According to Dr. Xianming Chen (USDA-ARS plant pathologist), actively sporulating stripe rust was easily found on susceptible varieties in experimental plots on both the Palouse Conservation Field Station and Spillman Agronomy Farm during the past two weeks (April 2-14, 2024). In his most recent stripe rust update on April 13, Dr. Chen noted that this is the earliest stripe rust has been found in the Palouse since 2011, which reinforces the continuing concern for potentially severe stripe rust in the 2024 growing season.
In addition to the eastern Palouse (Whitman County), Dr. Chen’s team found stripe rust in all of their disease monitoring and germplasm nurseries in eastern Washington including Walla Walla (Walla Walla County), the Lind Dryland Research Station (Adams County), and Central Ferry (Garfield County). Stripe rust was also found in winter wheat and triticale plots at the Oregon State University Hermiston Agricultural Research and Extension Center (Umatilla County). The only areas where stripe wasn’t found was in western Walla Walla County and the Horse Heaven Hills (Benton County).
The early appearance of stripe rust across a wide swath of eastern Washington is much greater rust pressure than we’ve experienced during the past three years and Dr. Chen’s predictions for potential yield loss of 51% on highly susceptible varieties has not changed since his March 1 forecast. It’s important to remember that these yield loss estimates are based on a highly susceptible variety that is not grown commercially. However, that does not reduce the potential severity of stripe rust this season, which for current commercially grown varieties rated 5-9 (moderately to highly susceptible) ranges from 9 to 33% yield loss without fungicide application. Consequently, early season prophylactic fungicide application is recommended for fields planted with winter wheat varieties rated 5 to 9 (moderately to highly susceptible) at the time of herbicide application. Varieties rated 1-4 likely won’t benefit from a fungicide application based on Dr. Chen’s research.
A second fungicide application may be needed 20 to 30 days after the first application, depending on the material applied and the weather. We recommend scouting fields and looking for active stripe rust on 1-5% of the flag leaves to determine whether a second application is needed. In general, single mode of action fungicides provide about 3 weeks of protection and those with two or three modes of action will provide another 7-10 days of protection.
Spring wheat is also at risk. If you haven’t already done so, I encourage you to select the most resistant variety possible, preferably rated 1-4 as these varieties are unlikely to benefit from a fungicide application. If you have already planted a variety rated 5 or higher (moderate to highly susceptible), an early application of fungicide with herbicide will likely be beneficial. Depending on weather conditions, a second fungicide application may be needed 20 to 30 days after the first.
I will provide more information regarding future updates as conditions change. Additional information about stripe rust, including photos showing rust percentage, can be found under Foliar Fungal Diseases in the Disease Resources section of the WSU Wheat and Small Grains website. Updated rust ratings for winter and spring wheat varieties can be found in my presentation “Diagnosing and Managing Diseases of Wheat” from the 2023 Wheat Academy.
For questions or comments, contact Tim Murray via email at tim.murray@wsu.edu, via phone at (509) 335-7515, or by following him on Twitter @WSUWheatDoc.