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Performance Characteristics of Dicloran, Iprodione, and Vinclozolin for Control of Sclerotinia Blight of Peanut. T. B. Brenneman, Research Associate, Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg 24061. P. M. Phipps, and R. J. Stipes. Associate Professor of Plant Pathology, Virginia Polytechnic Institute and State University, Tidewater Research Center, Suffolk 23437; and Professor of Plant Pathology, Virginia Polytechnic Institute and State University, Blacksburg 24061. Plant Dis. 71:546-548. Accepted for publication 26 January 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0546.

A technique using peanut stems was devised to quantify the persistence of three fungicides and their toxicity to Sclerotinia minor. Dicloran, iprodione, and vinclozolin were applied in the field to peanut stems until runoff at rates of 10, 3.3, and 2.5 mg/ml, respectively. The persistence of fungicidal activity on stems was quantified weekly via a bioassay involving inoculation of 8.5-cm-long stem segments with mycelial plugs of S. minor. Inhibition of resulting lesions showed vinclozolin to be the most persistent fungicide followed by iprodione and dicloran. Comparisons of fungicidal and nonfungicidal treatments indicated that vinclozolin and iprodione act primarily to prevent initial infection. Although dicloran was the least fungicidal, it was the most effective inhibitor of lesion elongation and therefore appears to have a different mode of action. Time, solar radiation, and precipitation were each correlated (P = 0.01) with reduced levels of inhibition by the fungicides over time. ED50 concentrations of dicloran, iprodione, and vinclozolin were 42.3, 7.6, and 2.5 g/ml, respectively, according to bioassays performed immediately after treatment of stems in the laboratory. Slopes of the dosage-response curves for both iprodione and vinclozolin were much steeper than that of dicloran, which helps explain the observed differences in activity in the field study.

Keyword(s): Arachis hypogaea, fungicide persistence.