Evaluation of potassium borate as a volatility-reducing agent for dicamba

Abstract

Dicamba was labeled in dicamba-resistant cotton (Gossypium hirsutum L.) and soybean [Glycine max (L.) Merr.] in 2017, resulting in a record number of off-target complaints. To address off-target movement via volatilization, experiments were conducted to evaluate the effectiveness of potassium tetraborate tetrahydrate (KBo) as a volatility-reducing agent (VRA) with dicamba. Low-tunnel experiments examined: 1) whether KBo functions as a dicamba VRA, 2) the relationship between KBo concentration and dicamba volatilization, 3) the effectiveness of KBo compared to potassium acetate as a VRA, and 4) the impact of KBo on dicamba volatilization with and without glufosinate. In a large-scale trial (0.4-ha plots), the effectiveness of KBo in reducing dicamba volatilization was quantified relative to a commercial dicamba application labeled for use in 2020. The addition of KBo to dicamba reduced volatility over dicamba alone and a dicamba plus potassium acetate premix. As KBo concentration increased in the dicamba spray solution, volatilization was reduced exponentially. Dicamba volatilization with the addition of KBo at 0.01 M was comparable to dicamba plus potassium acetate at 0.05 M. Potassium tetraborate tetrahydrate was more effective than potassium acetate at reducing volatility of a dicamba plus glufosinate mixture. In large-scale experiments over a 30-hr period, the addition of KBo to a DGA dicamba plus glyphosate mixture lowered dicamba volatilization 82 to 89% over the herbicide mixture alone. Overall, the addition of KBo to dicamba appeared promising as a VRA compared to what is commercially available.

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

“…According to the results of this research, to minimize dicamba volatility, the addition of a VRA and the removal of glyphosate from the solution with dicamba substantially reduced the concentration of dicamba in air samples following application, and the impact to soybean bioindicator, particularly injury, and distance of lateral movement determined until 5% injured plants, regardless to surface treatment. These findings agree with those of previous research that reported that glyphosate enhanced dicamba volatility while the buffering activity of VRAs reduced its volatility by up to 89% (Castner et al 2022; Glenn 2022).…”

“…The reduction in dicamba emissions was expected by including VRA, as its main component (acetate) scavenged protons in the solution, reducing the conversion of dicamba salt to the acid form of the herbicide, with a high volatility potential (Abraham 2018). This research used potassium acetate-based VRA (VaporGrip Xtra), which was comparable with the formulation used in previous studies that measured the of potassium carbonate-based VRA (commercially known as Sentris) and experimental potassium borate-based VRA on dicamba volatility (Castner et al 2022; Mueller et al 2022). The pH measurements of solutions used in this experiment were similar to those mentioned above.…”

“…Three experiments were conducted at the Milo J. Shult Agricultural Research and Extension Center near Fayetteville, AR (36.0989°N, 94.1792°W), from 2018 to 2022 growing seasons. The procedures employed in each of the three experiments to evaluate dicamba volatility relied on the establishment of low tunnels, high-volume air sampling, and evaluations of dicamba injury symptoms on bioindicator susceptible soybean, which were similar to published methods (Castner et al 2022; Oseland et al 2020; Striegel et al 2020). The common methods for these experiments have been described below, followed by a detailed description of each experiment.…”

“…Experiments using controlled environments in a laboratory allow comparisons using different treatment combinations to measure the relative impact on dicamba volatility; however, they do not represent field conditions, where multiple environmental factors interact simultaneously, affecting the potential to detect herbicide emissions. Low-tunnel experiments were carried out to examine herbicide volatility (Castner et al 2022; Oseland et al 2020; Sosnoskie et al 2015; Striegel et al 2020) because they allow multiple treatment comparisons, including mixtures with dicamba, where dicamba volatility can quantified by air sampling or injury symptom evaluation on susceptible vegetation, without the impact of particle drift.…”

Dicamba air concentrations in eastern Arkansas and impact on soybean

“…Research has shown off-target dicamba movement to occur via primary drift, secondary movement, and tank contamination (Cundiff et al 2017; Jones et al 2019b; Maybank et al 1978; Teske et al 2002). Research has shown that one of the main sources of the secondary movement of dicamba is volatility (Castner et al 2022; Egan and Mortensen 2012; Jones et al 2019b; Mueller and Steckel 2019b, 2021; Oseland et al 2020b; Soltani et al 2020; Zaccaro-Gruener et al 2022), and characteristics of the compound are important to consider for this type of transport.…”