Absorption and metabolism of the herbicide 3-(2'-methylphenoxy)pyridazine (H-722) by susceptible (barley) and tolerant (tomato) plants were investigated with a tritium labeled chemical to obtain fundamental information on residue analysis as well as on selective action. Four metabolites were clearly detected, for which chemical structures were assigned, except a minor one. They were 3-(2'-methylphenoxy)pyridazine-l-oxide, 3-pyridazinone-(2H) and 3-(1-β-D-glucosyloxy) pyridazine. The fate and behavior of o-cresol which should be a metabolite resulting from cleavage of the aromatic ether linkage in H-722 is considered a key to the mechanism of the herbicide's selective action.

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