well as potentially reducing pesticide reliance, green manures and cover crops consisting of cereal rye, green pea, or mustard were tested in western Washington. Green manures combined with or without glyphosate application prior to incorporation were tested in a commercial field trial. During the two and half years of study, weed biomass before cover crop termination was not affected by cover crop treatment. Flower quality also did not differ among cover crop treatments. Tulip grown after the glyphosate-treated mustard cover crop produced 92% of marketable bulbs, which ranked the lowest among all treatments. In a separate field trial, cover crops were seeded either in early July or early August, treated with glyphosate, and either incorporated or left on the soil surface prior to tulip bulb transplanting. Mustard seeded in July produced 77% more biomass than when seeded in August in 2013 and 29% more in 2014, while the rye and pea mixture produced 48 and 11% more biomass when seeded in July than when seeded in August in 2013 and 2014, respectively. Before cover crops were terminated, weed biomass was suppressed by at least 69% and 98% in 2013 and 2014, respectively. Tulip foliar biomass at the 2013-14 bulb harvest was reduced significantly by the pathogen, Botrytis tulipae, although August-seeded rye and pea and July-seeded mustard suppressed tulip foliar damage from that fungal pathogen. Average bulb yield was also reduced by Botrytis tulipae and only August-seeded rye and pea prevented this bulb loss.


SOIL SOLARIZATION, MICROWAVES, AND MUSTARD SEED MEAL TREATMENTS FOR WEED CONTROL IN ANNUAL STRAWBERRY PRODUCTION. J. Samtani1, J. Derr*1, C. Johnson2, M. Conway1, L. Darnell2, A. Rana1, R. Flanagan3; 1Virginia Tech, Virginia Beach, VA, 2Virginia Tech, Blackstone, VA, 3Virginia Cooperative Extension, Virginia Beach, VA (39)

ABSTRACT

Studies were initiated in the 2013-14 growing season at the Hampton Roads Agricultural Research and Extension Center (HRAREC) at Virginia Beach, VA, and the Southern Piedmont Agricultural Research and Extension Center (SPAREC) at Blackstone, VA, to evaluate certain non-fumigant treatments for their efficacy on weed control and impact on crop yields in annual plasticulture strawberry (Fragaria × ananassa Duchesne) production. At HRAREC, pre-plant treatments included 1,3-dichloropropene plus chloropicrin (40:60 by weight) shank fumigated at 220 kg ha-1 on broadcast basis, 6 week and 4 week soil solarization (SS) treatments, 4 week SS treatment replaced with Virtually Impermeable Film (VIF) tarp at planting, microwave treatment, and an untreated control. A custom-built 3.6 KW microwave radiations applicator was used to heat the top 5 cm of soil to 66 C. Two portable generators were used to power the microwave radiations applicator and two thermometers were used to measure soil temperature.  At SPAREC, pre-plant treatments included 1,3-dichloropropene plus chloropicrin (40:60 by weight) shank fumigated at 188 kg ha-1 on a broadcast basis, 8 week and 4 week SS,  mustard seed meal (MSM) pellets at 1,120 kg ha-1 applied 8 and 4 weeks prior to planting,  8 week SS + MSM pellets, and 4 week SS + MSM at 1,120 kg ha-1. SS treatments were covered with 1 mL clear polyethylene tarp and non-solarization treatments were covered with 1.25 mL VIF tarp at both sites. Following completion of the pre-plant treatments, strawberry ‘Chandler’ was planted at 36 cm in-row spacing on 4 Oct. at HRAREC, and on 2 Oct. 2013 at SPAREC, in 4.6 m long bed plots. Commercial production practices were followed throughout the growing season. Weed density counts were taken periodically through the growing season on bed tops in a 1.5 m long sample area. At HRAREC, plots treated with 6 week SS had the numerically lowest weed density but was not significantly different from the 4 week solar treatment and the microwave treatment. At SPAREC, plots treated with 8 week SS + MSM treatment had the numerically lowest weed density but not significantly different from 4 week and 8 week MSM treatments and 8 week SS treatment. There was no significant difference in crop yield among treatments at both sites, suggesting that pest populations may not have been high enough to impact crop yield.

 

 


INFLUENCE OF PLANTING DATE AND ROW WIDTH ON QUINOA AND GRAIN AMARANTH YIELD IN ONTARIO, CANADA. R. E. Nurse*, E. R. Page; Agriculture and Agri-Food Canada, Harrow, ON (40)

ABSTRACT

Quinoa (Chenopodium quinoa) and grain amaranth (Amaranthus hypochondriacus) are generating interest among growers and industry for production as crops in Southwestern and Southern Ontario.  However, there are few data related to the agronomy of these crops in Ontario. Therefore, two field trials were established at Harrow, ON in 2013 and 2014 to evaluate 1) planting date and 2) row width effects on and quinoa and grain amaranth growth and yield.  Brightest Brilliance and Burgundy were the varieties seeded for each crop, respectively.  Each trial consisted of a six planting date’s spaced 2 weeks apart with the first planting date starting in May.  The first trial was seeded with rows spaced 38 cm apart and in the second trial rows were spaced 75 cm apart.  Weed height and biomass was recorded in each treatment at 56 DAE and grain yield was measured at maturity.  Generally, crop biomass was highest when each crop was seeding at 75 cm row spacing in comparison to 38 cm.  There was an effect of row spacing on yield for both species.  Yields were highest when the crop was seeded at 75cm for grain amaranth and 38cm for quinoa.  The highest yields were measured in the first two planting dates (May) and yield decreased with the later planting dates.  These data may now be used to tailor integrated weed management options for each crop.                  


A 3D VIEW OF WEEDS IN HORTICULTURAL CROPS. B. Panneton1, A. Bizeau2, M. Simard*1; 1Agriculture and Agri-Food Canada, Saint-Jean-sur-Richelieu, QC, 2Universit de Sherbrooke, Sherbrooke, QC (41)

ABSTRACT

In many horticultural crops, weeding is challenging due to the limited availability of herbicides and the difficulty of implementing mechanical weed control. As a result, hand weeding is still routinely performed. This is time consuming and requires a lot of manpower. Robotic weeding could replace hand weeding. One of the key requirements for a robot to perform properly is the ability to use vision systems to discriminate crop from weeds. Color, near infrared (NIR) imagery coupled to plant height could all serve as inputs for algorithms aim at discriminating weeds from crop. To acquire such date, we developed an image acquisition platform for field use. It is based on two digital cameras. One is a standard color camera and the other is a modified sibling where the infrared filter has been removed and a notch filter was installed to block red light. In the blue and green channels, this modified camera captures the same information as the standard camera but its "red" channel now acquires NIR signal only. This pair of cameras opens the door to high definition stereo imaging. This was implemented and it was shown that good quality 3D images can be produced. The main challenge is dealing with noise when computing disparity maps. However if the objective is to estimate plant height, a fair amount of noise can be tolerated without affecting the result significantly. 


COMMON CRABGRASS PRE-CONTROL IN MIXING OF KENTUCKY BLUEGRASS AND RYEGRASS. C. Li*, G. Xue; East China Weed Technology Institute of Nanjing, Nanjing, Peoples Republic (42)

ABSTRACT


INFLUENCE OF NITROGEN FERTILIZATION AND IRRIGATION ON WHITE CLOVER INVASION IN KENTUCKY BLUEGRASS TURF. D. W. Morishita*1, K. G. Frandsen1, T. Salaiz2; 1University of Idaho, Kimberly, ID, 2McCain Foods, Aberdeen, ID (43)

ABSTRACT

White clover is one of the most commonly found weeds in turf and persists under mowed conditions. Common herbicides, such as dicamba or triclopyr, can successfully control white clover if applied at correct timings and rates. However, little scientific research exists which specifically evaluates nitrogen (N) fertility and irrigation management practices as a control method to reduce white clover in a turfgrass stand. Most turfgrass weed research evaluates weed control on weed species in the soil seed bank at the location where the research is conducted. Research was conducted from 2012 through 2014 to specifically evaluate white clover invasion and management under varying nitrogen fertility and irrigation regimes based on evapotranspiration (ET). The N rates were 0, 2.4, 4.9 and 7.3 g of N m-2. Irrigation treatments were established by watering to meet 70, 90 and 110% ET for turf. The experimental design was a split block randomized complete block with three replications. Irrigation treatment was the main plot and N rate was the sub-plot. Clover counts were the highest for the 0 and 2.4 g m-2 N treatments while clover counts were lowest for the 4.9 and 7.3 g m-2 N treatments. In 2014, other weed species began establishment in the study site. Common dandelion density was highest in the 0 g N rate and also higher in the 110% ET irrigation treatment compared to 70 and 90% ET. Field bindweed density was higher or at least tended to be higher with the two higher N rates. This was especially true early in May and June. Differences in turfgrass color relative to N treatment were observed in all months except August and September. Color and quality ratings were similar in that generally the 0 g N rate had the lowest color and quality ratings and the 7.3 g N rate had the highest ratings. Generally, irrigation treatment was not shown to have a significant effect on clover encroachment or persistence.

 


COMMON POLYPOGON POST-CONTROL IN SEASHORE PASPALUM. G. Xue*, C. Li; East China Weed Technology Institute of Nanjing, Nanjing, Peoples Republic (44)

ABSTRACT

Rabbitfoot polypogon (Polypogon monspeliensis) Post-control in Seashore Paspalum

 

Xue. Guang1 and Li Chunyan

East China Weed Technology Institute, Nanjing, China

 

Field studies were conducted during 2012 to 2014 at Hill view Golf Courses in Zhejiang province, China, to determine the Rabbitfoot polypogon (Polypogon monspeliensis) post-control in Seashore Paspalum with sulfosulfuron,tralkoxydime,chlorimuron-ethyl and chlortoluron. Seashore Paspalum (cv. Salum) tolerance was also evaluated. Rabbitfoot polypogon control with sulfosulfuron at 0.135 kg ai ha-1, tralkoxydime at 0.64 kg ai ha-1,chlorimuron-ethyl at 0.3 kg ai ha-1 and chlortoluron at 1.125 kg ai ha-1 was 69%,82%,67% and 29% in 2012. No injuring to Seashore Paspalum (cv.Salum) occurred with tralkoxydime at 0.64 kg ai ha-1 and chlortoluron at 1.125 kg ai ha-1 1-4 WAT. Slight injuring to turf was appeared 2-3 WAT and disappeared 4 WAT with chlorimuron-ethyl at 0.3 kg ai ha-1.Visible serious injuring to turf at 2-4 WAT with sulfosulfuron at 0.135 kg ai ha-1 in 2012.

 

Rabbitfoot polypogon control with sulfosulfuron at 0.1 kg ai ha-1, tralkoxydime at 0.96 kg ai ha-1,chlorimuron-ethyl at 0.45 kg ai ha-1 and tralkoxydime 0.48 kg ai ha-1+chlorimuron-ethyl 0.25 kg ai ha-1 was 66%,87%,76% and 89% in 2013. No injuring to turf occurred with tralkoxydime at 0.96 kg ai ha-1 and tralkoxydime 0.48 kg ai ha-1+chlorimuron-ethyl 0.25 kg ai ha-1. Visible injuring to turf was appeared 2-4 WAT with chlorimuron-ethyl at 0.45 kg ai ha-1.Visible injuring to turf at 2-3 WAT and disappeared 4 WAT with sulfosulfuron at 0.1 kg ai ha-1 in 2013.

 

With tralkoxydime at 0.32 kg ai ha-1, 0.64 kg ai ha-1,0.96 kg ai ha-1, and tralkoxydime 0.64 kg ai ha-1+chlorimuron-ethyl 0.2 kg ai ha-1,with surfactant #885 at 0.2% v/v in all above 4 treatments, Rabbitfoot polypogon control was 68%,91%,99% and 100% in 2014. No injuring to turf occurred with tralkoxydime at less than 0.96 kg ai ha-1. Slight injuring to turf was appeared 2 WAT with tralkoxydime 0.64 kg ai ha-1+chlorimuron-ethyl 0.2 kg ai ha-1+surfactant at 0.2% v/v in 2014.

 

Additional index word  Rabbitfoot polypogon (Polypogon monspeliensis) post-control; Seashore Paspalum vaginatum

Abbreviation: WAT, weeks after treatment.

 

1Associated Researcher, East China Weed Technology Institute, Nanjing, jiangsu ,210007,China
E-mail:xuegnj@sina.com

 

 


EFFECT OF PENDIMETHALIN APPLICATION ON SEASHORE PASPALUM AFTER CORING OPERATIONS. Q. Ma*; Weed Technology Institute of East China, Nanjing, Peoples Republic (45)

ABSTRACT


TURFGRASS SPECIES RESPONSE TO THREE HPPD-INHIBITING HERBICIDES. J. R. Brewer*1, J. Willis2, S. Askew1; 1Virginia Tech, Blacksburg, VA, 2Monsanto, Florissant, MO (46)

ABSTRACT

Turfgrass Species Response to Three HPPD-inhibiting Herbicides

 

J.R. Brewer, J.B. Willis, S.D. Askew

 

One of the newest site-of-action groups, 4-hydroxyphenylpyruvate dioxygenase-inhibitors (HPPD), has become an effective herbicide group to control many troublesome and resistant weeds in turfgrass. This inhibition of HPPD produces the well known bleaching effects seen in treated weeds that results in plant death. Three highly used active ingredients of the HPPD-inhibiting herbicide group includes: mesotrione, topramezone, and tembotrione. Out of the these three herbicides only mesotrione has had sufficient research conducted to evaluate the tolerance of different turfgrass species  to the herbicide, while topramezone has few published studies and tembotrione only has one. The first objective of our research was to test the turf tolerance of different species to topramezone and tembotrione, while using mesotrione as a comparison treatment. The second objective was to test the weed control efficacy of tembotrione and topramezone compared to mesotrione.

 

Six different turfgrass species were evaluated for tolerance including: bermudagrass (Cynodon dactylon), zoysiagrass (Zoysia japonica), creeping bentgrass (Agrostis stolonifera), Kentucky bluegrass (Poa pratensis), perennial ryegrass (Lolium perenne), and tall fescue (Lolium arundinaceum). Twelve separate trials were conducted to evaluate response of each of the six turfgrass species each in two different years. The first six trials were conducted in 2007 and each trial was repeated in 2014.  Herbicides included topramezone at 18.4, 36.8, and 55.2 g ai/ha-1; tembotrione at 138, 276, and 414 g ai/ha-1; and mesotrione at 280 g ai/ha-1. Each of these herbicide and rate combinations was applied once or twice for a total of 14 treatments plus a nontreated check. All treatments included NIS and sequential applications were applied 3 weeks after initial applications. Herbicides were applied with a CO2 powered hooded sprayer at 280 L/ha-1

 

When averaged over herbicide rates, tembotrione injured all turfgrasses except zoysiagrass more than topramezone based on area under the progress curve for visually-estimated injury. Tembotrione at 276 g/ha injured all turfgrasses equivalent to or more than mesotrione at 280 g/ha. Topramezone at 36.8 g/ha injured bermudagrass and zoysiagrass more than other herbicides but was equivalent to the least injurious herbicide for all other turfgrasses. Area under the progress curve for turfgrass injury increased for all turfgrasses when herbicides were applied twice compared to when applied only once. We can also conclude from the trial that sequential applications of all three herbicides will significantly increase the injury to all six turfgrass species. Injury ratings also exhibited significant increases as the rate went up on all three herbicides, and this was demonstrated in all six turfgrass species. The cool season grasses, excluding creeping bentgrass, typically demonstrated less injury to the HPPD-inhibiting herbicides then warm season grasses except for the injury caused by tembotrione and mesotrione on zoysiagrass, which was not significantly higher than injury found on the cool season turf grasses. Weed control efficacy was compared between the three herbicides based on area under the progress curve for visually-estimated control. None of the three herbicides had significantly higher control of smooth crabgrass (Digitaria ischaemum), but tembotrione had significantly higher control of buckhorn plantain (Plantago lanceolata) when compared to topramezone and mesotrione. The control of smooth crabgrass was significantly higher than the control of buckhorn plantain throughout the trials.

 


PESTICIDE PERSISTENCE AND BEHAVIOR IN TURFGRASS CLIPPINGS. M. Jeffries*, T. Gannon, K. Ahmed; NCSU, Raleigh, NC (47)

ABSTRACT

While turfgrass management practices are commonly performed to prevent off-target clipping transport, under certain conditions it is an inevitable occurrence.  Previous research has shown herbicide residues within clippings from previously treated turfgrass may become bioavailable as they decompose, potentially causing adverse effects on terrestrial and aquatic fauna/flora.  Field research was conducted to quantify pesticide residues in clippings from various turfgrass species.  A subsequent controlled-environment experiment was conducted to measure pesticide desorption from clippings into water.

Field research was conducted (Raleigh, NC) to quantify pesticide residues in clippings from three turfgrass species collected at various times after treatment.  Turfgrass species included hybrid bermudagrass (Cynodon dactylon L. x C. transvaalensis), tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] and zoysiagrass (Zoysia japonica Steud.) maintained at 5, 8 and 5 cm, respectively.  In short, 2,4-dichlorophenoxyacetic acid (2,4-D) and azoxystrobin were applied at 1.6 or 0.6 kg ai ha-1, respectively, to unique plots with a CO2-pressurized, three-nozzle boom calibrated to deliver 815 L ha-1 at 32, 16, 8, 4, 2, 1 or 0 d before clipping collection (DBCC).  From 32 to 5 DBCC, clippings were returned to all plots with a self-propelled rotary mower, and plots were not mown between 4 and 0 DBCC.  At 0 DBCC, pesticide treatments were applied and allowed to dry for 2 h before clipping collection occurred.  Clippings were collected from each experimental unit in a plastic-lined self-propelled rotary mower bag, homogenized, milled and subsampled to determine pesticide concentrations with high performance liquid chromatography–diode array detector (HPLC-DAD) methods.  Following turfgrass clipping collection, a controlled-environment experiment was conducted to evaluate pesticide desorption from previously-treated turfgrass clippings into water over time.  Water was collected from a local source (Raleigh, NC) with nondetectable 2,4-D and azoxystrobin concentrations.  At experiment initiation, 20 g clippings were mixed with 150 mL water in unique amber polyethylene containers (946 cm3).  Water samples (20 mL) were collected 2, 4, 8 and 16 days after clippings application to water (DACAW) and pesticide concentrations were determined with HPLC-DAD methods.

            Pesticide-clipping residue retention varied between compounds and species.  Overall, bermudagrass clippings (2 – 42% of the applied) had similar or greater pesticide residues than tall fescue (0 – 33%) or zoysiagrass (0 – 27%).  Further, residues in zoysiagrass were less than tall fescue at most clipping collection dates.  Differences between species suggests uptake, translocation and metabolism may vary, which may make certain turfgrass species less likely to transport pesticides away from the intended site via clipping displacement.  Pesticide concentrations in turfgrass clippings declined from 0 to 32 DBCC, with detectable residues of both compounds at 32 DBCC.  Overall, pesticide residues were detected in all water samples collected, confirming 2,4-D and azoxystrobin desorb from turfgrass clippings.  At most sampling dates 2,4-D and azoxystrobin desorbed into water from clippings similarly across turfgrass species.  Pooled over species, 2,4-D desorbed more than azoxystrobin.  At 4 DACAW, 2,4-D desorption from 2 DBCC clippings averaged 30% compared to 7% for azoxystrobin.  This is likely due in part to chemical properties that influence desorption from plant tissue into an aqueous environment differing between 2,4-D and azoxystrobin.

Data suggest pesticide residues in turfgrass clippings and subsequent desorption into aqueous systems is both pesticide- and species-dependent.  Overall, pesticide residue in turfgrass species ranked bermudagrass > tall fescue > zoysiagrass; while pesticides ranked 2,4-D > azoxystrobin.  In general, 2,4-D and azoxystrobin desorption from turfgrass clippings was not species or DBCC dependent.  Further, while a similar proportion of pesticide within turfgrass clippings desorbed into water across DBCC, the actual pesticide-water concentrations increased as DBCC decreased due to the vegetation having a relatively higher residue concentration.  This research will improve our knowledge of clipping management practices following applications of two commonly applied pesticides to three turfgrass species widely utilized in the United States.  By doing so, best management practices may be developed to avoid off-target environmental impacts associated with pesticide residues in turfgrass clippings. 


DOES ANNUAL BLUEGRASS INFLUENCE GOLF BALL DECELERATION AND TRAJECTORY ON PUTTING GREENS? S. S. Rana*, S. Askew, J. R. Brewer; Virginia Tech, Blacksburg, VA (48)

ABSTRACT

It is often speculated that annual bluegrass (Poa annua) infestation on putting greens can impact ball roll distance and trajectory.  Research at Virginia Tech showed that golf balls rolled 0.3 m less when putting greens were infested with over 50% annual bluegrass compared to methiozolin-treated turf with less than 15% infestation.  The ability to remove annual bluegrass from putting surfaces may increase interest in surface smoothness evaluation.  Several devices are now being marketed to golf superintendents for evaluating putting surface smoothness and ball roll distance and trajectory but few research studies have tested these devices for effects other than ball roll distance.  In addition, most studies suggest that statistical differences in ball roll distance are usually attributed only to treatments that create large differences.  Our hypothesis is that potential effects of annual bluegrass on ball roll distance and trajectory will be too small to measure with commercially-available devices.  Laboratory studies were conducted in 2014 at the Glade Road Research Facility at Virginia Tech to select among 6 devices and 13 gall ball types for consistency of distance and trajectory.  The ball roll devices used in the experiment included three commercially-available devices: USGA stimpmeter (US), Pelzmeter (PM), and Greenstester (GT); and three custom prototypes built at Virginia Tech: Putting Robot (PR) and two devices that used curvilinear inclined planes with a flexible ramp (FR) and carpet ramp (CR) designed to reduce golf ball oscillation.  Thirteen golf balls were selected based on use by both pro and entry level golfers covering almost all possible dimple patterns/designs and sizes.  The experiment was arranged as a split-plot design with 6 ball-roll-device main plots and 13 golf-ball-type sub-plots.  Each of the 13 golf balls were rolled 20 times with each of the six ball roll devices and repeated three times for a total of 4680 rolls.  A synthetic 11.5-stimp carpet manufactured for home-lawn putting greens was positioned on a leveled bench and brushed between each ball roll to control for legacy effects.  Ball dispersion was measured by identifying pixel coordinates of each ball from digital images analyzed in SigmaScan Pro software.  Skewness (deviation from expected trajectory) and distance of each ball resting position was analyzed using SAS 9.2 with sums of squares partitioned to reflect effects of ball roll device and ball type.  When averaged over golf balls, custom prototypes (PR being the best) were more consistent (3.02 to 3.63 cm skew) than commercially available ball roll devices (4.34 to 6.20 cm skew).  Although each ball roll device was calibrated to putt consistently at 3.5 m, there was a device by ball interaction for distance.  This interaction was possibly arising because of PR being very consistent within the ball type but most variable among different golf ball types.  Ability of PR to eliminate oscillation effects and inherent defects in linear or curvilinear devices mentioned above makes it the most consistent ball roll device within a given ball type.  Future efforts to measure influence of annual bluegrass on a golf ball deceleration and trajectory will utilize PR and TaylorMade TPX golf ball based on results of the laboratory study.

 


TOPRAMEZONE TIMING AND RATE FOR BERMUDAGRASS SUPPRESSION IN BENTGRASS PUTTING SURFACES. J. D. McCurdy*; Mississippi State University, Starkville, MS (49)

ABSTRACT

Bermudagrass (Cynodon spp.) control within creeping bentgrass (Agrostis stolonifera L.) putting greens is challenging. Chemical control options are limited due to the potential for bentgrass injury. Single and sequential applications of siduron have been shown to effectively control or suppress bermudagrass without injury to desired bentgrass turf; however, control may be inconsistent. Topramezone inhibits the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD) and is registered for the control of bermudagrass and other warm-season grass weeds within select turfgrasses, including centipedegrass, Kentucky bluegrass, fine and tall fescue, as well as perennial ryegrass. Bentgrass tolerance has been reported to be variable; therefore, study objectives were to evaluate rate and timing of topramezone summer applications for bentgrass safety and bermudagrass control.

Research was conducted on a putting green constructed according to USGA specifications at the Mississippi State University R.R. Foil Plant Science Research Center near Starkville, MS. Two identical studies were replicated on adjacent putting surfaces, which were TifEagle bermudagrass or an A1/A4 blended creeping bentgrass green mown daily at 3.8 mm mowing height. Herbicides were applied with a CO2 pressurized backpack sprayer in a water carrier volume of 280 L/ha. Studies were arranged as randomized complete blocks (3) with a two by four factorial (treatment date by herbicide). Experimental units were 1.0 m2. Treatments were applied sequentially three weeks apart at two application timings, either July 1 and 22 (application A and B) or August 15 and September 5 (application C and D). Herbicide treatments were: topramezone (Pylex®, BASF Corporation, Research Triangle Park, NC) at 12.3, 24.5, and 36.8 g ai/ha, including 0.5% methylated seed oil, and siduron (Tupersan®, PBI/Gordon Corporation, Kansas City, MO) at 18.3 kg ai/ha. Bermudagrass control and bentgrass injury were assessed visually 3, 7, and 14 days after treatment (DAT) on a 0 to 100% scale (0% = no visible injury/control; 100% = complete turfgrass death). Statistical analysis was performed using SAS procedure GLMMIX. Data were subject to analysis of variance. Means were separated using Fisher’s protected LSD (α = 0.05). Means differed due to treatment, application timing, and interaction effects. Results observed 14 DAT are discussed by application timing.

When assessed 14 days after application A (DAA), bermudagrass control was 10, 22, and 37%, respective to increasing topramezone rates, while siduron control of bermudagrass was 67%, which was greater than that of all other treatments. Creeping bentgrass injury was less than 2% across all treatments. Only bentgrass treated with topramezone at 36.8 g/ha retained injury greater than that observed in the non-treated. When assessed 14 days after application B (DAAB) of the AB sequential treatment, topramezone controlled bermudagrass 25, 30, and 52%, respective to increasing rates. Siduron controlled bermudagrass 71%, which was equaled only by the highest rate of topramezone. Bentgrass injury was less than 10% for all treatments.

Topramezone injury to bentgrass was between 35 and 43%, across topramezone rates, when observed 14 days after application C (DAC). Siduron injury to bentgrass (31%) was similar to that of all rates of topramezone. The lowest rate of topramezone failed to control bermudagrass when compared to the non-treated (only 20% control), while the 24.5, and 36.8 g/ha rates were only slightly higher, at 35 and 48% control, respectively. When observed 14 days after application D (DACD) of the CD sequential treatment, topramezone injury to bentgrass was unacceptable (between 58 and 77%), while siduron injury to bentgrass was 43%. Topramezone controlled bermudagrass 65, 77, and 83%, while siduron controlled bermudagrass less than all other treatments (43%).

Season long bermudagrass control was less than 15% for all AB sequential applications and less than 30% for CD sequential applications when assessed on October 15, 2014. In general, topramezone injury to bentgrass was acceptable (less than 20% injury and/or stand loss) during the AB sequential series; however, it was unacceptable (greater than 20%) during the CD sequential series. Conditions were warmer during the second sequential series of this study. It is believed that symptoms of topramezone and siduron application were exaggerated on bentgrass for this reason; however, bermudagrass injury was similar across series. Since bermudagrass overcame topramezone and siduron injury symptoms, it seems unlikely that bermudagrass was suppressed to an extent that bentgrass might succeed in its place during summer removal. Future research must evaluate spring and fall topramezone application timing for bermudagrass control while limiting bentgrass injury. 

 

 

 


UTILIZING INDAZIFLAM FOR ROADSIDE WEED CONTROL IN GEORGIA. P. McCullough*; University of Georgia, Griffin, GA (50)

ABSTRACT

Field experiments were conducted to evaluate the efficacy of indaziflam for weed control on roadsides in Griffin and Jackson, GA.  Treatments were applied in September or November at both sites and evaluations were carried out until the following April.  In bermudagrass, indaziflam at 52 and 73 g ai/ha applied at both timings provided good (80 to 89%) to excellent (90 to 100%) control of buckhorn plantain and Italian ryegrass.  In tall fescue, September applications of aminopyralid at 88 g ai/ha provided poor control (<70%) of buckhorn plantain, but indaziflam alone at 52 or 73 g ai/ha or in tank-mixtures with aminopyralid provided 100% control after 8 weeks.   Aminopyralid applied in September provided poor control of catsear dandelion, but tank-mixtures with indaziflam improved control to 100%.  Indaziflam alone did not control catsear dandelion or wild garlic.  Tall fescue injury was not detected from indaziflam alone or in tank-mixtures with aminopyralid.  Results suggest indaziflam alone has excellent activity for controlling ryegrass and buckhorn plantain.   Tall fescue tolerance to indaziflam was excellent and warrants further investigation under roadside conditions.  

 


KUDZU CONTROL OPTIONS: INITIAL EVALUATION. J. Omielan*1, D. Gumm2, M. Barrett1; 1University of Kentucky, Lexington, KY, 2Kentucky Transportation Cabinet, Jackson, KY (51)

ABSTRACT

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

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

All the treatments had kudzu control greater than 92% 32 DAT.  However by 62 DAT control with Patron 170 had declined to 72%.  Green vegetative cover 62 DAT ranged from 63 to 100% for most treatments except for Streamline with only 13% green cover.  Final assessments will be done in 2016.  There are a number of herbicide options which are selective and effective in kudzu control.


THE IMPACTS OF IMAZAPIC ON ALLIARIA PETIOLATA AND NON-TARGET FOREST FLOOR PLANTS IN CENTRAL KENTUCKY. P. Podapati*; University of Kentucky, Lexington, KY (52)

ABSTRACT


PERFORMANCE OF INVASIVE SWALLOWWORT JUVENILES (VINCETOXICUM SPP.) ACROSS A HABITAT GRADIENT AFTER 7 YEARS. L. R. Milbrath1, A. DiTommaso*2, J. Biazzo1, S. H. Morris2; 1USDA-ARS, Ithaca, NY, 2Cornell University, Ithaca, NY (53)

ABSTRACT

Vincetoxicum rossicum, pale swallowwort [PSW], and V. nigrum, black swallowwort [BSW] are two non-native perennial vines that are increasingly problematic in many regions of the northeastern U.S. and southern Canada.  The two species can grow in full sun or shaded forest understories, and infest a variety of habitats from agricultural to natural areas. Establishment and growth of vegetative juveniles may be an especially critical phase in the life cycle of plants and may be targeted for control of invasive species if this stage is important for population growth. We established a long-term field experiment in fall of 2007 to assess survival and growth of early-stage swallowworts in three different habitat types: an old field [high light], a forest edge [transition zone] and forest understory [low light] at a central New York State location where both species are present in the region although not at the experimental site.  The two swallowwort species were established from seed in a split plot design with habitat type as the whole plot treatment, swallowwort species as the subplot treatment, and 10 blocks for a total of 60 subplots.  From an initial cohort of 40 seedlings per subplot, survival and growth (i.e. height, time to first flower and pods, pod and seed production) of these plants have been monitored annually. From an initial 96% survival after one season of growth (2008), percentage survival of juvenile swallowworts decreased by 51-78% in the different habitats after two seasons. By the seventh year (2014), the survival rate of juveniles was 8.2 ±2.4% (field), 6.5 ±2.1% (ecotone), and 0.6 ±0.7% (forest).  Apart from the first year, BSW survival was greater than PSW every year, averaged across habitats. Also, juvenile BSW plants generally remained at least two times taller than PSW in all habitats. However, the two species were more similar in height after the fourth
year in the forest and forest edge habitats. A few BSW plants in the field flowered without producing seed in their second and third year of growth, but subsequently most plants flowered and produced seed within the same season. To date, BSW plants (field only) have required 5.0 ±0.4 and 5.3 ±0.5 years post-establishment to flower and produce seed, respectively (n= 85). Reproductive BSW had 105.3 ±20.4 cm long stems, a root dry mass of 4.5 ±1.0 g, and 3.3 ±1.4 pods with 7.5 ±1.0 viable seed per pod (several samples still being processed). Only three PSW plants from the field habitat have become reproductive in their sixth or seventh year. Reproductive PSW had 88.3 ±15.0 cm long stems and 7.7 ±5.1 pods (samples still being processed).  The low survival observed in this study may be due to both a dense cover of resident vegetation in the old field and leaf litter in the forest as well as wetter conditions than swallowwort tolerates. Also, this research confirms that BSW can reproduce earlier compared with the relatively longer juvenile phase for PSW.


ENLIST 360 EDUCATION SERIES: EDUCATION, TRAINING AND OUTREACH ON THE ENLIST WEED CONTROL SYSTEM. D. E. Hillger*1, A. Asbury2, R. Keller3, J. Laffey4, R. Lassiter5, J. Siebert6, J. Wiltrout7; 1Dow AgroSciences, Noblesville, IN, 2Dow AgroSciences, Dahinda, IL, 3Dow AgroSciences, Rochester, MN, 4Dow AgroSciences, Maryville, MO, 5Dow AgroSciences, Raleigh, NC, 6Dow AgroSciences, Greenville, MS, 7Dow AgroSciences, Indianapolis, IN (54)

ABSTRACT

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 DuoTM 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 retailers technology advancements, management recommendations and resources, and education and training.   A series of training activities, offered through a variety of delivery methods, were continued in 2014 to educate growers, ag retailers and applicators on the responsible use of the Enlist™ system. Participants learned how to minimize the potential for off-target movement, principles to promote weed resistance management practices, and biotechnology trait stewardship practices.  Dow AgroSciences is committed to responsibly commercializing the Enlist Weed Control System and to sustain its longevity.


HERBICIDE INJURY SYMPTOMS ON HORTICULTURAL CROPS – AN IN-SERVICE TRAINING FOR NC COOPERATIVE EXTENSION AND DEPARTMENT OF AGRICULTURE STAFF. J. C. Neal*1, K. Jennings1, B. Lassiter2, W. Mitchem3; 1NCSU, Raleigh, NC, 2NC Dept of Agriculture and Consumer Services, Raleigh, NC, 3NCSU, Mills River, NC (55)

ABSTRACT

Impending registration of auxinic herbicides for use on GMO row crops has led to increased concerns about herbicide spray drift injury to nearby non-GMO crops, especially susceptible horticultural crops.  However, few diagnostic or educational resources are available to cooperative extension and department of agriculture staffs who are often the “first responders” when herbicide injury is suspected.  In 2014 an in-service training program on herbicide injury symptom diagnosis was conducted for NC Cooperative Extension (CES) agents and NC Department of Agriculture (NCDA) inspectors. The training included a combination of lectures on herbicide modes of actions and symptoms of injury, field demonstrations of herbicide injury on common fruit, vegetable and ornamental crops, and a panel discussion on how to handle site visits.  Participants completed a survey documenting their affiliation, years of service, training background, prior experience with herbicide injury diagnostics, and their knowledge and confidence of the subject matter before and after the workshop.  Subject matter questions asked participants rank their knowledge or confidence in (1) impending uses of auxinic herbicides in GM crops, (2) diversity of herbicide injury symptoms, (3) recognizing herbicide injury, (4) diagnosing crop damage from herbicides, (4) conducting a site visit, and (5) outlining a course of action when herbicide injury is suspected.  There were 41 participants, about equally divided between CES and NCDA.  Twenty nine completed surveys were received. Participant years of service varied from 0 to 20, with a similar distribution among both CES and NCDA.  Despite similar years of service and similar training backgrounds, before the training, NCDA inspectors reported about a 20% greater confidence in their knowledge of the subject than CES agents.  Both groups reported increased knowledge or confidence in the subject matter as a result of the workshop but CES agents reported a greater percent increase than did NCDA inspectors.  Consequently, after the workshop there were few differences between CES and NCDA subject matter knowledge or confidence.  All participants reported the training to be valuable, easy to understand, and would recommend it to colleagues.  Although all respondents responded they were “satisfied” for “very satisfied” with each component of the training workshop, open ended questions revealed the most valued component of the training was the field demonstration of herbicide injury symptoms on crops.  This aspect of the workshop required the greatest man-hours and financial resources, and thus, it is not feasible to conduct on a regular basis.  However, the value of field demonstrations to participants should be considered when planning future in-service training for herbicide injury symptoms and diagnostics.


IBOOK FOR WEED IDENTIFICATION. B. A. Ackley*; The Ohio State University, Columbus, OH (56)

ABSTRACT

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

 


GEODATABASE \"WEEDMAP\" FOR RECORDING DATA ON WEED DISTRIBUTION. K. Hamouzova*, J. Soukup, M. Kolarova, P. Hamouz; Czech University of Life Sciences Prague, Prague, Czech Republic (57)

ABSTRACT

The WeedMap is a new database system being developed by the Department of Agroecology and Biometeorology of the Czech University of Life Sciences Prague and Geocentrum Olomouc for storage and processing of data on weed occurrence collected by researchers and public users. Initially, the WeedMap was dedicated to mapping of weed communities on agricultural and a non-agricultural land, but has been recently extended to include a herbicide resistance module. The database WeedMap allows the collection and the management of data from weed surveys (either vegetation relevés - any kind of plot listing each species cover-abundance values and the measured environmental variables, or single species data) based on the Document Management System (DMS).
This tool is primarily intended as a research tool for weed scientists and botanists and also for other users sharing data on-line. WeedMap is freely accessible through the internet on www.weedmap.eu. The data are primarily delivered by registered authors. WeedMap has both public and secured access allowing specific roles for entering and exploiting of data. The system allows submission of new records, on-line editing of records, displaying and export of data. Each entry includes a detailed description of conditions for each relevé including coordinates, site type, crop, date of observation, taxonomic details, etc. Entries based on bibliographic reference are also possible. The system contains over 300 records principally from the Czech Republic, along with some datasets from Finland. The intention is to continuously update the system with new and revised data. The database support complex queries and the results are displayed on maps. Information can all be extracted from the WeedMap at individual entry or in batch format. The output formats and data exports are designed to be used in special statistical software for botanists. In case of herbicide resistant population, the report also provide detailed information about species, its extension, a list of active ingredients with confirmed resistance and methods used for detecting herbicide resistance. This gives the most appropriate way to obtain a comprehensive overview based on case-by-case. The software is being tested with regional data and the authors are looking for collaborators worldwide.


AN ONLINE RESOURCE FOR HERBICIDE TARGET GENE SEQUENCES. D. A. Giacomini*1, I. M. Heap2, D. Sammons3; 1Colorado State University, Ft. Collins, CO, 2WeedSmart, Corvallis, OR, 3Monsanto, St. Louis, MO (58)

ABSTRACT

Although many new weed genomes have been sequenced and assembled since the advent of the next-generation sequencing revolution, the data is scattered and often difficult to access. Databases like GenBank attempt to centralize this information, but can be cumbersome to use due to inconsistencies in search term names and the overabundance of sequences from other species.  Additionally, sequence data is sometimes only found in the original source documents, e.g. research papers or patent applications.  To resolve this problem and provide an online resource for weed scientists, the cDNA sequences of seven major herbicide target genes across multiple weed species were extracted and compiled into a single database hosted on www.weedscience.org.  These gene sequences were obtained from patent and public databases using both BLAST and keyword-based searches within the GenomeQuest (GQ) sequence package.  Alongside the table of herbicide target genes are multiple sequence alignments for each gene (using the T-coffee alignment software) as well as resources for designing degenerate primers from the more conserved regions.  As more work is done to sequence additional weed species, this database is expected to expand and all weed researchers are encouraged to contribute.


DISTRIBUTION AND HERBICIDE RESISTANCE CHARACTERISTICS OF AMARANTHUS SPP. IN OHIO. S. N. Konkle*, M. M. Loux; Ohio State University, Columbus, OH (59)

ABSTRACT

The Amaranthus family contains several weedy members that can cause substantial problems in agronomic crop production.  Palmer amaranth (Amaranthus palmeri), waterhemp (Amaranthus rudis), and redroot pigweed (Amaranthus retroflexus) are all members of the Amaranthus family and have become successful weeds due to prolific seed production, rapid growth, plasticity in emergence and adaptation to conservation tillage.  The southern United States has experienced extreme to complete yield losses in soybeans as a result of glyphosate-resistant Palmer amaranth infestations.  Prior to 2012, only one grower in Ohio had experienced issues with Palmer amaranth, but OSU weed scientists received additional reports of Palmer amaranth starting in 2013 as growers became more aware of this weed due to our educational efforts.  Also prior to 2012, there were a few infestations of waterhemp that were known to be ALS and glyphosate-resistant, but they were isolated to a few areas of the state.  Redroot pigweed has been abundant in Ohio for decades.  Some populatopns are resistant to ALS inhibitors or triazine herbicides, but overall, redroot pigweed has been well controlled.  Because these weeds pose a threat to crop production, it is vital to monitor populations in Ohio to stay ahead of any issues.  The objectives of this research were to: i) determine frequency and distribution of Amaranthus spp. in Ohio, and ii) determine and characterize the presence of herbicide resistance in these populations.  We conducted a survey of soybean fields in 52 Ohio counties just prior to crop harvest in 2012, 2013, and 2014.  Transects of each county were driven while assessing infestation levels of all soybean fields encountered.  Seed samples were collected from infested fields.  We also asked growers, via newsletter, to submit samples.  The survey covered 3994, 3644, and 3479 soybean fields in 2012, 2013, and 2014, respectively.  Samples from infested fields collected from the survey and submitted by growers totaled 12, 34, and 34 in 2012, 2013, and 2014, respectively.  In 2014, 18 additional samples were collected from fields that were not considered to be infested, but had at least a few plants of an Amaranthus species.  A greenhouse study was conducted to screen populations collected in 2013 from the survey and submitted by growers for resistance to site 2, 9, and 14 herbicides.  The experiment was conducted twice.  The number of populations and herbicide response varied between experiments, based on seed viability and environmental conditions in the greenhouse; herbicides were overall less active in the first experiment compared with the second.  The number of populations screened in the first and second experiment were as follows: redroot pigweed - 19 and 23; waterhemp - 5 and 4; and Palmer amaranth - 3 and 2.  Several redroot pigweed populations exhibited some resistance to glyphosate in the first experiment, but this was not evident in the second.  About 50 to 75% of the redroot pigweed populations exhibited resistance to site 2 herbicides (imazethapyr), depending upon the experiment, and 25 to 65% showed some resistance to site 14 herbicides (fomesafen).  Several redroot populations appeared to be resistant to both site 2 and site 14 herbicides.  All of the waterhemp populations exhibited resistance to glyphosate and site 2 herbicides in the first experiment, and one appeared resistant to site 14 herbicides.  In the second experiement, all of the waterhemp populations were still resistant to site 2 herbicides, half were resistant to glyphosate, and none were resistant to site 14.  All of the Palmer amaranth populations were resistant to site 2 herbicides, none were resistant to glyphosate, and one had possible resistance to site 14. 


STOPPING THE PRODUCTION OF VIABLE WEED SEEDS - IT MAY OCCUR SOONER THAN YOU THINK. M. J. VanGessel*1, E. C. Hill2, K. A. Renner2, E. R. Gallandt3, C. Mohler4; 1University of Delaware, Georgetown, DE, 2Michigan State University, East Lansing, MI, 3University of Maine, Orono, ME, 4Cornell University, Ithaca, NY (60)

ABSTRACT

Integrated weed management (IWM) for agronomic and vegetable production requires using all available options to effectively management weeds.  IWM should address both the current season as well as considerations for future cropping seasons.  IWM needs to consider weed biology as well as weed control options.  There has been a renewed interest in eliminating the production of viable seeds as a mechanism of reducing weed density for subsequent crops.  Extension materials are being developed to highlight how soon after flowering, or seed head emergence, weeds need to be terminated to stop the production of viable seeds, and if termination method can reduce seed viability.  This information will be developed as an online factsheet and appropriate for all sizes of farming operations.


DESCRIPTION OF NEW 2,4-D AND DICAMBA ACID FORMULATIONS. J. T. Daniel*1, S. K. Parrish2, P. Westra3; 1Agricultural Consultant, Keenesburg, CO, 2AgraSyst Inc, Spokane, WA, 3Colorado State University, Ft. Collins, CO (61)

ABSTRACT

One of the most utilized herbicides in the world is 2,4-D.  It came to market as a herbicide in 1945, and  is commonly formulated in two forms, dimethyl amine salt (DMA) of 2,4-D and low volatile (LV) ester of 2,4-D.  The amine salts are water soluble and are formulated in water.  Low volatile esters are oils and are formulated as Emulsifiable Concentrates (EC). Dicamba was first registered in the United States in 1967. Dicamba is commonly formulated as a DMA salt or as a diglycolamine (DGA) salt.  Both are water based formulations. Recently new 2,4-D and dicamba acid base formulations have been introduced.  These formulations are characterized by increased herbicidal activity as compared to the amine salts and reduced volatility.  AgQuam of Spokane, WA has developed new self-buffering acid formulations, AQ990 a 2,4-D formulation, AQ991 a dicamba formulation, and AQ997 a mix of the two acid actives, that are higher loaded than current commercial acid herbicide formulations.

 

Several trials were conducted in both greenhouse and field to evaluate both volatility and efficacy as compared to the standards.  In general, the AQ acid formulations were less volatile and slightly more efficacious than the standard formulations.

 


SPRAY DROPLET SIZE EVALUATION OF BASF ENGENIA™ HERBICIDE AND EXISTING DICAMBA FORMULATION, ALONE AND IN TANK MIX COMBINATIONS. A. Clark*1, L. Magidow1, L. Bozeman2; 1WinField / Land O Lakes, River Falls, WI, 2BASF, Research Triangle Park, NC (62)

ABSTRACT

In many regions weeds are becoming resistant to herbicides, thus decreasing efficacy of such applications. BASF’s release of Engenia™ herbicide for use in POST applications on dicamba-resistant cotton, soybean, and corn will provide another mode of action that can be utilized as part of an herbicide stewardship program. Managing spray drift of dicamba will be critical as the Engenia™ system is adopted by growers. This study investigated the potential to optimize application of Engenia™ via nozzle selection with a drift reduction adjuvant and non-AMS water conditioner present in the tank mix. The droplet sizes produced by the tank mix and nozzle combination were compared to a current dicamba formulation. The target droplet spectrum for application of Engenia™ has a median droplet size > 450µm and volume of fine droplets (<150µm) < 3%. Droplet size testing via laser diffraction in the WinField Spray Analysis System demonstrated that the Greenleaf TDXL-D 11004, Spraying Systems TTI 11004, and Wilger DR 11008 nozzles, in conjunction with a drift reduction agent and an experimental non-AMS water conditioner, meet the necessary requirements to properly apply Engenia™.


INFLUENCE OF CARRIER WATER PH, FOLIAR FERTILIZER, AND PLANT HEIGHT ON HORSEWEED CONTROL WITH MESOTRIONE. P. Devkota*, W. Johnson; Purdue University, West Lafayette, IN (63)

ABSTRACT

Spray water quality is critical for effective herbicide applications. Likewise, weed height is an important consideration for obtaining good control with postemergence herbicides. A field study was conducted at Meigs Research Farm, Purdue University, IN to evaluate the effect of foliar fertilizers, carrier water pH, and plant height on mesotrione efficacy for horseweed control. Carrier water treatments consisted of combinations of zinc or manganese fertilizers (at 2.5 and 3.75 L ha-1, respectively) with water pH set at 4, 6.5, or 9. Mesotrione was applied at 105 gm ai/ha to 7.5-, 12.5-, or 17.5-cm tall horseweed. Zinc and manganese fertilizers did not reduce the efficacy of mesotrione on horseweed for percent control, height reduction, and dry biomass. Mesotrione applied with carrier water at different pH levels showed variable response on control and height reduction on horseweed. Mesotrione applied with water at pH 6.5 provided higher control compared to pH 9 at 2 and 4 wk after treatment (WAT), and resulted in shortest horseweed plants at the end-of the season. Similarly, mesotrione efficacy varied with respect to the horseweed height for percent control, plant height reduction, and biomass. Mesotrione sprayed on 7.5, 12.5, and 17.5 cm tall horseweed provided 91, 72, and 61% control, respectively, at 4 WAT which corresponded to the final plant height of 4.8, 19, and 33 cm, respectively. The dry biomass were 0.19, 2.05, and 5.6 gm plant-1 with mesotrione applied to 7.5, 12.5, and 17.5 cm tall horseweed. In conclusion, mesotrione applied with carrier water pH at 6.5 and when plants are up to 7.5 cm tall results in horseweed control ≥91%.


EFFECTS OF WATER QUALITY AND CONDITIONING AGENTS ON GLYPHOSATE PERFORMANCE. M. R. Manuchehri*1, P. A. Dotray2, J. Keeling3, T. Morris4; 1Texas Tech University, Lubbock, TX, 2Texas Tech University, Texas A&M AgriLife Research and Extension Service, Lubbock, TX, 3Texas A&M AgriLife Extension Service, Lubbock, TX, 4Texas A&M AgriLife Research, Lubbock, TX (64)

ABSTRACT

Effects of Water Quality and Conditioning Agents on Glyphosate Performance. M. R. Manuchehri*1, P. A. Dotray1, J. W. Keeling2, T. S. Morris2. 1Texas Tech University, Lubbock, TX, 2Texas 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 from 2012 to 2014. 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 1046 ppm, were selected from a survey of 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 1028 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 1028 PPM water source.  The addition of a water conditioner did not improve glyphosate performance.

 


IMPACT OF DEPOSTION AIDS ON HERBICIDE PENETRATION INTO CROP CANOPIES. C. A. Samples*1, D. M. Dodds2, A. Catchot2, G. R. Kruger3, J. Copeland2, D. Denton2; 1Mississippi State University, Starkville, MS, 2Mississippi State University, Mississippi State, MS, 3University of Nebraska-Lincoln, North Platte, NE (65)

ABSTRACT

EFFECT OF DRIFT RETARDANTS/DEPOSITION AIDS AND HERBICIDES ON INSECTICIDE CANOPY PENETRATION IN COTTON. C.A. Samples1, D.M. Dodds1, A.L. Catchot1, A.B. Denton1, 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. 

 


CHEMICAL CONTROL OF WILD BUCKWHEAT (POLYGONUM CONVOLVULUS L) AND FIELD BINDWEED(CONVOLVULUS ARVENSIS L) ON WHEAT IN MEXICO. E. Lopez*; Crop Protection R&D, Guadalajara, Mexico (66)

ABSTRACT


DICLOSUNAM TO CONTROL SEDGES AND OTHER WEEDS ON SUGARCANE IN GUATEMALA. E. Castaneda*1, E. Lopez2; 1Crop Protection R&D, Guatemala, Guatemala, 2Crop Protection R&D, Guadalajara, Mexico (67)

ABSTRACT


SEED DESICCATION TOLERANCE AND VIABILITY OF CHENOPODIUM ALBUM AS AFFECTED BY CUTTING METHOD AND TIMING. F. Kordbacheh1, C. Mohler2, A. DiTommaso*2, H. R. Mashhadi3, H. Alizadeh3; 1University of Tehran, Tehran, Iran, 2Cornell University, Ithaca, NY, 3University of Tehran, Karaj, Iran (68)

ABSTRACT

Greenhouse and field experiments were conducted to investigate the effect of different cutting methods and their timing on the viability of Chenopodium album L. (common lambsquarters) seeds. Three cutting methods were compared: (1) cutting the entire plant at soil level and allowing the plant material to dry on a greenhouse bench or on the soil surface in the field for four weeks (EPD); (2) detaching the terminal inflorescence and drying it on a greenhouse bench or on the soil surface for four weeks (ID); and (3) detaching the terminal inflorescence from the parent plant and immediately testing the viability of the freshly collected seeds (IF). Plants of the EPD and ID treatments were cut at 3, 13, 23, 33 and 43 days after flowering (DAF). Plants of the IF treatment were cut only at 33 and 43 DAF because at earlier stages seeds were not sufficiently developed to allow testing. Seeds were sorted into fully filled (mature) and immature categories. The ratio of mature to immature seeds was lower in the field than in the greenhouse, probably due to warmer temperatures and longer daylength in the greenhouse. In general, for plants cut 13 and 23 DAF, leaving plants for four weeks increased the number of viable seeds. However, under field conditions, plants cut at 33 and 43 DAF and left in the field had fewer viable seeds than plants assessed immediately. This decrease in seed viability did not occur in the greenhouse and may have been due to rapid aging of seeds under moist conditions in the field. In the greenhouse experiment, the number of seeds in the ID treatment was higher than in the IF treatment, possibly because seeds continued to develop on the detached inflorescence. The stage at which plants can be left after cutting without subsequent seed development depends on environmental conditions. In warm, dry conditions, viable seeds are produced by 23 DAF; whereas, in cool, moist conditions viable seed can be produced on plants cut at 13 DAF if they are allowed a period of post-cutting seed maturation.


POST-MORTEM SEED DEVELOPMENT: DOES TERMINATION TIMING OR METHOD MAKE A DIFFERENCE? E. C. Hill*1, K. A. Renner1, M. J. VanGessel2, B. Scott3; 1Michigan State University, East Lansing, MI, 2University of Delaware, Georgetown, DE, 3University of Delaware, Newark, DE (69)

ABSTRACT

Despite farmer’s best efforts, monetary losses due to weeds in 2010 were estimated to be over 2.6 billion dollars in the U.S. Most weed management approaches focus on strategies for the current season and do not focus on the weed seedbank. Late season weed control measures are often needed to improve crop harvest and stop additions to the weed seed bank. Weeds terminated after flowering may produce viable seed and termination method may influence viable seed production, however these areas are poorly understood for some of the most prevalent weeds in the northeast region of the U.S. The objectives of this research were to determine if plants terminated at flowering or with immature seeds present develop viable seeds, and if weed termination method affects viable seed production. Research was conducted in Michigan and Delaware over a two-year period. The weeds included: common lambsquarters (MI only), giant foxtail, jimsonweed, and velvetleaf. The termination timings were: flowering (except common lambsquarters), immature seeds present, and mature seeds present (MI only). Three termination methods were imposed: cutting at the base of the plant (simulating hand hoeing), chopping the whole plant (simulating mowing), and applying glyphosate. Following termination plants were either stored in mesh bags lying between rows of a soybean field (cut and chop) or were staked to remain standing and enclosed in mesh bag (glyphosate application). Bags were retrieved in mid-fall of each year and intact, full seeds were counted. Viability was then tested to determine the total number of viable seeds. The termination timing was often significant; however termination method did not influence viable seed development the majority of the time. Jimsonweed and velvetleaf did not produce seeds when terminated at the flowering stage. For giant foxtail, flower heads still emerging from the whorl (MI) were unlikely to produce seed, whereas fully emerged flower heads with anthers present on 50% of the plants (DE) resulted in an average of 230 and 1,200 viable seeds plant-1 in 2012 and 2013, respectively. All species produced some viable seed when immature seeds were present at the time of termination. The time from flowering to viable seed production ranged from 13 to 18 days for velvetleaf and giant foxtail and from 21 to 57 days for jimsonweed. Viable seed production was reduced by 99, 82, 94, and 96% when compared with plants terminated at maturity (i.e. some mature seed present) for common lambsquarters, giant foxtail, jimsonweed, and velvetleaf, respectively. Our results suggest that terminating common lambsquarters and giant foxtail prior to flowering, and terminating velvetleaf and jimsonweed less than two and three weeks after flowering, respectively, will drastically reduce inputs to the weed seed bank.


INFLUENCE OF PALMER AMARANTH DENSITY AND EMERGENCE DATE ON SEED PRODUCTION IN WIDE ROW AND DRILL-SEEDED SOYBEAN. N. E. Korres*, J. K. Norsworthy; University of Arkansas, Fayetteville, AR (70)

ABSTRACT

Knowledge of weed biology and population dynamics is essential for development of both economically and environmentally acceptable weed management systems. Two field experiments based on a completely randomized block design were conducted in Fayetteville, Arkansas during 2014 to examine the effects of crop density, Palmer amaranth (Amaranthus palmeri) emergence date, and interrow distance on Palmer amaranth seed production in wide-row and drill-seeded soybean. Palmer amaranth seedlings grown under greenhouse conditions were transplanted to the field at the 7- to 9-leaf growth stage and at intervals of 0, 1, 2, 4, 6, and 8 weeks after crop emergence (WAE) at density of 1 plant m-2. All other weed species were removed by hand from the experimental plots to avoid competition. In drill-seeded soybean, seeding rates of 0, 50,000, 125,000, and 200,000 seeds acre-1 were used for each Palmer amaranth emergence date whereas in wide-row soybean a rate of 130,000 seeds acre-1 was used for each treatment of Palmer amaranth emergence date and interrow planting distance (i.e. 0, 23, 46 cm from the soybean row). Palmer amaranth plants, both male and female, were harvested by cutting the shoots at the soil level and dry weight and height was recorded for each plant. After plant dry weight was determined, seeds were extracted from each female plant and seed production was determined by weighing five subsamples of 100 seeds from each treatment. Demographic characteristics of the Palmer amaranth population in both experiments were recorded at harvest. Differences in Palmer amaranth dry weight and seed production among emergence dates and crop densities in drill-seeded soybean were evident as early as 0, 1, and 2 WAE compared to other emergence dates. On the contrary in wide-row soybean, the effects of emergence date and interrow distance on dry weight and seed production were evident at only 0 and 1 WAE. Palmer amaranth emergence date had a significant effect on Palmer amaranth seed production through greater biomass production at earlier dates in both drill-seeded and wide-row soybean cropping systems. Interrow distance affected Palmer amaranth height and dry weight and consequently seed production. The greater the interrow distance from the top of the bed the lesser the competition effects from the crop on Palmer amaranth height, dry weight, and seed production, at 0 and 1 WAE compared to other emergence dates (i.e. 2, 4, 6, and 8 WAE). Results regarding Palmer amaranth population demographic characteristics and parameters are still under analysis. Upon their completion, we will be able to represent relationships between Palmer amaranth biological characteristics and Palmer amaranth population dynamics which can be used for modelling purposes in ongoing herbicide resistance research.


EFFECTS OF PESTICIDE SEED TREATMENTS ON WEED SEED BANKS IN CORN AND SOYBEAN. M. Morris*, L. W. Atwood, R. G. Smith; University of New Hampshire, Durham, NH (71)

ABSTRACT

Use of pesticide seed treatments (coating seeds with insecticide and/or fungicide active ingredients) is a common practice in conventional corn and soybean production. Despite its widespread use, however, little is known about how this practice may affect soil food webs and their associated ecosystem services. We conducted a two-year field experiment in Rock Springs, PA in which identical genotypes of corn (2013) and soybean (2014) were planted at recommended rates with and without pesticide seed treatments in a completely randomized design with five replications. We sampled the weed seed bank to a depth of 10 cm during both the corn (fall 2013) and soybean (late summer 2014) phases of the rotation. After each sampling event, soil samples were transported to the University of New Hampshire greenhouse facility and weed seed bank composition and density was assessed over a period of four months via the direct germination method. Seed bank data were analyzed with ANOVA and several multivariate techniques to determine the effect of seed treatments on seed bank density, diversity, and species composition. We hypothesized that pesticide seed treatments reduce the abundance of natural enemies (e.g., seed predators and pathogens) that damage or destroy weed seeds in the soil, and therefore seed banks in treated plots would be larger and less diverse than those in untreated plots.  In accordance with our hypothesis, weed seed banks were less diverse in treated compared to untreated plots (Shannon diversity, H; p = 0.007). While not statistically significant (p > 0.05), differences in mean weed seed bank density and species richness were also in the direction that we hypothesized. These data provide the first evidence that we are aware of that weed seed banks, and hence weed populations, may be influenced by pesticide seed treatments. Additional research will be necessary to determine the generality of these responses and their underlying mechanisms.


GLYPHOSATE EXPOSURE ALTERS FLOWERING AND SEED PRODUCTION IN SUMATRAN FLEABANE (CONYZA SUMATRENSIS). G. L. Gomes*1, C. A. Carbonari2, E. D. Velini2, B. Marchesi2, G. C. Macedo2, A. K. Matos2; 1Faculdade de Ciências Agronômicas / UNESP, Botucatu, Brazil, 2Faculdade de Cincias Agronmicas / UNESP, Botucatu, Brazil (72)

ABSTRACT

The objective of this research was to characterize the flowering and seed production of two glyphosate-resistant Conyza sumatrensis populations after glyphosate exposure. Seeds were collected at different fields of the Sao Paulo state, Brazil. Glyphosate was applied at the rosette stage at the following doses: 0, 45, 90, 180, 360, 720, 1440, 2880, 5760 and 11520 g ae ha-1. The experiments was arranged in a completely randomized design with five replications per treatment. Fourteen days after treatment (DAT) the leaves were harvested to shikimate determination. Four weeks after treatment, the plants were harvested at ground level, and their dry weight recorded and expressed as a percentage of dry weight of untreated control plants. Was evaluated the flowering and seed production, through assessments of total number of flowers (open flowers + flowers with seeds) and number of flowers with seeds in different periods for each population according to the development of each. Growth reduction (50%) values were lower for the population 2 compared to the population 1. Population 1 accumulated less shikimate than the population 2, which is consistent with the higher GR50 for population 1. Occurred anticipation of flowering and increase of the total number of open flowers and flowers with seeds in the both glyphosate-resistant C. sumatrensis populations after sub-lethal glyphosate exposure.

 


ALTERING TUBER PRODUCTION OF PURPLE NUTSEDGE (CYPERUS ROTUNDUS) WITH HERBICIDES. T. M. Webster*1, T. L. Grey2; 1USDA-ARS, Tifton, GA, 2University of Georgia, Tifton, GA (73)

ABSTRACT

Purple nutsedge is among the most troublesome weeds of many crops in the Southern US, including fruiting vegetables and cucurbits (#1 in GA and FL) and cole crops (#4 in GA and FL), and across the region (ranked #6 and #8 in peanut and cotton, respectively).  Purple nutsedge is a clonal species that relies on tubers to perpetuate it.  Studies have found that there are more than four tubers for every emerged foliar shoot, and single tubers reproduced into 530 tubers in a three-month period.  The persistence of purple nutsedge tubers in the soil was found to have a half-life of 17 months, with 99% mortality within 36 months.  In order to effectively manage purple nutsedge populations, practices should control vegetation and minimize production of new tubers.  However, the influence of herbicides on purple nutsedge tubers has not been extensively evaluated.  The objectives of this experiment were to evaluate the effectiveness of imazapic, a herbicide commonly used in peanut, on purple nutsedge foliar growth and tuber production, and compare to previous studies involving purple nutsedge and glyphosate (commonly used in cotton, corn, and soybean) and halosulfuron (commonly used in cucumber, tomato, and watermelon).  Studies were conducted in Tifton, GA in 2013 and 2014 in outdoor microplots.  Purple nutsedge tubers were pre-sprouted in the greenhouse and transplanted into microplots, a single tuber with emerged shoot per experimental unit.  After six weeks of growth, purple nutsedge plants were treated with imazapic, ranging from 1/16X- to 2X, using six rates with a common multiplier of 2.  The 1X rate of imazapic was 72 g ai/ha.  A nontreated control was included in the treatment structure.  Purple nutsedge plants were harvested seven weeks after herbicide application.  Shoot and tuber data were regressed on rate of imazapic and fit to log-logistic models.  The experiment had five replications in a RCBD, with blocking based on the number of shoots emerged at time of application, and the experiment was repeated in time.  The rate of imazapic that reduced foliar and tuber biomass 50% (I50) was 25.8 and 25.6 g/ha.  The ratio of 1X rate to I50 was 2.7 and 2.73.  Comparison of these ratios with those for glyphosate (1.50 to 1.58) and halosulfuron (17.30) suggest that imazapic is between these compounds in the relative efficiency of the herbicide.  Effective management requires reduction in both tuber production and tuber persistence; future studies should address how tuber persistence is affected by herbicides.


THE INFLUENCE OF CLIMATE ON THE DISTRIBUTION OF MAYWEED CHAMOMILE AND ITALIAN RYEGRASS IN THE PACIFIC NORTHWEST. N. Lawrence1, L. Bernacchi2, J. Wulfhorst2, I. C. Burke*1; 1Washington State University, Pullman, WA, 2University of Idaho, Moscow, ID (74)

ABSTRACT

Italian ryegrass (Lolium multiflorum L.) and mayweed chamomile (Anthemis cotula L.) are two well adapted weed species common in the inland Pacific Northwest (PNW) small grain production region. Both species are summer annuals with emergence occurring in the spring. To understand the relationship between climate, management practices, and distribution of pests, a producer survey was conducted that asked growers to identify observation and control of Italian ryegrass and mayweed chamomile. The respondents identified multiple field sites, and for each site they were asked which of the weeds affected their largest parcel, and the degree to which they were controlled. Observation of Italian ryegrass by cropping system is likely a result of increased annual precipitation. Seventy percent of respondents from the crop-fallow production system did not observe Italian ryegrass, whereas, 57 and 31% of respondents from the intermediate and annual cropping systems did not observe Italian ryegrass. A similar trend was observed with mayweed chamomile. In the crop-fallow production system Italian ryegrass was observed more often in areas where no-till was used. The presence of Italian ryegrass in the no-till areas of the crop-fallow production systems may be a consequence of greater soil moisture retention or a more stable seed bed. The observation of Italian ryegrass in the intermediate and annual cropping systems was not as variable by tillage practices as in the crop-fallow system, however control of Italian ryegrass was variable by tillage practices. Respondents from intermediate and annual cropping system who used conservation tillage rather than conventional tillage or no-till practices reported greater control of Italian ryegrass. Mayweed chamomile is much less common in the crop-fallow production system, likely due to moisture. In the intermediate cropping zone, mayweed chamomile is more common in tillage systems, and also more difficult to control. The opposite is true in the annual cropping system zone, where mayweed is less commonly observed in systems that use tillage. No-till and conventional tillage practices differ considerably in the reliance not only on tillage but also herbicide use. The greater control of Italian ryegrass observed when conservation tillage practices were used may reflect increased flexibility in tillage and herbicide use allowing growers to better adapt their practices for difficult to control weeds. Finally, it appears that Italian ryegrass and mayweed chamomile are useful species as climate indicators. Grower surveys can be useful tools for assessing, indirectly, climate effects on indicator species.

