Dr. Xianming Chen (ARS Plant Pathologist) released an updated stripe rust forecast Thursday, June 2, 2022 focusing on Whitman County, WA and Latah County, ID. In contrast to previous reports, stripe rust was common on lower leaves in inoculated experimental fields. Stripe rust intensity was light in breeding nurseries and not found in any of the commercial winter and spring wheat fields that were checked. Dr. Clark Neely (WSU Extension Agronomist & Cereal Variety Testing Lead) also released a stripe rust update based on his visits to WSU variety testing nurseries and notes that he is observing more stripe rust around eastern WA. Stripe rust was first observed in trace amounts on May 27 in the Walla Walla nursery and on June 1 in the Connell nursery, with somewhat greater amounts of rust in the Ritzville nursery on highly and moderately susceptible varieties. Dr. Neely also noted that several growers in the Horse Heaven Hills area sprayed fields of susceptible varieties due to rust build-up.
It’s no surprise that more stripe rust is being observed, but these reports are consistent with previous reports of overall low pressure from stripe rust compared to previous years. Given our recent cool and wet weather, we expect to continue seeing stripe rust develop over the next two weeks. Today’s 10-day forecast calls for below average temperatures with rain showers that are favorable for stripe rust infections to continue. New infections from stripe rust will not decrease until the weather warms and remains dry.
Our recommendations remain the same as earlier in the season: continue scouting fields for the presence of stripe rust and consider fungicide application when 2-5% of plants have active rust (yellow-orange sporulation on leaves). Given the continued late appearance and overall low intensity of stripe rust, it’s unlikely that highly and moderately resistant varieties (rust rating 1-4) will require fungicide application; however, rust may still develop on moderately and highly susceptible varieties (ratings 6-9) in the Washington State Crop Improvement Seed Buyer’s Guide and the Variety Selection tool on the Wheat & Small Grains website.
Given the late appearance of stripe rust, be sure to check plant growth stage before applying any fungicide to remain in compliance with labels since some should not be applied after anthesis (Feeke’s GS 10.5), whereas others have a 30-day preharvest restriction for application.
Additional information on stripe rust, including photos showing rust percentage, can be found under the Foliar Fungal Diseases in the Disease Resources section of the WSU Wheat and Small Grains website.
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.