Effects of Simulated Acidic Rain on Retention of Pesticides on Leaf Surfaces

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Abstract
Commerical formulations of cupric hydroxide, chlorothalonil and triphenyltin hydroxide (TPTH) fungicides were applied to leaves of potato or snap bean plants. After a 24 h drying period, the plants were exposed to a single application of simulated acidic rain at a rate of 1 cm/h. 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 ion commonly found in rain in the northeastern USA. Increases in acidity of simulated rain accelerated loss of cupric hydroxide and TPTH but not of chlorothalonil from plant leaves. The major influences 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 infuence of rainfall on wash-off of some pesticides.
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