 


WINTER ANNUAL WEED COMMUNITIES AS A RESULT OF FALL OR SPRING WEED CONTROL. M. J. VanGessel*1, Z. Zhang2, T. W. Ilvento2, B. Scott2, Q. R. Johnson1; 1University of Delaware, Georgetown, DE, 2University of Delaware, Newark, DE (75)

ABSTRACT

Timing of weed emergence has a significant role in the success of any weed management program.  The emergence patterns of winter annuals weeds in the Northeastern US has not received the attention of summer annual weeds.  Better understanding of winter annual weed emergence and weed population dynamics could improve our weed management decisions for no-till corn and soybean production, as well as fall-seeded wheat and barley.  The objectives of this trial was to determine emergence period of common winter annual weed species under continuous no-till, and the impact of weed management timing on population dynamics.  This study was conducted in Delaware in two different fields managed as continuous no-till soybeans.  Treatments were period of winter annual weed emergence achieved through non-selective herbicide application; only one application per treatment was applied and subsequent weed emergence was monitored.  Emergence periods were full emergence (no herbicide application); late fall (application in late November); early spring (application in mid-March); and late spring (application in late April).  A comparison treatment of multiple application timings was included.  Emergence periods were repeated for each plot for a five year period.  Emerged weeds were counted in early and late spring.  Soil seedbank was sampled in the fall of the fifth year.  When seed production of winter annuals was eliminated (repeated applications of non-selective) density of winter annual weeds present at planting was reduced from year one to year two, with no further decline.  Weeds emerging in the late fall or early-spring and allowed to produce seeds, generally increased in density over the five year period.  Weeds considered winter annuals tended to not emerge in the late spring, and if they did, seed production was not sufficient to increase weed density in subsequent years.  When management of winter annual weeds occurs in the fall, IWM approaches must account for plants emerging in the early spring. 


GROWING SEASON PHENOLOGY OF FOUR BROADLEAF SPECIES IN SOUTH DAKOTA. S. A. Clay*, M. Erazo-Barradas, G. Reicks; SDSU, Brookings, SD (76)

ABSTRACT

Weed phenology can aid weed management by better understanding the effects of the environment on growth in order to anticipate times of maximum susceptibility to control. Post-emergence herbicides have played an increasingly important role in weed management, but timing of application in relation to the growth stage of target weeds is a critical factor for obtaining the best efficacy. Calendar date is typically a poor predictor of weed emergence or growth rate because growth parameters often are temperature (growing degree day accumulation-GDDA) and soil moisture dependent, which are variable between years. This research examined the amounts of GDDA and the amount of precipitation required from emergence to physiological maturity of four broadleaf weed species [common lambsquarters (Chenopodium album L.), velvetleaf (Abutilon theophrasti Medik), field pennycress (Thlapsi arvense L.), and horseweed (Conyza canadensis L.)] of two different origins [a local accession from eastern South Dakota (SD) and a second from southern Illinois (IL supplied by A. Davis, USDA-ARS)]. Four replicates with about 100 seeds of each species and origin per replicate were seeded into a silty clay loam soil at the Aurora, SD field station in late July (field pennycress) or early November (other species) the year prior to the growing season of interest. The 2013 growing season was slightly warmer and drier than 2014. Field pennycress, predicted to be a winter annual, did not emerge in the fall,  with all species emerging in the spring after seeding.  The first 12 plants of each species/origin combination within a replication (total of 48 plants per species and origin) were tagged and followed from emergence to physiological maturity.  A 0°C base temperature was used to calculate GDD for all four species. GDD calculation started November 7, 2012 and November 14, 2013 for the experiments of 2013 and 2014, respectively, which were the dates of seeding all species except field pennycress. Date of emergence, flowering, and physiological maturity were recorded for each plant and GDDA calculated, then averaged within a species and origin across replications, and evaluated for consistency. These data were compared with corn growth (GDD base 10 and accumulated from planting each year to the V8 stage of growth) to determine if a domesticated crop fluctuated in growth in a similar manner as these weed species. Few GDD accumulated during the winter, but by late April, 102 (2013) and 231 (2014) GDDA were calculated. Although 2 times more GDDA were calculated for late April 2014, average emergence of field pennycress, velvetleaf, and horseweed required 34 to 64% more GDDAs to emerge depending on species and seed origin compared with the average GDDA required in 2013. Average emergence of common lambsquarters, in contrast, was similar between years for the IL seed but SD seed required 19% fewer GDD in 2014 when compared with 2013. On average, field pennycress, velvetleaf, and horseweed required a higher number of GDDA to begin flowering in 2014 than in 2013, whereas common lambsquarters needed 15% fewer GDDA to flower in 2014 than in 2013. Rainfall accumulation in 2013 and 2014 from emergence to flowering differed. In 2013, field pennycress, the earliest flowering species, and common lambsquarters, the latest flowering species, flowered after rainfall accumulations of 7.5 cm and 9.6 cm of rainfall, respectively. For 2014, field pennycress, the earliest flowering species, and horseweed, the latest flowering species, flowered after rainfall accumulations of 14 cm and 24.6 cm, respectively. On average, field pennycress and horseweed required about 30% greater GDDA to reach seed maturity in 2014 compared with 2013.  In contrast, corn reached V8 at similar thermal times each year (750 in 2013 and 760 in 2014), despite the differences in growing season temperature and rainfall patterns. While the differences in GDD requirements to get to different growth stages for these four species were more similar after plant emergence, the differences noted in emergence patterns between years, when control measures can be the most effective, need to be better understood to help producers optimize timing of weed control inputs.


GIANT  RAGWEED(AMBROSIA TRIFIDA L.) FECUNDITY AND REPRODUCTIVE ALLOMETRY IN MAIZE (ZEA MAYS L.) AND SOYBEAN (GLYCINE MAX (L.) MERR.). E. R. Page*, R. E. Nurse; Agriculture and Agri-Food Canada, Harrow, ON (77)

ABSTRACT

Over the past 15-20 years, giant ragweed has become an economically important weed of arable land in SW Ontario and many parts of North America; a fact that may be attributable to changes in cropping systems practices and the development of resistance to Group 2 and 9 herbicides (i.e., ALS/AHAS inhibitors and glyphosate, respectively).  The objective of this research was to 1) examine giant ragweed fecundity in maize and soybean crops representing over 50 years of cropping systems practices and 2) to develop a relationship to estimate giant ragweed fecundity based on non-destructive, easily measured physiological parameters. Overall, ragweed fecundity was 50% lower in maize than in soybean; when only the most recent cropping system is considered, this
disparity between crops increases to 77%. A relationship was developed to describe giant ragweed fecundity by calculating cylindrical plant volume based on measurements of plant height and stem diameter.  The slope of this relationship was influenced by crop type as giant ragweed plants growing in soybean produced 19% less seed per unit volume than did those growing in maize.  Similarly, the slope of the relationship between giant ragweed vegetative and reproductive biomass was decrease for plants grown in soybeans. This shift in the reproductive allometry of giant ragweed was indicative of the increase in branching and support tissue that characterized giant ragweed plants grown in soybeans.


EFFECT OF TEMPERATURE AND LIGHT INTENSITY ON THE EFFICACY OF SOME POSTEMERGENCE HERBICIDES ON HAIRY FLEABANE (CONYZA BONARIENSIS). M. Dennis, J. Bushoven, A. Shrestha*; California State University, Fresno, CA (78)

ABSTRACT

herbicides on glyphosate-susceptible (GS), glyphosate-resistant (GR), and glyphosate-paraquat-resistant (GPR) hairy fleabane plants.  Greenhouse-grown plants were treated at the 5- to 8-leaf stage with either glufosinate (5.74 kg/ha), glyphosate (1.1 kg ae ha-1), pyraflufen (280 gz/ha), or saflufenacil (70 g ha-1).  Ammonium sulfate was added at 2% w/v with the saflufenacil and glyphosate treatments, and at 1% w/v for the glufosinate treatment.  A 1% v/v crop oil concentrate was added to the pyraflufen treatment.  Immediately after treatment, the plants were exposed for 48 h to four different light intensities (shade levels) in an open field setting using shade cloth at 100% shade, 70% shade, 50% shade, and 0% shade (full sun).  The plants were returned to the greenhouse for survival evaluation for an additional 28 days and then harvested at 30 days after treatment and the above ground dry biomass was recorded.  The experimental design was a split-split plot replicated four times with light as main factor, biotypes as sub-factor, and herbicide treatments as sub sub-factor.  The experiment was conducted thrice (twice in spring and once in fall).  Interactions occurred between the seasons and treatments; therefore, data were analyzed separately for each season.  In the spring, glufosinate provided the most consistent control (88 to 100%) of all three biotypes at all light intensities.  Glyphosate controlled only the GS biotype at all light intensities.  The efficacy of saflufenacil was influenced by both light intensity and biotype, and control of any of the biotypes did not exceed 38%, whereas pyraflufen did not control any of the plants at any of the light intensities.  In the fall, glufosinate had consistent control (92 to 100%) of all the plants at all light levels.  However, contrary to spring, in the fall, glyphosate controlled 75 to 100% of the plants including the resistant biotypes.  Saflufenacil controlled 100% of the plants at all light levels, whereas pyraflufen controlled up to 50% of the plants and its efficacy was affected by light intensity.  Therefore, this study showed that glufosinate was the most effective treatment for the control of all the hairy fleabane types at all light levels in both seasons.  The efficacy of the other herbicides were influenced either by the season and/or light intensity.


ECOLOGICAL FITNESSES OF MULTIPLE HERBICIDE-RESISTANCE TRAITS IN THE ABSENCE OF HERBICIDE SELECTION DETERMINED FROM A MULTI-GENERATION GREENHOUSE STUDY OF WATERHEMP (AMARANTHUS TUBERCULATUS). C. Wu*, P. Tranel, A. Davis; University of Illinois, Urbana, IL (79)

ABSTRACT

The rapid evolution of herbicide resistance in waterhemp is an increasing threat to crop production in the Midwestern United States. Since 1990, common waterhemp has evolved resistances to herbicides from six site-of-action families. Ecological fitness of herbicide resistance in the absence of herbicide selection is an important parameter for modeling and predicting the evolution of herbicide resistance. Unfortunately, there is limited fitness data available from robust study systems. In particular, few previous studies contain all three of the following features of a successful fitness study: 1) control of genetic background; 2) assessment of fitness throughout the plant life cycle; 3) assessment of fitness under competitive growth conditions.  The objective of this study is to investigate fitness costs of five herbicide resistance traits (ALS inhibitors, PPO inhibitors, HPPD inhibitors, atrazine, and glyphosate) in waterhemp through a multi-generational greenhouse study. A synthetic waterhemp population, which is segregating for five different herbicide resistances, has been subjected to multiple generations of competitive growth conditions in the absence of herbicide selection. Each generation of growth includes thousands of plants (grown in greenhouse rooms with a soil floor) in three replicate growth rooms. For select generations, the frequencies of the different resistances were determined from both whole-plant herbicide treatments (atrazine) and molecular markers (PPO, ALS and Glyphosate) and compared to those in the starting generation. We are currently growing our last generation in the greenhouse. Our preliminary data, after three generations, indicates that most of the resistance traits (atrazine, PPO, ALS and mutation based Glyphosate resistance) have little or no fitness costs. In contrast, glyphosate resistance conferred by EPSPS gene amplification, has a significant fitness cost. The frequency of glyphosate resistant plants with high EPSPS copy numbers consistently drop from 30% to 10% in our third generations across all our three rooms. The results from this novelly designed fitness study will provide valuable data on understanding and modeling the evolution of herbicide resistance. 

 


SELECTION PRESSURE EFFECTS ON INTROGRESSED HERBICIDE AND DISEASE RESISTANCE ALLELE PROPORTION, GENE FLOW AND YIELD COMPONENTS IN JOINTED GOATGRASS (AEGILOPS CYLINDRICA). B. A. Martins*1, C. A. Mallory-Smith2; 1EMBRAPA, Sete Lagoas, Brazil, 2Oregon State University, Corvallis, OR (80)

ABSTRACT

In winter wheat, jointed goatgrass is one of the most troublesome weed species, while the pathogen Oculimacula spp. causes the strawbreaker foot rot disease. Imazamox- and foot rot-resistant wheat cultivars are widely grown in the Pacific Northwest of the USA, representing effective tools to control both the weed and the pathogen. However, gene flow from wheat to jointed goatgrass, hybrid and backcross plants could move the resistance genes to jointed goatgrass populations. Therefore, field experiments were conducted using herbicide and foot rot resistance genes introgressed into a single jointed goatgrass line to study allele proportion and gene flow with and without herbicide and disease selection pressure. The herbicide-resistance allele proportion in the progeny was greater when parent plants were treated with imazamox in both years. The disease-resistance allele proportion did not differ among the selection pressure treatments in the first year, but was greater with disease occurrence in the second year. The herbicide-resistance gene flow from resistant to susceptible plants was greater with herbicide selection pressure only in the first year. Disease resistance gene flow did not differ in either year. The results from these field experiments indicate that if plants of a jointed goatgrass population acquire the herbicide resistance allele the proportion would increase each generation under herbicide selection pressure. Selection pressure of herbicide plus disease reduced the yield components in the susceptible plants, compared to the resistant plants. The proportional increase in the yield components of the resistant parent plants promotes fitness advantage, favoring the success of plants carrying the resistance alleles. Given a population large enough to avoid genetic drift, in the absence of selection pressure, introgressed alleles without fitness costs persist in the population with a constant allele frequency. However, alleles that confer advantages will increase in frequency within a population under selection pressure. The rate of selection is faster in self-pollinated species such as jointed goatgrass compared to outcrossing species. The combined effect of many populations having a few resistant individuals within the meta-population of jointed goatgrass may be able to guarantee the persistence and possibly stabilization of the resistance alleles. Results from these field experiments are valuable for development of resistance management prediction models.


THE EFFECT OF COVER CROPS ON HORSEWEED GROWTH AND DEVELOPMENT. A. M. Christenson*, A. Dille, D. Peterson, K. Roozeboom; Kansas State University, Manhattan, KS (81)

ABSTRACT

With an increasing number of herbicide-resistant weed species, it has become apparent that alternative methods of weed suppression should be examined. The objective of this study was to quantify the interaction between various cover crop and herbicide systems and horseweed (Conyza canadensis) growth and development. Fall cover crops of wheat (Triticum aestivum), rye (Secale cereale), barley (Hordeum vulgare) and annual rye grass (Lolium multiflorum) were seeded in November 2013 and November 2014. A spring cover crop was seeded each year with spring oat (Avena sativa) planted in April 2013 or rye planted in March 2014. All cover crops were seeded into sorghum stubble (Sorghum bicolor) in Manhattan, KS. Other treatments included chemical fallow plots that received: fall-applied dicamba, fall-applied Valor XLT (flumioxazin and chlorimuron-ethyl) plus dicamba, spring-applied dicamba or spring-applied Valor XLT plus dicamba. Valor XLT and dicamba were also spring applied to plots of rye. Cover crop plots were divided in half and were terminated with a roller crimper or glyphosate application approximately one week before soybean planting. Soybeans were planted in June 2013 and May 2014, and mechanically harvested in October of both years. Horseweed density, biomass accumulation, and soybean yield data were quantified for the different cover cropping systems. Cover crops differed in their ability to suppress weeds, however, rye showed suppression levels of approximately 90% and was similar to levels achieved by herbicide systems. In both years, herbicide plots had lower horseweed biomass than any of the cover crop systems, while also having the greatest soybean yields. Plant height, whole plant seed production, and seed subsamples were recorded for horseweed in the fallow control, wheat, and rye plots. Differences among crops for total seed weight were found with rye and wheat having reduced seed production compared to the fallow control. No differences in 200-seed weights were detected. Seed production was widely variable across each plant in the study; seed production numbers ranged from 1,117,000 to 15,962,000 seeds per plant. Data indicates that combining both cover crop and herbicide systems may provide growers with an alternative method to suppress horseweed.


PERSPECTIVES ON CORN YIELD LOSSES DUE TO WEEDS IN NORTH AMERICA. A. Dille*1, P. H. Sikkema2, V. M. Davis3, I. C. Burke4, W. J. Everman5; 1Kansas State University, Manhattan, KS, 2University of Guelph, Ridgetown, ON, 3University of Wisconsin, Madison, WI, 4Washington State University, Pullman, WA, 5NCSU, Raleigh, NC (82)

ABSTRACT

Weeds are one of the most significant threats to crop production in North America.  Crop losses in yield and quality due to weed interference, as well as costs of controlling weeds, have a significant economic impact on crop production.  Previous WSSA Weed Loss committee reports, as chaired by Chandler (1984) and Bridges (1992), provided snapshots of the comparative losses due to weeds across geographic regions and crops within these regions.  This presentation begins a report from the WSSA Weed Loss committee on crop yield losses due to weeds, specifically in corn (Zea mays L.).  Yield loss estimates were determined from comparative observations of corn yields between the weedy control and plots with greater than 95% weed control in studies conducted from 2007 to 2013.  Researchers from each state and province provided at least three and up to ten individual comparisons, which were then averaged within a year, and then averaged over the seven years.  These percent yield loss values were used to determine total corn yield loss in bu/ac based on average corn yields for each state or province as well as current commodity prices for a given year as summarized by USDA-NASS and Statistics Canada.  Averaged across 2007 to 2013, weed interference in corn caused a 52% yield loss.  For example, in 2012, in the US and Canada corn was grown on 87,413,045 and 3,543,735 acres with production of 12,739 million and 200 million bushels, respectively. Using an average corn price in 2013 of US $6.15/bu, farm gate value would be reduced by US $41,378 million if no weed management tactics were employed.


TARGETED METABOLOMICS - A ROBUST ANALYTICAL APPROACH FOR AUGMENTING MECHANISTIC INSIGHTS INTO HERBICIDE RESISTANCE IN WEEDS. A. S. Maroli*1, V. K. Nandula2, N. Tharayil1; 1Clemson University, Clemson, SC, 2USDA, Stoneville, MS (83)

ABSTRACT

With the advent of Whole Genome Sequencing (WGS) and other high throughput technologies, we know have a plethora of information depicting genetic and transcript regulation. However, gene expression data alone does not reflect the “true” physiological state of the organism. To have a better understanding of the functional phenotypic characteristics of an organism metabolomics data too is required. Metabolomics, which involves capturing and analyzing metabolites, provides an unaltered snapshot of the “current” physiological state of the organism. Though a relatively new field, it produces vast amounts of data providing information of biological processes that forms the end results of the “biocascade” commencing with gene expression. Application of metabolomics in weed science research has not been extensively pursued. In this study, we employed targeted-metabolomic profiling to identify metabolite-level perturbations induced by glyphosate in two weed species- Amaranthus palmeri (Glyphosate susceptible and Glyphosate Resistant) and Ipomea purpurea (Glyphosate tolerant).

A.palmeri plants were subjected to a glyphosate concentration of 0.4kg ae Ha-1 and leaves were harvested after 8 and 72 hours after treatment (HAT). The resulting changes in carbon and nitrogen metabolism at the two time points were captured using gas and liquid chromatography-tandem mass spectrometry, followed by data processing and multivariate statistical approaches. The resulting data showed that in A.palmeri, glyphosate application had caused disruptions in both nitrogen and carbon metabolism within 8HAT. Metabolome profiling data significantly differentiated between the two biotypes and the treatments. Hierarchical clustering showed that at 8HAT, biotypes with same treatment clustered together indicating glyphosate perturbations within 8 h of application. This was substantiated with the concentration of shikmic acid levels. Shikimic acid (SA) accumulation, the physiological hallmark of glyphosate injury, was observed in both the susceptible and resistant biotypes of A.palmeri at 8HAT. However, at 72HAT, levels of SA decreased in the R-biotype while it increased considerably in the S-biotype.

Similarly, two biotypes of I.purpurea having varying tolerance (High Tolerance, WAS GR50 151.44 g ae/Ha and Low Tolerance, QUI 59.11 g ae/Ha) to glyphosate were used for metabolomic profiling study. The plants were treated with 0.1X glyphosate concentration (1X=0.84kg ae/Ha) and young leaves were harvested after 72h of application. Metabolomic profiling, followed by multivariate analyses captured the differences between the two biotypes as well as distinguished between the glyphosate and water (control) application. Compared to the water control treatment, glyphosate treated biotypes had a higher level of shikimate accumulation. Though WAS had a higher tolerance to glyphosate, it had a two-fold higher accumulation of SA as compared to QUI. Interestingly, glyphosate sprayed WAS biotype had a higher concentration of aromatic amino acids compared to its water control in spite of higher SA accumulation. However, in the QUI biotype, there was no significant difference in the levels of aromatic amino acids between the water and glyphosate treatments. This accumulation of aromatic amino acids in the WAS biotype despite an increase shikimate concentration highlights a possible disconnect between glyphosate response and interruption in amino acid metabolism. With respect to carbon metabolism, both the biotypes of I. purpurea responded negatively to glyphosate concentration. Application of glyphosate predominately resulted in the decrease of sugars (glucose, sucrose, talose, ribose, mannose and tagatose). The decrease in sugar levels could indicate higher metabolic activity to overcome the stress induced by glyphosate application.

Thus it can be concluded from our results that targeted metabolomics approach could be a powerful tool in probing the cellular physiology and metabolic pathways, which could provide real-time insight into the physiological mechanisms that regulate herbicide tolerance/resistance in weedy biotypes. The added advantage of metabolomics approach over other omics approaches is that it is species independent and therefore can be used as a robust tool for diagnosing herbicide resistance as well as compare and contrast wild-type weeds from genetically evolved weed biotypes. Also, by employing metabolomics profiling information, we can obtain the chemical fingerprint of the organism and then by integrating transcriptomics information, a complete picture of the type of resistance mechanism operating in a weed biotype can be determined. By targeting those metabolites, proteins or even the transcripts, we can employ a combination of herbicide with specific inhibitory action to effectively manage the weed population without contributing to its selection pressure.

 


USING RNA-SEQ TO IDENTIFY CANDIDATE RESISTANCE GENES IN ECHINOCHLOA IN MISSISSIPPI. A. A. Wright*1, K. Showmaker2, V. K. Nandula3, D. Peterson2, J. Bond1, D. Shaw2; 1Mississippi State University, Stoneville, MS, 2Mississippi State University, Mississippi State, MS, 3USDA, Stoneville, MS (84)

ABSTRACT

Echinochloa species are among the worst weeds in rice.  Controlling these species has become more difficult as the number of herbicide resistant populations is increasing.  A population of Echinochloa colona, MS1, from Sunflower County, MS, is resistant to imazamox, penoxsulam, bispyribac-sodium, fenoxaprop-P, quinclorac, and propanil.  Dose response studies were performed to assess the level of resistance to each herbicide.  Inclusion of malathion revealed the involvement of herbicide metabolism in the resistance mechanism to the ALS inhibitors and quinclorac.  A RNA-seq study was performed to explore the metabolic resistance mechanism.  RNA was harvested from MS1 and a sensitive biotype, Bond2, one hour after imazamox treatment and in the absence of herbicide treatment.  This was done in triplicate.  MiSeq runs and HiSeq runs were performed.  Transciptomes have been assembled for MS1 and Bond2 with 141, 473 and 151,707 transcripts respectively.  Differential gene expression analysis will be done both to investigate early response to herbicide exposure and differences between the resistant and sensitive biotypes to generate a candidate list of genes whose products may be involved in resistance.  Preliminary analysis of the transcriptome has revealed that no known resistance-conferring point mutation is present in the MS1 ACCase, suggesting a novel point mutation or a non-target site mechanism is responsible for fenoxaprop resistance.  Additional work is required to determine if the enzyme in MS1 is resistant to fenoxaprop.  The transcriptomes for resistant and sensitive Echinochloa colona biotypes will serve as a resource for further studies in understanding multiple herbicide resistance in this weed.

 


SCREENING FOR RESISTANCE TO 20X GLYPHOSATE IN BIOTYPES OF CONYZA CANADENSIS FROM SOYBEAN FIELDS AND NON-AGRICULTURAL HABITATS IN OHIO AND IOWA. Z. T. Beres*1, E. E. Ernst1, A. A. Snow1, J. T. Parrish1, M. D. Owen2, B. A. Ackley3, M. M. Loux1; 1Ohio State University, Columbus, OH, 2Iowa State University, Ames, IA, 3The Ohio State University, Columbus, OH (85)

ABSTRACT

Glyphosate is the leading herbicide throughout the world and is widely used with glyphosate-tolerant crops, but its efficacy has been compromised where weed species have evolved resistance. To better understand evolutionary outcomes of continued, strong selection from glyphosate exposure, we screened for variation in levels of resistance in Conyza canadensis (horseweed), a highly self-pollinating weed. We hypothesized that levels of glyphosate resistance would be greater in Ohio, where resistance in Conyza canadensis was first reported in 2003, compared to Iowa, where it was first reported in 2012. Within each state, we compared individual biotypes (maternal seed families) that had survived in no-till soybean fields vs. those found in non-agricultural sites such as abandoned fields and roadsides. In 2013, we collected seeds from one maternal plant in each of 88 populations in Ohio and 28 populations in Iowa. Populations were sampled from 6 counties in Ohio (3 southwest, 3 northeast) and 20 counties in Iowa, but we did not attempt to use systematic, random sampling methods. To evaluate resistance, we screened rosettes from each biotype at each of three dosages: 1X (=0.84 kg ae glyphosate/ha), 8X, and 20X, along with 0X controls. For ease of presentation, biotypes with at least 80% survival at each dosage were designated as either “resistant” (1X), “highly resistant” (8X), or “extremely resistant” (20X), respectively. Frequencies and spatial patterns of survival and damage at 1X, 8X, and 20X will be reported. Pooling data for both states, most of the biotypes from soybean fields were resistant at 1X or higher. We found that 40% and 36% of the biotypes from soybean fields were extremely resistant in Ohio and Iowa, respectively. For non-agricultural sites, 38% of the Ohio biotypes also were extremely resistant, while none of those from Iowa had such a high level of resistance and 93% of these Iowa biotypes were susceptible at 1X. Although our sampling strategy was not comprehensive, these results suggest that maternal families with resistance to 20X glyphosate occur in Ohio and Iowa, and that non-agricultural habitats in Ohio often support resistant plants. Possible reasons for finding relatively more resistant biotypes overall in sampled populations from Ohio, as compared to Iowa, could include earlier and more widespread selection pressures, stronger herbicide dosages used for weed management, and differences in the extent of seed-mediated gene flow from agricultural to non-agricultural habitats.

 


IDENTIFYING GENDER-SPECIFIC DNA MARKERS IN WATERHEMP (AMARANTHUS TUBERCULATUS). A. Sadeque*, P. Brown, P. Tranel; University of Illinois, Urbana, IL (86)

ABSTRACT

Abstract

Evolution of multiple herbicide resistance in waterhemp poses a huge threat to the agricultural community. One of the characteristics aiding waterhemp in evolving resistance is its dioecious nature. The genetics and evolution underlying this dioecious nature of the plant are still not understood. In current work we are utilizing Restriction-site Associated DNA sequencing (RAD-seq) to gain insights into the sex-determination mechanism in waterhemp. Approximately 200 plants each of males and females were sampled and used to make RAD-seq libraries. Libraries were separately barcoded and then sequenced using the Illumina platform. Sequence data were analyzed with TASSEL (Trait Analysis by aSSociation, Evolution and Linkage) with a goal of identifying gender-specific reads. Through the analysis pipeline approximately one million reads were obtained. Further analysis of the sequence data was carried out through Python and R, which helped in distinguishing between male and female reads. When sequence reads were evaluated with the criteria of being present at least 500 times in one sex and no more than 2 times in the other sex, 22 and 0 male-specific and female-specific reads, respectively, were identified. A few candidate male specific reads were selected and PCR probes were developed for these candidate sequences. The PCR markers were then evaluated for gender specificity using a different waterhemp population. One of the markers consistently distinguished male and female waterhemp plants. In the near term, gender-specific markers will be useful to the waterhemp research community (e.g., in selecting plants for crossing experiments). In the long term, this research will provide tools to begin detailed investigations of the molecular biology and evolution of dioecy in Amaranthus. Ultimately, manipulation of gender expression in waterhemp could provide a novel weed management strategy.

 


CHARACTERIZATION OF MULTIPLE-RESISTANT PALMER AMARANTH IN MICHIGAN. J. R. Kohrt*1, C. Sprague2; 1Michigan State University, Okemos, MI, 2Michigan State University, East Lansing, MI (87)

ABSTRACT

Since Palmer amaranth was first identified in Michigan in 2010, certain populations have demonstrated resistance to both glyphosate and the ALS-inhibitors.  However, in recent field trials we have observed a failure in Palmer amaranth control with atrazine indicating a possible 3-way resistance to glyphosate (Group 9), ALS-inhibitors (Group 2), and triazines (Group 5).  Greenhouse dose-response experiments were conducted to confirm the presence of 3-way resistance in this population.  Rate titrations of glyphosate, thifensulfuron, and atrazine were applied to both susceptible- and suspected-resistant populations of Palmer amaranth from Barry County, MI.  For each herbicide and biotype of Palmer amaranth rate ranges were applied postemergence (POST) in order to elicit a response ranging from no control to complete plant death.  This experiment was repeated twice with 6 replications per treatment.  Visual evaluations were made 7 and 14 days after treatment and plants were harvested for dry weights at the conclusion of visual evaluations.  In order to further evaluate the possible triazine resistance a preemergence (PRE) dose-response experiment was conducted.   A similar rate titration that was applied for atrazine POST was utilized in the PRE experiment.  A known amount of Palmer amaranth was planted in pots containing field soil, and atrazine was applied to the soil surface and watered in immediately after application.  Emergence counts were taken up to 28 DAT and all above ground biomass was harvested for dry weight.  Each treatment was replicated 7 times and the experiment was conducted twice.  Complete control of the suspected-resistant Palmer amaranth population was not achieved by any one single herbicide evaluated up to 32 times the normal field use rate.  The magnitude of resistance for 50% visual growth reduction (GR50) 14 DAT between the suspected-resistant population and the susceptible population was 13, 50, and 2 times more resistant for glyphosate (Group 9), thifensulfuron (Group 2), and atrazine (Group 5), respectively.  While the magnitude of resistance for atrazine was relatively low, there were still some surviving plants in the 17.95 kg ai ha-1 (16 times the normal use rate of atrazine) indicating this population may still be segregating.  However, 45 times more atrazine was required PRE to achieve a 50% reduction in biomass for the suspected-resistant population compared with the susceptible population.                  


ELUCIDATING THE GERMINATION MECHANISM OF PARASITIC OROBANCHACEAE THROUGH TRANSCRIPTOMICS. H. Larose*1, D. Plakhine2, M. Yahyaa2, H. Eizenberg2, D. Joel2, Y. Tadmor2, J. Westwood1; 1Virginia Tech, Blacksburg, VA, 2Newe Yaar Research Center, ARO, Israel, Ramat Yishay, Israel (88)

ABSTRACT

Elucidating the germination mechanism of parasitic Orobanchaceae through comparative transcriptomics

 

H. Larose, D. Plakhine, M. Yahyaa, H. Eizenberg, D. Joel, Y. Tadmor, J. Westwood1

 

Parasitic plants of the family Orobanchaceae are among the most persistent and economically damaging agricultural weeds, posing a major constraint to the production of many crops in the Mediterranean, Eastern European and African regions. One of the key features in the life cycle of obligate parasites is the ability of their minute seeds to lie dormant in the soil until a host-derived germination signal is perceived. This specificity prohibits seed germination in the absence of an acceptable host and is crucial, given that the seedling will die if its radicle (extending at most 1-2 millimeters) does not reach the host before the limited amount of resources stored in the seed are exhausted. Most naturally occurring germination stimulants of Orobanchaceae seeds are strigolactones (SLs), which have attracted intense research interest in recent years because of their role in non-parasitic plants mediating arbuscular mycorrhizal fungi interactions and functioning as an important plant hormone. Nevertheless, the mechanisms by which parasitic plants respond to specific germination signals remain unclear. We are using genetic and genomic approaches to elucidate this mechanism. We are using two closely related species, Orobanche cumana and O. cernua, which differ in germination stimulant specificity. Whereas O. cernua parasitizes tomato and responds to the SL orobanchol, O. cumana parasitizes sunflower and germinates in response to dehydrocostus lactone (DCL). Crosses of O. cumana and O. cernua produced hybrids that segregate for stimulant specificity, creating a tractable genetic system. As a first step, transcriptomes of the parental species were sequenced to identify genetic differences that may be related to stimulant specificity. Final de novo transcriptomes of O. cumana and O. cernua were assembled using Trinity de novo assembler and contain 143,285 and 132,608 contigs respectively. Differential expression analysis was performed using the EdgeR statistical package followed by the clustering software Proteinortho to identify orthologous genes that are differentially expressed between the two species at various stages of seed conditioning and germination stimulant exposure. Ongoing analysis of these gene groups includes SNP identification and the calculation of the nonsynonymous and synonymous substitution rates at each location. This research has potential to uncover the basis for germination specificity in parasitic weeds and reveal a mechanism of SL perception in plants.

 

 

 

 


THE CURRENCY OF A THIEF:  METABOLOMIC ANALYSIS OF HETEROTROPHIC NITROGEN IN PARASITIC PHELIPANCHE AEGYPTIACA . K. Clermont*, E. Collakova, J. Westwood; Virginia Tech, Blacksburg, VA (89)

ABSTRACT

Parasitic weeds of the family Orobanchaceae attach to roots of host plants via haustoria capable of drawing nutrients from host vascular tissue.  The development of the haustorium marks a shift in parasite metabolism from autotrophic to at least partially heterotrophic.  Transcriptome profiles of key stages surrounding haustorial development have been previously characterized in the Parasitic Plant Genome Project for three species of parasitic Orobanchaceae which differ in level of host dependence: Triphysaria versicolor, Striga hermonthica, and Phelipanche aegyptiaca.  While species within the family differ in the extent to which they fix their own carbon, significant parasitism for host nitrogen is a common characteristic across parasitic Orobanchaceae.  We hypothesize that if nitrogen is the target commodity common among the parasitic Orobanchaceae, then the tactics of the parasitic “thief” for acquisition and assimilation of nitrogen from the host are likely to be conserved.  Here we use comparative profiling of primary nitrogen metabolism to gain insight into the assimilation of nitrogen by P. aegyptiaca.  To this end, P. aegyptiaca amino acid profiles have been generated from key stages of parasitism, including seedlings before host attachment, seedlings in the process of making host attachments, and developing parasite tubercles.  P. aegyptiaca showed an increase in total amino acids after vascular attachment to the host, surpassing that of the host root.  During initial growth of the attached parasite tubercle the amino acid pool accumulated high levels of glutamine, but after further expansion and differentiation of the parasite the pool shifted to accumulate asparagine.  Enzymes involved in the synthesis of these two amino acids have been shown to be important to parasitic Orobanchaceae.  These results implicate the potential that disruption of nitrogen-assimilation enzymes will inhibit early development of parasitic weeds.  This work is a starting point for more detailed metabolomic analyses of related parasites in Orobanchaceae.  This data can be used in conjunction with existing transcriptome data to identify novel targets for controlling the damage caused by parasitic weeds.


OPTIMIZING CULTURED PHELIPANCHE REGENERATION FOR RESEARCH ON PARASITIC WEEDS. R. L. Warnock*, H. Gruszewski, J. Westwood; Virginia Tech, Blacksburg, VA (90)

ABSTRACT

Phelipanche aegyptiaca is a root holoparasite that decimates crops in the Mediterranean and Middle East regions. Because of its obligate nature, this parasite must perceive a host-derived signal molecule to ensure close proximity to a host root in order to germinate. The signal recognized by P. aegyptiaca is a strigolactone, a plant hormone used to regulate branching and to recruit mycorrhizal fungi. The overall goal of this project is to investigate P. aegyptiaca germination by silencing parasite genes that are hypothesized to be involved in strigolactone perception. In order to silence selected genes, double-stranded hairpin RNA interference constructs were generated. To date, constructs have been generated for two genes linked to perception (D14 and MAX2), as well as a gene essential to the production of strigolactones (CCD8). The transformation of these constructs into P. aegyptiaca will be mediated by Agrobacterium rhizogenes. Although the transformation of P. aegyptiaca has been reported by our group, use of the technique has been limited by low rates of regeneration of transformed parasite tissue. Therefore, one specific objective of this work was to optimize the methods for parasite regeneration. Regeneration of P. aegyptiaca callus tissue involves applying the parasite callus to roots of host plants grown in a rhizotron and allowing the parasite callus to attach to the host root.  Ideally, the parasite callus should form a physical connection to the host root and lead to development of a parasite shoot and flower.  However, in most cases the callus would senesce prior to attachment.  For this optimization experiment, we tested the effects of nutrient starvation prior to attachment and a technique to reduce callus contact with moisture in the rhizotrons. Low moisture was achieved by separating the host root and callus from the supporting medium using a glass microscope slide.  After three weeks of observing parasites growing in the rhizotron host system, the highest incidence (31%) of callus attachment occurred in a low moisture environment as compared to callus in direct contact with medium (5%). Ongoing experiments will confirm and further optimize conditions for regeneration of parasitic tissue, but these results are sufficient to proceed with research on transforming P. aegyptiaca with gene silencing constructs.

 


GENE FLOW FROM GLYPHOSATE-RESISTANT COMMON WATERHEMP UNDER FIELD CONDITION. D. Sarangi*1, A. J. Jhala2; 1University of Nebraska, Lincoln, NE, 2University of Florida, Lake Alfred, FL (91)

ABSTRACT

Glyphosate-resistant common waterhemp (Amaranthus rudis Sauer) is one of the difficult-to-control weeds in the Midwestern United States. The dioecious and anemophily natures of common waterhemp are believed to aid in rapid spreading of herbicide resistance genes. At the moment, there are few data available on common waterhemp regarding its pollen biology and dispersal; however there is a lack of information about pollen-mediated gene flow from glyphopsate-resistant to -susceptible biotypes. The experiments were conducted in 2013 and 2014 at Clay County, NE to quantify pollen-mediated gene flow from glyphgopsate-resistant to glyphosate-susceptible biotypes of common waterhemp. A donor (10-m diam; 80 sq m)-receptor (80 × 80 m) design was used for this study. Approximately 550 plants of glyphosate-resistant common waterhemp, considered as pollen source in this study, were transplanted in the pollen-donor block located at the center. Plants from a known glyphosate-susceptible common waterhemp biotype were planted in the receptor area divided into eight directional (four cardinal directions i.e. N, S, E, and W; and four ordinal directions i.e. NE, NW, SE, and SW) blocks. Flowering synchrony between donor and receptor, and hourly meteorological data were recorded throughout this study. Seeds from each glyphosate-susceptible common waterhemp plants grown up to 50 m distance from the donor were harvested separately and the seedlings were grown in the greenhouse to evaluate the pollen-mediated gene flow by using glyphosate-resistant trait as a selective marker. Results indicated that proportion of the glyphosate-resistant progeny was reduced exponentially with the increasing distance from the source. Frequency of gene flow was highest near to the source; averaging 0.5813 at 0.1 m from the source, whereas it was 0.1015 at 50 m. It is estimated that the gene flow was reduced by 50% (O50) and 90% (O90) at 12.1 m and 40.3 m, respectively. Results from this study indicated about the specific pattern of pollen-mediated gene flow from glyphosate-resistant common waterhemp biotypes to the glyphosate-susceptible biotypes under field condition. As high genetic variability is always present in common waterhemp biotypes, the data from ongoing in vivo shikimate accumulation assay and glyphosate resistance screening for more number of common waterhemp seedlings is warranted.


WEED EMERGENCE AND POPULATION DYNAMICS IN ALTERNATIVE IRRIGATION SYSTEMS IN CALIFORNIA RICE. W. B. Brim-DeForest, B. A. Linquist, A. J. Fischer*; University of California, Davis, Davis, CA (92)

ABSTRACT

Rice in California is largely continuously flooded, primarily for control of certain weed species. In recent years, due to unprecedented drought, concerns about water usage have increased and alternative irrigation methods have been proposed. Little is known about the implications of such methods on weed emergence and population dynamics. The primary objectives of this research were to quantify: 1) differences in field emergence patterns of Cyperus difformis L. (smallflower umbrella sedge) and Echinochloa phyllopogon (Stapf.) Koss (synonym E. oryzicola Vasinger; late watergrass) under dry and flooded conditions; and 2) species-specific relationships for major weed species between percentage cover at canopy closure, biomass at harvest, and yield loss under alternative irrigation systems.

All studies were conducted at the Rice Experiment Station, in Biggs, CA, in 2013. Two fields with large populations of susceptible C. difformis and E. phyllopogon were selected to count emergence. The experiment was set up as a Randomized Complete Block Design (RCBD) with three replications per irrigation treatment: 1) Drill-seeded alternate wet and dry (DS-AWD): drill-seeded, then flushed each time volumetric water content (VWC) of the soil reached 35% (approximately −2.0 MPa); and 2) Water-seeded conventional (WS-Control): permanent flood of 10-15 cm, drained one month prior to harvest. Daily counts of emerged seedlings were conducted in three 25 cm2 quadrats per replication. Plants were removed at each count until no more plants emerged (before canopy closure of the rice).

To assess population-level dynamics, three irrigation systems were evaluated in an RCBD with three replications per irrigation treatment: 1) DS-AWD; 2) Water-seeded alternate wet and dry (WS-AWD): flooded for initial seeding up to canopy closure of the rice, subsequently allowed to drain and then flushed again each time VWC reached 35%; and 3) WS-Control. At canopy closure, visual assessments of relative weed cover of major weed species (Echinochloa spp., C. difformis, Leptochloa fusca spp., Schoenoplectus mucronatus (L.) Palla, and Ammannia spp.) were taken from an herbicide-free section of each treatment. At harvest, measurements of fresh and dry biomass per-species were taken from the same untreated areas. Rice was harvested from two 18.5-m2 areas in the weedy section of each treatment, as well as in the weed-free sections of each treatment.

The total number of C. difformis seedlings emerged from DS-AWD was less than emerged from WS-Control (ANOVA, p < 0.005). The total number of E. phyllopogon emerged from DS-AWD was not different from that of WS-Control (ANOVA, p > 0.05). Yields were not different across treatments when weeds were fully controlled with herbicide (Tukey’s Mean Separation Test, α = 0.05). Without weed control, yields were zero in the DS-AWD, and were reduced by the WS-AWD treatment. Grasses (Echinochloa spp. and L. fusca spp.) were the main drivers of yield loss across all irrigation systems, both when evaluated at canopy closure and at harvest. Grasses outcompeted rice, sedges and broadleaves. In the presence of grasses, sedges and broadleaves did not contribute significantly to yield loss across all irrigation systems. E. phyllopogon emerged under both aerobic and anaerobic conditions, making it highly competitive regardless of irrigation system. C. difformis emerged at high numbers under flooded conditions, but was not competitive against other species after emergence. Low C. difformis numbers in DS-AWD may suggest temporary moisture stress as a control method for this aquatic weed.

 


PLANT SIZE AND ALS-INHIBITING HERBICIDE DOSE INFLUENCE THE CONTROL OF ALS-RESISTANT SHATTERCANE POPULATIONS. R. Werle*1, R. L. Martins2, L. Sandell3, J. Lindquist1; 1University of Nebraska-Lincoln, Lincoln, NE, 2So Paulo State University, Botucatu, Brazil, 3Valent Corporation, Lincoln, NE (93)

ABSTRACT

Traditional breeding technology is currently being used to develop grain sorghum germplasm that will be tolerant to acetolactate synthase (ALS)-inhibiting herbicides. Use of ALS-inhibitors for weed control during the 1980’s and 1990’s resulted in the evolution of resistance to ALS-inhibitors in shattercane, a weedy relative of sorghum. A recent survey conducted with shattercane populations from Nebraska and Kansas revealed that ALS-resistant shattercane populations are still present in corn-soybean production systems. The presence of ALS-resistant shattercane populations and gene flow from crop to weed are the major concerns regarding the introduction of this new technology. The objective of this study was to evaluate the response of several shattercane populations to nicosulfuron applied at different rates and plant growth stages. Six shattercane populations were selected from the aforementioned survey (2 resistant, 2 intermediate, and 2 ALS-susceptible populations). ALS-tolerant and susceptible sorghums were included as controls. Plants were grown under greenhouse conditions in square plastic pots (13 cm wide and 15 cm high) filled with commercial potting mix. The study was arranged in a randomized complete block design with four replications and was conducted twice. Three planting times were scaled at 2 week intervals. At 2 weeks after the last planting time, plants were treated with 0, 0.5, 1 or 2 times the recommended nicosulfuron rate (35 g ai ha-1). Plants from the first, second, and third planting time were, on average, at V7 (V6-V8; 92±4 cm; average ± standard error), V4 (V4-V5; 46±1 cm), and V1 (V1-V2; 14±1 cm) growth stage, respectively, at herbicide application time. Plants were harvested at 21 days after treatment, dried to constant weight at 60 C, dry weight of individual plants recorded and dry weight reduction calculated (DWR; compared to untreated plants for each population/growth stage combination). A three-way interaction between population, growth stage, and herbicide rate was detected (P<0.01); therefore, the response of each population to each herbicide rate and plant growth stage combination was evaluated separately. When applied at V7, herbicide treatments were not very effective, even on susceptible populations (DWR<70%). When treated at V4, plants from the susceptible populations were controlled (DWR>80%) but intermediate and resistant populations were not. When treated at V1, susceptible populations were controlled and intermediate and resistant populations had significant reduction in plant development when using the recommended herbicide rate (DWR>70%). When a 2X rate was used at V1 better weed control was achieved but crop injury was also observed. Nicosulfuron application at young growth stages using the labeled rate resulted in adequate control of susceptible shattercane populations and lowered the biomass of intermediate and resistant populations. According to our results, early weed control is likely to reduce competition with crop and also the spread of resistance in subsequent cropping seasons (by reducing fitness of resistant biotypes). Molecular work will be conducted to further explore the underlying cause of ALS-resistance in the shattercane populations used in this study. 


POSTEMERGENCE CONTROL OF BROADLEAF WEEDS WITH THE BIOHERBICIDE THAXTOMIN A (MBI-005). J. C. Wolfe*, J. C. Neal, C. D. Harlow; NCSU, Raleigh, NC (94)

ABSTRACT

The market for natural products for pest control has grown considerably over the past decade. Consumers in both North America and Europe have expressed concerns about the safety of widespread synthetic pesticide usage, particularly in amenity areas such as turf.  Unfortunately few natural products are currently available which can provide effective weed control. The bioherbicide thaxtomin A (MBI-005), has been reported to have both preemergence and postemergence activity on broadleaf and grassy weeds but safe on established turfgrass. However, limited information is available on Thaxtomin A efficacy on broadleaf weeds in turf.

Experiments were conducted at the North Carolina State University Horticultural Field Lab in October of 2012 and 2013 to determine the efficacy of thaxtomin A for postemergence control of seedling broadleaf weeds. Broadleaf weeds were surface seeded into 1 L pots filled with a hammer-milled pine bark substrate in September of both years, and treatments were applied four weeks after seeding and re-applied four weeks later. Treatments in these experiments included thaxtomin A at 190 and 380 g ai ha-1, plus an industry standard postemergence broadleaf herbicide, Weed B Gon MAX RTU (0.22% mecoprop, 0.12% 2,4-D, 0.05% dicamba) at 412 g ai ha-1. A non-treated control was also included. Treatments were applied in a randomized complete block design with five replicates in 2012 and six replicates in 2013. Species evaluated included yellow woodsorrel (Oxalis stricta), marsh yellowcress (Rorippa palustris), ivyleaf speedwell (Veronica hederifolia) flexuous bittercress (Cardamine flexuosa), hairy galinsoga (Galinsoga quadriradiata), dandelion (Taraxacum officinale), henbit (Lamium amplexicaule) and common chickweed (Stellaria media). Percent weed control compared to the non-treated plants was visually evaluated weekly. In the first year of the study, fresh weights were also recorded; this data was highly correlated with visual ratings, and thus was not collected in year two. Data for the 2 years were combined and subjected to ANOVA and mean separation using Fisher’s protected LSD (p=0.05).

Thaxtomin A at 380 g ai ha-1 provided equal or better control of ivyleaf speedwell, henbit, yellow woodsorrel, and hairy galinsoga than the industry standard synthetic herbicide. While not equivalent to the standard, thaxtomin A at 380 g ai ha-1 also provided 81% control of flexuous bittercress and 84% control of marsh yellowcress. Common chickweed was not well controlled by thaxtomin A, providing only 44% control at 380 g ai ha-1.   These results indicate that two applications of thaxtomin A at 380 g ai ha-1 can provide commercially acceptable control of several important winter annual broadleaf weeds, while significantly suppressing others. Further study into optimizing application timing, along with the potential for improved long-term control by combining pre- and early postemergence applications of thaxtomin A is needed.


META-ANALYSIS OF SEED PREDATION BY VERTEBRATES AND INVERTEBRATES IN SEED REMOVAL ASSAYS. C. K. Blubaugh*, I. Kaplan; Purdue University, West Lafayette, IN (95)

ABSTRACT

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INHIBITION OF BROOMRAPE DEVELOPMENT UNDER LOW LIGHT INTENSITY. A. Cochavi1, J. E. Ephrath1, S. Rachmilevich1, C. Miao1, H. Eizenberg2; 1French Associates Institute for Agriculture and Biotechnology of Drylands, Sede Boqer, Israel, 2Newe Yaar Research Center, ARO, Israel, Ramat Yishay, Israel (96)

ABSTRACT


GENOTYPIC VARIATION IN PHENOLOGICAL PARAMETERS OF YELLOW NUTSEDGE POPULATIONS IN RESPONSE TO PHOTOPERIOD. P. Tehranchian*, J. K. Norsworthy; University of Arkansas, Fayetteville, AR (97)

ABSTRACT

Yellow nutsedge is one the most problematic monocots in direct-seeded, rice-soybean systems in Arkansas. In 2012, an acetolactate synthase (ALS)-inhibiting herbicide, halosulfuron, at a labeled field rate (53 g ai ha-1) failed to control a novel nutsedge biotype in an eastern Arkansas rice field. This putative resistant biotype (Res) was later proven to be resistant to halosulfuron and several other ALS-inhibiting herbicides. The Res biotype was identified as yellow nutsedge by a USDA plant taxonomist (Dr. Charles Bryson). An in vitro morphometric study was conducted to determine variation in reproductivity between Res and three susceptible (Sus) biotypes under different photoperiod regimes (12-, 14-, and 16-h). A genetic analysis was also performed to elucidate evolutionary relationships between Res and Sus biotypes. Phylogenetic trees were constructed based on ribosomal DNA internal transcribed spacer and mitochondrial nad4 gene intergenic spacer region sequences. In general, differences in quantitative traits (e.g. shoot development and tuber production) were recorded between Res and Sus biotypes and within Sus biotypes. Shoot development was increased in all biotypes at photoperiods greater than 12-h. The maximum Res tuberization was recorded at a 14-h photoperiod and inflorescence formation was only observed for this biotype over 90 days.  Phylogenetic analysis suggested that the Res biotype was closely related to yellow nutsedge; albeit, identical nad4 gene sequences between the Res biotype and a reference purple nutsedge suggested that the Res biotype was likely a result of hybridization between yellow and purple nutsedges. These findings perhaps explain those of previous research where this Res biotype was shown to mimic patterns of vegetative spread similar to that of purple nutsedge.

 


DID ALS INHIBITOR RESISTANCE IN AMARANTHUS SPINOSUS COME FROM A. PALMERI? W. Molin*1, A. A. Wright2, V. K. Nandula3, J. Bond2; 1USDA-ARS, Stoneville, MS, 2Mississippi State University, Stoneville, MS, 3USDA, Stoneville, MS (98)

ABSTRACT

                Among the most problematic weed species in Mississippi are members of the Amaranthus genus.  Some populations have evolved resistance to different classes of herbicides, making them more difficult to control.  It has been well established in the greenhouse and field that some members of this genus can hybridize and, by doing so, can transfer alleles conferring herbicide resistance to glyphosate or acetolactate synthase (ALS) inhibitors or both. Recently, it was shown that this can also occur in the field.  A population of glyphosate resistant Amaranthus spinosus located near Water Valley, MS was found to be the result of hybridization between a glyphosate resistant A. palmeri and a glyphosate sensitive A. spinosus.  This resulted in the transfer of glyphosate resistance from one species to another and generated a hybrid with some of the worst weedy characteristics of both species.  Additional work since then has revealed that ALS inhibitor resistance may also have transferred with glyphosate resistance.  Sequencing of ALS in the hybrids revealed the presence of a tryptophan 574 to leucine (W574L) substitution, known in other species to confer resistance to many ALS inhibitors.  Sequencing of the upstream regions of several A. palmeri, A. spinosus, and hybrid plants revealed sequence similarities between the hybrids and A. palmeri that were absent in A. spinosus, suggesting that the resistant allele came from the A. palmeri parent.  The simultaneous transfer of multiple resistances along with undesirable weedy traits prognosticates an ever widening resistance problem and a driving factor in the evolution of new weedy traits and resistance enhancement characteristics.


MULTIPLE ALLELES FOR ALS INHIBITOR RESISTANCE IN AMARANTHUS PALMERI IN MISSISSIPPI. W. Molin*1, A. A. Wright2, V. K. Nandula3; 1USDA-ARS, Stoneville, MS, 2Mississippi State University, Stoneville, MS, 3USDA, Stoneville, MS (99)

ABSTRACT

                Weedy Amaranthus species have become notoriously difficult to control as many populations have evolved resistance to various modes of action.  In the Mississippi Delta, glyphosate resistant A. palmeri populations are well established and pose a serious threat to agriculture.  An added challenge for growers is that many populations of A. palmeri have evolved resistance to acetolactate synthase (ALS) inhibitors.  To identify the mechanism of ALS inhibitor resistance, the gene encoding the target enzyme, ALS, was sequenced from several resistant and sensitive individuals.  Two resistance alleles were identified.  One allele contained the tryptophan 574 to leucine (W574L) substitution and the other contained the serine 653 to asparagine (S653N) substitution.  Efforts are underway to establish sensitive populations and resistant populations that are homozygous for each allele.  Once these lines have been established, dose responses and enzymatic assays will be performed to determine the level of resistance to representative members of each class of ALS inhibitors.  Knowledge about  the level of resistance conferred by each allele and to which ALS inhibitor group will aid in addressing control options for this already problematic weed.  This research is particularly important as there are a growing number of populations that are resistant to both glyphosate and ALS inhibitors.


NON TARGET SITE RESISTANCE TO ACCASE INHIBITORS IN GRASS WEEDS - A NEW PERSPECTIVE. M. Matzrafi*, B. Rubin, Z. Peleg; Hebrew University of Jerusalem, Rehovot, Israel (100)

ABSTRACT

Climate changes challenge crop production for the ever-increasing world population. While the effect of rising temperatures on crop-plants has been widely studied, only little is known on the effect it might have on herbicide resistance evolution. In recent years, inconclusive cases of ACCase-resistant grass weeds were reported both from field and greenhouse studies. We tested the response to diclofop-methyl in sensitive Lolium spp. populations, under different temperature regimes [10/16°C, 16/22°C, 22/28°C and 28/34°C (night/day)] and short day (10h) conditions. Interestingly, we noted that temperature elevation increases plant tolerance to the herbicide significantly. Hence, we hypothesis that this temperature-dependent response is due to a non-target site (NTS) mechanism, such as enhanced activity of detoxifying enzymes (e.g., GST and CYT P450). To overcome the genetic variation in herbicide response of individual Lolium plant, we used the model weed Brachypodium hybridum. A NTS ACCase resistant accession (BrI-782) was treated with pinoxaden and grown under different temperature regimes as described above. Under the low temperatures (10/16°C), none of the plants survived pinoxaden treatment, even at half of the recommended dose (X=30 g ai ha-1), whereas under the highest temperatures (28/34°C) plants survived up to 4X (120 g ha-1). These data indicate that variation between farmers' reports and lab experiments may be due to different environmental conditions. Our results point out the increasing risk for the development of weeds with enhanced metabolic herbicide resistant due to the projected global warming. Using the autogamous B. hybridum as a model weed may shed light on the NTS mechanisms endowing herbicide resistance and can facilitate the attempts to prevent its expansion.

 


ACCASE INHIBITOR RESISTANCE IN LEPTOCHLOA FUSCA SPP. FASCICULARIS (BEARDED SPRANGLETOP) IN CALIFORNIA RICE. W. B. Brim-DeForest, R. Alarcon-Reverte, A. J. Fischer*; University of California, Davis, Davis, CA (101)

ABSTRACT

Leptochloa fusca (L.) Kunth ssp. fascicularis (Lam.) N. Snow (bearded sprangletop) is a native weed of rice in California common to dry-seeded systems or systems where the water level has been allowed to recede. Herbicide resistance in Leptochloa species has been documented in other parts of the world, but this is the first reported instance in Leptochloa fusca. Resistance has not yet been found in the species L. fusca spp. uninervia (J. Presl) N. Snow (Mexican sprangletop), also a weed of California rice. Anecdotal evidence of resistance to cyhalofop has been recently noted by California rice growers. Growers are currently limited in the number of available herbicides that can control this species (cyhalofop, clomazone and thiobencarb). Thus, the objectives of this research were: 1) to confirm resistance to ACCase inhibitors in L. fusca spp. fascicularis (bearded sprangletop) in California rice; and 2) to determine a possible mechanism of resistance.

Seeds from two populations of L. fusca spp. fasicularis (bearded sprangletop) were collected from fields in Butte County, CA, in 2012 and 2013. Greenhouse experiments for whole plant bioassays were conducted at the Rice Experiment Station, in Biggs, CA in 2014. Single-seed lines of two populations, one presumed resistant (RI1) and one known susceptible (F) were used. Clethodim, cyhalofop and quizalofop were applied using a cabinet track sprayer when plants were at the 1-2 leaf stage.  Clethodim was applied at 0, 26.3, 52.5, 105.1, 192.7, 280.2, 560.5 and 1121 g ai ha-1, cyhalofop was applied at 0, 67.7, 156.3, 271, 302.2, 333.5, 667, 1334 g ai ha-1, and quizalofop was applied at 0, 9.6, 19.3, 38.5, 65.5, 92.5, 185 and 277.4 g ai ha-1. Partial sequencing of the ACCase gene in susceptible and resistant biotypes was conducted to elucidate the possible presence of resistance-conferring mutations.

Evaluation of the whole-plant bioassays confirmed resistance to cyhalofop and quizalofop, but not to clethodim, suggesting that resistance selected by cyhalofop use confers cross-resistance to quizalofop but not to clethodim. Preliminary evidence suggests that the mechanism of resistance to the cyhalofop and quizalofop involves a target-site alteration. The resistant biotype has a substitution at Trp2027Cys in the ACCase gene, a nucleotide change from guanine to thymine (TGG to TGT) at the third position of the codon encoding the amino acid tryptophan (Trp), which translates to a change from tryptophan to cysteine (Cys). This point mutation is known for conferring resistance to “fop” herbicides. 

Since cyhalofop resistance appears to be target-site and unless another source of resistance is unveiled, current recommendations for growers are to use herbicides with a different mode of action, such as thiobencarb, clomazone or benzobicyclon.


EVIDENCE FOR FOMESAFEN-INDUCED STIMULATORY EFFECTS ON GERMINATION OF AMARANTHUS TUBERCULATUS AT SUB-LETHAL DOSES. R. Wuerffel*, B. G. Young; Southern Illinois University, Carbondale, IL (102)

ABSTRACT

Preventing weed emergence by means of soil-applied herbicides is an important strategy for managing the growing problem of evolved herbicide resistance. However, herbicides from multiple sites of action (phytoene desaturase inhibitors, protoporphyrinogen oxidase [PPO] inhibitors) reportedly can stimulate seed germination or seedling emergence of certain weed species when present in a low concentration in the soil solution. This stimulatory effect is beneficial when enhanced seed germination ends in seedling mortality due to herbicide toxicity; however, reports of concomitant seedling mortality are inconsistent following observed stimulation of seedling emergence. Soil-applied PPO-inhibiting herbicides are widely used for suppressing seedling emergence of several pernicious Amaranthus species; however, low-dose stimulatory effects of these herbicides are unknown for the aforementioned genera. Therefore, the objectives of this research were to 1) understand if a low-dose PPO inhibitor (fomesafen) has stimulatory effects on waterhemp [A. tuberculatus (Moq.) Sauer (syn. rudis)] seed germination or seedling emergence, and 2) to elucidate if any perceived stimulatory effects were due to soil- or seed-borne pathogen interactions.

In a greenhouse experiment, 100 waterhemp seeds were planted into pots containing soil previously subjected to various sterilization treatments to modify microbial abundance, including steam sterilization and an application of a soil fungicide drench. Fomesafen was applied from 0.00132 to 13.2g ai ha-1 and seedling emergence was recorded every other day for two weeks. A separate experiment was conducted in a growth chamber in the absence of soil. Waterhemp seeds were sterilized with 2.5% sodium hypochlorite (bleach) or 30% ethanol to remove seed-borne pathogens, with and without scarification, respectively. Non-steam sterilized seeds were treated with sterile water. One hundred seeds from each seed sterilization group were placed in petri dishes containing 0.05 to 5000µM fomesafen, and then germinated waterhemp was enumerated every two days for a total of 10 days. Soil sterilization treatments in the greenhouse experiment dramatically reduced microbial abundance; however, waterhemp emergence in pots treated with low-dose fomesafen did not display stimulated waterhemp emergence in comparison to the non-herbicide-treated control. In the absence of soil in the growth chamber the speed of waterhemp germination and total germination, as measured by radicle protrusion, was stimulated by 0.05µM fomesafen in ethanol- and non-sterilized seeds, but not bleach-treated seeds. While a stimulatory effect was observed, regardless of seed-borne microbes, the effect was minor and likely has limited direct consequences in practical field situations. Nevertheless, the detected stimulatory response does posit interesting questions regarding the interactions of PPO-inhibiting herbicides and seed dormancy in A. tuberculatus. As use of soil-residual herbicides continues to increase it is critical to understand the potential stimulatory effects that soil-active herbicides may have on weed seedling emergence. 

 


SENSITIVITY OF DIFFERENT CORN CULTIVARS TO FORAMSULFURON. A. Paporisch, B. Rubin*; Hebrew University of Jerusalem, Rehovot, Israel (103)

ABSTRACT

Foramsulfuron (FS) is a sulfonylurea herbicide, inhibiting acetolactate synthase (ALS), registered in Israel for selective post emergence weed control in corn (Zea mays). It is commonly formulated with the safener isoxadifen-ethyl (IDE) in order to reduce crop injury. Our aim was to investigate the mechanism of corn sensitivity to FS, and examine its heredity. Four Sh2 corn genotypes were tested- two homozygous inbred lines (IBER001 and IBER002), their hybrid (ER00X) and a hybrid from different genetic background (PVS). IBER001 and PVS were sensitive to FS+IDE application, with ED50 values of 3.6 and 43.6 g ai ha-1, respectively, while IBER002 and ER00X were resistant- with ED50 of 794 and 421 g ai ha-1, respectively. IBER001 was sensitive to several other ALS inhibitors as well as 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor tembotrione+IDE, while IBER002 and ER00X were tolerant to recommended doses. PVS was sensitive to tembotrione+IDE . Malathion (P450 inhibitor) pre-treatment increased FS phytotoxicity to resistant inbred and hybrid, but had no effect when FS+IDE was applied. FS sensitivity inheritance was examined in F2 populations. ER00X F2 population segregated, with 1:3 sensitive:resistant, while in PVS F2 population, all plants tested were sensitive. Segregating population is polymorphic in a SSR marker, previously shown to be linked to nsf1 allele conferring sensitivity to P450 metabolized herbicides. Hypothesized mechanism of heredity in Sh2 genotypes is a single gene with recessive allele, conferring sensitivity to FS. Recessive allele might be a mutated P450 encoding gene or a transcription factor, resulting in sensitivity to several P450 metabolized herbicides.

 


CONFIRMATION OF GLYPHOSATE-RESISTANT KOCHIA IN IDAHO AND OREGON. P. Jha*1, D. W. Morishita2, J. Felix3, V. Kumar1, M. Flenniken4; 1Montana State University, Huntley, MT, 2University of Idaho, Kimberly, ID, 3Oregon State University, Ontario, OR, 4Montana State University, Bozeman, MT (104)

ABSTRACT

Occurrence of herbicide-resistant kochia (Kochia scoparia L. Schrad.) is an increasing concern for growers in the northwestern United States.  Based on grower complaints of poor kochia control with repeated applications of glyphosate (at the recommended field-use rate) in glyphosate-resistant (GR) sugar beet in eastern Oregon and western Idaho in 2014, we collected and investigated putative GR kochia accessions from those sugar beet fields; three accessions from eastern Oregon (designated ALA, VAL, and DB) and one accession from western Idaho (designated WIL).  The objective of this research was to confirm the level of resistance and investigate the molecular mechanism of resistance to glyphosate in the selected kochia accessions.  On the basis of whole-plant dose-response assays, ALA, VAL and DB accessions from Oregon had I50 (dose needed for 50% control) R/S ratio (resistance index) of 2.1, 7.0, and 9.7, respectively, and the R/S ratio of WIL accession from Idaho was 4.7.  For glyphosate resistance, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene was analyzed for target-site mutations (PCR and sequencing) and relative increase in gene copy numbers through qPCR.  No target-site mutations were detected at Pro106 of the EPSPS gene.  All GR kochia accessions had ~ 3 to 8 copies of the EPSPS gene compared with a single EPSPS gene copy of a susceptible accession.  This is the first confirmation of the evolution of glyphosate-resistant kochia in Idaho and Oregon.  Because of lack of alternative, effective and economical herbicide options for kochia control in sugar beet, growers need to proactively manage the GR kochia seed bank with alternative effective modes of action herbicides in crops such as corn or wheat/barley grown in rotation with GR sugar beet, with the integration of tillage practices.


