Cereal Disease Update

June 17, 2005

Winter wheat is maturing from northeastern Oregon to central Washington, and ranges from milk to soft dough stages in eastern Washington and northern Idaho. Spring wheat ranges from late stem elongation stage to milk. Wheat stripe rust has occurred everywhere when wheat is grown in the Pacific Northwest. The disease has passed its peak development on winter wheat and is still developing on spring wheat. Most of fields grown with susceptible and moderately susceptible winter and spring cultivars have been sprayed with fungicides. Because the rust started very early, the weather has been extremely favorable to the disease (cool and wet), and the inoculum load has been heavy, cultivars with low to moderate levels of high-temperature, adult-plant (HTAP) resistance, which is generally adequate in years of normal weather, have shown heavy infection. Many fields grown with cultivars with such levels of HTAP resistance warrant a fungicide spray.

Barley stripe rust has developed up to 40% of severity on susceptible varieties in nurseries, and has been observed in commercial fields at very low levels. Only few fields grown with susceptible malting barley cultivars have been sprayed with fungicides.

Leaf rust is heavy on wheat in our nurseries near Mt. Vernon in northwestern Washington. Barley leaf rust is observed at the same location. Wheat leaf rust is developing in central Washington, mainly in seed production fields under irrigation.

Powdery mildew is more common and severe than any year in the past 10 years in eastern Washington and northern Idaho, but still on lower leaves.

Physiological leaf spot is severe on wheat in the Pacific Northwest. Even fields that have been treated with potassium chloride still got severe physiological leaf spot.