Ae Ha-1 Research Articles

Southern Sandbur (Cenchrus echinatus L.) Control in Bermudagrass Pastures with Indaziflam Herbicide Systems

Field studies were conducted during 2019 growing season in north-central, south-central, and the Coastal Bend areas of Texas to evaluate indaziflam herbicide systems for southern sandbur control and Coastal bermudagrass tolerance. Indaziflam caused no bermudagrass stunting at any location when applied preemergence (PRE) at 0.04 to 0.07 kg ai ha-1. Glyphosate at 0.35 kg ae ha-1 caused bermudagrass stunting which ranged from 16 to 65% when evaluated 3 to 5 weeks after application; however, when evaluated at the end of the growing season, no bermudagrass stunting was evident when compared with the untreated check. Southern sandbur control with indaziflam, when evaluated 28 to 32 weeks after the initial indaziflam PRE application, ranged from 85 to 99% in north-central Texas, 65 to 95% in south-central Texas, and 95 to 100% in the Coastal Bend region. Southern sandbur control with pendimethalin PRE system ranged from 74 to 100%, 11 to 85%, and 100% in those regions, respectively. Indaziflam represents a safe option for forage and hay producers in Texas to control southern sandbur.

Chlorophyll a Fluorescence Parameters do not Detect Yield-limiting Injury from Sub-lethal Rates of 2,4-Dichlorophenoxyacetic Acid (2,4-D) in Cotton (Gossypium hirsutum)

Aims: Determine if the use of novel chlorophyll a fluorescence parameters could be utilized to predict yield loss of cotton exposed to sublethal rates of 2,4-dichlorophenoxyacetic acid (2,4-D) at various growth stages.
 Study Design: All trials were arranged in a randomized complete block design with four replications. Treatment means were subjected to analysis of variance and linear regression was utilized to determine relationship between chlorophyll a parameters and yield.
 Place and Duration of Study: University of Georgia Gibbs Farm in Tifton, GA, USA and the Sunbelt Agricultural Exposition in Moultrie, GA, USA during the 2013 growing season.
 Methodology: Two sublethal rates of 2,4-D were applied to cotton at six distinct growth stages. The rates consisted of 2 g and 40 g ae ha-1 equivalent to 1/421 and 1/21 of the full rate (0.532 kg ae ha-1), respectively. The sublethal rates were applied to cotton at six growth stages, including the four leaf, nine leaf, first bloom, two, four and six weeks after first bloom growth stages. A fluorometer was used to obtain the fluorescence parameters Fv/Fm, ΦEO and PIABS from the uppermost fully expanded leaves at various intervals after 2,4-D exposure.
 Results: Despite yield losses ranging from 20 – 90% of the non-treated control, no consistent patterns resulted from utilizing fluorescence transients to detect 2,4-D injury and overall instances of significant difference were minimal and typically not biologically relevant. In many cases, treatments exposed to 2,4-D that exhibited yield loss showed evidence of greater photosynthetic efficiency than the non-treated control. In the majority of instances, many of fluorescence parameters measured fell within ranges observed in previous studies in cotton produced under typical or non-stressed conditions.
 Conclusion: While it has been proven as a valuable tool in other plant screening endeavors, chlorophyll a fluorescence were not able to detect the effects of sub-lethal rates of 2,4-D on cotton, even in instances that resulted in severe yield loss.