GLYPHOSATE RESISTANCE IN COMMON RAGWEED FROM MISSISSIPPI. V. K. Nandula*1, M. Crampton2, V. Kalavacharla2, J. Bond3, T. Eubank4; 1USDA, Stoneville, MS, 2Delaware State University, Dover, DE, 3Mississippi State University, Stoneville, MS, 4Mycogen Seeds, Greenville, MS (105)

ABSTRACT

Glyphosate is one of the most commonly used broad-spectrum herbicides over the last 40 years. It acts by inhibiting the
enzymatic activity of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), which is part of the shikimate pathway. This pathway leads to the production of the aromatic amino acids, tyrosine, phenylalanine, and tryptophan, and several
essential secondary compounds. Due to widespread adoption of glyphosate-resistant crop technology, especially, corn, cotton, and soybean, several weed species in agronomic situations have developed resistance to this herbicide. Nine glyphosate resistant (GR) weed species have been documented in Mississippi, with common ragweed being the most recent. Research was conducted to confirm and characterize magnitude and mechanism of glyphosate resistance in two GR common ragweed biotypes from Mississippi, MS1 and MS2. A susceptible biotype, MAD, was included for comparison. ED50 (effective glyphosate dose to
reduce growth of treated plants by 50%) values for MS1, MS2, and MAD biotypes were 0.58, 0.46, and 0.11 kg ae/ha, respectively, indicating that MS1 and MS2 were 5- and 4-fold, respectively, more resistant than MAD to glyphosate . Initial
studies on 14C-glyphosate absorption and translocation did not indicate any difference between the MS1 and MS2 biotypes compared to MAD. Research investigating shikimate accumulation in response to glyphosate treatment and molecular mechanism (sequence analysis, genomic copy number, and gene expression of EPSPS) in the resistant and susceptible biotypes is underway. The results from these studies will help devise meaningful long-term GR common ragweed management strategies.


MECHANISM OF RESISTANCE TO GLYPHOSATE IN PALMER AMARANTH (AMARANTHUS PALMERI) POPULATIONS FROM NEW MEXICO. M. Mohseni-Moghadam*1, J. Ashigh2, J. Schroeder2; 1Ohio State University, Wooster, OH, 2New Mexico State University, Las Cruces, NM (106)

ABSTRACT

Two populations of Palmer amaranth from New Mexico have been confirmed to be resistant to glyphosate. In the present
study, the molecular basis of resistance and the mode of inheritance of resistance in those populations were investigated.
Quantitative real-time polymerase chain reaction analysis indicated up to an eightfold increase in genomic EPSPS copy
number in glyphosate resistant plants compared with susceptible plants. The relative genomic EPSPS copy number of
resistant plants was positively correlated with the relative EPSPS cDNA expression levels. Eight hours after treatment with
glyphosate, the shikimate accumulation levels in resistant plants were negatively correlated with the genomic EPSPS copy
numbers. Multiple sequencing of the EPSPS cDNA of resistant plants did not reveal any glyphosate resistance-conferring
mutations. The evaluation of F1, reciprocal F1, and F2 Palmer amaranth families indicated that resistance to glyphosate
does not follow a single-gene segregation pattern. Results suggest that the EPSPS amplification is the primary molecular
basis of resistance in glyphosate resistant populations of Palmer amaranth from New Mexico.

MULTIFACTORIAL HERBICIDE RESISTANCE IN ECHINOCHLOA PHYLLOPOGON OF CALIFORNIA RICE FIELDS. A. J. Fischer*, R. Alarcon-Reverte; University of California, Davis, Davis, CA (107)

ABSTRACT

Multifactorial herbicide resistance in Echinochloa phyllopogon of California rice fields

 Albert J. Fischer

Department of Plant Sciences University of California-Davis, One Shields Ave.95616, ajfischer@ucdavis.edu

 

 Abstract. Echinochloa phyllopogon is a major weed of rice in California.  This species has evolved resistance to multiple herbicides within a water seeded, continuously flooded, monocropped and heavily herbicide dependent rice system.   Use of enzyme inhibitors, enzyme activity assays and metabolomics suggested resistance to multiple herbicides resulted from enhanced herbicide metabolism via inducible P450s, GSTs and glycosyl transferases. Resistant plants also exhibit insensitivity to ethylene stimulation by quinclorac, enhanced detoxification of cyanide from ethylene biosynthesis, and mitigate paraquat induced photooxidative stress. Candidate gene transcription assays suggest resistance could relate to adaptive stress tolerance.  Use of synergistic herbicide combinations, different herbicide mechanisms of action, alternation of dry and water seeding methods, and use of stale seedbed techniques in combination with no-till are resistance mitigation attempts.  New diversification options are needed to sustain a system compromised by herbicide resistance evolution to multiple herbicides in major weeds.

 


TARGET-SITE RESISTANCE TO PROPANIL IN CYPERUS DIFFORMIS L.: IMPLICATIONS FOR MANAGEMENT IN RICE FIELDS OF CALIFORNIA. R. M. Pedroso, R. Alarcon-Reverte, A. J. Fischer*; University of California, Davis, Davis, CA (108)

ABSTRACT

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.


RICE SEEDLING GENE EXPRESSION IN RESPONSE TO COLD STRESS AND HERBICIDES. L. A. Avila*1, C. E. Schaedler2, L. F. Martini1, J. A. Noldin3, P. D. Zimmer4, M. Zimmer4, D. Agostinetto4, C. T. Borges4; 1Federal University of Pelotas (UFPel), Pelotas, Brazil, 2Universidade Federal do Pampa, Itaqui, Brazil, 3Epagri, Itaja, Brazil, 4Universidade Federal de Pelotas, Pelotas, Brazil (109)

ABSTRACT

The weed control improvement on modern rice crop production allowed to shift the planting time to early spring, which is very important management practice to achieve high yield. However early planting time exposes the rice seedlings to cold stress, impairing the crop establishment and also herbicide selectivity. The objective of this study was to evaluate the effect of cold stress combined with bispyribac-sodium application on molecular and physiological patterns of rice seedlings. A greenhouse experiment was conducted in 2010 at Universidade Federal de Pelotas, RS, Brazil. The treatments were composed by factorial design: factor A - planting times: late September and early November; factor B - bispyribac-sodium application and untreated check. Injury at 7, 14, 21 and 28 days after treatment (DAT); lipid peroxidation and total phenols at 7 DAT and APX, CAT, SOD, OsDREB1A, OsFAD8, OsCDPK13, CYP72A21, OsGSTL2 and OsGSTU10 gene expression at 12, 24, 48 hours after treatment HAT and 14 DAT were evaluated. Early planting time promoted greater bispiribac-sodium injury on rice seedlings. Lipid peroxidation and total phenols accumulation was stimulated by low temperature, however were not affected by bispyribac-sodium application.  SOD, CAT, APX, OsDREB1A, OsCDPK13, CYP72A2 and OsGSTL2 were responsive to low temperature and presented overexpression when exposed to herbicide, evidencing cross-talk between those two stress agents. OsFAD8 and OsGSTU10 presented significant expression under cold, however not responsive to herbicide. These results supports that cold affect not only herbicide metabolism but also on antioxidant machinery in order to cope secondary effect promoted by them.


DOES EPSPS GENE AMPLIFICATION CONFER FITNESS COST IN GLYPHOSATE-RESISTANT KOCHIA? V. Kumar*1, P. Jha1, M. Flenniken2, S. Misra3; 1Montana State University, Huntley, MT, 2Montana State University, Bozeman, MT, 3University of Georgia, Athens, GA (110)

ABSTRACT

Glyphosate-resistant (GR) kochia is an increasing threat to the sustainability of no-till GR cropping systems in the Northern Great Plains of North America. We reported the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene amplification as a mechanism of glyphosate resistance in GR kochia biotypes from Montana. The EPSPS gene amplification could potentially impact the fitness of GR kochia due to (1) metabolic cost incurred for additional EPSPS enzyme production, (2) functional disruption of other genes by insertion of the EPSPS gene in GR kochia genome. Greenhouse experiments were conducted to investigate the influence of the EPSPS gene amplification on (1) fitness traits and (2) glyphosate resistance level in GR kochia.  Inbred lines (developed after three generations of recurrent selection) of glyphosate-susceptible (designated SUS) and GR (designated CHES01 and JOP01) kochia biotypes were grown under intraspecific competition (1, 4, and 8 plants pot-1). Growth and fitness traits including plant height, plant width, primary branches, leaf area, shoot biomass, 1000-seed weight, and seed production plant-1 were evaluated. Survival of GR kochia inbreds when exposed to glyphosate at 870 (field-use rate) and 4350 g ae ha-1 (five times the field-use rate) was assessed. Results indicated no fitness penalty conferred by 2- to 14-folds amplification of the EPSPS gene in GR kochia plants. GR kochia with ~ 5 to 14 relative EPSPS gene copies survived glyphosate applied at 4350 g ae ha-1; plants with ~ 2 to 4 copies of the EPSPS gene survived the low rate, but failed to survive the high glyphosate rate. In the absence of a fitness cost, and with the additive effect of the EPSPS gene amplification on glyphosate resistance levels, GR kochia with high EPSPS gene copies will most likely persist in field populations, irrespective of glyphosate selection pressure. Growers should target the GR kochia seed bank with alternative, effective modes of action herbicides and integrate non-chemical control methods, including crop rotation and tillage.  


EFFECT OF PLANTING TIME AND BISPYRIBAC-SODIUM ON GENE EXPRESSION OF RICE SEEDLINGS. L. F. Martini1, J. A. Noldin*2, L. A. Avila1, C. E. Schaedler3, C. T. Borges4, P. D. Zimmer4, D. Agostinetto4; 1Federal University of Pelotas (UFPel), Pelotas, Brazil, 2Epagri, Itaja, Brazil, 3Universidade Federal do Pampa, Itaqui, Brazil, 4Universidade Federal de Pelotas, Pelotas, Brazil (111)

ABSTRACT

The weed control improvement on modern rice crop production allowed to shift the planting time to early spring, which is very important management practice to achieve high yield. However early planting time exposes the rice seedlings to cold stress, impairing the crop establishment and also herbicide selectivity. The objective of this study was to evaluate the effect of cold stress combined with bispyribac-sodium application on molecular and physiological patterns of rice seedlings. A greenhouse experiment was conducted in 2010 at Universidade Federal de Pelotas, RS, Brazil. The treatments were composed by factorial design: factor A - planting times: late September and early November; factor B - bispyribac-sodium application and untreated check. Injury at 7, 14, 21 and 28 days after treatment (DAT); lipid peroxidation and total phenols at 7 DAT and APX, CAT, SOD, OsDREB1A, OsFAD8, OsCDPK13, CYP72A21, OsGSTL2 and OsGSTU10 gene expression at 12, 24, 48 hours after treatment HAT and 14 DAT were evaluated. Early planting time promoted greater bispiribac-sodium injury on rice seedlings. Lipid peroxidation and total phenols accumulation was stimulated by low temperature, however were not affected by bispyribac-sodium application.  SOD, CAT, APX, OsDREB1A, OsCDPK13, CYP72A2 and OsGSTL2 were responsive to low temperature and presented overexpression when exposed to herbicide, evidencing cross-talk between those two stress agents. OsFAD8 and OsGSTU10 presented significant expression under cold, however not responsive to herbicide. These results supports that cold affect not only herbicide metabolism but also on antioxidant machinery in order to cope secondary effect promoted by them.

Acknowledgments: CNPq and Fapesc for the finacial support.

 


PHYSIOLOGICAL EFFECTS OF GLUFOSINATE AMMONIUM ON CONVENTIONAL, GLUFOSINATE-RESISTANT AND WIDESTRIKE® COTTON. C. A. Carbonari*1, D. O. Latorre1, A. L. Cavenaghi2, E. D. Velini1, G. L. Gomes3; 1Faculdade de Cincias Agronmicas / UNESP, Botucatu, Brazil, 2UNIVAG, Cuiab, Brazil, 3Faculdade de Ciências Agronômicas / UNESP, Botucatu, Brazil (112)

ABSTRACT

This study assessed the physiological changes in conventional, glufosinate-resistant (Liberty Link®) and Widestrike® cotton cultivars after application of different glufosinate doses.  The cotton cultivars FM 993 (non-transgenic), FM 975WS (Widestrike®), and IMACD 6001LL (Liberty Link®) were grown in plastic pots in a greenhouse and were subjected to two glufosinate ammonium applications (at 25 and 40 days after plant emergence) at doses of 200, 400, and 600 g a.i. ha-1 and a control treatment without glufosinate ammonium application.  The experiments followed a completely randomized design, with four replicates.  The photosynthetic electron transport rate (ETR) was assessed using a portable fluorometer, and the plant injury was assessed visually.  Tissue samples were collected from the plants two days after the application of each dose, and the glutamate and ammonia levels in the plant tissue were determined by chromatography/mass spectrometry and by spectrophotometry, respectively.  Based on the ammonia and glutamate levels, ETR, and level of injury in the plants, the Widestrike® cultivar demonstrated a good level of resistance to glufosinate ammonium.  However, its level of resistance to this herbicide was slightly lower than that of the Liberty Link® cultivar, which is specifically marketed for this feature.

 


DEVELOPMENT OF PCR BASED TESTS TO IDENTIFY WEEDY AMARANTHUS SPECIES. A. A. Wright1, W. Molin*2, V. K. Nandula3; 1Mississippi State University, Stoneville, MS, 2USDA-ARS, Stoneville, MS, 3USDA, Stoneville, MS (113)

ABSTRACT

  The genus Amaranthus has many weedy species.  Current interest in the Amaranths stems from the development of herbicide resistance to several herbicide classes, including glyphosate and acetolactate synthase inhibitors, in some of the more important weedy Amaranths such as A. palmeri, A. retroflexus, and A. tuberculatus.  Accurate identification of Amaranthus species is important for efficient weed control as it can be very difficult to distinguish between the more common weedy Amaranths, especially at the seedling stage. Several molecular techniques have been devised and applied to distinguish between selected Amaranthus species including AFLP and restriction enzyme analysis of regions of internal transcribed spacer (ITS) of nuclear ribosomal DNA.  Although this technique distinguished eight weedy species, it failed to distinguish among hybrids.  A new target for distinguishing weedy Amaranths at early stages may be intron one of the gene encoding 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS).  EPSPS coding sequences are very similar among weedy Amaranths however, the intron sequences can vary greatly, as has already been established in A. palmeri and A. spinosus.  Efforts are underway to sequence intron one in six additional weedy Amaranths.  From the sequence data, species specific primers will be developed.  These will be checked against other populations of the same species and against other species to validate the usefulness of these primer sets in distinguishing weedy Amaranths.  Simple and quick PCR tests will facilitate rapid identification of Amaranthus species that are difficult to distinguish at the seedling stage.  This study may also serve as a template for similar studies in other groups of closely related weed species.


STATEWIDE POSTEMERGENCE SCREENING FOR PPO INHIBITOR RESISTANCE IN PIGWEEDS IN MISSISSIPPI. V. K. Nandula*1, A. A. Wright2, W. Molin3; 1USDA, Stoneville, MS, 2Mississippi State University, Stoneville, MS, 3USDA-ARS, Stoneville, MS (114)

ABSTRACT

Widespread adoption of glyphosate-resistant (GR) crops and associated use of glyphosate has resulted in evolution of GR weeds in several states including Mississippi. Currently, Mississippi leads the nation with 9 GR weed species. Among these are several pigweed (Amaranthus) species including Palmer amaranth, tall waterhemp, and spiny amaranth. GR Palmer amaranth populations, in particular, are spread across the state with some exhibiting multiple resistance to acetolactate synthase (ALS) inhibiting herbicides such as pyrithiobac. Protoporphyrinogen oxidase (PPO) inhibiting herbicides are one of the few chemical options left for managing GR weeds, pending commercialization/availability of auxin-type herbicide resistant crops. A Mississippi-wide survey was conducted to screen for resistance to several PPO inhibitors in approximately 200 pigweed accessions (both GR and non GR) comprising Palmer amaranth, tall waterhemp, spiny amaranth, and redroot pigweed. Flumioxazin (PRE) and fomesafen, lactofen, and saflufenacil (all applied POST to 5- to 10-cm tall plants) were included in the resistance evaluation. None of the pigweed accessions emerged through the flumioxazin treatment. Several pigweed accessions survived fomesafen and/or lactofen and/or saflufenacil. These accessions are presently being grown for second generation seed, which will be further screened for PPO resistance. Preliminary molecular analysis of putative resistant pigweed accessions showed no deletion of the glycine codon
at position 210 in PPX2L, a known target site mutation in PPO inhibitor resistant waterhemp.


CONVENTIONAL SOYBEAN GRAFTED TO GLYPHOSATE-RESISTANT ROOTSTOCK EXPRESS HERBICIDE TOLERANCE AT THE WHOLE-PLANT LEVEL. Y. Chen*1, J. Blakeslee1, D. Doohan2; 1The Ohio State University, Wooster, OH, 2Ohio State University, Wooster, OH (115)

ABSTRACT

Previous research established that grafting imparts herbicide tolerance from a glyphosate tolerant (RR) soybean rootstock to a conventional (CN) scion. However, no information is available regarding how soybean growth stage, soybean genotype and environment affects the tolerance level expressed in the CN scion. Several experiments were conducted in 2013 and 2014 to determine the effect of these variables. Three soybean growth stages (3-leaf, 6-leaf and 10-leaf stage), 15 soybean genotype grafted combinations (including CN/CN, CN/RR and RR/RR) and 2 temperature conditions were evaluated. Glyphosate rates used were 0.84 and 1.68 kg ae ha-1.  Genotypes were provided by Seed Consultants, Inc., Washington Court House, Ohio.  In every experiment all chimeras of CN/CN died and all RR/RR chimeras were injury free. The mean injury level of 3-leaf and 6-leaf stage chimeras was 72% while for the 10-leaf stage chimeras injury was 63% 24 days after treated with 0.84 kg ae ha-1glyphosate. When the glyphosate concentration was increased to 1.68 kg ae ha-1, the injury level of 3-leaf and 6-leaf stage chimera was 83% and the 10-leaf stage chimera injury level was 74%. Statistical analysis indicated that there was a significant difference in injury level between 3 or 6-leaf stage chimera and 10-leaf stage chimera. Genotype of the CN scion affected the expressed tolerance level of CN/RR chimeras; whereas, genotype of the RR rootstock had no effect on tolerance. Among CN/RR combinations, 352/9392 and 352/9328 were most tolerant while 5388/9392 was most susceptible. The impact of environmental variation (day/night temperatures were 28/22 ℃ or 24/18℃) on tolerance varied between genotypes. Tolerance of 352/352 (CN/CN) to glyphosate application increased when the temperature was lower.


METHIOZOLIN AND TYROSINE AMINOTRANSFERASES (TATS). C. Brabham, J. Gollihue*, S. Debolt, M. Barrett; University of Kentucky, Lexington, KY (116)

ABSTRACT

Methiozolin is a recently introduced herbicide for selective control of Poa annua in golf greens. The objective of this study is to characterize the herbicide symptomologies exhibited by Arabidopsis thaliana treated with a range of methiozolin rates (5nM to 50uM) and to provide further insight into its potential mode of action. Treated seedlings exhibited a range of unique visual characteristics. Root growth was inhibited by methiozolin at 5 nM but this rate had little effect on chlorophyll content at 7 or 14 days after treatment (DAT). Chlorophyll content was significantly different between 7 and 14 DAT and was significantly reduced at rates greater than 5 nM at 14 DAT. Analysis of cell expansion in methiozolin treated Arabidopsis seedlings were inconsistent with the radial cell swelling symptomology indicative of cellulose biosynthesis inhibitors. Methiozolin has also been proposed to be a pigment inhibitor by inhibiting the conversion of tyrosine to 4-hydroxyphenylpyruvate by the enzyme tyrosine aminotransferase (TAT). Arabidopsis has six predicted TATs enzyme and we test five out of the six gene knockouts to screen for their increased susceptibility to methiozolin. 


EFFECT OF DROUGHT ON HOST PARASITE RELATIONSHIP IN PHELIPANCHE AEGYPTIACA: PHYSIOLOGICAL STUDY. A. Cochavi1, J. E. Ephrath2, S. Rachmilevich2, H. Eizenberg3; 1French Associates Institute for Agriculture and Biotechnology of Drylands, Sede Boqer ‎, Israel, 2French Associates Institute for Agriculture and Biotechnology of Drylands, Sede Boqer, Israel, 3Newe Yaar Research Center, ARO, Israel, Ramat Yishay, Israel (117)

ABSTRACT

Egyptian broomrape (Phelipanche aegyptiaca) is an obligate root parasitic weed, which is completely dependent on the host plants due to the lack of chlorophyll and functional roots. An arid and semi-arid regions, where water is limited are favorable conditions for broomrape parasitism. In this study, a split-root system was used to investigate the interaction of P. aegyptiaca and its host tomato (Solanum lycopersicum) under drought stress. Tomato plants were grown with root split between two attached 4 litter pots, under the interaction of two factors: P. aegyptiaca infestation (15 mg seeds Kg-1) in three combinations (i.e. without infestation, one side infested, or both sides infested) and irrigation methods (i.e. partial drying or both side irrigated). Physiological measurements were taken during the growth season twice a week. The development stages of P. aegyptiaca were recorded at the end of the experiment. Results indicated that the biomass of P. aegyptiaca was decreased, and the development was inhibited under drought stress. Compared with control, P. aegyptiaca decreased stomatal conductance, chlorophyll content, and biomass of tomato plants. The severe damage to the host was caused under the combined stress (both sides infested by P. aegyptiaca and one side partially dried(. In conclusion, although P. aegyptiaca damage to the host decreased under drought stress, the parasite remained vital. In addition, when one side of the host remain stress-free (i.e. without broomrape or drought stress), host plant managed to compensate the damage better than plants stresses both sides. 

 


RATES OF ARSENIC SPECIATION TRANSFORMATION FOLLOWING MONOSODIUM METHYL ARSENATE APPLICATION TO SOILS. L. Ou*, D. Mahoney, T. Gannon, D. L. Hesterberg, M. L. Polizzottoo; NCSU, Raleigh, NC (118)

ABSTRACT

Monosodium methyl arsenate (MSMA) is an organic arsenical herbicide currently labeled in cotton and turfgrass which has high water solubility (Ks = 1,040,000 mg L-1), low lipophilicity (log Kow < 0), and pKa of 4.1 and 9.02. The Environmental Protection Agency phased out all organic arsenicals including MSMA in 2006, and extended the deadline for turfgrass usage, which initially was December 31, 2013. When MSMA is applied to agricultural systems, various processes ensue including adsorption and transformation. The amount adsorbed may affect the environmental fate of MSMA. Species transformation is important due to varying levels of toxicity of each species. There are many factors that influence these processes such as soil texture, pH, mineral oxides/hydroxides content, and soil organic carbon (SOC) content. The effect of SOC is not well understood due to its complexity. The objectives of this research were to: 1) determine the effect of texture and SOC on As binding and speciation, and 2) evaluate As kinetics and speciation transformation in a controlled system for 28 d.

Laboratory experiments were conducted to quantify adsorbed and solution As and also determine As speciation in aerobic soils. Two soil textures (sandy soil and sandy clay loam) and four organic carbon contents were included. Sphagnum peat was utilized as the organic carbon source with 0%, 2.5%, 5% and 10% (by weight) added to each soil. There were triplicates for each treatment for both soils. The system was equilibrated for 48 h after hydrated peat, soil, and water were mixed together. MSMA was spiked (1024 ppb) and the suspension was incubated until specified sampling time (0, 0.5, 1, 3, 5, 7, 10, 14, 21, and 28 d after treatment (DAT)). Samples were centrifuged and filtered, and the soil solution was analyzed using inductively coupled plasma mass spectrometry (ICP-MS) for total As and Fe, and high-performance liquid chromatography, and ICP-MS for As speciation. The solid samples were saved for synchrotron based micro-X-ray fluorescence (μ-XRF) and micro-X-ray absorption near edge structure (μ-XANES) spectroscopy at beamline 2-3 of the Stanford Synchrotron Radiation Lightsource (SSRL). Statistical analyses were performed using PROC ANOVA in SAS 9.4.

From 0 to 28 DAT, total As decreased in soil solutions of sandy soil and sandy clay loam, with more decrease in sandy clay loam (100-fold) than in sand (10-fold). Total As in sandy clay loam decreased more rapidly than in sandy soil. In both soils, with increasing SOC, total As present in soil solution increased. For sandy soil, the speciation data showed that the proportion of As V increased as SOC increased, especially after two wk. When 10% peat was added, As V became the dominant species in soil solution. For sandy clay loam, in the data collected so far, dimethyl arsinic acid increased as SOC increased and comprised 40% of total As when 10% peat was added.

In conclusion, these data indicate that: 1) sandy clay loam adsorbed more As than sandy soil and adsorption was more rapid, 2) SOC may compete with binding of As to clay minerals, which may decrease adsorption and increase total As in soil solution, and 3) SOC influenced As speciation in soil solution in both soils.  Implication of this research may allow best management practices to be developed minimizing adverse environmental effects from MSMA use. This research could help answer the question if MSMA should still be used, and what environment(s) it should be used in.

 

 

 


NITROUS OXIDE OUTPUT BASED ON WEED MANAGEMENT SYSTEMS. A. M. Knight*1, W. J. Everman1, S. C. Reberg-Horton2, S. Hu2, D. L. Jordan1, N. Creamer2; 1NCSU, Raleigh, NC, 2North Carolina State University, Raleigh, NC (119)

ABSTRACT

Agriculture accounts for a large portion of land use worldwide.  In the U.S. specifically, the World Bank indicated that agriculture accounts for roughly 45% of land use.  Agriculture is estimated to contribute greatly to the output of one of the main greenhouse gases, nitrous oxide (N2O), which is suspected of contributing to climate change, contributing an estimated 59 percent to emissions. These large percentages are suspected to partially be due to one-third of nitrogen applied to cropping systems being utilized by the system while the additional two-thirds are lost to the environment.  With different agricultural practices contributing to these greenhouse gas emissions, finding how various production practices contribute to greenhouse gas emissions will help in the recommendation of best management practices to minimize gas emissions by agriculture in the southeastern U.S.  Field studies were conducted in 2013 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 m2-1day-1 more) while weedy areas emit more nitrous oxide in organic systems (0.5-10 mg N m2-1day-1 more).  In addition, tillage plays a significant role in gas emissions across cropping systems.  Full tillage systems were emitting upwards of 12 mg N m2-1day-1 while no-till or minimum tillage systems were emitting roughly 3 mg N m2-1day-1 on the same dates.   


THE ENVIRONMENTAL IMPACT QUOTIENT (EIQ) SHOULD NOT BE USED TO COMPARE HERBICIDES. A. R. Kniss*, C. M. Coburn; University of Wyoming, Laramie, WY (120)

ABSTRACT

There is a desire by scientists and the general public to reduce the environmental impact of pesticides. Quantification of pesticide environmental impacts, however, is difficult and complex. A pesticide that is highly toxic to mammals may be relatively non-toxic to fish or birds. A pesticide that is highly persistent in soil may break down quickly in an aquatic environment. This complexity makes it difficult to declare any given pesticide as uniformly “better” or “worse” for the environment. The EIQ converts physiochemical and toxicological information on pesticide active ingredients into scores that are then combined mathematically and weighted into an index that purportedly quantifies relative risk to farm workers, consumers, and the environment. While criticized by others in the past, the EIQ continues to see regular use in the weed science literature. In particular, the EIQ is often used to compare herbicides used in genetically engineered herbicide resistant crops. A simulation and sensitivity analysis was conducted to investigate the relative sensitivity of the EIQ to changes in risk factors relevant to herbicides. Dermal and chronic toxicity have a relatively large impact on the EIQ, as expected. Two important risk factors for herbicides, leaching and surface runoff potential, have little impact on herbicide EIQ values. Most troubling, the risk factor with the greatest influence on the EIQ value is arbitrarily assigned to herbicides without any supporting quantitative data. The EIQ is a poor measure of a herbicide's environmental impact and should not be used to compare herbicides.


COMPETITIVE AND WEED SUPPRESSIVE EFFECTS OF COVER CROPS IN MIXTURE AND MONOCULTURE. A. A. Holmes, S. E. Wortman*; University of Illinois at Urbana - Champaign, Urbana, IL (121)

ABSTRACT

Cover crop use has been increasing in the north central US and many farmers are interested in growing diverse mixtures of cover crops. Cover crop mixtures have been shown to suppress weeds through competitive and negative soil residual effects (e.g., allelopathy), but the effects of individual species in a mixture is often unclear. The objective of this study is to assess the relative contribution of individual cover crop species to weed suppression through competitive and residual effects when planted in monoculture or mixture. Field trials were started in 2014 on two organic farms in central and northern Illinois and will continue through 2016. To elucidate species effects in mixture, 18 different cover crop species are planted across each of three seasons (six species per season) in monoculture and all possible five-way cover crop mixtures. Cover crop and weed biomass data is collected and residual crop and weed suppression is estimated using the “ragdoll” bioassay method. Oat was among the most productive species across both sites in the spring, yielding 4159 kg ha-1 in central Illinois and 2518 kg ha-1 in northern Illinois. Weed biomass was lowest in yellow mustard (8 g m-2) and oat (11 g m-2) monocultures in central and northern Illinois, respectively. Spring cover crop mixtures reduced weed biomass by 48 to 76% relative to monocultures. When mustard was excluded from the five-way mixture in central Illinois, weed biomass increased by 76% relative to all other five-way mixtures that included mustard. Sudangrass was the highest yielding summer cover crop in central Illinois (8862 kg ha-1), whereas corn (4454 kg ha-1) and buckwheat (4365 kg ha-1) were greatest in northern Illinois. Summer cover crop mixtures reduced weed biomass by 47% relative to monocultures across both farms. Weed biomass was lowest in buckwheat (37 g m-2) and sudangrass (69 g m-2). Soil incorporation of cover crops did not influence weed germination in bioassays, and effects on radicle length were inconsistent across location and season. First year results suggest that cover crop mixtures provide the most consistent level of weed suppression through competition, but residual weed suppression is less predictable. 

 


EFFECT OF COVER CROPS ON THE RELATIVE COVER AND WEED BIOMASS. H. A. Acciaresi*1, G. Picapietra2; 1Instituto Nacional Tecnologia Agropecuaria, Pergamino, Argentina, 2UNNOBA-INTA, Pergamino, Argentina (122)

ABSTRACT

The use of cover crops is an important alternative cultural weed management. Cover crops have gained importance in the Rolling Pampas due to the increasing resistance of weeds against different herbicides. Accordingly, the aim of this study was to evaluate the relative cover and weed aboveground biomass in eight cover crops.
Significant differences in the relative weed cover were observed, recorded the lowest values in Vicia sativa and Vicia sativa/Avena sativa. Cover crops significantly affected the aboveground biomass. The increasing order of aboveground biomass was: Vicia villosa <Vicia sativa/Avena sativa <Lolium multiflorum<Avena sativa = Hordeum vulgare <Bromus unioloides <Brassica napus <Raphanus sativus L. This cover crops appeared as a cultural alternative which reduced the presence of winter weeds, favouraging less use of herbicides in crop rotation.


DIFFERENTIAL RESPONSE TO GLUFOSINATE AND OXIFLUORFEN IN GLYPHOSATE-RESISTANT GRASS WEED SPECIES. P. T. Fernndez-Moreno1, R. Alcantara de la Cruz2, M. M. Trezzi3, J. Menndez Calle4, R. A. De Prado*1; 1Universidad de Crdoba, Crdoba, Spain, 2Universidad de Cordoba, Cordoba, Spain, 3Universidade Tecnologica Federal Do Parana, Pato Branco, Brazil, 4Universidad de Huelva, Huelva, Spain (123)

ABSTRACT

The continuous use of glyphosate during the last 20 years as the only chemical method of weed control in several parts of the world has led to the selection of many resistant weeds, such as Lolium muliflorum, Eleusine indica, Leptochloa virgata and Chloris elata. As a management strategy, farmers have applied oxyfluorfen and glufosinate to control these populations. The inadequate management of these herbicides have produced multiple-resistance. These glyphosate resistant populations were collected from several parts of the world and exposed to oxyfluorfen and glufosinate. A previously characterized resistant glyphosate grass weed showed high values of growth reduction 50% (GR50) with resistance factors (RF) between 2.43 and 4.80. The order of resistance was the following: L. virgata > L. multiflorum > E. indica > C. elata. Dose-response experiments with glufosinate showed that the resistant population of L. muliflorum was 3.17 times more resistant to the susceptible population. In addition, L. muliflorum population also showed a level of resistance to oxyfluorfen, which was 2.67 times more resistant to the susceptible population. L. virgata, E. indica and C. elata did not show any resistance to glufosinate and oxyfluorfen. These results confirm a very high-level glyphosate resistance, as well as a new cross-resistance to glufosinate and oxyfluorfen in L. multiflorum.


GLYPHOSATE RESISTANCE VARIABILITY IN CHLORIS SPP COLLECTED IN CUBA. R. Alcantara de la Cruz*1, P. T. Fernndez-Moreno2, M. M. Trezzi3, J. Menndez Calle4, R. A. De Prado2; 1Universidad de Cordoba, Cordoba, Spain, 2Universidad de Crdoba, Crdoba, Spain, 3Universidade Tecnologica Federal Do Parana, Pato Branco, Brazil, 4Universidad de Huelva, Huelva, Spain (124)

ABSTRACT

The citrus crops in Cuba are distributed throughout the island. The weed management is generally carried out using herbicides, mainly glyphosate. In 2013 a prospection weed was conducted in grass weeds which were difficult to be controlled with glyphosate. Three species of the Chloris genus were chosen to present the highest density and suspected resistance in those citrus groves. The main objectives of this work were to determine the resistance in those Chloris populations; and to carry out the characterization of the morphological parameters and use molecular markers of these species. The efficacy of glyphosate on the ED50 parameter was also studied. The results showed that the order of efficacy of glyphosate was C. ciliata > C. inflata > C. elata. There were no significant differences in the contact angle and retention in spray assays between species. The morphological characterization showed significant characteristics in each species. The fertile floret of C. inflata was glabrous; C. ciliata has the smallest awn of fertile floret; and C. elata, besides having the leaves about twice the width of C. ciliata and C. inflata, it also has the largest number of spikelets per raceme and per inflorescence. These characteristics indicate that C. elata is capable of producing more seeds than the other two species. The results at the molecular level, based on AFLP analyses, were fairly consistent. The individuals analized were separated clearly in three groups. Future studies should be conducted comparing the efficacy of glyphosate with populations never treated with this herbicide to allow us to determine the resistance level due to herbicide selection pressure.


RESPONSE TO GLYPHOSATE IN BORRERIA LATIFOLIA POPULATIONS FROM BRAZIL. F. Diesel1, M. Gallon1, R. Alcantara de la Cruz2, P. T. Fernndez-Moreno3, M. M. Trezzi*1, R. A. De Prado3; 1Universidade Tecnologica Federal Do Parana, Pato Branco, Brazil, 2Universidad de Cordoba, Cordoba, Spain, 3Universidad de Crdoba, Crdoba, Spain (125)

ABSTRACT

The broadleaf buttonweed (Borreria latifolia, syn. Spermacoce latifolia) is considered a weed tolerant to glyphosate and is an increasing problem in many crops in Brazil. The objective of this study is to evaluate the response of broadleaf buttonweed to glyphosate in biotypes collected in soybean fields from Paraná and Santa Catarina states, located in the Southern region of Brazil. A dose-response experiment was carried out under greenhouse conditions in a completely randomized design with four replications. The  treatments consisted of increasing rates of glyphosate (0, 74, 163, 360, 792 and 1742 g a.e. ha-1) applied to thirteen biotypes of broadleaf buttonweed originated from RR soybean fields and one biotype from a field without history of glyphosate spraying. The control at 14 and 28 days after application (DAA) and the shoot dry mass (DM) at 28 DAA were evaluated. The biotypes presented great response variability to glyphosate. Three biotypes were not controlled with doses above the usually employed in the fields (720 g a.e. ha-1) with ED50 of  404, 405 and 385 g a.e. ha-1, respectively. These biotypes had lower DM reductions than the biotypes collected in areas without application of glyphosate, whose ED50 was 99,4 g a.e. ha-1, indicating biotype selection by the repeated use of the herbicide.

 


QUICK TESTS: GLYPHOSATE-RESISTANT KOCHIA AND PINOXADEN-RESISTANT GRASS WEEDS. J. Pratchler*1, S. W. Shirriff2, H. J. Beckie2; 1University of Saskatchewan, Saskatoon, SK, 2Agriculture and Agri-Food Canada, Saskatoon, SK (126)

ABSTRACT

Rapid herbicide-resistant weed bioassays can facilitate timely and economical screening of suspected populations as a first step in
their management. Growth chamber studies were conducted to determine the feasibility of developing a quick, yet reliable bioassay to detect glyphosate-resistant (GR) kochia (Kochia scoparia L. Schrad.) and pinoxaden (ACC inhibitor, Group 1)-resistant wild oat (Avena fatua L.) and green foxtail (Setaria viridis L. Beauv.). Seeds of six kochia populations, three GR and three non-GR (susceptible), were placed on filter paper in petri dishes treated with varying doses of glyphosate. After 7-d incubation, seedlings with a true leaf (i.e., not cotyledons) at 25 mg L-1 glyphosate accurately distinguished GR from susceptible kochia populations. Shoot length inhibition and presence of seedlings with shoot tips exhibiting chlorophyll (with or without emerged first leaf) at 16 µM
pinoxaden reliably identified herbicide-resistant and -susceptible wild oat and green foxtail populations in a 7-d agar dish bioassay. These bioassays can facilitate more timely identification of GR kochia and the pinoxaden-resistant grass weed populations, thereby aiding resistant weed management.


PALMER AMARANTH IN CALIFORNIA: PLANNING AHEAD FOR GLYPHOSATE RESISTANCE MANAGEMENT. S. I. Rios1, S. D. Wright2, A. Ferry-Abee2, G. Banuelos2, E. Padilla2, S. Parry2, A. Shrestha*3; 1University of California Cooperative Extension-Riverside County, Moreno Valley, CA, 2University of California Cooperative Extension-Tulare/Kings Counties, Tulare, CA, 3California State University, Fresno, CA (127)

ABSTRACT

Glyphosate is the most popular herbicide for weed management in agriculture and non-crop areas globally. However, heavy reliance on glyphosate has resulted in the evolution of several glyphosate-resistant (GR) weed species globally. One such species of great concern in the U.S. is Palmer amaranth (Amaranthus plameri). GR populations of this species have been confirmed throughout the southeast U.S. since 2005 causing huge economic losses. In recent years, growers in the San Joaquin Valley (SJV) have observed poor control of Palmer amaranth in some glyphosate-tolerant crops and other crop and non-crop areas. It is not known if these are GR populations or application of glyphosate at more tolerant stages of the weed. This study evaluated Palmer amaranth populations from 23 different locations of the SJV. Plants from two locations that showed some tolerance to glyphosate at the label rate (840 g ae ha-1) were further compared to a known GR population from New Mexico. Five- to 8-leaf stage plants were treated with glyphosate rates ranging from 0 to 3.36 kg ae ha-1. Most of the SJV plants died at the label rate. Hence, the presence of GR Palmer amaranth in the SJV could not be definitely determined. Plant mortality was also evaluated at 3 different growth stages with several herbicides under greenhouse and field conditions. Tolerance to some herbicides including glyphosate was observed at more mature growth stages. Several herbicides and herbicide mixtures were identified for control of Palmer amaranth should GR populations be definitively documented in the SJV in future.


CROSS RESISTANCE TO ACCASE HERBICIDES IN ELEUSINE INDICA BIOTYPES COLLECTED IN BRAZIL. P. T. Fernndez-Moreno1, R. Alcantara de la Cruz2, M. M. Trezzi3, J. Menndez Calle4, R. A. De Prado*1; 1Universidad de Crdoba, Crdoba, Spain, 2Universidad de Cordoba, Cordoba, Spain, 3Universidade Tecnologica Federal Do Parana, Pato Branco, Brazil, 4Universidad de Huelva, Huelva, Spain (128)

ABSTRACT

Eleusine indica is a diploid grass weed, which has developed resistance to ACCase inhibitors during the last ten years due to the intensive and frequent use of this herbicide to control grass weeds in crops in Brazil. The objective of this study is to evaluate the cross-resistance to several ACCase-inhibiting herbicides on plants of biotypes E. indica collected in Brazil and evaluated in greenhouse. The parameter to growth reduction of 50% (GR50) to several products of the ariloxyphenoxypropionate and cyclohexanedione groups was studied. Studies on dose-response showed that the resistant biotypes were more resistant than the susceptible biotypes that had never been treated with herbicides. Resistance factors (RF) greater than two in all treatments were obtained, being Cyhalofop-butyl the highest (96.28 times more resistant). FR´s were ranked as follows: Cyhalofop-butyl (96.28) > Sethoxydim (21.11) > Diclofop (14.12) > Haloxyfop-p-metyl (13.34) > Pinoxadem (13.11) > Clethodim (10.35) > Fluazifop-butyl (6.87) > Tralkoxydim (3.62) > Tepraloxydim (3.26) > Butroxydim (2.42). These results confirm that E. indica has cross-resistance to ACCase-inhibiting herbicides.

 


PERFORMANCE OF WEED MANAGEMENT SYSTEMS WITHOUT ATRAZINE IN NORTH AMERICAN PROCESSING SWEET CORN. Z. F. Arslan*1, R. Becker2, V. A. Fritz3, R. E. Peachey4, T. L. Rabaey5, M. M. Williams II6; 1University of Illinois, Urbana, IL, 2University of Minnesota, St. Paul, MN, 3University of Minnesota, Waseca, MN, 4Oregon State University, Corvallis, OR, 5University of Minnesota, LeSueur, MN, 6USDA-ARS, Urbana, IL (129)

ABSTRACT

Atrazine has been the most widely used herbicide in North American processing sweet corn for decades; however, increased restrictions in recent years has reduced or eliminated atrazine use in certain production areas.  The objective of this study was to identify the best stakeholder-derived weed management alternatives to atrazine in processing sweet corn.  In field trials throughout the major production areas of processing sweet corn, including three states over four years, one dozen atrazine-free weed management treatments were compared to three standard atrazine-containing treatments and a weed-free treatment.  Treatments varied with respect to herbicide mode of action, herbicide application timing, and interrow cultivation.  All treatments included a PRE appliation of dimethenamid-P.  No single weed species occurred across all sites; however, weeds observed in three or more sites included common lambsquarters, morningglory species, velvetleaf, and wild-proso millet.  Standard treatments containing both atrazine and mesotrione POST provided the highest weed control among treatments and resulted in crop yield comparable to the weed-free treatment, thus demonstrating the value of atrazine in sweet corn production systems.  Timely interrow cultivation in atrazine-free treatments did not consistently improve weed control.  Crop injury to one hybrid indicates sweet corn breeding efforts have not yet completely addressed the decades-old problem of herbicide sensitivity, which may hamper adoption of certain herbicide alternatives to atrazine.  Only two atrazine-free treatments consistently resulted in weed control and crop yield comparable to standard treatments with atrazine POST, including treatments with tembotrione POST either with or without interrow cultivation.  This work demonstrates that ceratin atrazine-free weed management systems, derived from the sweet corn growers and processors who would adopt this technology, are comparable in performance to standard atrazine-containing weed management systems.  

 


ATRAZINE AND PENDIMETHALIN WEED CONTROL IS REDUCED IN SOILS AMENDED WITH BIOCHAR. N. Soni*1, R. G. Leon1, J. E. Erickson2, J. A. Ferrell2, M. L. Silveira3; 1University of Florida, Jay, FL, 2University of Florida, Gainesville, FL, 3University of Florida, Ona, FL (130)

ABSTRACT

Atrazine and Pendimethalin Weed Control is Reduced in Soils Amended with Biochar. N. Soni*1, R.G. Leon1, J.E. Erickson2, J.A. Ferrell2, and Maria Silveira3. 1University of Florida, Jay, FL, 2University of Florida, Gainesville, FL, 3University of Florida, Ona, FL.

 

Biochar is a by-product of pyrolysis, which is used for biofuel production and has potential as a soil amendment. Despite the benefits that biochar can bring for soil fertility, their addition to the soil might affect preemergence herbicide activity. Previous studies have shown that biochar has a high herbicide adsorption capacity, but there is little 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 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. Linear regression analysis showed that the slope for atrazine and pendimethalin adsorption was 16 and 4 times higher in soil with biochar than in 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. 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.

 

 


INFLUENCE OF TILLAGE METHODS ON  MANAGEMENT OF AMARANTHUS SPECIES IN SOYBEAN. J. A. Farmer*1, V. M. Davis2, W. Johnson3, M. M. Loux4, J. K. Norsworthy5, L. E. Steckel6, K. Bradley1; 1University of Missouri, Columbia, MO, 2University of Wisconsin, Madison, WI, 3Purdue University, West Lafayette, IN, 4Ohio State University, Columbus, OH, 5University of Arkansas, Fayetteville, AR, 6University of Tennessee, Jackson, TN (131)

ABSTRACT

The increasingly difficult challenge of managing herbicide-resistant weeds has led to a renewed interest in cultural control methods such as tillage for weed control. An identical field trial was conducted in 2014 in Arkansas, Illinois, Indiana, Ohio, Tennessee, Wisconsin, and at two sites in Missouri to determine the effects of four tillage treatments on season long emergence of Amaranthus species in glufosinate-resistant soybean. The tillage treatments evaluated included deep tillage which consisted of a fall moldboard plow followed by (fb) one pass with a field cultivator in the spring, conventional tillage which consisted of a fall chisel plow fb one pass with a field cultivator in the spring, minimum tillage which was one pass of a vertical tillage tool in the spring, and a no-tillage treatment that received a burndown herbicide treatment at approximately the same time as the spring tillage passes. Each tillage treatment also received two herbicide treatments; a preemergence (PRE) application of flumioxazin fb a postemergence (POST) application of glufosinate plus S-metolachlor, and POST-only applications of glufosinate. The experimental design was a split-plot arrangement of treatments with four replications.  Whole plots consisted of tillage types while subplots were herbicide treatments. Weed counts were taken in two 1-m2 quadrants within the middle two rows of each plot every 2 weeks following planting up to the R6 stage or soybean senescence. Following each count the entire trial was sprayed with glufosinate and emerged seedlings were removed to ensure no weed escapes.  Six, 2.5 cm soil cores were also taken to a depth of 25-cm from each plot after soil preparation and prior to planting and herbicide application to determine the vertical distribution of weed seed in the soil profile. Each soil core was divided into six sections corresponding to depths of 0-1, 1-5, 5-10, 10-15, 15-20, and 20-25 cm in the soil profile. Each soil segment was spread as a topsoil layer over 3-cm deep containers filled with commercial potting medium. Seedling emergence was monitored over a 3 month time period. Emerged weed seedlings were counted and identified to species every 2 weeks, then removed from the pots after counting.  Across all locations and tillage types, cumulative weed emergence was at least 50% less with the residual herbicide compared to the POST-only herbicide program. Across the 4 locations that had a deep tillage treatment and a cumulative emergence of Amaranthus spp. > 50 plants/m2, cumulative weed emergence was 44 to 92% lower in response to deep tillage compared to the no-tillage treatment. Conventional tillage also reduced Amaranthus spp. emergence from 38 to 80% compared to the no-tillage treatment. Based on soil cores collected following the tillage operations, between 71 and 100% of the total Amaranthus spp. seedbank was concentrated in the upper 5 cm of soil in the no-tillage, conventional and minimum tillage treatments while only 20 to 25% of the total Amaranthus spp. seedbank was concentrated in the upper 5 cm of soil in the deep tillage treatment.


ROLE OF BACILLUS AND PSEUDOMONAS SPP ON THE MANAGEMENT OF PHALARIS MINOR. S. Singh*, M. Phour, S. S. Sindhu; CCS Haryana Agricultural University, Hisar, India (132)

ABSTRACT


CARRYOVER OF COMMON CORN AND SOYBEAN HERBICIDES TO VARIOUS COVER CROP SPECIES IN MISSOURI. C. Cornelius*, J. A. Farmer, M. D. Bish, A. Long, M. Biggs, K. Bradley; University of Missouri, Columbia, MO (133)

ABSTRACT

The recent interest in cover crops as a component of Midwest corn and soybean production systems has led to the need for additional research, including the effects of residual corn and soybean herbicide treatments on fall cover crop establishment. Field studies were conducted in 2013 and 2014 to investigate the effects of common residual herbicides applied in corn and soybean on establishment of winter wheat, tillage radish, cereal rye, crimson clover, winter oat, Austrian winter pea, Italian ryegrass, and hairy vetch. Following removal of the previous corn or soybean crop for forage, each cover crop species was planted on September 11 and 10 in 2013 and 2014, respectively. The experimental design was a split-plot arrangement of treatments with four replications.  Whole plots consisted of herbicide treatments while subplots were cover crop species.  In general, more herbicide carryover injury occurred to cover crops in 2013 than 2014. This is most likely due to the greater amount of rainfall that occurred in 2014 than 2013; 67 cm was received from April through September of 2013 while 92 cm of rainfall during this same time period. Of all the cover crop species evaluated, tillage radish was most affected by previous herbicide residues. Herbicide treatments that contained fomesafen, imazethapyr, flumetsulam, acetochlor plus clopyralid plus flumetsulam plus atrazine or S-metolachlor plus fomesafen resulted in stand and biomass reductions of tillage radish by 28 days after emergence (DAE). These treatments reduced tillage radish density by approximately 14 plants per m2 and reduced tillage radish biomass by 44 to 67% compared to the non-treated control. Winter oats and Italian ryegrass were both affected by pyroxasulfone treatment in corn and soybean trials. Compared to the non-treated control, winter oats were reduced by 46 to 52 plants per m2. Italian ryegrass stand density was reduced by 73 and 90 plants per m2 and biomass was reduced 41 and 80% in the corn and soybean experiments, respectively. Fomesafen plus S-metolachlor reduced wheat biomass 39% and nicosulfuron reduced stand densities by 63 plants per m2. Flumioxazin and S-metolachlor reduced Austrian winter pea biomass 39 to 41% respectively. Several corn herbicide programs such as, tembotrione, callisto, or topramozone resulted in no stand loss or biomass reduction for any of the cover crops in this study when compared to the non-treated control. Similarly the cloransulam and sulfentrazone soybean treatments resulted in no stand loss for any of the cover crops in this study across both years.  

 


APPLICATION TIMING EFFECT ON SICKLEPOD AND MORNINGGLORY CONTROL AND SEED PRODUCTION OF SURVIVING PLANTS AFTER APPLICATIONS WITH GLYPHOSATE, 2,4-D, AND DICAMBA COMBINATIONS. R. G. Leon*1, J. A. Ferrell2; 1University of Florida, Jay, FL, 2University of Florida, Gainesville, FL (134)

ABSTRACT

Application Timing Effect on Sicklepod and Morningglory Control and Seed Production of Surviving Plants after Applications with Glyphosate, 2,4-D, and Dicamba combinations. R.G. Leon*1 and J.A. Ferrell2. 1University of Florida, Jay, FL, 2University of Florida, Gainesville, FL.

 

The upcoming introduction of 2,4-D- and dicamba-resistant cotton varieties with stalked resistance to glyphosate represents an important opportunity to control glyphosate resistant (GR) weeds. Growers are considering not using glyphosate in fields with GR weeds, but this could affect the control of other weed species. A study was conducted to identify application timings and rates for glyphosate, 2,4-D and dicamba alone or in tank-mixtures to control sicklepod and pitted morningglory, two important weed species in cotton production in Florida. Field experiments were conducted in 2013 and 2014 at the West Florida Research and Education Center in Jay, FL. 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. Total weed biomass at the end of the experiment was lower when applications were done when plants reached 6-12 inches with tank-mixtures. 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. Tank mixtures provided more consistent sicklepod and pitted morningglory control than the herbicides alone at full label rates. At 6 WAT, the pattern of 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.

 

 


DRIP HERBIGATION OF IMAZAPIC BASED ON DEGREE DAYS MODEL FOR EGYPTIAN BROOMRAPE (PHELIPANCHE AEGYPTIACA) CONTROL IN PROCESSING TOMATO IN ISRAEL. E. Avivi*1, G. Achdari2, Y. Kleifeld3, H. Eizenberg4; 1Ein Harod farm R&D, Kibutz Ein Harod, Israel, 2Department of Weed Research and Phytopathology, Ramat Yishay, Israel, 3Netafim Ltd R&D, Tel Aviv, Israel, 4Newe Yaar Research Center, ARO, Israel, Ramat Yishay, Israel (135)

ABSTRACT

The obligate root parasitic weed broomrape (Orobanche and Phelipanche spp.) causes severe damage to vegetable and field crops worldwide. In Israel, Egyptian broomrape (P. aegyptiaca) is considered as the major pest in processing tomato, endangering this crop in most growing regions. Most of the life cycle of these parasitic weeds takes place in the soil subsurface, including seed germination, attachment to the host root, penetration and establishment in the host tissues. Toward the end of their life cycle these weeds emerge from the soil and produce inflorescences bearing hundreds of thousands of seeds. It was found that the optimal time for effective chemical control, when it is more sensitive to herbicides, occurred in the subsurface developmental stage. A robust thermal time model to predict this sensitive stage was developed. The first attachment of the parasite to the host plant could be observed after 200 degree days (Tbase=10ºC). Because broomrape seeds germinate throughout the growing season when exposed to tomato root exudates, treatments must be repeated every 200 degree days. We have developed a decision support system (DSS) 'PICKIT', based on thermal time model and an integration of soil-applied herbicides for prophylactic treatments, together with POST attachment applied herbicides for P. aegyptiaca control. Soil applied herbicide include pre planting incorporation (PPI) of 37.5 g ai.ha-1 of sulfosulfuron, followed by drip herbigation of 4.8 g ai.ha-1 imazapic 400, 600 and 800 degree days after tomato planting (facilitating a thermal time model for parasitism dynamics). Imazapic herbigation is applied using low flow drip irrigation, 1.0 l/h (Uniram Netafim), that uniformly delivers the herbicide into the soil. For optimal herbigation, herbicide must be applied at the last third of each irrigation cycle. Twelve experiments at nine locations for field validation of the DSS 'PICKIT' were conducted in 2013-2014 in Israel. The use of the DSS lead to effective control of P. aegyptiaca in commercial fields under varied infestation levels. For example, in Ein Harod Ihud, located at northern Israel, 1200 P. aegyptiaca shoots were counted in 20 m2 in the non-treated control compared to complete control when the DSS 'PICKIT' was used. The yield increased by 40 tons per ha compared to the non-treated control.

 


CROP COMPETITION EFFECTS ON WEED SEED RETENTION AND HARVEST WEED SEED CONTROL. M. Walsh*, S. Powles; University of Western Australia, Perth, Australia (307)

ABSTRACT

Crop Competition Effects on Weed Seed Retention and Harvest Weed Seed Control

M. J. Walsh* and S. B. Powles, Australian Herbicide Resistance Initiative, University of Western Australia, Perth, Australia

ABSTRACT

Harvest weed seed control (HWSC) systems have been developed in Australia for use during grain harvest in response to major herbicide resistant weed problems exploiting a biological weakness of many annual weed species which is that high proportions (>75%) of total seed production are retained at maturity on upright tillers and branches, above a low crop harvest height (e.g.15cm). HWSC systems including chaff carts, narrow windrow burning, bale direct and Harrington seed destructor, are now becoming widely adopted with an estimated 30% of Australian growers using these systems to target annual ryegrass (Lolium rigidum), wild radish (Raphanus raphanistrum) and wild oats (Avena spp.). However, the efficacy of these systems is directly dependant on high weed seed retention levels. Although seed retention has been identified as being relatively high (>75%) at the commencement of harvest, there is a need to increase seed retention towards improving the potential efficacy of HWSC systems. Towards this a target-neighbour designed pot based competition study examined the effects of six wheat plant densities (0, 60, 120, 200, 300 and 400 plants/m2) on the seed production and seed retention of annual ryegrass, wild radish and wild oats. Wheat competition effects had a major impact with substantially reductions (>50%) in the seed production of each species even at the lowest wheat plant density (60 plants/m2). The highest wheat plant density (400 plants/m2) resulted in seed productions of annual ryegrass, wild radish and wild oats being reduced by 80, 93 and 96% respectively. More importantly, in the presence of wheat competition, these weed species retained seed on more upright plant parts and tillers. The proportion of seed retained above 20cm increased from 90, 60 and 21% for annual ryegrass, wild radish and wild oats in the absence of competition to 100, 100 and 48% respectively at 400 wheat plants/m2. The combination of reduced seed production and elevated seed retention meant that the amount of seed potentially avoiding HWSC decreased from 217 to 0 seed/plant for annual ryegrass, 1451 to 0 seed/plant for wild radish and from 2237 to 154 for wild oats. The dual effects of wheat crop competition in reducing seed production and increasing the susceptibility to HWSC can result in dramatic short-term reductions in seedbank levels of targeted weeds. This study highlights the potential for using agronomy to enhance the efficacy of physical weed control practices such as HWSC.


CONSTRAINTS AND OPPORTUNITIES FOR GENOMICS IN WEED SCIENCE. P. Tranel*; University of Illinois, Urbana, IL (136)

ABSTRACT

Over the past few years there has been a surge in weed genomics research. Transcriptomes of several weed species are now publically available and the first draft genome of a major agronomic weed (Conyza canadensis) has just been published. Weed genomic approaches are already providing new insights into the challenging problem of non-target-site herbicide resistance, and into fundamental weed biology questions pertaining to competition and dormancy. As DNA sequencing costs continue to decrease, and as more young scientists with training in genomics enter into our discipline, contributions to weed science by genomics approaches will continue to grow. Currently, however, applying genomics to improve weed management remains a significant challenge. Aside from the daunting task of translating weed genomics knowledge to the practice of weed control, there remain constraints to weed genomics research. Many weeds have large genome sizes, are polyploids, and are highly heterozygous; all of which exasperate whole genome sequencing and assembly. Consequently, finished genome sequences of most weed species likely will remain unavailable for some time. Fortunately, however, many weed science questions can be answered with genomics approaches that do not require a whole-genome sequence. For example, whole-transcriptome sequencing (RNA-Seq) enables rapid identification of candidate genes for a variety of research questions, and restriction site-associated DNA sequencing (RAD-Seq) is a powerful approach for population genomics; neither of these approaches require a draft genome. Although DNA sequencing technology has largely removed acquisition of the raw data as a hurdle, bioinformatics of the raw data can be expensive and exceedingly difficult. Another challenge is that genomics technology, both for data acquisition and analysis, continues to change at a rapid pace. Despite these challenges, we should expect a new era of weed science research as weed scientists begin to embrace the burgeoning field of genomics.


TRANSLATING POPULATION GENOMICS MODELS TO INFORM WEEDY SPECIES MANAGEMENT. A. L. Lawton-Rauh*; Clemson University, Clemson, SC (137)

ABSTRACT

Divergence population genetics analyses of DNA sequence data obtained from weed populations can be used to estimate and compare the effective population sizes, rates and patterns of gene flow, connectivity among genetic populations, and coalescent divergence times of populations or groups of populations. Such information enables researchers to determine the genetic origins of resistant weedy biotypes that impact agro-ecosystems. Recently developed technologies for large-scale genome sequencing have also made it possible to use high throughput computing and analyses to test specific hypotheses about populations and address important questions related to resistance management issues. An example of such an application is identifying and tracking population origins and connectivity dynamics of glyphosate resistance in Amaranthus palmeri. The glyphosate resistance target gene EPSPS (5-enolpyruvylshikimate 3-phosphate synthase; critical aromatic amino acid biosynthesis enzyme) and a suite of non-target genes that were determined via transcriptome comparisons of resistant and sensitive Palmer amaranths were each sequenced across the genus Amaranthus and from several populations of the rapidly-adapting species Amaranthus palmeri. Additionally, EPSPS gene copy numbers were estimated across representative Amaranthus and in the resistant and sensitive populations of A. palmeri. In A. palmeri populations that predated glyphosate exposure and in other Amaranthus species, EPSPS has patterns consistent with continuous selection. At the population level, the best fit models of population structure and genetic history indicate more than one origin of glyphosate resistance, and a statistically significant association between copy number and resistance level within the independently-derived populations. Together, these results suggest that EPSPS gene copy number increase and its rampant proliferation are very recently derived, unique to herbicide-stressed A. palmeri populations, and originated through several independent events in genetically distinct populations.


GENES REGULATING PARASITISM IN CUSCUTA. N. Sinha*; University of California, Davis, Davis, CA (138)

ABSTRACT

Infection of crop species by parasitic weeds results in crop losses affecting nearly 300 million farmers worldwide. Cuscuta spp (dodders) are successful obligate holoparasitic weeds distributed throughout the world, and suppress the growth of cultivated crops, trees, shrubs and weeds. Cuscuta use their vine-like stems to attach to aboveground parts of host plants, develop haustoria, invade and extend inside the host stem. Successful parasitism is an interactive process between the host and parasite, conditioned by a number of genetic and physiological factors. We are working to elucidate the molecular mechanism underlying these processes. We have generated extensive transcriptional data from numerous Cuscuta tissues including LCM dissected haustoria and the surrounding tomato host tissue. We have used high-throughput RNAseq experiments to identify C. pentagona genes that are central to and likely regulate the parasitism process. We have also used RNAseq to identify tomato genes involved in the response to attachment by C. pentagona. The combined study of the parasite mode of action and the defense activated by tomato will allow us to develop tomato lines with higher resistant to the parasitic weed using transgenic technologies. Our functional genomic studies on the agricultural pest C. pentagona and its host could yield tool to reduce the parasite loads and crop productivity in tomatoes as well as other crops parasitic plant pathosystems.


RESIDUAL CONTROL OF WATERHEMP WITH DICAMBA. S. T. Logan*1, S. M. Allen2, T. D. White3, J. L. Matthews4, J. M. Young5, B. G. Young5; 1Monsanto Company, Pinckneyville, IL, 2Monsanto Company, Bonnie, IL, 3Monsanto Company, St. Louis, MO, 4Southern Illinois University, Carbondale, IL, 5Purdue University, West Lafayette, IN (139)

ABSTRACT

Soybean production in recent years has become increasingly more difficult due to the prevalence of hard-to-control and glyphosate-resistant weeds such as waterhemp. Glyphosate-resistant waterhemp has quickly grown to become one of the most problematic weeds in soybean production today and the lack of effective herbicides in soybean for management presents an increasingly difficult challenge for soybean producers. The potential future use of dicamba in dicamba-tolerant soybeans will provide an additional herbicide to gain more effective control of problematic weeds such as waterhemp in both preplant and postemergence applications.  The foliar activity of dicamba on waterhemp may not be the only benefit from a dicamba tolerant soybean system as some soil residual activity of dicamba may be evident on waterhemp, subject to weather conditions and rainfall.

In 2012, 2013, and 2014 experiments were established on glyphosate-resistant waterhemp populations in DeSoto and Murphysboro, IL to evaluate the efficacy of preemergence applications of dicamba and 2,4-D applied alone and in combination with the commercial standard residual herbicides acetochlor, sulfentrazone & chlorimuron, and flumioxazin & chlorimuron. Both locations had a silt loam soil type with organic matter of 1.8 to 2.1% and a cation exchange capacity ranging from 6 to 13. Herbicides were applied to weed-free, no-till sites. In 2012 the DeSoto site received only 1.8 cm cumulative rainfall with the Murphysboro site receiving just 1.1 cm of rainfall up to six weeks after application. Under these low rainfall conditions dicamba applied at 0.56 kg ae/ha provided 95 to 99% control of glyphosate-resistant waterhemp at 21 DAT with an experimental 2,4-D choline formulation applied at 0.84 kg ae/ha providing 92 to 96% control. Furthermore, under these dry conditions, these same applications of dicamba provided 41 to 83% control at 56 DAT while experimental 2,4-D choline provided 20 to 54% control of glyphosate-resistant waterhemp.

In 2013 and 2014 these same experiments were performed at the DeSoto and Murphysboro locations with sites receiving greater overall rainfall (up to 18 cm after 6 weeks) throughout the duration of the experiment and having early rainfall following herbicide application to allow for herbicide activation.  The application of 2,4-D and dicamba, pooled over herbicide rate, resulted in 52 and 67% waterhemp control at 21 DAT, respectively, and 15 and 25% control at 56 DAT.  The combination of either 2,4-D or dicamba with standard residual herbicides did not influence early-season control of waterhemp.  However, control of waterhemp at 56 DAT was 11 to 12% higher for the commercial standard residual herbicides when applied with dicamba compared to the same herbicides applied without dicamba.  Conversely, the addition of 2,4-D to the commercial standard residual herbicides failed to increase control at 56 DAT by more than 3%.  This research suggests dicamba has the potential to contribute some level of residual waterhemp control.  Since rainfall patterns after dicamba application dramatically influence the residual activity, the primary focus for dicamba use should still be on the foliar activity with the soil residual activity representing a potential benefit.


