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Ecology and Epidemiology

Weather Factors Affecting Downy Mildew Epidemics of Hops in the Yakima Valley of Washington. Dennis A. Johnson, Extension plant pathologist, Washington State University, Irrigated Agriculture Research and Extension Center, Prosser 99350; C. B. Skotland(2), and J. R. Alldredge(3). (2)Plant pathologist, Washington State University, Irrigated Agriculture Research and Extension Center, Prosser 99350; (3)Assistant professor, Statistical Services and Biometry, Washington State University, Pullman 99164. Phytopathology 73:490-493. Accepted for publication 12 October 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-490.

Weather records were compared with the occurrence of downy mildew epidemics of hops over a 28-yr period in the Yakima Valley in Washington. Above-normal temperatures in April and wet weather in April and May favored development of downy mildew, but wet weather with low minimum temperatures did not. The amount of initial inoculum influenced the occurrence of epidemics. Potential incidence of hop downy mildew in the Yakima Valley could be determined in early May based on above-normal temperatures and rainfall in April, the incidence of systemically infected shoots in hop yards, and the likelihood for wet weather in May.