Behavior of Five Sulfonylurea Herbicides and a Low-Dose Glyphosate on Cynodon nlemfuensis Pasture

African star grass (Cynodon nlemfuensis Vanderyst) is an excellent forage for animal feed, especially in tropical and subtropical climates. However, there is little information on weed management in African star grass pastures. Two experiments were carried out in 2017 and 2018 to evaluate the response of African star grass to five herbicides of the sulfonylureas chemical group and glyphosate at a low dose. The treatments were as follows: metsulfuron-methyl (Ally®) (7.8 and 15.6 g ai ha-1 plus 0.1% v/v mineral oil); chlorimuron-ethyl (Staron®) (15.0 and 30.0 g ai ha-1 plus 0.05% v/v mineral oil); halosulfuron (Sempra ®) (112.5 and 225.0 g ai ha-1 plus 0.1% v/v surfactant); ethoxysulfuron (Gladium®) (150.0 and 300.0 g ai ha-1); nicosulfuron (Sanson®) (60.0 and 120.0 g ai ha-1); glyphosate (Roundup Original®) (360 g ae ha-1); and a control without herbicide application. The herbicides nicosulfuron (60.0 and 120.0 g ai ha-1) and glyphosate were the most phytotoxic treatments; however, none of the treatments caused the total death of African star grass plants. The herbicides metsulfuron-methyl, chlorimuron-ethyl, halosulfuron and ethoxysulfuron were selective and are potential products for use in African star grass pastures.

Drift Potential from Glyphosate and 2,4-D Applications as Influenced by Nozzle Type, Adjuvant, and Airspeed

<b>Highlights</b> <list list-type=bullet><list-item> The AIXR nozzle and modified vegetable oil reduce drift potential. </list-item><list-item> Downwind spray deposition increases non-linearly as airspeed increases. </list-item><list-item> Nozzle selection is more important than adjuvant to mitigate spray drift. </list-item></list> <b>Abstract</b>. Spray drift is a critical concern for pesticide applications and the largest focus for its reduction has been placed on increasing droplet size. The objectives of this research were to evaluate the influence of nozzle type, adjuvant, and airspeed on the droplet spectrum and spray drift deposits from applications of glyphosate plus 2,4-D in a wind tunnel. Two studies were conducted using three 11002 nozzles types (XR, DG, and AIXR) individually attached to a one-tip boom. The working pressure was 207 kPa. The first study evaluated drift from the potassium salt of glyphosate (1260 g ae ha-1) plus 2,4-D amine (450 g ae ha-1) tank-mixed with four adjuvants (individually) sprayed at 2.2 m s-1 airspeed. A glyphosate plus 2,4-D solution with no tank-mixed adjuvants was also evaluated. The second study evaluated drift from glyphosate plus 2,4-D applications in four airspeeds (0.9, 2.2, 3.6, and 4.9 m s-1). Drift potential was determined using 2 mm monofilament line collectors and a 1,3,6,8-pyrenetetrasulfonic acid tetra sodium salt (PTSA) fluorescent tracer added to solutions, quantified by fluorometry. Nozzles and adjuvants influenced droplet size distribution of glyphosate plus 2,4-D solutions. Among the nozzles, the AIXR produced the coarsest droplets and the lowest tracer deposits (12 ηg cm-2) at 12 m downwind regardless of solution type. When nozzles were pooled, the modified vegetable oil (MVO) reduced the spray deposition by 36% at 12 m compared to the solution without adjuvant. At 4.9 m s-1 airspeed, tracer deposit at 12 m downwind was 2-fold lower when applications were made through low-drift nozzles (DG and AIXR) compared to the XR nozzle. Results suggest that drift-reducing adjuvants tested in this study may not reduce drift and nozzle selection should be considered as a more important factor than adjuvants in order to mitigate spray drift.

Glyphosate-Resistant Canada Fleabane Control with Three-Way Herbicide Tankmixes in Soybean

