Evaluation and Development of Effective Tank Cleanout Procedures Following Dicamba Use

Sprayer hygiene and concerns of off-target injury from auxin herbicides have increased in recent years. New auxin tolerant crops have broadened the use patterns of these herbicides. Therefore, experiments were conducted across two locations in Mississippi in 2016, 2017, and 2018 to evaluate sprayer cleanout procedures to aid in dicamba removal. Standard sprayer cleanout consisted of a triple rinse of 10% tank volume, with either a tank cleaner or ammonia added in the second rinse. Samples collected in each rinse step for all treatments were applied to actively growing soybean and dicamba concentration quantified with HPLC. Experiments were conducted to determine if various tank cleaners and ammonia produce visual injury when applied to actively growing soybean and cotton alone and in conjunction with glyphosate. No tank cleaner caused visual injury nor affected plant heights or yield. Furthermore, experiments were conducted to evaluate tank cleaner effectiveness to remove dicamba utilizing the standard cleanout procedure, with increased rinse volumes, sequence of water and tank cleaner rinses, and cleanout effectiveness following durations of idle time from application to cleanout. No tank cleaner provided greater dicamba removal, with all cleaners performing the same as cleanouts utilizing water alone. Increasing rinse volumes did not positively affect dicamba removal compared to 10% rinse volumes. Multiple rinse steps utilizing a tank cleaner or altering the standard cleanout procedure utilizing a water-tank cleaner-water rinse sequence did not result in greater dicamba removal from contaminated sprayer systems. Finally, increases in time between contamination with dicamba and cleanout did not negatively influence dicamba removal using the standard cleanout procedure

Dicamba tank mixtures and formulations and their effects on sensitive crops during cleanout procedures

The introduction of dicamba-tolerant (DT) soybeans (Glycine max L. Merr) and cotton (Gossypium hirsutum L) in 2017 provided an additional tool for herbicide resistant weeds management. In the subsequent years, off-target movement of dicamba allegedly caused damage to sensitive crops and vegetation. Possible causes of off-target movement include tank contamination, physical drift, and volatility. Additional products, such as herbicides to control grass, are often added to tank with dicamba, which is used to control broadleaf weeds, to increase the spectrum of control and application efficiency. Dicamba products registered for DT crops require the use of drift reducing agents to mitigate unintended effects to adjacent crops. Sprayers are complex machines with valves, hoses, tanks, and nozzles that can retain herbicide residues and cause symptomology and/or injury to crops if proper cleanout procedures are not performed. Recommended cleanout procedures can be found in dicamba product labels, but there is no information available reporting the effect of tank mixtures or different dicamba formulations on retention of residues. The objective of this research was to: 1) evaluate the dicamba retention of potential tank mixtures with dicamba and drift reducing adjuvants, clethodim as well as tank-cleaning agents on non-DT soybeans, 2) evaluate the cleanout procedures of commonly used dicamba products, on non-DT soybean, and 3) investigate how the rinsate following cleanout procedures of dicamba mixtures affect such as soybean, cotton, tomatoes (Lycopersicon esculentum) and peanuts (Arachis hypogaea L.). Advisor: Christopher Procto

Dicamba Retention in Commercial Sprayers Following Triple Rinse Cleanout Procedures, and Soybean Response to Contamination Concentrations

The commercial launch of dicamba‐tolerant (DT) crops has resulted in increased dicamba usage and a high number of dicamba off‐target movement complaints on sensitive soybeans (Glycine max L.). Dicamba is a synthetic auxin and low dosages as 0.028 g ae ha−1 can induce injury on sensitive soybean. Tank contamination has been identified as one of the sources for unintended sensitive crop exposure. The labels of new dicamba formulations require a triple rinse cleanout procedure following applications. Cleanout efficacy might vary based on the sprayer type and procedure followed. This study was performed to quantify dicamba retention in commercial sprayers and assess the risk for crop injury from remaining contaminants. The results indicate triple rinse with water was comparable to cleanout procedures utilizing ammonium, commercial tank cleaners, and glyphosate in rinses. Dicamba contaminants in final rinsates resulted in \u3c15% visual injury and no yield response when applied to sensitive soybeans at R1 stage. A survey of 25 agricultural sprayers demonstrated a cleanout efficacy of 99.996% by triple rinsing with water following applications of dicamba at 560 g ae ha−1, with concentrations of less than 1 ug mL−1 detected rinsates from the fourth rinse. A dose response experiment predicted dosages causing 5% visual injury and the yield losses were 0.1185 and 2.8525 g ae ha−1. However, symptomology was observed for all tested dosages, including the rate as low as 0.03 g ae ha−1. The results from this study suggest triple rinsing with sufficient amount of water (≥10% of tank volume) is adequate for the removal of dicamba residues from sprayers to avoid sensitive soybean damage. This study can provide producers with confidence in cleanout procedures following dicamba applications, and aid in minimizing risk for off‐target movement through tank contamination

