ABSTRACT
Pesticides are an essential component of modern farming practice. A great deal of effort has been devoted to studying the effects of herbicides on plant pathogens and plant diseases, leading to a number of comprehensive reviews on the subject. This chapter emphasizes the effects of pesticides, including fungicides and insecticides, on crops. The total number of microorganisms in soil is seldom changed with the normal rate of herbicide application on agricultural lands, since the herbicide may benefit one group of organisms and injure another group. Herbicide persistence in soil depends on many factors, including the chemical structure of the herbicide, rainfall or irrigation, temperature, soil moisture, pH, organic matter, clay content of soil, and soil microorganisms. As with greenhouse tests, field tests demonstrating nontarget effects of herbicides are variable. One of the best documented examples of beneficial side effects of herbicides is the reduction of root rot of peas caused by Aphanomyces euteiches.
