Higley, 1992; Tette and Jacobsen, 1992; Zalom and Fry, 1992). Indeed, some scientists have proposed that the term biologically intensive IPM be used to distinguish IPM strategies that rely on biologically based tools from those that depend primarily on conventional broad-spectrum pesticides (Edwards, 1991; Ferro, 1993; Frisbie and Smith, 1989; Pedigo and Higley, 1992; Prokopy, 1993; Zalom and Fry, 1992). The historical emphasis on arthropod control, and the subsequent lower priority of pathogen and weed management, does create some confusion for IPM practitioners seeking environmentally sound and economically feasible answers to pest management problems.

Naturally occurring compounds, biological-control organisms, and resistant plants have been developed and used for most of the history of pest management. With the advent of synthetic chemical pesticides, emphasis in research and practice shifted away from biologically based strategies. However, contemporary advances in scientific knowledge coupled with the long experience of the past provides a solid foundation for renewed effort in identifying appropriate ecological approaches to pest management.

OBSTACLES TO CONTINUED USE OF BROAD-SPECTRUM PESTICIDES

Pesticides were readily accepted by growers because, at least initially, they were quite successful at suppressing pests. However, problems began shortly after pesticide use became widespread. Arthropod resistance to DDT was first observed in Sweden in 1946, only 7 years after DDT was introduced. By 1948, 14 species of arthropods were reported to be resistant to DDT, cyclodienes, organophosphates, carbamates, or pyrethroid insecticides; that number exceeded 500 by 1990 (Gould, 1991). But the problem is not simply that some pests develop resistance; some were never controlled by pesticides. For some soilborne pathogens, nematodes, arthropods, and aquatic weeds, there are no acceptable conventional chemical pesticides.

Widespread use of pesticides has also raised concerns about the health effects of pesticide residues in foods humans and livestock animals eat. In 1954, the Food, Drug, and Cosmetic Act was amended to set maximum tolerance levels of pesticide residues in raw agricultural commodities because of concern about health effects and dietary exposure.

Problems and Limitations of Pesticides

The early success of broad-spectrum, synthetic pesticides raised hopes that pest problems that had plagued agriculture from its inception had finally been solved. The inability to sustain the initial effects achieved by conventional pesticides, however, is an important reason to be concerned about continued dependence on ineffective pesticides that may also adversely impact nontarget species



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