Environmental and human impacts on off-target movement of dicamba

Widespread use of dicamba on tolerant soybeans (Glycine max L.) since 2017 has resulted in reports of off-target movement. Although symptomology is quite striking, the relationship of sensitive soybean damage to crop yield is unclear. Field studies were established in 2018 and 2019 at three locations in central Missouri to assess the response of sensitive soybean to driftable concentrations of dicamba. Effects of dicamba were observed as early as 7 days after treatment (DAT). Apical meristem growth was reduced 10 to 54% and visual injury ranged from 15 to 47% at 21 DAT. Average soybean yield was significantly reduced by dicamba concentrations as low as 25 ppm and influenced by the developmental stage (V3 and R1) at the timing of dicamba exposure. Model statements were generated to predict yield reduction based on known dicamba concentrations and visual injury ratings 21 days after dicamba exposure. Statistical analysis of the prediction equations found the dicamba concentrations and soybean injury were adequate and accurate to predict soybean yield reductions in response to dicamba. Lastly, a subset of soybeans exposed to dicamba concentrations (0, 150, and 300 ppm dicamba) were collected prior to harvest, extracted using the rapid and effective (QuEChERS) method, and quantified by high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS). Using HPLC, mean dicamba residues in soybean samples were 0.0, 0.72, and 0.81 mg kg-1 following exposure to 0, 150, and 300 ppm dicamba, respectively. Location significantly impacted residual dicamba concentrations, averaging 0.70, 0.35, and 0.54 mg kg-1 at Bradford (2018), Boonville (2018), and Bradford (2019), respectively. Individual samples did not exceed 10 mg kg-1 but samples with dicamba concentrations exceeding 0.5 mg kg-1 dicamba could violate residue limits for USDA National Organic Program standards. This study would suggest that sensitive soybeans that were injured by dicamba drift and allowed to go to yield would be safe for human consumption in the United States but could potentially violate the USDA regulations if driftable concentrations of dicamba moved off-target onto soybeans produced organically.Includes bibliographical references

Effects of Tank Contamination and Impact of Drift-Reducing Agents on Weed Control in Response to Dicamba Applications

Availability of dicamba-tolerant (DT) crops from 2017 provided farmers with additional herbicides for weed control management in row crops. However, the technology alike this one has concerns regarding dicamba off-target movement (OTM) causing undesirable effects on sensitive vegetation. Even though dicamba has high water solubility OTM that has often been overlooked when it comes to unintended crop exposure is dicamba tank contamination. Considering the complexity of spraying equipment soybean response may be expected even when small amounts of residues are left in the spray equipment. Typically, the same field spray equipment is used to perform herbicide application through growing season there is a limited knowledge how various postemergence (POST) programs impacts soybean response when found in scenario with dicamba tank contamination and requires additional research. Furthermore, as one way to mitigate OTM potential release of DT crops was followed with registration of various agents also known as drift-reducing agents (DRAs). Increased awareness of both growers and commercial applicators to reduce unintended adjacent crops injury use of labeled DRAs in combination with drift-reduction nozzles represent common practice. Exposure of sensitive crops to sublethal doses of dicamba has been well documented over several years; however, there is limited information available how combination with commonly used DRA’s may impact application process and weed control. Considering limitations on available literature the main objective of this research were: 1) evaluate response of non-DT soybean variety when exposed to commonly applied POST herbicide program in combination without or with dicamba as tank-contaminant and 2) evaluate impact of DRAs on weed control in response to dicamba applications. The results of this research expanded knowledge and will help in education in the future management decisions about potential implications associated with common mitigation techniques used with dicamba application as well as helped with understanding how various POST herbicide program affect soybean response. Advisor: Greg R. Kruge

Evaluation of dicamba volatility when applied under field and controlled environmental conditions

Dicamba resistant (DR) cropping technology has increased dicamba use, resulting in observation of dicamba off-target-movement (OTM). Volatility is one form of this movement. Tank mixtures and environmental conditions impact the volatile behavior of dicamba following application. Research was conducted in 2018, 2019, and 2020 to further assess and understand volatility mitigation by understanding tank-mix effects and utility of irrigation on volatility mitigation. Low tunnel and humidome methodology were used to analyze impact of tank mixtures and irrigation on dicamba volatility. Data suggest tank mixing encapsulated chloroacetamide formulations can mitigate volatility when comparing identical active ingredients formulated as emulsifiable concentrates. Tank-mixed glyphosate increases dicamba volatility regardless of salt form, with dimethylamine salt of glyphosate having the most volatile effect. Manipulation of environmental conditions can also assist in mitigation efforts when applicable through use of irrigation. Increasing amount of irrigation applied following dicamba application has a positive effect on mitigation

