Stripe Rust in the Pacific Northwest
On May 2-3, we were planting spring nurseries and take stripe rust notes in Mount Vernon (Skagit County), WA. Winter wheat ranged Feekes 5 to 7. As usual, wheat stripe rust developed up to 40% 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% of plants to almost every plants 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 US 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.
Figure 1. Stripe rust foci (hotspots) in a winter wheat field in Lincoln County, WA on May 4, 2017
Figure 2. Active stripe rust infection producing spores (May 4, 2017)