Dr. Xianming Chen, USDA-ARS Research Plant Pathologist in Pullman, and Dr. Mike Flowers, Oregon State University Extension Cereal Specialist, released disease updates (Dr. Chen’s update and Dr. Flower’s update) during the past week.
Not surprisingly, stripe rust has continued to develop on winter wheat across the region and is relatively easy to find. Dr. Flowers reported finding stripe rust at variety testing locations near Dufur and Moro, OR, and in a commercial field near Moro. Dr. Chen reported finding actively sporulating stripe rust during the week of April 5 in over 80% of the approximately 70 fields checked in Adams, Benton, Columbia, Franklin, Garfield, Walla Walla, and Whitman Counties in WA, and Umatilla County in OR.
Stripe rust was most active near Walla Walla and Pendleton, where many fields have been sprayed with fungicide already. In other areas, rust ranged from 1 to 5% and is less severe than last year at this time due to lower temperatures. The Palouse in Whitman County is an exception, with stripe rust appearing about one month earlier than normal and similar to the severe epidemic years of 2011 and 2016.
Current weather forecasts continue to favor rust infection and spread, raising the potential for another severe stripe rust epidemic year. High-temperature adult-plant resistance (HTAP) has not kicked in yet and won’t become fully effective until nighttime/daytime temperatures are above 50°F/65°F. Going forward, it will be important to continue scouting all winter wheat fields and consider using a fungicide with herbicide application if the variety is moderately susceptible or susceptible (rating 4 or greater in the Seed Buyers Guide) or active stripe rust is found on 2-5% of the plants in a field regardless of variety rating. Continue to monitor sprayed fields throughout the spring, especially near the end of fungicide effectiveness (3 to 4 weeks, depending on the fungicide). For spring wheat, plant the most resistant variety available, preferably those rated 1 to 2.
Additional rust updates will be released as the growing season continues and conditions change. You can find additional information on stripe rust, including photos showing rust percentage, under Foliar Fungal Diseases in the Disease Resources section of the WSU Wheat and Small Grains website.
For questions or comments contact Tim Murray by email (firstname.lastname@example.org), by phone (509) 335-7515, or Twitter (@WSUWheatDoc). For additional information contact Dr. Chen at email@example.com or (509) 335-8086; or Mike Flowers at (541) 737-9940 or at Mike.Flowers@oregonstate.edu.