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.