The Effect of Climate Variability on Stripe Rust of Wheat in the Pacific Northwest

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Abstract
Wheat stripe rust (Puccinia striiformis West) epiphytotics are confined predominantly in the USA to the Pacific Northwest and intermountain states because of the climate. Because stripe rust epiphytotics were frequently only since 1960, the possibility that climate variability could explain in part the pattern of epiphytotics was investigated. Detailed meteorological data for 1961-1975 were obtained for Pendleton, Oregon; temperature, precipitation, relative humidity and combinations of these variables were studied for various time segments of data. An increased number of days in Jan. and Feb. with favorable temperatures for rust development could be used to separate years of severe epiphytotics from mild stripe rust years. In 1961-1975 the average temperature in Jan. and Feb. was 2.degree. C higher than for those same months in 1935-1960. In contrast the average April temperature was over 1.2.degree. C cooler. Warmer-than-normal winter and cooler April temperatures favor the development of stripe rust epiphytotics. Cool spring temperatures delay temperature-sensitive adult-plant resistance in wheat cultivars such as Gaines and Nugaines.

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