Dicamba off‐target movement from applications on soybeans at two growth stages

Abstract

The objective of this study was to evaluate dicamba off‐target movement during and after applications over soybean at two growth stages. Dicamba‐tolerant soybean [Glycine max (L.) Merr.] at V3 and R1 growth stages in Nebraska and Mississippi fields were treated with diglycolamine salt of dicamba (560 g ae ha−1), potassium salt of glyphosate (1260 g ae ha−1), and a drift‐reducing adjuvant (0.5% v v−1). Filter papers positioned outside the sprayed area were used to determine primary movement and air samplers positioned at the center of sprayed area were used to calculate dicamba flux from 0.5 up to 68 hours after application (HAA). Flux was calculated using the aerodynamic method. Soybean growth stage did not affect dicamba deposition on filter papers from 8 to 45 m downwind from the sprayed areas. At 33 m downwind (i.e., distance of the labeled buffer zone), a spray drift of less than 0.0091% (0.05 g ae ha−1) of applied rate is estimated. Dicamba secondary movement may not be affected by soybean growth stage during the application. Although dicamba was detected in air samples collected at 68 HAA, the majority of the secondary movement was observed in the first 24 HAA. Dicamba cumulative loss was lower than 0.77% of applied rate. Results suggest the more stable the atmospheric conditions, the higher the dicamba flux. Thus, meteorological conditions after applications must be considered, and tools to predict the occurrence of temperature inversion are needed to minimize secondary movement of dicamba.

Chemical Weed Control and Crop Injuries Due to Spray Drift: The Case of Dicamba

“…Soybean (Glycine max (L.) Merr.) [7,17,18] Rice (Oryza sativa L.) [19] Cotton (Gossypium hirsutum L.) [20] Peanut (Arachis hypogaea L.) [21] Tomato (Solanum lycopersicum L.) [18,22,23] Lettuce (Lactuca sativa L.) [18] Pumpkin (Cucurbita maxima Duch) [18] Oilseed rape (Brassica napus L.) [18] Pepper (Capsicum annuum L.) [18] Sunflower (Helianthus annuus L.) [18] Cucumber (Cucumis sativus L.) [7] Eggplant (Solanum melongena L.) [7] Snap bean (Phaseolus vulgaris L.) [7] Potato (Solanum tuberosum L.) [24] Sweetpotato (Ipomoea batatas (L.) Lam.) [25] Mandarin (Citrus reticulata) [26] Grapevine (Vitis vinifera L.) [27] Brazilian peppertree (Schimus terebinthifolius Raddi.)…”

“…In particular, a downwind buffer is required in areas with endangered species concerns, and such distances are increasing in the new labels in order to minimize drift, reduce pesticide exposure, and avoid damaging neighboring crops and non-crop vegetation. Air temperature fluctuations and inversions promote drifting and, therefore, farmers and applicators should avoid sowing their crops in the low parts of their fields and stop spraying early in the morning [8,17]. As Soltani et al [8] suggested, further research is necessary in order to determine the secondary movement of dicamba under various environmental conditions.…”

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

“…Off-target dicamba movement, in principle, can occur through multiple processes during or after application; ,, among these processes, volatilization of dicamba has been identified as an important pathway for off-target dicamba movement after application. − The role of volatilization has been specifically elucidated in field trials, as well as emphasized in a 2021 US EPA report on dicamba off-target movement, which stated that “Officials from numerous states posit that secondary movement, or volatility, is the cause of the majority of off-target incidents.” Although dicamba volatilization remains a persistent problem, efforts have been made to reduce dicamba volatilization by adding additional chemical agents to dicamba formulations. , These agents include amines, which deprotonate dicamba to its nonvolatile anion. , Amines in current dicamba formulations approved for postemergent application include diglycolamine (DGA) and n , n -bis­(3-aminopropyl)­methylamine (BAPMA) salts, which decrease dicamba volatilization relative to dimethylamine (DMA) and isopropylamine (IPA) formulations. − Recently, pH buffers have also been added to dicamba formulations to maintain the pH of the formulation solution above the p K a of dicamba (p K a = 1.9) . Although the inclusion of these buffers reduces dicamba volatilization compared to unbuffered solutions, , dicamba volatilization (i.e., after spray application) does not consistently correlate with solution pH, ,, suggesting that other factors beyond pH control of formulation solutions may affect volatilization.…”