production. Yields have increased steadily and dramatically since the 1940s, and specialized production of one or a few crops has become the norm for growers.

Insecticides

By the 1950s, insecticides were used broadly on high-value crops especially susceptible to arthropod attack: cotton (66 percent treated, by area), fruits and nuts (81 percent), potatoes (80 percent), vegetables (74 percent), and tobacco (58 percent). During the 1960s and 1970s both herbicides and insecticides were used on corn and tobacco, and use was expanded to include other major field crops such as cotton, soybean, sorghum, rice, peanuts, wheat and other small grains, hay, and pasture (Osteen and Szmedra, 1989).

From 1964 to 1982 the total volume of insecticide use on cotton declined (Osteen and Szmedra, 1989) after the introduction of pyrethroids, a pesticide used at much lower rates but applied more frequently (Zalom et al., 1992). During this same period, the volume of insecticide applied to corn and soybean nearly doubled. In 1982 the amount of insecticide used on soybean and corn exceeded that used on cotton for the first time in the United States (Osteen and Szmedra, 1989).

Herbicides

During the 1960s and 1970s, increased herbicide applications on corn and soybean accounted for the largest pesticide use increases (Lin et al., 1995). By the 1980s herbicides accounted for 75 percent of total volume of pesticides applied to agricultural crops. The total amount of herbicides used decreased in the 1990s in part because newly introduced herbicides were used at lower application rates. Rice crops, though their total acreage is small, receive the most intensive use of herbicides, 2.5 kg/hectare (5.6 lb/acre). Herbicides account for more than 90 percent of pesticide applications in corn and soybean production today (Lin et al., 1995).

Declining Use

Since peaking in 1982, pesticide use declined from 270 million kg (600 million lb) in 1982 to 260 million kg (570 million lb) in 1992. Currently, corn and soybean production, occupying the largest percentage of crop acreage in the United States, dominate pesticide use. On a per-acre basis, however, pesticides are used more intensively on many fruit and vegetable crops, including potatoes, than on corn; for example, fungicides applied to citrus and apple trees (3.6 million kg or 8 million lb) account for 23 percent of all fungicides used. Cotton accounts for about 10 percent of all pesticides used. Pesticide applications on



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