Stripe Rust Update

May 17, 2006

I was checking wheat fields on May 15 and 16 in eastern Washington, northern Idaho, and northeastern Oregon. Winter crops varied from the stem elongation stage to flowering. Spring crops varied from just seeded to the tillering stage. No stripe rust was found in the Palouse region (around the Moscow and Pullman region). At the Central Ferry, stripe rust occurred as hot spots in irrigated experimental plots. Plants in the center of a hot spot had 80% severity. Both stripe rust and leaf rust were heavy on bluegrass. Stripe rust was spreading in our non-irrigated trap plots near Walla Walla. Susceptible entries had up to 60% rust severity. No rust was found in our trap plots and other experiment nurseries at the Pendleton Experimental Station. Stripe rust occurred as hot spots in experimental nurseries at the Hermiston Station. Plants had 80% rust severity in the hot spots. Except for the Horse Heavy Hills area, no stripe rust was found in commercial fields from Pullman to Walla Walla, Pendleton, Hermiston, and the Connell areas. Some winter wheat fields had quite severe physiological leaf spot, which should not be confused with stripe rust. In general, stripe rust is much less than the epidemic situation this time of the last year.

The light stripe rust could be attributed to the later planting in the south central Washington and other areas, cold weather conditions in last December and February. The low temperatures in March and April made the rust development slow. The dry conditions in May and the suddenly hot weather this week have not been favorable for stripe rust infection. However, the forecasted cooler and moist weather conditions in the next week might be favorable for the rust development. Rain-fed fields of susceptible cultivars should be checked after the next week of possible moist and cool conditions while irrigated fields of susceptible cultivars should be checked more often. Because of later occurrence of stripe rust and so far the low rust inoculum pressure, moderately resistant to moderately susceptible cultivars, which needed fungicide spray last year, may not need spray this year. Even through the currently low rust pressure, spring wheat may be still vulnerable to stripe rust if the weather conditions is favorable (cool and wet) to the disease from now on.

Nationwide, the stripe rust situation has been similar to that in the Pacific Northwest. Except for the severe stripe rust in commercial fields in California, the disease is generally light throughout the country due to the dry weather conditions. So far, wheat stripe rust has been reported in Arizona, California, Oregon, Washington, Montana, Texas, Louisiana, Alabama, Arkansas, Georgia, North Carolina, and Minnesota. Barley stripe rust was reported in Arizona, California, Oregon, and Washington.