Eight field trials (2 in 2016, 3 in 2017, 3 in 2018) were conducted in farmers’ fields with heavy infestations of GR Conyza canadensis (Canada fleabane, horseweed or marestail) to evaluate glyphosate (900 g ae ha-1) plus saflufenacil (25 g ai ha-1), 2,4-D ester (500 g ai ha-1) or paraquat (1100 g ai ha-1) applied preplant (PP) as 2-way tankmixes, or in 3-way tankmixes with sulfentrazone (140 g ai ha-1), flumioxazin (107 g ai ha-1) or metribuzin (400 g ai ha-1) for the glyphosate-resistant (GR) C. canadensis control in GR soybean. Glyphosate plus saflufenacil applied PP controlled GR C. canadensis as much as 90%. The addition of sulfentrazone, flumioxazin or metribuzin to the tankmix provided as much as 93%, 96% and 97% control of GR C. canadensis, respectively. Glyphosate plus 2,4-D ester applied PP provided as much as 59% control of GR C. canadensis. The addition of sulfentrazone, flumioxazin or metribuzin to the tankmix provided as much as 60%, 59% and 91% control of GR C. canadensis, respectively. Glyphosate plus paraquat applied PP provided as much as 85% control of GR C. canadensis. The addition of sulfentrazone, flumioxazin or metribuzin to the tankmix provided as much as 88%, 89% and 98% control of GR C. canadensis, respectively. Density and biomass reductions of GR C. canadensis with herbicides evaluated followed the same pattern as weed control evaluations. GR C. canadensis interference reduced soybean yield 66%. Reduced GR C. canadensis interference with the preplant herbicides evaluated provided soybean yield similar to the weed-free control. Results from this study show that glyphosate plus saflufenacil, glyphosate plus 2,4-D ester or glyphosate plus paraquat tankmixed with metribuzin can provide effective control of GR C. canadensis in GR soybean.

Hormesis of 2,4-D Choline Salt in Biometric Aspects of Cotton

Plant hormesis is a phenomenon that involves the presence of toxic compounds at high doses but can be beneficial at low doses. Thus, the aim of this study was to use dose-response curves to assess the effect of hormesis caused by sub-toxic of 2,4-D choline herbicide on biometric variables of cotton plants. The study adopted a completely randomized experimental design with seven replications, and the treatments consisted of nine fractions of the average rate indicated on the 2,4-D choline salt herbicide label: 0 (control); 0.4275; 0.855; 1.71; 3.42; 8.55; 17.1; 34.2 and 68.4 g ae ha-1 applied at phenological stages V4 or B4 of cotton plants. The plants were assessed for the main morphological parameters. The results were subjected to analysis of variance and, when significant, the hormesis model was tested aiming to describe the dose-response curves with low rates stimulation. The maximum hormesis effect for the variables plant height and number of leaves in cotton plants at stage V4 was estimated, in due order, for sub-doses between 1.14 and 3.02 and 1.37 and 5.54 g ae ha-1 of 2,4-D choline. The hormesis effect was not significant for total dry matter production when 2,4-D choline was applied at stage V4, irrespective of the year of study. Sub-doses between 0.855 and 1.71 g ae ha-1 of 2,4-D choline salt applied at stage B4 caused hormesis in the height, number of leaves, shoots dry matter and total dry matter of cotton plants.

Sugarcane cultivar response to glyphosate and trinexapac-ethyl ripeners in Louisiana.

Sugarcane ripening in Louisiana is necessary to ensure adequate sucrose levels in early-season harvested sugarcane. The response of nine sugarcane cultivar’s yield components to glyphosate and trinexapac-ethyl ripeners was determined in field trials. Glyphosate (210 g ae ha-1) and trinexapac-ethyl (200 g ai ha-1) treatments failed to increase sucrose yields more than non-ripened sugarcane. Sugarcane ripened with glyphosate or trinexapac-ethyl increased theoretical recoverable sucrose (TRS) 4 to 12% more than non-ripened sugarcane in seven out of nine cultivars, but greater TRS values were counterpoised by lower sugarcane stalk weight. An unintentional consequence of reduced late-season vegetative growth may benefit growers by allowing them to harvest more sugarcane hectares to meet their daily load quota and exposes fewer hectares to a freeze event. The cultivars HoCP 00–950, Ho 09–804, and HoCP 09–840 were not responsive to glyphosate or trinexapac-ethyl ripeners and should not be treated. A delayed harvest from 28 to 49 days after treatment (DAT) coincided with greater TRS values and 17% more sucrose yield.

