Stripe Rust Update 5/17/07

May 17, 2007

Xianming Chen

I was checking wheat fields and experimental nurseries on May 16 and 17 in Whitman, Garfield, Columbia, Walla Walla, Benton, Franklin, and Adams counties in Washington. Winter wheat crop ranged from stem elongation to flowering, and was generally in good shape. Spring wheat ranged from just emerged to stem elongation.

Stripe rust is generally under control in the Horse Heaven Hills and Connell areas (hard red winter wheat regions). Most fields grown with Finley and Buchanan have been sprayed. Stripe rust were found in every checked fields, but usually less than 1% severity and prevalence. Inactive stripe rust pustules due to application of fungicides were noticed. As the weather conditions become dry in this area, stripe rust development should be slowed down. For irrigated fields, growers should check their fields about 4 weeks after the first fungicide spray. If stripe rust starts redeveloping, consider about second application of fungicides. For most of rain-fed fields in this area, the second application should not be necessary, but depending upon if it is going to have good precipitation within a month.

Stripe rust started showing up in the Palouse region (Whitman county), Central Ferry (Garfield County), and Walla Walla. The rust was found in our disease monitoring nurseries (around Pullman and Walla Walla) and breeding nurseries (Central Ferry) in low prevalence (less than 1%) and severity (usually less than 2%) with some small hot spots of severities up to 40%. Stripe rust was not found in all checked commercial fields of soft white wheat–producing regions.

The observations fit our previous prediction of a light to moderate stripe rust of this year. Cultivars with moderate to high levels of high-temperature, adult-plant (HTAP) resistance should not have the stripe rust problem this year. Cultivars without HTAP resistance, but have been resistance in the recent years, generally should not have the stripe rust problem also. However, if you grow winter or spring wheat cultivars that were susceptible in 2005, you should check your fields for stripe rust and consider using fungicides if the rust develops to 5 to 10% severities and prevalence. In many areas, especially the Palouse region, wheat fields still produce dew on plants at the night and in the early morning, which allows rust to infect. Temperatures are favorable to stripe rust development. However, the current moisture conditions in most part of the Pacific Northwest are towards the dry side and the forecast for the next two weeks appears dry. Therefore, rust infection should be slow until the next rain.