Sethoxydim Metabolism in Monocotyledonous and Dicotyledonous Plants

14 C-Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} was rapidly metabolized by quackgrass [ Agropyron repens (L.) Beauv. ♯ AGRRE], barnyardgrass [ Echinochloa crus-galli (L.) Beauv. ♯ ECHCG], alfalfa ( Medicago sativa L. ‘Saranac’), and navy bean ( Phaseolus vulgaris L. ‘Seafarer’). One hour after application, 46, 27, 38, and 46% of the total 14 C in the ethyl acetate-soluble fraction from treated leaves was sethoxydim, respectively. After 24 h, less than 2% was sethoxydim in any species. Nine metabolites were found, seven of which cochromatographed with photo- and thermal-transformation products of sethoxydim. Two metabolites, previously shown to be phytotoxic to barnyardgrass, contained the majority of 14 C up to 24 h after application. Quantitative or qualitative differences in the metabolites of treated leaves could not account for the observed differences in selectivity.