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Permethrin and Sulprofos Washoff from Cotton Plants as a Function of Time between Application and Initial Rainfall

USDA-ARS, Soil and Water Research Unit, 4115 Gourrier Ave., Baton Rouge, LA 70808;
USDA-ARS National Sedimentation Laboratory, P.O. Box 1157, Oxford, MS 38665.

^* Corresponding author.

ABSTRACT

Understanding pesticide foliar washoff is important in environmental modeling, pest management, and development of integrated management systems. This study was conducted to determine the effect of elapsed time between spray application and initial rainfall on insecticide washoff from foliage. Permethrin [(3-phenoxyphenyl)-methyl(1K,S)-cis,trans-3-(2,2-dichloroethenyl)2,2-dimethylcyclopropanecarboxylate] and sulprofos [O-ethyl O-(4-methylthiophenyl)-S-propyl phosphorodithioate] were applied to mature cotton (Gossypium hirsutum L.) plants as tank-mixed emulsifiable concentrates with a water carrier. Simulated rain (51 mm in 1 h) was applied to the cotton plants at different times after insecticide application to determine washoff characteristics for both compounds. Residues of both insecticides became increasingly resistant to washoff with increasing time interval between insecticide application and initial rainfall. The mean amounts of both insecticides washed from the plants were related to the mean insecticide loads on the plants and decreased with time. On the average, the first 2 to 3 mm of rain removed 50% of the total amounts of insecticide washed from the plants by the 51-mm storm.

(retired)

In cooperation with the Louisiana Agric. Exp. Stn., Lousiana State Univ. Agric. Center; and the Mississippi Agric. and Forestry Exp. Stn.

Received for publication December 9, 1992.