Stripe rust update 06/02: June forecast conditions favorable for disease development

By Xianming Chen

On June 1,  I was checking fields in the Palouse region (Whitman County, Wash., and Latah County, Idaho). Winter wheat ranged from Feekes 7 to Feekes 10, and spring wheat ranged from Feekes 2 to Feekes 5. Stripe rust was severe on low leaves and reached top leaves of winter wheat and started showing up on spring wheat in all our experimental fields around Pullman, which were artificially inoculated in April. In contrast, stripe rust was hardly found in breeding nurseries and was not found in any of checked commercial fields.

As the relatively cool temperature and high moisture conditions occurred in May and forecast for the first half month of June are favorable for stripe rust infection and development and winter wheat crop reaches the heading and flowering stages in some regions, it is critical to check fields for stripe rust. If active rust pustules are found, fungicide should be applied before the incidence (number of plants having rust) or severity (infected leaf areas) reaches 5 percent. In general, fields planted with susceptible or moderately susceptible varieties of winter wheat (stripe rust ratings 6-9) should be sprayed with fungicide before flowering. For spring wheat, fungicide application is recommended for fields planted with susceptible and moderately susceptible varieties (stripe rust ratings 6-9) at the herbicide application time.

Stripe rust in the country 

So far, stripe rust has been reported on wheat in Louisiana, Texas, Washington, Oregon, Georgia, California, Oklahoma and Maryland and on triticale in California. Barley stripe rust has been reported in Washington and California.