DICLOFOP-METHYL PERSISTENCE IN SOUTHWESTERN ONTARIO SOILS AND EFFECT OF PH ON HYDROLYSIS AND PERSISTENCE

Abstract

The persistence of the herbicide diclofop-methyl, methyl 2-(4-(2,4-dichlorophenoxy)) phenoxy)propionate, was measured in two soils under field conditions in southwestern Ontario. The hydrolysis of the herbicide ester to its corresponding acid, diclofop, 2-(4-(2,4-dichlorophenoxy)phenoxy)propionic acid, was slower at pH 5.5 than at higher pH but soil pH had no effect on subsequent degradation of diclofop or metabolites formed. After hydrolysis of the ester the acid degraded to 12–39% of the original concentration in 34 days and less than 14% of the applied herbicide, identified as diclofop, was recovered at the end of the growing season. During the course of the degradation small amounts of the metabolites 4-(2,4-dichlorophenoxy)phenol and 4-(2,4-dichlorophenoxy)phenetole were identified from their relative retention time (Rf) on silica gel plates along with traces of other nonidentified compounds. None of the identifiable products except diclofop was present at the last sampling date. Combustion of soils treated with 14C-diclofop-methyl revealed 26–32% of the radioactivity was not extracted at the end of the growing season. Key words: Hoegrass, diclofop degradation, soil residue, soil reaction, 14C-diclofop-methyl