Chlorotoluron Metabolism in Leaves of Resistant and Susceptible Biotypes of the Grass Weed Alopecurus myosuroides

The metabolism of the herbicide chlorotoluron by susceptible and resistant biotypes of the grass weed, Alopecurus myosuroides, was examined. After administration of radiolabelled herbicide to leaves, metabolites were extracted and analysed. The metabolites identified consisted of mono‐demethylated‐, di‐demethylated‐ and ring methyl‐hydroxylated chlorotoluron. Metabolism was more extensive in the resistant biotype, yielding principally the non‐phytotoxic ring methyl‐hydroxylated metabolite. The metabolites observed are characteristic of the activity of cytochrome P450 mixed‐function oxygenase action. The specific cytochrome P450 inhibitor, 1‐aminobenzotriazole, reduced accumulation of the ring methyl‐hydroxylated metabolite in the resistant biotype.