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Effect of Downy Mildew Epidemics on the Seasonal Carryover of Initial Inoculum in Hop Yards. Dennis A. Johnson, Associate Plant Pathologist, Washington State University, Irrigated Agriculture Research and Extension Center, Prosser 99350. W. L. Anliker, Research and Development Representative, Ciba-Geigy Corporation, Vancouver, WA 98664. Plant Dis. 69:140-142. Accepted for publication 27 July 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-140.

Incidence of hop downy mildew was reduced significantly by a spray-band application of metalaxyl over hop crowns bearing small shoots, whereas it was not reduced when metalaxyl was injected into the soil near the hop crown. Incidence of primary spikes of downy mildew was significantly less the year after downy mildew was controlled with metalaxyl than when the disease had not been controlled. Incidence of primary spikes increased when severity of the epidemic had increased the preceding season. Severity of hop downy mildew one year has an effect on the level of initial inoculum the following year.