Discuss why the pesticides are used in very accurate concentration and at very appropriate time.

Pesticides are very toxic substances, they should not be used indiscriminately. Only very accurate dose should be applied at appropriate time. Even slight excess of the pesticides is extremely harmful.

(i) Pesticides are harmful to soil biota. Therefore, they reduce soil fertility.

(ii) They pass into groundwater and make it toxic.

(iii) They enter the crop plants and make their products (leaves, stem, flowers, fruits and seeds) toxic.

(iv) Pesticides pass into surface water through runoff from sprayed fields and harm the aquatic life.