Soybean (Glycine max) are highly sensitive to dicamba (3,6-dichloro-2-methoxybenzoic acid), an auxin-type herbicide, making them at risk for injury from drift events. Analysis of plant samples following a drift event often occurs weeks after the exposure, by which time dicamba has dissipated below the detection limits of currently available analytical methods. Consequently, the impact of environmental factors on the dissipation of dicamba following a drift event are poorly understood. To determine the dissipation of dicamba and the effect of water stress, a simulated drift event of dicamba at 5.6 g acid equivalent ha-1 (a 1/100th labeled rate of Engenia™, BASF Corporation) was applied to soybean at V1 growth stage. Soybean were maintained at field capacity or at a low soil moisture content to induce drought stress. Plants were visually assessed for symptomology at 3, 7, 14, 21, and 28 days after the simulated drift treatment (DAT). Shoots, roots, and soil were collected for analysis of dicamba and metabolites concurrent with visual assessment ratings, and included additional sampling times at 0, 1, and 2 DAT. Herbicide residue analyses were performed using LC/MS/MS methods developed to optimize quantification for low concentrations of the parent and metabolites. Preliminary results indicate that the drought-stressed soybean display reduced injury compared to plants that were maintained at field capacity. These findings suggest that environmental factors, such as soil moisture content, may impact the dissipation of dicamba in susceptible soybean varieties, and could help agencies target analytes for drift-complaint cases and provide additional information for estimating timing and initial concentrations.

Impact of water stress on dicamba dissipation in susceptible soybean

254th National Meeting (2017)

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