Stripe Rust Update 6/8/07

June 8, 2007

Xianming Chen

Yesterday, I was checking wheat fields in the Othello and Lind areas in Adams county and Whitman county. With the recent moist and cool weather conditions, both winter wheat and spring wheat crops looked good. Winter wheat ranged from boot to early milk stages and spring wheat ranged from tillering to heading stages. Stripe rust was found in some winter wheat lines on the WSU Othello Farm, but still at low severity levels (up to 10%) and incidences (up to 10%). No stripe rust was found on spring wheat plots on the farm. At the Lind station, stripe rust was up to 20% severity and 40% incidence on susceptible check varieties in our winter wheat plots and up to 10% severity and 20% incidence on susceptible check varieties in the spring wheat plots. Stripe rust increased incidence (up to 40%) on susceptible checks in our experimental fields near Pullman, but the severity was low (up to 10%). No stripe rust or very low incidence and severity (less than 1%), but with resistance reaction, was found in commercial wheat fields. Stripe rust was not observed on barley in either experimental and seed production fields or disease nurseries.

By the end of May, wheat stripe rust was reported in experimental fields in Pendleton, Oregon and Moscow, Idaho.

Over Mt. Vernon in northwestern Washington, stripe rust developed to 100% severity on susceptible winter wheat entries and 40% severity on susceptible spring wheat entries by the end of May. Barley stripe rust developed up to 80% severity. Wheat leaf rust was not found, but barley leaf rust was up to 100% severity.

In the eastern Pacific Northwest (PNW), stripe rust is still in the low side, which is mainly due to the long period of dry weather conditions up to the mid May. Although the weather conditions (moist and cool) have been favorable to stripe rust since late May, the disease development has been slow because of the low inoculum load. The application of fungicides in the Horse Heaven hard red spring wheat the Horse Heaven region in Washington has helped to reduce the rust pressure. However, wheat crops will remain green for over a month in many areas of the PNW, stripe rust is already in the region, and the weather will be generally favorable to the disease in next two weeks based on the forecast. Therefore, stripe rust still has potential to cause some damage, especially in hard red winter and susceptible spring wheat fields. Infections that occurred during the raining days early this week will show up in about 10 days. Check your fields more frequently if you grow susceptible cultivars.

Nationwide, stripe rust has been reported in Texas, Louisiana, Alabama, Arkansas, Kansas, Colorado, Nebraska, Virginia, California, Washington, Oregon, Idaho, and Montana. The rust has been generally low, except that it has developed quickly in Kansas and Colorado in the late crop growth stages due to the recent high moist conditions.