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Disease Control and Pest Management

Sites of Action of Fungicides in the Control of Citrus Melanose. J. O. Whiteside, Professor of Plant Pathology, University of Florida, Institute of Food and Agricultural Sciences, Agricultural Research and Education Center, P. O. Box 1088, Lake Alfred, FL 33850; Phytopathology 67:1067-1072. Accepted for publication 1 March 1977. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1067.

Major sites of action against Diaporthe citri were determined for basic copper sulfate (BCS), captafol, dithianon, benomyl, and chlorothalonil. Relatively long protectant action on fruit rind was provided by single postbloom sprays of BCS, captafol, and dithianon, but not by chlorothalonil, thus explaining, at least in part, why field control of melanose with chlorothalonil has been variable and often poor. Benomyl provided little protectant action, but, unlike the other fungicides, it inhibited inoculum production on dead twigs. Such antisporulant action probably explains why prebloom benomyl sprays have reduced melanose severity on rind. Redistribution of applied material from sites of application to newly exposed susceptible tissue apparently played a major role in disease control only with captafol. Although captafol did not reduce inoculum production, it did reduce the number of viable conidia that reached the surface of previously unprotected tissue. Captafol deposits on bark were more lethal than were deposits of the other fungicides to conidia suspended in water that contacted briefly a treated bark surface.