Management of Arthropod Pests in Cotton Production

The history of pesticide-induced pest problems in cotton production serves as one of the most compelling examples of the limitations of broad-spectrum chemical pesticides to provide long-term pest control. The development of resistance to pesticides by primary cotton pests such as the boll weevil combined with simultaneous pesticide-induced outbreaks of secondary pests led to a dramatic reduction in the early 1980s in acreage planted to cotton in the southeastern states and threatened to curtail cotton production in the Rio Grande Valley of Texas, the Imperial and Central Valleys of California, and in various Central American countries (Carlson et al., 1989; DeBach and Rosen, 1991).

Boll Weevils vs. The Chemicals

The history of attempts to manage the boll weevil (Anthonomous grandis) in the Cotton Belt is a classic example of the pesticide treadmill. The standard treatment from about 1910 through 1949 was multiple applications of calcium arsenate dust. This method was quickly replaced in 1950 when chlorinated hydrocarbon compounds such as DDT, aldrin, and dieldrin were introduced along with broad-spectrum pesticides such as toxaphene. These materials, applied either alone or in combination, were successful in managing the boll weevil—and its natural predators—until 1954 when the boll weevils development of resistance to DDT was first reported (Johnston, 1961; Smith et al., 1964).

Between 1956 and 1958, organophosphates, particularly methyl parathion, and several others such as malathion, methomyl, azinphos-methyl, carbaryl, endrin, and heptachlor, were introduced to replace DDT and other materials that had become ineffective in the battle against the boll weevil. Widespread use of these toxic, broad-spectrum insecticides eliminated the natural organisms that controlled bollworm (Heliothis zea) and tobacco budworm (H. virescens). Populations of these formerly minor pest species increased, which contributed to additional serious economic losses. DDT was then reintroduced to control bollworm, but by as early as 1962 this pest became resistant to DDT and to other chlorinated hydrocarbon and carbamate insecticides. Growers then switched back to methyl parathion; again, resistance soon developed, and by 1968 it was not uncommon for growers to apply 15 to 18 treatments per season without achieving satisfactory insect control. Rainwater (1962) estimated that one-third of all insecticides used for agricultural purposes were being applied for control of cotton pests, primarily the boll weevil. Bollworms and budworms, which had reached pest status through the use of insecticides applied to control the boll weevil, now rivaled the boll weevil as the most serious pests in cotton production.

Fortunately, pioneering work by Brazzel and colleagues (1961) showed that a series of four malathion pesticide treatments applied in the fall would reduce by 90 percent the population of boll weevils emerging in the spring. The effectiveness of this new management procedure was demonstrated in the Texas High Plains-



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