Interaction Effects of Selected Pesticides on Soil Enzymes

The laboratory studies were conducted to resolute the effects of imidacloprid (insecticide) and triadimefon (fungicide) singly and in combination on enzymatic activities of soil microorganisms in tomato cultivated soils at different concentrations of 0.2, 0.5 and 0.7 kg/ha. The rate of amylase activity was stimulated by the application of pesticides at field rate. High dosage decreased the activity of amylase. Decline in the activity of cellulase was observed at all concentrations than control. Imidacloprid had an improved activity of cellulase at 0.5 μg/g than tridimefon and combination. At higher concentration (0.7 μg/g), the combination of insecticide and fungicide showed an antagonistic interaction toward cellulase. After 24 h, maximum inhibition was observed in invertase enzyme rate at all examined dosages. After 48 h, the activity was revived to some extent and imidacloprid showed enhanced activity at 0.5 μg/g (field rate). However at 0.7 μg/g, imidacloprid has a noticeable effect on the invertase. The pesticide application in single and in combination (0.2‑0.7 μg/g soil) triggered the dehydrogenase activity. At field rate triadimefon significantly quickened the activity.