Persistence of isofenphos (Amaze®) soil insecticide under laboratory and field conditions and tentative identification of a stable oxygen analog metabolite by gas chromatography

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Abstract
Field plots in central and northern Illinois [USA] were treated with isofenphos (Amaze 20G) 1.12 kg AI[active ingredient]/ha in an 18 cm band over the corn row at planting time. Soil samples were collected at .apprx. 2 wk intervals for 2 mo. after application. In the central Illinois field, isofenphos concentration was virtually unchanged after 35 days in spite of heavy rains, and the DT-50% (the time interval until 50% of the initial insecticide residue disappeared) was .apprx. 43 days. In the northern Illinois field, a shorter lag period was observed, and the DT-50% was .apprx. 31 days. Isofenphos oxon was detected in both fields within 2 wk after treatment, and by 2 mo. its concentration had increased to 0.35 and 1.34 .mu.g/g, or 17 and 21% of the initial parent insecticide recovered in the northern and central Illinois fields, respectively. Isofenphos oxon was a stable degradation product that was produced in nearly quantitative amounts from the parent insecticide in laboratory studies. The rate of isofenphos loss from soil in laboratory experiments depended on initial insecticide concentration. The toxicological significance of isofenphos and its own oxon to corn rootworm control was discussed.

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