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Fate of Diclofop-methyl After Application to a Wheat Field¹

ABSTRACT

Dissipation of diclofop-metnyl, the methyl ester of the herbicide diclofop ((±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid), and its acid metabolite (diclofop) in atmospheric, agronomic, and edaphic components were measured in a wheat (Triticum aestivum L.) field during and following application on 29 June 1982. Drift losses during application were <0.1% of the applied herbicide. Air samples, collected at six heights (ranging from 30–200 cm) above the crop canopy during the first 7 d after application did not show measurable levels of diclofop-methyl, thus indicating minimal losses due to volatilization. The crop canopy intercepted 21% of the applied ester. On entry into the crop, the ester was rapidly hydrolyzed to the metabolite diclofop acid, so that after 5 d only 2% of the intercepted ester could be solvent washed from the treated wheat. At first there appeared to be a rapid metabolism of diclofop acid in the wheat, with approximately 5% of initially applied ester remaining in the acid form after 5 d. Thereafter, the rate of loss of the acid was slower, but metabolism of the diclofop acid was essentially complete after 32 d. No diclofop ester or acid was detected in the wheat straw or grain at harvest 88 d after application. In the soil, hydrolysis of the methyl ester to diclofop acid was rapid and complete within 9 d of application. The acid underwent slow breakdown in the field soil and on 14 October, 126 d after application, 19% of the initial herbicide treatment was still present in the top 7.5-cm soil depths as diclofop acid.

Key Words: air concentration • drift • herbicide • herbicide vapor flux • post-application losses • residues • Triticum aestivum L.

¹ Contribution of Environmental Chemistry of Herbicides Section, Research Station, Agriculture Canada, Regina, SK S4P 3A2, Canada.

² Residue Chemist, Section Head, Residue Chemist, Meteorologist (Sask. Res. Council, Saskatoon, SK), and Agronomist, respectively. Please direct all communications to Dr. Grover.

Received for publication July 29, 1985.

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