Quantifying Dicamba Volatility under Field Conditions: Part II, Comparative Analysis of 23 Dicamba Volatility Field Trials.

This study summarizes 23 field trials (over six geographic locations, with each trial composed of a separate field site and an application event) for quantifying the postapplication volatilization of dicamba from fields treated with an array of dicamba-containing formulations and tank adjuvants at an application rate of 0.56 or 1.12 kg dicamba acid equivalents (a.e.) per hectare (0.5 or 1.0 lb dicamba a.e. per acre). The data span 3 years of testing over a range of locations, field types, and environmental conditions. The aerodynamic and the integrated horizontal flux methodologies were employed (and then averaged) for estimating the vertical flux from the field for periods extending to approximately 72 h post application. In all cases, the vertical flux peaked within 24 h of application and then decayed to much lower levels by day 3. Total volatile losses among all formulations and conditions ranged from 0.023 ± 0.003 to 0.302 ± 0.045% of the applied dicamba (median = 0.08%). Analysis of the recorded meteorological and soil conditions for each field trial failed to identify any single soil or weather parameter as a dominant driver of total volatile losses. Air concentrations of dicamba observed in the course of these trials were all below the no observed adverse effect concentration for conventional soybean plant height or yield, indicating that air concentrations directly above or outside of the dicamba-treated area would not cause a reduction in plant height or yield of conventional soybean.