UTILITY OF VALENT HERBICIDE PORTIFOLIO IN A DICAMBA OR 2-4D TRAITED SOYBEAN SYSTEM. D. Refsell*1, J. Pawlak2; 1Valent USA, Lathrop, MO, 2Valent USA, Lansing, MI (140)

ABSTRACT

With the development of dicamba and 2,4-D tolerant soybeans, growers will now have another postemergence option for control of glyphosate-resistant weeds.  The high demand for new weed management options in soybeans may lead to growers abandoning flumioxazin based residual herbicides (Valor®, Valor® XLT, Fierce®, Fierce® XLT) and/or lactofen based products, such as Cobra® and Phoenix®.  To demonstrate the advantage of including flumioxazin+pyroxasulfone (71.5 g ai/ha and 89 g ai/ha) and/or lactofen (220 g ai/ha) to a 2,4-D or dicamba tolerant soybean herbicide program for residual and/or post control of glyphosate-resistant weeds such as Conyza canadensis, Amaranthus spp., and Ambrosia  spp.   Trials were conducted in 2014 in various locations across the Midwest and Mid-South.   There were 14 locations evaluating the dicamba system, while 15 locations were used to evaluate the 2,4-D system.    Trials were established utilizing bare ground.  Postemergence applications were based on weed size.   Efficacy was evaluated at 28 and 56 DAP.   Regardless of weeds management system utilized, season-long Amaranthus spp. control required a preemergence foundation herbicide, such as flumioxazin+pyroxasulfone.  Within the dicamba system, Chenopodium album and Kochia scoparia control were enhanced with the addition of the preemergence application of flumioxazin+pyroxasulfone.  A postemergence lactofen application was also beneficial in managing Amaranthus palmeri in the dicamba system The 2,4-D system was enhanced with the addition of flumioxazin+pyroxasulfone specifically for the control of Abutilon theophrasti and Kochia scoparia.  The best control utilized both a preemergence application of flumioxazin+pyroxasulfone followed by a postemergence tank-mix partner of lactofen. 

 


REMOTELY SENSED SPECTRAL CHARACTERIZATION OF SOYBEAN RESPONSE TO SIMULATED DICAMBA DRIFT. K. N. Reddy*1, Y. Huang2; 1USDA, Stoneville, MS, 2USDA-ARS, Stoneville, MS (141)

ABSTRACT

Dicamba drift onto non-target crops is a major concern because it is highly active on susceptible crops even at low doses. Early detection of crop injury is critical in crop management. Subtle changes in canopy reflectance could present useful information to detect the onset of crop stress. A field study was conducted to determine spectral characteristics of soybean (Progeny P4819LL) treated with dicamba. Dicamba drift was simulated by direct application at 0.05 and 0.1X of the recommended label rate (X = 0.56 kg ae/ha) to soybean at 5- to 6-trifloliolate leaf, approximately 6 weeks after planting. The canopy spectral measurements were taken at 24, 48, and 72 hours after treatment (HAT) using an ASD Handheld 2 portable spectroradiometer (325 to 1075 nm range,  ±1 nm accuracy) on 3 randomly selected plants within each plot with device optimization and data calibration. For data analysis, rNDVI (red Normalized Difference Vegetation Index) and gNDVI (green Normalized Difference Vegetation Index) were focused, based on the sensitive bands at 550 nm (green), 673 nm (red), and 800 nm (NIR – near-infrared).  The results indicated that both rNDVI and gNDVI could reliably detect soybean injury from dicamba sprayed at 0.1X at 24, 48, and 72 HAT with a 95% confident level. Simulated dicamba drift injured soybean and reduced soybean yield by 71 and 90% at 0.05 and 0.1X rate, respectively. This study demonstrated that hyperspectral remote sensing has a potential in early detection of soybean injury from exposure to off-target dicamba drift at sublethal rates in the field.


MANAGEMENT OF GLYPHOSATE-RESISTANT PALMER AMARANTH IN COTTON WITH DICAMBA. M. D. Inman*, D. L. Jordan, A. C. York, W. J. Everman, K. Jennings, D. W. Monks; NCSU, Raleigh, NC (142)

ABSTRACT

MANAGEMENT OF GLYPHOSATE-RESISTANT PALMER AMARANTH IN COTTON WITH DICAMBA            M. Inman*, D. Jordan, A. York, K. Jennings, W. Everman, D. Monks; North Carolina State University, Raleigh, NC

 

Research was conducted from 2011-2014 to evaluate long-term management and weed population dynamics of glyphosate-resistant Palmer amaranth with herbicide programs consisting of glyphosate, dicamba, and residual herbicides in dicamba-tolerant cotton. Prior to preemergence herbicide application and after planting, ten soil cores (approximately 4 L) from each plot were collected at random in May 2011-2014 and in December 2014.  Soil cores were placed in greenhouse flats and grown under favorable conditions for seed germination.  Weed diversity and density were recorded once germination occurred. Frequency of glyphosate resistance was determined following a treatment of glyphosate at 946 g/ae ha by counting the surviving seedlings.  Nine herbicide treatments were imposed in the experiment. By the end of the experiment, higher populations of Palmer amaranth were observed when glyphosate was the only postemergence herbicide applied regardless of whether residual herbicides were applied or not. The lowest populations were noted where dicamba was applied. Population levels in treatments alternating years of glyphosate and glyphosate plus dicamba were intermediate between glyphosate only and glyphosate plus dicamba. Differences in resistance levels were noted in the first two years with glyphosate only POST treatments compared with treatments containing dicamba, but by the third year the frequency of resistance was similar for all herbicide programs. Density of Palmer amaranth was determined each year in August and showed similar trends to soil cores in greenhouse. 

 


APPLICATION STEWARDSHIP OF ENGENIATM HERBICIDE IN DICAMBA TOLERANT CROPS. D. Westberg*, C. Feng, C. Brommer, W. E. Thomas; BASF Corporation, Research Triangle Park, NC (143)

ABSTRACT

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.  Engeniaherbicide, 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. 


WEED MANAGEMENT STEWARDSHIP OF ENGENIATM HERBICIDE IN DICAMBA TOLERANT CROPS. C. Brommer*1, J. Frihauf2, S. Bowe1; 1BASF Corporation, Research Triangle Park, NC, 2BASF Corporation, Raleigh, NC (144)

ABSTRACT

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. 

 

 


ENLIST™ TECHNOLOGY IN TEXAS HIGH PLAINS COTTON. M. R. Manuchehri*1, P. A. Dotray2, J. Keeling3, T. Morris4, M. L. Lovelace5; 1Texas Tech University, Lubbock, TX, 2Texas Tech University, Texas A&M AgriLife Research and Extension Service, Lubbock, TX, 3Texas A&M AgriLife Extension Service, Lubbock, TX, 4Texas A&M AgriLife Research, Lubbock, TX, 5Dow AgroSciences, Lubbock, TX (145)

ABSTRACT

ENLIST™ TECHNOLOGY IN TEXAS HIGH PLAINS COTTON. M. R. Manuchehri*1, P. A. Dotray1,2, J. W. Keeling2 , T. S. Morris2, M. L. Lovelace; 1Texas Tech University, Lubbock, TX, 2Texas A&M AgriLife Research and Extension Center, Lubbock, TX.

Enlist™ technology, utilizing 2,4-D + glyphosate (Enlist Duo™) and glufosinate crop tolerance, has the potential to effectively manage Palmer amaranth (Amaranthus palmeri S. Wats.), Russian-thistle (Salsoga tragus L.), and other difficult-to-control weeds in Texas High Plains cotton. However, there will be challenges associated with this technology. One challenge is the risk of drift and spray tank contamination. To evaluate both the potential benefits and challenges associated with Enlist Weed Control Systems™, multiple trials were conducted near Lubbock, TX in 2013 and 2014. Weed management trials assessed Enlist Duo™ alone and in combination with glufosinate and several soil-residual herbicides for postemergence control of glyphosate-susceptible Palmer amaranth. Simulated drift and spray tank contamination trials assessed the sensitivity of cotton that is not tolerant to 2,4-D at various rates and growth stages. In the simulated drift studies, cotton plants were sprayed with two rates of 2,4-D amine (0.002 and 0.04 kg ae ha-1) at six different growth stages (4 leaf, 9 leaf, first bloom, first bloom+2 weeks, first bloom+4 weeks, and first bloom+6 weeks). In the tank contamination study, cotton plants were sprayed with five rates of Enlist Duo™ (0.0000183, 0.000183, 0.00183, 0.0183, and 0.183 kg ae ha-1) at two growth stages (nine leaf and first bloom). The above rates are similar to tank contamination of Enlist Duo™ solution at concentrations of 0.0008, 0.008, 0.08, 0.8, and 8%, respectively. Visual control of target weed species and crop injury were recorded at 14, 21, and 28 days after treatment (DAT). Crop yield was also recorded. For the 2013 systems trial 28 days after the mid-postemergence (MPOST) application, Palmer amaranth was controlled approximately 97% for all herbicide systems with the exception of systems that included a MPOST application of glufosinate alone. For the same trial in 2014, Palmer amaranth control was similar across herbicide systems (approximately 97%) with the exception of: trifluralin PPI fb glufosinate EPOST fb glufosinate MPOST; trifluralin PPI fb glufosinate + acetochlor EPOST fb glufosinate MPOST; and trifluralin applied PPI alone. For the simulated drift studies, there were no yield differences for cotton sprayed at 0.002 kg ae/ha, regardless of cotton stage in both 2013 and 2014. However, applications of 0.04 kg ae/ha decreased yields compared to the nontreated control for four leaf, nine leaf, and two weeks after first bloom cotton in 2013 (38, 63, and 25%, respectively) and for four leaf and nine leaf cotton in 2014 (67 and 81%, respectively). For the tank contamination study in 2013, yields were similar for 9 leaf and first bloom cotton at the three lowest application rates; however, yields decreased for nine leaf cotton by 57 and 81% and for first bloom cotton by 36 and 90% for concentrations of 0.8 and 8%, respectively. In 2014, yields were similar for nine leaf and first bloom cotton at the two lowest application rates. However, yield decreased for nine leaf cotton by 19, 84, and 96% for concentrations of 0.08, 0.8, and 8%, respectively while first bloom yields decreased by 19 and 72% for concentrations of 0.8 and 8%, respectively. Overall, several effective treatments were identified in the systems trials as sustainable treatments will likely result from a systems approach that involves soil residual herbicides. Simulated drift and tank contamination studies suggest that nontolerant cotton is most sensitive to 2,4-D between growth stages of 4 leaf to two weeks after first bloom while rates as little as 0.0183 kg ae/ha can decrease yields up to 84% during this critical growth period.

 


CONTROL OF GLYPHOSATE-RESISTANT GIANT RAGWEED IN SOYBEAN TOLERANT TO 2,4-D, GLUFOSINATE AND GLYPHOSATE. A. J. Jhala*1, K. Rosenbaum2; 1University of Florida, Lake Alfred, FL, 2Dow AgroSciences, Lincoln, NE (146)

ABSTRACT


ARE MULTI-CULTIVAR FORAGE STANDS MORE EFFECTIVE AT SUPPRESSING WEEDY SPECIES THAN SINGLE CULTIVAR STANDS? F. W. Pollnac*, R. G. Smith, N. Warren; University of New Hampshire, Durham, NH (147)

ABSTRACT

Renovating established pastures, or converting unmanaged land to productive pasture, often requires some level of disturbance which can facilitate invasions of weedy species.  Even when care is taken to avoid the introduction of weeds from outside sources, weeds germinating from the seedbank can be problematic.  This is particularly challenging in organically managed systems, where herbicide use is not an option.  In these instances, the use of ecologically based strategies for weed suppression is often the only option.  This research focuses on the use of forage species cultivar diversity as one potential way to suppress weedy species during pasture establishment.  Three studies were established at the University of New Hampshire to assess the effects of incorporating cultivar diversity into organically managed perennial forage stands.  Weed abundance data were collected in all of these experiments during their establishment phases.  We hypothesized that weedy species could be suppressed by cultivar diversity through two mechanisms: 1) increased forage biomass and 2) increased preemptive use of resources.  We assessed evidence for each of the hypothesized mechanisms by evaluating the relationship between weed biomass and both forage crop biomass and forage crop functional diversity.  We found evidence that increasing forage crop biomass limited weed abundance; however, this was not universal.  We found no evidence that functional diversity limited weed abundance.  These results suggest that, while weeds may be suppressed by cultivar mixtures, suppression is related more to forage biomass than the diversity effects investigated here. 


TRANSLOCATION AND METABOLISM OF 2,4-D IN SENSITIVE AND TOLERANT RED CLOVER (TRIFOLIUM PRATENSE) LINES. T. L. Burke*, M. Barrett; University of Kentucky, Lexington, KY (148)

ABSTRACT

Incorporation of a legume, such as red clover (Trifolium pratense), into grass-based pasture systems would offer many benefits. However, susceptibility of red clover to herbicides commonly applied in these systems for broadleaf weed management limits its use. A 2,4-D tolerant red clover would expand the weed management options for mixed grass-clover pastures, as 2,4-D has been the standard for broadleaf weed management in grass pastures for decades. A Florida red clover line with improved 2,4-D tolerance was crossed to the 2,4-D susceptible, but widely used and adapted to the transition zone,  red clover cultivar Kenland. The resulting population was annually reselected for 2,4-D tolerance from 2006 to2013. To assess progress towards a 2,4-D tolerant Kenland line, plants were grown in the greenhouse from seed collected after the 2010, 2011 and 2012 selections and treated with 0.0, 0.56, 1.12, 1.68, or 2.24 kg ha-1 2,4-D. Plant visual injury ratings taken two weeks post-treatment were compared to those for the similarly treated parent lines. The 2010 and 2011 lines had 2,4-D tolerance levels similar to the Florida parent. Thus, while the cross to the 2,4-D tolerant Florida line increased 2,4-D tolerance compared to Kenland, little additional gain had been made in 2,4-D tolerance beyond that of the Florida line, despite numerous rounds of selection.  To identify the basis for the improved 2,4-D tolerance, foliage of Kenland plants and  plants grown from seed following the 2013 selection were treated with 14C labeled 2,4-D and uptake, translocation and metabolism of the herbicide examined.  Plants of Kenland and the 2,4-D tolerant line absorbed the 14C in similar amounts but there were significant differences in 2,4-D translocation and metabolism between the two lines.  The tolerant line metabolized 2,4-D more in the untreated shoots and translocated less to the untreated portions of the plant than 2,4-D susceptible Kenland.  This suggests that the increased 2,4-D tolerance is based on enhanced 2,4-D metabolism, which also restricts 2,4-D movement in the plant.

 


AMINOCYCLOPYRACHLOR PLUS METSULFURON REDUCES TALL FESCUE SEED HEADS AND IMPROVES FORAGE QUALITY. T. D. Israel*, G. Rhodes, Jr., T. C. Mueller, G. E. Bates, J. C. Waller; University of Tennessee, Knoxville, TN (149)

ABSTRACT

Tall fescue (Lolium arundinaceum) is the predominant grass species in pastures in the mid-South. It occupies 35 million acres and supports over 8.5 million beef cows in the United States. 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, ergot alkaloids produced by the endophyte are detrimental to livestock and contribute to fescue toxicosis. Increased body temperature, rough hair coats, and reduced average daily gain (ADG) are all symptoms of fescue toxicosis. Since the alkaloids are highly concentrated in seeds and stems, a potential way to reduce the harmful effects is by suppressing seed heads with herbicides. Metsulfuron, an acetolactate synthase (ALS) inhibitor, is well documented to limit seed head formation, but also damages 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 MAT28 pasture herbicide product to be registered is anticipated to be a premixture containing metsulfuron.

 

Research was conducted from 2012-2014 using MAT28 plus metsulfuron applied at different rates and timings to determine the effects on tall fescue growth and development and forage quality. Sites chosen were well-established tall fescue pastures with 85% endophyte infection rate in Alcoa and Crossville, Tennessee. Experimental design was a randomized complete block with four replications while treatment design was a modified factorial arrangement with four rates of MAT28 plus metsulfuron and two application timings and an untreated control.  All herbicide treatments included non-ionic surfactant at 0.25%.  Visual ratings were performed monthly to evaluate fescue discoloration and stunting on a 0-99% scale. Plots were harvested in late spring to determine yield and seed head density. Forage quality measurements were determined using NIRS.

 

Stunting at harvest averaged 12 and 31% from fall and spring applications, respectively. Reductions in yield compared to the untreated control were 19 and 42% for fall and spring applications, respectively. Across both timings, yield reductions ranged from 20% with MAT28 plus metsulfuron (47+7 g ai/ha)  to 39% with MAT28 plus metsulfuron (155+23 g ai/ha). Timing did not affect seed head density at harvest as seed heads were reduced 52 and 53% from untreated for fall and spring applications, respectively. Relative Forage Quality (RFQ) of untreated forage was 105 compared to 114 and 117 for fall and spring applications, respectively. RFQ values ranged from 112 to 120 with MAT28 plus metsulfuron (47+7 g ai/ha)  to MAT28 plus metsulfuron (155+23 g ai/ha). Compared to the spring application, fall application of MAT28 plus metsulfuron improved tall fescue yield with no change in seed head reduction. MAT28 plus metsulfuron may be applied in the fall to suppress tall fescue seed heads with less injury than spring applications and also improves forage quality.

 


EVALUATION OF DERIGO (FORAMSULFURON + IODOSULFURON + THIENCARBAZONE) FOR WEED CONTROL IN GRASSY ROADSIDES IN GEORGIA. P. McCullough*; University of Georgia, Griffin, GA (150)

ABSTRACT

Field experiments were conducted from 2012 to 2014 to evaluate the efficacy of Derigo (thiencarbazone + foramsulfuron + iodosulfuron) for control of problem weeds on roadsides in Georgia.  Applications were made on research farms and roadsides in Griffin, Newnan, and Jackson, GA.  Spring applications of the 76 to 115 g ai/ha provided poor control (<70%) of broomsedge, but tank-mixtures with glyphosate at 420 g ae/ha improved control to 88%.  Applications of Derigo alone from 51 to 115 g ai/ha in April provided 88 to 100% control of buckhorn plantain after 8 weeks and were more effective than the standard combination of imazapic + aminopyralid at 105 + 77 g ai/ha, respectively.  On roadsides, September and November applications of Derigo with indaziflam at 52 or 73 g ai/ha provided good (80 to 89%) to excellent control (>90%) of Italian ryegrass, catsear dandelion, and buckhorn plantain by the following April.  However, control of wild garlic was poor.  In bahiagrass growth regulation experiments, Derigo treatments from 38 to 153 g ai/ha provide complete control of bahiagrass seedheads from 4 to 10 weeks after treatments.  Bahiagrass foliage height reductions from the nontreated following Derigo treatments were comparable to imazapic and sulfometuron treatments.  However, all rates of Derigo provided excellent control of catsear dandelion after 8 weeks, while no control was observed from imazapic or sulfometuron.  

 


JAPANESE KNOTWEED (FALLOPIA SPP.) CONGENER STAND REDUCTION FOLLOWING MID-SEASON HERBICIDE TREATMENTS - YEAR ONE. A. Z. Skibo*1, M. J. VanGessel2, M. Yost3; 1SePRO Corporation, Fort Collins, CO, 2University of Delaware, Georgetown, DE, 3DNREC, Dover, DE (151)

ABSTRACT

Japanese knotweed (Fallopia japonica SYN Reynoutria japonica SYN Polygonum cuspidatum) and the related congers and hybrids within the genus have been documented in all but eight U.S. states and are commonly found established as dense monocultural stands along frequently disturbed waterways and waste areas.  This species, sensu lato, is known to spread prolifically via vegetative propagation while sexual reproduction and subsequent, viable seed dispersal have been increasingly documented across the US. 

Historically, this heavily rhizomatous perennial invasive has been managed most successfully via chemical intervention though these programs require repeated applications and a comprehensive restoration plan to effectively control established stands much less hope for eradication.  Further, as the preferred habitat of this genera is generally riparian, herbicide selection is constrained to those registered by the USEPA for use in these ecologically sensitive areas, significantly reducing herbicide chemistry selection to the applicator. 

Previous herbicide screening trials have documented the efficacy of a number of systemic herbicides such as glyphosate, imazapyr, triclopyr with varying degrees of success during season of application and during subsequent seasons. One of the chief issues with the aforementioned chemistries has been a lack of immediate destruction of treated foliar biomass and the potential for further dispersal of vegetative propagules thus further hampering site remediation efforts.  In a field trial initiated mid-summer 2014, a number of systemic active ingredients (imazamox, imazapyr, triclopyr, and glyphosate) known to have excellent activity on Japanese knotweed were applied alone and in combination with Stringray™ (active ingredient: carfentrazone-ethyl) to elucidate any increases in immediate efficacy seen with these combinations during season of application.  A mechanical mowing program was conducted as a positive check.  Data will be collected to +1 YAT.  Preliminary results of this trial will be discussed as will implications of this chemistry to the riparian manager’s portfolio.    


BROWNOUT FOLLOWING APPLICATION OF MIXTURES WITH SAFLUFENACIL IN FORESTRY SITE PREPARATION ACTIVITIES. A. W. Ezell*1, A. B. Self2; 1Mississippi State University, Starkville, MS, 2Mississippi State University, Grenada, MS (152)

ABSTRACT

Perhaps the greatest challenge in forestry site preparation in the southern United States at this time is the control of natural pines. Saflufenacil has demonstrated excellent potential for improving the control of seedling pines in site preparation activities and a study was conducted to determine the influence of this active ingredient on both brownout and final control of natural pines.  A total of 10 active treatments were applied to a recently harvested area in northern Mississippi whch had 30,000 -50,000 natural pine seedlings across most of the site in addition to hardwood sprouts, seedlings, saplings and  well established herbaceous cover . Treatments contained vaying mixes of imazapyr, glyphosate, saflufenacil, aminopyralid, and MSO.  Plots were examined at 7DAT, 15DAT, 30DAT, and 60 DAT with brownout ratings of all vegetation categories completed at the latter two timings. The influence of saflufenacil was evident even at the early timings. For managers wishing to burn following chemical site preparation, these results will be especially beneficial.


HERBICIDES FOR HARDWOOD MANAGEMENT- A COMPILATION OF RESEARCH STUDIES. A. W. Ezell*; Mississippi State University, Starkville, MS (153)

ABSTRACT

The use of herbicides for hardwood management in the southern United States continues to increase, and application potential has been significantly increased by research regarding crop tolerance and treatment efficacy. Some of the greatest challenges have been to identify materials and applications which can control the target species with little or no damage to the hardwoods being managed. This problem is accentuated by the fact that most of the effective herbicides in forestry were formulated to control hardwood species. This paper presents information gathered from  a number of individual studies involving competition control in hardwood stands which were completed at Mississippi State University over an extended period of time. Included in the presentation is information on site preparation, herbaceous weed control, differing natural regeneration situations, and the control of noxious/invasive vines ( 7 species), cogongrass, subarborescents (4 species), Chinese tallowtree, bamboo, and switchcane. Herbicide choices and rates of application will be covered for all species presented.


APPLICATION BEST MANAGEMENT PRACTICES FOR BALANCING DRIFT MITIGATION AND WEED CONTROL WITH THE ENLIST WEED CONTROL SYSTEM. D. E. Hillger*1, A. Asbury2, P. Havens3, R. Keller4, J. Laffey5, R. Lassiter6, J. Schleier3, J. Siebert7; 1Dow AgroSciences, Noblesville, IN, 2Dow AgroSciences, Dahinda, IL, 3Dow AgroSciences, Indianapolis, IN, 4Dow AgroSciences, Rochester, MN, 5Dow AgroSciences, Maryville, MO, 6Dow AgroSciences, Raleigh, NC, 7Dow AgroSciences, Greenville, MS (154)

ABSTRACT

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.


EXPLORING THE POTENTIAL FOR SELECTIVITY IN BERMUDAGRASS USING MICROWAVE RADIATIONS FOR WEED CONTROL. A. Rana*, J. Derr; Virginia Tech, Virginia Beach, VA (155)

ABSTRACT

A study was conducted to explore the possibility of selective weed control using microwave radiations for weed control. Bermudagrass [Cynodon dactylon (L.) Pers.] infested with yellow woodsorrel   (Oxalis stricta L.) and common chickweed [Stellaria media (L.)  Vill.] was treated with 54, 90, 126 & 162 J/cm2 of microwave radiations (MW) using a stationary microwave unit and a custom-built running belt microwave radiation applicator to avoid any lag period. Two magnetrons each with 900 Watt output power of microwave radiations were used. The microwave applicator was able to deliver 18 joules/cm2/sec. Total microwave radiations exposure period of a target weed species was controlled by a potentiometer which regulated the speed of the running belt system. Plant injuries were comparatively higher using the running belt microwave radiations applicator in comparison to the stationary microwave unit. There were significant differences in injuries caused by microwave radiations to common chickweed, yellow woodsorrel and bermudagrass at 90 J/cm2 dose of microwave radiations, demonstrating the possibility for selectivity. There was a significant interaction between microwave radiations dose and plant species. Bermudagrass was injured 58%, while common chickweed was completely controlled when microwave energy was applied at 90 J/cm2. Differences in injury between bermudagrass (58%) and yellow woodsorrel (70%) were statistically nonsignificant at 90 J/cm2. The two highest levels of microwave radiations energy (126 and 162 J/cm2) severely injured all three species over 90%. No significant differences were seen between plant species at these two higher rates of microwave radiations. The higher microwave energy levels were apparently sufficient to raise plant tissue temperature regardless of plant anatomy.

 


INFLUENCE OF CARRIER WATER PH AND FOLIAR FERTILIZERS ON WEED CONTROL WITH POSTEMERGENCE HERBICIDES. P. Devkota*, W. Johnson; Purdue University, West Lafayette, IN (156)

ABSTRACT

Water is a primary solvent for herbicide application and efficacy of herbicides can be reduced by poor spray water quality. Likewise, cations from co-applied foliar fertilizers have potential to antagonize herbicide activity. Field studies were conducted to evaluate effect of carrier water pH and foliar fertilizers on mesotrione, and a premixed formulation of 2,4-D plus glyphosate (Enlist Duo) activity on horseweed. In addition, effect of carrier water pH, foliar fertilizers, and ammonium sulfate (AMS) on Enlist Duo activity on giant ragweed and Palmer amaranth were evaluated in greenhouse studies. Treatments in field studies consisted combinations of zinc or manganese fertilizers (at 2.5 and 3.75 L ha-1, respectively) and water pH of 4, 6.5, or 9. At carrier water pH of 6.5, mesotrione efficacy was higher compared to water pH of 4 and 9 for horseweed control. Likewise, glyphosate plus 2,4-D applied with carrier water pH of 4 provided greater control of horseweed compared to carrier water pH of 9. In the greenhouse study, treatments consisted of either 2.5% V/V AMS or no AMS along with the treatment combinations mentioned on the field study. Effect of water pH was significant for Palmer amaranth control. Similarly, effect of foliar fertilizers and AMS were significant for giant ragweed and Palmer amaranth control and biomass reduction at 3 wk after treatment (WAT). Palmer amaranth control was higher with Enlist Duo applied at water pH 4, or 6.5 (≥79%) compared to pH 9 (≤69%) at 3 WAT. Enlist Duo activity on giant ragweed and Palmer amaranth was reduced from co-applied manganese fertilizer compared to the application without fertilizer. At 3 WAT, giant ragweed control was ≥92 and ≤87%; and Palmer amaranth control was ≥81 and ≤69% from Enlist Duo applied without fertilizer and with manganese fertilizer, respectively. Addition of AMS increased activity of Enlist Duo on giant ragweed and Palmer amaranth control and reduced dry wt. In conclusion, alkaline water pH reduces the activity of mesotrione and Enlist Duo. Co-applied manganese fertilizer with Enlist Duo results into lower weed control, and addition of AMS enhances the activity of Enlist Duo. 

 


EVALUATION OF PHYSICAL DRIFT AND VAPOR DRIFT OF SEVERAL DICAMBA AND 2,4-D FORMULATIONS AND THE IMPACT OF VOLATILITY REDUCTION ADJUVANTS. S. K. Parrish*1, J. T. Daniel2, P. Westra3; 1AgraSyst Inc, Spokane, WA, 2Agricultural Consultant, Keenesburg, CO, 3Colorado State University, Ft. Collins, CO (157)

ABSTRACT

Increased vapor injury was documented with the addition of ammonium sulfate (AMS) to the spray solutions of 2,4-D dimethyl amine salt (DMA), dicamba DMA salt and dicamba diglycolamine salt (DGA). A series of greenhouse volatility studies were undertaken to explore what effects different spray solution additive components had on the volatility of phenoxy herbicides.  Additive components tested were; salts, acids, oils, surfactants and emulsifiers. These components were tested with 2,4-D (DMA), 2,4-D low volatile ester (LV6), 2,4-D acid formulations, dicamba DMA, dicamba DGA and dicamba acid formulations. Salts, other than AMS, generally decreased vapor injury. Acid generally increased vapor injury. Surfactants had effects on volatility depending upon surfactant type. Emulsifiers were mostly neutral. The best reductions in vapor injury were seen with combinations of ingredients. Field studies were conducted to establish if greenhouse result translated to field conditions. In field trials, AMS increased volatility injury of the DGA salt of dicamba to soybeans. Other additives were successful in reducing volatility injury of Dicamba DGA salt to soybeans.

 


INTERDEPARTMENT COORDINATION OF INVASIVE PLANT POLICY AND REGULATION. C. P. Dionigi*; National Invasive Species Council, Washington, DC (158)

ABSTRACT

In the years since 1999 when the Executive Order 13112 on invasive species was signed the term “invasive species” has become well-known by the public.  Most recently invasive species are being seen as an integral component of climate resilience. The October 2014, Priority Agenda: Enhancing the Climate Resilience of America’s  Natural Resources calls for the Department of the Interior and the National Invasive Species Council to work with states and tribes to develop a framework for a national Early Detection and Rapid Response program that will build on existing programs to assist states and tribes in forestalling the stress caused by the establishment and spread of additional invasive species populations, thereby improving the resilience of priority landscapes and aquatic areas. This will include the development of a plan for creating an emergency response fund to increase the capacity of interagency and inter-jurisdictional teams to tackle emerging invasive species issues across landscapes and jurisdictions.  This initiative represents significant opportunity prevent the establishment and spread of invasive plants and other invasive species. 

 


APHIS UPDATE ON NOT ALLOWED IMPORT PENDING PEST RISK ANALYSIS CATEGORY: ROUNDS 2 AND 3. A. V. Tasker*; USDA, APHIS, Plant Protection & Quarantine, Riverdale, MD (159)

ABSTRACT

Prior to 2011 APHIS Regulations for 7 Code of Federal Regulations §319.37 (commonly known as Q-37) categorized plants to be imported for planting as either prohibited (not allowed) or restricted (allowed under certain conditions) and did not require a pest risk analysis prior to the importation of a new taxonomic group of plants. This differs from APHIS' fruits and vegetables regulation (Q-56) where the importation of fruits and vegetables is prohibited until the completion of such an analysis, and to the Federal Noxious Weed regulation. The Not Allowed Pending Pest Risk Analysis (NAPPRA) category currently lists 31 taxa of plants for planting that are quarantine pest plants (weeds) and 107 taxa of plants for planting that are hosts of 13 quarantine pests. Taxa proposed for addition to NAPPRA are currently 22 taxa of plants for planting that are potential quarantine plants (weeds) and 37 taxa of plants for planting that are hosts of 8 quarantine pests, and will soon be posted to the Federal Register as final. Taxa in review for Round 3 of listing for NAPPRA are 21 taxa of plants for planting that are potential quarantine pest plants (weeds) and 389 taxa of plants for planting that are hosts of 12 quarantine pests. Further analysis may eliminate some of these hosts as already regulated. APHIS has recently been involved in documenting our priority setting and review process for candidate taxa for NAPPRA and Federal Noxious weed evaluation and/or regulation.


THE PPQ WEED RISK ASSESSMENT MODEL: CURRENT STATUS AND USE. A. L. Koop*1, L. Kohl1, L. Newton1, B. Caton1, L. Miller1, B. Randall-Schadel1, I. Baez1, S. Emerine2; 1USDA-APHIS, Raleigh, NC, 2NCSU, Raleigh, NC (160)

ABSTRACT

USDA's Animal and Plant Health Inspection Service, Plant Protection and Quarantine Program (PPQ) is responsible for regulating plants that are determined to pose a threat as either noxious weeds or invasive plants. PPQ uses a variety of risk assessment tools to help determine whether a plant species meets the criteria for listing under its Federal Noxious Weed and/or Not Authorized Pending Pest Risk Analysis regulations. Of those tools, the PPQ Weed Risk Assessment model is the most rigorous as it examines a variety of plant traits to characterize and predict the risk potential of a species. Since PPQ developed this model in 2010, we have evaluated 89 species. Because of budget cuts in 2012, PPQ's weed program is now focusing on identifying potential new weeds and invasive plant species, and preventing their entry into the United States. We are using published lists of major weeds and invaders to identify potential threats and then are following up with the appropriate risk assessment tool to determine if they are good candidates for regulatory action.


TRANSCRIPTOMIC APPROACHES TO INVESTIGATE DORMANCY IN UNDERGROUND ADVENTITIOUS BUDS OF PERENNIAL WEEDS. M. E. Foley*, M. Dogramaci, D. Horvath, W. S. Chao, J. V. Anderson; USDA-ARS, Fargo, ND (161)

ABSTRACT

Underground adventitious buds, commonly referred to as crown and root buds, facilitate asexual vegetative reproduction that furthers the spread and persistence of many broadleaf perennial weeds such as Canada thistle (Cirsium arvense) and leafy spurge (Euphorbia esula).  For a number of years, the Plant Biology group has been conducting fundamental research on dormancy and vegetative reproduction in leafy spurge. Leafy spurge is a noxious perennial weed infesting non-cultivated ecosystems within the Great Plains of North America. Early investigations determined that crown buds of leafy spurge grown in the field manifest three types of dormancy: para-, endo-, and eco-dormancy. To further investigate signals and mechanisms for the induction, maintenance, and release of crown bud dormancy, we developed a protocol to induce and release endodormancy under controlled environmental conditions. Likewise, an expressed sequence tag database was developed to undertake transcriptomics approaches, specifically microarray analysis and qRT-PCR, in our dormancy investigations. As technology improved, we transitioned to RNAsequencing for our investigations. Vast amounts of transcriptome data were analyzed using various bioinformatics tools, such as gene set enrichment analyses to determine if predefined sets of genes were over-represented between treatments, and sub-network enrichment analyses to built relationships between our data and existing databases, identify central hubs, or regulators, and also visualize the networks involved in dormancy. Ultimately transcriptome and genome data facilitated development of models for control of dormancy, formulation of testable hypotheses, and identification of regulatory components for further investigation. Finally, based on earlier research, we initiated transcriptome and hormone profiling investigations of uncontrolled bud outgrowth, that is, witches’ brooming, of leafy surge shoot and root buds induced by high, but sub-lethal rates of glyphosate. We observed significant changes in abundance of transcripts involved in auxin transport in response to glyphosate treatment. Overall, our research and associated resources have laid the foundation for other research groups to develop new insights into dormancy and vegetative reproduction of broadleaf perennial weeds.


TRANSCRIPTOMIC APPROACHES TO STUDY HERBICIDE RESISTANCE IN WEEDS. T. A. Gaines*; Colorado State University, Ft. Collins, CO (162)

ABSTRACT

Transcriptomics is an increasingly accessible approach for studying weedy traits such as herbicide resistance. Techniques such as high-throughput sequencing of RNA allow both gene expression quantification (RNA-Seq) and single nucleotide polymorphism (SNP) characterization. A reference transcriptome sequence is needed to conduct analysis of high-throughput sequence data. Reference transcriptomes for several weed species have been assembled using various next-generation sequencing platforms, including Roche-454 and Illumina. Metabolism-based herbicide resistance (referred to as metabolic resistance) has been studied using transcriptomics, including metabolic resistance in Lolium rigidum.  An RNA-Seq transcriptome analysis was used to find candidate genes conferring metabolic resistance to the herbicide diclofop in a diclofop-resistant L. rigidum population.  A reference cDNA transcriptome of 19,623 contigs was assembled and annotated, and gene expression was quantified using RNA-Seq. Candidate genes were identified for validation experiments, and four genes (including two cytochrome P450 genes and a glucosyl transferase) were strongly associated with metabolic diclofop resistance. Utilizing transcriptomics to study herbicide resistance in weeds requires a suitable reference transcriptome, bioinformatics infrastructure to analyze the sequence data, and biological experiments to test candidate genes identified by RNA-Seq.

 


USING OMICS APPROACHES TO STUDY NON-TARGET GLYPHOSATE RESISTANCE IN HORSEWEED (CONYZA CANADENSIS). Y. Peng*1, Y. Sang1, R. Ye1, Q. Jia1, S. Allen1, D. Sammons2, N. Stewart1; 1University of Tennessee, Knoxville, TN, 2Monsanto, St. Louis, MO (163)

ABSTRACT

Weeds are responsible for an estimated $36 billion loss annually in the USA alone and represent the most difficult pest for farmers to control. Glyphosate is the most widely used herbicide in the world. However, the widespread use of glyphosate has exerted selection pressure on various species of weeds. Horseweed (Conyza canadensis L.) was the first broadleaf weed to evolve glyphosate resistance in agriculture, and also is the most widely distributed glyphosate-resistant weed in the United States and the world. Horseweed is a true diploid (2n=18), and has the smallest genome (~335 Mb) of any agricultural weeds, and was suggested to be among the best candidates of model weedy plants. We have recently participated in a phylogeographic study that gives evidence that horseweed has evolved glyphosate resistance independently in many locations in the USA. Is there a shared mechanism of glyphosate resistance for biotypes that evolved independently? If not, how many mechanisms exist for glyphosate resistance, at least for the existing resistant biotypes? What genes and pathways are involved in the glyphosate resistance? To address these issues, Omics approaches including de novo genome sequencing and resequencing, deep RNAseq and proteomics have been used.  The first draft genome of an agricultural weed will help us to understand the genetic and genomic basis of weediness. Comparative global gene expression analyses using RNASeq have been performed between susceptible and resistant, treated and un-treated samples. Quantitative protein profiling of tonoplast samples comparing between TN-R and TN-S biotypes have been performed by using LC-MS/MS peptide sequencing platform. Specific expressing gene/proteins in R samples were isolated and suggested involved in the resistance via alternative glyphosate translocation pattern.


OMICS APPROACHES TO NATURAL PRODUCTS RESEARCH. S. O. Duke*; USDA, ARS, Oxford, MS (164)

ABSTRACT

Our laboratory has used omics approaches (transcriptomics, proteomics, and metabolomics) to probe and clarify the mode of action of several natural phyotoxins.  Transcriptomics failed to provde a clue to the mode of action of BOA, a common allelochemical, although it provided considerable information about plant defenses to it. Microarray-based transcriptomic methods were used to the proble the mode of action of cantharidin, a plant serine-threonine protein phosphatase inhibitor.  The results strongly reflected the mode of action.  However, subsequent proteomics study of treated tissues from the same experiment were difficult to interpret in the context of the transcriptome results.  Metabolomic studies of the mode of action of several phytotoxins have been generally more useful.  Metabolomic responses of duckweed to ascaulitoxin aglycone revealed considerable disruption of amino acid metabolism, which supported physiological studies.  Looking at the complete literature of the use of omics to determine mode of action of phytotoxins, I conclude that these methods are not very useful in pinpointing target sites, but can provide a wealth of information about secondary and tertiary effects.  Relatively little research on allelopathy has used omics approaches.  Metabolomics can be useful in such studies if the allelochemical is known.  In summary, omics methods can generate huge amounts of information, but unless a study is properly designed to use these methods, results can be difficult to interpret.


HERBICIDE RESISTANCE AND TOLERANCE IN WEEDS: INSIGHTS FROM METABOLOMICS AND ENZYME ANALYSIS. N. Tharayil*, A. S. Maroli; Clemson University, Clemson, SC (165)

ABSTRACT

Rapidly evolving resistance in weeds to commonly used herbicides have catapulted the herbicide-resistance research to the forefront of activities in weed science discipline, and current herbicide studies prioritize the mechanisms of resistance-development in weedy biotypes.  Application of genomics and transcriptomics technologies have successfully identified common genetic factors of herbicide resistance in many weed biotypes. However, the molecular markers that are tracked using genomics, transcriptomics and proteomics (DNA, RNA and proteins, respectively) are susceptible to functional alteration either by epigenetic modifications or post-transcriptional and post-translational modifications, resulting in altered phenotypes. Thus, the above traditional ‘omics’ approaches provide an incomplete picture of the real-time phenotypic manifestations of resistance in action. To bridge this knowledge gap between the genotype and its eventual phenotype, integration of genomics, transcriptomics and proteomics with modern ‘omics’ approaches including metabolomics, metabonomics, phenomics has been proposed.

Metabolomics is a rapidly emerging field that attempts to quantify all small molecules in a dynamic framework of the metabolome. Deciphering the metabolome is vital as it is a direct reflection of the metabolic state of a cell that manifest as the phenotype, and thus offers an unprecedentedly powerful approach for real-time molecular phenotyping. Lethality of most systemic herbicides could mainly be attributed to their disruption of essential metabolic pathways in plants, thus the metabolomic approach presents a unique opportunity not only to gain a comprehensive understanding on the modes of action of herbicides and natural compounds, but also to outline the possible cellular-level metabolism that confers tolerance/resistance to some weedy biotypes. Thus while genomics and proteomics provide information about the processes that could potentially happen, the metabolomics give a more definite, real-time representation of the processes happening within a living organism exposed to a given environment, and thus is highly complementary to other omics approaches.

We used a targeted-metabolomics approach to study the metabolic responses of glyphosate-resistant (R) and susceptible (S) biotypes of Amaranthus palmeri and glyphosate-tolerant Ipomea purpurea to glyphosate application. The ensuing changes in both carbon and nitrogen metabolism were captured at multiple time points using gas and liquid chromatography-tandem mass spectrometry platforms, followed by data processing and multivariate statistical approaches. Application of glyphosate (0.4kg ai/ha) caused a 15 fold increase in shikimic acid (SA) concentration in both S- and R- biotypes within 8 hours after treatment (HAT), indicating a rapid disruption of shikimate pathway. This blockage of the shikimate pathway reverberated across other biochemical pathways and processes as evident by the fluxes of intermediaries of TCA cycle and glycolysis. The concentration of aromatic amino acids (Tyr, Phe, Trp) decreased in the susceptible biotypes, however, despite a similar SA accumulation, there was no significant decrease in the concentration of aromatic amino acids in the resistant biotype. Compared to 8HAT, accumulation of SA in the glyphosate-treated S-biotypes increased by 4 fold at 72HAT, while the SA in R-biotype remained unchanged. Moreover, the overall metabolomic profile of the glyphosate sprayed R-biotype were similar to that of the water treated control plants. In the glyphosate sprayed S-biotype, there was a higher accumulation of sugars, with sucrose being the highest. The difference in levels of sugars between the S- and R- biotypes in response to glyphosate application could potentially result from the under-utilization of the carbohydrates due to growth inhibition by glyphosate toxicity, as well as inhibition of phosphenolpyruvate carboxylase (PEPC) by the accumulated shikimic acid.

I. purpurea biotypes of varying tolerance (WAS GR50 151.44 g ae/ha, and  QUI 59.11 g ae/ha) was treated with 84 g ae/ha glyphosate, and the young leaves were harvested after 72 HAT. Metabolomic profiling, followed by multivariate analyses captured the differences between the two biotypes and also between glyphosate and water (control) application.  Shikimate accumulation was observed in both glyphosate treated biotypes. Glyphosate sprayed WAS biotype had a higher concentration of aromatic amino acids compared to its water control. However, in the QUI biotype, there was no significant difference in the levels of aromatic amino acids between the water and glyphosate treatments. This accumulation of aromatic amino acids despite an increase in SA concentration highlights a possible disconnect between glyphosate response of WAS biotype and the interruption in amino acid metabolism. Overall, our results indicate that targeted metabolomics approach is a powerful tool for probing the cellular physiology and metabolic pathways of weedy biotyes in relation to herbicide resistance. Application of stable isotope fluxomics approaches to quantify the intracellular metabolite fluxes in response to herbicide application will be discussed. 

 


AN UPDATE ON HPPD-RESISTANCE IN AMAPA AND AMATA POPULATIONS. C. L. Dunne*1, R. Jain1, V. K. Shivrain2, G. D. Vail2; 1Syngenta Crop Protection, Vero Beach, FL, 2Syngenta Crop Protection, Greensboro, NC (166)

ABSTRACT

HPPD-inhibitor herbicides have been very effective as pre-emergence and post-emergence for weed management in corn. Resistance to postemergence applied HPPD-inhibitors has recently been documented in waterhemp (Amaranthus tuberculatus or AMATA) and Palmer amaranth (Amaranthus palmeri or AMAPA). Greenhouse studies were conducted to determine the levels of HPPD resistance in these AMATA and AMAPA biotypes. In addition, response of AMATA and AMAPA accessions obtained from various states in the mid-west and mid-south, respectively, to mesotrione applied post-emergence at 3- and 6-inch height of plants was also investigated in the greenhouse.

Significant differences in control were observed between these accessions treated at the same rate of mesotrione. Also, the control for all accessions in all treatments decreased significantly when the applications were made to 6 inch versus 3 inch plants. The variability in control of various accessions at the same rate of herbicide indicates that there are inherent differences in the sensitivity of AMATA and AMAPA populations to HPPD herbicides with respect to both origin and height at the time of treatment. These data clearly suggest that mesotrione is most effective and consistent in controlling sensitive AMATA and AMAPA populations when applied to smaller (up to 3 inch) plants.


EVALUATION OF WEED CONTROL PROGRAMS UTILIZING HPPD-TOLERANT SOYBEANS. J. C. Holloway*1, D. E. Bruns2, T. H. Beckett3, B. R. Miller4, D. J. Porter5; 1Syngenta Crop Protection, Jackson, TN, 2Syngenta Crop Protection, LLC, Marysville, OH, 3Syngenta Crop Protection, Greensboro, NC, 4Syngenta Crop Protection, LLC, Minneapolis, MN, 5Syngenta Crop Protection, LLC, Greensboro, NC (167)

ABSTRACT

Evaluation of Weed Control Programs Utilizing HPPD-Tolerant Soybeans. James C. Holloway, Jr.,*1, Dain E. Bruns2, Monika Sani3, Brett R. Miller4, Donald J. Porter3, 1Syngenta, Jackson, TN 2Syngenta, Marysville, OH, 3Syngenta, Greensboro, NC, 4Syngenta, Minnetonka, MN.

 

Field trials were conducted from 2012 to 2014 to evaluate mesotrione-based weed control programs in HPPD-tolerant soybeans stacked with glyphosate tolerance.  These multiple mode-of-action herbicide tolerant soybeans enable the use of mesotrione and isoxaflutole pre-emergence in addition to glyphosate post-emergence.

 

Several mesotrione-based herbicide programs provided control of key weed species, including glyphosate resistant populations.  The most successful and consistent weed control was achieved with two-pass programs that included pre-emergence residual herbicides and multiple, overlapping modes of action.  These programs were designed to align with HRAC principles of weed resistance management. The use of these chemically diverse and novel programs will offer effective, safe and sustainable weed management options for soybean growers.


PALMER AMARANTH SOIL SEEDBANK MANAGEMENT: INTEGRATING HARVEST WEED SEED CONTROL STRATEGIES AND OTHER FALL PRACTICES WITH HERBICIDES. J. K. Norsworthy*1, M. Walsh2, S. Powles2; 1University of Arkansas, Fayetteville, AR, 2University of Western Australia, Perth, Australia (168)

ABSTRACT

With the widespread evolution of glyphosate-resistant Palmer amaranth across the midsouthern and southeastern United States, there is a pressing need to identify effective strategies that lower the weed seedbank and lessen the likelihood of resistance evolving to herbicides.  In Australian cropping systems, Harvest Weed Seed Control (HWSC) strategies are routinely used at crop harvest as a means of reducing weed seed inputs into the soil seedbank.  These strategies have mainly been used in wheat and have not been tested in U.S. soybean production systems.  Recent research has shown that more than 99% of Palmer amaranth seed persist on the plant through soybean harvest, and thus, there is potential to capture and destroy this seed during crop harvest.  Use of cover crops is another strategy that has potential to increase seedbank losses via predation as well as suppress subsequent Palmer amaranth emergence.  From fall of 2010 to spring of 2014, a large plot field experiment was conducted at the Northeast Research and Extension Center in Keiser, AR to understand the impact of fall management practices and herbicide programs (or trait selection) on the population dynamics of Palmer amaranth.  The experiment consisted of a split plot treatment in a randomized complete block design with three replications. Six fall management strategies were evaluated as main plots which included: (Fall 1) a standard practice where the straw spreader was attached to the combine, soybean residue following harvest was not burned, and there was no subsequent fall tillage; (Fall 2) straw spreader attached to combine and soybean residue not burned with the plots rebedded immediately following harvest; (Fall 3) straw spreader attached to combine and cereal rye drill seeded without fall tillage; (Fall 4) straw spreader removed from combine and residue windrowed but not burned without fall tillage; (Fall 5) straw spreader removed from combine and residue windrowed and burned without fall tillage; and (Fall 6) all straw and chaff residue exiting combine caught and removed from the field with no fall tillage. The subplots (8 rows by 64 m) consisted of three different herbicide regimes: (Herb 1) glyphosate at 870 g ae ha-1 at V2 soybean fb glyphosate at 870 g ha-1 at V7 soybean; (Herb 2) flumioxazin at 71 g ai ha-1 preemergence (PRE) followed by (fb) glyphosate at 870 g ha-1 + a premix of S-metolachlor at 1,215 g ai ha-1 and fomesafen at 266 g ai ha-1 at V2 fb glyphosate at 870 g ha-1 at V7; and (Herb 3) flumioxazin at 71 g ha-1 PRE fb glufosinate at 594 g ai ha-1 + a premix of S-metolachlor at 1,215 g ha-1 and fomesafen at 266 g ha-1 at V2 fb glufosinate at 594 g ha-1 at V7.   The entire test was oversprayed with glyphosate at 870 g ha-1 at 2 to 3 weeks prior to planting to control the existing weeds and rye cover crop.  Immediately after planting, the test was again oversprayed with paraquat at 700 g ai ha-1.  Herbicide programs had a stronger influence on the density of Palmer amaranth at crop harvest than did the fall management practices; however, HWSC practices that further removed weed seed at crop harvest did result in approximately a three-fold reduction in Palmer amaranth density, a testament to the effectiveness of these strategies.   This presentation will further our understanding of the value of using HWSC strategies in soybean for Palmer amaranth management and point to some of the benefits and challenges around use of these strategies.


INTERACTION OF SOIL-RESIDUAL HERBICIDE COMBINATIONS AND RATES ON THE CONTROL OF WATERHEMP AND SOYBEAN GROWTH AND DEVELOPMENT. N. T. Harre*1, J. L. Matthews2, J. M. Young1, M. L. Bernards3, A. G. Hager4, B. G. Young2; 1Purdue University, West Lafayette, IN, 2Southern Illinois University, Carbondale, IL, 3Western Illinois University, Macomb, IL, 4University of Illinois, Urbana, IL (169)

ABSTRACT

A common management tactic to combat problematic and herbicide-resistant weeds, such as waterhemp, in soybean is the utilization of soil residual herbicides as these enable the integration of more diverse herbicide chemistries than POST applications.  However, the effectiveness of soil residual herbicides are strongly regulated by precipitation and edaphic factors and may occasionally provide unsatisfactory weed control.  In recent years, increasing application rates and applying multiple soil residual herbicides in combination has become routine for some growers to extend the length of residual weed control, but may be a cause of concern as this arguably increases the frequency of soybean injury.

Field experiments were conducted at Southern Illinois University and the University of Illinois in 2011, 2012, and 2014.  The first experiment evaluated the influence of full and reduced rates of sulfentrazone and flumioxazin in combination with five tank-mix partners on residual waterhemp control.  A second experiment assessed the effect of the same herbicide treatments at a 1x (full) and 2x field use rate on soybean growth, development, and grain yield in a weed-free environment.  Droughty conditions persisted through the early growing season in 2012 and resulted in poor weed emergence and negligible soybean injury.  In 2011 and 2014, the most consistent and prolonged residual control was achieved through the use of full rates and multiple soil residual herbicides.  A full rate of sulfentrazone or flumioxazin alone provided similar waterhemp control as a reduced rate of these herbicides applied with soil residual tank mixtures at 21 and 42 d after planting (DAP).  At 63 DAP, waterhemp control was greater for the reduced rate tank mixtures than the full rates of sulfentrazone of flumioxazin applied alone.  Soil residual herbicide tank mixtures also enhanced control of secondary weeds evaluated in the study such as giant foxtail, velvetleaf, and pitted morningglory.  Soybean injury, expressed primarily as stunting, was greater in treatments containing flumioxazin compared to sulfentrazone and when 2x field use rates were applied; however, stunting from soil residual herbicides did not delay vegetative or reproductive development.  Soil residual herbicide tank mixtures applied at a full rate caused no reduction in soybean grain yield over any site-year.  At a 2x field use rate, flumioxazin applied with pendimethalin or pyroxasulfone were the only treatments that reduced grain yield and seed weight and occurred in 2 of 7 site-years.  Soybean injury present at 21 DAT (n = 265) was weakly correlated to grain yield loss (R2 = 0.14) while, injury that persisted to 63 DAP (n = 64) had a stronger relationship with yield reductions (R2 = 0.51).  These results suggest applying multiple soil residual herbicides at full use rates are an effective early-season strategy to control waterhemp and soybean injury from these herbicides is typically transient with no concomitant grain yield loss.  However, individuals applying these herbicides at full rates should be cognizant of the potential soybean injury and increased risk of yield loss in field areas that receive an overlapping application from the spray boom.


SEEDLING SOYBEAN BIOASSAY FOR EVALUATION OF TOLERANCE TO METRIBUZIN. T. L. Grey*; University of Georgia, Tifton, GA (170)

ABSTRACT

Glyphosate-resistant weeds have become one of the most common and troublesome issues in soybeans in the southeastern US. Glyphosate is still used as a control for weeds; however farmers also use residual herbicides to maintain season long weed control. Metribuzin could potentially be used to provide residual weed control of herbicide resistant weeds in soybeans. Metribuzin has been shown to provide some control of glyphosate resistant Palmer amaranth and other weeds in the southeast. However, metribuzin has been shown to cause injury to certain soybean cultivars of the past. Therefore it is necessary to evaluate current soybean cultivars to metribuzin.  With hundreds of cultivars field testing limits the number that can be screened. Therefore, experiments were conducted in 2010, 2011 and 2012 in laboratory and growth chambers involving three general soybean groups. Conventional, Roundup Ready, and Liberty Link soybean cultivars of more recent release were evaluated in a bioassay using multiple rates of metribuzin in a hydroponic solution.  Soybean was pre-germinated for up to 3 days prior to individual seed with radicles being placed into a single cuvette containing a rate of metribuzin: 0.0, 0.1, 1.0, 10, or 100 ppm.  Cuvettes were then placed into a wooden box designed to prevent light exposure to the developing roots.  After 14 days in the growth chamber, soybean was evaluated for injury in the form of chlorosis, then destructive measures of length and biomass of shoots and roots.  Cultivars were then analyzed by soybean traits including maturity group (V, VI, VII, or VIII), flower color (purple or white), or plant pubescence (tawny or gray).  There was no correlation across cultivar maturity group, flower color, or plant pubescence and metribuzin exposure.  In contrast, Liberty Link cultivars exhibited negative seedling response in the form of shoot reduction.  Overall cultivars exhibited negative shoot and root growth to metribuzin at 100 ppm.  With the correct choice of soybean cultivar and weed management program, metribuzin could play an important part of controlling current herbicide resistant weeds and preventing similar future weed pest problems.

 


USING DOSE-RESPONSE CURVES ON CONTINUOUS DATA TO ASSESS RESISTANCE IN WEED BIOTYPES. J. C. Streibig*1, A. R. Kniss2; 1University of Copenhagen, Taastrup, Denmark, 2University of Wyoming, Laramie, WY (171)

ABSTRACT

Confirming herbicide resistance typically involves comparing dose-response curves from resistant and susceptible populations. Ideally, the doses required to kill 50% of each weed population would be estimated, in the same way xenobiotics are classified into toxic categories on the basis of the LD50. But to calculate the LD50, we limit our data collection on the binomial response (dead or alive), which spans between 0 to 1. It is sometimes impractical to assess alive or dead plants due to experimental constraints. Using continuous responses (like dry weight or seed production) often poses problems because nontreated controls vary among populations. The problem of differential response in nontreated controls must be addressed, although it is often ‘side-stepped’ by rescaling the response. Transforming continuous data to percent of the nontreated control for each population forfeits important information about the growth conditions of the test plants.

 


CONTROL OF GLYPHOSATE RESISTANT HORSEWEED AND GIANT RAGWEED IN THE SAME FIELD OF SOYBEAN. P. H. Sikkema*, N. Soltani; University of Guelph, Ridgetown, ON (172)

ABSTRACT

Glyphosate resistant (GR) horseweed and giant ragweed have been confirmed in 25 and 7 counties in Ontario, respectively. The geographic area affected is expected to increase. Yield loss in soybean due to interference from GR horseweed and giant ragweed is greater than 90% in some Ontario studies. Although there is excellent information on the control of GR horseweed and giant ragweed, there is little information on the best compromise solution when they occur together in the same field of soybean. Five separate field studies for each weed (GR horseweed and giant ragweed) were conducted in growers’ fields in southwestern Ontario during 2013-2014 to evaluate preplant herbicide tankmixes for the control GR horseweed and giant ragweed in glyphosate resistant soybean. Glyphosate alone or in tankmix with saflufenacil, amitrole, 2,4-D ester, saflufenacil plus amitrole, saflufenacil plus 2,4-D ester and amitrole plus 2,4-D ester provided 1, 54, 77, 43, 87, 72 and 82% control of GR horseweed and 4, 58, 91, 90, 87, 97 and 97% control of GR giant ragweed at 8 WAA in soybeans, respectively. Density and biomass reduction for GR horseweed and GR giant ragweed with the preplant herbicides evaluated were similar to the control ratings. Based on these studies, the two-way tankmix of glyphosate + amitrole and the three-way tankmix of glyphosate plus amitrole plus 2,4-D ester are the best herbicide tankmix options for the control GR horseweed and giant ragweed if both weeds exist in the same field of soybean in Ontario.


INFLUENCE OF COVER CROPS ON MANAGEMENT OF AMARANTHUS SPP. IN SOYBEANS. M. M. Loux*1, A. Dobbels1, K. Bradley2, V. M. Davis3, W. Johnson4, J. K. Norsworthy5, L. E. Steckel6, B. G. Young7; 1Ohio State University, Columbus, OH, 2University of Missouri, Columbia, MO, 3University of Wisconsin, Madison, WI, 4Purdue University, West Lafayette, IN, 5University of Arkansas, Fayetteville, AR, 6University of Tennessee, Jackson, TN, 7Southern Illinois University, Carbondale, IL (173)

ABSTRACT

A field study was conducted in 2013-14 at a total of six sites in Ohio, Missouri, Illinois, Arkansas, Tennessee and Indiana to determine the effect of a cover crop on control of Amaranthus spp. in soybeans when integrated with herbicides.  There was one redroot pigweed site, two waterhemp sites, and three Palmer amaranth sites.  Cereal rye was included at all sites, and a second cover of oats, tillage radish, or annual ryegrass was also included at each site along with a no cover treatment.  Covers were planted between September 23, and November 20, 2013, and terminated with glyphosate/2,4-D between March 20 and May 20, 2014.  Soybeans were planted between May 5, and May 27.  The two other factors in the study were the type of herbicide-tolerance trait (glyphosate- vs glufosinate-resistant) and the type of herbicide treatment.  The latter included: 1) none; 2) preemergence followed by postemergence/residual – flumioxazin followed by either glyphosate/fomesafen/metolachlor or glufosinate/metolachlor; and 3) preemergence followed by postemergence/residual followed by late postemergence residual – same as previous treatment with the addition of a later application of acetochlor.  Control and population density were measured prior to each postemergence application and at harvest, along with crop yield.  Herbicide treatment was the primary factor affecting weed control, population density, and crop yield, when sites were combined for analysis.  Control and yield were lower, and population density higher, for the nontreated compared with the herbicide treatments.  There was an interaction between cover and herbicide treatment for early- and mid-season control, which primarily reflected the 10 to 20% higher control from rye versus the other cover and the no cover treatments, in the absence of herbicides.  Control at the end of the season exceeded 92% for both herbicide treatments, averaged over other factors, and there was no effect of cover.  Analysis of sites separately resulted in infrequent significance of main factors or interactions that deviated from the results of combined analysis.  At one waterhemp site, population density was lower for the radish cover compared with the rye or no cover, and yield was lower for the rye compared with radish or no cover.  At the other waterhemp site, control and yield were higher for the glyphosate treatments compared with the glufosinate treatments.  At one Palmer amaranth site, mid-season control in the presence of herbicides was lower for the rye cover than the oats or no cover treatments, but the rye was more effective at the other two Palmer sites.  This study is being repeated in 2014-15.

 

 


COVER CROP ESTABLISHMENT ISSUES FOLLOWING CORN AND SOYBEAN HERBICIDES IN THE UPPER MIDWEST. D. H. Smith*1, T. R. Legleiter2, E. J. Bosak1, W. Johnson2, V. M. Davis1; 1University of Wisconsin, Madison, WI, 2Purdue University, West Lafayette, IN (174)

ABSTRACT

Cover Crop Establishment Issues Following Corn and Soybean Herbicides in the Upper Midwest

Daniel H. Smith, Graduate Research Assistant1,Travis R. Legleiter, Research Associate2, Elizabeth J. Bosak, Outreach Specialist1, William G. Johnson, Professor2, Vince M. Davis, Assistant Professor 1

1-Department of Agronomy University of Wisconsin-Madison; 2-Department of Agronomy Purdue University

Abstract

Cover Crops are a growing interest for corn and soybean producers in the upper Midwest due to the benefits of reducing soil erosion, providing and scavenging nutrients, and increasing soil organic matter. This study was conducted to determine whether common soil applied herbicides with residual weed control properties applied in the spring during the establishment of corn and soybean crops affect the subsequent establishment of cover crops in the fall. Corn and soybean trials with glyphosate-resistant cultivars were established at Arlington Agricultural Research Station, Arlington, WI on June 2, 2013 and May 28, 2014. Similar trials were also conducted at Throckmorton Purdue Agriculture Center in Lafayette, IN and these trials were established for corn on May 16, 2013 and April 27, 2014 and for soybean May 16, 2013 and May 7, 2014. Corn and soybean trials in Wisconsin had fourteen herbicide treatments and in Indiana there were 10 treatments for soybean and 11 for corn. All treatments were applied at common labeled rates and timings with four replications. Each crop included a control treatment where no residual herbicide applied, however weeds were managed with postemergence (POST) glyphosate for all treatments to remove potential effects from weed competition or residues. Trials conducted in Arlington, WI were harvested for silage near the beginning of September, and cover crops were seeded with a no-till grain drill uniformly across all herbicide treatments. Trials conducted in Lafayette, IN were seeded by hand broadcasting seed at the end of August to simulate aerial seeding and the main crops then were harvested for grain at the end of September. The cover crops included were Tillage Radish® (Raphanus sp;), crimson clover (Trifolium incarnatum), winter rye (Secale cereal), a mixture of 70% oat (Avena sativa) plus 30% peas (Pisum sativum), only at Arlington, WI, and four different annual ryegrass (Lolium multifloram) varieties. The annual ryegrass varieties included ‘Bruiser’ and ‘Gulf’ in Lafayette, IN and ‘King’ and a tetraploid in Arlington, WI. ‘Bruiser,’ ‘Gulf,’ and ‘King’ were all diploids. Nearly two months after seeding, the cover crops were evaluated for herbicide injury. In Arlington, WI percent ground cover was assessed using digital imagery analysis, and accumulated biomass was collected from a 0.25m2 quadrat, dried, and weighted. Herbicide injury included the evaluation of plant stunting and loss of plant greenness. In Lafayette, IN injury was assessed by stand counts and visually rating of percent stand reduction.  In 2013, winter rye was the only cover crop without negative growth effects associated from the herbicide treatments applied in the corn or soybean trials (both p-values < 0.05) at both locations.  All other cover crops had significantly reduced biomass (P < 0.05) and percent cover (P < 0.05) for at least one of the residual herbicide treatments applied in the corn and soybean trial. In 2014 at Arlington, WI ‘King’ and the tetraploid annual ryegrass were the only cover crops that had growth inhibition because of herbicide treatments applied in the corn or soybean trials (both p-values <0.0001). All other cover crops did not have significantly reduced percent cover (P<0.05) for all of the residual herbicide treatments. At Lafayette, IN none of the cover crops had significant (P<0.05) reduction in stand found from stand counts and visual ratings. From these results we suggest several commonly used corn and soybean herbicides have the potential to adversely affect the establishment of many different cover crops, but the severity of damage will be determined by weather, cover crop species, and the specific herbicide combination.  More research will be needed to establish best management practices for farmers interested in the use of cover crops following conventional Midwest corn and soybean production.

 

 

 


A NEW GLYPHOSATE RESISTANT WEED SPECIES CONFIRMED FOR NORTHERN NSW (AUSTRALIA) AND THE WORLD &NDASH; COMMON SOWTHISTLE (SONCHUS OLERACEUS). T. S. Cook*, W. P. Davidson, B. L. Miller; NSW Weed Society, Tamworth, Australia (175)

ABSTRACT

Sowthistle (Sonchus oleraceus) is an annual broad-leaf weed of grain, cotton crops and non-crops areas in northern NSW and Queensland. Its abundance in these areas is primarily due to reduced tillage farming systems that allow the surface germinating seed to establish. Recently, farmers and agronomists have noticed its ability to tolerate glyphosate applications. This may be due to antagonism between glyphosate and 2,4-D or the possibility of glyphosate resistance.

