July 27, 2012
Stripe rust on winter wheat
The stripe rust season is basically over, but stem rust and leaf rust have become a problem in eastern Washington and northern Idaho.
On July 12, few stem rust pustules were found in the wheat field next to the barberry bush near Potlatch in northern Idaho. On July 16, Mike Pumphrey found hotspots of stem rust in his spring wheat nurseries at the Spillman Farm near Pullman. Yesterday (26), Kent Evans found a couple of stem rust pustules in our spring wheat nurseries north of Pullman. Mike Pumphrey collected stem rust from 7 or 8 fields of spring wheat in a 60 mile loop while visiting breeding and variety trial locations north of Pullman. He also found stem rust in every of about four commercial spring barley fields he checked. Rust reached 20-100% incidence, and about 1-10% severity. Today, Ken Fuchs brought stem samples from two spring barley ‘Lenetah’ fields south of Spokane with rust severities about 10%. All these observations indicate a widespread of stem rust on spring wheat and barley in Whitman and Spokane counties and possibly in Stevens County of Washington, and Latah County of Idaho.
I found leaf rust in our spring wheat nurseries (up to 10% severity) near Pullman.
Much of the stem rust and leaf rust we see now was resulted from infection occurred during the showers in late June and further increased by the showers in middle July. The rusts can become worse in fields that still have good moisture to produce dews on plants during night. Late crops are more vulnerable to both stem rust and leaf rust. Please check your spring wheat crop (for both stem and leaf rusts) and spring barley crop (for stem rust). If your crop has not reached soft dough stage, will not harvest within a month, and still can see dew formation in very early morning, you may consider spraying with a fungicide. After flowering stage, only Tebuconazole (Folicur) can be used up to 30 days before harvest. Spring crops which have already pasted soft dough, damage by stem rust and/or leaf rust may not be significant. If the crop will be ready for harvest within 30 days, any fungicide cannot be used.