Stripe Rust Update: Stripe rust has developed slower this year than in 2011, with levels lower than 2011 or 2010. There have been a few reports of it in Umatilla and Walla Walla Counties, but it is not widespread and is about normal for the stage of development for wheat in the area. In eastern Washington and northeastern Oregon, stripe rust has started showing up, but still remained hard to find. Dr. Xianming Chen, USDA ARS, Pullman, was checking fields in western Whitman, Columbia, Walla Wall, Franklin, and Adams counties in eastern Washington and around Pendleton and Hermiston (Umatilla Co.) in eastern Oregon this week. He notes that winter wheat ranged from early jointing (Feeks 4) to early boot (Feeks 10). He only found stripe rust on lower leaves of one volunteer plant in our stripe rust nursery (planted in late September) near Walla Walla. No stripe rust was found on any entries and spreader rows of a highly susceptible genotype. No stripe rust was found in any commercial fields checked including those around Prescott and in the Horse Heaven Hills.
The following graph, provided by Dr. Mike Flowers, OSU, shows the generation time which is the time from infection to visible stripe rust in Hermiston area. As the temperatures increase, the generation time decreases. As you can tell from the graphs, the generation time for stripe rust is currently running around 15-20 days, depending on location.
Figure: Stripe Rust Generation, April 24, 2012
Please check your fields before spraying. Our general recommendation is no spray without seeing rust and spray when rust reaches to 1 to 5% prevalence (percent of plants with rust pustules). Based on current low stripe rust pressure, susceptible and moderately susceptible varieties may just need only one application at the flag-heading stage; and moderately resistant varieties may or not need to spray fungicides (depending upon weather conditions in May) according to Dr. Chen. The long-term weather forecast for May to July just issued today predicted a slightly cooler than average (just 1oF difference) for the PNW.