Xianming Chen
Stripe rust is forecasted to be in the moderate epidemic level in the eastern Pacific Northwest
Wheat stripe rust is forecasted to be in the moderate epidemic level range (20-40% yield loss) in the 2023 growing season, based on the predication models using the weather data from November 2022 to February 2023. The models predicted highly susceptible varieties to have 37% yield loss with a standard deviation of 16%. This value is higher than the 21% forecasted in January based only on the November-December weather conditions. According to the current prediction, susceptible and moderately susceptible commercially grown varieties will likely have 7 to 27% yield losses, or 6% yield loss on average for commercially grown varieties.
Stripe rust has not been found in eastern Washington
So far, stripe rust has not been found in fields in eastern Washington. We checked wheat fields in Whitman, Adams, Lincoln, Grant, and Douglas counties on November 16, 2022; and Garfield, Columbia, Walla Walla, Benton, Franklin, and Adams on March 9, 2023, but did not find any rust (Figure 1). Stripe rust will likely to have a relatively late start in the eastern Pacific Northwest.
Recommendations for the eastern Pacific Northwest
As stripe rust has not been found and the disease is likely to have a late start, fungicide application is not recommended in the early growth season at the time of herbicide application for winter wheat, unless stripe rust is observed in the fields. Fungicide application may be needed later in the flag leaf stage for fields planted with moderately susceptible and susceptible varieties (stripe rust ratings 6 – 9). Winter wheat varieties with stripe rust ratings 1 – 5 may not need fungicide application. For spring wheat, resistant or moderately resistant varieties (stripe rust ratings 1 – 5) should be selected for planting.
Stripe rust in the country
By this time of the year, stripe rust is expected to occur in western Washington as always. In the country, stripe rust has been reported so far only in Texas.
Figure 1. A wheat field in Adams County on November 16, 2022 (left) and a wheat field in Benton County (right), Washington showing winter injury on March 9, 2023.