Subdoses of Dicamba Herbicide on Yield Componentes in Function of the Soybean Growth Stage

Soybean cultivars without tolerance can suffer injury from exposure to tank herbicide residues. This study aimed at assessing the potential effects of the broad spectrum herbicide dicamba on sensitive soybean during its vegetative and reproductive stages. The trial was performed in a randomized complete block design with four replications. Six rates (1.4, 2.8, 5.6, 11.2, 16.8 and 28.0 g ae ha-1) of dicamba were applied at two soybean growth stages (V3 and R2). The soybeans were planted in Passo Fundo, Rio Grande do Sul state in 2015/16 agricultural year. The dicamba induced symptoms of soybean phytotoxicity showed a steady rise at all the assessment times. The soybean decreased in height as the subdose of the herbicide increased. Dicamba was observed to negatively affect the number of nodes alone, during the V3 and R2 stages. The grain yield was adversely affected at the 28.0 g ae ha-1 subdose, in the V3 application stage, and in response to the 16.8 and 28.0 g ae ha-1 subdoses in the R2 stage.

Glifosato, trinexapaque-etílico e cloreto de mepiquate no desempenho produtivo de feijão-vagem de crescimento determinado

Studies aimed at improving production and yield of bush snap beans are desirable; the results may provide growers with new techniques to improve profitability. In the literature, there are few reports on the productive performance of vegetables subjected to doses of glyphosate and plant regulators. Thus, this study aimed to evaluate the effect of glyphosate, trinexapac-ethyl, and mepiquat chloride doses on the production components and yield of bush snap beans. We tested various doses: a) glyphosate: 0.0; 18.0; 36.0; 72.0; and 144.0 g acid equivalent (ae) ha-1; b) trinexapac-ethyl: 0.0; 62.5; 125.0; 250.0; and 500.0 g ae ha-1; and c) mepiquat chloride: 0.0; 25.0; 50.0; 75.0; and 100.0 g ae ha-1. The experimental design was completely randomized, with four replications per treatment. We evaluated plant height, stem diameter, number and mass of pods per plant, mass, length, and diameter of pod, and yield. The analysis of variance was conducted by applying the F test, and the doses were submitted to regression analysis (p &lt; 0.05). Each active ingredient was considered separately. Productive performance was favored by using doses up to 16.0 g ae ha-1 of glyphosate, showing increased pod mass per plant and yield. As trinexapac-ethyl doses increased, the number of pods per plant decreased but mean pod mass increased. Doses of mepiquat chloride up to 59.5 g ae ha-1 increased mean pod mass. Finally, pod yield was not influenced by trinexapac-ethyl and mepiquat chloride.

Glyphosate resistant soybean growth and yield affected by glyphosate and phosphate fertilization

Glyphosate is the most used herbicide worldwide and glyphosate-tolerant soybean planted in almost all cultivated areas. In Brazil, the area cultivated with transgenic soybean reaches more than 90%. Recently, the application of glyphosate in tolerant soybean has assumed the possibility to injury the crop under certain conditions and herbicides formulations. Phosphate fertilization can directly influence glyphosate uptake in plants because glyphosate translocation inside cells is related with phosphate transporters. Therefore, a study was conducted in two steps intended to determine if different doses of phosphate fertilization and/or glyphosate mode of spraying could modify glyphosate susceptibility of glyphosate-tolerant soybean, affecting crop development and yield. We tested two glyphosate doses and its interaction with mode of spraying and different glyphosate doses interaction with phosphate soil-fertilization. Experiment I was set up in a two by two factorial design, testing two doses of isopropylamine salt glyphosate (960 and 1,440 g ae ha-1) and two modes of glyphosate application (single spraying and sequential spraying). Experiment II was set up in a two by three factorial design, testing two doses of glyphosate (960 and 1,440 g ae ha-1) and three doses of phosphate fertilization (54, 108 and 162 kg ha-1 of P2O5). In both experiments, weed community was evaluated based on number of individuals and their respective dry mass accumulation. Crop was evaluated in dry mass of leaves, dry mass of stem, dry mass of pods, dry mass of shoot, plant height and grain yield. The use of glyphosate in a sequential spraying (960 + 480 g ae ha-1) or in higher dose (1,440 g ae ha-1) provides a highly efficient weed control and a high-performance crop growth and yield. The additional soil-fertilization with phosphate in this case does not affect soybean since no crop injury was observed.

