Stripe rust update 05/12: Disease expected to develop in eastern PNW

By Dr. Xianming Chen 

On May 11, we were checking winter wheat fields in Whitman, Garfield, Columbia, Walla Walla, Franklin and Adams counties in Washington. Because of the high moisture, wheat crops look good with winter wheat ranging from early jointing (Feekes 5) to boot (Feekes 10), and spring wheat ranging from just emerged to late tillering (Feekes 3). Stripe rust was found at a very low level in our experimental fields near Pullman (artificially inoculated) in the Palouse region, Central Ferry (not inoculated, but rust might be from the inoculated breeding nursery) in Garfield County, and Walla Walla (natural infection). The low level of stripe rust in Walla Walla is about one month later than the last year and more than two months later than normal. For commercial fields, stripe rust was found in only two fields in Walla Walla County between Waitsburg and Walla Walla. Although the incidences were very low, the observed rust pustules were active, producing new spores.

According to several scientists, stripe rust was found in Gilliam and Morrow counties in northcentral Oregon in the last week.

Although the current pressure is low, stripe rust is expected to develop in the eastern Pacific Northwest in the next few weeks because of the vigorously growing crops and the rust-favorable weather conditions in the past weeks and forecast for the next couple of weeks. Fungicide application is recommended for fields planted with susceptible and moderately susceptible varieties of winter wheat (stripe rust ratings 6-9) before flowering stage. It is good to check fields planted with moderately resistant varieties (stripe rust ratings 4 and 5). Growers should check fields immediately in southcentral and central Washington, Oregon and southern and central Idaho for stripe rust. Fields in the Palouse region of Washington and Idaho and further north should be checked starting about 10 days from now. For those trying to use one application to keep rust under control, fungicide application can be done when rust incidence or severity is between 1 to 5 percent, but not later than 10 percent. For spring wheat, fungicide application is recommended for fields planted with susceptible and moderately susceptible varieties (stripe rust ratings 6-9) at the time of herbicide application.

Stripe rust in the country 

So far, stripe rust has been reported on wheat in Louisiana, Texas, Washington, Oregon, Georgia and California and on triticale in California. Barley stripe rust has been reported in Washington and California. Due to drought conditions, stripe rust has not been found in the central Great Plains.