Pesticide applications of copper on perennial crops in California, 1993 to 1998.

Inorganic copper is used as a broad-spectrum fungicide and bacteriocide on a variety of agricultural crops. After application, the copper residue typically accumulates in the upper 15 cm of soil. Data from the California Pesticide Use Reports were used to estimate the augmentation of copper in the soil that resulted from pesticide applications for the six years from 1993 to 1998 on 12 crops that are grown without rotation. The estimated mean mg Cu kg(-1) soil added to the upper 15 cm during the six years was the following: walnut (Juglans regia L.), 28; peach [Prunus persica (L.) Batsch var. persica], 22; nectarine [Prunuspersica (L.) Batsch var. nucipersica (Suckow) C.K. Schneid], 19; cherry (Pseudolmedia oxyphyllaria Donn. Sm.), 18; rice (Orvza sativa L.), 16; apricot (Prunus armeniaca L.), 11; orange [Citrus sinensis (L.) Osbeck) and plum (Prunus domestica L. subsp. domestica ), 9; lemon [Citrus limon (L.) Burm.f.] and almond [Prunus dulcis (Mill.) D.A. Webb], 6; pear (Pyrus communis L.), 4; and grape (Vitis vinifera L.), 3. In addition, for the first five of these crops, we estimated the area that was treated with each level of kg Cu ha(-1). For example, for walnut orchards, we estimated that 12 500 ha, or 17% of the planted area, was treated with a quantity of Cu that would increase the total concentration of Cu in the upper 15 cm of soil by at least 50 mg Cu kg(-1) soil. A comparison of the amount of Cu per unit planted area that was applied in the first and second half of the study indicated that the intensity of copper use is either relatively constant or increasing, depending on the crop. The findings are discussed in relation to the potential effect of continued long-term use of Cu pesticides on soil sustainability.