Alternative Herbicides for Control of Glyphosate-Resistant Giant Ragweed in Nebraska

Giant ragweed is an early emerging and one of the most competitive summer annual species found in many fields throughout North America. Extensive use of glyphosate in glyphosate-tolerant (GT) crops has evolved giant ragweed populations with glyphosate resistance. Field dose-response studies were conducted to determine the influence of growth stage on the level of glyphosate resistance in a suspected giant ragweed population. In addition, efficacy of alternative pre-plant, pre-emergence (PRE) and post-emergence (POST) herbicides were evaluated in corn and soybeans for glyphosate-resistant (GR) giant ragweed control. The field glyphosate dose-response studies confirmed that the suspected giant ragweed population were resistant ranging from 14- to 32-fold resistance depending on the growth stage of glyphosate application. The 10, 20 and 30 cm tall giant ragweed had 14, 17 and 32X resistance level, respectively. The dose-response studies indicated that the 10, 20, and 30 cm tall GR giant ragweed was controlled 90% with 214, 402 and 482 g ae ha-1 of dicamba, respectively, when tank-mixed with glyphosate (1060 g ae ha-1) 21 days after treatment (DAT). All evaluated pre-plant herbicides for corn provided &amp;ge; 90% control of the GR giant ragweed at 30 DAT; among which the best control (100%) was achieved with pre-plant application of atrazine (2240 g ai ha-1), isoxaflutole (90 g ai ha-1), and premix of flumioxazin/pyroxasulfone (315 g ai ha-1). Herbicide combinations of different site of action provided greater than 90% control of the GR giant ragweed population in a PRE followed by POST herbicide program in corn and soybean, suggesting that alternative herbicide for giant ragweed control are available.

Drift of 2,4-D and dicamba applied to soybean at vegetative and reproductive growth stage

ABSTRACT: The introduction of dicamba and 2,4-D-resistant soybean will increase the use of auxin herbicides for management of herbicide-resistant weeds, increasing risk of drift in non-target crops. The field experiment was conducted in 2016/17 to evaluate injury, growth, yield, germination and seeds vigor of soybean effects to simulated drift of 2,4-D and dicamba applied to soybean at the V3 and R2 growth stages. To simulate drift, 2,4-D was applied at 0; 5.16; 10.4; 20.8 e 41.5g ae ha-1 and dicamba at: 0; 3.7; 7.4; 14.9 e 29.8g ae ha-1. The injury of the dicamba is greater than 2,4-D, and the V5 stage is more susceptible to both herbicides. The greatest reductions in soybean yield follow the drift of dicamba in R2 and 2,4-D in V5. The physiological quality seeds of the soybean is reduced by dicamba and 2,4-D drift at both the V5 and R2 stages of the soybean. Soybean is highly sensitive to low rates of 2,4-D and dicamba at the vegetative or reproductive growth stages. Dicamba causes greater negative effects than 2,4-D on soybean. The low rate of 2,4-D and dicamba reduce germination and vigor seed on soybean offspring.

