Hydrogen Bonding Site Number Predicts Dicamba Volatilization from Amine Salts

Amine-based formulations are widely used to decrease volatilization of carboxylic acid-containing herbicides including dicamba. Despite our reliance on these formulations, the underlying amine properties that determine their ability to control herbicide volatilization are poorly understood. In this study, we measured dicamba volatilization from solid (BAMPA) on glass as with dimethylamine (DMA), diglycolamine (DGA), and N,N-bis(3-aminopropyl)methylamine (BAPMA) as a function of temperature and amine-to-dicamba ratio, as well as in the presence of glyphosate. In all cases, we found that BAPMA had a greater ability to lessen dicamba volatilization than DMA or DGA. Even when only 1 BAPMA molecule was present for every 10 dicamba molecules, dicamba volatilization was still decreased by 70% relative to the free acid case. The particular ability for BAPMA to control dicamba volatilization could be attributed to several molecular features (i.e., molecular weight, type and number of amine functional groups). Using a set including 5 additional amines, we determined that dicamba volatilization is primarily influenced by the number of functional groups in the amine that can participate in hydrogen bonding. From these results, we propose that ability of an amine to form multiple intermolecular interactions (i.e., hydrogen bonds) in the residue may best predict their potential to prevent herbicide volatilization.