Understanding Off-Target Movement in Dicamba Applications

Dicamba applications on dicamba-tolerant (DT) soybeans have been highly scrutinized over the last five years. With continuing label changes and off-target movement issues, it is essential to understand current dicamba application practices and investigate potential areas that need attention to improve future dicamba applications. Additionally, the use of drift reducing adjuvants (DRAs) became mandatory in almost every dicamba application on DT crops, but limited information is available about their impact. Therefore, a unique series of studies was conducted to examine the impact of DRAs tank-mixed with dicamba on spray droplet size distribution, physicochemical properties, spray pattern uniformity, spray coverage, and weed control. The first study investigated current dicamba application practices on corn and DT soybeans through a statewide survey. Results showed great adoption of important practices to reduce spray particle drift and other aspects that need special attention. Results highlighted the importance of better management of dicamba applications on corn. The second study investigated the impact of DRAs tank-mixed with dicamba on solution’s physical properties and consequent impact on spray pattern uniformity. DRAs significantly increased the viscosity leading to improper overlap between nozzles. Approved sprayer setup configurations may result in spray pattern collapse. The third study investigated the impact of DRAs on spray droplet size distribution, physicochemical properties, and spray coverage of commonly used dicamba tank-mixtures. DRAs effectively increased spray droplet size and reduced driftable fines but can be unstable under high pressures. Most important factors impacting spray droplet size was discussed as well as the most consistent nozzle design and DRA combination. The last study examined the impact of different dicamba tank-mixtures containing DRA on weed control. Tank-mixture efficiency was dependent on weed species and field location characteristics