Two populations of sowthistle were identified in northern NSW, surviving straight applications of glyphosate. These were subsequently tested as glyphosate resistant following applications of glyphosate at 720 g a.i. ha-1.  This news represents the first reporting and confirmation of a glyphosate resistant Sonchus species internationally. It is now the seventh recognised glyphosate resistant weed in Australia.

Growth stage of sowthistle at the time of treatment had a noticeable effect on the survival rates. The disparity in control between resistant and susceptible populations was more pronounced once sowthistle surpassed the early stem elongation stage.  In essence, it appears that control of glyphosate resistant sowthistle may be feasible if treated at the early rosette stage, even with glyphosate. This interaction between growth stage and glyphosate resistance status is common amongst other glyphosate resistant weed species.

These findings have serious implications to grain producers in the northern grain and cotton zone and for those that manage non-crop areas, such a roadsides and railway corridors. These areas have often relied heavily upon glyphosate as their herbicide of choice. The alternative options may not be as effective and as robust as glyphosate.

 


HERBICIDE RESISTANT LOLIUM SPP. IN ITALY AND MEDITERRANEAN AREA. A. Collavo*, R. Beffa, H. Strek; BayerCropScience AG Frankfurt, Frankfurt, Germany (176)

ABSTRACT


PYROXASULFONE RATE AND TIMING EFFECTS ON ITALIAN RYEGRASS CONTROL IN WHEAT. A. M. Knight*1, Z. Taylor2, L. Grier2, W. J. Everman1; 1NCSU, Raleigh, NC, 2North Carolina State University, Raleigh, NC (177)

ABSTRACT

Currently, weed resistance is a problem of concern in NC wheat with Italian ryegrass being the number one problem weed.  Recent studies have shown Italian ryegrass having resistance to Powerflex, Hoelon, and Axial in NC.  This problem leaves growers looking for alternative options for control.  Pyroxasulfone, an active ingredient in Zidua (85% pyroxasulfone) is active on a wide range of weeds species including annual grasses and many broadleaf weeds. Field studies were conducted in the fall/winter of 2011, 2012, and 2013 in NC to evaluate weed control efficacy in winter wheat (Triticum aestivum).  The study was conducted throughout the state of North Carolina at research stations in Clayton (2011, 2012, 2013), Salisbury (2011, 2013), and an on farm site in Edgecombe County (2012).  A total of nine treatments were applied and compared back to a non-treated control.  Treatments included PRE only applications of Zidua at 1, 1.25, and 1.5 oz A-1 and a combination of Zidua (1 oz A-1) + Sharpen (2 oz A-1).  Two application treatments included a Zidua PRE application of 1 oz A-1 followed by a POST application of Zidua at 0.5 or 1 oz A-1.  These PRE Zidua programs were compared to POST only programs of Prowl H2O (2 pt/A) + Axial XL (16.4 oz/A), Axiom (8 oz/A) alone, and Osprey (4.75 oz/A) + Harmony (0.6 oz/A).  Weed control data was collected on Italian ryegrass (Lolium multiflorum), henbit (Lamiaceae amplexicaule), wild radish (Raphanus raphanistrum) and spotted spurge (Euphorbia maculata) according to species naturally present in the field.  Italian ryegrass was best controlled with programs containing Zidua PRE.  In the 2012 season, the Zidua+ Sharpen program provided the most control with 93% mid-season while in 2013 the most control was noted with the Zidua (1oz) PRE + Zidua (1oz) POST program (95%).  However, this control was not maintained throughout the season in 2013.  The greatest control of henbit was noted with the use of Axiom alone maintaining a 95% level of control throughout the season.  Spurge and wild radish additionally showed the best control with the Axiom (75-93%) or Zidua + Sharpen PRE (65-93%) treatments.  Treatments resulted in no crop injury or yield reduction with no significant differences observed in wheat yield.    

 


CONTROL OF BRAZILIAN PEPPERTREE AND AUSTRALIAN-PINE USING AMINOCYCLPYRACHLOR. B. A. Sellers*1, J. A. Ferrell2, G. E. MacDonald2; 1University of Florida, Ona, FL, 2University of Florida, Gainesville, FL (178)

ABSTRACT

Brazilian peppertree and Australian-pine have infested over 250,000 and 190,000 hectares, respectively, in Florida.  While there are standard herbicide programs for removal of these invasive trees, aminocyclopyrachlor is a relatively new herbicide that may have activity on these species.  Experiments were conducted from 2011 through 2013 to determine the effect of cut-stump and basal applications of aminocyclopyrachlor on Brazilian peppertree.  Aminocyclpyrachlor premixes were applied foliarly to both Brazilian peppertree and Australian-pine.  The oil formulation of aminocyclpyrachlor applied as a basal application resulted in 100% control of Brazilian peppertree 365 days after treatment (DAT) at concentrations as low as 5% v/v mixed in basal oil.  The aminocyclopyrachlor concentration required for complete kill of cut-stumps was at least 6.7% v/v.  Fall foliar applications of aminocyclopyrachlor plus metsulfuron or plus imazapyr and metsulfuron resulted in at least 85% control of Brazilian peppertree.  However, a summer application of aminocyclopyrachlor plus metsulfuron did not result in consistent control at currently labeled rates for this premix (Streamline™).  Conversely, Australian-pine control with aminocyclopyrachlor plus metsulfuron provided consistent control following a summer application versus a late fall application.  Labeled rates of aminocyclopyrachlor plus metsulfuron or imazapyr and metsulfuron resulted in 100% mortality of Australian-pine when applied during the summer.  Control following a late fall application of aminocyclopyrachlor + metsulfuron was not consistent among treated plants; however, mortality remained above 85%.  The addition of imazapyr to aminocyclopyrachlor and metsulfuron (Viewpoint™) resulted in complete mortality of Australian-pine, regardless of application time.  These data suggest that products containing aminocyclopyrachlor can be used to effectively manage these invasive species.  The timing of application should be investigated further for optimum efficacy of these products.


OPERATIONAL USE OF HERBICIDE BALLISTIC TECHNOLOGY (HBT) ON A HELICOPTER PLATFORM REDUCING NASCENT MICONIA (MICONIA CALVESCENS DC) POPULATIONS IN THE EAST MAUI WATERSHED. J. Leary*1, J. Gooding2, B. Mahnken3, R. Rodriguez4, D. Jenkins4; 1University of Hawaii, Kula, HI, 2Haleakala National Park, Makawao, HI, 3Maui Invasive Species Committee, Piiholo, HI, 4University of Hawaii at Manoa, Honolulu, HI (179)

ABSTRACT

Herbicide Ballistic Technology (HBT) is a novel pesticide application system for surgically administering small aliquots 
of herbicide encapsulated into 0.68 caliber soft-gel projectiles that are propelled by a pneumatic device with an effective 
range of 30 m to target.  This herbicide delivery system was developed in Hawaii in collaboration with the Nelson Paint 
Company (Kingsford, MI) utilizing their liquid encapsulation (i.e., paintball) technology. The product HBT-G4U200 with 
Garlon 4 Ultra (Triclopyr 200 mgae) is a registered 24(c) Special Local Need pesticide for targeting satellite populations 
of highly invasive, exotic miconia (Miconia calvescens) colonizing remote watersheds of Maui, which are inaccessible to 
ground-based operations.    The HBT platform is best used in aerial surveillance and reconnaissance operations on a 
Hughes 500D helicopter platform, featuring real-time capabilities in eliminating nascent targets upon detection.  
Starting in 2012, we have conducted >70 intervention missions with >300 hrs of operational flight time; dispatching 
>13,000 miconia targets.  With this intensified aerial intervention strategy, we have measurably reduced target densities, 
protecting >6000 ha of forested watershed on Maui. We can also highlight that 89% of the total treated area has received 
<1% of the maximum allowable use rate.  This is a testament to the surgical approach of an HBT application providing 
effective weed management, while presenting the smallest footprint on the landscape.

 

For video rendition of the HBT helicopter platform please visit:

http://www.youtube.com/watch?v=988i6SQKSzY 



NUISANCE AQUATIC VEGETATION CONTROL: IMPLICATIONS FOR FISH AND WILDLIFE. R. S. Haynie*1, S. B. Wilde2, S. R. Dodd3; 1SePRO Corporation, Carmel, IN, 2University of Georgia, Athens, GA, 3Nutter and Associates, Inc., Athens, GA (180)

ABSTRACT

Cyanobacterial toxins have been implicated in fish, wildlife, livestock and human mortality events. Responses by wildlife resource managers to these events are typically reactive due to the dynamic nature of algal blooms. Avian Vacuolar Myelinopathy (AVM) is a lethal neurologic condition, affecting waterbirds and their avian predators, namely the Bald eagle (Haliaeetus leucocephalus). The disease is caused by the recently described toxin-producing cyanobacterium, Aetokthonos hydrillicola. This cyanobacterium grows epiphytically on nonnative submerged aquatic vegetation (SAV). The seasonal nature of the disease and monitoring effort by state and federal biologists allows resource managers to implement proactive management strategies to reduce disease prevalence: nonnative SAV control has been initiated in several reservoirs where AVM epizootics routinely occur. We conducted a two year field study in two drinking water reservoirs in Henry County, Georgia. Both reservoirs were infested with Hydrilla (Hydrilla verticillata), but only one reservoir had an active SAV management plan. Triploid carp (Ctenopharyngodon idella) were stocked (10 fish/vegetated ha) into the treatment reservoir, Spring 2011. We monitored Hydrilla biovolume, A. hydrillicola presence and AVM prevalence in the reservoirs from July 2011 to December 2012. To evaluate AVM prevalence sentinel birds, wing-clipped, farm raised mallards (Anas platyrhynchos), were released onto the reservoirs mid-November. Disease prevalence was not significantly different between treatment and control reservoirs in 2011, presumably because the level of SAV control was not sufficient to reduce sentinel bird exposure to the putative toxin. Additional grass carp stocking and chemical control measures were implemented in the treatment reservoir (during Spring, Summer 2012). In year two of the study, disease prevalence was significantly lower (p=0.0019, Fishers exact) in the managed reservoir.  The results of these field studies demonstrate that a marked reduction in SAV biovolume is necessary to detect a reduction in disease prevalence in large systems with severe SAV infestations. This proactive management approach may be applied in other aquatic systems where AVM epizootics routinely occur in order to promote wildlife health.


THE POTENTIAL IMPACTS OF EVOLUTION ON EURASIAN WATERMILFOIL MANAGEMENT. R. A. Thum*1, L. A. Schulte2, S. Parks2, J. N. McNair2; 1Montana State University, Bozeman, MT, 2Grand Valley State University, Muskegon, MI (181)

ABSTRACT

It has become clear that not all Eurasian watermilfoil is the same. Some populations grow more aggressively than others, and some are harder to kill than others. For example, hybrid Eurasian watermilfoil (Eurasian x northern watermilfoil) tends to grow more aggressively and can be more tolerant to herbicide than pure Eurasian watermilfoil. Moreover, there is considerable genetic diversity among hybrid watermilfoils, and traits such as growth rate and 2,4-D response exhibit broad-sense heritabilities. Thus, populations of Eurasian watermilfoil may be more evolutionarily and ecologically dynamic than previously appreciated, as new lineages are generated (e.g., through introgressive hybridization) and/or replace existing lineages. In this presentation, I will review the empirical evidence for evolutionary potential and dynamics in Eurasian watermilfoil populations. I will then introduce a numerical simulation model that we are using to integrate information about life-cycle components (e.g., sexual versus asexual reproduction), evolutionary potential, and management options to gain a better understanding of population dynamics under different management strategies. 

 


LABORATORY STUDIES AND RECENT FIELD MONITORING AND ASSESSMENT OF  SONAR® (A.I., FLURIDONE) EFFICACY FOR CONTROL AND ERADICATION OF NEW INFESTATIONS OF MONOECIOUS HYDRILLA. M. A. Heilman*1, M. D. Netherland2, R. J. Richardson3, J. J. Nawrocki3; 1SePRO Corporation, Carmel, IN, 2US Army Engineer Research and Development Center, Gainesville, FL, 3NCSU, Raleigh, NC (182)

ABSTRACT

For over three decades, the monoecious biotype of hydrilla (Hydrilla verticillata) has spread from sites of early introduction in mid-Atlantic and western US states to now posing a major threat to more inland US waterways.  While many past infestations have occurred within lower-diversity reservoirs, recent infestations in New York, Indiana, Ohio, North Carolina and several other states are located in more diverse natural lake and riverine systems with direct connections and/or close geographic proximity to other important aquatic systems including the Great Lakes.   Efforts have been made in several US states over the last two decades to eradicate monoecious hydrilla from newly infested sites.  These efforts are complicated by monoecious hydrilla’s ability to produce subterranean turions, or tubers, which can remain dormant in infested sites for many years.   Eradication efforts therefore require strong management programs that prevent further spread and new tuber formation in a given season.  Recent management efforts are documenting that this effort must be repeated for 6 – 8+ years for full depletion of hydrilla tubers from infested sediments.   Various liquid and pellet formulations of Sonar® Aquatic Herbicide (a.i. fluridone) have been the primary means to achieve monoecious hydrilla eradication.  Sonar herbicide programs for eradication have typically maintained low concentrations of fluridone (<5 ppb) in infested areas for most or all of the growing season.  Each cycle of management reduces hydrilla tuber densities on average by 70-80%.   While a number of laboratory studies have been published documenting fluridone activity on hydrilla, the focus of those studies has been almost exclusively the dioecious biotype.   Due to limited published data on fluridone activity on the monoecious biotype, controlled studies were conducted under laboratory and greenhouse conditions to examine the activity of the herbicide on newly germinated monoecious tubers and more established plants.  Results show that monoecious hydrilla photosynthetic efficiency, vegetative growth, and ability to form new tubers were strongly impacted by fluridone concentrations as low as 1.5 ppb.  Slightly more established plants (3 weeks of growth following tuber germination) were also very sensitive to the herbicide, but the additional biomass put on by the hydrilla prior to treatment did respond less quickly in terms of biomass reduction over a 70-day period.   Three-day pulsed exposures (3 days of exposure followed by 3, 6, or 12 days without exposure) to 6 or 12 ppb produced the same photosynthetic stress to newly-germinated tubers  as static exposures.   These findings will be compared to monitoring results from recent operational Sonar treatments in the eastern US and implications for future management and eradication efforts will be discussed.


EFFECTIVENESS OF LONG-TERM MONOECIOUS HYDRILLA MANAGEMENT PROGRAMS IN NORTH CAROLINA. R. J. Richardson*, J. J. Nawrocki; NCSU, Raleigh, NC (183)

ABSTRACT

Hydrilla [Hydrilla verticillata (L.f.) Royle] is the most economically damaging aquatic weed in the United States. Long term hydrilla control is complicated by persistent subterranean turions (tubers) that the plant forms annually. Elimination of the tuber bank is essential for long term control or eradication efforts. Research was conducted on four North Carolina lakes to evaluate monoecious hydrilla tuber dynamics and to determine the effects of specific management techniques on monoecious hydrilla tuber numbers over time. Lake Gaston, Lake Tillery, Shearon Harris Lake, and the Tar River Reservoir were sampled for up to 7 years.  Management practices and their effects on tuber density were assessed on each lake.  Chemical control sites using fluridone were assessed on Lakes Tillery and Gaston whereas a combination of fluridone use, biological control through sterile grass carp, and physical control through drought induced summer drawdown was assessed on the Tar River Reservoir. Sites on Lake Gaston and Shearon Harris Reservoir with no active management were used as a control. De-watering and fluridone application in 2007 thru 2012 as well as a low density of grass carp stocking in 2013 resulted in an overall decrease in tuber density of 100% in the Tar River Reservoir.  Two tubers found on the Tar River Reservoir in fall 2012 were assumed to be 6 years or older and were still viable.   Lake Gaston sites subjected to fluridone treatment every other year demonstrated a tuber bank reduction of 26% after 2 years and 60% after 4 years.  Sites on Lake Gaston that were treated consecutively for 2 years exhibited a 75% reduction in tuber density.  On the unmanaged Shearon Harris Reservoir, average whole lake densities ranged from 838 to 2,050 tubers per m2 from 2008 to 2013.  At a single sample site a density of 3,244 tubers per m2 was recorded in the fall of 2008, which is higher than previously reported in situ.

 


SPECTRUM AND EFFICACY OF STINGRAYR FOR AQUATIC AND RIPARIAN USE PATTERNS. A. Z. Skibo*1, B. Willis2; 1SePRO Corporation, Fort Collins, CO, 2SePRO Research & Technology Campus, Whitakers, NC (184)

ABSTRACT

Stingray™(EPA Reg. No. 279-3279), active ingredient Carfentrazone-ethyl (HRAC E; WSSA 14), a triazolinone-type protoporphyrinogen oxidase inhibitor, was first registered for use in production agriculture by FMC in 1997 with efficacy on a wide range of common broadleaf weeds in rice, sorghum, small grains and as a harvest aid for desiccation of some Solanaceous crops.  Stingray™ was subsequently USEPA approved for use in aquatic and riparian environments circa 2004 for control of Pistia stratiotes, Eichornia crassipes, Salvinia spp., Lemna spp., Azolla spp., Ipomea aquatica, Wolffia spp., and for suppression of Alternitheria philoxeroides and Ludwigia octovalvis

Greenhouse mesocosm trials on Variable-leaf Watermilfoil (Myriophyllum heterophyllum) and Giant Salvinia (Salvinia molesta), which indicated that treatments of Carfentrazone (.002 and .004 Kg ai/Ha, respectively) plus glyphosate (0.75, 1.52 and 4.54 Kg ai/Ha, respectively) was statistically equivalent to applications of flumioxazin plus glyphosate and provided control similar to operational applications of diquat plus glyphosate commonly used by the Lousiana Department of Wildlife and Fisheries (LDWF).  Creeping water primrose (Ludwigia peploides) was controlled with combinations of Stingray (0.006 Kg ai/Ha)) plus Renovate 3 (ai: triclopyr, 1.68 Kg ae ai/Ha) and combinations of Stingray (0.006Kg/Ha) plus Clearcast (ai: imazamox, 0.28Kg ai/Ha).  Field demonstrations in the 2014 showed a high degree of efficacy on Butomus umbellatus at rates far below maximum labelled rate (0.225 Kg/Ha) and on Water hyacinth (Eichornia crassipes) when applied in combination with Clearcast (0.03 + 1.52 Kg ai/Ha) while exhibiting excellent safety on Nuphar spp. and Southern cutgrass (Leersia hexandra).

The developing aquatic efficacies of Stingray™, when combined with known species spectrum from terrestrial use patterns, increases apparent activity on submersed aquatic vegetation (SAV) when combined with systemic active ingredients such as imazamox and triclopyr, adds rapidity of burn-down to riparian weed control programs utilizing systemic herbicides commonly used in the aquatic and riparian niche market, such as imazapyr, imazamox, fluridone, glyphosate, penoxsulam, triclopyr etc.; the implications of which will be discussed as will preliminary results of several field programs conducted in 2014.         


DEVELOPING LONG-TERM CONTROL TECHNIQUES FOR FLOWERING RUSH:  MESOCOSM TRIALS AND FIELD IMPLEMENTATION. J. D. Madsen*1, K. D. Getsinger2, G. Turnage3; 1USDA ARS, Davis, CA, 2US Army Engineer Research and Development Center, Vicksburg, MS, 3Mississippi State University, Mississippi State, MS (185)

ABSTRACT

Flowering rush (Butomus umbellatus L.) is an invasive aquatic weed that has been spreading throughout waters of the Pacific Northwest, Midwest, and Northeastern United States.  Flowering rush can grow in habitats ranging from moist soil to submersed in more than 3 m of water, and as either an emergent or submersed plant.  Previous work has documented the importance of the rhizome bud as the most important meristematic tissue for recovery from management and perennation.  We tested a new approach to reducing the density of rhizome buds using combinations of herbicides in a mesocosm study at the R.R. Foil Plant Research Center, Mississippi State University.  Six treatments [diquat (0.19 mg/L) alone, triclopyr (2 mg/L) alone, fluridone (30 µg/L) alone, diquat plus fluridone, and triclopyr plus fluridone] were tested along with an untreated reference, with each treatment replicated in four tanks.  We used 389 L tanks with seven 3.8L pots planted with flowering rush per tank.  All tanks were drained 72 hours after treatment (HAT), and flushed twice to remove all herbicides.  All pots were harvested eight weeks after treatment (WAT), sorted to above and belowground biomass, dried at 70C, and weighed.  Rhizome buds in each pot were counted.  The triclopyr only treatment did not reduce rhizome bud density, but all treatments with fluridone or diquat significantly reducing rhizome bud density.  Aboveground biomass was reduced in all treatments with diquat or fluridone, with the diquat plus fluridone treatment having significantly less biomass than fluridone alone or with triclopyr.  All treatments with diquat or fluridone significantly reduced belowground biomass.  This study indicates other potential herbicides for management of flowering rush, and demonstrates that fluridone as well as diquat, and mixtures with fluridone, will reduce flowering rush rhizome bud density.   


HERBICIDE MIXTURE AND SEQUENTIAL APPLICATION FOR MANAGING RESISTANT PHALARIS MINOR. S. Singh*; CCS Haryana Agricultural University, Hisar, India (186)

ABSTRACT

Phalaris minor (Littleseed canarygrass) has attained the notoriety of most troublesome weed of wheat, significantly affecting its productivity in north India. Over the years it has evolved multiple resistance to isoproturon (PSII), diclofop-methyl, fenoxaprop-P-ethyl, clodinafop-propargyl, pinoxaden (ACCase), sulfosulfuron and premix of mesosulfuron+iodosulfuron (ALS inhibitors) mediated by enhanced metabolism and target site mutation.  In the absence of molecules of new site of action, its management has become challenging as farmers have to spray repeatedly without satisfactory control. Studies were conducted at University Research farm and resistance affected farmers’ fields in Haryana State (India) during the winter seasons of 2011-12 and 2012-13 using various combinations and sequences of herbicide applications for the control of resistant populations.  The results revealed that pendimethalin 1.5 kg/ha  PRE followed by pinoxaden 50 g/ha or sulfosulfuron 25 g/ha POE provided good control of P. minor, though both POE herbicides required a mixture of broadleaf herbicides for the complex weed flora. In the absence of PRE herbicides; sequential application of sulfosulfuron 20-25 DAS (before first irrigation) followed by pinoxaden 40-45 DAS was quite effective; however, clodinafop followed by pinoxaden failed to control resistant populations. Other PRE combinations with effective control of P. minor were pendimethalin + pyroxasulfone or metribuzin; though higher amount of metribuzin caused crop injury particularly under higher moisture conditions. Flufenacet tank mixed with pendimethalin was better than metribuzin (PRE) or their EPOE application.  Clodinafop, pinoxaden, mesosulfuron + iodosulfuron and sulfosulfuron tank mixed with metribuzin (POE) significantly improved P. minor control than their alone applications; but higher propensity of P. minor for enhanced metabolism of PSII inhibitors may not be very effective against the use of metribuzin in the long run. Also some wheat varieties are more sensitive to metribuzin applied POE. Regeneration of herbicide treated plants and emergence of P. minor in three flushes has further complicated the management strategy as Indian farmers are habitual of applying herbicides only once in wheat crop and two or three applications in the sequence or mixture may not be easy for the majority of small and marginal farmers due to higher cost and technical knowhow. 

 

 


INTEGRATED MANAGEMENT OF GLYPHOSATE-RESISTANT GIANT RAGWEED WITH TILLAGE AND HERBICIDES IN CORN. Z. A. Ganie*1, L. Sandell2, J. Lindquist1, G. R. Kruger3, M. Jugulam4, D. B. Marx5, A. J. Jhala6; 1University of Nebraska-Lincoln, Lincoln, NE, 2Valent Corporation, Lincoln, NE, 3University of Nebraska-Lincoln, North Platte, NE, 4Kansas State University, Manhattan, KS, 5University of Nebraska-Lincoln, USA, Lincoln, NE, 6University of Florida, Lake Alfred, FL (187)

ABSTRACT

Glyphosate-resistant giant ragweed (Ambrosia trifida) is a very competitive and difficult to control weed in several agronomic crops including corn throughout the United States. Giant ragweed has vast genetic diversity, early and extended germination period, rapid growth rate, and greater potential for evolution of herbicide-resistance. Rapid evolution of resistance to acetolactate synthase (ALS) inhibitors has been documented in giant ragweed. More recently, resistance to glyphosate has also been shown. Therefore, management of this weed is challenging with control strategies entirely based on PRE or POST herbicides. This research was initiated based on hypothesis that integration of preplant tillage with PRE and/or POST herbicides will provide early and season-long control of glyphosate-resistant giant ragweed. The objective of this study was to evaluate preplant tillage followed by (fb) PRE and/or POST herbicide-mixtures with different modes of action. Two field experiments were conducted in 2013 and 2014 at Clay Center (40.52° N, 98.05° W) and David City (41.25° N, 97.12° W), NE, respectively. Both the sites were selected based on the presence of confirmed glyphosate-resistant giant ragweed biotypes. Results indicated that preplant tillage results in ≥80% control of glyphosate-resistant giant ragweed 10 d after tillage. However, a comparable control (mostly >90%) of glyphosate-resistant giant ragweed was observed following herbicide treatments, irrespective of preplant management. Throughout the growing season, giant ragweed density was lower following integrated management (preplant tillage fb PRE and/or POST herbicides) compared to the control program based on herbicides alone. However, giant ragweed biomass (90 DAT) was the same under both weed control strategies. Overall, results showed that the integration of preplant tillage with PRE and/or POST herbicides reduced early season giant ragweed pressure by up to 20%, and was very effective in season-long management of glyphosate-resistant giant-ragweed with minimum dependence on herbicide.


MANAGEMENT OF DIFFICULT-TO-CONTROL WEEDS IN WHEAT (TRITICUM AESTIVUM L.) IN NORTHERN INDIA. M. S. Bhullar*, T. Kaur, S. Kaur; Punjab Agricultural University, Ludhiana, India (188)

ABSTRACT


INTRA-SPECIFIC VARIATION FOR POSTEMERGENCE HERBICIDE TOLERANCE IN PEANUT. R. G. Leon*1, B. L. Tillman2; 1University of Florida, Jay, FL, 2University of Florida, Marianna, FL (189)

ABSTRACT

Intra-Specific Variation for Postemergence Herbicide Tolerance in Peanut. R.G. Leon*1 and B.L. Tillman2. 1University of Florida, Jay, FL, 2University of Florida, Marianna, FL.

 

Although herbicide tolerance is critical for grower adoption of new peanut cultivars, little is known about the variability of this trait in peanut germplasm. Thirty-five randomly selected breeding lines from the Peanut Mini-Core Collection plus commercial cultivars 'Florida-07' and 'Georgia-06G' were evaluated for tolerance to 11 herbicides under greenhouse conditions. Variation among peanut lines in herbicide tolerance measured as dry weight reductions (DWR) compared to nontreated plants, was similar across herbicides and tended to show a normal distribution. The commercial cultivars frequently ranked in the top 25% most tolerant among the evaluated peanut lines. Dose-response experiments showed that differences among breeding lines for the rate required to reduce dry weight 50% (GR50) commonly ranged from 0.4 to 2-fold, but in a few cases reached up to 13-fold depending on the herbicide. The most tolerant lines were consistently tolerant to herbicides with different mechanisms of action suggesting that non-target site mechanisms are more likely to be responsible for the tolerance than target site mutations. These results confirmed peanut-breeding programs would greatly benefit from screening breeding lines for tolerance to key herbicides and develop an herbicide tolerance inventory. In this way breeders could design strategies to develop new cultivars with adequate or enhanced herbicide tolerance levels. 

 


THE WEED SEED BANK IS MORE DIVERSE AND DYNAMIC IN A SOD-BASED THAN A CONVENTIONAL PEANUT-COTTON ROTATION. R. G. Leon*1, D. L. Wright2, J. J. Marois2; 1University of Florida, Jay, FL, 2University of Florida, Quincy, FL (190)

ABSTRACT

The Weed Seed Bank is More Diverse and Dynamic in a Sod-Based than a Conventional Peanut-Cotton Rotation. R.G. Leon*1, D.L. Wright2, and J.J. Marois2. 1University of Florida, Jay, FL, 2University of Florida, Quincy, FL.

 

Many row crop rotations are limited to two crops although it has been proposed that adding a third crop, especially perennial grass crop, would increase crop rotation benefits. Growers might be reluctant to adopt a more diverse rotation if this causes changes in weed populations that make crop management more difficult. We compared the weed seed banks of a sod-based rotation (bahiagrass-bahiagrass-peanut-cotton) and a conventional peanut-cotton rotation (peanut-cotton-cotton) and evaluated the importance of crop phase in weed seed bank dynamics in a long-term experiment initiated in 1999 in Florida. Extractable (ESB) and germinable (GSB) seed banks were evaluated at the end of each crop phase in 2012 and 2013, and total weed seed or seedling number, diversity, richness, and evenness were determined. Weed diversity, richness, and total weed density were higher in the sod-based compared to conventional rotation in both ESB and GSB tests. Crop phase was a determinant factor in the differences between crop rotations. Most of the differences between rotations in weed seed bank structure were due to the first year of bahiagrass (B1). The high values for the different parameters observed in B1 in the sod-based rotation were transient, and in the second year of bahiagrass (B2) weed numbers and diversity decreased and reached levels equivalent to those in the conventional peanut-cotton rotation. The B1 phase increased the germinable fraction of the seed bank, but not the total number of weed seeds as determined by ESB. The increases in diversity and richness in bahiagrass phases were mainly due to grass weed species. The results of the present study demonstrated that including bahiagrass as a third crop in a peanut-cotton rotation could increase weed communities, mainly by favoring richness and diversity, but the structure and characteristics of the rotation would prevent continuous increases in the weed seed bank preventing any additional complications in weed management in the peanut and cotton phases.

 


EARLY SEASON WEED CONTROL- GETTING TO THE ROOT OF THE PROBLEM. J. Gal, M. Afifi, E. Lee, L. Lukens, C. J. Swanton*; University of Guelph, Guelph, ON (191)

ABSTRACT

Plant competition studies rarely determine how plant to plant interactions can affect roots.   In this study, we explored how the presence of neighbouring weed seedlings could alter soybean root structure and physiology.  We hypothesized that in the presence of above ground weed seedlings, soybean root biomass and nodulation would be reduced and that the reduction in nodulation would be caused by a loss in total flavonoid root content.  University of Guelph soybean variety, OAC Wallace was selected to be used in this experiment as it was known to exhibit the classic shade avoidance response in the presence of weeds.  Ryegrass was used as the model weed species. The potting arrangement isolated the roots of soybean seedlings from those of the perennial ryegrass, thereby, eliminating the effects of direct root competition for water, nutrients or allelopathy. The results from this study supported our hypothesis.  In the presence of above ground weeds, soybean root biomass and nodulation were reduced, an accumulation of hydrogen peroxide and an increase in lipid peroxidation were also observed.  In addition, total flavonoid content was reduced.  These physiological changes occurred in soybean seedlings grown under conditions of non-limiting resources in response primarily to the detection of the R:FR signal reflected from above ground neighbouring weeds.  The response to and the recovery from the presence of above ground weed seedlings may contribute to our understanding of how a soybean plant loses yield.

 


A DECISION SUPPORT SYSTEM FOR EGYPTIAN BROOMRAPE (PHELIPANCHE AEGYPTIACA) CONTROL IN PROCESSING TOMATO IN ISRAEL. H. Eizenberg*1, G. Achdari2, Y. Kleifeld3, E. Avivi4; 1Newe Yaar Research Center, ARO, Israel, Ramat Yishay, Israel, 2Department of Weed Research and Phytopathology, Ramat Yishay, Israel, 3Netafim Ltd R&D, Tel Aviv, Israel, 4Ein Harod farm R&D, Kibutz Ein Harod, Israel (192)

ABSTRACT

A
Decision Support System for Egyptian Broomrape (Phelipanche
aegyptiaca
) Control in Processing Tomato in Israel

The broomrapes (Orobanche and Phelipanche spp.) are obligate root parasites causing severe damage to processing tomato in Israel. Most of their life cycle takes place in the soil subsurface, including seed germination, attachment to the host root, penetration and establishment in the host tissues, and tubercle production. Toward the end of their life cycle they emerge from the soil and produce inflorescence bearing hundreds of thousands of seeds. In the underground stages of their life cycle, the root parasitic weeds are more sensitive to herbicides than in the above ground developmental stages. Thus, data on their infestation level or phenological stage are essential for effective control. In this presentation a decision support system (DSS) 'PICKIT' for rational management of the parasite will be discussed. The DSS includes: a) a model for quantification of the temporal variation and prediction of broomrape parasitism by thermal time; (b) a model for estimation of the spatial variation of broomrape infestation using geographical information systems (GIS); herbicide applications via sprayer or via low flow drip herbigation. The DSS was developed during the last 8 years and was validated in 2013 and 2014. An example of assimilating the DSS 'PICKIT' for rational chemical control of P. aegyptiaca in processing tomato will be presented. In the example the DSS was examined at 9 commercial tomato fields (field size ranged between 2-8 ha) under varied infestation levels. It was found that using the DSS 'PICKIT' in heavy broomrape infested fields completely controlled the parasite and increase tomato yield by 40 tons per hectare.


GROWTH, REPRODUCTION, AND WEED RISK ASSESSMENT SCORING OF ENERGYCANE (SACCHARUM SPP. × SACCHARUM SPONTANEUM) CLONES VARY WHEN GROWN IN TROPICAL VS. SUBTROPICAL CONDITIONS. R. G. Leon*1, R. A. Gilbert2, J. C. Comstock3; 1University of Florida, Jay, FL, 2University of Florida, Gainesville, FL, 3USDA-ARS, Canal Point, FL (193)

ABSTRACT

Growth, Reproduction, and Weed Risk Assessment Scoring of Energycane (Saccharum spp. × Saccharum spontaneum) Clones Vary When Grown in Tropical vs. Subtropical Conditions. R.G. Leon*1, R.A. Gilbert2, and J.C. Comstock3; 1University of Florida, Jay, FL, 2University of Florida, Gainesville, FL, 3USDA-ARS Sugarcane Field Station, Canal Point, FL.

 

The importance of renewable energy has increased significantly during the last decade. Biofuel crops have been proposed as an important component of renewable energy supply. Many efforts have been devoted to study biofuel crops in subtropical and temperate regions, but there is little information available for the humid tropics. We studied the growth and productivity of 14 energycane clones, elephantgrass and two sugarcane varieties in the humid tropics in Costa Rica and eight energycane clones in the subtropics of Florida. In the tropics, energycane showed high variation in biomass production and growth parameters across the different clones. However, the best performing clones produced almost twice the dry biomass  (>64 Mg ha-1) compared with sugarcane varieties reaching dry biomass production levels that are significantly greater than previous reports for energycane and other feedstocks. Elephantgrass exhibited the highest dry biomass in the plant crop (75 Mg ha-1), but in the first ratoon dry biomass was one of the lowest (40 Mg ha-1).  In the subtropics, energycane fresh (52 to 79 Mg ha-1) and dry (20 to 30 Mg ha-1) weights were less than half of those in the tropics. Although energycane clones flowered in both environments, pollen viability was significantly higher (>40%) in the tropics than in the subtropics (0 to 18%), and viable seeds were found only in the tropics. Weed risk assessment (WRA) scores were higher in the tropics than in the subtropics and varied among clones. In the subtropics WRA scores were negative for all evaluated clones. Conversely, in the tropics several clones had WRA scores (>6) that suggested a higher risk of weedy behavior. The results confirmed that energycane is a promising feedstock for biomass production and could play an important role as a bioenergy crop when grown in the tropics and subtropics, but due to genotype × environment interactions, the tradeoff between biomass production and weedy/invasive risk must be assessed for each individual clone and environment. 

 

 


INTELLIGENT CULTIVATORS- NEW TOOL FOR IMPROVED IWM IN VEGETABLE CROPS. R. N. Lati*1, S. A. Fennimore2; 1UC Davis, Salinas, CA, 2University of California Davis, Salinas, CA (194)

ABSTRACT

Mechanical weed control has been used for decades but with limited ability to remove intra-row weeds. The standard cultivators remove only inter-row weeds, and traditional intra-row tools (e.g., finger weeder) can only be used for short periods of time when the crop is small. A potential solution to this problem is the use of advanced intelligent cultivators (ICs). ICs are robotic image-based machines that automatically remove weeds from within the crop rows. ICs are promising new tools for integrated weed control especially for crops like vegetables that have few herbicides and are dependent on hand weeding. Integrating ICs into on-going practices is crop and region specific, and requires better understanding of their capabilities and limitations. Nonetheless, this data is not yet available; ICs are just coming into use and the scientific data about their performances is lacking. The Robovator mechanical intra-row weed control system (K.U.L.T. Kress Umweltschonende, Germany) is a new IC that is already commercialized. The objective of this study was to evaluate the potential for integration of the Robovator into the local vegetable weed management system. The Robovator was evaluated in transplanted lettuce and broccoli with and without herbicides. The Robovator was found to be effective and safe for these crops. There was no crop damage or yield reduction compared to the standard cultivator. Weed control was improved by 42% and hand weeding time was reduced by 40% compared to the standard cultivation. Furthermore, utilizing the IC without herbicide provided similar weed control compared to the standard cultivation with herbicide. These results indicate the potential of IC to improve the level of weed control provided by cultivation which is relevant for both conventional and organic systems. However, more research is needed to optimize the application of this new tactic in various crops and regions. 

 


WEED MANAGEMENT IN STRIP-TILLED SWEET CORN AND CABBAGE. E. Haramoto*1, D. Brainard2; 1University of Kentucky, Lexington, KY, 2Michigan State University, East Lansing, MI (195)

ABSTRACT

Systems-level field experiments were conducted to determine how deep nitrogen (N) banding combined with strip tillage (ST) affected soil nitrogen and final weed biomass in a sweet corn / cabbage rotation.  Treatments included ST with strips located in the same position from year to year (ST same), ST with strip location offset from year to year (ST offset), and full-width tillage (FWT).  In both ST treatments, all N was applied in the crop row (IR); initial N applications were broadcast in FWT so between 50-75% of N was applied to the IR zone.  Two weed management intensities were also examined—just herbicides (low intensity) and herbicides plus a hand-weeding pass (high intensity). 

Between the crop rows (BR), the season-long average of soil inorganic N (nitrate plus ammonium) was greater in FWT than in both ST treatments in both crops and years; relative strip placement did not influence BR soil N.  In cabbage, final BR weed biomass was also lower in ST than in FWT in both years.  Final weed biomass in sweet corn was not affected by tillage in 2012 and was higher in ST offset than both FWT and ST same with low intensity weed management in 2013.  ST same also had higher BR weed biomass than ST offset and FWT following high intensity management in 2013.  BR soil N was positively correlated with final weed biomass in only one crop*year combination—2012 in cabbage. 

In both crops and years, season-long average IR soil N was greater in ST than in FWT.  Relative strip placement did not influence IR soil N.  Tillage either had no effect (both crops in 2012) or ST offset had higher weed biomass than FWT and ST same (both crops in 2013).  However, weed biomass in this zone was very low—typically less than 50 g m-2—so these treatment effects are not likely sufficient to impact crop yields. 

These results suggest that ST with deep N banding can differentially impact BR weeds depending on the crop.  For cabbage, a less competitive crop in which canopy closure does not occur when grown on 76 cm row spacing, ST with deep N banding may contribute to weed management in the BR zone.  However, soil N was only correlated with final weed biomass in one year, suggesting that other factors remain important.  Relative strip placement influenced BR weeds in sweet corn and IR weeds in both crops in 2013 but did not influence average soil N content—further support that tillage effects on weed biomass likely result from complex interactions between multiple factors.

 


BLASTING THE COMPETITION AWAY: ABRASIVE WEED MANAGEMENT IN ORGANIC VEGETABLE CROPPING SYSTEMS. S. E. Wortman*; University of Illinois at Urbana - Champaign, Urbana, IL (196)

ABSTRACT

Weeds are a top management concern among organic farmers, but current management tactics do not consistently provide season-long weed suppression and many have deleterious environmental impacts. Abrasive-weeding is a novel organic weed management tactic that uses air-propelled abrasive grits to destroy weed seedlings within crop rows. Organic fertilizers may have potential as abrasive grits allowing farmers to manage weeds and soil fertility in one field pass. The potential for abrasive-weeding in vegetable crops has been demonstrated in a greenhouse trial, but the objective of this study was to quantify the effect of abrasive grit type and application frequency on weed suppression and yield in tomato (Solanum lycopersicum L.) and bell pepper (Capsicum annuum L.) field production systems. Field studies were conducted in 2013 (tomato) and 2014 (bell pepper) in Urbana, IL. Abrasive grits were applied 1, 2, 3, or 4 times after transplanting and included corn cob grit, walnut shell grit, soybean meal, and greensand fertilizer (2013 only). Two applications of grit reduced weed density by 62 and 80% in tomato and bell pepper, respectively. Regardless of grit type or number of applications, abrasive-weeding reduced end-of-season weed biomass by 66% in tomato and 97% in bell pepper relative to the weedy control. Similarly, abrasive-weeding increased tomato yield by 44% and bell pepper yield by 30% relative to the weedy control. Application of grits can cause minor stem and leaf tissue damage to the crop, but total yield and marketability of tomatoes and bell peppers were not reduced by abrasive-weeding. Abrasive-weeding has significant potential to increase farmer profitability, but further research is needed to identify optimum grits, application rates and timing intervals, and to quantify the effect of organic fertilizer grits on crop – weed competition. 

 


INFLUENCE OF COVER CROP TERMINATION TIMING AND HIGH-RESIDUE CULTIVATION ON WEED COMMUNITIES IN A REDUCED-TILL ORGANIC GRAIN SYSTEM. J. M. Wallace*1, M. Ryan2, C. L. Keene3, S. Mirsky4, M. J. VanGessel5, W. S. Curran3; 1Pennsylvania State University, State College, PA, 2Cornell University, Ithaca, NY, 3Penn State University, University Park, PA, 4USDA, Beltsville, MD, 5University of Delaware, Georgetown, DE (197)

ABSTRACT

Shifting weed community composition towards less-detrimental species is an important goal of ecologically based weed management.  Previous studies have demonstrated that crop rotation and tillage practices are important management filters that alter weed community composition. Fewer studies have examined how multiple within-season control strategies influence weed community composition. The Reduced-tillage Organic Systems Experiment (ROSE) was recently completed at three Mid-Atlantic locations (Pennsylvania, Maryland, and Delaware). The experiment investigated a cover crop-based, organic rotational no-till system for annual grain production in the Mid-Atlantic.  This system involves growing large amounts of cover crop biomass, mechanically terminating cover crops with a roller-crimper and no-till planting cash crops into the resulting mulch. The ROSE investigated multi-tactic weed control practices within a corn-soybean-wheat rotation that used a hairy vetch-triticale cover crop before corn and cereal rye before soybean. Two weed control strategies, delayed cover crop termination and high-residue, inter-row cultivation, were examined using a factorial treatment structure.  Three cover crop termination treatments (early, middle, late) were applied based on cover crop phenology, occurring at approximately 7-10 day intervals.  Delayed cover crop termination produces several agronomic tradeoffs, but from a weed management perspective, it was hypothesized that delayed termination would increase weed suppression due to higher-levels of cover crop mulch and by avoiding periods of peak weed seedling emergence. Cultivation at 4 and 6 weeks after cash crop planting was compared to no cultivation. The effectiveness of high-residue cultivation is a function of weed emergence periodicity and the growth stage of weed species at cultivation. Unlike conventional inter-row cultivation, smaller weeds are more likely to re-root and survive following cultivation with the high residue machine. To determine if these control strategies produced shifts in weed community structure and composition, we used permutation-based multivariate analysis of variance (Bray-Curtis dissimilarities) and indicator species analysis to test for cover crop termination timing and high-residue cultivation effects on plant community composition. Analyses were limited to the soybean crop phase in 2012 and 2013 at the Pennsylvania and Maryland study sites. Weed species that occurred in more than 2% of the plots were included in analyses – 30 species in Pennsylvania and 38 species in Maryland. Weed species richness ranged from 1 to 15 species per 0.5 m2 across treatments at the Pennsylvania site and from 1 to 19 species at the Maryland site. Multivariate analysis indicated that high-residue cultivation and cover crop termination timing had a significant effect on weed community composition at both sites but the interaction among treatments was not significant. At the Pennsylvania site, indicator species analysis showed that only cereal rye, which was a volunteer weed due to inconsistent termination, was associated with high-residue cultivation. Five weed species were associated with the absence of high-residue cultivation including two perennial species (yellow nutsedge and dandelion).  Similarly, three species were associated with the absence of high-residue cultivation at the Maryland site including one perennial species (curly dock), suggesting that within season cultivation improves perennial weed control.  At the Pennsylvania site, no particular species were associated with the early and middle termination timing, and only volunteer cereal rye was associated with the late timing. At the Maryland site, common ragweed was associated with the early termination timing, barnyardgrass and henbit were associated with the middle timing and Pennsylvania smartweed and crabgrass species were associated with the late timing. These results suggest that even less-intensive management filters such as delayed cover crop termination or high-reside cultivation can lead to a shift in weed community composition. Multi-tactic, within-season management strategies will be necessary to diversify mortality pressure on weed communities in cover crop-based, organic rotational no-till systems. Manipulation of cover crop termination timing as a weed management strategy can be improved with a more thorough understanding of the influence of high biomass cover crop mulches on weed germination.


MAJOR INVASIVE PLANT SPECIES ON GUAM AND BIOLOGICAL CONTROL. G. Wiecko1, G. Reddy*2; 1University of Guam, Mangilao, GU, 2Montana State University, Conrad, MT (198)

ABSTRACT

For the first time, the top 20 invasive weeds in Guam have been identified. Additionally, the management practices for these weeds were also developed and established. Some of the major weeds identified were Bidens alba, Panicum maximum, Stachytarpheta jamaicensis, Antigonon leptopus, Paspalum paniculatum, Miscanthus floridulus, Euphorbia heterophylla, Chromolaena odorata, Mikania micrantha, Synedrella nodiflora, Chamaesyce hirta, Mimosa pudica, Leucaena leucocephala, Pennisetum polystachion, Euphorbia cyathophora, Sida rhombifolia, Momordica charantia, Chrysopogon aciculatus, Chamaesyce hypericifolia, and Chloris barbata.  The biological control programs was carried out for C. odorata, M. micrantha, Coccinia grandis, Heteropsylla spinulosa, Mimosa diplotricha. The post-release monitoring work conducted to assess the impact of the established natural enemies of the weeds at various locations on Guam. The rate of establishment of these natural enemies and other results will be discussed.


PUTTING WEED SEED PREDATORS TO THE TEST: WEED GERMINATION REDUCTIONS ATTRIBUTABLE TO VERTEBRATE AND INVERTEBRATE GRANIVORES IN FALLOW SYSTEMS. C. K. Blubaugh*, I. Kaplan; Purdue University, West Lafayette, IN (199)

ABSTRACT

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I need to withdraw my talk.  Sorry I won't be able to join you in Lexingon!


PROVISIA™ RICE SYSTEM; WEED MANAGEMENT STRATEGIES FOR RICE. C. Youmans*1, J. Guice2, S. Bowe3, G. Armel3, L. Mankin3, D. Carlson3, J. Harden3; 1BASF Corporation, Dyersburg, TN, 2BASF Corporation, Winnsboro, LA, 3BASF Corporation, Research Triangle Park, NC (200)

ABSTRACT

The Provisia™ Rice System, a new non-GM herbicide tolerant system under development by BASF which complements the Clearfield® Rice System, will provide growers with another effective tool for weed control and resistance management. 
This system will be a combination of Provisia™ rice treated with Provisia™ Herbicide.  In field trials, Provisia rice has exhibited excellent tolerance to single and sequential herbicide applications of Provisia Herbicide.  Provisia Herbicide will be a postemergence graminicide which controls Non-Provisia rice, including “weedy rice” [red rice, volunteer conventional rice types (Oryza sativa L.), hybrid rice types, and Clearfield rice] and other common annual and perennial grasses, including barnyardgrass
(Echinochloa crus-galli L).  Optimum control of red rice and other grass species was obtained with sequential applications.  Provisia Herbicide, when tankmixed with other rice herbicides, provided control of broadleaf and grass weed species.  Studies show that herbicides which cause necrosis to the grass leaf may reduce the efficacy of Provisia Herbicide.   An example of a Provisia Rice System resulting in season long weed control typically includes a preemergence herbicide (example: clomazone or quinclorac); followed by an early postemergence application (1-3 leaf timing) of Provisia Herbicide + a broadleaf tankmix partner herbicide; followed by a mid postemergence application (1-2 tiller; just prior to flood) of Provisia Herbicide.  Future research continues to focus on weed control systems to optimize the performance of the Provisia Rice System and mitigate the potential for the development of
herbicide resistant weeds.


INTRODUCTION TO A NEW ARYLPICOLINATE HERBICIDE FROM DOW AGROSCIENCES WITH UTILITY IN RICE AND OTHER CROPS. M. R. Weimer*, C. N. Yerkes, P. R. Schmitzer, R. K. Mann; Dow AgroSciences, Indianapolis, IN (201)

ABSTRACT



RinskorTM active (Dow AgroSciences code number XDE-848; proposed ISO name in review) is a new arylpicolinate herbicide being developed by Dow AgroSciences with global utility in seeded and transplanted rice and other crops.  Data from field trials conducted since 2010 have demonstrated that Rinskor has broad-spectrum activity on important grass, sedge, and broadleaf weed species in rice.  Common use rates are 5 to 50 g ai ha-1 depending on use pattern and target species.  Selectivity in certain crops can be enhanced with the use of herbicide safeners such as cloquintocet-mexyl, isoxadifen-ethyl, cyprosulfamide, or mefenpyr.  Key species controlled within defined use patterns include: Echinochloa crus-galli; Echinochloa colonum; Echinochloa oryzicola; Urochloa plantaginea; Urochloa platyphylla; Leptochloa chinensis; Cyperus difformis; Cyperus iria; Cyperus rotundus; Fimbristylis miliacea; Abutilon theophrasti; Aeschynomene spp.; Amaranthus spp.; Ambrosia spp.; Chenopodium album; Conyza spp.; Heteranthera spp.; Ludwigia octovalis; Monochoria vaginalis; Sagittaria trifolia; Sesbania exaltata and Xanthium strumarium.  As arylpicolinates are unique auxin chemotypes, Rinskor has demonstrated a unique spectrum of activity and the ability to control ALS, ACCase, propanil, and quinclorac-resistant grass and broadleaf species.  Favorable environmental fate, toxicology, and ecotoxicology properties are anticipated for Rinskor.  The first registrations of Rinskor are expected in 2017 or 2018.

 

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

™Rinskor is not registered with the US EPA at the time of this presentation. The information presented is intended to provide technical information only and is not an offer for sale.


DISCOVERY OF A NEW ARYLPICOLINATE HERBICIDE FROM DOW AGROSCIENCES WITH UTILITY IN RICE. C. N. Yerkes*, G. J. Deboer, C. T. Lowe, K. Myung, P. R. Schmitzer; Dow AgroSciences, Indianapolis, IN (202)

ABSTRACT

A new arylpicolinate molecule was discovered at Dow AgroSciences that will provide broadspectrum weed control in multiple rice culture systems.  The discovery of Rinskor™ active started with a retrospective search of the arylpicolinate chemistry focused on sedge weed control and utilized structure-activity relationships and biological characterization to identify the desired molecule.  Development of the most efficacious form of the molecule was guided by the control of key rice weeds coupled with rice crop selectivity.  Rinskor is a low use rate, phloem mobile herbicide with an auxinic mode of action and will be positioned for selective control of key broadleaf, grass, and sedge weeds via foliar and in-water applications.  The weeds controlled include Echinochloa species, Cyperus species, Aeschynomene sensitiva, Alternanthera philoxeroides, Ammannia coccinea, Eclipta alba, Fimbristylis miliacea, Heteranthera limosa, Lindernia dubia, Monochoria vaginalis, Sagittaria trifolia, Schoenoplectus juncoides, Sesbania exaltata, Sphenoclea zeylanica, and Urochloa platyphylla.  Some weed biotypes resistant to existing herbicides are also controlled by Rinskor.  Rinskor is rapidly degraded in the soil which will result in favorable crop rotation flexibility.  Rice tolerance to Rinskor is due to reduced translocation coupled with metabolism of the molecule to non-herbicidal metabolites.

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

™Rinskor is not registered with the US EPA at the time of this presentation. The information presented is intended to provide technical information only and is not an offer for sale.


FIELD AND LABORATORY CHARACTERIZATION OF THE SOIL PERSISTANCE AND ACTIVITY OF A NEW ARYLPICOLINATE HERBICIDE. M. Miller*, J. K. Norsworthy; University of Arkansas, Fayetteville, AR (203)

ABSTRACT

Historically, herbicides have been the primary method used to control barnyardgrass  (Echinochloa crus-galli) in rice. As a result, this troublesome weed has evolved resistance to at least 9 sites of action globally and at least 7 sites of action in the United States. RinskorTM active is a new rice herbicide being developed by Dow AgroSciences, which is the second herbicide in a new structural class of synthetic auxins in the arylpicolinate herbicide family. This new herbicide provides broad-spectrum postemergence control of broadleaf, grass, and sedge species at low use rates with a alternative mode of action for rice. Many U.S. rice producers commonly grow rice in rotation with soybean. Therefore, a field experiment was designed to evaluate potential plant-back restrictions to soybean following an application of Rinskor. The experimental design was a randomized complete block with a two factor factorial treatment structure comprised of two rates of Rinskor: 30 and 60 g ai ha-1 applied at four timings: 56, 28, 14, and 0 days prior to planting soybean. The concentration of Rinskor and its primary metabolites present in soil at the time of planting were determined by collecting 5 soil cores at a 15-cm depth in each plot at the time of planting and quantified in the laboratory using LC-MS/MS. Visual estimates of soybean injury were highest 21 days after planting when 30 or 60 g ha-1 of Rinskor was applied 0 days before planting, exhibiting 97 and 99% injury, respectively.  These injury assessments corresponded to the highest concentration of Rinskor and its metabolites recovered from soil at the time of planting. Soybean injury 21 days after planting was 56% when 30 g ha-1 of Rinskor was applied 14 days before planting whereas 60 g ha-1 applied 28 and 14 days before planting resulted in 65 and 85% soybean injury, respectively.  Soybean injury was <10% when 30 or 60 g ha-1 of Rinskor was applied 56 days before planting. By the end of season, soybean had not recovered due to the primary injury observed in the treatments was in the form of stand loss. Soybean yield was similar to the non-treated control when 30 or 60 g ha-1 of Rinskor was applied 56 days prior to planting whereas all other treatments had significantly lower yield.  The replant interval following an application of Rinskor will likely be determined by several factors including soil moisture, amount of compound applied, and the crop selected for replanting. The results found in this study indicated a short replant interval for soybean relative to other herbicides commonly applied in rice, and there is unlikely to be restrictions on planting of soybean the year following a Rinskor application in rice.

 

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

 


UTILITY OF A NEW ARYLPICOLINATE HERBICIDE FROM DOW AGROSCIENCES IN U.S. MID-SOUTH RICE. D. H. Perry*1, A. T. Ellis2, V. B. Langston3, R. Lassiter4, G. D. Thompson5, R. P. Viator6, L. C. Walton7, M. R. Weimer8; 1Dow AgroSciences, Greenville, MS, 2Dow AgroSciences, Arlington, TN, 3Dow AgroSciences, Woodlands, TX, 4Dow AgroSciences, Raleigh, NC, 5Dow AgroSciences, Omaha, AR, 6Dow AgroSciences, Houma, LA, 7Dow AgroSciences, Fulton, MS, 8Dow AgroSciences, Indianapolis, IN (204)

ABSTRACT

Rinskor™ active (ISO name applied for) is a new postemergence herbicide being developed by Dow AgroSciences for use in global seeded and transplanted rice markets.  Rinskor is the second member of a new arylpicolinate class of herbicides that exhibits broad-spectrum herbicidal activity on select grass, sedge, and broadleaf weed species.  Mid-South U.S. rice weeds susceptible to Rinskor include:  Echinochloa crus-galli, Echinochloa colona, Urochloa platyphylla, Leptochloa panicoides, Cyperus iria, Cyperus esculentus, Sesbania herbacea, Aeschynomene spp., Conyza spp., Amaranthus spp., Ambrosia spp., Alteranthera philoxeroides, Eclipta prostrata, Heteranthera spp. and Sagittaria spp.  The unique weed spectrum of Rinskor is complemented by its ability to control ALS-, ACCase-, propanil-, and quinclorac-resistant species. Grass and sedge weeds treated with Rinskor exhibit swelling and necrosis of the crown while broadleaf weeds treated with Rinskor exhibit an epinastic response. Rinskor exhibits excellent safety to both medium-grain and long-grain rice varieties and hybrids within conventional and Clearfield® rice systems. The first registrations of Rinskor are expected in 2017 or 2018. 

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

™Rinskor is not registered with the US EPA at the time of this presentation. The information presented is intended to provide technical information only and is not an offer for sale


OPTIMIZING THE ACTIVITY OF A NEW ARYLPICOLINATE HERBICIDE FOR USE IN RICE. M. Miller*, J. K. Norsworthy; University of Arkansas, Fayetteville, AR (205)

ABSTRACT

Barnyardgrass (Echinochloa crus-galli), broadleaf signalgrass (Urochloa platyphylla), hemp sesbania (Sesbania herbacea), and yellow nutsedge (Cyperus esculentus) continue to be some of the most troublesome weeds of rice today. As the evolution of herbicide resistance continues and herbicide modes of action that provide control are lost, the development of a new herbicide active is needed. The introduction of RinskorTM active brings a valuable tool to weed control by having a alternative mode of action for use in rice that provides broad-spectrum postemergence control of broadleaf, grass, and sedge species. Studies were conducted to evaluate the efficacy of Rinskor as influenced by formulation and adjuvant rate, spray volume, time of flooding, and tank-mix compatibility.  Two formulations of Rinskor were evaluated in a formulation and adjuvant rate experiment using an SC formulation containing no preloaded adjuvant and a NeoECTM formulation preloaded with methylated seed oil (MSO). Each formulation was applied at 15 and 30 g ai ha-1 at six rates of MSO: 0, 0.7, 1.4, 2.1, 2.8, and 3.5 L ha-1. Weeds evaluated included barnyardgrass, broadleaf signalgrass, hemp sesbania, yellow nutsedge, and Palmer amaranth (Amaranthus palmeri) planted in a non-flooded dryland setting. Results from these studies indicated that increasing rates of MSO improve overall weed control with both NeoEC and SC formulations, with the NeoEC requiring less MSO due to its presence in the preloaded formulation. A spray volume and adjuvant rate experiment were conducted with the same weed spectrum as in the formulation and adjuvant rate experiment. Factors included 15 and 30 g ha-1 Rinskor formulated as an SC applied at three volumes: 47, 94, and 187 L ha-1 across four rates of MSO: 0, 1.2, 2.3, and 3.5 L ha-1. Results indicated that 30 g ha-1 provided better control than 15 g ha-1, regardless of spray volume or MSO rate, and control with 30 g ha-1 improved as spray volume and MSO level increased. A time to flooding experiment was conducted using soil-filled plastic tubs planted with quinclorac-resistant barnyardgrass. Treatments included three factors including flood depth: 0 and 8 cm, time of flooding after application of Rinskor: 1, 7, 14, or 28 days after application, and Rinskor rate: 0 and 30 g ha-1. Rinskor was applied to 3- to 4-leaf barnyardgrass. Rinskor at 30 g ha-1 provided control of quinclorac-resistant barnyardgrass and flooding quickly after application enhanced weed control.  A tank-mix experiment was also conducted in fields planted to rice. Rinskor was applied alone and in combination with other systemic rice herbicides to observe tank-mix compatibility. All treatments were applied at the early-postemergence timing. No antagonism was observed when Rinskor was applied in mixture with imazethapyr, penoxsulam, or quinclorac, and therefore these herbicides are suitable tank-mix partners.

 

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

 


ANALYSIS OF PUTATIVE HERBICIDE TOLERANT ACCESSIONS OF ECHINOCHLOA ORYZOIDES (ARD.) FRITSCH. IN RICE. E. K. Altop1, H. Mennan2, J. C. Streibig*3, U. Budaka1, C. Ritz4; 1Ondokuz Mays University, Agriculture Faculty, Samsun, Turkey, 2Ondokuz May�s University, Agriculture Faculty, Samsun, Turkey, 3University of Copenhagen, Taastrup, Denmark, 4University of Copenhagen, Frederiksberg, Denmark (206)

ABSTRACT

Inconsistent control of E. oryzoides has been reported repeatedly by farmers in major rice growing regions of Turkey. Greenhouse studies confirmed the existence of cross and multiple herbicide tolerant accessions to ALS inhibitors and acetyl ACCase inhibitors.  From greenhouse screening, comparison of lower confidence intervals of ED90 and twice the recommended field rates of the herbicides showed some, but not distinct separation of susceptible and tolerant accessions. 

We demonstrate a novel statistical method to separate heterogeneous data without a priori knowledge of more than one group. On the basis of the distribution of log (ED90) it was possible to identify two distinct groups of the 172 accessions tested, 78% were not controlled by ALS inhibitors at recommended field rates; and 38% were not controlled by the ACCase Inhibitors at twice the field rates. Fourteen accessions showed multiple tolerances to ALS and ACCase Inhibitors.

 

 


ALS RESISTANCE IN LOOSE SILKY BENTGRASS (APERA SPICA-VENTI) - GROWING ISSUE FOR EUROPEAN SMALL GRAIN PRODUCTION. J. Soukup*, K. Hamouzova, M. Jursik, P. Kosnarova; Czech University of Life Sciences Prague, Prague, Czech Republic (207)

ABSTRACT

Apera spica-venti (APESV) is the most important weedy grass of winter cereals in Central and NW part of Europe where they are grown as main cash crop. Centre of the APESV occurrence is located in countries such as Czech Republic, Poland, S, E and NW part of Germany. In surrounding countries such as Slovakia, Austria, Switzerland, Denmark and Scandinavia, its occurrence is lower but continuously increasing. The grass produces up to 10 thousands tiny seeds which are easily distributed by wind and do not survive in soil profile for longer time. The competiveness of this grass is very high at the time of wheat grain filling and ripening which affected both yield and quality. Control problems appear if the populations become resistant.

Many new cases of APESV resistance have been reported on www.weedscience.org since 2005, most of which are bearing the ALS resistance.  Nowadays, most frequent are the cross-resistances against the sulfonylureas and triazolopyrimidines (frequently used are chlorsulfuron, sulfosulfuron, iodosulfuron, mesosulfuron, pyroxsulam, penoxsulam and some others). Resistance factors are very high, often more than 200 in whole plant assays. In our studies, both altered target site of the als gene and enhanced metabolism were confirmed. Mutations at position 197, 574 and rarely in other (likely non-coding) regions of the als gene were found. Als gene has been sequenced and placed in the database http://www.ncbi.nlm.nih.gov under accessions JN646110.1 and HM854301.1.

Main reasons why the resistance has emerged is large area of winter cereals (w. wheat, w. barley) and use of ALS inhibiting herbicides because of their user friendliness and limited choice of other modes of action for spring control. Influence of soil tillage on emergence of resistance was not confirmed yet but many studies indicate that shallow tillage in narrow crop rotations increases APESV population densities and risk of resistance is increasing. But changing of current cropping systems is hardly feasible. Main anti-resistance measure is to prevent a reliance on ALS inhibitors and alternate them with older soil active products applied in autumn such as flufenacet, isoproturon, prosulfocarb, pendimethalin, flurtamone with different mode of action and lower probability of resistance development. Other, not chemical weed control measures are neither efficient nor economical. Resistant APESV becomes together with Alopecurus myosuroides and Bromus sterilis an important issue for cereal growers in Europe.  


PROMOTING ADOPTION OF COVER CROPS FOR WEED SUPPRESSION BY BROADENING THEIR UTILITY. C. A. Chase*, G. B. Braz, M. E. Swisher; University of Florida, Gainesville, FL (208)

ABSTRACT

A process involving focus groups, field research, and stakeholder evaluation is being used to evaluate and promote the use of cover crops for weed suppression in organic strawberry.  Off-season, leguminous cover crops (Aeschynomene americana, Crotalaria breviflora, Crotalaria juncea, and Indigofera hirsuta) were of interest because of their potential to provide multiple ecological services to the subsequent strawberry crop.  During the 2013 trials, C. juncea produced the most shoot biomass; however, I. hirsuta and A. americana were as effective as C. juncea in suppressing weeds.  Stakeholder recommendations were for further evaluations of C. juncea and I. hirsuta and, additionally, to evaluate cover crop mixtures and cover crops that produce a saleable product.  During the 2014 trials, weed suppression with a 4-way mixture of all the legume cover crops, Sesamum indicum (a “cash” cover crop), and I. hirsuta was not significantly different from that obtained with C. juncea.  Greenhouse assessment of Belonolaimus longicaudatus (the sting nematode) suppression by Crotalaria cover crops revealed differential susceptibility to this important pest of strawberries in Florida.


