Abstract

                                It is not always true that crops grown in soils with nutrients optimum for vigorous plant growth are able to with stand the attack. of insect pests better than the crops grown in deficient soils. Experimental facts are available where certain pests have shown a greater preference for crops having luxurient growth as a result of increased plant nutrients in the soil. Schoene (1941) showed that the injury to apple trees by the mealy bug, Pseudococcus comstockii Kuw., was most severe in orchards that had been treated with nitrogenous fertilizers for several years but no damage occurred on unfertilized trees. Gadd (1943) noted increased damage to tea plants by the borer, Xyleborus fornicatus Egg., following increased amounts of nitrogenous, phosphatic and potassium fertilizers. The results of the field experiments conducted by McGarr (1943) showed that the nitrogenous fertilizers caused a definite increase in the number of aphids, Aphis gossypii Glov,, on cotton. Eden (1953) found that the damage of the rice weevil on the maize in the field încreased with the addition of nitrogen in the soil. During the past several years it has been observed that pyrilla infestation was severe in sugarcane fields with higher level of manuring. Similar observations have also been made by Mathur and Gupta (1940) and Mathur (1941).

Key words :