WAWG
By Xianming Chen
Stripe rust has been continually developing in the Pacific Northwest. The relatively dry conditions between the middle of April and middle May slowed the rust development little bit, but the periodical showers and relatively low temperatures in the last couple of weeks have been pushing for stripe rust to increase further. We have completed collecting stripe rust data in our winter wheat and barley nurseries at Central Ferry (Garfield County), Walla Walla (Walla Walla County), Lind (Adams County), Mount Vernon (Skagit County), and Hermiston (Umatilla County in Oregon). Susceptible varieties had up to 100% severity at these locations at the time we took notes. For the winter wheat germplasm nurseries at the Pullman location, where we will take stripe rust notes in the coming week, stripe rust also developed up to 100% severity by May 29.
Based on the stripe rust data in our experimental field in various locations so far, no major changes in stripe rust reactions have been found for winter wheat varieties. The stripe rust race identification data so far has not shown major shifts in races compared to those of last year. However, because of the widespread stripe rust infection last fall, high survival rates during the warm winter, early start of development in this spring, and relatively low temperatures so far not allowing full effect of high-temperature adult-plant (HTAP), varieties with only low to moderate levels of HTAP resistance have shown more rust levels than in the last year.
In commercial fields by the last week, the winter wheat crop ranged from heading to milk depending upon areas and planting dates. Stripe rust was generally under control with some fields showing stripe rust infections. Spring wheat ranged from early jointing to boot, and stripe rust was found at low levels in some fields from Adams County to Whitman County in the last week.
The weather conditions in the last two weeks and forecast for the next two weeks have been and will be continually favorable to stripe rust infection and development. For winter wheat, stripe rust control is over for fields of crops after the flowering stage. However, for fields of crops not reaching the flowering stage (Feekes 10.5) but with active stripe rust, fungicide application may still be needed. For spring wheat and barley, fungicide application is needed for fields planted with susceptible or moderately susceptible varieties (stripe rust ratings 6-9). For fields planted with any variety, it is always a good idea to check fields. If active stripe rust is found, consider applying fungicide before rust incidence or severity reaches 5%.
Barley stripe rust has occurred in winter barley nurseries in all our experimental fields with severity reaching 80 to 100% at Central Ferry and Mount Vernon. The above recommendations for spring wheat are also applicable to spring barley. In addition, wheat leaf rust and barley leaf rust, up to 80% severity, were found on some varieties in the experimental fields at Mount Vernon.