Soybean Response to Dicamba: Associated Injury Criteria and Development of a Model to Predict Yield Loss

In research conducted using indeterminate soybean [Glycine max (L.) Merr.], fourteen injury criteria observed following dicamba at 0.6 to 280 g ae ha-1 (1/1000 to ½ of 560 g ha-1 use rate) were rated using a scale of 0= no injury, 1= slight, 2= slight to moderate, 3= moderate, 4= moderate to severe, and 5= severe. Greatest crop injury 15 d after treatment (DAT) was observed following dicamba applied at 0.6 to 4.4 g ha-1 at V3/V4 for upper canopy pale leaf margins (3.8 to 4.2) and at R1/R2 for terminal leaf cupping (4.1 to 5.0) and, following 0.6 to 8.8 g ha-1 dicamba applied at V3/V4 for upper canopy leaf cupping (3.8 to 4.8) and upper canopy leaf surface crinkling (3.4 to 4.4). At 15 DAT, injury was no greater than the nontreated control when dicamba rate was as high as 4.4 g ha-1 for lower stem base swelling (V3/V4 application) and for upper canopy leaf rollover/inversion and terminal leaf necrosis (R1/R2 application) and for rates as high as 8.8 g ha-1 for leaf petiole base swelling and stem epinasty (R1/R2 application) and lower stem base lesions/cracking (V3/V4 and R1/R2 applications). In contrast, overall injury ratings (0 to 100%) showed a steady increase as dicamba rate increased. Injury data were analyzed using multiple regression with a forward selection procedure to develop yield prediction models. Variables included in the V3/V4 15 DAT model were lower stem base lesions/cracking, plant height reduction, terminal leaf epinasty, leaf petiole droop, leaf petiole base swelling, and stem epinasty. For the R1/R2 15 DAT model, variables included lower stem base lesions/cracking, terminal leaf chlorosis, leaf petiole base swelling, stem epinasty, terminal leaf necrosis, and terminal leaf cupping. To validate the models, experiments were conducted at two locations and predicted yield reduction for each dicamba rate was compared with observed yield reduction. For dicamba at 0.6 to 4.4 g ha-1, the V3/V4 15 DAT model either underestimated or overestimated observed yield loss by 1 and 3 percentage points and the R1/R2 15 DAT model overestimated observed yield loss by 3 to 5 percentage points

EVALUATION OF THE INFLUENCE OF DICAMBA EXPOSURE ON CROP INJURY AND CANOPY CLOSURE OF GLUFOSINATE RESISTANT SOYBEAN

Dicamba-resistant soybean along with lower volatility dicamba formulations have been introduced in an attempt to control herbicide resistant weeds such as Amaranthus palmeri. This introduction has increased the amount of dicamba being applied later in the growing season increasing the prevalence of dicamba off-target movement. Dicamba damage was simulated by applying low rates of dicamba directly on soybeans at rates (0.5 g ae ha-1, 1 g ae ha-1 and 5 g ae ha-1 dicamba) and five-exposure timings from June 1 to July 10. The experimental design was a randomized complete block with four replications at five locations. Crop and trifoliate injury ratings were taken 21 and 28 DAE (days after exposure) as well as yield, canopy closure ratings 21, 28 and 35 DAE and Palmer amaranth density was determined in both 2018 and 2019. When comparing injury across exposure dates it was observed that the early June exposures resulted in peak injury at 21 DAE whereas the late June and early July exposure peaked at 28 DAE. Yield was only reduced in 2019 with the lowest yield occurring due to exposure on June 20 at 5g ae ha-1. Differences were observed in canopy closure in both years, with a more pronounced and prolonged canopy closure delay in 2019. Overall dicamba exposure date had a greater influence on canopy development than exposure rate likely due to variations in soybean growth stages at the different exposure dates

Sensibilidade de plantas de eucalipto (Eucalyptus urograndis) à subdoses do herbicida dicamba

