Dissipation behaviour of spinosad insecticide in soil, cabbage and cauliflower under subtropical conditions.

Background: Pesticides used on cauliflower and cabbage, which are important vegetable crops for India, must be investigated for the persistence and magnitude of their residues in the crops and soil to ensure human and environmental safety. The behaviour of spinosad, an effective insecticide with a favourable environmental profile, was investigated in field trials under subhumid and subtropical conditions.

Results: The persistence of spinosad in soil, cabbage and cauliflower was evaluated at two application rates (17.5 and 35.0 g ha(-1)) by high-performance liquid chromatography (HPLC). At 17.5 g ha(-1), spinosad persisted up to 7 days in soil, cabbage and cauliflower. However, at 35.0 g ha(-1), spinosad residues persisted up to 7 days in soil and 10 days in cabbage and cauliflower.

Conclusion: The dissipation of the insecticide from soil, cabbage and cauliflower appeared to occur in a single phase and conformed to first-order kinetics. The half-lives of spinosad residues in cabbage, cauliflower and soil were calculated as 1.5, 2.8 and 2.8 days respectively for the 17.5 g ha(-1) treatment, and as 2.6, 2.0 and 2.0 days for the 35 g ha(-1) treatment.