Previous View
 
APSnet Home
 
Phytopathology Home


VIEW ARTICLE

Ecology and Epidemiology

Weather and Downy Mildew Epidemics of Hop in Washington State. Dennis A. Johnson, plant pathologist, Department of Plant Pathology, Washington State University, Pullman 99164; J. Richard Alldredge(2), and Jennifer R. Allen(3). (2)(3)associate professor and technical assistant, respectively, Program in Statistics, Washington State University, Pullman 99164. Phytopathology 84:524-527. Accepted for publication 15 February 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-524.

Relationships between weather and downy mildew epidemics of hop in the Yakima Valley of Washington State over a 38-yr period were examined with linear discriminant and logistic regression analyses. A linear discriminant function with minimum temperature in April × the total number of rainfall days in April and May, an indicator variable for the presence of an epidemic the preceding year, and the minimum temperature in May × the number of occurrences of three or more consecutive rainfall days in May correctly classified the epidemic status for 92% of the years. The percentage of years with mild epidemics correctly classified (specificity) and years with severe epidemics correctly classified (sensitivity) for a 10-yr test data set were 86 and 100%, respectively. Logistic regression, which requires fewer assumptions, had results very similar to those of the discriminant analysis.