Effects of Field Application Methods on the Persistence and Metabolism of Phorate in Soils and Its Translocation into Crops1

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Abstract
The effects of application methods of phorate at 10 lb/acre on its metabolism, toxicity, and translocation into crops were studied under field conditions. Residues were least persistent when phorate was applied solely to the soil surface; 6 days were required until 1/2 of the applied dosage could no longer be detected in the form of phorate and its metabolites. Residues were more persistent after the insecticide had been mixed with the upper 4- to 5-in. soil layer, and 30 days were required until 1/2 of the applied dosage could no longer be detected. Less than 1.6% of the applied phorate was measured 14 and 30 days after its application to the soil surface or the upper 4- to 5-in. soil layer, respectively. Highest amounts of phorate sulfoxide (3.2 and 4.88 lb. acre) were recovered from both field soils 6 days after phorate application. subsequently, the concentration of phorate sulfoxide in these soils declined rapidly, while the amounts of phorate sulfone increased, until they in turn reached their peak (1.44 and 3.5 lb/acre) at one month after soil treatment. Residues consisting entirely of phorate sulfone were found 2 months after application of phorate to the soil surface but 5 months after mixing of the insecticide with the upper soil layer. Insect mortalities were obtained with both field soils. Potatoes grown in these soils during 1971 and 1972 did not contain measurable insecticide residues. Corn silage contained phorate sulfone at 0.03 and 0.18 ppm in 1971, but no measurable residues in 1972. Carrots from both field plots contained in 1971 phorate sulfone at 0.12 and 0.50 ppm and in 1972 at 0.04 ppm after growing in the soil whose upper layer had originally been mixed with the insecticide.

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