ENVIRONMENTAL CORRELATES WITH WEED SEED BANK COMMUNITY COMPOSITION IN ORGANIC VEGETABLE FARMS ACROSS NORTHERN NEW ENGLAND. R. G. Smith*1, E. R. Gallandt2, S. C. Bosworth3, T. M. Davis1, B. Brown2, E. Venturini2, N. Warren1, A. Hazelrigg3; 1University of New Hampshire, Durham, NH, 2University of Maine, Orono, ME, 3University of Vermont, Burlington, VT (209)

ABSTRACT

Understanding the relative importance of climatic versus edaphic factors in determining weed community composition and the distribution of species will aid in the development of weed management practices that are robust under a changing climate.  We sampled weed seed banks and measured soil physical and chemical variables from 77 organic vegetable farms across Vermont, New Hampshire, and Maine.  The seed bank composition and abundance data were combined with the soil physiochemical and weather station data and analyzed using multivariate procedures to assess the strongest abiotic correlates with patterns of weed community variation.  Nonmetric multidimensional scaling ordination revealed a strong longitudinal gradient in weed community composition at the region-level.  Relative to the soil variables, geographic-climatic variables (longitude, latitude, summed degree days, max temperature) were more strongly correlated with variability in weed community composition in this dataset. State-level analyses revealed relatively strong associations between seed bank composition and latitude, elevation, and maximum temperature in two of the three states and weaker associations with soil texture variables.  Soil chemical variables were not consistently associated with weed community composition in any of the analyses, suggesting that weed communities on organic vegetable farms in northern New England are strongly influenced by climate variables and that future changes in these variables will likely lead to range shifts in some problematic weed species.


WEED SEED SURVIVAL IN CORN AND ALFALFA SILAGE: AN EVALUATION USING EXPERIMENTAL MINI-SILOS. M. Simard*1, C. Lambert-Beaudet2; 1Agriculture and Agri-Food Canada, Saint-Jean-sur-Richelieu, QC, 2Universit Laval, Quebec, QC (210)

ABSTRACT

The management of herbicide resistant or invasive weeds that escape treatment can be particularly challenging. Producing crops that are ensiled could be a management option allowing a reduction of the seed input of these problem weeds as any harvested seed will potentially be killed during silage fermentation and rumen digestion. However, few studies have evaluated the survival of weed seeds in silage. This study aimed at evaluating the viability of seven weed species stored in experimental mini-silos of corn and alfalfa. The species tested included weeds for which glyphosate-resistant biotypes have been reported in Canada [common ragweed (Ambriosia artemisiifolia), horseweed (Conyza canadensis), kochia (Kochia scoparia)] or the USA [redroot pigweed (Amaranthus retroflexus)], an invasive weed regulated in Canada [woolly cupgrass (Eriochloa villosa)] and two species of weeds expected to present low [barnyardgrass (Echinochloa crus-galli)] or high [velvetleaf (Abutilon theophrasti)] survival in silage. Nylon mesh bags containing one hundred seeds of either weed species were inserted at random locations in mini-silos filled with compacted silage corn or alfalfa (1200 kPa pressure) and stored for one, three and six months. The experiment included five mini silos per silage type and storage time as well as untreated seeds. Storage time was by far the most influential variable on seed survival (p<0.0001). After three and six months of storage few seeds were viable (<0.1% of all seeds tested). Differences between weed species and silage type were only observable after one month of storage. After a single month, a reduction of at least 87% in viability was observed for all species in both silage types, except velvetleaf in corn (no significant reduction), barnyardgrass in alfalfa (-45%) and redroot pigweed in alfalfa (-59%). Ensiling for six months could be used to kill harvested weed seeds of herbicide resistant or invasive weeds. Further evaluations in commercial farm silos could be done to support results.


USDA BIOFUEL REVIEW PROCESS. J. Jones*; USDA-APHIS, Riverdale, MD (211)

ABSTRACT

In 2013, Environmental Protection Agency (EPA) published a Final Rule amending their regulations for biofuel producers using two invasive species for feedstock, Arundo donax (Giant cane) and Pennisetum purpureum (Napier grass). To address the risk of spread and unintended environmental impact of these two species, applicants must provide a Risk Management Plan (RMP) for all field sites in the United States growing these species. When biofuels from these are produced outside the United States with the biofuel for shipment to the United States, the applicant must also produce an RMP or justify why a RMP is not required. The RMP must demonstrate that growing the plants will not pose a significant likelihood of spread beyond the planting area, as well as a detailed response plan if spread is found; and including the shutting down of a site at the end of production. In their rule, EPA identified the United States Department of Agriculture (USDA) as having the required expertise in invasive plant species and tasked that evaluation to that Department. 

 


AMBROSIA CONFERTIFLORA - AN INVASIVE WEED IN ISRAEL. Y. Yair*, M. Sibony, B. Rubin; Hebrew University of Jerusalem, Rehovot, Israel (212)

ABSTRACT

Ambrosia confertiflora DC (weakleaf bur ragweed) is a very aggressive and competitive perennial weed that forms large stands reaching heights above 3 m with a very dense subterranean vegetative propagation system. In the past three decades, it invaded vast areas in Israel through imported feed grains, spreads along river banks, roadside and railway tracks and by soil movement. Spatial and temporal maps constructed indicate the rapid spread of A. confertiflora in Israel. In this study, we examined the development of plants grown under different temperature regimes. Results indicate that: shoot elongation is inhibited by low (10/16°C and 16/22°C, n/d) temperatures and the plants remain in the rosette form. However when grown under warmer regimes (22/28°C and 28/34°C, n/d) fast shoots elongation was observed.  A. confertiflora reproduces from seeds and rhizomes. Seed germination occurs mostly from the soil surface in moderate temperature (16/22°C and 22/28°C). The numbers of sprouts with and without main shoot cutting (mowing) is not significantly different, indicating no apex dominance. Sprout number however, is higher under cold conditions (10/16°C n/d) compared to the other regimes. Biomass production varies at different temperatures, and is higher under warm condition (22/28°C and 28/34°C). Ambrosia species are wind pollinated, producing large quantities of highly allergenic pollen. A. confertiflora flowers between August and December. We monitored the pollen quantities in the air in several locations in central Israel and found varying amounts of pollen in the air. Pollen dispersal occurs mostly in the morning. Allergy skin tests were performed in two hospitals in Israel, using pollen extracts prepared from locally collected pollen of three ragweed species: A. confertiflora, A. tenuifolia and A. artimisiifolia. Results from 162 volunteers show that 21% of patients reacted at least to one of the species and that A. confertiflora is much more allergenic (17%) than A. artemisiifolia (5%) and A. tenuifolia (5%). Our studies indicate that A. confertiflora poses a real threat to both annual and perennial crops as well as the public health.


RECENT INVASIONS OF PARTHENIUM HYSTEROPHORUS IN NATURAL AND AGROECOSYSTEMS IN NEPAL. J. D. Ranjit1, S. Pokhrel2, A. Shrestha*3; 1Nepal Agricultural Research Council, Kathmandu, Nepal, 2Winrock International - Nepal, Lalitpur, Nepal, 3California State University, Fresno, CA (213)

ABSTRACT

The presence of ragweed Parthenium, or carrot weed, (Parthenium hysterophorus) in Nepal was first identified in 1982.  However, herbarium samples indicate its presence in 1967. Since then, it has become a major invasive weed in natural- and agro-ecosystems in the subtropical, tropical, and temperate regions of Nepal.  This species belongs to the Asteraceae family and is an annual, erect, and multi-branched plant.  Each plant can produce up to 100,000 seeds that are easily dispersed by wind, water, animals, humans, vehicles, and implements.  In recent years, it has become even more noticeable on roadsides, national parks, vacant lots, field margins, and in several crop fields such as beans, tomatoes, pepper, onion, garlic, corn, and upland rice.  The International Union for Conservation of Nature lists this species as one among the top ten invasive plant species in Nepal.  It is believed that this weed entered Nepal through India, as it was first reported in India in 1814.  This species has been reported to cause allergic reaction in humans with symptoms like dermatitis, watery eyes, and constant coughing at night.  It is also considered toxic and unpalatable to livestock, and widespread invasions have seriously reduced the amount of suitable grazing land in some regions of Nepal.  Allelopathic properties of this species have also been reported.  The species is now of national significance and awareness campaigns have been launched in Nepal.  Efforts are underway to study the biology and ecology of this plant so that biological, cultural, mechanical, or chemical control methods may be developed.  A beetle (Zygogramma bicolorata) has recently been identified as a possible biocontrol agent in Nepal. Herbicides such as 2, 4-D, ametryn, atrazine, fomesafen, linuron, metobromuron, metribuzin, oxadiazon, prometryn, and simazine have been recommended for control of this weed in certain cropping systems.  However, the wide-scale invasions in non-crop areas and natural ecosystems warrant additional research where chemical control may not be a viable option in sensitive habitats of Nepal. 


PHENOTYPIC DIFFERENTIATION, PLASTICITY, AND A SURPRISING HABITAT SHIFT IN ONE OF THE WORLD'S WORST WEEDS. J. N. Barney*1, D. Atwater1, U. Sezen2, A. Paterson2; 1Virginia Tech, Blacksburg, VA, 2University of Georgia, Athens, GA (214)

ABSTRACT

Phenotypic plasticity and local adaptation are thought to promote establishment and spread of introduced species. Here we use the results of genetic analyses, a common garden experiment, and niche reconstructions to link genetic, phenotypic, and habitat variation in Johnsongrass (Sorghum halepense), which is regarded as one of the world’s worst invasive species. We examined accessions representing 70 populations collected from across the US, representing a range of home climates and habitats. In the US, Johnsongrass expansion has produced surprising population-level genetic diversity. The climate and habitat from which the population was collected were associated with two-fold changes in biomass. Phenotypic variation in Johnsongrass mirrored patterns of genetic variation, with genetically distinct subpopulations from distinct climates having characteristic phenotypes. Ecological niche models showed that the climatic niche shifted and expanded as it invaded the US, with more recently derived populations colonizing colder, wetter, and more diverse climates. In keeping with the hypothesis that population divergence is highest at range margins, niche differentiation was greater in derived subpopulations at the invasion frontier than in central, ancestral populations. Differentiation did not involve evolutionary changes in plasticity. Our results reveal that local genetic differentiation resulted in strong and consistent phenotypic differentiation as Johnsongrass colonized the United States, and supports the hypothesis that local adaptation of nascent populations at invasion margins is important in the success of invasive species.

 


NATURAL SELECTION ON MORPHOLOGICAL TRAITS OF ROADSIDE WEED POPULATIONS IN SOUTHWESTERN UNITED STATES. B. Alfaro*; University of New Mexico, Albuquerque, NM (215)

ABSTRACT

The consequences of microevolutionary processes on phenotypic and genetic variation is an important problem in weed biology. Central to this work is the identification of ecologically important traits, and teasing apart patterns of variation. Here, I present results from a pilot study, wherein I examined morphological and phenological traits in six populations of Sahara mustard (Brassica tournefortii Gouan) across southwestern United States via a common greenhouse experiment. In this study, I asked the following questions:

  1. What traits are variable in Sahara mustard?
  2. Do these traits differ between populations and families?
  3. What traits are correlated?
  4. Are these traits associated with fitness components?

I identified eight traits that are important variables for ongoing and future experiments on evolution of this species. Not surprisingly, I found that traits related to plant size and branching patterns of Sahara mustard were variable and related to number of fruits per plant. Interestingly, number of leaf serrations and days to bolting were also variable and associated with fitness components. These results provide preliminary findings that are very useful for testing and explaining local adaptation, phenotypic plasticity, and gene flow in this exotic desert weed.


A PRIMER ON UNDERSTANDING GLYPHOSATE TRANSLOCATION AND RESISTANCE. D. Sammons*1, A. Herr1, R. Eilers1, D. Wang1, E. Ostrander2; 1Monsanto, St. Louis, MO, 2Washington University, St. Louis, MO (216)

ABSTRACT

One of the major properties of glyphosate as a broad spectrum herbicide is it’s whole plant systemic movement, especially to all
growing points in the plant.  This follows a source to sink directed flow that piggy backs on the plants normal phloem
distribution of assimilants (sugars) manufactured in the mature chloroplasts of the leaves.  The efficacy of glyphosate is dependent on the spray formulation for leaf uptake, but is critically dependent on plant growth for phloem distribution.  Glyphosate’s efficiency as a herbicide depends on the dose and formula, and primarily on the growth/health status of the targeted plant.  Realizing the importance of systemic movement glyphosate resistance has been characterized as “decreased
translocation” in some plants which resulted in the resistance mode of action being labeled as a ‘translocation’ or more vaguely as a non-target site mechanism.   The herbicidal effect of glyphosate will decrease translocation or systemic movement and so it is auspicious that resistant plants have translocated less glyphosate then sensitive plants in side by side comparisons.  Of course
translocation itself is not a mechanism but rather a phenotype of an underlying biochemical or physiology mechanism.  Our
studies then have focused on separating out these physiological mechanisms to lead us to the particular enzyme resulting in the resistance trait which necessarily requires understanding how glyphosate loads cells to enable systemic movement.  We have identified cases of equal cellular uptake but decreased phloem distribution due to vacuole sequestration; cases of decreased cellular loading and decreased phloem movement; and finally cases of equal cellular loading and equal distribution
when R is significantly more resistant than S implicating a disconnect between toxicity and phloem movement.  Summarizing these results will help us consider simple ways to categorize the kinds of ‘translocation mechanisms’ there are.


NOT ALL WHO WANDER ARE LOST:  A BAC-BASED PURSUIT FOR THE FULL SEQUENCE OF THE EPSPS GLYPHOSATE RESISTANCE ELEMENT IN AMARANTHUS PALMERI. W. Molin*1, A. A. Wright2, C. Saski3; 1USDA-ARS, Stoneville, MS, 2Mississippi State University, Stoneville, MS, 3Clemson University, Clemson, SC (217)

ABSTRACT

                Acquiring and expressing glyphosate resistance in Amaranthus palmeri is a complex mechanism involving amplification of the gene encoding the target enzyme, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS).  Previous research to determine EPSPS plasticity involved southern blots and sequencing of fosmid clones containing EPSPS demonstrated that a fragment of at least 30 kb was amplified throughout the genome.  For larger-scale resolution, a bacterial artificial chromosome (BAC) library was generated to isolate and sequence the complete repeated sequence.  Screening of the library with a probe for EPSPS identified 680 BACs containing the amplicon.  These were fingerprinted and assembled for overlap.  Four consensus clones were selected and sequenced with Illumina and PacBio sequencing technologies.  Assembly of the reads generated a single 228 kb contig and annotation revealed the genomic landscape surrounding EPSPS to be highly repetitive.  A putative transposase along with a series of 2.5 kb repeats were found upstream and downstream of the EPSPS.  It is unknown if the amplified EPSPS fragment is inserting into a region of the genome that is highly repetitive or if the amplified region exceeds the 228 kb contig.  Additional real-time PCR experiments and Southern blots are needed to address this question.  The BAC library has been screened a second time using probes  flanking the existing contig and selected extension BACs will be sequenced to expand the contig upstream and downstream.  Determining the genomic landscape underpinning how this novel resistance mechanism is achieved will not only provide information on how the plant became resistant, but also provide insight into weedy species plant biology and evolution.


EXTENDING THE EPSPS AMPLICON: STEPS TOWARDS DEFINING THE DUPLICATION MECHANISM. D. A. Giacomini*1, N. Tao2, T. Ulmasov2, P. Latreille2, R. Kerstetter2, S. M. Ward1, P. Westra1, D. Sammons3; 1Colorado State University, Ft. Collins, CO, 2Monsanto, Chesterfield, MO, 3Monsanto, St. Louis, MO (218)

ABSTRACT

The duplication mechanism responsible for increased EPSPS (5-enolpyruvylshikimate-3-phosphate) gene copy number in Palmer amaranth has been eluding weed scientists since its discovery in 2010.  New sequence data sheds light on this problem, extending the duplicated element (or “amplicon”) out in either direction from the EPSPS gene and identifying novel elements surrounding the duplicated gene.   Included in this new data are: (1) Illumina and PacBio reads from 40kb fosmids containing the EPSPS gene, (2) a 20kb mate pair library to span regions that are difficult to assemble, and (3) long Illumina reads (Moleculo) across the entire Palmer amaranth genome.  Combining these datasets, we have not only extended the duplicated amplicon to a little over 110kb, but also revealed the highly repetitive sequence surrounding the EPSPS gene element.  Joining these recent discoveries with the past research that has shown rapid loss and gain of EPSPS genes over reproductive and clonal generations, it appears the best explanation for EPSPS gene duplication is unequal recombination.  Under this duplication system, the repeat elements surrounding the gene misalign during mitosis and meiosis, leading to increases and decreases in EPSPS gene number in the daughter cells.


CONFIGURATION OF EPSPS GENE COPIES ON GLYPHOSATE-RESISTANT COMMON WATERHEMP (AMARANTHUS RUDIS) CHROMOSOMES. A. Dillon, T. Danilova, D. Peterson, B. Gill, M. Jugulam*; Kansas State University, Manhattan, KS (219)

ABSTRACT

Recently, evolution of resistance to glyphosate in several common waterhemp populations was documented in Kansas.  In a previous study we found that the glyphosate resistance in common waterhemp populations (KS) is due to amplification of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene and the resistant plants possess ~2 to 20 EPSPS:ALS relative genomic copies. Sequencing of the EPSPS gene showed no known proline 106 mutations that are commonly associated with glyphosate resistance. The objectives of this research were, using a known glyphosate-susceptible (GS) and three sets of glyphosate-resistant (GR) common waterhemp plants measuring 2 to 4; 5 to 10 and >10 EPSPS:ALS relative copies: a) determine the relationship between EPSPS copies and gene expression, and b) investigate the configuration of EPSPS copies on mitotic metaphase chromosomes. Quantitative RT-PCR on cDNA was used to measure the relative expression of EPSPS gene. The genomic organization of the amplified EPSPS copies was determined using fluorescent in situ hybridization (FISH). The results of qRT-PCR on cDNA revealed a positive correlation between EPSPS copies and gene expression. FISH analysis of GR common waterhemp plants with 2 to 10 EPSPS copies displayed a brighter hybridization signal on one pair of homologuous chromosomes likely near the centromeric region compared to a faint hybridization site in susceptible plants. Interestingly, in some plants with >10 EPSPS copies, an additional chromosome with EPSPS hybridization signals all around the chromosome was found; however, the homolog of this chromosome displaying hybridization signal(s) was not found. The results of this study suggest that although belong to the same genus, Palmer amaranth and common waterhemp appear to have evolved resistance to glyphosate via different mechanisms of EPSPS amplification. Such differences in the mechanism of EPSPS gene amplification and the subsequent disparity in the configuration of EPSPS gene copies in these two Amaranthus species will likely influence the rate of evolution of glyphosate resistance, and the extent of the EPSPS gene amplification, their inheritance and stability.


STABILITY OF EPSPS GENE COPIES IN GLYPHOSATE-RESISTANT PALMER AMARANTH (AMARANTHUS PALMERII). A. Godar*, D. Koo, D. Peterson, B. Gill, M. Jugulam; Kansas State University, Manhattan, KS (220)

ABSTRACT

Amplification of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene (>100 copies in a short generational time-frame) in glyphosate-resistant (GR) Palmer amaranth is a notable example of exceptionally rapid plant genome evolution. Previous studies reported an inconclusive inheritance pattern of the EPSPS gene copies and suggested a possible role of an involvement of transposable elements for such amplification. In this study, we investigated the somatic stability of EPSPS gene copies in three GR Palmer amaranth plants from Kansas using SYBR green-based quantitative real-time PCR (qRT PCR) assay. Genomic DNA was extracted from two very young leaves (~50 mg fresh wt) of nine growing points (one sample each from three primary and secondary branches) of each of three GR plants (GR1, GR2, and GR3). The three primary branches of GR1 and GR2 were vegetatively cloned from ten-week old mother plants, eight weeks prior to tissue collection. The GR3 plant was also similar in age as GR1 and GR2 but constant vegetative growth was maintained. The EPSPS copy number was quantified using by ΔΔCt method using ALS gene as an endogenous control and DNA from two glyphosate-susceptible plants as reference. The qRT PCR assay was performed with 3 replicates and was repeated three times. Analyses of variance was performed on the EPSPS gene copy data for each plant separately. The analyses showed differences in the EPSPS gene copies among the samples in all three GR plants. The EPSPS gene copies (mean ± se) ranged from 8 ± 0.8 to 33 ± 2.29, 34 ± 1.2 to 54 ± 1.3, and 46 ± 0.8 to 79 ± 0.4, respectively for GR1, GR2, and GR3 plants. These results suggest that variation in the EPSPS gene copies in somatic cells of GR Palmer amaranth possibly occur de novo. Whether such de novo genomic alteration is transferred successfully to the next generation remains unknown; however, such mechanism may be, in part, explains complex inheritance pattern and the rapid accumulation of EPSPS gene copies in GR Palmer amaranth.

 


MAPPING OF EPSPS GENE COPIES ON PACHYTENE CHROMOSOMES OF GLYPHOSATE-RESISTANT WATERHEMP (AMARANTHUS RUDIS) ​. A. Godar*, D. Koo, D. Peterson, B. Gill, M. Jugulam; Kansas State University, Manhattan, KS (221)

ABSTRACT

Increased copies of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene as a mechanism of resistance to glyphosate has been reported in Amaranthus species including waterhemp (Amaranthus rudis). A previous analysis of fluorescent in situ hybridization (FISH) on mitotic metaphase chromosomes of glyphosate-resistant (GR) waterhemp revealed a single EPSPS gene hybridization signal in pericentromeric region, unlike a complex EPSPS gene hybridization pattern observed in GR Palmer amaranth. To map EPSPS gene copies at a higher resolution, preparations of meiotic prophase I at pachytene stage from anthers of two GR waterhemp plants (haploid EPSPS gene copy number = 6 to7) originating from two different locations in Kansas were hybridized with an approximately 1.8-kb fluorescently labeled EPSPS cDNA probe. The pachytene FISH analysis displayed distinguishable EPSPS gene signals between the homologous chromosomes in both GR waterhemp plants indicating the presence of unequal number of EPSPS gene copies on homologous chromosomes. Several EPSPS gene signals on one of the homologous chromosomes of both plants were differentiated with some degree of overlap. These results suggest that the amplified EPSPS gene copies in GR waterhemp are present in such a proximity that can possibly be resolved with the FISH on extended DNA fibers (Fiber FISH). Future studies will employ a high resolution Fiber FISH analysis coupled with nucleotide sequence information spanning the amplified region to better elucidate the molecular mechanism(s) of EPSPS gene amplification in waterhemp; which will also help us understand the rate of evolution of glyphosate resistance, and the extent of occurrence of EPSPS gene amplification in this species.

 


BIODIRECT(TM) AND MANAGING HERBICIDE RESISTANT AMARANTHS. D. Sammons*, S. Navarro, K. Croon, J. Schmuke, D. Wang, N. Rana, G. Griffith, R. Godara; Monsanto, St. Louis, MO (222)

ABSTRACT

Twelve Amaranth species are listed as resistant to herbicides on the International Survey of Herbicide  Resistant weeds (www.weedscience.org ,August 2014) comprising 41% (172) of all reported cases and these involve 9 different sites
of action.  Only 4 of these species, A. hybridus, A. palmeri, A. retroflexus, and A. turberculatus account for 146 of these cases and 22 of these involve multiple herbicide resistance.  Together with the high rate of seed production and the significant crop competition the Amaranthus sp. complex is one of the most serious weeds in row crop agriculture. The resistance of A.
palmeri
and A. tuberculatus to glyphosate has seriously complicated weed management in glyphosate tolerant crops. 
The innovation of BioDirect™ with the topical application of oligonucleotides targeting herbicide resistant genes offers promise for the management of the Amaranthus sp.  Examples of controlling glyphosate resistant A. palmeri and A. tuberculatus as well as improving herbicides targeting ALS on these species demonstrates the opportunity.  Studies on how siRNA silencing of the small
subunit of ALS results in reversing resistance to Classic® and Staple® is detailed.


UNDERSTANDING THE SOCIAL WITHIN A HOLISTIC WEED MANAGEMENT STRATEGY. R. A. Jussaume*; Michigan State University, East Lansing, MI (223)

ABSTRACT

To fully understand the issue of weed resistance to herbicides, and thus to develop a workable response, one must recognize that the evolution of weed resistance is as much a social problem as it is a biological one.  This presentation will present some key insights into how to view weed resistance as a social phenomonone, and how a holistic approach to weed management that links the social and natural sciences, is necessary.


THE ECONOMICS OF RESISTANCE MANAGEMENT. G. Frisvold*1, T. Hurley2; 1University of Arizona, Tucson, AZ, 2University of Minnesota, St. Paul, MN (224)

ABSTRACT


TOWARD A COMMUNITY-BASED APPROACH FOR WEED MANAGEMENT. D. E. Ervin*1, G. Frisvold2; 1Portland State University, Portland, OR, 2University of Arizona, Tucson, AZ (225)

ABSTRACT

Early research on managing pest resistance concluded that mobility applied only to insects, but a growing body of 
evidence indicates that it also applies to weeds. If herbicide resistance traits are mobile across farms, the susceptibility 
of those weeds to herbicides is a resource shared by all operators in the farm community.  In such circumstances, it is in the 
collective, long-term interest of farmers to delay resistance and to conserve the usefulness of a herbicide as a weed 
management tool. Yet, steps taken by individual farmers in the short-run to conserve the usefulness of a herbicide (such as 
using alternative weed control tactics) can be costly. Thus, delaying resistance becomes a “common pool” problem – 
each farmer has an individual incentive to use the herbicide in the short run without considering effects on resistance. 
As such, individual farmers may not manage resistance because they are not assured their neighbors will match their actions. 
There have been three stereotypical approaches to managing common pool resources. A first approach is to impose 
government regulation requiring all growers to comply with specified weed management practices enforced with 
noncompliance penalties. Historically, such command-and control approaches to resource management have proved costly. 
This can occur because uniform standards do not provide adequate flexibility or incentives for innovation, while monitoring 
and enforcement can be costly.  A second approach, using incentive schemes (public or private), offers growers payments 
or rebates to alter behavior.  Incentive schemes are more popular with those being regulated, but in agriculture, require 
private or public funds to implement and also can suffer from high monitoring costs and lack of flexibility. The third, 
community-based approach would encourage programs led by growers themselves. This approach has the advantage 
that growers actively design the management program and oversee its implementation, perhaps in collaboration with 
industry, government and universities. The role of government here is distinctly different from that of the top-down, 
command-and-control or incentive approaches. It is often as a facilitator and provider of scientific knowledge and 
complementary investments. Implementation and compliance still require significant design and monitoring effort and cost 
as well as a clear delineation of the relevant community of stakeholders.  Yet, there are past examples in agriculture, such 
as groundwater management, pest eradication programs, and area-wide invasive weed control programs where community 
based approaches have succeeded.

CARROTS AND STICKS: INCENTIVES AND REGULATIONS FOR HERBICIDE RESISTANCE MANAGEMENT AND CHANGING BEHAVIOR. M. Barrett*1, D. Shaw2, J. Soteres3; 1University of Kentucky, Lexington, KY, 2Mississippi State University, Mississippi State, MS, 3Monsanto (retired), St. Louis, MO (226)

ABSTRACT

How can new thinking on incentives and/or regulations help achieve a different outcome for the future of herbicide resistance?   Government financial incentives have promoted the adoption of insect pest management and soil conservation practices showing that incentives, whether public or private, could help overcome financial barriers to greater use of herbicide resistance BMPs.  There are efforts in some areas to consider herbicide resistance management options as part of soil conservation programs.  But, for successful incentive programs, there must be sufficient funds for both the inducements and running the program.  As an example, industry incentives to diversify herbicide programs have successfully increased preemergence herbicide use in conjunction with postemergence applications.  However, it is also critical that incentives, either public or private, be only used to promote trial use of BMPs.  Sustained use of these practices must be based upon the realized benefits, not continuing incentives.  Experience has shown that participation in voluntary, not legally required, herbicide resistance management (HRM) programs can be successful with strong enough incentives, well-defined participation standards, and measured results.   In the case of regulation for herbicide resistance management, even the threat of credible government regulation can serve as a strong incentive for behavior change and participation in voluntary HRM programs. The Environmental Protection Agency-Office of Pesticide Programs (EPA-OPP) regulates herbicide use under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) and has a major interest in solving the problem of herbicide resistance to extend the useful life of these chemicals.  Jack Housenger, Director of EPA-OPP, said during his presentation at the Herbicide Summit II that EPA will require specific measures to address weed resistance on all new registration actions for herbicide resistant crops.  The required active monitoring, reporting and mitigation program for new resistance cases has potential, if carefully designed and implemented, to help curb further resistance development and spread.  In addition, while the initial focus will be on herbicide uses on new herbicide resistant crops, EPA will also utilize the registration review process to strengthen resistance management for pesticides, including glyphosate.  So, there are some new things happening in both the public and private sectors for incentives and regulations to address HRM.  These efforts need to be coordinated to change the future of herbicide resistance.   In addition, as these are new initiatives, it will be important to assess whether these proactive practices are being used and whether they are being effective in HRM.  A proactive approach to HRM that allows local flexibility in designing appropriate HRM strategies is preferred over any attempt to define a “one size fits all” approach.


APPROACHES TO HOLISTIC WEED MANAGMENT IN ORDER TO MANAGE HERBICIDE-RESISTANT WEEDS. M. D. Owen*; Iowa State University, Ames, IA (227)

ABSTRACT

There is a critical need to expand the adoption of diverse tactics, in addition to other than herbicides, to more effectively and robustly manage herbicide-resistant weeds and to mitigate the selection for evolution of herbicide resistance where it has not yet become a problem.  The burgeoning issues of evolved herbicide resistances in key weeds reflects agricultural systems where herbicides have been the principle tactic for more than 45 years.  The inclusion of alternate strategies for weed control has declined steadily over the same time frame and the loss of weed management diversity resulted in evolved resistance to a number of herbicide groups, notably Groups 2 and 5.  For the last decade, there has been only one herbicide, glyphosate, used in a majority of the row crop acres in the United States.     There are many reasons and justifications for this important change in weed control including, but not limited to: time management efficiency, cost, effectiveness, and the simplicity and convenience of herbicide-based weed control.  Not unexpectedly, the ecologically narrow focus of this approach has resulted in widespread evolved resistance to glyphosate within important weed populations to the extent that it should be clear that weed management in row crops is not sustainable if based primarily on a single herbicide, in the absence of other management practices.  However, it must be understood that herbicides will continue to play a significant role in the weed management, including those populations that have evolved herbicide resistance(s).  Consider that new crop cultivars with genetically engineered resistance to auxinic (Group 4) herbicides and other herbicide groups in the future will bring other technological concerns into play.  Older weed management tactics must be revisited and new technological approaches and new equipment should be considered as important additions for robust weed management.  Cultural and biological tactics that can supplement mechanical and herbicide-based weed management approaches will be important components of successful of herbicide-resistant weed management programs in the future.  The key will be for all entities involved in weed management, private, commercial and government, to consider more diverse approaches for weed management and contribute by recommending and supporting robust herbicide-resistant weed management programs.  

 


RETHINKING EDUCATION AND OUTREACH FOR SUCCESSFUL HERBICIDE RESISTANCE MANAGEMENT. A. Asmus1, J. Schroeder*2; 1Asmus Farm Supply, Inc, Rake, IA, 2New Mexico State University, Las Cruces, NM (228)

ABSTRACT

Education is a key component of the outreach effort on Herbicide Resistance Management (HRM). Grower willingness to accept and use available information and technology to execute best management practices for HRM is complicated by the social, economic, and regulatory barriers to adoption. We must consider that the traditional approach of “delivering” education must be accompanied by a clear understanding of the target audiences, a willingness to adopt new, diverse technologies, and engage the affected community in developing solutions.  The keys to successful outreach include the recognition that growers have intimate knowledge of what practices work on their farms and they have access to many, sometimes competing and conflicting, information sources.  The creators of these information sources and the key influencers have a responsibility to provide complete, non-biased, scientifically-sound and consistent information to decision makers and to be willing to partner with others to provide the best HRM options and advice.  Nationally, the agricultural industry, government, and university community must recognize that the resources used by growers, the most effective management practices, and the barriers to adoption of HRM will vary greatly across management systems and regions.  Our perception of educators must expand to include not only Extension specialists but also consultants, retailers, industry representatives, pesticide applicators, commodity organizations, farm press, growers, land managers, federal, state and tribal agencies and others. Therefore, traditional approaches for delivery of information must be reevaluated.  Education and outreach with regards to HRM must be integrated into all the information provided for crop production and land management. Educators must understand their audience; their learning styles, access to technology and information, risk tolerance, economic flexibility and more.  In addition, educators must be flexible in how they structure their outreach, which can include traditional education, but must consider new, non-traditional approaches as well as participating in community-based solutions. Partnerships among stakeholders, including agricultural groups, regulatory agencies, financial providers, retailers, farm managers, industry research, marketing and sales, educators, sociologists and economists are needed to provide current information, to adapt information delivery, and engage communities to solve the herbicide resistance problem.


A CALL TO ACTION FOR HERBICIDE RESISTANCE MANAGEMENT. H. Coble*; NC State University, Cary, NC (229)

ABSTRACT

The most effective approach to management of herbicide resistance is for every person and organization in the agricultural community to be involved. The agricultural community is made up of a large number of people and organizations, including growers, advisors, input supply networks, local, state, and federal governments, state, federal, and independent researchers, farm commodity organizations, public interest groups, professional societies, the agricultural press, and perhaps others. This call to action will enumerate some, but not all, of the opportunities for these groups to be involved in herbicide resistance management.


CAN YOU MANAGE HERBICIDE RESISTANCE BETTER THAN A FRESHMAN? A ROLE-PLAYING GAME TO DEMONSTRATE COMMUNITY-BASED RESISTANCE MANAGEMENT. G. Frisvold*1, A. Asmus2; 1University of Arizona, Tucson, AZ, 2Asmus Farm Supply, Inc, Rake, IA (230)

ABSTRACT


CAN YOU MANAGE HERBICIDE RESISTANCE BETTER THAN A FRESHMAN (CONTINUED). G. Frisvold*; University of Arizona, Tucson, AZ (231)

ABSTRACT


WEED CONTROL AND RADISH RESPONSE TO S-METOLACHLOR IN ORGANIC SOIL. D. C. Odero*, J. V. Fernandez, N. Havranek; University of Florida, Belle Glade, FL (232)

ABSTRACT

Field experiments were conducted in 2013 and 2014 to determine weed control and radish (Raphanus sativus) response to s-metolachlor on organic soil in the Everglades Agricultural Area (EAA). The soil type was Dania Muck with a pH of 7.3 and 80% organic matter. Radish ‘red silk’ was directly seeded on beds followed by preemergence application of s-metolachlor at 0.35, 0.7, 1.4, 2.8, 5.6, and 11.2 kg ha-1. Predominant weed species were common lambsquarters (Chenopodium album), spiny amaranth (Amaranthus spinosus), and fall panicum (Panicum dichotomiflorum). S-metolachlor at 1.4 to 11.2 kg ha-1 resulted in 4 to 25% and 2 to 20% radish injury 14 and 28 days after treatment (DAT), respectively. There was no radish injury observed at 0.35 and 0.7 kg ha-1 of s-metolachlor. At 14 DAT, s-metolachlor at 2.67, 1.49, and 1.17 kg ha-1 was required to provide 90% common lambsquarters, spiny amaranth, and fall panicum control, respectively. For 90% control of common lambsquarters, spiny amaranth, and fall panicum 28 DAT, s-metolachlor at 3.10, 1.64, and 1.30 kg ha-1, respectively was required. These results indicate that higher rate of s-metolachlor are required to provide season-long control of common lambsquarters in radish grown on organic soils in the EAA.

 


PRELIMINARY TRIALS FOR WEED MANAGEMENT IN QUINOA. T. W. Miller*, C. R. Libbey; Washington State University, Mount Vernon, WA (233)

ABSTRACT

Among the most promising of new crops being tested in Washington is quinoa (Chenopodium quinoa), a South American plant grown for its edible, high protein (up to 14%) seed.  Quinoa has been cultivated for at least the last 3000 years, and currently is widely produced in Peru, Chile, and Bolivia.  Worldwide quinoa production has increased significantly in recent years, from an estimated 3 million pounds in 2004 to over 80 million pounds in 2011.  Most of this increase has occurred because of increasing demand in the US, perhaps primarily because quinoa seed does not contain gluten, making its food products of interest to people with celiac disease, who are allergic to wheat, or have difficulty digesting wheat gluten.  There are no herbicides currently registered for use in quinoa, so weed control depends upon cultivation and hand weeding.  In preliminary testing at WSU Mount Vernon NWREC during 2014, quinoa was treated with herbicides used in spinach seed production.  Herbicides causing no or only slight injury to quinoa were asulam, cycloate, ethofumesate, flufenacet, fomesafen, s-metolachlor, quinclorac, and rimsulfuron.  A stale seedbed trial was also conducted, with seedbeds prepared in late May and early June into which quinoa was seeded up to 7 days later.  Nonselective herbicides were then applied immediately prior to quinoa emergence in effort to kill early-emerging weeds.  Conventional herbicides tested were glufosinate, glyphosate, paraquat, and pyraflufen.  Clove oil and propane flaming were also tested in this trial, for potential use in organically-grown quinoa.  This trial was not as successful as hoped, primarily because quinoa emerged only 3 days after seeding.  Therefore, earlier seeding dates (April to early May) and a longer interval between final seedbed preparation and seeding (up to 14 days) are proposed to be tested in 2015 in effort to improve in–row weed management.


INFLUENCE OF GROUND-COVER COMPETITION ON GROWTH, YIELD, AND BERRY QUALITY IN CABERNET FRANC GRAPE. N. T. Basinger*, K. Jennings, D. W. Monks, S. E. Spayd, S. Chaudhari; NCSU, Raleigh, NC (234)

ABSTRACT

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.  


CRITICAL PERIOD OF WEED REMOVAL FOR QUINOA AND GRAIN AMARANTH IN ONTARIO CANADA. R. E. Nurse*, E. R. Page; Agriculture and Agri-Food Canada, Harrow, ON (235)

ABSTRACT

Quinoa (Chenopodium quinoa) and grain amaranth (Amaranthus hypochondriacus) are generating interest among growers and industry for production as crops in Southwestern and Southern Ontario.  Two field trials were established at Harrow, ON in 2013 and 2014 to evaluate the duration of the weed-free period in quinoa and grain amaranth.  Brightest Brilliance and Burgundy were the varieties seeded for each crop, respectively.  Each trial consisted of five treatments; 3 treatments in which the crop was kept weed-free for a specified duration after crop emergence (7, 14, and 28 DAE), and season-long weedy and weed-free treatments.  Weed height and biomass was recorded in each treatment at 56 DAE and grain yield was measured at maturity. There was equal exposure to both dicots and annual grasses at densities as high as 120 plants m-2.  The most common weed species were Digitaria sanguinalis, Echinochloa crus-galli, Amaranthus retroflexus, and Chenopodium album.  The critical weed-free period in both quinoa
and grain amaranth was less than 21 days after crop emergence. Therefore, tillage can be used as an effective means of early season weed control in both crops.  Amaranthus and quinoa yields were increased by 3% and 1.4%, respectively for each day the crops remained weed-free.


IR-4 UPDATE AND NEW STRATEGIC PLAN: VISION 2020. D. L. Kunkel*1, M. Arsenovic1, J. J. Baron1, M. K. Braverman1, R. Batts2; 1Rutgers University, Princeton, NJ, 2North Carolina State University, Raleigh, NC (236)

ABSTRACT

The IR-4 Specialty Crop Program is a publicly funded program that develops and submits regulatory data for the registration of pest control products on specialty crops.  IR-4 has a long history of providing herbicide registrations for specialty or minor crop growers.  In 2014, IR-4 data was used to support a number of new herbicide registrations. These included new registrations for linuron, clomazone, and fenoxaprop-ethyl with others to follow in 2014, such as new uses for sethoxydim.  A large number of herbicide submissions were made to EPA in 2014.  These included S-metolachlor for lettuce and other crops, prohexadione calcium for strawberry, ethofumesate to reduce plant back restrictions, halosulfuron-methyl on a number of fruit crops, pronamide re-activation for leaf lettuce, with others submissions to follow by the end of 2014, such as carfentrazon-ethyl, clethodim, fluaziflop-p-butyl and penoxsulam.  The 2015 IR-4 research plan will likely include close to 40% herbicide projects.  The bioherbicide Tobacco Green Mosaic Virus for the management of Tropical Soda Apple is under review at EPA.

The new IR-4 strategic plan (2015-2020) was approved in 2014 (http://www.ir4.rutgers.edu/Other/AnnualReports/IR-4%20Vision%2020208_13_14.pdf).  The IR-4 Project will remain a responsive and efficient organization that supports US stakeholders by facilitating U.S. regulatory approvals for crop protection tools.  IR-4 will continue with a research focus on low risk pesticide registrations that support integrated pest management systems.  There will likely be more emphasis on efficacy and crop safety data to determine products that can manage hard to control pests and mitigate invasive species.  There will be continued support for products that can be used for organic growers as well as cutting edge biotechnology products.  Other areas expected to have greater importance will be in the area of international harmonization, to assist in exports of U.S. grown specialty crops and removing pesticides as a technical trade barrier.

Please see www.ir4.rutgers.edu for additional information.  


WEED CONTROL IN CULINARY HERBS. C. J. Phillippo*, B. H. Zandstra; Michigan State University, East Lansing, MI (237)

ABSTRACT

WEED CONTROL IN CULINARY HERBS.  C. P. Phillippo; B. H. Zandstra; Michigan State University, East Lansing, MI

 

Culinary herbs are very minor crops with few labeled herbicides. During the past 10 years, we have conducted herbicide tolerance trials in basil, established and seeded chives, cilantro, dill, Florence fennel, green onion, mint, parsley, and rosemary in Michigan and Illinois.

In basil, linuron applied preemergence (Pre) at 0.25 lb ai/a caused minimal injury. Halosulfuron applied Pre and postemergence (Post) at 0.023 lb ai/a both injured basil and reduced yield.  Napropamide was safe in basil and is now labeled for use.

Herbicides were applied to established chives early in the season, before new growth was active.  Dimethenamid-P at 0.98 lb ai/a, oxyfluorfen at 0.25 lb ai/a, and acetochlor at 1 lb ai/a were safe on established chives and resulted in good yields.  Pyroxasulfone at 0.186 lb ai/a and ethofumesate at 2 lb ai/a caused some crop injury and slight yield reduction. In seeded chives, Pre application of bicyclopyrone at 0.033 lb ai/a caused severe injury and yield reduction.  Pyroxasulfone applied Pre at 0.1 lb ai/a killed seeded chives.

In cilantro, Pre applications of pendimethalin at 0.5 lb ai/a, clomazone at 0.25 lb ai/a, bicyclopyrone at 0.045 lb ai/a, and bensulide at 6 lb ai/a were safe.  Pyroxasulfone at 0.1 lb ai/a applied Pre caused injury and reduced yield by 67%.

In dill, pendimethalin at 0.5 lb ai/a, clomazone at 0.25 lb ai/a, and bensulide at 6 lb ai/a applied Pre caused minimal injury and no yield reduction.  S-metolachlor at 0.95 lb ai/a, pyroxasulfone at 0.1 lb ai/a, and bicyclopyrone at 0.045 lb ai/a applied Pre to dill caused severe injury and near total yield loss.  Linuron at 0.5 ai/a and prometryn at 1 lb ai/a were safe on dill and are now registered for weed control.

Preemergence applications to Florence fennel of linuron at 0.5 lb ai/a, trifluralin at 0.5 lb ai/a, and clomazone at 0.25 lb ai/a were safe. Pyroxasulfone at 0.1 lb ai/a and bicyclopyrone at 0.045 lb ai/a caused severe yield reduction. S-metolachlor at 0.63 lb ai/a and pendimethalin at 0.7 lb ai/a were safe in 2008, but caused significant injury in 2013 at rates of 0.95 lb ai/a and 0.5 lb ai/a, respectively.

In parsley, Pre applications of pendimethalin at 0.5 lb ai/a, clomazone at 0.25 lb ai/a, ethofumesate at 1 lb ai/a, and trifluralin at 0.5 lb ai/a were safe on parsley and did not reduce yields. Pyroxasulfone at 0.1 lb ai/a and bicyclopyrone at 0.045 lb ai/a caused almost total crop loss. S-metolachlor was safe in 2007 at 0.63 lb ai/a, but not in 2013 at 0.95 lb ai/a.

S-metolachlor was safe on rosemary both pre-transplant and Post at rates of 1.27 lb ai/a and 2.54 lb ai/a, respectively.

Pyroxasulfone applied Pre to native spearmint did not injure the crop at 0.053 lb ai/a, but it caused mild crop injury at 0.11 lb ai/a and caused significant injury at 0.21 lb ai/a. Bicyclopyrone applied Pre caused significant injury at 0.033 lb ai/a and 0.045 lb ai/a.

 


NEW PERSPECTIVES ON PREEMERGENCE ONION WEED CONTROL. B. H. Zandstra*, C. J. Phillippo; Michigan State University, East Lansing, MI (238)

ABSTRACT

NEW PERSPECTIVE ON PREEMERGENCE ONION WEED CONTROL. B. H. Zandstra, C. P. Phillippo; Michigan State University, East Lansing, MI

 

 

Onion is grown primarily on high-organic muck soils in Michigan. Onion acreage peaked at 12,700 in 1935 and has declined to about 3,000 in 2014. Average yield is 600 50-lb bags per acre. Weed control is a major cultural activity and expense. Common weeds challenge growers and additional weed species occasionally emerge as serious pests. Use of effective preemergence herbicides is critical to obtain season-long weed control in seeded dry bulb onion.

 

Weed trials are conducted annually in grower fields on muck soil. Preemergence (PRE) treatments are applied after seeding and subsequently at the 1-2 leaf stage (LS) and 3-6 LS. Onion is planted in mid - late April and reaches the 1-2 leaf stage by May 25 – June 1. The 3-6 LS is reached June 15 – July 1. Postemergence (POST) herbicides are applied with subsequent PRE herbicide applications.  Onions need to be maintained weed free throughout the season to obtain maximum yield, to improve foliar disease and insect control, and to facilitate machine harvest.

 

A typical onion preemergence program includes three applications of pendimethalin at 2.13 kg ai ha-1 for a total of 6.38 kg ai ha-1. Applications after the 2 LS often include flumioxazin at 0.036 or 0.712 kg ai ha-1 for a total of 0.10 kg ai ha-1 per year. Other preemergence herbicides labeled for use after the 2 LS are s-metolachlor at 1.4 kg ai ha-1 (2 applications) and dimethenamid-P at 1.1 kg ai ha-1. Various combinations of these herbicides result in suppression of most annual grasses and broadleaves, but several weeds persist. Ladysthumb (Polygonum persicaria), marsh yellowcress (Rorippa islandica), and common lambsquarters (Chenopodium album) are serious problems in many onion fields.

 

In experiments over 5 years, flumioxazin was applied preemergence at 0.036 kg ai ha-1 with pendimethalin and at the 1-2 LS and 3-6 LS. It also was applied at 0.072 kg ai ha-1 at the 2 LS plus 0.036 kg ai ha-1 at the 4-6 LS. The application of flumioxazin PRE did not injure onions or reduce yield in any year. In most years, application of flumioxazin increased onion yield as a result of better ladysthumb control.

 

In other treatments, s-metolachlor was applied at 1.4 kg ai ha-1 twice after pendimethalin, or in a single application of 2.8 kg ai ha-1 at the 2 LS followed by dimethenamid-P at 1.1 kg ai ha-1 at the 4-6 LS. All of these treatments improved ladysthumb control and increased onion yield over pendimethalin alone.

 

Pyroxasulfone and bicyclopyrone were applied PRE and at the 1-2 and 4-6 LS. Pyroxasulfone at 0.2 and 0.4 kg ai ha-1 was marginally safe PRE on onion and very safe with no yield reduction when applied at the 2 and 4 leaf stages. It gave fair to good control of ladysthumb.

 

Bicyclopyrone applied PRE at 0.05 kg ai ha-1 did not control ladysthumb, but when applied POST at the 2 and 3-4 LS it controlled ladysthumb. Onion yield was not reduced by bicyclopyrone.

 

Preemergence labels for flumioxazin, pyroxasulfone, and bicyclopyrone should improve broadleaf weed control in onion and result in larger yields. 

 


EVALUATION OF THE CARRYOVER POTENTIAL OF SULFENTRAZONE IN CALIFORNIA VEGETABLE CROPS. S. A. Fennimore*, J. S. Rachuy; University of California Davis, Salinas, CA (239)

ABSTRACT

The potential for herbicide soil residues to injure rotational crops is one of the key reasons why there are so few herbicides available for vegetable crops in coastal California. Two to four vegetable crops are grown in each field in any given year, therefore ensuring safety of an herbicide to rotational crops is of critical importance. The objective of this work was to determine the potential for soil residues to injure vegetable crops planted 3, 6, 9 and 12 months after sulfentrazone application.

A trial was conducted near Salinas, CA; on a sandy loam soil with a pH of 7.2 and 1% organic matter.  The trial was established as a split plot.  The main plot was time after sulfentrazone application of 3, 6, 9 and 12 months, and the subplot was sulfentrazone rate of 0, 0.11, 0.22 and 0.34 kg ha-1.  The trial was arranged in a randomized complete block design, with treatments replicated four times.  Each replicate consisted of two 2 m wide beds by 7.6 m long.  Snap beans (Phaseolus vulgaris, cv. Jade) were planted into the entire trial May 8, 2012.  Sulfentrazone was applied May 9, 2012 as a broadcast spray at 374 l ha-1 over the respective plots, using a tractor-mounted sprayer.  After sulfentrazone application, the trial was watered with 5cm of sprinkler irrigation. Data were subjected to analysis of variance and mean separation was performed using LSD’s at P=0.05.

Snap beans were mowed down on July 25, 2012.  On August 9, 2012, beds in each of the four plantback plots were cultivated 5cm deep and reshaped.  The 3 month treatments were planted August 9, 2012 with carrot, tomato, snap bean, spinach, onion and lettuce.  The 6, 9 and 12 month plots were planted with fava bean (Vicia faba).  At 14 and 19 days post-plant (DPP), stand and injury (phytotoxicity) evaluations were made, respectively, for each crop.  At 36 to 54DPP, fresh biomass samples for each crop were collected, dried, and dry-weights recorded. 

The process for the 6, 9 and 12 month plots was the same as the 3 month process described above. The 6, 9 and 12 month planting dates were October 22, 2012, February 11, 2013 and May 9, 2013, respectively.

Carrot was slightly injured by sulfentrazone at 0.34 kg ha-1 at 3, 6 and 9 months post-application. Tomato was slightly injured by sulfentrazone at 0.22 and 0.34 kg ha-1 at 3 months after application.  Sulfentrazone did not reduce carrot or tomato dry weight at any planting date. Sulfentrazone did not injure or reduce snap bean dry weights. Spinach was sensitive to all rates of sulfentrazone at 3, 6, and 12 months after application. Sulfentrazone reduced spinach dry weights at the 0.34 kg ha-1 rate 3 months after application, and at all rates at the 6-month interval. Sulfentrazone at all rates caused slight injury to green onion at 3, and 12 months after application, but no reduction in onion dry weight at any interval. Lettuce was sensitive to all rates of sulfentrazone at 3 months after application.  However sulfentrazone did not reduce lettuce dry weights at any planting date. 


IMPLICATIONS OF OFF-TARGET HERBICIDES IN POTATO SEED PRODUCTION. J. Colquhoun*, D. Heider, R. Rittmeyer; University of Wisconsin, Madison, WI (240)

ABSTRACT

The introduction of new agronomic crop herbicides in recent years that are active at low doses, as well as the pending introduction of crop traits conferring resistance to additional herbicides, have spurred an interest among specialty crop producers in knowing more about the potential off-target implications of these tools. In 2013 we initiated the first replication of a 2-year study investigating the implications of potato seed crop exposure to off-target herbicides (such as through tank contamination) on daughter tuber germination, growth and yield.  Thirteen herbicides commonly used in agronomic and non-crop areas nearby potato seed production were evaluated at 1% of the commercial use rate applied at potato tuber initiation.  Glyphosate was also evaluated at 2 and 4% of typical use rates.  In the seed crop production year (2013), potato injury visually estimated 5 days after treatment (DAT) was greatest where mesotrione was applied.  By 28 DAT, potato injury differed from the non-treated check only where dicamba or aminopyralid were applied.  Other than the aforementioned herbicides, injury from other herbicides was 5% or less at all visual evaluation timings.  Total potato tuber yield and individual potato grade class weights were similar among herbicide treatments and the non-treated check.  Additionally, non-marketable and misshapen cull tuber weight did not differ among treatments.  Seed from the mother plants was stored and planted in the 2014 growing season. Interestingly, potato injury was sporadically observed among plants within a plot, where affected potato plants were often surrounded by healthy plants.  The percentage of affected plants didn’t differ from the non-treated potatoes with any treatment or in any evaluation timing and was most often below 10%.  Total potato yield from the daughter tuber plants did not differ among treatments or from the non-treated check.  However, production of tubers in the 283-369 g weight range was reduced compared to the non-treated check where dicamba, cloransulam or tribenuron were applied.  This was the first replicate of this study; a second replicate was initiated in 2014 and subsequent seed potatoes will be planted in 2015.

 


SEASON-LONG WEED MANAGEMENT PROGRAMS IN GARDEN BEETS. D. Heider*, J. Colquhoun, R. Rittmeyer; University of Wisconsin, Madison, WI (241)

ABSTRACT

SEASON-LONG WEED MANAGEMENT PROGRAMS IN GARDEN BEET (Beta vulgaris).  D.J. Heider*, J.B. Colquhoun, R.A. Rittmeyer; University of Wisconsin, Madison WI.

ABSTRACT

Herbicide options in garden beet (Beta vulgaris) have become limited in recent years.  The losses of the active ingredients pyrazon and desmedipham has raised questions about redroot pigweed (Amaranthus retroflexus) control in garden beet.  Studies were conducted in 2013 and 2014 in both irrigated sand and non-irrigated loam production systems.  A total of 10 multiple application herbicide programs were evaluated over four garden beet varieties, including: ‘Ruby Queen’, ‘Detroit Supreme’, ‘Red Ace’ and ‘Red Titan’.  Acceptable weed control was observed from all treatments across both years and locations.  Nearly perfect redroot pigweed control was obtained from all tested treatments.  Crop injury did vary significantly across treatments and application timing, and in some instances was variable by beet variety.  Yields tended to reflect crop injury ratings, with several treatments yielding at or above industry norms. 


IMPACT OF AIR TEMPERATURE AND HERBICIDE CONCENTRATION ON ROOT UPTAKE OF GRAMOXONE IN PEPPER. N. Boyd*; University of Florida, Wimauma, FL (242)

ABSTRACT

Vegetable root uptake of paraquat applied between the rows for weed control has been reported in Florida vegetable production systems.  Greenhouse experiments were conducted at the Gulf Coast Research and Education Center in Balm, Florida, to determine the impact of application rate, active ingredient concentration, and temperature on root uptake of paraquat in pepper.  Pepper transplants were grown in pots that were placed in plastic tubs containing paraquat to simulate herbicide root uptake.  The first experiment was set up as a 4x5 factorial with 8 blocks. The first factor was growth room temperature which was: 1) 18 C throughout the experiment, 2) 18 C throughout experiment except for 29 C during the exposure to paraquat, 3) 29 C throughout experiment, and 4) 29 C throughout experiment except for 18 C during the exposure to paraquat.  The second factor was paraquat rate which was 0, 0.048, 0.096, 0.191, and 0.3828 g ai/plant diluted in 1L of water.  The second experiment was a 5x3 factorial.  The first factor was paraquat rate which was the same as experiment 1 and the second factor was the dilution volume which was 1, 0.5, and 0.25 L of water.  In experiment 1, shoot biomass was impacted by paraquat rate (p=0.0218) and temperature (p<0.0001) with the effect of rate constant across temperature regimes.  The highest paraquat rate decreased shoot biomass by 34% compared to the untreated control.  Pepper biomass was 57% less in plants grown at 18 versus 29 C and even a short 4 day exposure to 29 C with plants grown at 18 C increased biomass by 34% compared to plants grown in a constant 18 C environment.  Paraquat rate and temperature had similar impacts on pepper yield with the highest rate decreasing yield by 60% compared to the untreated control.  In experiment 2, paraquat rate had a significant impact on shoot (p=0.0005) and root (p=0.0005) biomass with a 21 and 37% reduction in shoot and root biomass, respectively, at the highest rate compared to the untreated control.  Active ingredient concentration did not have a consistent impact on growth.  We conclude that temperature and concentration of the active ingredient did not affect paraquat root uptake but shoot, root, and fruit biomass decreased as paraquat rate increased.

 

 


ABSORPTION, TRANSLOCATION, AND METABOLISM OF HALOSULFURON IN GRAFTED SOLANACEOUS CROPS. S. Chaudhari*, K. Jennings, D. W. Monks, F. Louws; NCSU, Raleigh, NC (243)

ABSTRACT

Research was conducted to characterize absorption, translocation, and metabolism of halosulfuron in grafted and non-grafted Solanaceous crops including tomato and eggplant. Plant type included non-grafted tomato (Amelia cultivar), and eggplant (Santana cultivar), Amelia grafted onto Maxifort tomato rootstock (A-Maxifort) and Santana grafted onto Maxifort rootstock (S-Maxifort). Plants were treated POST with commercially formulated halosulfuron at 0.039 kg ai ha-1 followed by 14C-halosulfuron under controlled laboratory conditions at North Carolina State University (Raleigh, NC). Amount of 14C-halosufuron was quantified in leaf wash, treated leaf, scion-shoot, rootstock-shoot and root at 6, 12, 24, 48, and 96 h after treatment (HAT) by using liquid scintillation spectrometry. No differences were observed between the plant type with regard to absorption, and translocation of 14C-halosulfuron. Absorption of 14C-halosulfuron increased with time, reaching 10 and 74% at 6 and 96 HAT, respectively. Translocation of 14C-halosulfuron was limited to the treated leaf, which reached maximum (66%) at 96 HAT, whereas less than 4% traslocation occurred in scion-shoot, rootstock-shoot and root combined. Results from this study indicate that graft union did not affect the absorption and translocation of halosulfuron in tomato and eggplant.

 

 


COMMON RAGWEED COMPETITION IN POTATO GROWN IN SEEPAGE IRRIGATION AT DIFFERENT WATER TABLE DEPTHS. P. J. Dittmar*, L. Zotarelli; University of Florida, Gainesville, FL (244)

ABSTRACT

Seepage irrigation is cheap and easy to operate, however, uses large quantities of water for irrigating the crop.  Best management practices may restrict the amount of water available for irrigation. The objective of this research was yield and growth restrictions of common ragweed in potato growing in three different water table depths. The experiment treatments were a factorial design with 3 water table depths x 5 common ragweed populations. The water table depths were low, average, and high water tables. The ragweed populations were 0, 3, 8, 14, and 20 plants plot-1. Plots were 20’ long and potato ‘Fabula’ seed pieces were planted at 12” spacing.  Common ragweed (3-5” tall) were transplanted at the required treatment spacing after all plots were boarded off. Potato tubers were harvested at maturity and graded according to size. On the day before harvest, ragweed height and width were measured and dry weight was collected. The A1 and A2 potato grades were greater in the 0 and 3 plants plot-1 plant densities. No differences between depths for A1 and A2 potato grades. The ragweed height, width, and dry weight were not different among depths or populations. A ragweed density of 3 ragweed plants has minimal impact on potato growth. ‘Fabula’ potato grows quickly and the habit is large and could be competitive against the ragweed. The ragweed growth was greater later in the potato production season after tuber set. Further research will include different cultivars with various growth habits to understand the impact of intraspecific competition.

 


THE EFFECT OF INDAZIFLAM ON BERMUDAGRASS HEALTH AND GROWTH. L. Ou*, M. Jeffries, T. Gannon; NCSU, Raleigh, NC (245)

ABSTRACT

Indaziflam, an alkylazine herbicide that inhibits cellulose biosynthesis, is predominately applied for PRE control of annual broadleaf and grass weeds in sites including residential and commercial turfgrass, ornamentals, commercial nurseries, roadsides and forestry. ‘Tifway 419’ bermudagrass (Cynodon dactylon L. x C. transvaalensis) is a warm-season turfgrass commonly established in temperate climates on athletic fields and golf courses.  Since indaziflam was registered in 2010 in the United States, sporadic cases of bermudagrass thinning and/or injury have been reported and the cause has not been elucidated. The objective of this research was to determine the effect(s) of various indaziflam application rates and timings on bermudagrass growth.

Two experimental runs of field research (Wilmington, NC) were conducted from 2012 to 2014 evaluating: indaziflam application rates (16 + 16 (30 d interval), 33, 49, or 65 g ai ha-1), application timings (fall only, fall + spring, or spring only), and growth conditions (stressed – poor air flow/light quality and trafficked; or non-stressed – ideal growing conditions). Data collected to characterize bermudagrass growth included: visual foliage cover (0 – 100% scale; 0 = no cover and 100 = complete cover), green foliage cover determined by digital image analysis (DIA; 0 – 100% scale; 0 = no cover and 100 = complete cover), normalized difference vegetation index (NDVI; 0 – 1), root length (cm), and root mass (g). Visual estimations of bermudagrass cover and DIA showed a strong positive relationship 21 and 42 d after last spring treatment (DALST) (r = 0.75 and 0.94, respectively; P < 0.0001), indicating visual cover and DIA cover increased similarly. Due to indaziflam’s propensity for root uptake, a bioassay experiment to quantify downward indaziflam movement in soil and bioavailability was also conducted by collecting field cores (5 cm diam x 20 cm depth) at various times after application, transporting cores to the greenhouse where they were cross-sectioned to expose the soil profile, seeded with perennial ryegrass (Lolium perenne L.; indaziflam-sensitive species) and vegetation was harvested following a 28 d growing period. Ryegrass was harvested in 2.5 cm increments to a 12.5 cm depth and fresh and dry mass were recorded. The field and greenhouse experiments were arranged as a randomized complete block split plot and randomized complete block designs, respectively, and PROC MIXED and PROC GLM of SAS 9.4 were used for data analyses (P < 0.05).

Bermudagrass growth was affected differently between experimental runs (years); therefore, data are reported separately. In experimental run one, biologically-significant differences between evaluated parameters were not detected in any data collected through 56 DALST, while in run two bermudagrass cover varied between growth conditions. Indaziflam applied at 49 and 65 g ha-1 in stressed conditions had 36 and 64% less cover 56 DALST (run two), respectively, compared to non-stressed conditions. Within the stressed condition, these application rates also reduced bermudagrass cover compared to the nontreated. Across all evaluated parameters in this research, bioassay data showed that indaziflam did not significantly reduce ryegrass biomass beyond a 2.5 cm depth indicating if indaziflam moved deeper, it was not bioavailable suggesting other factors may have caused bermudagrass growth reduction in run two. A review of climatic conditions during experimental periods indicate air temperature fell below freezing more frequently and to a greater extent in run two. The more severe weather, coupled with relatively poorer growth conditions in stressed areas may have attributed to bermudagrass growth reduction. Data from this research suggest indaziflam applications to established bermudagrass in areas with suitable bermudagrass growth conditions are safe for practitioners; however, applications in areas with poor growth conditions may cause unacceptable bermudagrass injury and should be made with caution.  Further, as with many residual herbicide, harsh winters may exacerbate turfgrass injury and delay recovery. 

 

 

 

 

 

 


SINGLE AND SEQUENTIAL APPLICATIONS OF INDAZIFLAM FOR BROADLEAF AND LONG-TERM ANNUAL GRASS CONTROL IN WARM-SEASON TURFGRASS. B. J. Brecke*, R. G. Leon; University of Florida, Jay, FL (246)

ABSTRACT

Studies were conducted at the University of Florida West
Florida Research and Education Center, Jay, FL from 2010 through 2014 to
determine the effectiveness of indaziflam for broadleaf and long-term annual
grass control in warm-season turfgrass.  Indaziflam
applied once at 30 g a.i./ha provided 80% control of goosegrass (Eleusine indica (L.) Gaertn.) when
evaluated 4 mo after treatment while indaziflam at 40 or 50 g/ha provided 90 to
95% control.  When indaziflam was applied
twice at 50 g/ha with a 12 mo interval between applications, goosegrass control
was 85% when evaluated 24 mo after initial treatment.  Prodiamine applied twice at 0.8 kg/ha or
oxadiazon applied twice at 3.6 kg/ha at 12 mon intervals provided less than 60%
goosegrass control 24 mo after initial treatment.   A
single early-season indaziflam application at 35 g/ha provided less than 60% doveweed
(Murdannia nudifolia (L.) Brenn) control
90 days after treatment.  Three applications
of indaziflam at 10 g/ha provided 95% control 60 d after initial treatment and 80%
at 133 days.  A single indaziflam
treatment at 30 g/ha control chamberbitter (Phyllanthus
urinaria
L.) at 100% for 90 days after treatment.  Control decreased to 80% by 123 days after treatment
with no advantage of three applications at 10 g/ha over a single application at
30 g/ha.


DALLISGRASS MANAGEMENT IN TURFGRASS. J. Derr*, A. Nichols; Virginia Tech, Virginia Beach, VA (247)

ABSTRACT

Dallisgrass (Paspalum dilatatum) is a troublesome weed in both cool-and warm-season turf.   Its wide blades and tall seedheads make the weed especially apparent in bermudagrass turf.   MSMA, the most commonly-used herbicide for dallisgrass control, currently can only be used in golf courses, sod production, and rights of way areas, and even in those areas there are restrictions on use.   It is unclear what turf labels will exist for MSMA in the future.    Additional control options are therefore needed for this weed in turf.  Trials were conducted to evaluate herbicides, herbicide combinations, and herbicide application timing for dallisgrass control in bermudagrass [Cynodon dactylon (L.) Pers.] and tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbyshire].   In bermudagrass, the herbicides tested included foramsulfuron, a three-way combination of iodosulfuron, thiencarbazone, and dicamba, a three way combination of foramsulfuron, thiencarbazone, and halosulfuron, and trifloxysulfuron.    MSMA was included for comparison.    Multiple spring, multiple fall, and spring followed by fall applications were evaluated.  Various adjuvants, including crop oils, methylated seed oils, and ammonium sulfate, were evaluated with these herbicides. Four applications of MSMA (two in spring, two in fall) gave the greatest reduction in dallisgrass cover.  Utilizing four applications of trifloxysulfuron, or two trifloxysulfuron applications and two applications of foramsulfuron plus two applications of iodosulfuron plus thiencarbazone plus dicamba significantly reduced dallisgrass cover but dallisgrass was able to recover.   All applications of foramsulfuron plus thiencarbazone plus halosulfuron significantly reduced dallisgrass cover in December, but dallisgrass exhibited significant regrowth by June.  All applications significantly reduced dallisgrass seedhead production in the fall.  This should provide a long term benefit since dallisgrass can spread by seed.  Obtaining long-term control of dallisgrass is difficult with the alternatives to MSMA we currently have available for use in bermudagrass.

