SOUTHERN JOURNAL OF AGRICULTURAL ECONOMICS JULY, 1973 A SIMULTANEOUS EQUATION MODEL OF THE ECONOMIC-ECOLOGIC SYSTEM IN CITRUS GROVES*

In 1964, 89 percent of the citrus acreage in the of an economic-ecologic system thus places emphasis U.S. was treated with pesticides. The percentage on the interrelationships of economic plants and increased to 97 percent in 1966. Total expenditures animals with their environment. In a citrus grove, the for pesticides during the two years were 13.8 and living organisms include the citrus trees, insects, 21.3 million dollars, respectively. Expenditures on a disease pathogens, and plants. Organisms included in per acre basis were $12.74 and $18.82, respectively, this study were the citrus tree and insects thought to in these years [9, p. 9]. The trend in pesticide use on be of economic consequence. Emphasis was placed on citrus pest control has been upward. the insect populations and the yield of citrus trees. The increased usage indicates that pesticides are The structural form of this system can be written as: recognized by growers as important inputs to increase Citrus production = f (physical attributes of the output and/or improve fruit quality. The negative grove, weather conditions, side effects of pesticides on the environment are also management and cultural being increasingly recognized. practices, pest populations); Insect populations and fruit yield of citrus trees Pest populations = g (physical attributes of the are determined simultaneously by physiological grove, weather conditions