Stripe Rust Update, May 21, 2025

Stripe rust has been developing in Washington

Since the last stripe rust update on May 7, stripe rust has been developing in the Pacific Northwest (PNW), especially in Washington. After the update, we received a report of stripe rust in commercial fields of winter wheat in Franklin County, Washington. On May 9, we checked the fields planted with Piranha CL+ and Nova AX, and stripe rust was easy to find (Figure 1) although the incidence was less than 1%. The Nova AX field was sprayed with fungicides a day before and the Piranha field was sprayed on that day. We checked more than ten additional commercial fields of winter wheat fields in Franklin and Adams counties and found stripe rust in three fields with incidence less than 0.1%.

On May 15, we were checking our experimental fields around Pullman, Washington (Whitman County). Stripe rust was easier to find than a week earlier on spreader rows planted with a highly susceptible winter wheat variety, but still below 1% incidence. No rust was found in commercial winter wheat fields in the Palouse region.

On May 20, we were taking stripe rust data in our winter germplasm screening nurseries at the Central Ferry station (Garfield County), Washington. Winter wheat reached the flowering stage (Feekes 10.51-10.53) and barley reached Feekes 10.53-10.54. As expected, stripe rust reached 90 to 100% severity on susceptible varieties of both wheat and barley (Figure 2). The stripe rust fungus turned into the black telial stage (Figure 3), which no longer produces infectious, orange-colored spores. Some strains of the stripe rust fungus turn into the telial stage faster than others.

Stripe rust in the country

Since the last update (May 7), stripe rust has not been reported in any additional states. Thus, only eight states, Louisiana, Texas, Georgia, Washington, Oregon, California, Oklahoma, and Kansas, have been reported to have stripe rust so far. Even in these states, stripe rust has appeared at relatively low levels compared to last year, except California. However, stripe rust may still have time and conditions to develop to epidemic levels in some regions.