Stripe Rust Update 4/9/08

April 9, 2008

Xianming Chen
Stripe rust in eastern Washington

Spring is taking baby steps to come to the Pacific Northwest. The Palouse region in eastern Washington, especially the Pullman campus of Washington State University, received several inches of snow on April 8 and 9.

I was checking wheat fields in the Horse Heaven Hills area, south of Tri-Cities and the Connell area in central Washington on April 8. Plants of winter wheat ranged from FS stage 2 to 5. Plant stands were not uniform in most fields, which might be due to the lack of moisture in the last fall. There was no winter kill observed.

Stripe rust was just shown up in the Horse Heaven Hills area and in relatively low incidence compared the situation this time of the last year. Actually, I found stripe rust only in one of many fields checked. One spot had 4 to 6 low leaves with actively sporulating rust pustules and a couple of unrelated leaves with small infected patches just starting sporulation. There was no rust found in the Connell area. The low rust incidence and severity are due to the relatively low temperatures so far. As the weather is predicted to warm up next week, stripe rust will develop in these areas. Growers in these areas should check their fields in two weeks, and consider using fungicides when rust incidence and severity reach 5 to 10%.

Yesterday, I also found powdery mildew in a couple of fields, one was the same field with stripe rust in the Horse Heaven Hills and another in the Connell area. Powdery mildew was on low leaves and was easier to found than stripe rust. Generally, powdery mildew is not a big concern in these areas without irrigation.

Stripe rust in western Washington

As usual, stripe rust is severe in Mt. Vernon in the Skagit Valley, western Washington. By April 3, stripe rust reached 100% prevalence and 50% severity on highly susceptible entries in our experimental nurseries. Similar levels of rust severities in commercial fields planted with susceptible varieties. Growers in the Skagit Valley should consider use of fungicides whenever machinery can be operated in the fields. Two applications of fungicides with longer duration of effect may be necessary to protect wheat crops in this area. The last spray should be close to FS 10.5 to maximally protect the grain filling stage.

Stripe rust in other states

So far, stripe rust has been reported in Texas, Louisiana, Arkansas, Georgia, and California. In General, the disease is in low levels, except in the Sacramento Valley and the Sacramento/San Joaquin Delta area, where Dr. Lee Jackson observed severe stripe rust in some commercial fields. Lee also found stripe rust on barley in California.