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 ground water 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 run off form sprayed fields and harm the aquatic biota.