Pesticides are double edged, sword extensively used for the control of pest in agriculture and in public health programme. Pesticides have helped to provide man with a healthier and cleaner environment in which to live by the control of vector disease and improvements in agricultural output. Insecticides, herbicides, rodenticides, agricultural seed dressings, plant growth regulators and others are all vital to modern man and the ever expanding human population.
Pesticides when applied to crops, is either taken up by plants and animals or is degraded by microbial or chemical processed. However, a portion is widely dispersed, some is vaporized to be eventually deposited in rainfall, and some remains in soils, while other reaches surface and ground water through run-off or leaching. Over use or misuse of pesticides affect the
environment to larger extent with serious implications on public health wildlife useful insect’s food, aquatic food chains and other habitat.
The excessive and indiscriminate use of pesticides has made the air, water and soil component of the environment polluted. The pesticides through these sources reach into the plant, enrich and human system. The non- persistent pesticides do not pose any serious problem, but the persistent ores because of their specific nature of being strongly lip phobic tend to accumulate in fat bodies and thus are of great concern. Several studies have indicated presence of pesticide residue in food commodities.
The residues find their way in human bodies through consumption of commodities with the higher level of pesticides. Chlorinated insecticides such as DDT are comparatively more persistent in the nature as compared to other classes of insecticides like organ phosphorus, carbonates and synthetic parathyroid.
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Most of the pesticides applied ultimately find their way into the soil. It has been estimated that as much as fifty per cent of the pesticides applied to crop foliage reaches soil which find its way into the aquatic system or may get accumulated in plants and crop residues. The persistence of pesticides in soil depends upon a number of factors such as soil type, organic matter content, clay content, the pH, the micro flora and fauna present in the soil. Studies have also shown the presence of pesticides in water bodies of major rivers.
At the present time, the science of plant protection and pesticides is undergoing a tremendous change. There is going to be a greater emphasis on biodegradable photosensitive and environmentally safe pesticide. It has been recently shown that biotechnology can eliminate the use of pesticides altogether.
Among the botanical pesticides, neem products have been found to be effective in controlling more than 200 species of insect, pests on different crops. Neem cake is an effective nitrification inhibitor and is blended with nitrogenous fertilizers for developing slow N- release products. Neem products also show significant nematicidal, spermicidal and ant feeding activity.