The heavy snow in the Palouse region in the morning of June 10 signified the unusually cool weather conditions by then in the Pacific Northwest (PNW). Since then, it has been warming up with daytime temperatures reaching upper 70s and lower 80s and night temperatures in 40s to lower 50s. The weather conditions have been generally favorable for stripe rust infection, but little bit lower than the optimum for rust sporulation. In general, stripe rust inoculum is low in the eastern PNW.
On June 10, stripe rust was not found in the Mosses Lake area in central Washington. Up to 2% of stripe rust severity and incidence was found on susceptible spreader rows in our rust monitoring nursery at the Lind Dryland Experiment Station. The nurseries were under irrigation. No rust was found in commercial fields in this area.
On June 16, stripe rust severities and incidences were much higher than those observed two weeks ago in rust monitoring nurseries at the Pendleton Experiment Station in Oregon. However, the rust severities were not uniform and still at relatively low levels. The susceptible check variety had 10-20% severities with few hot spots reaching 80% in winter wheat nurseries. Spring wheat nurseries had only few plants with stripe rust on lower leaves.
On June 17, wheat stripe rust reached 5-10% severities and about 20% incidence on the susceptible spreader rows in our winter wheat nurseries at all locations near Pullman. Rust in few hotspots reached 60% severity. Very few winter wheat entries out of over 6,000 in the nurseries had stripe rust. Stripe rust was not found in the spring wheat and barley nurseries. Also, no rust was found in commercial fields near Pullman.
With the winter wheat crops have passed the flowering stage in the south-central and central Washington and the low rust inoculum, stripe rust will not likely do much damage in this area.
In the eastern Washington, winter wheat crops range from the boot to flowering stages, stripe rust still has time to occur in fields grown with susceptible varieties. As the most of fields are grown with resistant varieties, stripe rust damage on winter wheat will likely be minimal. However, as the weather conditions have been and will continue favorable for stripe rust in the next two weeks, spring wheat crops are still vulnerable to stripe rust infection, especially for fields grown with susceptible varieties. These fields should be checked in a week or so for stripe rust infection.