Pesticides Residues from Sequential and Mixture Applications and their Impact on Soil Microbial Population of Tomato Field

Tomato (Lycopersicon esculentum Mill.) crop suffers devastation due to infestation by insect pests (such as fruit borer, white fly, aphids etc.), diseases (early blight and late blight, leaf curl, buck eye rot or fruit rot etc.) and weeds (like Cynodon dactylon, Euphorbia hirta etc.) that cause tremendous yield losses. To protect the health of crop, farmers apply insecticides, fungicides, nematicides and herbicides sequentially in tomato crop at various growth stages. This often leads to contamination of soil with various pesticides which have deleterious impact on soil microbial population. Studies were undertaken to evaluate persistence and residual fate of pesticides in soil when applied sequentially and/or simultaneously as mixture in tomato crop. Four pesticides were chosen for the crop, pendimethalin as pre-emergence herbicide, imidacloprid and chlorothalonil as soil treatment followed by imidacloprid, chlorothalonil and endosulfan as foliar spray during early stage of growth. The different treatments were combined keeping the pendimethalin and non-pendimethalin treated plots as the main plots. Results revealed that sequential application of pesticides left their residues in soil which reduced microbial population in soil. But instead, if applied simultaneously as mixture, the combination effectively controlled various insect pests and diseases improving health of the crop. The mixture application reduced pesticide contamination in soil eventually deterring its ill effect on soil microbial population and retaining soil fertility as it is.