The misapplication of insecticides may result in damage to crops.
Evidence is accumulating to show that the excessive or continuous use of insecticides may damage crop yields. Continuous use of chlorinated hydrocarbons, such as DDT, which decompose very slowly in the soil, may increase chemical levels to a point where crop growth, especially of sensitive plants such as cucumbers and potatoes, is seriously retarded. The organophosphorus aphicides can also adversely affect plant growth and development. These insecticides, particularly Thionazin, when mixed with sand on field soil, delayed the germinations of wheat seeds by two weeks, produced abnormalities among those that did grow, and appreciably lowered their growth. In beans, effects can be seen at a concentration of 27 ppm of chemical - for example, necrotic leaf lesions where the insecticide is accumulating. Growth of the seed leaves of beet is inversely related to the concentration of insecticide applied. Germination is also delayed, and with 125 ppm of phosphate or Thionazim, germination is reduced to 60 to 70%.