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Disease Control and Pest Management

Differential Sensitivity to Mancozeb of Metalaxyl-Sensitive and Metalaxyl-Resistant Isolates of Pseudoperonospora cubensis. Yair Samoucha, Graduate student, Department of Life Sciences, Bar Ilan University, Ramat Gan, Israel; Yigal Cohen, professor, Department of Life Sciences, Bar Ilan University, Ramat Gan, Israel, Present address of junior author: Department of Plant Pathology, University of California, Riverside 92521. Phytopathology 74:1437-1439. Accepted for publication 30 April 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-1437.

Eight field isolates of Pseudoperonospora cubensis, the fungal causal agent of downy mildew in cucurbits, were tested for sensitivity to metalaxyl and mancozeb. While mancozeb efficiently controlled downy mildew in cucumbers inoculated with three metalaxyl-sensitive isolates, it failed to do so in cucumbers inoculated with five other metalaxyl-resistant isolates. The practical and theoretical implications of this finding are discussed.