Activity of Captan and Prochloraz on Benomyl-Sensitive and Benomyl-Resistant Isolates of Monilinia fructicola. J. P. Dijkhuizen, Graduate Student, Department of Plant Pathology, University of California, Davis 95616. J. M. Ogawa, Professor, and B. T. Manji, Research Associate IV, Department of Plant Pathology, University of California, Davis 95616. Plant Dis. 67:407-409. Accepted for publication 12 September 1982. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-407.

A benomyl-resistant Monilinia fructicola isolate grew as fast as a sensitive isolate on a medium free of fungicides but grew more slowly on a medium containing 10 μg/ml of captan or 1 μg/ml of prochloraz. Conidial germination was inhibited by captan but not by prochloraz. Yet when conidia exposed to fungicides were transferred onto a fungicide-free potato-dextrose agar (PDA) medium, spores exposed to 10 μg/ml of captan germinated and formed colonies, whereas conidia germinating in contact with prochloraz made no further growth. Benomyl-resistant or -sensitive conidia germinated on PDA were not affected by exposure to captan for 16 hr, but exposure to prochloraz for 4 hr severely reduced further germ-tube growth. Blossom blight on peaches was not reduced with a single spray of captan applied at pink bud or initial petal fall, but applications at pink bud followed by a spray at 75% petal fall reduced blossom blight equivalent to that of benomyl spray or combination of benomyl and captan at pink bud. Effective disease control was provided by a single spray of prochloraz at pink bud but not at initial petal fall. Blighted blossoms sprayed with prochloraz had the fewest conidia. Peach fruits dipped in prochloraz failed to develop Monilinia decay when flesh surrounding the pit was inoculated with conidia, indicating systemic activity.