By Dr. Xianming Chen
May 5, 2017
On May 2-3, we were planting spring nurseries and taking stripe rust notes in Mount Vernon (Skagit County), Wash. Winter wheat ranged Feekes 5 to 7. As usual, wheat stripe rust developed up to 40 percent severity on susceptible varieties. Barley stripe rust was found only in two rows of the same susceptible check of winter barley. No leaf rust was found on either wheat or barley.
On May 4, we were checking fields in Grant, Douglas, Lincoln and Whitman counties. Winter wheat ranged Feekes 4 to 8. Stripe rust was found in most of the fields checked, ranging from less than 1 percent of plants to almost every plant infected. In some fields, yellow foci of several yards in diameter could be seen (Figure 1). However, most infected plants had necrotic stripes or blotches without much rust pustules due to the control of stripe rust by fungicides and/or high-temperature, adult-plant resistance. Actively sporulating (producing new spores) leaves were found in some fields, but mostly in low canopy (Figure 2). In general, stripe rust was less severe in Whitman County than the other counties checked in this survey.
Weather conditions have been conducive and will continue being conducive for stripe rust. If not applied, first application of fungicides is recommended for fields planted with varieties with stripe rust ratings of 4 and higher. Second application is recommended for fields when new active infections start appearing as shown in Figure 2, but on upper leaves. Check fields for new infection about three weeks after the first application. Fungicide application is not needed for fields without rust.
Stripe Rust in the U.S. and Canada
In the United States, stripe rust has been reported so far in Texas, Louisiana, Arkansas, Mississippi, North Carolina, Oklahoma, Kansas, Washington, Oregon, Wisconsin, Virginia, Delaware, Tennessee, Michigan, Kentucky, Nebraska, Indiana, Georgia, Idaho, Arizona and California. In Canada, stripe rust has been reported in Alberta and Ontario.