Row Crop Sensitivity to Low Rates of Foliar-Applied Florpyrauxifen-benzyl

In a greenhouse experiment, soybean, cotton, corn, grain sorghum, and sunflower were subjected to 1/10 (3 g ai ha-1), 1/100 (0.3 g ai ha-1), or 1/500 (0.06 g ai ha-1) of the 1X rate of florpyrauxifen-benzyl. Visible injury 14 days after treatment (DAT) was the greatest with soybean (96%) when exposed to the highest drift rate of 1/10x or 3 g ai/ha-1 of florpyrauxifen-benzyl and was significantly higher than all other crops and drift rates. Cotton and sunflower were also injured 85 and 83%, respectively, by the 1/10x rate but had less injury when a 1/100x or 1/500x rate was applied (injury ranging from 9 to 33%). It was concluded that the negative effects on soybean, cotton, and sunflower primarily resulted from exposure to the highest rate tested (1/10x) and only soybean expressed negative effects even at the lower rate of 1/100x. A field study was also conducted to (1) evaluate the sensitivity of soybean to low concentrations of florpyrauxifen-benzyl during vegetative and reproductive development and (2) compare soybean injury and yield following applications of florpyrauxifen-benzyl and dicamba across various growth stages and concentrations. Soybean plants were treated with 1/10, 1/20, 1/40, 1/80, 1/160, 1/320, or 1/640 of the 1X rate of florpyrauxifen-benzyl (30 g ai/ ha-1) or dicamba (560 g ae ha-1) at the V3 and R1 growth stage. Florpyrauxifen-benzyl applied at a rate of 1/10 to 1/40X caused foliar injury and subsequent height reduction. In comparison, dicamba applied at the same rates caused slightly less injury and growth reductions. As rate of florpyrauxifen-benzyl decreased from 1/10 to 1/640X, the level of soybean injury dissipated rather quickly. However, this was not the case with dicamba, as substantial injury was observed with rates as low as 1/640X.

Rush Skeletonweed (Chondrilla juncea) Control in Pacific Northwest Winter Wheat

AbstractRush skeletonweed is emerging as a regionally important weed of winter wheat production in eastern Washington. Field studies were conducted during the 2016 and 2017 crop years to evaluate several auxin herbicides applied at two seasonal timings (fall or spring) for control of rush skeletonweed in winter wheat. Clopyralid (210 g ae ha-1) provided&gt;90% visual control of rush skeletonweed in both years of the study and aminopyralid (10 g ae ha-1) provided&gt;80% visual control. Aminocyclopyrachlor, dicamba, and 2,4-D provided&lt;55% control of rush skeletonweed. Season of application did not meaningfully affect efficacy of any herbicide tested. Wheat yields were reduced by 39 to 69% compared to the non-treated check when aminocyclopyrachlor was applied in the spring. Clopyralid is an effective option for control of rush skeletonweed in Pacific Northwest winter wheat.

SELECTIVITY OF HERBICIDES APPLIED SEPARATELY OR IN COMBINATION IN THE POST EMERGENCE OF RR2 MAIZE

The goal was to evaluate the tolerance of maize hybrids 2B810 PW and 30F35 HR to herbicides applied alone and in combination. Trials were carried out in the field in a randomized block design with four replicates. The treatments were three herbicides, alone or in combination, in addition to the control. Herbicides were: atrazine (2000 g ai ha-1); nicosulfuron (50 g ai ha-1) and glyphosate (1080 g ae ha-1). Crop injury was evaluated at 7, 14, 21, and 28 days after application and also SPAD index, height, ear height, stem diameter, 1000-grain weight, and yield. In general, the variables were not affected by the treatments. Hybrids 2B810 PW and 30F35 HR showed tolerance to the application in post-emergence (V4) of the herbicides used.

