Volatilization of Standalone Dicamba and Dicamba Plus Glyphosate as Function of Volatility Reducer and Different Surfaces

Abstract

Dicamba is a herbicide with a moderate volatility profile. Such volatility behavior can be significantly diminished with formulation technology and volatilization reducers. The objective of this study was to quantify the volatility potential of dicamba diglycolamine salt (DGA) in a standalone application or in tank mixture with glyphosate (potassium salt) (GK), with and without volatilization reducer (acetic acid—VaporGrip®) from different surfaces. The combination of these products was applied on four different surfaces (glass slides, corn straw, and dry and moist sandy soil) with three replications, and the experiment was duplicated. The application was performed indoors with an automated sprayer. After application, targets were positioned in cartridges containing two filters in series. Cartridges were placed in a vapor collection system that consisted of a chromatographic oven with constant temperature of 40 °C attached to a vacuum pump for 24 h. After this period, liquid samples were obtained from an extraction procedure of filters and surfaces, which corresponded to the volatilized and deposited portions of the herbicides, respectively. The samples were analyzed by liquid chromatography–tandem mass spectrometry (LC-MS/MS). The use of this method provided a rapid and consistent evaluation, in which the treated surface exerts a direct influence on the amount of volatilized dicamba. The mixture of dicamba and glyphosate solutions exhibited different volatility profiles as a function of the treated surfaces. The DGA applied alone had the largest level of volatility when applied on moist soil and the lowest level of volatility in dry soil and straw. The DGA with GK had volatilities similar in dry soil, wet soil and straw. The volatility reducer in the tank mixture was effective in reducing DGA dicamba volatilization, regardless of the sprayed surface and the tank mixture, making the application of dicamba safer from the volatilization standpoint.

Evaluating methods and factors that affect dicamba volatility

“…In Brazil, with the greater adoption of the no-tillage system in soybean, corn and cotton and the double-crop system in the Cerrado region (soybean/corn), a significant amount of the dicamba will be deposited in straw after spraying. The no-tillage system in Brazil is implemented on approximately 33 million hectares and continues to be expanded (Instituto Brasileiro de Geografia e Estatistica, 2017), and the relation of the dicamba with the mulch surface is different from that with the soil or plant leaf surface (Carbonari et al, 2020). In this study, for all treatments and surfaces tested, the addition of a VR significantly reduced volatilization, highlighting the importance of its use in dicamba applications.…”

“…This is a method that allows the quantification with precision and in controlled conditions of the volatilized dicamba, allowing to simulate different situations that occur in the field, as well as to compare different treatments in the same condition. In the same way, with the same advantages, (Carbonari et al, 2020) developed a method for evaluating volatilization from a vapor sampled system composed of a PVC tube with inlets to hold 24 cartridges and an outlet containing a connection (3 mm) to a vacuum pump (30 mL min -1 ). This system was placed inside a precision chamber to maintain a constant temperature at 40 °C.…”

“…In addition, pH levels lower than 5.0 may increase the dicamba volatility potential, and using pH modifiers approved by the US Environmental Protection Agency (EPA) to increase the pH of the solution is recommended. (Carbonari et al, 2020) found that even with the addition of potassium salt to a dicamba solution, volatilization did not increase for some surfaces, such as glass and wet soil. Sharkey et al (2020) also found that the association of glyphosate to a dicamba solution significantly decreased the pH value; however, volatilization did not increase significantly, indicating that even with lower pH values, there may be no increases in volatilization.…”

“…While the efficacies of different salts may be equivalent, the volatilities of the different dicamba salts are different. The literature indicates that the DGA or BAPMA dicamba salts are less susceptible to volatilization than the DMA dicamba salt under controlled or field conditions (Mueller et al, 2013;Egan, Mortensen, 2012;Carbonari et al, 2020;Mueller, Steckel, 2019a). The volatilization of dicamba applied in the form of DGA salt was reduced by 94% compared to that of dicamba applied in the form of DMA salt (Mueller et al, 2013).…”

“…In this study, for all treatments and surfaces tested, the addition of a VR significantly reduced volatilization, highlighting the importance of its use in dicamba applications. However, application on wet soil increased volatilization in relation to dry soil or straw (Carbonari et al, 2020). This may have occurred due to the high-water solubility of dicamba together with its low affinity with the solid soil phase (Kerle et al, 2007).…”