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

Authors: KRUGER, GREG - University Of Nebraska; ALVES, GUILHERME - University Of Nebraska; SCHROEDER, KASEY - University Of Nebraska; GOLUS, JEFFERY - University Of Nebraska; REYNOLDS, DANIEL - Mississippi State University; DODDS, DARRIN - Mississippi State University; BROWN, ASHLI - Mississippi State University; Fritz, Bradley; HOFFMANN, WESLEY - Retired ARS Employee

Submitted to: Agrosystems, Geosciences & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/20/2022
Publication Date: 4/7/2023
Citation: Kruger, G.R., Alves, G.S., Schroeder, K., Golus, J.A., Reynolds, D.B., Dodds, D.M., Brown, A., Fritz, B.K., Hoffmann, W.C. 2023. Dicamba off-target movement from applications on soybean at two growth stages. Agrosystems, Geosciences & Environment. 6. Article e20363. https://doi.org/10.1002/agg2.20363.
DOI: https://doi.org/10.1002/agg2.20363

Interpretive Summary: The recent intensified use of dicamba due to the development of dicamba-tolerant crops, and the need to treat glyphosate-resistant weeds has led to increased problems with off-target movement into susceptible crops and a need to understand and improve the application process. In this study, the off-target movement of dicamba during and after applications over soybean at two growth stages, and under different environmental conditions, was evaluated. While growth stage had little impact on off-target movement, the greatest flux of dicamba occurred shortly after application and under stable environmental conditions. This highlights the need to consider and account for meteorological conditions, both during the time of application and for several hours afterwards, to minimize the off-target movement both during and after the time of application.

Technical Abstract: Three years after low-volatile dicamba formulations were launched on the market, questions still remain regarding the causes of dicamba off-target movement (OTM) related to complaints about many nonsprayed fields showing symptomology from dicamba exposure. As physical drift depends upon meteorological conditions and crop growth stage during the pesticide applications, the objective of this study was to evaluate dicamba OTM during and after applications over soybean at two growth stages under different environmental conditions. Dicamba-tolerant soybean at V3 and R1 growth stages in NE and MS fields were treated with diglycolamine salt of dicamba (560 g ae ha-1) plus potassium salt of glyphosate (1260 g ae ha-1) plus 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 in 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 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), it is estimated less than 0.0091% (0.05 g ae ha-1) of applied rate. Dicamba molecules were detected on upwind filter papers. Dicamba secondary movement may not be affected by soybean growth stage during the application. Although dicamba was detected in the 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 that 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.