Persistence of isofenphos and isazophos in a mineral and an organic soil

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Abstract
Isofenphos (Amaze, Oftanol, BAY 92114, 1-methylethyl 2-[[ethoxy[(1-methylethyl)amino] phosphinothioyl]oxy]benzoate) (20% granular) and isazophos (Miral, CGA 12223, 0,0-diethyl O-[1-isopropyl-5-chloro-1,2,4-triazolyl]phosphorothioate) (50% emulsifiable concentrate) were applied at 3.4 kg AI[active ingredient]/ha and incorporated into sand and muck soil contained in small field plots. Soil samples were taken at intervals, extending over 2 yr in the case of isofenphos. Radishes and carrots served as indicator crops for absorption of insecticides. Soil and crop samples were extracted and analyzed for the insecticides by GLC. Isazophos residues in soil declined rapidly with .apprx. 50% of the initial applications remaining after 2 and 5 wk in the sand and muck, respectively and < 1 and 3% after 1 yr. Isofenphos residues declined slowly with .apprx. 50% of the initial application remaining at 12 wk in both soil types. Residues of isofenphos after 1 yr were 15 and 45% of the initial application to sand and muck, respectively, and after 2 yr they had declined to 4 and 14%, respectively. Residues of both materials in radishes and carrots generally did not exceed 0.04 ppm except for carrots grown the 1st yr in isofenphos treated sand, where 0.25 ppm were found.