Selectivity Mechanisms for Foliar Applications of Diclofop-methyl. II. Metabolism

The fate of foliarly applied 14 C diclofop-methyl {methyl 2-[4-(2,3-dichlorophenoxy)phenoxy] propanoate} was determined in intact plants of barnyardgrass [ Echinochloa crus-galli (L.) Beauv.], a susceptible (S) grass; proso millet ( Panicum miliaceum L.), a moderately susceptible (MS) grass; longspine sandbur [ Cenchrus longispinus (Hack.) Fern.], a tolerant (T) grass; soybean [ Glycine max (L.) Merr. ‘Hark’], and cucumber ( Cucumis sativus L. ‘Green Star’), both T broadleaf plants, 1,3, and 5 days after treatment (DAT). Diclofop-methyl accounted for 94% of the radioactivity washed from the leaf surfaces of all species. Plant extracts contained diclofop-methyl, diclofop, and water-soluble conjugates. Barnyardgrass (S), proso millet (MS), and soybean (T) had 75, 68, and 66% of the extracted radioactivity as diclofop and diclofop-methyl. Longspine sandbur (T) and cucumber (T) had 71 and 84% of the extracted radioactivity as water-soluble conjugates. Acid hydrolysis of the water-soluble conjugates yielded 84 and 71% diclofop in barnyardgrass (S) and proso millet (MS). Cucumber (T), soybean (T), and longspine sandbur (T) had 43, 23, and 25% ring-OH diclofop. Alkaline hydrolysis of the non-extracted plant residue yielded diclofop as the major component in all species.