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

Abstract

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.

Spray solution pH and soybean injury as influenced by synthetic auxin formulation and spray additives

“…The two meta-analyses on dicamba volatility focused on visual injury and soybean yield (Egan et al 2014;Kniss 2018). Sall et al (2020) recently reported that no impact on plant height or soybean yield was detected after exposure to dicamba volatility in 23 field studies. The low-tunnel methodology used in the current study is a valuable tool to compare the effect of dicamba volatility on soybean.…”

“…Secondary dicamba movement via volatility is well documented (Behrens and Lueschen 1979;Egan et al 2014;Egan and Mortensen 2012;Jones et al 2019a;Sall et al 2020;Sciumbato et al 2004a;Soltani et al 2020) and may have been the culprit of some nontarget injury complaints over the 2017 through 2019 growing seasons. The seminal paper on dicamba volatility was published in 1979, reporting secondary movement from applications of dimethylamine (DMA) salt of dicamba in corn under field conditions in Minnesota (Behrens and Lueschen 1979).…”

Dicamba emissions under field conditions as affected by surface condition

“…Although the sensitivity of these bioassays is more than adequate, a quantitative assessment via air sampling followed by chemical extraction and analysis may yield more direct indications of herbicide behavior (Mueller et al 2013;Mueller 2015). In a multi-state dicamba field flux study, dicamba OTM was reported at all locations, and up to 0.3% of applied dicamba was measured (Riter et al 2020;Sall et al 2020). There was no apparent relationship between recorded meteorological and soil conditions for each trial and the observed dicamba OTM.…”

Quels enseignements tirer du retrait de l’atrazine dans le cadre de l’interdiction prévue du glyphosate ?

“…Actuellement, il conviendra donc d'assumer la réduction de l'usage de ces molécules herbicides très efficaces dont l'utilisation est remise en cause par une partie de la population. Aux États-Unis, ce sont les dégâts liés à la volatilité du dicamba qui font fortement débat, du fait de son utilisation importante pour contrôler les adventices résistantes au glyphosate dans les PGM (Sall et al, 2020).…”