Crop yields in the United States are reduced by the effects of a variety of pests, including some 160 species of bacteria, 250 kinds of viruses, 8000 species of pathogenic fungi, 8000 species of in-sects, and 2000 species of weeds (/). Weeds are potentially the most damaging pests, followed by insects, plant pathogens, and nematodes (2). In spite of mechanized agriculture and advanced technology, losses of about 33 percent of potential production (J) or $20 billion annually (4) continue.
Batra, Suzanne W. T., "Biological Control in Agroecosystems" (1982). Ba. Paper 104.
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