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

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

Dicamba off‐target movement from applications on soybeans at two growth stages

Abstract The objective of this study was to evaluate dicamba off‐target movement during and after applications over soybean at two growth stages. Dicamba‐tolerant soybean [Glycine max (L.) Merr.] at V3 and R1 growth stages in Nebraska and Mississippi fields were treated with diglycolamine salt of dicamba (560 g ae ha−1), potassium salt of glyphosate (1260 g ae ha−1), and a drift‐reducing adjuvant (0.5% v v−1). Filter papers positioned outside the sprayed area were used to determine primary movement and air samplers positioned at the center of sprayed area were used to calculate dicamba flux from 0.5 up to 68 hours after application (HAA). Flux was calculated using the aerodynamic method. Soybean growth stage did not affect dicamba deposition on filter papers from 8 to 45 m downwind from the sprayed areas. At 33 m downwind (i.e., distance of the labeled buffer zone), a spray drift of less than 0.0091% (0.05 g ae ha−1) of applied rate is estimated. Dicamba secondary movement may not be affected by soybean growth stage during the application. Although dicamba was detected in air samples collected at 68 HAA, the majority of the secondary movement was observed in the first 24 HAA. Dicamba cumulative loss was lower than 0.77% of applied rate. Results suggest the more stable the atmospheric conditions, the higher the dicamba flux. Thus, meteorological conditions after applications must be considered, and tools to predict the occurrence of temperature inversion are needed to minimize secondary movement of dicamba

Dicamba off-target movement from applications on soybeans at two growth stages

The objective of this study was to evaluate dicamba off-target movement during and after applications over soybean at two growth stages. Dicamba-tolerant soybean [Glycine max (L.) Merr.] at V3 and R1 growth stages in Nebraska and Mississippi fields were treated with diglycolamine salt of dicamba (560 g ae ha−1), potassium salt of glyphosate (1260 g ae ha−1), and a drift-reducing adjuvant (0.5% v v−1). Filter papers positioned outside the sprayed area were used to determine primary movement and air samplers positioned at the center of sprayed area were used to calculate dicamba flux from 0.5 up to 68 hours after application (HAA). Flux was calculated using the aerodynamic method. Soybean growth stage did not affect dicamba deposition on filter papers from 8 to 45 m downwind from the sprayed areas. At 33 m downwind (i.e., distance of the labeled buffer zone), a spray drift of less than 0.0091% (0.05 g ae ha−1) of applied rate is estimated. Dicamba secondary movement may not be affected by soybean growth stage during the application. Although dicamba was detected in air samples collected at 68 HAA, the majority of the secondary movement was observed in the first 24 HAA. Dicamba cumulative loss was lower than 0.77% of applied rate. Results suggest the more stable the atmospheric conditions, the higher the dicamba flux. Thus, meteorological conditions after applications must be considered, and tools to predict the occurrence of temperature inversion are needed to minimize secondary movement of dicamba