Stripe Rust Update and Fungicide Application
Wheat stripe rust is now almost everywhere in Washington, western and northeastern Oregon, and northern Idaho with various severity levels. I was checking commercial fields in Whitman and Spokane county of Washington along Highway 195 and Benewah and Latah counties of Idaho along Highway 95, and found stripe rust in all regions. Dr. Jim Peterson and Richard Smiley of Oregon State University reported wheat stripe rust in the Pendleton area and western Oregon.
In Lind, WA, susceptible winter wheat varieties in our experimental field had up to 30% rust severity by June 10. Varieties Hatton, Buchana, CDC Falcon, Columbia 1, and Quantum had 20% rust; and Basin, Wanser, WPB 470, Symphony, and Walladay had 10-15% rust. Susceptible spring wheat had up to 10% rust.
On June 10, Kim Kidwell, Gary Shelton and I checked spring wheat plots in Moses Lake, WA. Susceptible varieties had up to 90% of rust severity. Varieties that were susceptible or moderately susceptible (with 40-90% of infection severity and abundant rust pustules) included Fielder, Edwall, Penawawa, Zak, Wawawai, Calorwa, Treasure, Whitebird, Eden, Macon, and Scarlet. Application of fungicides is necessary for fields grown with above winter and spring wheat cultivars.
Resistances in winter wheat varieties like Eltan, Madsen, Rod, Stephens, Hill 81, Bruehl, Rely, Coda, Chukar, Finch, Lambert, Finley, and many others are effective and adequate. Fungicide application is not needed for fields grown with these varieties. Similarly, spring wheat varieties Wakanz, Nick, IDO377s, Lolo, IDO597, Blanca Grande, Hollis, Tara 2002, Jefferson, and Jerome are still resistant and fungicide spray is not needed. Variety Hank was resistant in the Moses Lake nurseries. Hank fields should be watched closely for changes of stripe rust reaction.
Varieties Alpowa and Express have moderate level of high-temperature, adult-plant resistance, which is generally adequate under normal weather and rust conditions. This type of resistance does not change with races of the rust, but under the influence of temperature, plant growth stage, and rust inoculum pressure. For example, Alpowa had 50% of severity but mainly dead leaf tissues with limited number of rust pustules in the Moses Lake field plots by last week. When checked on June 16, Alpowa fields had 2-10% of severity with resistant to susceptible reactions in Whitman, Spokane, Benewah and Latah counties. Based on our research, Alpowa can have yield losses up to 20%, much lower than 60% for susceptible varieties. This year, Alpowa fields may potentially suffer yield losses of between 5 to 15%. Whether to spray Alpowa and Express fields or not depends upon yield potential in your area.
Based on the weather forecast for next 10 days, temperatures will continue being favorable for stripe rust. Current moisture condition in the Palouse region is still adequate and temperatures are just perfect for stripe rust infection and development. Under current conditions, it takes two to three weeks from infection to rust appearance. Wheat crops in eastern Washington, northern Idaho, and northeastern Oregon have been under stripe rust infection roughly since mid May. Therefore, stripe rust of wheat will continue increasing even without more precipitations for the next three weeks. It is good that many fields of susceptible wheat have been sprayed with fungicides. If your fields of susceptible varieties mentioned above or other varieties susceptible have not been sprayed, please consider to spray. Now is the right time for fungicide application. The currently registered fungicides (Tilt, Quadris, Headine, Stratego, and Quilt) are systematic and their effectiveness generally lasts about one month. One application should be generally adequate for the eastern Pacific Northwest. Please keep in mind that all registered fungicides cannot be used after Feeks stage 10.5 (late heading stage) or within 45 days before harvesting.
Barley stripe rust was found in our experimental field in Lind, WA last week, and also found in a field of a 6-row barley north of Steptoe along HW 195 at the 59 milestone on June 15. Although the rust level is low, it will develop quickly in the susceptible field and other fields of susceptible barley varieties like Steptoe, Morex, and Harrington. Therefore, fields of such barley fields should be watched closely and fungicide application should be considered if stripe rust develops to 5-10% of severity. Stripe rust has not been found in barley fields appearing like Baronesse that has moderate level of high-temperature, adult-plant resistance.