Identification of environmental factors that influence the likelihood of off‐target movement of dicamba

BACKGROUND Commercialization of dicamba‐resistant soybean and cotton and subsequent post‐emergence applications of dicamba contributed to at least 1.4 and 0.5 million hectares of dicamba‐injured soybean in the United States in 2017 and 2018, respectively. This research was initiated to identify environmental factors that contribute to off‐target dicamba movement. A survey was conducted following the 2017 growing season to collect information from dicamba applications that remained on the target field and those where dicamba moved. Weather and environmental data surrounding applications were collected and used to identify factors that reduce the likelihood of off‐target movement. Soil pH was one factor identified in the model, and field experiments were conducted in 2018 and 2019 to validate the model. Three commercially‐available dicamba formulations and one formulation currently in development were applied to soil at five distinct pH values. Sensitive soybean was used as a bioassay plant to detect dicamba volatilization. RESULTS Wind speeds the day of and following application, nearest water source to the field, soybean production acreage in the county, and soil pH were identified as factors that influence the likelihood for off‐target movement. In the field study, when dicamba was applied to pH‐adjusted soil and placed under low tunnels for 72 h, dicamba volatility increased when soil pH decreased as the model predicted. Dicamba choline, which is not commercially available, had reduced volatility compared to other formulations tested. CONCLUSION Results of this study identified specific factors that contribute to successful and unsuccessful dicamba applications and should be considered prior to applications. © 2020 Society of Chemical Industry