The Degradation Pattern of Soil Applied Insecticides

The degradation pattern of soil applied insecticides was studied in the field during main (April - June) and autumn (July - September) seasons. Samples were collected from potato field treated with carbofuran (1.0 kg a.i./ha), quinalphos (1.25 kg a.i./ha) and phorate (2.5 kg a.i./ha),the commonly used insecticides to combat the major soil pests like cutworms Agrotis ipsilon (Hfn), white grubs Holotrichia sp., tuber moth Pthorimaea operculella(Zeller) and golden cyst nematode Globodera rostochinensis (Wollenweber). The rate of initial dissipation in carbofuran was 32.0 per cent in first 15 days of application in main season and up to 51.4 per cent at 30 days of application in autumn. A 70.0 per cent reduction in the initial deposit was observed for quinalphos residues up to 30 days in both seasons. The initial loss is more in phorate which declined to an extent of >80.0 per cent on day 15 in both seasons. For all the three insecticides studied the residues reached below detectable limit on 90 days after application. The respective half life values for carbofuran, quinalphos and phorate were 15.06, 14.14 and 6.99 during main season and 15.97, 12.67 and 14.17 days during autumn seasons. The degradation pattern followed first order kinetics for all three insecticides applied during both season.

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