the decrease in useful pests how its affect plant health
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The damage to plants caused by competition from weeds and by other pests including viruses, bacteria, fungi, and insects greatly impairs their productivity and in some instances can totally destroy a crop. Today, dependable crop yields are obtained by using disease-resistant varieties, biological control practices, and by applying pesticides to control plant diseases, insects, weeds, and other pests. In 1983, $1.3 billion was spent on pesticides—excluding herbicides—to protect and limit the damage to crops from plant diseases, nematodes, and insects. The potential crop losses in the absence of pesticide use greatly exceeds that value.
For about 100 years, breeding for disease resistance has been an important component of agricultural productivity worldwide. But the successes achieved by plant breeding are largely empirical and can be ephemeral. That is, because of a lack of basic information about the function of genes for resistance, studies are often random rather than specifically targeted explorations. In addition, any results can be short-lived because of the changing nature of pathogens and other pests as new genetic information is introduced into complex agroecological systems.
An excellent example of the effect of genetic change is the sterile pollen trait bred into most major corn varieties to aid in the production of hybrid seed. Plants containing Texas (T)