Persistence and degradation of monocrotophos in cabbage

Foliar application of monocrotophos in cabbage resulted in high initial residues of 6.00 and 7.54 microg g(-1) for the recommended dose (2 mL L(-1)) and double the recommended dose of monocrotophos (4 mL L(-1)) respectively. However, in farmer's practice treatment, it was found to be 2.54 microg g(-1) where it was sprayed once as fourth spray. Monocrotophos residues in cabbage after spray persisted for more than 30 days at both recommended and double the recommended dose of monocrotophos. The farmer's practice showed persistence of monocrotophos for only 15 days. Degradation of monocrotophos residues in cabbage followed first order exponential equation. Monocrotophos residues in cabbage degraded with a half-life of 2.87 to 3.05 days for four sprays at the recommended and double the recommended level of application. However, showed a half-life of 1.99 days for one spray of monocrotophos according to farmer's practice. Waiting periods /safe intervals for monocrotophos on cabbage were found to be 13.79, 15.90 and 8.55 days for the recommended, double the recommended dose and farmer's practice of monocrotophos application respectively.

Persistence and degradation of metalaxyl, mancozeb fungicides and its metabolite ethylenethiourea in soils

The degradation pattern of metalaxyl, mancozeb and its metabolite ethylenethiourea (ETU) residues indicated a close correspondence to first order exponential degradation kinetics in soils. Degradation of fungicides in soils was predominantly biological as well as chemical in nature. Slower degradation ofmetalaxyl was noticed in the soils and their half-life values were higher than mancozeb and ETU as evident by wide range of half-life values from 41.24 to 165.11 days. In case of metalaxyl, Hiriyur soil was found to be superior in degrading the metalaxyl. Lower persistence of mancozeb and ETU was observed in soils resulting in rapid rate of degradation at smaller half-life values as compared to metalaxyl indicating the faster degradation of mancozeb and ETU. In mancozeb applied soils, the ETU formation was increased up to 30 days of incubation and thereafter it declined. Amongsoils, degradation of either mancozeb or ETU is not influenced by soil types. However, mancozeb persistence was higher in Hiriyur soils than Chettalli and Bangalore soils.