Use of low tunnels to describe effects of herbicide, adjuvant, and target surface on dicamba volatility

Abstract

Investigations of the relevance of low tunnel methodology and air sampling concerning the off-target movement of dicamba were conducted from 2018 to 2022, focused primarily on volatility. This research, divided into three experiments, evaluated the impact of herbicides and adjuvants added to dicamba and the type of surface treated on dicamba volatility. Treatment combinations included glyphosate and glufosinate, the presence of a simulated contamination rate of ammonium sulfate (AMS), the benefit of a volatility reduction agent (VRA), and a vegetated (dicamba-resistant cotton) or soil surface treated with dicamba. Volatility assessments included air sampling collected over 48 h. Dicamba treatments were applied four times to each of two bare soil or cotton trays and placed inside the tunnels. The extraction and quantification of dicamba from air samples were conducted. Field assessments included the maximum and average visible injury in bioindicator soybean and the lateral movement of dicamba damage expressed by the furthest distance from the center of the plots to the position in which plants had 5% injury. Adding glufosinate and glyphosate to dicamba increased the dicamba amount in air samples. A simulated tank contamination rate of AMS (0.005% v/v) did not impact dicamba emissions compared to a treatment lacking AMS. Adding a VRA reduced dicamba in air samples by 70% compared to treatment without the adjuvant. Dicamba treatments applied on vegetation generally produced greater amounts of dicamba detected than treatments applied to bare soil. Field assessment results usually followed differences in dicamba concentration by treatments tested. Results showed that low tunnel methodology allowed simultaneous comparisons of several treatment combinations concerning dicamba volatility.

Elucidating Factors Contributing to Dicamba Volatilization by Characterizing Chemical Speciation in Dried Dicamba-Amine Residues

“…16,18,84 Beyond dicamba, amine, and residual water, authentic residues generated in practice may contain other chemical constituents, including additional compounds commonly added to dicamba-containing spray solution (i.e., other herbicides, surfactants, adjuvants, volatilization, and driftreducing agents), 7 some of which have been observed to influence dicamba volatilization. 25,26,32,85 The impact of these additional constituents on dicamba protonation in residues may be employed to characterize their influence on dicamba volatilization. We demonstrated that one of these constituents, the herbicide S-metolachlor, did not affect dicamba proto- nation in the residues, which was consistent with its negligible effect on dicamba volatilization.…”