Stripe rust update 06/04: Weather conditions conducive to disease development

Dr. Xianming Chen

This week, we were completing stripe rust notes of winter cereal nurseries in Mount Vernon (Skagit County), Wash.; Hermiston (Umatilla County), Ore.; and Walla Walla (Walla Walla County), Wash. Winter wheat and barley ranged from flowering to soft dough stage. Wheat stripe rust developed to 100 percent severity on susceptible winter varieties in these locations. Barley stripe rust developed up to 80 percent severity at Mount Vernon and up to 40 percent severity at Walla Walla on susceptible barley varieties. Stripe rust was quite common on spring wheat at all three locations. 

Yesterday, I was checking fields around Pullman (Whitman Country), Wash. Stripe rust has developed fast over the last two weeks in our experimental fields. Winter wheat ranged from boot to heading stage, and spring wheat from late tillering (Feekes 3) to early jointing (Feekes 5). Stripe rust was up to 50 percent incidence and averaged 20 percent severity on susceptible winter wheat varieties. In spring wheat nurseries, stripe rust was easily found in all sites. 

Chris Mundt reported that winter wheat variety “Bobtail” had more stripe rust than ever before in experimental fields in Corvallis (Benton County), Ore. We did not see any rust on Bobtail in the nurseries in the nurseries at Hermiston, Oreg., and Walla Walla, Wash. Bobtail has been highly resistant to stripe rust until Chris’ observation. 

Chris found stripe rust on winter wheat variety “UI Magic” at Adams (Umatilla County), Ore. Similarly, we also saw quite severe stripe rust on this variety at Hermiston and Walla Walla. Stripe rust was quite common on this variety in some commercial fields in central Washington last year. Based on the last year’s data, this variety was rated moderately susceptible. In this growing season, stripe rust has been reported by growers in commercial fields in southeastern Washington, northeastern Oregon and western Idaho. 

Weather conditions has been conducive for the past two weeks and will continue to be favorable for stripe rust in the next two weeks. Please check wheat fields for stripe rust. For winter wheat, if active stripe rust is present and the crop is before flowering, fungicides can be used. For fields planted with moderate susceptible to susceptible spring varieties (stripe rust ratings 6 to 9), fungicide should be applied at the herbicide application time. If already applied, check fields again about three to four weeks after the application. A second application may be needed if stripe rust develops again and the crop is before flowering. 

Stripe rust in the country 

So far, wheat stripe rust has been reported in Oregon, Washington, Texas, Louisiana, Oklahoma, California, Kansas, Kentucky, Virginia, Illinois and Idaho. Barley stripe rust has been reported in California, Oregon and Washington.