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Effects of Simulated Acidic Rain on Retention of Pesticides on Leaf Surfaces. J. Troiano, Boyce Thompson Institute at Cornell University, Ithaca, NY 14853, Present address: California Department of Food and Agriculture, 1220 N St., Room A149, Sacramento 95814; E. J. Butterfield, BASF Wyandotte Corp., Agricultural Chemicals Division, 100 Cherry Hill Road, Parsippany, NJ 07854. Phytopathology 74:1377-1380. Accepted for publication 26 May 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-1377.

Commercial formulations of cupric hydroxide, chlorothalonil, and triphenyltin hydroxide (TPTH) fungicides were applied to leaves of potato or snap bean plants. After a 24-hr drying period, the plants were exposed to a single application of simulated acidic rain at a rate of 1 cm/hr. Solutions were acidified to desired levels of pH with a mixture of sulfuric and nitric acids at a 2:1 ratio of nitrate:sulfate and background ions commonly found in rain in the northeastern United States. Increases in acidity of simulated rain accelerated loss of cupric hydroxide and TPTH but not of chlorothalonil from plant leaves. The major influence of acidity occurred in the initial phases of wash-off. Thus, experiments using deionized or tap water as surrogate rain solutions could significantly underestimate the influence of rainfall on wash-off of some pesticides.

Additional keywords: acidic precipitation, weathering.