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Disease Control and Pest Management

A Statistical Model of Fungicide Deposition on Potato Foliage. J. A. Bruhn, Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Present address of senior author: E. I. du Pont de Nemours & Co., Biochemicals Department, Experimental Station, Wilmington, DE 19898; W. E. Fry, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 72:1301-1305. Accepted for publication 12 February 1982. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1301.

The amount of chlorothalonil deposited on potato foliage was monitored via gas-liquid chromatography to develop a mathematical description of fungicide deposition under a variety of application conditions. The effects of canopy density, potato cultivar, application method, and application dosage on the initial deposition of chlorothalonil were assessed. More fungicide was deposited on foliage at the top of the canopy than on foliage near the ground. The amount of fungicide deposited on leaves was highly variable throughout the potato canopy. The relative frequency distribution of residue levels was skewed; there were greater frequencies of low than high concentrations. These characteristics were accurately described by a model in which the amount of fungicide deposited on potato foliage was described by a separate gamma probability distribution for each of four canopy strata. This model was appropriate under a broad range of application conditions, but factors such as plant growth, potato cultivar, application method, and application dosage affected the magnitude of the parameters. Fungicide models that ignore the variability in fungicide residue levels will overestimate the impact of fungicides on pathogen development, even when accurate plant disease models are used.