Sensitivity of Grape and Tomato to Micro-rates of Dicamba-based Herbicides

There is Agro-climatic concern that the widespread use of dicamba-based herbicides in Dicamba-Tolerant (DT) soybeans can result in un-intended drift onto non-DT crops in nearby field due to windy conditions and volatility. New dicamba-based products such as Engenia® and XtendiMax® with Vapor Grip technology were developed to reduce volatility, however, they are not completely volatile-free. A study was conducted to evaluate the sensitivity of pot-grown grape and tomato to six micro-rates of three dicamba-based products (Clarity®, Engenia® and XtendiMax®) in 2016 and 2017, at Haskell Ag Lab, Concord (42.37oN, 96.68oW), NE, USA. The tested dicamba formulations negatively impacted growth of grape and tomato as measured by vine length and plant height respectively, as well as by plant biomass. About 2% of the label rate was high enough to cause 50% injury and reduction in vine length or plant height. For example, a dose of 6.54 to 9.13 g ae ha-1 and 3.98 to 5.35 g ae ha-1 caused 50% injury in grape and tomato respectively, at 21 DAT. At 50% injury and vine reduction threshold, grape appeared more sensitive to XtendiMax® than Clarity® and Engenia®. For instance, a dose of 1.83 g ae ha-1 of XtendiMax® was required to cause 50% reduction in vine length (~49 cm) compared to significantly higher dose of 5.64 and 7.59 g ae ha-1 required for Clarity® and Engenia®, respectively. However, in tomato, there was no significant difference in sensitivity to all three products. In general, the present study showed that grape and tomato were very sensitive to micro-rates of all three dicamba products, irrespective of the of the new dicamba technology that reduces volatility. Hence, efforts should be made to avoid drift of dicamba onto these crops.

Control of Glyphosate-Resistant Waterhemp with Two-Pass Weed Control Strategies in Glyphosate/Dicamba-Resistant Soybean

Waterhemp is a small-seeded, dioecious, broadleaf weed that emerges throughout the growing season. If left uncontrolled, waterhemp interference can reduce soybean yield up to 73%. Glyphosate-resistant (GR) waterhemp was first discovered in one county in Ontario in 2014; as of 2017, it has been found in two other counties. Glyphosate/dicamba-resistant soybean can be sprayed with glyphosate and/or dicamba preplant (PP), preemergence (PRE) and/or postemergence (POST). The objective of this study was to determine the control of GR waterhemp in glyphosate/dicamba-resistant soybean with PRE residual herbicides, glyphosate/dicamba applied POST or a two-pass program of a PRE residual herbicide followed by glyphosate/dicamba applied POST. At 8 weeks after application (WAA), pyroxasulfone (150 g ai ha-1), S-metolachlor/metribuzin (1943 g ai ha-1), pyroxasulfone/sulfentrazone (300 g ai ha-1) and flumioxazin/pyroxasulfone (240 g ai ha-1), applied PRE, resulted in 71%, 85%, 82% and 90% GR waterhemp control, respectively. The same PRE herbicides, followed by glyphosate/dicamba (1800 g ae ha-1) POST, improved control to greater than 96%. This study concludes that a two-pass program of an effective soil applied residual herbicide followed by glyphosate/dicamba POST controlled GR waterhemp in glyphosate/dicamba-resistant soybean.

Carinata Tolerance to Preemergence and Postemergence Herbicides

Carinata is a new biofuel crop that was recently introduced in the southeastern USA as a winter crop. This crop is competitive after canopy closure, but there is a need for weed control options at earlier growth stages. Field experiments were conducted from 2014 to 2016 to determine the safety of several PRE and POST herbicides in carinata. Pendimethalin at 1080 g ai ha−1 applied preplant incorporated (PPI) and PRE caused no carinata injury, or plant density and yield reductions. S-metolachlor was also safe at 694, 1070, 1390, and 2780 g ai ha−1 applied at PRE, 3 d after planting (DAP) and at the 2- to 6-leaf stage. Flumioxazin at 72 g ai ha−1 applied PRE was highly injurious on carinata preventing its establishment. Among the POST herbicides evaluated, clopyralid at 210 g ae ha1 and clethodim at 136 g ai ha−1 caused minor injury to carinata but did not reduce yield compared to the nontreated control. Acifluorfen at 420 g ai ha−1, bentazon at 840 g ai ha−1, and carfentrazone at 18 g ai ha−1 applied POST to carinata caused 75 to 100% injury. Under stressful conditions (i.e. high summer temperatures) all POST herbicides caused more injury than under more favorable conditions for growth in Florida (i.e. winter). The present study identified pendimethalin, S-metolachlor, clopyralid and clethodim as potential herbicides for weed control in carinata, and flumioxazin, acifluorfen, bentazon, and carfentrazone as herbicides that can be used to control volunteer carinata plants in rotational crops.

