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Effect of Fungicides and Water on Sporulation of Uncinula necator. D. O. Chellemi, Graduate Research Assistant, Plant Pathology Department, University of California, Davis 95616. J. J. Marois, Associate Professor, Plant Pathology Department, University of California, Davis 95616. Plant Dis. 75:455-457. Accepted for publication 8 October 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0455.

Five treatments (triadimefon, wettable sulfur, sulfur dust, water, and an unsprayed control) in combination with four temperatures (19, 22, 26, and 30 C) and two grape cultivars (Vitis vinifera cvs. Carignane and Chardonnay) were examined for their effect on sporulation of Uncinula necator, the cause of grape powdery mildew. Fungicides and water were applied on the seventh day after inoculation of cultivars with individual conidia. The numbers of conidia produced from the developing colonies were determined 10 and 15 days after inoculation. After 10 days, temperature, fungicides, and water had a significant effect on sporulation; after 15 days, significant interactions between temperature and chemical treatments and between cultivar and chemical treatments were also observed. Maximum sporulation after 15 days occurred at 26 C for all treatments and both cultivars. Application of water and fungicides reduced sporulation, but the magnitude of the reduction depended on temperature.