Studies on the fate of fungicides in different soil environments

The present investigation was undertaken to study the persistence, degradation and metabolism of the metalaxyl-mancozeb in soil under laboratory; greenhouse and field experimental conditions. The degradation pattern of metalaxyl, mancozeb and ethylenethiourea (ETU) residues followed first order exponential degradation kinetics in different soil environments. Slower degradation of metalaxyl and mancozeb was noticed and their half-life values ranged from 41.24 to 165.11 days in soils under laboratory incubation. The half-life values for metalaxyl were in the range of 6.52 to 9.57 days, while those of mancozeb ranged from 9.74 to 12.41 days for different treatments in greenhouse condition. The rapid disappearance of metalaxyl and mancozeb residues to the extent of 59.2 to 72.4 and 3.81 to 48.3% was found within 10 days of fungicide application at the two application rates. The degradation of fungicide residues in soils under the field conditions was faster than in laboratory incubation studies. The half-life values were less than 10 days for metalaxyl, and 7 days for mancozeb. The residues of both the fungicides received by the soil from foliar application to tomato crop, did not persist beyond 30 days.