Based on the weather data in November and December 2021, stripe rust in the 2022 wheat growing season is forecasted to be in the middle range of the moderate epidemic level (20-40% yield loss on susceptible varieties). Using the forecast models based on the 2021 November and December weather data, yield loss of highly susceptible winter wheat varieties in the 2022 crop season is predicted to be between 25 to 40% with an average of 34% and 5% standard error. This percentage is lower than the forecast (39%) made last January for the 2021 crop season due to the relatively cold weather of the late December in 2021 compared to that of 2020. Currently grown varieties in the Pacific Northwest are forecasted to have yield losses ranging from 0 to 17% depending upon the level of resistance or susceptibility of individual varieties. Based on the forecast, fields planted with resistant or moderately resistant varieties (stripe rust ratings 1 to 5 in the Seed-Buying Guide) will not need fungicide application while fields planted with moderate susceptible or susceptible winter wheat varieties (stripe rust ratings 6 to 9) may need the early fungicide application at the time of herbicide application. This early prediction is often close to the real situation but may not be as good as the prediction in March based on the weather data of the entire winter from November to February. Therefore, we will make another prediction in early March. However, stripe rust resistant or moderately resistant spring wheat varieties (stripe rust ratings 1 to 5) are recommended for planting.
We checked some wheat fields in Whitman, Adams, Lincoln, Douglas, and Grant counties of Washington on November 23, 2021. Wheat plants ranged from Feekes 2 to 5 and generally in good condition (Figure 1). No stripe rust was found.
Figure 1. A wheat field in Adams County, WA (November 23, 2021)