Stripe rust is forecasted to be in the severe epidemic level in the eastern Pacific Northwest
Based on the predication models using the weather data from November 1, 2019 to February 29, 2020, wheat stripe rust is forecasted to be in the severe epidemic level range (40-60% yield loss) in the 2020 growing season. The models predicted highly susceptible varieties to have 44% to 53% with an average of 48% yield loss. This number is higher than the 44% forecasted in January based only on the November-December weather conditions. According to this prediction, susceptible and moderately susceptible commercially grown varieties will likely to have up to 24% yield losses.
Stripe rust was found in eastern Washington and Oregon
On February 26, we were checking wheat fields in Lincoln, Douglas, Grant, Adams, Franklin, Benton, and Walla Walla counties of Washington. Wheat was still dormant in Lincoln and Douglass counties, but has started growing in other counties, especially in Benton and Walla Walla counties. We found one leaf with active stripe rust (Figure 1) in a field in Lincoln County, where we easily found stripe rust in last November. We did not find rust in Douglass County, even in the fields where we easily found stripe rust in last November. No stripe rust was found in other counties, except in our experiment field near Walla Walla. When we arrived at the field, it was already dark but we managed to find stripe rust on the susceptible check variety with cell phone light. One spot had 3-4 leaves producing active rust spores (Figure 2).
Figure 1. Stripe rust observed in a winter wheat field between Creston and Wilbur (Lincoln County), Washington on February 26, 2020.
Figure 2. Stripe rust found in a disease monitoring nursery near Walla Walla, WA on February 26, 2020.
On February 26, Christina Hagerty found active stripe rust on the same highly susceptible wheat variety in our stripe rust monitoring nursery planted in Pendleton (Umatilla County), Oregon (Figure 3).
Figure 3. Stripe rust in a disease monitoring nursery at Pendleton, Oregon on February 26, 2020. (Courtesy of Christina Hagerty)
Recommendations for the Pacific Northwest
As the stripe rust has started, management of the disease on winter wheat should start at the time of herbicide application based on the stripe rust ratings in the Seed Buying Guides (such as http://washingtoncrop.com/wp-content/uploads/2019/09/2019-portrait.pdf). For fields planted with varieties rated 5-9 (such as Keldin, LCS Jet, WB4311, Curiosity CL+, Eltan, UI Magic CL+, Xerpha, and ORCL 102), fungicide should be used at the time of herbicide application. For fields planted with varieties rated 4, scout the fields and use fungicide at the time of herbicide application only when active rust is found. For fields planted with varieties rated 1-3, fungicide is not needed.
As stripe rust will be likely severe, planting spring varieties with ratings 1 to 4 may void using fungicide.
Stripe rust in the country
In addition to Oregon and Washington, stripe rust has been reported in Louisiana.