Stripe rust update 06/07: Rust spreading due to cool, wet weather

By Dr. Xianming Chen

As the weather has been cool and wet for the eastern Pacific Northwest (PNW), stripe rust has developed and spread quickly in the region. This week, we recorded stripe rust data in the experimental fields at Hermiston, Ore. (Umatilla Co.), Walla Walla, Wash. (Walla Walla Co.), and Lind, Wash. (Adams Co.). Stripe rust reached the highest severity level on susceptible varieties in the winter wheat nurseries and significant levels in spring wheat nurseries. Stripe rust developed to flag leaves and up to 80 percent severity in our winter wheat nurseries and quite common in spring nurseries around Pullman, Wash. (Whitman Co.).  Stripe rust can be easily found on some grasses, especially jointed goatgrass, which is caused by the wheat stripe rust pathogen.  In the commercial fields, stripe rust has become relatively easy to spot. We have received several reports of stripe rust in fields planted with winter wheat varieties UI Magic and Curiosity in Adams, Benton, Franklin and Walla Walla counties and a field planted with winter wheat variety Stingray in Whitman County.  Stripe rust on these varieties is expected based on the past data.

For winter wheat, 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. Because high-temperature, adult-plant resistance does not work maximally under the cool and wet conditions in the recent and next two-week weather conditions, it is critical to check fields planted with varieties with ratings 4 and 5 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. For fields sprayed with fungicides more than 20 days ago, a second application may be considered if active rust pustules can be spotted.

Each fungicide is labeled with the latest growth stage or date by which it can be applied. Feekes 10.5 (complete heading and before flowering) is labeled for the following fungicides: Aframe Plus, Approach, Bumper, Custodia, Evito, Fitness, Headline, Priaxor, Propiconazole E-AG, PropiMax, Quilt, Quilt Xcel, Stratego 250EC, Stratego YLD, Tilt, and Twinline.  Thirty days before harvest is labeled for Alto, Avaris, Caramba, Embrace, Folicur, Monsoon, Muscle, Onset, Orius, Proline, Prosaro, Tebucon, Tebuster, Tebuzol, Tegrol, Toledo, Topguard, and Viathon.  In addition, Absolute, Stratego 250EC, and Stratego YLD are labeled as 35 days before harvest; Evito as 40 days before harvest; and Approach and Quadris as 45 days before harvest.

So far, wheat stripe rust has been reported 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.