Dicamba Spray Drift as Influenced by Wind Speed and Nozzle Type

With the release of dicamba-resistant crops, it is necessary to understand how technical and environmental conditions affect the application of dicamba. This study sought to evaluate drift from dicamba applications through flat-fan nozzles, under several wind speeds in a wind tunnel. Dicamba applications were performed through two standard (XR and TT) and two air induction (AIXR and TTI) 110015 nozzles at 0.9, 2.2, 3.6 and 4.9 ms−1 wind speeds. The applications were made at 276 kPa pressure and the dicamba rate was 561 g ae ha-1. The droplet spectrum was measured using a laser diffraction system. Artificial targets were used as drift collectors, positioned in a wind tunnel from 2 to 12 m downwind from the nozzles. Drift potential was determined using a fluorescent tracer added to solutions, quantified by fluorimetry. The air induction TTI nozzle produced the lowest percentage of dicamba drift at 2.2, 3.6 and 4.9 ms−1 wind speeds at all distances. Dicamba spray drift from XR, TT and AIXR nozzles increased exponentially as wind speed increased, whereas from TTI nozzle drift increased linearly as wind speed increased. Drift did not increase linearly as the volume percentage of droplets smaller than 100 µm and wind speed increased.

A Diagnostic Assay to Detect Herbicide Resistance in Annual Bluegrass (Poa annua)

Turfgrass managers currently have few readily available means of evaluating herbicide resistance in annual bluegrass during the growing season. Research was conducted to determine if agar-based diagnostic tests developed for agronomic weeds could be used to reliably confirm herbicide resistance in annual bluegrass harvested from golf course turf. Annual bluegrass phenotypes with target-site resistance to acetolactate synthase (ALS; R3, R7), enolpyruvylshikimate-3-phosphate synthase (EPSPS; R5), and photosystem II (PSII; R3, R4) inhibiting herbicides were included in experiments along with an herbicidal susceptible phenotype (S). Single tiller plants were washed free of soil and transplanted into autoclavable polycarbonate plant culture boxes filled with plant tissue culture agar amended with a murashigee-skoog medium and trifloxysulfuron (6.25, 12.5, 25, 50, 75, 100, or 150 μM), glyphosate (0, 6, 12, 25, 50, 100, 200, or 400 μM), or simazine (0, 6, 12, 25, 50, 100, 200, or 400 μM). Mortality in agar was assessed 7 to 10 days after treatment (depending on herbicide) and compared to responses observed after treating individual plants of each phenotype with trifloxysulfuron (28 g ai ha-1), glyphosate (1120 g ae ha-1), or simazine (1120 g ai ha-1) in an enclosed spray chamber. Fisher’s exact test (α = 0.05) determined that mortality in agar with 12.5 μM trifloxysulfuron and 100 μM glyphosate was not significantly different than treating whole plants via traditional spray application. Mortality with all concentrations of simazine in agar was significantly different than that observed after treating resistant and susceptible phenotypes via traditional spray application. Our findings indicate that an agar-based diagnostic assay can be used to detect annual bluegrass resistance to ALS- or EPSPS-inhibiting herbicides in less than 10 days; however, additional research is needed to refine this assay for use with PSII-inhibiting herbicides.