For dallisgrass control in tall fescue, applications of fluazifop alone or in combination with mesotrione or mesotrione plus triclopyr were evaluated.  Tank mixes of topramezone plus triclopyr and mesotrione plus triclopyr were also tested. A total of four applications, two in the fall and two in the spring, were made and a crop oil concentrate was added to all treatments. Four applications of fluazifop gave excellent dallisgrass control.  Adding mesotrione to fluazifop did not improve dallisgrass control. Topramezone plus triclopyr and mesotrione plus triclopyr decreased dallisgrass cover when evaluated in May but dallisgrass quickly outgrew the injury.  In a similar fashion, the three way combination of fluazifop plus mesotrione plus triclopyr decreased dallisgrass cover in May but dallisgrass recovered rapidly.  It appears that there is some antagonism of fluazifop’s activity against dallisgrass when mesotrione plus triclopyr are added.  All treatments containing fluazifop reduced dallisgrass seedhead production.  Fluazifop is an effective control option for dallisgrass in tall fescue. 

 


INVESTIGATING CREEPING BENTGRASS RESPONSE TO METHIOZOLIN, ETHEPHON AND AERATION. K. A. Venner*, S. Askew; Virginia Tech, Blacksburg, VA (248)

ABSTRACT

Methiozolin (PoaCure) is a new herbicide developed by Moghu Research Center in Daejeon, Korea for safe and selective removal of annual bluegrass (Poa annua) from creeping bentgrass (Agrostis stolonifera) turf.  Ethephon (Proxy) is a plant growth regulator which is used to temporarily suppress annual bluegrass seedheads.  Previous research conducted on two Virginia golf courses indicated that methizolin efficacy for annual bluegrass control and creeping bentgrass response may be impacted by ethephon.  Four studies were initiated in 2012, 2013 and 2014 to determine whether or not the addition of ethephon to methiozolin programs would influence annual bluegrass control and creeping bentgrass safety.  The first trial was initiated on March 13, 2012 at Blacksburg Country Club (BBC) in Blacksburg, Virginia on a mixed variety creeping bentgrass putting green.  Sequential applications were made on April 16.  The second trial was initiated on April 12, 2013 at the Virginia Tech Golf Course (VTG) in Blacksburg, Virginia on a ‘C-19 Congressional’ creeping bentgrass putting green.  Sequential applications were made on May 14.  The third and fourth trials were initiated on April 10, 2014 at the VTG (VTG2) and Turfgrass Research Center (TRC) in Blacksburg, Virginia on a mixed ‘C-19 Congressional’/’C-1 Arlington’ and ‘Penneagle’ putting greens, respectively.  Sequential applications were made on May 10, 2014.  BBC and TRC sites were aerated in conjunction with the sequential application. Methiozolin at 500, 1000 and 2000 g ai ha-1 was applied alone or with ethephon at 3818 g ai ha-1.  A comparison treatment of 1000 g ai ha-1 methiozolin + 3818 g ai ha-1 ethephon+ 48 g ai ha-1 trinexapac-ethyl as well as an untreated check were also included. 

Initial annual bluegrass cover on the putting greens ranged from 48 to74%.  At 2 WAIT, annual bluegrass control at BBC was 32% at 2000 g ai ha-1 versus 52% at VTG, respectively.  Annual bluegrass was not controlled at VTG2, but was controlled 12% at TRC.  Methiozolin applied at 500 and 1000 g ai ha-1 were not significantly different from one another at BBC, VTG2 and TRC.  At VTG, methiozolin applied at 1000 g ai ha-1 controlled annual bluegrass more than 500 g ai ha-1. At 6 WAIT, or 2 weeks after the sequential application, annual bluegrass was controlled 89 to 90% with 1000 to 2000 g ai ha-1 and 37% with 500 g ai ha-1 methiozolin at BBC.  Annual bluegrass at the VTG was controlled 90, 39 and 8% with 2000, 1000 and 500 g ai ha-1 methiozolin, respectively.  At VTG2, annual bluegrass was controlled 82 to 97% with 1000 to 2000 g ai ha-1 and % with 500 g ai ha-1 methiozolin.  Annual bluegrass at the TRC was controlled 48% at 2000 g ai ha-1 and 30 and 27% at 1000 and 500 g ai ha-1, respectively.  At 8 WAIT, addition of ethephon influenced methiozolin applications at BBCC and TRC, but not at VTG or VTG2. At the conclusion of the study, annual bluegrass was nearly completely controlled with all treatments with the exception of methiozolin applied at 500 g ai ha-1. No undesirable turfgrass injury was observed at VTG or VTG2 but severe creeping bentgrass injury was observed at BBC and TRC.  At 8 WAIT, methiozolin applied alone did not significantly injure bentgrass regardless of rate while combinations of ethephon with 1000 or 2000 g ai ha-1 methiozolin injured creeping bentgrass 23 and 80%, respectively at BBC. Similar results were observed at TRC.  Injury occurred at BBC and TRC when the sequential application was applied immediately following an aeration event.  This phenomenon was not observed at the VTG or VTG2, as aeration did not occur during the course of the study.  These data suggest that depending on site conditions and cultural practices, methiozolin and ethephon should not be applied together to avoid potential, undesirable turfgrass injury. 

 


ANNUAL BLUE-EYED GRASS (SISYRINCHIUM ROSULATUM) CONTROL IN BERMUDAGRASS. M. L. Flessner*1, S. McElroy2; 1Virginia Tech, Blacksburg, VA, 2Auburn University, Auburn, AL (249)

ABSTRACT

Annual blue-eyed grass is a member of the iridaeceae family and functions as a winter annual weed in bermudagrass. It can also persist as a perennial. Little information is available for herbicidal control, whether preemergence (PRE) or postemergence (POST) applied. The objectives of this research were to evaluate PRE and POST herbicides for blue-eyed grass control.

Field and greenhouse experiments were conducted from 2013 to 2015. Studies included PRE and POST experiments in both field and greenhouse settings, respectively. All studies were conducted in Auburn, AL with the exception of 2013 POST field study, which was located in Montgomery, AL. POST greenhouse study treatments were applied in March and included foramsulfuron (Revolver; Bayer Environmental Science, Research Triangle Park, NC) at 29 g ai ha-1, thiencarbazone + iodosulfuron + dicamba (Celsius; Bayer Environmental Science) at 233 g ai ha-1, thiencarbazone + foramsulfuron + halosulfuron (Tribute Total; Bayer Environmental Science) at 136 g ai ha-1, metsulfuron + rimsulfuron (Negate; Quali-Pro; Pasadena, TX) at 35 g ai ha-1, 2,4-D + MCPP + dicamba (Trimec Classic; PBI Gordon Corp., Kansas City, MO) at 1110 g ai ha-1, sulfentrazone + imazethapyr (Dismiss South; FMC Corp., Philadelphia, PA) at 504 g ai ha-1, imazaquin (Image, BASF Crop., Research Triangle Park, NC) at 560 g ai ha-1, quinclorac (Drive XLR8; BASF Crop.) at 840 g ai ha-1, and trifloxysulfuron (Monument; Syngenta Crop Protection, LLC, Greensboro, NC) at 28 g ai ha-1. POST field studies included the same treatments as the greenhouse study with the addition of rimsulfuron (TranXit; Dupont, Wilmington, DE) at 35 g ai ha-1, and 2,4-D + MCPP + dicamba + carfentrazone (Speedzone; PBI Gordon Corp.) at 1230 g ai ha-1. PRE field experiment treatments were applied in early September and included indaziflam (Specticle Flo; Bayer Environmental Science) at 54 g ai ha-1, oxadiazon (Ronstar; Bayer Environmental Science) at 3360 g ai ha-1, pendimethalin (Pendulum AquaCap; BASF Corp.) at 1850 g ai ha-1, prodiamine (Barricade; Syngenta Crop.) at 1120 g ai ha-1, and dithiopyr (Dimension; Dow AgroSciences LLC, Indianapolis, IN) at 426 g ai ha-1 followed by dithopyr 12 weeks later at 426 g ai ha-1. PRE greenhouse experiments included the same treatments as PRE field experiments with the exception of dithiopyr only applied once at 560 g ai ha-1 and the addition of propyzamide (Kerb; Dow AgroSciences LLC) at 1120 g ai ha-1, isoxaben (Gallery; Dow AgroSciences LLC) at 1490 g ai ha-1, and S-metolachlor (Pennant Magnum; Syngenta Crop Protection LLC) at 2780 g ai ha-1. All experiments included a nontreated check, utilized a randomized complete block design with a minimum of three replications, and were applied at 280 L ha-1. Annual blue-eyed grass control was visually evaluated relative to the nontreated check on a 0 (no control) to 100 (complete plant necrosis) scale. Visible control was assessed 3, 6, and 9 weeks after treatment (WAT) in POST field studies, 2, 4, and 6 WAT in POST greenhouse studies, and monthly from December to May in PRE field studies. Annual blue-eyed grass plant counts per pot and above ground dry biomass were assessed 10 WAT in PRE greenhouse studies. Data were subjected to ANOVA and effects were considered significant when P < 0.05 followed by means separation using Fisher’s protected LSD (P < 0.05).

All POST treatments resulted in ≥ 93% control 6 WAT. Speedzone resulted in the fastest control, 98% 2 WAT. In greenhouse POST experiments, all treatments except foramsulfuron and imazaquin resulted in ≥ 90% control 4 WAT. Overall, these data indicate that annual blue-eyed grass is susceptible to a many common turfgrass herbicides applied for winter annual weed control. All field PRE treatments resulted in 0% control from December to May, likely indicating that this was a perennial population. All PRE greenhouse treatments significantly reduced population and above ground biomass relative to the nontreated. Oxadiazon, pendimethalin, prodiamine, dithiopyr, and S-metolachlor all resulted in complete control in both experimental runs. These data indicate that PRE herbicides evaluated do result in annual blue-eyed grass control, but the weed must be establishing from seed.

 


DISLODGEABLE 2,4-D ON OVERSEEDED AND NON-OVERSEEDED BERMUDAGRASS ATHLETIC FIELDS. M. Jeffries*, T. Gannon, K. Ahmed; NCSU, Raleigh, NC (250)

ABSTRACT

2,4-dichlorophenoxyacetic acid (2,4-D) is a selective post-emergence broadleaf herbicide currently registered for use in over 300 distinct agricultural and residential use sites, including athletic fields. Athletic fields in temperate climates are commonly overseeded with perennial ryegrass (Lolium perenne L.) in the fall to improve playing surface quality throughout the winter. Previous research has shown 2,4-D may dislodge from treated turfgrass; however, research to date has not compared turfgrass species. Further, research has not evaluated if dislodgeability differs within a day in these systems.

A field trial (Raleigh, NC) was initiated April 8, 2014 to quantify dislodgeable 2,4-D plant residues over time: 1) between overseeded and non-overseeded bermudagrass (Cynodon dactylon L. x C. transvaalensis); and 2) within a day in each system. 2,4-D was applied at 2.1 kg ha-1 with a single 8004 E nozzle calibrated to deliver 187 L ha-1 to unique non-overseeded dormant bermudagrass and dormant bermudagrass overseeded with perennial ryegrass. In short, dislodgeable 2,4-D plant residues were quantified by rolling a soccer ball double-wrapped with a 5 cm x 120 cm strip of a cellulose-based absorbent sheet over a 3.7 m distance within a unique plot. The soccer ball was mounted to a PVC apparatus that allowed the ball to rotate end over end in the same direction as the absorbent strip, thus allowing for constant strip contact to the treated turfgrass surface. To determine total 2,4-D on/in vegetation at a given sample time, a turfgrass core (92 cm2) was harvested within each plot. 2,4-D residues were quantified with high performance liquid chromatography–diode array detector methods. Dislodgeable 2,4-D plant residues were quantified at two times within a day (TWD; 7:00:00 or 14:00:00 EST) in each of 6 d after treatment (DAT; 1, 2, 3, 6, 12 or 24).  Samples were also collected immediately and 1 h after treatment. Three replicates of each turfgrass-sample timing combination were arranged in a completely randomized split plot design, with plots split on sample timing.  Dislodgeable 2,4-D plant residue concentrations were converted to a percent of the applied as well as the total on/in vegetation at respective sample timings.  Data were subjected to ANOVA (P = 0.05) and means were separated according to Fisher’s Protected LSD (P < 0.05).

Overall, dislodgeable 2,4-D plant residues declined to nondetectable concentrations after 6 DAT. General trends between dislodge as percent of the applied or total on/in vegetation were similar, thus data are presented as percent of the applied. Immediately following 2,4-D application, 9.9 and 2.3% of the applied was dislodged from overseeded and non-overseeded plots, respectively, and declined to 0.5 and 0.1% of the applied after a 1 h drying period, respectively. At 1 DAT, more 2,4-D was dislodged at 7:00:00 than 14:00:00 in both turfgrass systems, while differences were only detected between TWD from 2 to 6 DAT in overseeded bermudagrass. Within the 7:00:00 sample timing, 2,4-D was consistently more dislodgeable in overseeded compared to non-overseeded bermudagrass. At 1, 2, 3 and 6 DAT 3.1, 1.1, 2.3 and 1.7% more of the applied was dislodged at 7:00:00 from overseeded compared to non-overseeded bermudagrass, respectively. At 14:00:00 no differences were detected between overseeded and non-overseeded bermudagrass, with maximum dislodge being < 0.5% of the applied from either turfgrass system.  

Data from this research suggest 2,4-D dislodgeability varies both between turfgrass systems, as well as within a day in respective systems. 2,4-D is believed to be more dislodgeable from overseeded than non-overseeded bermudagrass due to the increased aboveground biomass in this system, which would increase plant-herbicide spray interception and retain a larger portion of the applied in aboveground biomass, ultimately increasing the total amount to potentially be dislodged. Further, morphological differences between perennial ryegrass and dormant bermudagrass vegetation may affect 2,4-D sorption and consequently, its propensity to dislodge. Regarding TWD, data suggest 2,4-D re-suspends on treated turfgrass vegetation overnight, as the amount dislodged increased from 14:00:00 to 7:00:00 on the following sample collection day. This trend is attributed to 2,4-D’s very high water solubility (Ks = 796,000 mg L-1; 20 °C) and moderate soil organic carbon sorption coefficient (Koc = 20 mL g-1), coupled with environmental conditions favoring increased turfgrass canopy moisture at 7:00:00 compared to 14:00:00. This research will improve our knowledge on the potential for 2,4-D to dislodge from treated turfgrass vegetation in various systems and conditions within a system. Ultimately, this information may be used to develop best management practices that minimize human-pesticide exposure.


EVALUATION OF SELECTIVE HERBICIDES FOR DEERTONGUE CONTROL IN FINE FESCUE. S. S. Rana*, S. Askew, J. R. Brewer; Virginia Tech, Blacksburg, VA (251)

ABSTRACT

Deertongue (Dichanthelium clandestinum) is a perennial, cool-season grass native to the eastern United States and southeastern Canada that is primarily used for revegetation of disturbed areas.  Deertongue produces short, strong rhizomes, and under favorable conditions can grow up to 3 ft tall.  On a golf course, deertongue primarily grows in non-mow or less-disturbed areas.  Tall, thick, and dense cover of deertongue in roughs make it almost impossible for a golfer to find and advance a golf ball from an errant shot.  Currently, the only two control options known for deertongue are hand-pulling and using a non-selective herbicide, glyphosate.  Since both hand-pulling and using non-selective herbicides have obvious disadvantages, research was conducted to evaluate several selective herbicides for deertongue control in fine fescue (Festuca rubra), the most common turfgrass managed on golf course non-mow areas.  Preliminary greenhouse studies evaluated 25 treatments and indicated 6 herbicides had potential for deertongue control.  Field treatments were designed around results from greenhouse studies.  Two trials were conducted at The Highland Course, Primland Resort in fall 2014.  The first trial was initiated May 16, 2014 on a woodland edge.  The second trial was initiated June 27, 2014 on the edge of a golf fairway, approximately 50 m from the tree line.  Thus, the second site can be characterized as receiving more direct sunlight than the first.  Treatments for both trials were arranged as a randomized complete block design with three replications.  The following treatments were evaluated in the field studies: glyphosate at 1.12 kg ai/ha, glyphosate at 0.56 kg/ha plus imazapic at 0.05 kg/ha, fluazifop at 0.42 kg/ha applied once or three times at 3 week intervals, topramezone at 0.03 kg/ha applied thrice at 3 week intervals, imazapic at 0.11 kg/ha, and a premix of thiencarbazone, iodosulfuron, and dicamba (TID) at 0.23 kg/ha.  Treatments also included a non-treated check for comparison.  Response of deertongue to herbicidal treatments was similar for both sites; therefore, data were pooled across locations.  Fluazifop applied once or thrice did not injure fine fescue more than commercially acceptable levels (<30%).  At 13 weeks after initial treatment (WAIT), glyphosate containing treatments controlled deertongue 99% and higher than other treatments.  Fluazifop applied thrice controlled deertongue 96% and higher than fluazifop applied once (79%), topremazone (70%), imazapic (74%), and TID (78%).  All treatments injured fine fescue at both sites; however, fine fescue completely recovered from injury following all herbicides applications, except glyphosate containing treatments applied on the site under shade, by the end of growing season.  Fine fescue was injured more at the site that was under shade compared to the site that received full sunlight.  At 13 WAIT, glyphosate containing treatments injured fine fescue 55% at the site under shade and 0% under full sun.  At 13 WAIT, fine fescue did not manifest any injury following fluazifop and topremazone applications and <30% injury following imazapic and DIT applications at either of the sites.  Injury from imazapic and DIT was primarily stunting.  Data from the two studies indicate that fluazifop at 0.42 kg/ha applied thrice at 3 weeks interval provides the best selective deertongue control with excellent safety to fine fescue.  The trials will be evaluated further in spring 2015 to determine long-term deertongue control.

 


IMPACT OF APPLICATION PARAMETERS ON THE EFFICACY OF THE BIOHERBICIDE FEHEDTA. J. C. Wolfe*, J. C. Neal, C. D. Harlow; NCSU, Raleigh, NC (252)

ABSTRACT

The worldwide market for biopesticides has increased dramatically in recent years. Consumer concerns about the safety of synthetic pesticide use has generated interest in alternatives, but few natural products are available for weed control in turfgrass. FeHEDTA has recently been granted EPA registration as a bioherbicide, and is labelled for selective postemergence control of broadleaf weeds in turf. Current recommendations on application volume, dilution rates, and overall FeHEDTA dosing for effective weed control vary greatly. Further exploration into the influence of these factors is required in order to determine optimal treatment parameters for weed control with FeHEDTA.

The objectives of these studies were to evaluate the effects of spray volume and dilution on the control of broadleaf weeds with FeHEDTA. Experiments were conducted at the North Carolina State University Lake Wheeler Field Lab in Raleigh, NC, on established stands of white clover (Trifolium repens). One experiment was conducted in October of 2012 and repeated in May of 2014. Treatments included a  factorial arrangement of  four spray volumes (467, 935, 1870, 3741 L ha-1) and three dilutions (1.95, 3.9, 7.8% by volume) of a commercially available FeHEDTA formulation (Fiesta, 26.52% FeHEDTA), along with a non-treated control. A second experiment, conducted in April of 2014, evaluated a factorial combination of three spray volumes (935, 1870, 3741 L ha-1) and four product doses (2.36, 4.72, 9.44, 18.88 kg ai ha-1). All FeHEDTA treatments were re-applied four weeks after an initial application. All experiments were conducted in randomized complete block designs with four replicates, and were evaluated weekly for percent weed control and percent white clover cover. Data were subjected to ANOVA and means were separated using Fisher’s protected LSD (p=0.05).

In the first experiment, control of white clover increased with increases in spray volume and concentration, with no interaction between these factors. This data suggested that increased product dose improved control regardless of spray volume or dilution. The second experiment tested this assumption. At all rating dates, identical doses of FeHEDTA resulted in similar reductions in white clover cover regardless of spray volume.

These findings indicate that the efficacy of FeHEDTA is not influenced by spray volume or concentration, but overall dose of FeHEDTA is significant. Further, this data suggests that optimal control of moderately susceptible weeds such as white clover can be obtained with two applications of FeHEDTA at 9.44 kg ai ha-1. Additional studies are required to determine the rates required to control other weed species.


OCCURRENCE OF ARABLE WEEDS ALONG ROADSIDES IN EASTERN ARKANSAS. N. E. Korres*1, J. K. Norsworthy1, M. V. Bagavathiannan2; 1University of Arkansas, Fayetteville, AR, 2Texas A&M University, College Station, TX (253)

ABSTRACT

The occurrence of 36 arable weed species across 13 counties in the Eastern Arkansas Mississippi Delta area on 489 randomly selected road sites was surveyed in 2012. Species occurrence at and within sampling site and species distribution across surveyed counties, provided a qualitative comparison among survey sites among and across counties after raw data were filtered and processed. Nominal logistic regression was used to identify the most important roadside parameters affecting weed infestations in the surveyed area. Among the thirty-six species recorded, Palmer amaranth (Amaranthus palmeri), johnsongrass (Sorghum halepense), large crabgrass (Digitaria sanguinalis), barnyardgrass (Echinochloa crus-galli), prickly sida (Sida spinosa), and broadleaf signalgrass (Urochloa platyphylla) were the top six weed species, occurring at 313, 294, 261, 238, 176, and 136 sites, respectively. Weed species, road side topography (i.e. road shoulder, field shoulder, and road ditch), ditch slope, nearby land use and road type were the most important parameters that affect weed occurrence. More particularly, weed species differences significantly affected weed occurrence. Barnyardgrass, johnsongrass, and Palmer amaranth were 3.6 to 4.3 times more likely to occur than all other species recorded indicating an equal chance for these species to co-exist in surveyed sites. Weed occurrence on road shoulders was 8.0 and 3.1 times more likely than along field shoulders or the ditch, respectively. Similarly, weed occurrence on field shoulders was 2.6 times more likely to happen than in ditches. Differences in weed occurrence among various types of roadside topography may be a function of microenvironments. Differences in weed occurrence were observed among ditches of variable slope. More particularly, ditches with moderate to steep slopes were more suitable habitats for barnyardgrass, johnsongrass, and Palmer amaranth than those of shallower slope. Occurrence of these species was six times more likely (0.60) on these steep ditches compared to those of shallower slope (0.1). Differences in weed occurrence among arable (i.e. soybean, cotton, corn, rice, grain sorghum, winter wheat) and non-arable crop land uses (i.e. residential, pastoral, and natural) were detected such as that weeds in sites adjacent to arable land were 1.9 to 2.8 times more likely than along non-arable land. Weed species occurrence near a gravel or a paved road are 1.2 times more likely than a state highway because there is little effort to maintain less traveled roads. Weed occurrence near dirt roads, although not statistically different, was recorded in lower levels compared to paved or gravel roads. The information revealed in this survey can be an invaluable source for developing effective weed management programs for Eastern Arkansas roadsides.


VALIDATION OF A MODEL TO SIMULATE HERBICIDE RESISTANCE EVOLUTION IN BARNYARDGRASS IN RICE-SOYBEAN PRODUCTION SYSTEM. M. V. Bagavathiannan*1, J. K. Norsworthy2, K. L. Smith3, P. Neve4; 1Texas A&M University, College Station, TX, 2University of Arkansas, Fayetteville, AR, 3Cheminova, Groveton, TX, 4Rothamsted Research, Harpenden, England (254)

ABSTRACT

Barnyardgrass (Echinochloa crus-galli) is the most problematic grass weed in rice-soybean production systems of the midsouthern US. Resistance has been widespread in this species to a number of commonly used rice herbicides, leaving only a few alternative herbicide modes of action for effective management. It is imperative that the available herbicides are preserved through integration of diverse, non-chemical strategies. A model was recently developed to simulate simultaneous evolution of resistance to ALS-and ACCase-inhibiting herbicides in barnyardgrass and develop best management practices for integrated resistance management. Subsequently, field experiments were conducted in Keiser, AR from 2012-2014 in an attempt to validate the robustness of model predictions. The experiment was conducted in split-plot arrangement with crop rotation (two levels: rice-rice-rice and rice-soybean-rice) as the main-plot factor and herbicide programs (three levels: Non-ALS program; ALS-only program; and a program tested in the model) as the sub-plot factor. One thousand ALS-inhibitor-resistant barnyardgrass seeds were introduced to each plot and the barnyardgrass population dynamics was monitored over the three-year period. Specifically, barnyardgrass density and seed production were estimated from four 1 m2 quadrats at the end of each season and residual seedbank size was estimated in the following spring. The measured variables are being used for model validation. 


ROLE OF ANTI-OXIDANT MACHINERY IN CONFERRING GLYPHOSATE RESISTANCE TO AMARANTHUS PALMERI. A. S. Maroli*1, V. K. Nandula2, N. Tharayil1; 1Clemson University, Clemson, SC, 2USDA, Stoneville, MS (255)

ABSTRACT

Metabolomics, a comparatively new field, provides a broader scope in understanding the functioning of a physiological system that works towards quantifying small molecules in a dynamic framework of the metabolome. Identification of the metabolites that confer the tolerance to biotic and abiotic stresses have directed the development of genetically modified plants with desired traits. Unlike other fields, application of metabolomics in weed science have not been extensively pursued. In this study, we employed metabolomic profiling and biochemical assays to identify metabolite-level perturbations induced in glyphosate susceptible (S-biotype) and glyphosate resistant (R-biotype) Amaranthus palmeri. Metabolomic profiling using GC-MS identified more than 90 unique low molecular weight metabolites and Principle component analysis (PCA) performed on the identified metabolites showed a significant clustering of these metabolites based on the biotype and treatments. Hierarchical clustering analysis grouped the R- and S-biotypes into distinct clusters and within each biotype-clusters the metabolic profile of water-sprayed control was significantly different from that of the glyphosate treatment. Most of the organic acids (such as succinic acid, glyceric acid, malonic acid, citric acid etc.) and aromatic amino acids were higher in the R- biotype while the S-biotype showed a higher abundance of sugar metabolites (glucose, sucrose, fructose, talose etc.) and branched chain amino acids. Another observation was that glyphosate excerts its effects on the shikimate pathway within 8 hours after treatment (HAT) in both the S- and R- biotypes. This is indicated by the accumulation of shikimic acid in both the glyphosate treated S- and R- biotypes at 8HAT, indicating that EPSPS in both biotypes are susceptible to inhibition by glyphosate. However, compared to the 8 HAT, at 72 HAT the accumulation of shikimic acid decreased by 82% in R- biotypes, while the shikimate concentration increased by 11 fold in S-biotype. While the continued accumulation of shikimic acid in S-biotype is an indication of loss of feedback control of the shikimate pathway, the significant decrease in SA levels in R-biotype is an indication of delayed resistance mechanism acting in this R-biotype. 

Furthermore, biochemical assays on lipid peroxidation and glutathione reductase enzyme activity showed that R-biotype had lower ROS damage than the S-biotype. Compared to R-biotype, the glyphosate treated S-biotype accumulated 49% higher levels of malondialdehyde (MDA), an end product of lipid peroxidation, after 72 HAT. Reduced levels of MDA accumulation in the glyphosate treated R-biotype could indicate the up-regulation of enzymes and compounds which can effectively quench the free radicals. In plants, the glutathione reductase (GR) enzyme system comprising of oxidized glutathione disulfide (GSSG) and its antioxidant compound, glutathione (GSG) serves as the major anti-oxidant machinery. Increased activity of GR results in increased production of GSG. In the R- biotype there is a 52% reduction in NADPH levels, an indication of accelerated NADPH consumption and thereby increased GR activity. In comparison, the S- biotype showed no significant change in GR activity on exposure to glyphosate despite a higher level of oxidative damage as indicated by the accumulation of MDA, which highlights the inability S-biotypes to quench the free radicals thus validating the metabolomic profiling observations.

It is thus imperative that metabolomic profiling in conjunction with biochemical assays shows that though the primary site of action of glyphosate is the shikimate pathway, glyphosate induced metabolic perturbations is not limited to this pathway alone as most of the measured metabolite changes occur in the linked pathways of glycolysis, oxidative pentose pathway (HMP shunt) and the tricarboxylic acid (TCA) Cycle. Accumulation of metabolites having a role reactive oxygen scavenging pathways and depletion of anti-oxidant metabolites in the in the R-biotypes indicates that glyphosate resistance in these R-biotype could be due to increased ROS scavenging efficiency. Thus the general metabolic responses across the biotypes highlights the robustness of metabolomics approach not only in identifying the differential physiological response of  S- and R- biotypes to glyphosate, but also in differentiating the inherent metabolism of R- and S-biotypes even in the absence of herbicidal stress.

 


DIFFERENCES IN FINAL BIOMASS AMONG GLYPHOSATE-RESISTANT AND GLYPHOSATE-SUSCEPTIBLE MATERNAL FAMILIES OF CONYZA CANADENSIS IN OHIO: A PILOT FIELD EXPERIMENT. Z. T. Beres*, A. A. Snow, J. T. Parrish; Ohio State University, Columbus, OH (256)

ABSTRACT

To date, over 30 weed species have evolved resistance to glyphosate, which is considered to be the most commonly used herbicide worldwide. However, few studies of glyphosate-resistant (GR) species have tested for fitness costs, or even benefits, of GR in the absence of exposure to this herbicide. This information is needed to anticipate the continued spread and persistence of GR biotypes over time. Conyza canadensis (horseweed) is a self-pollinating, annual weed that was reported as GR in Ohio starting in 2003. Here, we compared the performance of maternal families with different levels of GR in a common garden experiment. We focused on individual maternal families, rather than pooled samples from many families, because some populations may represent mixtures of susceptible and resistant plants. Initially, we screened progeny of one maternal plant from each of 88 populations in southwest or northeast Ohio for resistance (see Poster #85). Approximately half of these biotypes (i.e., maternal seed families) were collected from no-till soybean fields in the fall of 2013, and the other half came from nonagricultural habitats. Rosettes of each biotype were screened for percent survival after treatment at three dosages: 1X (=0.84 kg ae glyphosate/ha), 8X, and 20X, along with 0X controls. Based on a threshold of 80% survival at each dosage, these biotypes were ranked as susceptible (S), resistant (R), highly resistant (HR), or extremely resistant (ER; i.e., 80% survival at 20X). We then selected the 19 least resistant and 21 most resistant biotypes from the sampled populations, for a total of 40 biotypes to be compared in the common garden experiment. Eight of these biotypes were scored as S, 11 as R, two as HR, and 19 as ER. The experiment was established at two nearby, recently tilled fields, each with a randomized block design and 20 replicate plants per biotype, in Columbus, Ohio, in 2014. Performance was evaluated by recording survival, rosette size at four weeks after germination, days to bolting, days to flowering, final height, and biomass. We also recorded the timing and occurrence of pathogen damage, which was common; heavily damaged plants were excluded from other statistical analyses. Data analyses are ongoing and will be reported in the presentation. Initially, it appears that several of these biotypes showed statistically significant differences in the measured traits. We did not see clear differences due to varying levels of resistance, although sample sizes were limited in some cases.


EFFECT OF WATER STRESS ON GROWTH AND SEED PRODUCTION OF GLYPHOSATE-RESISTANT AND –SUSCEPTIBLE COMMON WATERHEMP. D. Sarangi*1, S. Z. Knezevic2, J. Lindquist3, S. Irmak1, A. J. Jhala4; 1University of Nebraska, Lincoln, NE, 2University of Nebraska, Concord, NE, 3University of Nebraska-Lincoln, Lincoln, NE, 4University of Florida, Lake Alfred, FL (257)

ABSTRACT

Glyphosate-resistant common waterhemp (Amaranthus rudis Sauer) is one of the most commonly encountered and troublesome weeds in Midwestern United States. Being a C4 weed with rapid growth habit, prolific seed production ability and long-term seed viability; common waterhemp is considered a highly competitive weed species having considerable detrimental effects on crop yields. Generally, C4 plants have higher water use efficiency (WUE) and production potential that allows them to grow successfully in a wide range of climatic gradients. Adverse climatic conditions such as drought may affect common waterhemp growth and fecundity; however, there is no information available on response of common waterhemp to water stress conditions. Greenhouse experiments were conducted at the University of Nebraska-Lincoln in 2013 and 2014 to determine the effect of degree and duration of water stress on the growth, development, and fecundity of common waterhemp and to compare the responses of glyphosate–resistant and –susceptible biotypes under water stress conditions. Results indicated that glyphosate–resistant and –susceptible common waterhemp biotypes responded similarly (P>0.05) under water stress situations and the treatment-by-year interaction was non-significant; the data from both the biotypes and both the years were combined and presented. With different degrees of water stress, the common waterhemp plants that received water equivalent to 100% of field capacity produced the highest aboveground biomass (72 g plant-1) and seeds (>34,000 seeds plant-1), whereas the most stressed plants (received water equivalent to 12.5% of field capacity) produced comparatively less amount of aboveground biomass (15 g plant-1) and no seeds. Plant height, leaves per plant, growth index, total leaf area and root biomass were reduced sharply with increasing degree of water stress. The results from another experiment to determine the effect of duration of water stress on common waterhemp suggested that the 10-d interval of water stress reduced aboveground biomass by 51% when compared with the 2-d water stress interval; whereas, the plants produced a considerable number of seeds (>7,000 seeds plant-1) with the 10-d interval. The results of this study showed that common waterhemp can grow and produce substantial amount of biomass and seeds even under extreme water stress conditions like 25% of field capacity or 10-d interval of water stress. Therefore, effective weed management strategies are necessary to minimize weed-crop competition for limited available water.


QUANTIFYING WEED SEEDBANK DENSITY EFFECTS ON PENDIMETHALIN CONTROL OUTCOMES. B. J. Schutte*, A. Cunningham; New Mexico State University, Las Cruces, NM (258)

ABSTRACT

Pendimethalin control failures on tall morningglory are critical shortcomings in weed control programs for chile pepper production in New Mexico.  Using both pendimethalin application rates labeled for chile pepper production and a seedbank augmentation experimental approach, we conducted field studies to: 1) determine pendimethalin efficacy responses to increasing population density in tall morningglory seedbanks, and 2) identify weed community factors that influence labor efforts for eliminating weed escapes from pendimethalin.  Field studies were complimented with a growth chamber study conducted to clarify the effects of pendimethalin application rate on the association between tall morningglory seedbank density and pendimethalin efficacy.  Following square-root transformations of the dependent variable, effects of seedbank density (tall morningglory seeds m-2) on the frequency of pendimethalin control failure (tall morningglory plants m-2) were described with natural logarithmic functions.  Although pendimethalin control failures generally increased in response to increasing seedbank density, tall morningglory seedbank density influenced labor efforts for eliminating escapes only at a site-year characterized by low population densities in ambient weed communities.  In growth chambers, the likelihood of control failure for each additional seed in the seedbank decreased as pendimethalin application rate increased from 0.5 kg ai ha-1 to 1.6 kg ai ha-1.  The results of this study indicate that pendimethalin control outcomes in chile pepper production can be improved by reducing population densities in tall morningglory seedbanks.  More broadly, the functional relationships for seedbank density effects on weed control outcomes may facilitate the adoption of tactics that target weed seedbanks.


CROPPING SYSTEMS AND THE PREVALENCE OF GIANT RAGWEED (AMBROSIA TRIFIDA L): FROM THE 1950'S TO PRESENT. E. R. Page*, R. E. Nurse; Agriculture and Agri-Food Canada, Harrow, ON (259)

ABSTRACT

Giant ragweed has become an increasingly important weed of arable land in many parts of North America. Although it has historically been considered a weed of roadsides, fence rows and ditches, the prevalence of giant ragweed in Ontario agriculture has increased over the past half-century. While the development of resistance to Group 2 and 9 herbicides has certainly contributed to recent difficulties in controlling giant ragweed populations, it is unclear what other factors may have impacted the preceding increase in the prevalence of this species in arable lands.  The objective of this research was to examine the effect of changes in cropping systems practices over the past 50yrs on the fecundity of giant ragweed in maize and soybean.  Three eras of cropping systems practices (i.e., the 1950s, 1980s and 2000s) were established using historic soybean varieties and maize hybrids that were seeded and fertilized at the plant population densities (PPD) and rates recommended for their respective time periods.  Giant ragweed seedlings were transplanted into these eras at a density of 2 plant m-2 at crop emergence and 14 days after.  The fecundity of giant ragweed in maize declined by 54% from the 1950s to the 2000s. In contrast, giant ragweed fecundity in soybean remained the same across eras.  Results of this study suggest that, while increases in the plant population density of maize has decreased the in-crop fecundity of giant ragweed over the past half -decade, the combination of soybeans’ poor competitiveness with giant ragweed and the increase in soybeans acreage from the 1950s to present has likely contributed to the increased frequency with which giant ragweed is observed in present day cropping systems.      


CROP SPECIES AND SEEDING RATE EFFECTS ON LIGHT QUALITY AND WEED POPULATIONS. K. N. Harker*, J. T. O'Donovan; Agriculture & Agri-Food Canada, Lacombe, AB (260)

ABSTRACT

Light quality can influence weed emergence and growth as well as weed-crop competition outcomes.  A direct-seeded experiment to determine crop canopy effects on light quality and weed germination and growth was conducted at Lacombe, Alberta from 2012 to 2014.  Barley, canola, field peas and wheat were seeded at two rates.  No in-crop herbicides were applied.  Weed emergence and crop biomass were determined weekly until canola canopy closure.  Light quality near the soil surface was determined at the same weekly intervals using a spectroradiometer.  Green foxtail (Setaria viridis) (2013-14 only), henbit (Lamium amplexicaule) and shepherd’s-purse (Capsella bursa-pastoris) populations were sufficient for data collection.  Barley usually produced the greatest crop biomass.  However, at canopy closure, the crops leading to the least red light and the most far red light near the soil surface were: canola > barley > wheat > field pea.  In terms of causing the lowest weed biomass, crops were also ranked in the same order.  Weed emergence results were much more variable and did not always align with light quality and weed biomass data.  Our hypothesis that barley would be the most competitive crop and produce a crop canopy environment least favourable for weed growth was rejected. Given the relatively cool, high moisture conditions that often prevail at Lacombe, similar studies at other locations in different environments would likely prove interesting.

 


KIN RECOGNITION AND THE POTENTIAL TO INFLUENCE COMPETITIVE INTERACTIONS IN CROPS. G. P. Murphy*, R. C. Van Acker, I. Rajcan, C. J. Swanton; University of Guelph, Guelph, ON (261)

ABSTRACT

Intraspecific competition is a key process that has a high impact on plant yield. In recent years, it has been shown that plants can recognize the identity of their neighbors and behave differentially towards siblings and strangers. So far, most evidence of kin recognition in plants has come from experiments on wild species that show high genetic diversity. However, with the exception of a single study in rice, there is no evidence of kin recognition in crop species. Here, we investigated responses of wild (Glycine soya) and commercial soybean (Glycine max) to growing with siblings and strangers. We found that wild soybean plants were more elongated and allocated more carbon to stems when growing with strangers. However, when growing with siblings, wild soybeans were less elongated and allocated carbon to leaves and roots at the expense of stems. These results suggest a less competitive aboveground behavior towards siblings consistent with kin selection theory. In contrast, commercial soybean plants displayed no differential behavior towards siblings and strangers suggesting either an inability to distinguish neighbor identity or insufficient genetic diversity among varieties to trigger a response. Further elucidating how soybeans respond to neighbor identity is paramount, since kin recognition influences plant intraspecific competition and ultimately final yield. 

 


TRANSCRIPTIONAL ANALYSES OF SWEET CORN COMPETITION. E. Choe, M. M. Williams II*; USDA-ARS, Urbana, IL (262)

ABSTRACT

A molecular basis of how corn tolerates plant competition may lead to improvements in crop productivity.  Our objectives were to 1) explore gene expression patterns among sweet corn hybrids grown under elevated competition, and 2) identify linkages between phenotypic responses and gene expression patterns. Grown under conditions of elevated, intraplant competition, three competition-tolerant hybrids and three competition-sensitive hybrids were grouped for transcriptional and phenotypic analyses. Transcriptional analyses identified from 426 to 937 differentially expressed genes (DEGs) for each hybrid. Large gene expression pattern variation among hybrids and only 31 common DEGs across all hybrid comparisons were identified, suggesting each hybrid has unique mechanisms in response to competition. Biological functions of DEGs were similar among competition-tolerant hybrids, with large percentages of up- and down-regulated DEGs in enzyme families and proteins. Biological functions of DEGs varied more among competition-sensitive hybrids. Clusters of genes (modules) were significantly different between tolerant and sensitive groups. Correlation and cluster analyses of modules and phenotypic response showed strong positive association 1) between yield traits and modules with up-regulation in competition-tolerant hybrids, and 2) between plant traits and modules with down-regulation in competition-tolerant hybrids. Functional analysis of modules and common DEGs identified candidate mechanisms for sweet corn tolerance to competition, including transcription regulation, DNA structure, cell wall degradation, hormone synthesis, glycolysis, and polyamine-involved primary metabolic pathways.

 


GROWTH CHARACTERISTICS OF A WEED-SUPPRESSIVE INDICA X NON-SUPPRESSIVE TROPICAL JAPONICA RICE MAPPING POPULATION. D. R. Gealy*, Y. Jia, S. Pinson; USDA-ARS, Stuttgart, AR (263)

ABSTRACT

Growth Characteristics of a Weed-suppressive Indica x Non-suppressive Tropical Japonica Rice Mapping Population. D. R. Gealy*, Y. Jia, S. Pinson; USDA-ARS, Stuttgart, AR

The indica rice cultivar, PI 312777, can be highly productive as well as suppressive to C4 grass species such as barnyardgrass (Echinochloa crus-galli).  A recombinant inbred line (RIL) mapping population was developed using single seed descent from a cross between ‘Katy’ (non-weed-suppressive) and PI 312777 (weed-suppressive, allelopathic) for the purpose of identifying the genetic basis of weed suppression.  Two replications of 15 seeds each of 350 RILs from the mapping population (F7 generation) were drill-seeded in the field in 1.5 m-long, single-row plots spaced 0.6 m apart. Nitrogen fertilizer was broadcast at a rate of 110 kg ha-1 as urea before application of the permanent flood, and plots were maintained weed-free using commercial herbicides. Transgressive variation was observed among several phenotypic traits that can be associated with weed suppression.  These included plant height, tiller number, tillering angle (plant type), and days to heading.  Five weeks after emergence, the heights of PI 312777 and Katy were 41 and 50 cm, respectively, and the RIL heights ranged from 20 to 69 cm. In a subjective rating of tiller number, where the value for Katy was 1 (few tillers) and the value for PI 312777 was 5 (many tillers), the RILs ranged from 1 to 6. Using the protocol of the International Rice Research Institute to determine tiller angle, where a value of 1 is the most erect and a value of 7 is the most prostrate, the RILs ranged from 1 to 7, and the value for both Katy and PI 312777 was 3. In the late season, maximum plant heights of PI 312777 and Katy were 92 and 108 cm, respectively, and the RIL heights ranged from 60 to 169 cm.  Late season tiller angle values for Katy and PI 312777 were 1 and 3, respectively, and the RILs ranged from 1 to 7.  Heading for PI 312777 and Katy was 92 and 91 days after emergence, respectively, and ranged from 60 to 139 days for the RILs.  These results will help identify rice genotypes that optimize both weed suppression and crop productivity for reduced-input systems.  A subset of these RILs will be selected based on contrasting phenotypes, evaluated in weed-suppression experiments in the field and greenhouse, and analyzed using QTL mapping.   


CONNECTIONS ARE EVERYTHING: INFLUENCE OF HOST SPECIES ON MRNA EXCHANGE BETWEEN DODDER AND ITS HOSTS. G. Kim, J. Westwood*; Virginia Tech, Blacksburg, VA (264)

ABSTRACT

Recent studies indicate that RNA trafficking takes place between parasitic plant Cuscuta pentagona and its hosts.  RNA movement between Arabidopsis and Cuscuta appears to occur on a large scale as well as in a bidirectional manner.  Similar studies using tomato hosts indicated that RNA movement was more limited in this interaction.  Given the characteristic ability of Cuscuta to attack a wide range of hosts, it is important to characterize RNA movement in a broader range of host-Cuscuta combinations. We generated transcriptome data via Illumina sequencing from Cuscuta stems near the point of attachment to Arabidopsis, tomato, Medicago and beet hosts. Analyses demonstrated that Arabidopsis-Cuscuta connections are clearly the most efficient in allowing haustorial transfer of host transcripts, whereas tomato, Medicago and beet hosts showed fewer transcripts moving. This experiment also provided insight into Cuscuta gene expression near the point of attachment. Most parasite genes were expressed consistently regardless of host being attacked, as exemplified by genes related to cell wall modification, which were expressed in all interactions.  However, Cuscuta also expressed smaller subsets of genes in patterns that were specific for each different host. Taken together, these results indicate that Cuscuta interacts with each different host in a specific manner. 

 


DOES PREVIOUS ATRAZINE HISTORY ENHANCE ATRAZINE DEGRADATION IN US SOILS? T. C. Mueller*1, W. S. Curran2, R. Scott3, C. Sprague4, D. Stephenson5, D. Miller6, E. Prostko7, W. Grichar8, J. Martin9, L. Krutz10, K. Bradley11, L. E. Steckel12, M. L. Bernards13, M. D. Owen14, P. A. Dotray15, R. Currie16, S. A. Clay17, S. Z. Knezevic18, V. M. Davis19, R. Klein20; 1University of Tennessee, Knoxville, TN, 2Penn State University, University Park, PA, 3University of Arkansas, Lonoke, AR, 4Michigan State University, East Lansing, MI, 5LSU AgCenter, Alexandria, LA, 6Louisiana State University, St. Joe, LA, 7University of Georgia, Tifton, GA, 8Texas A&M AgriLife Research, Lubbock, TX, 9University of Kentucky, Princeton, KY, 10Mississippi State University, Stoneville, MS, 11University of Missouri, Columbia, MO, 12University of Tennessee, Jackson, TN, 13Western Illinois University, Macomb, IL, 14Iowa State University, Ames, IA, 15Texas Tech University, Texas A&M AgriLife Research and Extension Service, Lubbock, TX, 16Kansas State University, Manhattan, KS, 17SDSU, Brookings, SD, 18University of Nebraska, Concord, NE, 19University of Wisconsin, Madison, WI, 20University of Nebraska, North Platte, NE (265)

ABSTRACT

The literature suggests that atrazine dissipation in surface soils can be more rapid once microbes adapt to the presence of the triazines.  This research surveys soils from across the corn growing  region in the United State to determine how widespread this enhancement is at this time.  A sub-sample of each soil was dried and shipped to MidWest Labs in Omaha, Nebraska.   Each sample was assessed for various soil parameters including nutrient levels, OM, and texture.

Each soil was examined using the following procedure.  A portion of each soil sample was placed into a 500 mL Styrofoam Squat cup in which 5 holes have been placed.  Add water to each sample to saturate the soil.  Allow to drain for 24 hours.  Place ~ 5.0 grams of each soil into a 20 mL glass vial for later atrazine fortification.  This established each soil at a moist, near field-capacity status.

Each vial was then fortified with an aqueous atrazine solution that was incubated at a constant temperature for a time course is -1, 0, 3, 7, 14, 21, 28 and 42, with duplicate samples of each.  The -1 DAT sample is to quantify any residual atrazine or metabolite. Subsequent analysis showed few detections of atrazine in any of the soil samples.  Each vial was stored in a freezer at the appropriate DAT, and all samples within an experiment analyzed at the same time by adding methanol, shaking, filtration, and analysis on LC-MS.  Lab analysis determined parent and the 3 major metabolites simultaneously, with adequate recoveries.  All soils had similar recovery, with initial atrazine concentrations being ~ 2200 ppb .

Since we are only looking at fields with 0 or 5+ years of atrazine use, we are seeing if enhanced atrazine degradation is a widespread, region-wide phenomenon, and not determining how many years of exposure are needed for the enhancement.  Another factor not considered is the atrazine use rate, which varies depending on the region of the country.  Enhanced atrazine degradation was observed in most states, with enhancement indicating reduced residual weed control where atrazine was used in multiple consecutive years.


THE EFFECT OF PH ON AMICARBAZONE PERSISTENCE IN AEROBIC SOILS. K. Ahmed*, T. Gannon, M. Jeffries; NCSU, Raleigh, NC (266)

ABSTRACT

Amicarbazone is a selective triazolinone herbicide (photosystem-II inhibiting) for PRE/POST annual grass and broadleaf weed control and was first registered in 2005 in corn (Zea mays L.). In 2012, it was registered to include field plantings (soybeans and Christmas trees) and turfgrass (golf courses, sod farms, residential and commercial turfgrass sites, parks, and recreational areas). It is moderately persistent in acidic soils but breaks down slowly in alkaline soils. Current product labels prohibit application if soil pH is greater than 7.4 due to formation of an eco-toxicologically concerning metabolite. Previous research suggest field half-life ranging from < 24 hr to 50 d. The objective of this research was to determine the effect of pH and soil texture on amicarbazone persistence.       

Two experimental runs of laboratory experiments were conducted to determine the effect of soil pH and texture on amicarbazone persistence in aerobic soils. A combination of two pH [(acidic; 4.8-4.9) or (alkaline; 7.2-8.2)] and three soil textures [loam (Drummer; Savory, IL); sandy loam (Lubbock; Lubbock, TX); or sandy clay loam (Cecil; Raleigh, NC)] were included in each experiment. The sandy clay loam was naturally acidic (pH 4.9) while the loam and the sandy loam were alkaline (pH 7.2 and 7.7, respectively). Soils were sieved, dried, milled, and pH was adjusted appropriately and allowed to stabilize. The acidic (Cecil) and two alkaline (Drummer and Lubbock) soils were evaluated, as well as each respective soil with pH adjusted to the alternate pH range to determine the effect of texture and pH on amicarbazone persistence.

Experiment one investigated amicarbazone persistence: 25 g of each soil was placed in a wide mouth 240 mL amber high density polyethylene bottle and spiked with amicarbazone (14 ppm) and samples were shaken vigorously to ensure distribution. Tap water was added to each vessel to obtain 75% field capacity and maintained throughout the experiment; bottles remained closed during the day and open overnight to ensure aerobic conditions and prevent photolysis. At sampling times, bottles were removed and stored at -18 °C until analysis. Eleven sampling times (0, 1, 2, 7, 14, 21, 28, 42, 56, 84, and 126 d after treatment) were included. The entire sample was extracted with 170 mL methanol: water: acetic acid 80:19:1% v v-1, extract was cleaned-up and amicarbazone residues were quantified with high performance liquid chromatography with diode array detection methodology. 

Experiment two investigated amicarbazone adsorption: 10 g of each soil was placed in a 50 mL amber centrifuge tube and spiked with amicarbazone (14 ppm) and samples were shaken vigorously to ensure distribution. 30 min later, 30 mL water was added to each tube and were closed and placed on a horizontal shaker. After 10 hr, tubes were opened for one min and reclosed to ensure aerobic conditions. After 24 hr, all samples were collected and centrifuged at 3500 rpm for 15 min. The liquid was separated from the soil and both subsamples were stored at -18 °C until analysis. All liquid samples were cleaned–up, diluted, and injected, while soil samples were extracted with 60 mL methanol: water: acetic acid 80:19:1% v v-1. Amicarbazone residues were quantified as previously described. Amicarbazone parent was detected with wavelength of 221 nm and retention time of 1.98 min out of 3.5 min run in C-18 column with isocratic elution.

These data indicate that amicarbazone persistence varies widely with pH and texture.  Amicarbazone is more persistent in alkaline compared to acidic soil pH ranges. Further, amicarbazone persistence increased in sandy clay loam, loam, and sandy loam textures, respectively. Adsorption data indicate that varying persistence across texture and pH was not solely due to differential adsorption. Adsorption distribution coefficients (Kd) suggest that amicarbazone adsorption by sandy loam was slightly different from loam and sandy clay loam. Results of this research indicate inconsistent amicarbazone efficacy (weed control and plant tolerance) may be explained in part by pH variations across application sites. Additional research is needed to examine additional soil textures and pH ranges as well as elucidating specific mechanisms of degradation under each scenario.


THE EFFECT OF SOIL MOISTURE CONTENT AT TREATMENT ON LATERAL HERBICIDE MOVEMENT. T. Gannon*, M. Jeffries, D. Mahoney; NCSU, Raleigh, NC (267)

ABSTRACT

Off-target injury into ecologically sensitive areas following herbicide application is concerning from human and environmental health perspectives.  Some herbicide labels define concerns around soil moisture prior to, and rainfall following application with respect to product efficacy; however, most labels do not describe the effect of soil moisture with respect to off-target movement and subsequent injury.  While the effect of soil moisture on herbicide leaching has been researched and issues in and around sensitive areas have been reported, its effect on subsurface lateral herbicide movement has not been reported.  The objective of this research was to determine the effect of soil moisture content, at application, on subsurface lateral herbicide movement.

Field research (Raleigh, NC) was conducted summer, 2014 to elucidate the effect of soil moisture content, at application, on subsurface lateral herbicide movement.  White clover (Trifolium repens L.) plots (1.5 x 1.5 m) were established downslope of ‘Tifway 419’ bermudagrass (Cynodon dactylon L. x C. transvaalensis; 2.5 cm height of cut) plots (1.5 x 1.5 m).  Soil type was a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludults).  Each bermudagrass/white clover plot represented a unique soil volumetric water content (VWC) condition at herbicide application including saturated (48% ± 2%), field capacity (35% ± 3%), and wilting point (15% ± 2%).  Herbicides evaluated included aminocyclopyrachlor (AMCP; 105 g ae ha-1), metsulfuron-methyl (MET; 42 g ai ha-1) and fluroxypyr (FLUR; 210 g ai ha-1).  The selected herbicides have all previously caused off-target plant injury and have physicochemical properties suggesting lateral movement potential ranks AMCP = MET > FLUR.  Further, white clover is susceptible to all three herbicides.  Following a 2 wk soil VWC adjustment period, herbicides were applied with a CO2-pressurized sprayer (four 11004 AI XR nozzles) calibrated to deliver 746 L ha-1.  Following a 4 h drying period, one pore volume of irrigation (3.3 cm H2O) was applied to the trial area in 2.5 h to prevent runoff, as the research focused on subsurface movement.  Data collection included: visual cover (0 – 100% scale; where 0 = no cover and 100 = complete cover) and injury estimations (0 – 100% scale; where 0 = no injury and 100 = complete death); normalized differenced vegetation index (0 – 1); and plant-intersect grid counts (11 x 14 with 10 cm spacings) at 2, 4 and 6 wk after treatment (WAT).  Further, at 6 WAT total aboveground clover vegetation was harvested (0 – 0.3, 0.3 – 0.6, 0.6 – 0.9, 0.9 – 1.2 and 1.2 – 1.5 m downslope from the treated area) to quantify herbicide movement within a plot.  Three replicates of each soil moisture-herbicide combination were arranged in a completely randomized split plot design, with plots split on herbicide.  Data were subjected to ANOVA (P = 0.05) and means were separated according to Fisher’s Protected LSD (P < 0.05).

Data suggest VWC at application differentially affected subsurface lateral movement of the evaluated herbicides.  Across VWCs for FLUR, white clover cover reduction at 6 WAT was < 5%.  White clover cover reduction increased as VWC increased in areas downslope of both AMCP and MET treatments.  Metsulfuron applied at 15, 35 and 48% VWCs caused 3, 32 and 52% white clover cover reduction 6 WAT; while AMCP applied at the aforementioned VWCs caused 25, 46 and 93% cover reduction, respectively.  Further, visual estimations of white clover cover were very strongly positively correlated with plant-intersect grid counts at 6 WAT (r = 0.99; P < 0.0001).  Finally, white clover biomass reduction at 6 WAT aligned with cover reduction.  Across all herbicides applied at 15% VWC, clover biomass was reduced < 10% at all downslope harvest increments; while AMCP and MET applied at 48% VWC reduced biomass > 40% to 0.6 and 1.5 m, respectively, downslope from the treated area.  Implications from this research will allow turfgrass managers to define best management practices and reduce potential for off-target movement and injury.  Further, this information will preserve human and environmental health, specifically ecologically-sensitive areas, by defining problematic herbicide application timings or conditions.

 


EFFECT OF HERBICIDE MANAGEMENT STRATEGY ON N2O EMISSIONS FROM NON-CROP, CORN, AND SOYBEAN SYSTEMS. R. R. Bailey*, T. R. Butts, V. M. Davis; University of Wisconsin, Madison, WI (268)

ABSTRACT

Emissions of nitrous oxide (N2O), a potent greenhouse gas, are positively correlated with increased soil nitrate, soil moisture, mineralizable carbon, and temperature. In the absence of preemergence (PRE) herbicides, weeds compete with crops and reduce soil nitrate and moisture levels, which may reduce N2O emissions relative to a weed-free environment. However, after weeds are terminated with postemergence (POST) herbicides, emissions may increase as the weed residues encourage N cycling and increase soil moisture. To determine this relationship, three non-crop greenhouse studies, two non-crop field studies, four corn studies, and two soybean studies were conducted in 2013 and 2014 to compare the effects of PRE + POST and POST-only weed management strategies on N2O emissions before and after weed termination. All studies included the main effect of weed management strategy (weed), which was combined in a factorial treatment structure with nitrogen (N) rates of 0 or 200 kg N ha-1 (non-crop greenhouse), 0 or 225 kg N ha-1 (non-crop field), and 0, 90, or 180 kg N ha-1 (corn), or row widths of 38- or 76-cm (soybean). Gas samples were collected at least weekly from static sampling chambers, and N2O emissions from each study were evaluated for the periods before weed termination (i.e., between planting and POST application), after weed termination (i.e., from POST application to the end of the study), and for the full study duration.  N2O emissions were not influenced by weed*N in the non-crop greenhouse, non-crop field, or corn studies for any measurement period at p≤0.05, but higher N rates led to increased N2O emissions (p<0.0001) in all these studies. In the soybean study, neither weed*width nor width had a significant impact on N2O fluxes. Weeds in the POST-only treatment significantly increased total N2O emissions (p=0.0004) and emissions after termination (p=0.0003) in the non-crop greenhouse study, but otherwise weed had no significant effect in the other studies for any measurement period. Interestingly, POST-only treatments had lower emissions than PRE + POST treatments on the sampling day immediately prior to POST application in the soybean study (p=0.0002). Corn and soybean yields were higher in the PRE + POST vs. POST-only management systems (p<0.0001 for corn, p=0.0007 for soybean). These results indicate that although season-long N2O emissions were not different between PRE + POST and POST-only herbicide management strategies, use of a PRE herbicide was still important for preventing yield loss in the corn and soybean systems.

 


A NOVEL TEST SYSTEM TO QUANTIFY DIFFERENCES IN TANK CLEANER EFFECTIVENESS. T. C. Mueller*1, F. Sexton2; 1University of Tennessee, Knoxville, TN, 2Exacto, Inc, Sharon, WI (269)

ABSTRACT

With greater complexity of herbicide use patterns, tank contamination is a challenge.  The primary goal of this project was to develop an experimental test system to discern differences in commercially available tank cleaners used to clean herbicide residues from tanks/hoses/etc.  A literature search found no refereed articles on this subject.  

The tank cleaners examined in the study were provided by Exacto, a leading formulator of agricultural adjuvants.  The primary data involved chemical assays, although several greenhouse bioassays were first conducted.  The chemical assays proved to be more sensitive to treatment differences, and thus were the focus of our method development.

The spray tank mixture used in our study was flumioxazin (Valor 50 DF) mixed at a dosage of 3 oz/acre with a simulated carrier volume of 10 GPA.  Our test system used 3 liters of spray mixture in a glass, 4 L beaker that was mixed with a stir bar to fully agitate the spray solution.  The proposed test system is flexible in that any possible pesticide mixture can be examined. 

Plastic tank parts are “spotted” with a known amount of mixture and allow to dry overnight.  This provided uniform loading and this procedure is flexible, in that can be used for different tank materials, hoses, etc.  In our study, each tank part was 1 replicate or experimental unit. The tank cleaners were added to 400 ml DI water at a dosage of 0.25% v:v.  Several tank cleaners were examined.  The dried tank parts were placed in each respective tank cleaner for ~ 3 seconds; then removed and placed into 400 mL of methanol for extraction.  Each sample was compared to samples with no “tank cleaner”, and data converted to percent of this control.  Herbicide concentrations were quantified with LC-MS.  

 The study was conducted 4 times, and this data summarized over all runs (2 to 5 reps).  All treatments still had detectable flumioxazin concentrations in our LC-MS.  pH measurements and the tank cleaners were different.  Means were separated by Fisher’s protected LSD, and a range of tank cleaner responses were noted.

 The method has some opportunities for optimization since the results can be sensitive to operator, such as how long or how vigorously the tank part is agitated.  For some individual runs, the treatment differences are not big (< 6 %). The pH measurement serves as internal check for verifying proper tank cleaner treatment.  Another observation of the test system is that tank mixtures behave differently than individual products. 

 The proposed test system can determine the relative effectiveness of tank cleaners to remove pesticide residues from spray equipment.  It is flexible to examine different matrixes, pesticides, etc.  We believe tank contamination will only grow in importance as new herbicide trait technologies promote the use of different herbicides in our production systems.


A PRODUCT PORTFOLIO FOR SELECTIVE WEED CONTROL IN CORN: FLEXIBLE SOLUTIONS BASED ON VARIOUS HERBICIDE AND SAFENER ASSETS. C. H. Rosinger*; Bayer CropScience, Frankfurt, Germany (270)

ABSTRACT

It is well documented that corn requires early weed control intervention to prevent significant yield loss. In order to address this issue Bayer CropScience conducted intensive research to identify strong herbicides. However, it is also known that herbicides with a strong and broad weed control spectrum will tend to also injure the crop, specifically under challenging growing conditions. Therefore, research was also conducted into safener-based selectivity technologies for corn. The outcome of these research programs was a range of herbicide and safener assets which could be developed in various combinations in order to provide strong pre- and post-emergence weed control with good and consistent selectivity. Based on the weed control spectrum and application windows of each herbicide and the differences in safening characteristics of the safeners the products cover key corn grower requirements. This presentation will mainly use the products Laudis® (tembotrione + isoxadifen) and Corvus® (isoxaflutole, thiencarbazone and cyprosulfamide) to demonstrate the benefits of developing tailor-made solutions, combining various herbicide and safener technologies.


CHARACTERIZATION OF MULTIPLE HERBICIDE RESISTANCE IN KOCHIA ACCESSIONS FROM MONTANA. P. Jha*, C. A. Lim, V. Kumar, S. Leland; Montana State University, Huntley, MT (271)

ABSTRACT

Herbicide-resistant kochia (Kochia scoparia (L) Schrad.) is an increasing concern for growers in the Northern Great Plains of the United States, including Montana, and in the Canadian prairies. On the basis of our recent (2012) confirmation of glyphosate-resistant (GR) kochia in Montana, a random field survey was conducted in fall of 2013 to determine the distribution, frequency, and level of resistance in suspected herbicide-resistant [glyphosate-, dicamba-, and ALS-inhibitor herbicide] kochia populations from northern Montana, with characterization of mechanisms of resistance to glyphosate and ALS-inhibitor herbicides. Kochia populations (fully mature seeds) were sampled from chemical fallow-wheat fields, field edges/ fence lines, and roadsides. A total of 150 populations were included in the survey. Kochia plants were treated with a discriminating dose of the herbicide [glyphosate (1260 g ae ha-1), dicamba (280 g ae ha-1), or thifensulfuron + tribenuron + metsulfuron (18 g ai ha-1)] at the 8- to 10-cm-weed height. At 21 DAA, plant response to the herbicide application was visually scored as susceptible: dead or nearly dead, or resistant: some injury but new growth, or no injury, in comparison to herbicide-treated and untreated susceptible and resistant control populations. Further dose response studies for each herbicide was conducted in the greenhouse using the seeds obtained from the survivors of the discriminating-dose screening.  The frequency of glyphosate-resistant (GR) individuals in a population varied from 46 to 100%, with 2- to 11-fold levels of resistance to glyphosate.  ALS-inhibitor resistance (ALS-R) was found in >95% of the survey populations, with resistance frequency of 67 to 100% in a population and >30-folds level of resistance. The frequency of dicamba-tolerant individuals in confirmed populations varied from 5 to 51%. Out of the total, 4 populations were resistant to all three herbicide modes of action (GR, ALS-R, and DR), whereas >30 populations showed two-way resistance (ALS-R and DR). Results from the RT-qPCR analysis of the genomic DNA suggest that the glyphosate resistance in those Montana kochia populations were conferred by 3- to 14-folds increase in the EPSPS gene copy number compared to a susceptible Montana accession with only one copy of the EPSPS gene. For majority of the confirmed populations, resistance to the ALS-inhibitor herbicide (sulfonylurea) was conferred by a single point mutation at the Pro197 position of the ALS gene. Growers need to adopt multiple control tactics (including tillage and crop rotation) to manage the occurrence of multiple herbicide-resistant kochia in the cropping systems of this region.