In view of the widespread increase in herbicide-resistant weeds, biotechnology companies have developed dicamba-tolerant soybean and cotton cultivars. This technology can, however, increase the risk of the product drifting to adjacent areas. This study was developed with the objective of the to evaluate the phytotoxicity and biometric variables of young eucalyptus plants exposed to subdoses of the herbicide dicamba. The experiment was carried out under field conditions in Rio Verde, state of Goiás, Brazil. The treatments were represented by the application of 0 (control), 7.5, 15, 30, 60, 120 or 240 g ae ha-1 of dicamba 45 days after the seedlings were planted in the field. In terms of phytotoxicity, the dicamba doses of 120 and 240 g ae ha-1 caused greater damage to the eucalyptus plants in all periods of evaluation. The predominant symptoms were epinasty, increased number of shoots and necrosis and senescence of young branches and leaves. The herbicide doses of 120 and 240 g ae ha-1 significantly compromised plant height and diameter, number of branches and dry mass of leaves and roots, interfering with the growth and development of the eucalyptus crop. The results indicate that the effect of subdoses of the herbicide dicamba can interfere with the proper development of young eucalyptus plants, which may cause losses in the initial planting phase and future losses for producers.Em decorrência do aumento generalizado de plantas daninhas com resistência a herbicidas, empresas de biotecnologia desenvolveram cultivares de soja e algodão tolerantes ao herbicida dicamba. Essa tecnologia pode, no entanto, aumentar o risco do produto ser deslocado para áreas adjacentes às aplicadas. Neste trabalho objetivou-se avaliar a fitotoxicidade e variáveis ​​biométricas de plantas jovens de eucalipto tratadas com subdoses do herbicida dicamba. O experimento foi realizado em condições de campo em Rio Verde, Goiás, Brasil. Os tratamentos foram representados pela aplicação de 0 (testemunha), 7,5, 15, 30, 60, 120 ou 240 g ea ha-1 de dicamba aos 45 dias após o plantio das mudas no campo. Em termos de fitotoxicidade, as doses de dicamba de 120 e 240 g ea ha-1 causaram maiores danos às plantas de eucalipto em todos os períodos de avaliação. Os sintomas predominantes foram epinastia, aumento do número de brotações e necrose e senescência de ramos e folhas jovens. As doses de herbicidas de 120 e 240 g ea ha-1 comprometeram significativamente a altura e diâmetro das plantas, número de ramos e massa seca de folhas, caules e raízes, interferindo no crescimento e desenvolvimento da cultura do eucalipto. Os resultados indicam que o efeito de subdoses do herbicida dicamba pode interferir no bom desenvolvimento de plantas jovens de eucalipto, podendo causar prejuízos na fase inicial de plantio e prejuízos futuros para os produtores

Stewarding 2,4-D- and dicamba- based weed control technologies in cotton and soybean production systems

Distinguishing 2,4-D and dicamba herbicide formulations in cotton and soybean tissue is challenging in regulation of crop injury from these herbicides. Additionally, stewardship of 2,4-D and dicamba technologies is important to maximize their longevity and efficacy. Research was conducted to (1) characterize cotton and soybean response to various formulations of 2,4-D or dicamba with or without glyphosate, (2) develop a method for classifying these formulations in crop tissue, and (3) optimize use of chloroacetamide herbicides in dicamba systems for mitigation of selection pressure on dicamba. Formulations evaluated include dicamba diglycolamine (DGA), dimethylamine (DMA), N,N-Bis-(3-aminopropyl) methylamine (BAPMA), and DGA plus potassium acetate (KAc); and 2,4-D DMA, acid, isooctyl ester (ESTER), and choline. Weed management by the chloroacetamides s-metolachlor and acetochlor was evaluated with applications preemergence (PRE), early postemergence (EP), late postemergence (LP), PRE followed by (fb) EP, PRE fb LP, and EP fb LP. Cotton and soybean response differed by 2,4-D and dicamba formulation, and glyphosate presence. Cotton yield was reduced by 200 to 500 kg ha-1 following exposure to 2,4-D choline or DMA relative to acid or ESTER. Glyphosate presence led to a reduction in cotton and soybean yield of 377 and 572 kg ha-1, respectively. Exposure to dicamba DMA resulted in a 263 kg ha-1 reduction in soybean yield relative to dicamba DGA, and glyphosate presence reduced yield by 439 and 246 kg ha-1 in cotton and soybeans, respectively. Chemometric analyses generated models capable of up to 85% accuracy in identifying dicamba formulation in cotton and soybean tissue, and up to 80% accuracy in identifying 2,4-D formulation. Split chloroacetamide applications improved cotton yield up to 60%, reduced weed densities up to 90%, and improved control up to 56% relative to single applications. Cotton height was reduced up to 23% if a single chloroacetamide application was made. Soybean yield was maximized following any chloroacetamide application timing except PRE alone, and weed control was reduced up to 31% following single chloroacetamide application relative to split applications. These results will aid regulatory bodies in managing use of new weed control technologies and will assist producers in stewarding these new technologies