scanty. There is no single, comprehensive data source, derived from actual sampling, on pesticide usage for all crops and all chemicals.

The U.S. Department of Agriculture's (USDA) Economic Research Service (ERS) conducted national surveys of pesticide use in 1964, 1966, 1971, 1976, and 1982; smaller areas and fewer crops have been included in successive surveys. The 1964, 1966, and 1971 surveys included field crops, fruits, vegetables, and livestock. In 1976 fruits and vegetables were excluded from the survey, and in 1982, only major field crops (e.g., corn, soybeans, cotton, wheat, barley, oats, peanuts, tobacco, alfalfa, and hay) were sampled (Osteen and Szmedra, 1989). The foci of later reports on pesticide usage are even narrower: vegetable, melon, and strawberry crops in Arizona, Florida, Michigan, and Texas (USDA, 1991); fruits and nuts, in 12 states (USDA, 1992a); and eight field crops (corn, cotton, peanuts, potatoes, rice, sorghum, soybeans, and wheat) in different numbers of states, ranging from 47 states for corn down to 2 states for rice and 1 for durham wheat (Osteen and Szmedra, 1989).

Resources for the Future maintains a county-based file of annual pesticide usage estimates by county and by crop for the 184 widely used pesticides that appear on EPA's list for the National Ground Water Survey and the California Priority Pollutant List (Gianessi, 1986). The usage information was derived from the limited ERS surveys and from the annual California survey (State of California, 1981), which included only restricted-use of chemicals until 1991, when the state's reporting system was extended to all pesticides, including unrestricted chemicals. Resources for the Future has also estimated the amounts of pesticides applied to lawns and in nurseries.

The data in Table 6-1 illustrate the variation in the kind and amount of pesticides used on crops in various geographic regions. The corn belt, for example, accounted for 39% of all pesticides used on major crops in 1982. Most of this volume was represented by herbicides; fungicides constituted only 2% of total usage. In contrast, the southeast accounted for only 8% of total pesticide applications but for 66% of fungicides used. There are similar differences in use patterns between other regions.

The implications for residue and exposure estimation are more clearly illustrated in Table 6-2, which focuses on one crop (fall potatoes) and one class of pesticides (fungicides) and their application in the northeast, midwest, and western regions of the United States. In 1991, 96% and 90% of croplands planted with potatoes in the northeast and midwest, respectively, were treated with fungicides, while only 52% of croplands in the west were treated. Fungicides were also applied more times during the growing season in the northeast and midwest. As a result, the northeast, which accounts for 11% of the hectares planted with potatoes, accounts for 30% of all fungicide hectare treatments

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