DISTRIBUTION AND DOSE RESPONSE OF ALS-INHIBITING HERBICIDE RESISTANT SHATTERCANE AND JOHNSONGRASS POPULATIONS FROM KANSAS AND NEBRASKA. R. Werle*1, A. J. Jhala1, M. K. Yerka2, J. Lindquist1; 1University of Nebraska-Lincoln, Lincoln, NE, 2ARS-USDA, Lincoln, NE (272)

ABSTRACT

Traditional breeding technology is currently being used to develop grain sorghum germplasm that will be tolerant to acetolactate synthase (ALS)-inhibiting herbicides. Use of ALS-inhibitors for weed control during the 1980’s and 1990’s resulted in the evolution of resistance to ALS-inhibitors in shattercane, a weedy relative of sorghum that is prevalent in Nebraska. The objective of this study was to assess the baseline presence of ALS resistance in populations of shattercane and johnsongrass, another weedy sorghum relative. The populations were obtained from numerous locations, including where known resistance occurred in the past in Nebraska. In the fall of 2013, seeds from 190 shattercane and 58 johnsongrass populations were collected from northern Kansas, western Missouri, and southern Nebraska. In the summer of 2014, a preliminary field experiment was conducted near Mead, NE to evaluate the presence or absence of herbicide resistance in the aforementioned populations. Treatments consisted of four herbicides applied at their labeled rate: clethodim, glyphosate, imazethapyr, and nicosulfuron. Clethodim and glyphosate controlled all shattercane and johnsongrass populations evaluated. Some populations showed signs of resistance to imazethapyr and/or nicosulfuron. Putative ALS-resistant populations were further exposed to a dose-response study under greenhouse conditions. Imazethapyr and/or nicosulfuron were applied at 0, 0.5, 1, 2, 4, 8, 16, and 32 times their labeled rates (70 and 35 g ai ha-1, respectively) to 3 plants of each population 3 weeks after planting (plants were at V3-V4 growth stage). ALS-tolerant and susceptible sorghums were included as controls. Visual injury data were collected at 21 DAT and the effective dose to cause 70% visual injury (ED70) estimated using the DRC package in R. The study was conducted twice. 13.4 and 4.5 g ai ha-1 of imazethapyr and nicosulfuron, respectively, were necessary to cause 70% injury in ALS-susceptible sorghum. For imazethapyr, the ED70 of 4 shattercane and 4 johnsongrass populations were at least 2-fold greater than the one required for sorghum. For nicosulfuron, the ED70 of 8 shattercane and 2 johnsongrass populations were at least 2-fold greater than the one required for sorghum. The ED70 was used as our response variable because for some populations this was the maximum injury observed. Most of the ALS-resistant populations were collected from south-central and eastern Nebraska and north-east Kansas. Even though ALS-inhibitors have not been widely used to control shattercane and johnsongrass since the commercialization of glyphosate-tolerant crops, the resistance trait is still present in locations where resistance was reported in the 1990’s, indicating the lack of a strong fitness cost associated with ALS-resistance in weedy sorghum populations. Molecular work is being conducted to further explore the underlying mechanism of resistance. The results of this research will identify regions where shattercane and johnsongrass should be carefully managed prior to and during the commercialization of ALS-tolerant sorghum.


CORN AND GRAIN SORGHUM YIELD RESPONSE TO IRRIGATION AND WEED MANAGEMENT. B. W. Schrage*, W. J. Everman; NCSU, Raleigh, NC (273)

ABSTRACT

CORN AND GRAIN SORGHUM YIELD RESPONSE TO IRRIGATION AND WEED MANAGEMENT.  B. W. Schrage, W. J. Everman, North Carolina State University, Raleigh, North Carolina

 

ABSTRACT

 

In 2013 and 2014 a split plot experiment was conducted at the Upper Coastal Plain Research Station near Rocky Mount, NC to evaluate the impact of irrigation frequency and variety on herbicide efficacy and yield. Irrigation regimes of 2X per week, 1X per week, and no irrigation were established. Within each irrigation frequency, weed management programs of Bicep II Magnum at 3.24 kg ai ha-1 (2.1 qt/A) PRE, Bicep II Magnum PRE followed by Warrant at 0.42 kg ai ha-1 (3 pt/A) plus atrazine at 1.11 kg ai ha-1 (1 qt/A), and no herbicide treatment were applied to 2 corn hybrids (P1498YHR and P1529YHR) and 2 sorghum hybrids (84P80 and 83P17). The weed management programs were standardized to give similar levels of weed control across corn and sorghum. Hybrids were selected to represent drought tolerant hybrids for the Southeastern region.

 

2013 was an exceptionally cool and wet year. The weather dictated the necessity to irrigate, and with excessive rainfall most of the season.  There was no significant effect of irrigation on yield.  There was a significant impact of herbicide program on yield, with lowest yields observed in the non-treated plots. For most treatments, the two-pass weed management program resulted in greater yields, although for sorghum in the no irrigation, 83P17 in the 1X irrigation, and corn in the 2X irrigation greater yields were observed in the one pass weed management program. There was little difference in efficacy in 2014, although irrigation did assist in the control of Digitaria sanguinalis.

 


GRASS CONTROL IN SORGHUM AS IMPACTED BY CULTURAL PRACTICES AND WEED MANAGEMENT. T. E. Besancon*, W. J. Vincent, A. M. Knight, W. J. Everman; NCSU, Raleigh, NC (274)

ABSTRACT

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 spacings (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. 

 


TOLPYRALATE (SL-573): A NEW POST-EMERGENCE HERBICIDE FOR WEED CONTROL IN CORN. H. Kikugawa*1, Y. Satake2, D. J. Tonks3, M. Grove4, S. Nagayama5, M. Tsukamoto2; 1Ishihara Sangyo Kaisha, LTD, Osaka, Japan, 2Ishihara Sangyo Kaisha, LTD, Shiga, Japan, 3ISK Biosciences, Kearney, MO, 4ISK Biosciences, Spring, TX, 5Ishihara Sangyo Kaisha, LTD, Mie, Japan (275)

ABSTRACT

Tolpyralate (Code Number SL-573) is a new selective herbicide for weed control in corn, which was discovered by Ishihara Sangyo Kaisha Ltd. and is currently under worldwide development. Tolpyralate controls a wide range of weeds, not only broadleaves but also grasses, with excellent selectivity on field corn, seed corn, popcorn and sweet corn. The mode of action of Tolpyralate is inhibition of HPPD (4-hydroxyphenyl-pyruvate dioxygenase) enzyme which ultimately causes the destruction of chlorophyll followed by death in sensitive plants. Corn can rapidly detoxify Tolpyralate after application without being affected by weather conditions or mixture with organophosphorus insecticides, etc., which contributes to Tolpyralate’s safety to corn. As Tolpyralate is gradually decomposed in the soil after application, the effect on the rotational crops is negligible. Greenhouse tests and practical field trials carried out to date have demonstrated that Tolpyralate is a promising compound as a corn herbicide compared to the commercial standards.


TOLPYRALATE (SL-573): AN OVERVIEW OF PERFORMANCE FOR WEED CONTROL IN CORN IN THE U.S. D. J. Tonks*1, M. Grove2, H. Kikugawa3, M. Parks1, S. Nagayama4, M. Tsukamoto5; 1ISK Biosciences, Kearney, MO, 2ISK Biosciences, Spring, TX, 3Ishihara Sangyo Kaisha, LTD, Osaka, Japan, 4Ishihara Sangyo Kaisha, LTD, Mie, Japan, 5Ishihara Sangyo Kaisha, LTD, Shiga, Japan (276)

ABSTRACT

Tolpyralate (code number SL-573) is a new post-emergence herbicide being developed in the US by ISK Biosciences. It is an HPPD (4-hydroxyphenyl-pyruvate dioxygenase) inhibitor. Field trials have shown that tolpyralate is safe when applied to field corn, sweet corn, and popcorn. Tolpyralate generally controls weeds equal to or better than mesotrione, topramazone, or tembotrione. Tolpyralate + atrazine is effective for controlling many broadleaf weeds such as Amaranthus species, ragweed species, common lambsquarters, velvetleaf, kochia and cocklebur and gives good to excellent control of foxtail species and large crabgrass.  Tolpyralate is an excellent tank-mix partner with commonly used herbicides such as chloroacetamides, glyphosate, glufosinate, and dicamba.


IMPACTS OF ATRAZINE PROHIBITION ON ROUNDUP READY ADOPTION, TILLAGE, AND NUMBER OF HERBICIDE SITES-OF-ACTION USED IN WISCONSIN CROP PRODUCTION. F. Dong1, P. D. Mitchell*1, R. A. Recker2, V. M. Davis1; 1University of Wisconsin, Madison, WI, 2Monsanto, Mankato, MN (277)

ABSTRACT

The state of Wisconsin began establishing atrazine prohibition areas in 1990 and by 2011, 1.2 million acres were in these prohibition areas in which the use of atrazine is prohibited.  These areas offer a unique opportunity to examine the impact of atrazine prohibition on crop management practices.  This study examines the effects of atrazine prohibition on farmer tillage practices and investigates whether the prohibition of atrazine reduces diversity in weed management practice use and thus contributes to development of herbicide resistant weeds.  The primary data are a USDA survey of 383 Wisconsin farms growing corn, of which 105 were in atrazine prohibition areas, conducted in 2010 and focused on corn management practices.  We find that the atrazine prohibition did not affect tillage directly, but it did increase farmer adoption of Roundup Ready® seeds, which motivated more conservation tillage.  We also find that the prohibition of atrazine decreased the average number of herbicide sites-of-action used, which increases the risk of developing herbicide resistant weeds. 

 


ASSESSMENT OF WISCONSIN CROP PRODUCTION SYSTEMS WITHOUT RECENT ATRAZINE USE AND THE IMPACT TO HERBICIDE RESISTANCE MANAGEMENT. V. M. Davis*1, R. A. Recker2, F. Dong1, P. D. Mitchell1; 1University of Wisconsin, Madison, WI, 2Monsanto, Mankato, MN (278)

ABSTRACT

Herbicide-resistant weeds continue to threaten the sustainability of crop production in the US. Integrated management practices designed to avoid herbicide resistance evolution should include the use of multiple effective herbicide modes-of-action. The biggest threat of herbicide resistance impacting sustainable crop production is arguably glyphosate-resistant weeds because glyphosate has so many positive use characteristics. However, the herbicide atrazine has been used to control many small and large seeded broadleaf weeds, as well as some grass weed species, in US corn fields since the late 1950’s. There are also atrazine resistant weeds, but atrazine can still serve as an additional mode-of-action to compliment glyphosate and reduce the risk of glyphosate-resistant weed evolution. Unfortunately, atrazine use is also associated with environmental concerns including both surface and ground water contamination, and its use is prohibited in many parts of Wisconsin. The objectives of this research were i) to compare late-season weed community composition in Wisconsin corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] fields with different management, including past atrazine use and tillage. A late-season weed survey was conducted in Wisconsin corn and soybean fields in 2012 and 2013 to document weed community composition, evaluate the relative abundance of weeds in different management systems, and measure components of relative abundance including weed species frequency, uniformity, and density. The late-season weed survey revealed that in sampled fields where atrazine has not been used within the past decade, broadleaf weeds were found more frequently, (73 vs. 61%; P=0.03), they had 50% greater in-field uniformity (P=0.002), and density was 0.19 vs. 0.4 plants m-2 (i.e. 2-fold greater; P < 0.0001), in discontinued versus recent atrazine use fields, respectively. Moreover, several of these differences were most evident with key broadleaf weeds that are major herbicide resistance threats such as Amaranthus species and giant ragweed (Ambrosia trifida L.). Additionally, total broadleaf weeds were more frequent, uniform, and dense in full tillage fields compared to no-till fields, but giant ragweed and waterhemp [Amaranthus tuberculatus (Moq.) Sauer var. rudis (Sauer) Costea and Tardif] had higher relative abundance rankings in no-till fields. These results may have negative long-term implications for the evolution of glyphosate resistance as growers increase reliance on glyphosate in place of atrazine and tillage.


INTRODUCTION OF SYN-A205 FOR ATRAZINE-FREE WEED CONTROL IN CORN. R. D. Lins*1, T. H. Beckett2, S. E. Cully3, J. Foresman2, G. D. Vail2; 1Syngenta Crop Protection, Renville, MN, 2Syngenta Crop Protection, Greensboro, NC, 3Syngenta Crop Protection, Marion, IL (279)

ABSTRACT

SYN-A205 is a new selective herbicide for weed control in field corn, seed corn, popcorn and sweet corn.  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.  In 2014, field trials were conducted to evaluate SYN-A205 for weed control and crop tolerance.  Results show that SYN-A205 very effectively controls many difficult weeds and provides improved residual control and consistency compared to other atrazine-free commercial standards. 


ACURON HERBICIDE: PREEMERGENCE WEED CONTROL AND CORN SAFETY. R. Jain*1, M. A. Cutulle1, T. H. Beckett2, S. E. Cully3, R. D. Lins4, G. D. Vail2; 1Syngenta Crop Protection, Vero Beach, FL, 2Syngenta Crop Protection, Greensboro, NC, 3Syngenta Crop Protection, Marion, IL, 4Syngenta Crop Protection, Renville, MN (280)

ABSTRACT

Acuron™ is a multiple mode-of-action herbicide premix that provides preemergence and postemergence grass and broadleaf weed control in field corn (as well as seed corn, sweet corn and yellow popcorn).  In addition to mesotrione, s-metolachlor, and atrazine, Acuron™ also contains bicyclopyrone, a new HPPD (4-hydroxyphenyl-pyruvate dioxygenase) inhibitor.  Acuron™ applied preemergence is effective on difficult-to-control weeds, including common lambsquarters (Chenopodium album), common ragweed (Ambrosia artemisiifolia), giant foxtail (Setaria faberi), giant ragweed (Ambrosia trifida), Palmer amaranth (Amaranthus palmeri) and waterhemp (Amaranthus rudis) with improved residual control and consistency compared to commercial standards.  Additionally, preemergence applications of Acuron™ are safe to corn.  Pending regulatory approvals, first commercial applications are anticipated in the 2015 growing season. 


PETHOXAMID-A NEW HERBICIDE FOR USE IN AGRONOMIC & HORTICULTURAL CROPS. B. Hunt*1, J. Barrentine2, T. Hayden2, B. Jacobson2, A. Kendig2, M. Krull2, T. Ksander2, G. Radeva3, K. L. Smith4; 1Cheminova A/S, Lemvig, Denmark, 2Cheminova Inc, Research Triangle Park, NC, 3Cheminova Canada Inc, Kilworth, ON, 4Cheminova, Groveton, TX (281)

ABSTRACT

Authors:  Barrie S. Hunt1, Michael Krull2, James Barrentine2, Ken Smith2, Brent Jacobson2, Thomas Hayden2, Andrew Kendig2, Tim Ksander2 & Galina Radeva3

1 Cheminova A/S, Lemvig, Denmark; 2 Cheminova Inc., RTP, NC; 3 Cheminova Canada Inc., Kilworth, ON.

 

Abstract:

Pethoxamid [2-chloro-N-(2-ethoxyethyl)-N-(2-methyl-1-phenylprop-1-enyl)acetamide] is a novel selective chloroacetamide herbicide being developed by Cheminova Inc. for use in North America.  It can be safely applied PRE and POST in a very wide range of arable and horticultural crops including canola, corn, cotton, soybean & sunflower.  Pethoxamid herbicide delivers effective control of a broad spectrum of important grass and broadleaf weeds including Bracharia, Digitaria,  Echinochloa,  Panicum, Setaria,  Amaranthus including Palmer amaranth & waterhemp,  Chenopodium & Solanum.   Owing to its mode of action - Group 15 Very Long Chain Fatty Acid Elongase (VLCFAE) inhibition - and application timing it is expected that resistance development will be slow; pethoxamid will therefore provide a valuable tool in the management of herbicide resistant biotypes.  Pethoxamid is being developed as both a straight product and in mixture with a number of complementary active ingredients.

 


PERFORMANCE OF A NOVEL CLETHODIM FORMULATION. R. L. Pigati*1, G. K. Dahl2, J. V. Gednalske3, E. P. Spandl1, L. J. Hennemann3, J. A. Gillilan4, L. Magidow5, A. Clark5; 1Winfield, Shoreview, MN, 2Winfield Solutions LLC, St. Paul, MN, 3Winfield, River Falls, WI, 4Winfield, Springfield, TN, 5WinField / Land O Lakes, River Falls, WI (282)

ABSTRACT

Section® Three is a novel 3 lb/gal (359.5 g/L) clethodim formulation developed by Winfield. The higher concentration of clethodim compared to the 2 lb/gal (239.67 g/L) formulation, Section® 2EC, provides more convenience to the user. Clethodim based products can be applied to emerged broadleaf crops and controls volunteer corn and sorghum, as well as other annual and perennial grasses. The labeled use rate range of Section Three® is 2.67-10.67 fl oz/A (195.4 – 781 ml/ha). The new formulation was tested in 2013 and 2014 at multiple locations across the U.S. for weed control (e.g., volunteer corn and sorghum and annual and perennial grasses), antagonism and adjuvant influence on performance. Data were subjected to repeated measures ANOVA and means were separated according to Fisher’s Protected LSD (P<0.1). Performance of Section® Three across many weed species was equal to or greater than Section® 2EC when applied at the same a.i./A. The use of adjuvants generally improved weed control and the use of a crop oil concentrate (COC) or methylated seed oil (MSO), such as Superb® HC or Destiny® HC, respectively, is required for consistent, effective control. Finally, when tested with other herbicides, insecticides, fungicides and micronutrients, Section® Three did not antagonize tank-mix partners nor was antagonized.


LIGHT, WEEDS AND CARBON PARTITIONING – HOW DOES A NEIGHBOUR DO IT? A. G. McKenzie-Gopsill*, S. Amirsadeghi, L. Lukens, E. Lee, C. J. Swanton; University of Guelph, Guelph, ON (283)

ABSTRACT

            Plants have the ability to detect the presence of neighbouring plants through changes in the red: far-red ratio of light reflected or transmitted off vegetation. This triggers the shade avoidance response before direct shading occurs and has been shown to be important in understanding yield loss especially when it occurs during the critical period for weed control. Previous work in our lab has shown that this response is triggered upon emergence and can have long lasting negative effects on plant yield. While the morphological and hormonal changes associated with this response are well documented, investigations into how carbon assimilation may be impacted are lacking. Through a growth chamber study, we hypothesized that soybean seedlings exposed to weedy conditions and non-limiting resources would have reduced rates of carbon assimilation and in turn direct consequences on the sugar and starch pools, compared to weed-free plants. Through direct measurements of photosynthesis, chlorophyll content and soluble and insoluble sugars, we indentified key changes to carbon partitioning in plants exposed to early season neighbouring weeds. A better understanding of carbon partitioning during plant-weed interactions, will shed light on the mechanisms of yield loss in soybean. This work can help improve our understanding of yield loss in soybeans and can be applied to management and breeding programs to improve plant health. 

 


THIAMETHOXAM ENHANCES SOYBEAN COMPETITIVE ABILITY WITH WEEDS. H. Kim*, M. Afifi, G. Bozzo, E. Lee, L. Lukens, C. J. Swanton; University of Guelph, Guelph, ON (284)

ABSTRACT

In the absence of direct resource competition, neighbouring weeds can trigger physiological changes in soybean seedlings that may ultimately result in yield loss. These changes can occur in soybean seedlings grown under conditions of non-limiting resources in response primarily to the detection of the R:FR signal reflected from above ground neighbouring weeds. Recently, research has shown that maize seedlings arising from seeds treated with thiamethoxam did not experience these same physiological changes. In this experiment, we hypothesized that in the presence of above ground weeds, soybean seedlings emerging from seed treated with thiamethoxam would not express differences in root morphology or isoflavonoid content. A detailed morphological and physiological analysis of soybean roots was conducted. The data confirmed soybean seedlings emerging from seeds treated with thiamethoxam maintained root structure and isoflavonoid content in the presence of above ground weeds. This study suggests that the role of seed treatments be expanded beyond crop protection to explore the potential of new chemistries which may enhance the tolerance of soybeans to early weed competition.


SARMENTINE, A NATURAL HERBICIDE FROM LONG PEPPER (PIPER LONGUM) FRUIT WITH MULTIPLE MECHANISMS OF ACTION. F. E. Dayan*1, D. K. Owens1, R. Asolkar2, L. Boddy2; 1USDA-ARS, University, MS, 2Marrone Bio Innovations, Davis, CA (285)

ABSTRACT

Sarmentine, 1-​(1-​pyrrolidinyl)​-​(2E,​4E)​-2,​4-​decadien-​1-​one, is a natural product isolated from the fruits of Piper species.  The compound has a number of  interesting biological properties, including its broad-spectrum activity on weeds as a contact herbicide.  Initial studies highlighted a similarity in response between plants treated with sarmentine and herbicidal soaps such as nonanoic acid (pelargonic acid). However, little was known about the mechanism of action leading to the rapid desiccation of foliage treated by sarmentine.  In cucumber cotyledon discs assays, sarmentine induced rapid light-independent loss of membrane integrity at 100 µM orhigher concentration, whereas 3 mM pelargonic acid was required for similar effect.  Sarmentine was between 10 and 30 times more active than pelargonic acid on wild mustard, velvetleaf, redroot pigweed and crabgrass.  Additionally, the potency of 30 µM sarmentine was greatly stimulated by light, suggesting that this natural product may also interfere with photosynthetic processes.  This was confirmed by observing a complete inhibition of photosynthetic electron transport at that concentration.  Additional studies on isolated thylakoid membranes confirmed that sarmentine acted as a PSII inhibitor by competing for the binding site of plastoquinone.  This can be attributed in part to structural similarities between herbicides like diuron and sarmentine.  While this mechanism of action accounts for the light stimulation of the activity of sarmentine, it does not account for its ability to destabilize membrane in darkness.  In this respect, sarmentine has some structural similarity to crotonoyl-CoA, the substrate of enoyl-ACP reductase, a key enzyme in the early steps of fatty acid synthesis.  Inhibitors of this enzyme, such as triclosan, cause rapid loss of membrane integrity in the dark.  Sarmentine inhibited the activity of enoyl-ACP reductase, with an I50app of 18.3 µM.  Therefore, the herbicidal activity of sarmentine appears to be a complex process associated with multiple mechanisms of action.


BACKGROUND, HISTORY, AND CURRENT STATUS OF DICAMBA RESISTANT KOCHIA IN THE WESTERN US AND CANADA. P. Westra*1, T. A. Gaines1, M. Jugulam2; 1Colorado State University, Ft. Collins, CO, 2Kansas State University, Manhattan, KS (286)

ABSTRACT

Following the evolution of widespread triazine and ALS herbicide resistance in kochia, dicamba emerged as an important PGR herbicide for kochia management in small grains, corn, and fallow.  By the early to mid 1990s, reports of dicamba Lack of Control (LOC) complaints surfaced in multiple locations.  Assessment of the severity of this issue was complicated by the difference in dicamba rates labeled in small grains vs corn.  As no-till grain production expanded in the high plains, dicamba was frequently included in fallow herbicide treatments to aid in kochia control.  A 2001 publication from the Dyer lab at Montana State University suggested a strong probability that dicamba resistance in kochia was not due to differential uptake, translocation, or metabolism of dicamba in R vs S plants.  A 2009 publication by Preston et al suggested that resistance was due to a single allele with a high degree of dominance.  We are currently screening over 250 CO kochia accessions collected from 2011 to 2014 to assess dicamba resistance levels and the spatial distribution of resistant populations using georeferenced data for all samples.  To date, however, the mechanism of dicamba resistance in kochia has not been identified.  A highly inbred set of R and S kochia lines were developed at Colorado State University using multiple generations of self-pollination.  These lines are being used in initial efforts to sequence the full genome of kochia, and to use transcriptome sequencing to search for the molecular basis of dicamba resistance in kochia.

 


MECHANISM OF ATRAZINE AND MESOTRIONE RESISTANCE IN PALMER AMARANTH (AMARANTHUS PALMERII). B. Sridevi, A. Godar, C. Thompson, D. Peterson, M. Jugulam*; Kansas State University, Manhattan, KS (287)

ABSTRACT

Recently, evolution of the first case of hydroxyphenylpyruvate dioxygenase (HPPD) (e.g. mesotrione)-inhibitors resistance in Palmer amaranth populations (AMR) was documented in Kansas, USA. These populations were also found resistant to PS-II inhibitors (e.g. atrazine). The objective of this study was to investigate target-site and/or non-target-site mechanisms of atrazine and mesotrione resistance in these populations using a known susceptible Palmer amaranth population (AMS) as a reference. Nucleotide sequence analysis of AMR and AMS plants detected no difference in chloroplastic psbA gene, the target of atrazine; suggesting that the atrazine resistance is not maternally transmitted. Furthermore, analysis of progeny generated from reciprocal crosses between AMR and AMS Palmer amaranth clones, showed segregation for atrazine resistance or susceptibility, conferring nuclear inheritance of this trait. To investigate mechanism of resistance to mesotrione, absorption, translocation and metabolism of 14C-mesotrione and gene expression of the target enzyme (HPPD) were investigated in AMR and AMS. It was found that the mesotrione resistance in AMR was not due to reduced absorption, translocation; however, at 16 and 24 hours after treatment, mesotrione was metabolized to polar compounds more rapidly in AMR than AMS. More importantly, we found at least 10 fold increase in the HPPD gene expression in AMR compared to AMS. Overall, these studies suggest evolution of non-target, potentially metabolism-based resistance to atrazine, whereas, elevated rates of metabolism of mesotrione coupled with altered target gene expression contribute to mesotrione resistance in AMR. Evolution of metabolism-based resistance to herbicides is a serious threat to sustained weed management as such mechanism(s) may confer resistances to several herbicides with different modes of action.

 


PLOIDY AND MULTIPLE RESISTANCE IN ECHINOCHLOA SPP. N. R. Burgos*1, C. E. Rouse1, A. J. Fischer2, A. L. Lawton-Rauh3; 1University of Arkansas, Fayetteville, AR, 2University of California, Davis, Davis, CA, 3Clemson University, Clemson, SC (288)

ABSTRACT

The Echinochloa genus is comprised of at least 60 species, several of which are weeds in major agronomic crops. These species generally thrive in high-moisture environments; thus, the weedy species flourish in rice production fields.  The Echinochloa crus-galli/colona complex is arguably the number one weed in rice production worldwide.  Recent research indicates that junglerice (E. colona) is the most common species found in Arkansas rice fields.  Herbicide resistance profiles were generated for samples collected between 2010 and 2014. Experiments were conducted on a population of junglerice (ECH100) that showed resistance to three herbicides with different modes of action. ECH100 survived separate applications of field use rates of imazethapyr (0.11 kg ha-1), propanil (4.5 kg ha-1), and quinclorac (0.56 kg ha-1). A mixture of any two of these herbicides did not kill this population. Dose response experiments were conducted using imazethapyr (10 rates up to 24x), propanil (7 rates up to 16x), and quinclorac (8 rates up to 8x). ECH100 is highly resistant (40-fold) to imazethapyr and resistant to propanil beyond 16 times the field use rate. Resistance to quinclorac is low (2.1-fold), but is causing individuals to escape the field use rate.  Experiments were conducted to determine the mechanisms endowing multiple resistance. The involvement of cytochrome P-450-mediated metabolism was evaluated using malathion (0.99 kg ha-1), a cyP-450 inhibitor. Data suggested a cytochrome P-450-mediated metabolism of propanil and imazethapyr. Elevated β-cyanoaniline synthase activity was observed in other quinclorac-resistant populations, but not in ECH100. Preliminary analysis of the ALS gene sequence did not show any amino acid mutation in the catalytic sites, which supports the involvement of non-target site resistance mechanism.  The genomic content and estimated ploidy of this multiple-resistant junglerice is the same as of the susceptible population and others with different resistance patterns.  The genomic content of E. colona is lower than that of E. crus-galli, which is a hexaploid. This case indicates that complex resistance mechanisms could evolve in E. colona and, by extension, other weedy Echinochloa species, which presents a difficult challenge in managing this weed.


HERBICIDE-RESISTANT WEEDY RICE TRAITS AND MANAGEMENT. V. Singh*1, N. R. Burgos1, S. Singh1, L. Earnest2, R. Scott3, S. Basu1, A. Pereira1, D. Gealy4, A. Caicedo5; 1University of Arkansas, Fayetteville, AR, 2University of Arkansas, Rohwer, AR, 3University of Arkansas, Lonoke, AR, 4USDA- ARS, Stuttgart, AR, 5University of Massachusetts Amherst, Amherst, MA (289)

ABSTRACT

 Weedy rice (Oryza sativa) is a serious problem in many rice-producing regions. Volunteer rice is also a problem in rice production when a substantial volume of seeds shatter in the field. Volunteer rice plants from hybrid rice, segregates into several weedy types, and are expected to have poor grain yield and quality. If originating from herbicide-resistant (HR) rice, volunteer rice act as agents for gene flow to weedy rice that escape weed control measures. Volunteer rice from hybrid rice is a population of F2 plants that are segregating in genetic and phenotypic traits. Studies were conducted at RREC, Stuttgart, AR in 2011, to survey the occurrence of HR weedy rice plants and characterize these for principal weedy traits including seed shattering and dormancy. Samples were collected from remnant weedy rice in fields with history of HR rice crop. Seventy-nine percent of samples were resistant to imazethapyr. More than 50% of the HR weedy rice flowered later than HR rice and seed shattering ranged from 15% to 87%. Seventy-four percent of weedy rice accessions had 91% germination (similar to cultivated rice). Field experiments were conducted to study the efficacy of 12 herbicides and rate combinations for volunteer rice control with winter flood treatments at Stuttgart and, Rohwer, AR (2012-13 and 2013-14). Herbicides were applied in the fall and at 35 days prior to planting rice in the spring. ClearfieldTM inbred rice 'CL152' was used as the volunteer rice material and 'Jupiter' (inbred, conventional rice) was planted in May as cultivated rice crop. Crop injury was higher in treatments without flood compared with those that were flooded over the winter. Pyroxasulfone (0.12 kg ha-1, fall); 2,4-D (2.24 kg ha-1, pre-plant); and pyroxasulfone (0.12 kg ha-1, pre-plant) reduced the volunteer rice population. However, the pre-plant treatmentscaused significant crop injury (20% and 47%, respectively). Application of pyroxasulfone (0.12 kg ha-1) in the fall followed by 2,4-D (1.12 kg ha-1)  35 d pre-plant in the spring did not cause crop injury and controlled 73% of the volunteer rice which was  9% higher than pyroxasulfone application in the fall without follow-up treatment in the spring, and the best treatment thus far. 


MODE-OF-ACTION ANALYSIS OF A NEW ARYLPICOLINATE HERBICIDE FROM DOW AGROSCIENCES. J. L. Bell*1, P. R. Schmitzer1, M. R. Weimer1, R. M. Napier2, J. M. Prusinska2; 1Dow AgroSciences, Indianapolis, IN, 2University of Warwick, Coventry, England (290)

ABSTRACT

RinskorTM active (Dow AgroSciences code number XDE-848; ISO name applied for but not yet obtained) is the trade name for a new herbicidal compound developed by Dow AgroSciences with intended use in rice and other crops. Structurally, Rinskor is a novel 6-arylpicolinate (6-AP) molecule consisting of a highly substituted 4-amino-pyridine ring (4-amino-3-chloro-6-(4-chloro-2-fluoro-3-methoxyphenyl)-5-fluoro-pyridine-2-benzyl ester). Rinskor shares structural similarity with the recently introduced Dow AgroSciences herbicide: ArylexTM active. Foliar application of Rinskor induces growth phenotypes similar to that of other auxin-like herbicides and growth regulators. Sensitive species exhibit rapid onset of auxinic symptoms that include wilting, epinasty, leaf malformation, tissue swelling, and stunted growth with necrosis. Plant death often occurs in days to several weeks after herbicide application. In order to analyze the physiological mode of action and site of action for Rinskor, whole plant studies on wild type and mutant Arabidopsis thaliana (ARBTH) were conducted in conjunction with surface plasmon resonance (SPR) molecule-protein interaction studies of the auxin binding proteins TIR1 and AFB5. Mutants harbored amino acid missense or nonsense changes in AFB5. Plants were either treated foliarly as rosettes prior to bolting or seeded in agar media supplemented with herbicide. In foliar applications of Rinskor, there was a 10-33 fold resistance of the AFB5 mutants over WT plants depending on the mutant line (based on 50% growth reduction (GR50) values of plant dry weight). WT and AFB5 mutants exhibited similar sensitivity to 2,4-D with GR50 values of 2.2 g ai ha-1 and 2.7 – 9.9 g ai ha-1 respectively. Phenotypic symptoms designate the mode of action of Rinskor as an auxin-like response. The susceptibility of AFB5 mutants to 2,4-D suggests that the molecular recognition site for Rinskor is not TIR1 but rather the AFB5 receptor. SPR analyses indicate a stronger affinity of Rinskor to AFB5 over TIR1. Whole plant mutant studies and protein specific interaction analysis indicate that Rinskor is an auxin herbicide with high affinity to the AFB5 protein.


CHARACTERIZATION OF AN ALS-RESISTANT YELLOW NUTSEDGE POPULATION FROM AN ARKANSAS RICE FIELD. P. Tehranchian*1, J. K. Norsworthy1, S. McElroy2, V. K. Nandula3, D. Riar4, R. Scott5; 1University of Arkansas, Fayetteville, AR, 2Auburn University, Auburn, AL, 3USDA, Stoneville, MS, 4Dow AgroSciences, Indianapolis, IN, 5University of Arkansas, Lonoke, AR (291)

ABSTRACT

Yellow nutsedge is one of the noxious weeds infesting agricultural crops worldwide. It is known as a difficult-to-control weed in Arkansas rice-soybean systems, with regeneration predominantly occurring by tubers. Lack of control with the recommended rate of halosulfuron (53 g ai h-1) was reported in a rice field near Hoxie, Arkansas in the summer of 2012. In vitro studies were conducted to evaluate the level of resistance to halosulfuron and characterize cross resistance to acetolactate synthase (ALS)-inhibiting herbicides. An ALS enzyme assay was conducted and massively parallel sequencing using the Illumina HiSeq platform was used for ALS gene assembly, mapping, and single nucleotide polymorphism detection. The resistant biotype was >133 fold (13,568 g h-1) less sensitive to halosulforon compared to a susceptible biotype. It was cross-resistant to all evaluated ALS-inhibitors (e.g. imazamox, imazethapyr, penoxsulam, bispyribac, pyrithiobac-sodium, bensulfuron and halosulfuron) at their respective labeled field rate. The enzyme assay revealed that the resistant biotype was 2,540 times less responsive to halosulfuron, suggesting an altered target site as the probable mechanism of resistance. Of the identified nucleotide polymorphisms in both biotypes, a Trp574-to-Leu amino acid substitution, which was found in the resistant biotype, has previously been shown to confer target-site resistance to multiple ALS-inhibiting herbicide families in many weed species. This research reveals a high level of resistance to halosulfuron and resistance to other ALS-inhibiting herbicides resulting from a target-site alteration in yellow nutsedge.


UPTAKE AND TRANSLOCATION OF POSTEMERGENCE APPLIED C14-HALOSULFURON TO PURPLE NUTSEDGE. X. Li*1, T. L. Grey1, T. M. Webster2, B. H. Blanchett3; 1University of Georgia, Tifton, GA, 2USDA-ARS, Tifton, GA, 3University of Georgia, Valdosta, GA (292)

ABSTRACT

Purple nutsedge (Cyperus rotundus L.) is one of the most troublesome weeds in vegetable production of the southeast US.  Purple nutsedge forms extended rhizomatous chains from a parent plant, producing daughter plants from the basal bulbs and tubers.  Parent and daughter plants will remain connected over time by these rhizomatous chains.  The rate for reduction of tuber and daughter plant formation has been established, but the mobility of halosulfuron in this system has not been examined.  Therefore, a study was conducted to determine the absorption and translocation of 14C-halosulfuron from parent purple nutsedge plant through the tuber chain to daughter plants, and vice versa.  A single purple nutsedge tuber was planted in sand soil and allowed to establish for 2 to 3 wks in a greenhouse.  Shoot emergence was monitored with parent and daughter shoots were marked using plastic sheath slid during emergence.  The most fully developed leaf measuring greater than 5 cm long from the top of the plant, was entirely covered with a plastic sheath and then the entire plant was over sprayed with halosulfuron at 70 g ai/ha.  The plastic sheath was then removed and treated with a mixture containing the cold spray solution and 14C-halosulfuron.  Approximately 2.0 Becquerel’s of 14C-halosulfuron was applied on one parent or daughter leaf to evaluate translocation within a treated plant and along the rhizomatous chains.  Plants were then placed into a growth chamber for 72 hours.  Total 14C-halosulfuron recovery was at least 94.5%.  Recovery of 14C-halosulfuron was 65.7 and 81.3% in leaf wash, while treated leaf for the parent and daughter contained 26.8 and 24.9%, respectively.  In addition, 2.59, 0.36 and 0.16%, and 2.68, 0.40 and 0.23% of the 14C-halosulfuron applied remained in the shoots, tubers and roots of parent and daughter plant, respectively.  Results of this study also indicated that14C-halosulfuron mobility from the parent and daughter treated plants was similar, with 1.86 and 1.06% of 14C-halosulfuron moved out of parent and daughter treated plants to adjacent tissues. 

 


THE TOLERANCE MECHANISMS OF GRASSES TO ISOXABEN. C. Brabham*, T. L. Burke, M. Barrett, S. Debolt; University of Kentucky, Lexington, KY (293)

ABSTRACT

Isoxaben, a cellulose biosynthesis inhibitor, is labeled for selective pre-emergent control of broadleaf seedlings in turf and perennial cropping systems. The objective of this research was to elucidate the tolerance mechanism of grasses to isoxaben. We investigated potential target and non-target site resistant mechanisms. A dose response experiment was conducted to determine the tolerance level of the grass species Brachypodium distachyon. Based upon GR50 values, Brachypodium exhibited a 3 and 103-fold increase in isoxaben tolerance when compared to the dicotyledonous plants soybean (Glycine max) and Arabidopsis thaliana, respectively. Next, we investigated if known point mutations that confer isoxaben-resistance in Arabidopsis could explain the isoxaben tolerance observed in Brachypodium. However, the amino acids changes in isoxaben-resistant Arabidopsis mutants where not detected in the orthologous Brachypodium proteins. Gene redundancy/amplification failed to provide sufficient evidence to explain the observed tolerance. Furthermore, prior research has shown metabolism does not appear to have a role in the exhibited tolerance of grasses. Based on these data, we concluded that a novel non-target site mechanism might exist to explain the isoxaben tolerance in grasses. We will propose and discuss one potential tolerance mechanism that is based upon the unique characteristic of grass cell walls.

 


INTER-SPECIES PROTEIN TRAFFICKING ENDOWS DODDER (CUSCUTA PENTAGONA) WITH A HOST-SPECIFIC HERBICIDE-TOLERANT TRAIT. L. Jiang1, F. Qu2, Z. Li1, D. Doohan*2; 1China Agricultural University, Beijing, Peoples Republic, 2Ohio State University, Wooster, OH (294)

ABSTRACT

Besides photosynthates, dodder (Cuscuta spp.) acquires phloem-mobile proteins from host plants. Transfer of host phenotypes to the parasite by this process has not previosly been demonstrated. We tested the hypothesis that phosphinothricin acetyl transferase (PAT), that confers host plant glufosinate herbicide-tolerance, traffics from the host to dodder and functions inter-specifically. To examine this hypothesis we employed excised dodder tendrils that can grow in vitro for weeks, or resume in vivo growth by reparasitizing new hosts. The level of PAT present in vivo and in vitro dodder tendrils was quantified by enzyme-linked immunosorbent assay. The glufosinate sensitivity was examined by dipping the distal end of in vivo and in vitro tendrils, growing on or excised from LibertyLink (LL; PAT transgenic and glufosinate tolerant) and conventional (CN; glufosinate sensitive) soybean hosts,into glufosinate solutions for 5 s. After in vitro tendrils excised from LL hosts reparasitized new CN and LL hosts, the PAT level and the glufosinate sensitivity were also examined. When growing on LL host, dodder tolerated glufosinate and contained PAT at a level of 0.3% of that encountered in LL soybean leaf. Dodder tendrils removed from LL hosts and maintained in vitro became glufosinate sensitive after 6 days. Glufosinate sensitivity was coincident with degradation of most of the PAT that had been present when attached to the host. PAT mRNA was not detected by reverse transcription PCR in dodders. In conclusion, the results indicated that PAT inter-species trafficking confers glufosinate tolerance in dodder.

 


EFFECT OF SALINITY ON HOST PARASITE RELATIONSHIP IN PHELIPANCHE AEGYPTIACA: PHYSIOLOGICAL STUDY. A. Cochavi*1, J. E. Ephrath1, S. Rachmilevich1, H. Eizenberg2; 1French Associates Institute for Agriculture and Biotechnology of Drylands, Sede Boqer, Israel, 2Newe Yaar Research Center, ARO, Israel, Ramat Yishay, Israel (295)

ABSTRACT

Phelipanche aegyptiaca, an obligate root parasite chlorophyll lacking plant, is a worldwide threat to vegetables and field crops. Once directly attached to the roots, the parasite attracts water, minerals and sugars from the host. Therefore, high infestation levels in the soil can cause severe damage to crops. Water and salinity are increasing problems around the world, due to climate changes, lack of rainfall and intensive fertigation. In this study, the relation between salinity, P. aegyptiaca infestation and host-parasite relations were investigated. Two salinity levels (4 and 8 ds/m) and two P. aegyptiaca infestation levels (15 and 30 mg seeds Kg-1) were applied to tomato (Solanum lycopersicum) plants, grown in 18 litter pots. Physiological measurements and leaf spectral signatures were taken during the growing season once a week. P. aegyptiaca plants were unaffected by the salinity levels. The results indicate that in P. aegyptiaca infected tomato plants under salinity stress, carbon assimilation and stomatal conductance rates were lower than fresh water-irrigated infested plants; however, non-photochemical quenching (NPQ) values were affected only by infestation level and not by salinity level. In summary, prior infestation did not initiate a salinity acclimation effect and P. aegyptiaca plants were not affected by salt stress. 

 


EXPERIMENT DESIGN USING ARM SOFTWARE. S. R. Gylling*; Gylling Data Management, Inc., Brookings, SD (296)

ABSTRACT

One challenge of conducting experiments is designing the experiments to have a reasonable probability of distinguishing anticipated treatment differences. ARM software includes tools that assist with planning experiments, such as a statistical power test, a randomization quality review, and post-hoc power analysis. Using such tools can help improve the precision of upcoming experiments, and more efficiently plan follow-up experiments.


RSTATS4AG.ORG - A NEW WEBSITE TO HELP AGRICULTURAL RESEARCHERS LEARN R. A. R. Kniss*1, J. C. Streibig2; 1University of Wyoming, Laramie, WY, 2University of Copenhagen, Taastrup, Denmark (297)

ABSTRACT

There are many excellent books and websites available to students and practitioners who would like to learn the R statistical language. Even so, there are few resources that specifically address the type of designed experiments common in the plant and weed science disciplines. Statistics, and the R language, evolves over time. It is not uncommon for a book about R or statistics to become out of date within only a few years. So we decided to develop this material for the web rather than a textbook so that it could be more easily kept up to date. The Rstats4ag.org website is not meant to be a complete reference for all the capabilities of the R language, nor should it be used as as a substitute for consultation with a well-trained statistician. This site will not cover many of the underlying statistical concepts for the examples provided, and as such, it is certainly not a standalone statistics resource. The purpose of this site is simply to provide information and examples on how to use the R language to analyze statistical designs that are commonly used in agricultural experiments. A majority of agricultural research uses a small subset of experimental designs, and thus, there is a high probability that the examples presented will provide a framework for analysis of many agricultural experiments. To date, a majority of agricultural researchers have been trained to analyze data using SAS (and to a lesser extent, SPSS). SAS is an excellent tool for statistical analysis, and shares at least one characteristic with the R language: they can both be very difficult to learn. This is particularly true for researchers and graduate students without a programming background. Although the statistical concepts are the same, the language used to obtain the desired analysis and output can be dramatically different between the two programs. Many researchers who have made the switch from SAS to R will agree that when used properly, R is an extremely efficient and elegant tool for analyzing experimental data. While there are many texts already available for learning R, they are typically aimed broadly at statisticians, or targeted at a specific discipline ranging from ecology to the social sciences. This website is primarily focused on providing data and code examples for analyzing the most common experimental designs used by agronomists and weed scientists, and thus it will hopefully be useful to students and practitioners as they attempt to learn how to use a new statistical analysis environment.


PAY-FOR-PLAY PUBLISHING SCAMS: THE THREAT TO SCIENTIFIC JOURNALS. S. M. Ward*; Colorado State University, Ft. Collins, CO (298)

ABSTRACT

Increasing adoption of the open-access online model has radically changed the publishing landscape for academic journals, including those belonging to professional societies such as WSSA. Unfortunately, open access publishing has also allowed the proliferation of predatory publishing scams, where authors pay substantial fees in return for guaranteed online publication in a fake or poor-quality journal. Many of these journals list unqualified or non-existent editorial boards, conduct no peer review, claim false impact factors, publish plagiarized material, or have no archiving system. The general public, news media, and many in the scientific community remain unaware of this recent phenomenon, and incorrectly assume that all research papers published in online journals have undergone appropriate peer review. Recent examples of concern to weed scientists include a paper published in the online journal Interdisciplinary Toxicology claiming that celiac disease in humans is caused by glyphosate exposure. Despite such a connection having been debunked elsewhere, this paper is promoted by anti-GM campaigners as legitimate published research confirming the dangers of herbicide resistant crops.  Journals with low editorial standards are not a new phenomenon, but the current explosion of predatory substandard online journals soliciting manuscripts is unprecedented and threatens to undermine the integrity of scientific communication.

 


CAN WE LEARN FROM THE PAST?  ANTIQUE RESOURCES FOR WSSA. J. D. Byrd, Jr.*; Mississippi State University, Mississippi State, MS (299)

ABSTRACT

Can We Learn from the Past?  Antique Resources for WSSA

J. D. Byrd, Jr., Mississippi State University, Mississippi State, MS

The electronic technology age in which we live has created numerous opportunities that could not be imagined when computers were first developed.  One of the opportunities is online access to old agricultural literature that otherwise might not be available because it is housed in distant libraries or stored in special collections with limited accessibility.  Special grants to encourage digitizing literature, pictures, and other significant documents has helped accelerate the availability of this information online.  Some old literature is pertinent to the weed science community as several complete text books, monographs, and book chapters focused on weed identification, weed management, weed uses, plant taxonomy, regional flora, problematic weeds, etc. can be useful for a variety of educational purposes.  Digital format allows users to quickly, accurately, and thoroughly search documents for specific words or phrases of interest. This literature can be used to add interest in weed science classroom curricula, research, and extension training programs.  Individuals that lack hands on experience with manual weed control described in these old documents may better appreciate modern methods of weed management.  In 2014 and 2015, 22 digital documents relevant to weed science and published between the mid-1700’s and 1920 were uploaded to the Weed Science Society of America webpage to compile these resources in a single location that could be readily accessed by those in the weed science community. These documents can be accessed from the WSSA home page educational resources link or by typing the url http://wssa.net/weed/education/antique-literature/

Books with chapters or sections relevant to weed science:  

Tull, J. 1762. Of Weeds. Pages 73-79 in Horse Hoeing Husbandry: Or, an Essay on the Principles of Vegetation and Tillage. 4th edition. A. Millar, London, England.

Pitt, W.  1806. On the Subject of Weeding; or the Improvements to be effected in Agriculture by the Extirpation of Weeds. Pages 233-271 in Communications to the Board of Agriculture on Subjects Relative to the Husbandry, and Internal Improvement of the Country. Vol. 5. Part 1. W. Bulmer and Co., London, England.

Anonymous. 1896. Two Hundred Weeds: How to Know Them and How to Kill Them. Pages 592-611 in C. W. Dabney, Jr., ed. Yearbook of the United States Department of Agriculture 1895. Government Printing Office, Washington, DC.

Anonymous. 1898. Twenty Five Most Harmful Weeds. Pages 641-644 in G. W. Hill, ed. Yearbook of the United States Department of Agriculture 1897. Government Printing Office, Washington, DC.

Botany:

Elliott, S. 1821. A Sketch of the Botany of South Carolina and Georgia. Volume I.  J. R. Schenck, Charleston, SC. 606 p.

Elliott, S. 1824. A Sketch of the Botany of South Carolina and Georgia. Volume II.  J. R. Schenck, Charleston, SC. 743 p.

Torrey, J. and A. Gray. 1838-1840. A Flora of North America: Containing Abridged Descriptions of all the Known Indigenous and Naturalized Plants Growing North of Mexico; Arranged According to the Natural System. Wiley and Putnam, New York, NY.  711 p.

Weed Science:

Darlington, W. 1847. Agricultural Botany: an Enumeration and Description of Useful Plants and Weeds, which Merit the Notice or Require the Attention, of American Agriculturalist. J.W. Moore, Philadelphia, PA. 270 p.

Kay, G. F. and J. H. Lees. 1913. The Weed Flora of Iowa. Iowa Geological Survey Bulletin No. 4. Iowa State Printer, Des Moine, IA. 912 p.

Millspaugh, C. F. 1891. Your Weeds and Your Neighbor’s. Part 1. Weeds as Fertilizers. West Virginia Experiment Station Bull. No. 19, Vol. II, No. 7. M. W. Donnally, Charleston, WV. 6 p.

Millspaugh, C. F. 1892. Your Weeds and Your Neighbor’s. Part 2. West Virginia Experiment Station Bull. No. 22., Vol. II, No. 10. M. W. Donnally, Charleston, WV. 40 p.

Millspaugh, C. F. 1892. Illustrative Descriptive List of Weeds. Part 3. West Virginia Experiment Station Bull. No. 22., Vol. II, No. 10. M. W. Donnally, Charleston, WV. 93 p.

Harrison, F. C. 1900. Weeds of Ontario. Department of Ontario, Canada. 80 p.

Ball, C. R. 1902. Johnsongrass: Report of Investigations Made During the Season 1901. USDA Bureau of Plant Industry Bulletin 11. Government Printing Office, Washington, DC. 24 p.

Henkel, A. 1904. Weeds Used in Medicine. USDA Farmer’s Bulletin 188. Government Printing Office, Washington, DC. 47 p.

Dewey, L. H. 1905. Weeds and How to Kill Them. USDA Farmer’s Bulletin 28. Government Printing Office, Washington, DC. 28 p.

Clark, G. H. and J. Fletcher. 1906. Farm Weeds of Canada. Department of Agriculture, Dominion Canada. 103 p.

Cates, J. S. and W. J. Spillman. 1907. A Method of Eradicating Johnsongrass. USDA Farmer’s Bulletin 279. Government Printing Office, Washington, DC. 16 p.

Pammel, L. H. 1911. Weeds of the Farm and Garden. Orange Judd Co., New York, NY. 300 p.

Shaw, T. 1911. Weeds and How to Eradicate Them.  Webb Publishing Company, St. Paul, MN. 236 p.

George, A. E. 1919. A Manual of Weeds with Descriptions of All the Most Pernicious and Troublesome Plants in the United States and Canada, Their Habitats of Growth and Distribution, and Methods of Control. The MacMillan Company, New York, NY. 593 p.

Brenchley, W. E. 1920. Weeds of the Farmland. Longmans, Green and Co., London, England.  239 p.

 


BACK TO THE FUTURE WITH NON-GMO HERBICIDE PROGRAMS. D. Lingenfelter*, W. S. Curran; Penn State University, University Park, PA (300)

ABSTRACT

According to USDA-ERS data, adoption of genetically modified (GM or GMO) corn and soybean crops ranged from 80-90% of planted acres in 2013. However, for various reasons, currently there is an anti-GMO movement within the general public that urges mandatory labeling of products from food manufacturers. This and other factors could curtail these crop technologies. Because of this, recent trends indicate that non-GMO crops are making a comeback and the public may greatly increase consumption. Global consumption of non-GMO foods is estimated to increase 5 to 40% in the near future. Many large grain handlers in the Midwest are taking non-GMO corn for domestic and export uses. In most cases, it is still primarily a niche market and most require prior contracts with mills. However, 10-15% premiums can be obtained if the right market is established. A number of seed companies are now offering non-GMO or “conventional” corn and soybean varieties. Overall, GMO or “traited” corn and soybean seed costs more than non-GMO seed but the cost differences are complex. In general, GMO corn can range from $8 to 50 more per acre ($20–125/unit), whereas GMO soybean are $12 to 30 more per acre ($9–23/unit) compared to conventional varieties. These differences will mostly be reflected in total cost of weed control. In order to keep up with the non-GMO movement, herbicide programs must be aligned with these crops to provide adequate weed control and avoid crop injury. Weed control in conventional varieties varies depending on the crop. There are more broadleaf herbicide options in corn but POST control of grasses can be more challenging. Furthermore, there are fewer herbicide choices in soybean with POST broadleaf options being more limited than corn. In conjunction, more soybean injury will be expected compared to GMO varieties. Also, perennial weeds and resistant species can be problematic especially in continuous no-till systems. In summary, there will be increasing opportunities for farmers to grow non-GMO corn and soybean. In most cases, production costs can be less and yields competitive. However, other features of GMO crops such as insect protection traits, enhanced crop safety, elite variety lines, among others provide additional value to these crops. Therefore, farmers must consider all aspects of each system before deciding which type of crop to grow.


"ZERO TOLERANCE": A COMMUNITY-BASED MANAGEMENT PROGRAM FOR GLYPHOSATE-RESISTANT PALMER AMARANTH IN ARKANSAS. K. L. Smith*1, J. K. Norsworthy2, R. Scott3, A. M. Vangilder4, R. L. Nichols5, T. Barber6; 1Cheminova, Groveton, TX, 2University of Arkansas, Fayetteville, AR, 3University of Arkansas, Lonoke, AR, 4University of Arkansas, Rector, AR, 5Cotton Incorporated, Cary, NC, 6University of Arkansas, Little Rock, AR (301)

ABSTRACT

Utilizing techniques to reduce the soil seedbank is gaining acceptance throughout Western Australia and certain areas of the Southern U.S. as practical approaches for managing herbicide-resistant weeds that have short seed longevity.  Although Palmer amaranth has been shown to produce up to 1.8M seed on a single plant, research in Arkansas and Georgia showed that greater than 99% of these seed are expected to germinate or be lost to other means within 3 years in these biological and environmental conditions.  In Australia, mechanical destruction of weed seed at crop harvest has reduced annual ryegrass infestations the following year and in Arkansas, hand removal of Palmer amaranth that escaped herbicide treatments have reduced infestations by 87% over a two-year period.  Weed seed distribution by wind, water, and farm equipment has been well documented; thus, farmers attempting to manage the soil seedbank on their farms are often faced with renewed infestations from adjacent fields and non-cropland.  Zero Tolerance Zones were established in Arkansas as a means to manage Palmer amaranth populations and as an educational tool to encourage intensive management across areas greater than individual farms.  Several farmers were invited to be included in each zone with the objective to prevent any Palmer amaranth seed production throughout the designated area.  All participation was voluntary and no regulations were imposed, but university personnel monitored the areas routinely and encouraged compliance.  After 2 years, escapes requiring hand removal have been reduced 60-90% in many areas.  Details of setting up Zero Tolerance Zones as well as farmer results over a two- and three-year period will be discussed.  Keys for successful implementation as well as potential pitfalls will be presented. 

 


EFFECT OF HERBICIDE AND APPLICATION TIMING ON RESIDUAL CONTROL OF HORSEWEED RESISTANT TO GLYPHOSATE AND ALS INHIBITORS. B. Reeb*, M. M. Loux, A. Dobbels; Ohio State University, Columbus, OH (302)

ABSTRACT

Two field studies were conducted in west central Ohio to determine effective strategies for management of spring-applied residual herbicides for control of glyphosate-resistant horseweed (Conyza Canadensis) in no-tillage glyphosate-resistant soybeans.  The use of site 2 herbicides was deemphasized in these studies due to the prevalence of horseweed populations that are resistant to both glyphosate and site 2 herbicides. The objective of the first study, conducted in 2013 and 2014, was to determine the optimum combination of herbicides to maximize residual control of horseweed when applied in early spring.  Various combinations and rates of metribuzin, flumioxazin, saflufenacil, dicamba, and sulfentrazone were applied in early April, 30 days prior to planting.  Treatments were applied with glyphosate and 2,4-D (2,4-D was omitted from dicamba-containing treatments).  Through the time of POST application of glyphosate in early June, control exceeded 90% for all combinations of two or more herbicides, but among single herbicide treatments only saflufenacil (37 g ai/ha)  provided this level of control.  Control just prior to soybean harvest exceeded 90% only for the following combinations: 1) flumioxazin (90 g ai/ha) and metribuzin (310 g ai/ha); and 2) saflufenacil at (37 g/ha) with either flumioxazin (90 g ai/ha), sulfentrazone (200 g ai/ha); or 3) flumioxazin (90 g ai/ha) and metribuzin (530 g ai/ha).  Effectiveness of these treatments was reflected by the population densities, which ranged from 0.50 to 0.67 plants m-2.

The objective of the second study, conducted in 2014, was also to determine the optimum combination of herbicides when mixed with dicamba, for residual control of horseweed.     Methods and residual herbicides were similar to the first study with emphasis on use of herbicides other than site 2.  Treatments were applied 14 days prior to planting and at planting, and included glyphosate in addition to the residual herbicide and dicamba.  Control exceeded 93% for all treatments 15 days after planting, but only four treatments provided at least 90% control 15 days after the POST treatment in early June.  These four treatments were:  flumioxazin (90 g ai/ha) and saflufenacil (37 g ai/ha); sulfentrazone (180 g ai/ha) and metribuzin (420 g ai/ha); sulfentrazone (180 g/ha) and saflufenacil (37 g/ha); and flumioxazin (90 g/ha).  Population densities also reflected the effectiveness of these treatments.   Treatments were not evaluated in late season due to the effect of dicamba on soybean growth.    


OUR EFFORTS TO REDUCE THE INCIDENCE OF OFF-TARGET MOVEMENT OF AUXINIC HERBICIDES IN HIGH VALUE CROPS. G. Rhodes, Jr.*, T. D. Israel; University of Tennessee, Knoxville, TN (303)

ABSTRACT

 

Tennessee is similar to many other states in that both crops and livestock are of great value to our agricultural economy.  Beef cattle producers in our state are heavily dependent on grass pastures and hay fields for forage production.  Management of numerous herbaceous and woody weeds is a constant challenge.   Fortunately, a number of highly effective broadleaf herbicides, most of which are synthetic auxins, are available.   The oldest of these are various formulations of 2,4-D and dicamba.  Both herbicides have relatively short half-lives, and  therefore are relatively non-persistent.  Over the years, Extension agents and specialists, agribusiness personnel and consultants have spent much time investigating cases of reported damage by these herbicides to high value, non-target crops such as tobacco, cotton, tomato and grape.  These occurrences are often the result of drift (vapor or physical) or contaminated sprayers.  Fortunately due to the short half-lives of these herbicides, rotational  restrictions are relatively minimal. 

In 2000,  a premix of  picloram + 2,4-D (Grazon P+D) for use in pastures was introduced to a limited geography in Tennessee; a few years later aminopyralid was registered and  likewise introduced into the pasture market (ForeFront R&P, Milestone, GrazonNext HL).  The introduction of picloram and aminopyralid greatly improved the ability of cattle producers to manage troublesome perennials such as horsenettle (Solanum carolinense L.), tall ironweed (Vernonia gigantea (Walt.) Trel.), honeylocust (Gleditsia triacanthos L.), and many others.  Aminopyralid has also been widely utilized in the right-of-way vegetation market under other trade names.  While aminopyralid and picloram are relatively low in volatility compared to many formulations of 2,4-D and dicamba, they have much longer half-lives and are therefore relatively persistent.  While these two materials are extremely safe to cattle and other animals, the long persistence has implications for  grazing and movement of cattle from treated pastures, feeding of treated hay,  rotation of treated fields, and use of manure or treated grass in composting (both herbicides are stable in compost).  And unlike 2,4-D and dicamba, cases of drift or use of contaminated sprayers can complicate rotations for the next year or longer.  Registration of aminocyclopyrachlor, a new herbicide active ingredient, is expected for the pasture market in the near future.  This highly effective broadleaf herbicide is similar to aminopyralid in chemistry, behavior, and persistence.

In 2011,  we initiated a comprehensive educational program that stresses the importance of proper stewardship with the use of pasture and right-of-way herbicides.  The program has two fundamental goals: to help reduce the occurrence and impact of off-target damage to tobacco and other sensitive, high value crops; and to help with the diagnosis of suspected cases of off-target damage.  The initial work began with tobacco and later expanded to include cotton, tomato and grape.  Funding was obtained via grants from Philip Morris International, Altria Client Services, Dow AgroSciences and DuPont Crop Protection.  Herbicides we are addressing include 2,4-D, dicamba,  aminopyralid, aminocyclopyrachlor and  picloram.  Plants of each crop were grown in a greenhouse, and then they were treated foliarly with low rates of each herbicide to induce symptoms.  Treated ( and untreated) plants were photographed at various times following treatment to produce a library of still images for use as diagnostic aids.  Also, time-lapse photography was used to create videos for each crop and herbicide combination to show the development of symptomology over a 14 day period.  At the center of this effort is the program website, herbicidestewardship.utk.edu.  At this website, visitors can find the still images, time lapse videos and fact sheets, and other useful  information.


TEACHING UNDERGRADUATE WEED SCIENCE AS AN ONLINE COURSE:  STUDENT AND TEACHER PERSPECTIVES. P. B. Trewatha*; Missouri State University, Springfield, MO (304)

ABSTRACT

The desire for increased availability of online courses across all collegiate curriculums has created a demand for online college-level courses in various areas of plant science.  Frequently, the transition of courses to online has been for those that were lecture-only, where experiential learning was not a major component.  At Missouri State University, we have moved from a traditional to blended to online format for teaching undergraduate weed science. As we moved to a fully-online weed science course, a separate weed identification lab course was created to provide the hands-on instruction in weed identification.  The online course format included lecture PowerPoints, weed identification photos and short videos, outside readings, online discussions, written assignments and tests delivered through Blackboard (an online course delivery and management system).   Results of a survey administered to students at the end of the course indicated that 47 percent of the students still preferred the traditional format, but 74 percent indicated that they felt that the course met their learning and career goals as well as if it had been taught traditionally.  Over 60 percent of the students liked the course being online to give them the flexibility they needed due to distance from campus or work and family obligations, and over 80 percent indicated having the course materials online rather than having to come to lecture was a favorite component of the course.  The least favorite aspect of the online course was the inability to go to the field to see the weeds for identification.  However, 66 percent of the students indicated that having weed videos or still-photo PowerPoints with voice over weed descriptions was as useful as seeing live specimens of the weeds.  From the instructor’s perspective, the significantly greater time involved in online grading and student interaction must be carefully weighed against the flexibility of the online delivery system.

 


UNIFYING THE EFFORTS IN TEACHING, RESEARCH, AND EXTENSION IS VITAL FOR THE ADVANCEMENT IN WEED SCIENCE. H. Z. Ghosheh*1, L. Grabau2; 1Jordan University of Science and Technology, Irbid, Jordan, 2University of Kentucky, Lexington, KY (305)

ABSTRACT

Weeds are an important impediment to crop production because they are omnipresent, they reduce crop yields, and weed control often constitutes the major cost of producing a crop.  Weed effects on crops are slow, cumulative, and generally undramatic, but on the whole are at least as costly as those of insects and plant pathogens.  Virtually almost all surveys of pesticide use indicate that herbicides are by far the predominantly used class of pesticides. However, the discipline of weed science is facing great challenges after decades of close association with herbicide technology.  Public funds, student enrollment, employment and career opportunities are declining. In this presentation, we would like to highlight the current shortcomings in weed science teaching at educational institutions, and to provide insights into future endeavors designed to raise the profile of the discipline across university campuses.  We are proposing increasing weed science courses that are offered in educational institutions and will suggest a scheme for doing that. We speculate that this increase will have positive impacts on weed science resilience and advancement through increased graduate student enrollments, greater research frontiers, and higher future career opportunities.  We believe that further diffusion of current knowledge will be vital for the discipline of weed science to survive and flourish


MOBILE APPLICATIONS AS A PEST MANAGEMENT TOOL FOR EXTENSION SERVICES. A. Rana*, J. Derr; Virginia Tech, Virginia Beach, VA (306)

ABSTRACT

In our modern, fast-paced society, cell phones have become essential tools for everyone. Smart phone have capabilities beyond just being a communication device, including internet access, global positioning system applications, accelerometer, and a gyroscope, among others. Cell phones can play a vital role in agriculture, especially for extension services. Extension services can use this technology to provide farmers with appropriate information for increasing agricultural productivity and improving farm management. To address this need, several prototype mobile applications were developed to serve as decision support tools. Xcode was used for developing iOS mobile applications for weed management. Xcode is an integrated development environment (IDE) containing a suite of software development tools developed by Apple for developing software for OS X and iOS. Two approaches were used for the mobile application programming. Object-oriented C scripts were written for decision making using ‘if statements’ in the first approach. This approach was suitable for small applications. However, this approach is unsuitable for larger databases. In the second approach, a SQLite database was used in the decision-making processes. SQLite is a relational database management system contained in a C programming library. Obtaining internet access in rural areas are sometime challenging. Therefore, both types of mobile applications were designed to use offline. The developed mobile application allows the end user to identify effective herbicides for a given weed or to list weed species controlled by a given herbicide. Mobile phone applications can be a promising tool to deliver research-based agricultural information to farmers by extension personnel.