Factors Influencing the Persistence and Effectiveness of Chlorpyrifos in Soil

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Abstract
Chemical dissipation rates and insecticidal effectiveness against the cabbage maggot, Delia radicum (L.), were determined for row-band applications of chlorpyrifos at planting with two formulations, two methods of application, and three dilutions of water-based spray drenches in field tests on Sultan silt loam. Zero-day residues ranged from 85 to 97% of the amount applied. Time for 50% loss of insecticide ranged from 3 to 56 days. Insecticide applied in granular formulation dissipated slower than insecticide formulated as water-based spray emulsions, and soil-incorporated treatments always dissipated slower than unincorporated soil-surface treatments. Chlorpyrifos residues of water-based sprays that weathered under high mean temperatures disappeared considerably faster than residues that weathered under lower mean temperatures. Incorporated chlorpyrifos gave better cabbage maggot control than surface deposits. There was little difference in the degree of maggot damage between spring and summer tests even though residues of summer applications declined faster than those of spring applications. Increasing the water volume for soil-surface spray drenches from 3.5 to 33.2 liters of finished spray per 300 m of row increased chemical persistence and effectiveness, but only slightly.