Stem rust is raising its ugly head in the Pacific Northwest again this season. Stem rust is a sporadic problem in the Inland Pacific Northwest that can cause total yield loss in wheat or barley crops in years that have persistent, late-season rainfall or warm, humid nights. Unlike other parts of the U.S. and world, the stem rust fungus (Puccinia graminis f. sp. tritici) depends on common barberry (Berberis vulgaris), a woody shrub, that is the alternate host for the stem rust fungus. As a result of this dependence on barberry, there are many more races of the stem rust fungus present in the Pacific Northwest than the rest of the U.S., which makes breeding for resistance impractical. The best way to manage stem rust outbreaks is to identify the location of common barberry bushes and destroy them.
Starting in the 1940s, the federal barberry eradication program destroyed thousands of barberry bushes across the inland PNW. However, no eradication measures have been taken since the 1970s allowing barberries to recolonize areas resulting in many common barberry host plants around than we realize. When you discover a common barberry shrub, use a cut stump application method to kill the bush or a foliar application of imazapyr. Realize that a foliar application of imazapyr will kill surrounding vegetation that the herbicide contacts.
More information on stem rust of wheat and barley is available on our website, including the bulletin “Identifying Rust Diseases of Wheat and Barley”, Washington State University Extension Publication MISC0197E, “Control of Common Barberry to Reduce Stem Rust of Wheat and Barley”, Washington State University Extension Fact Sheet FS151E, and “Identification and Management of Stem Rust on Wheat and Barley.” Information on the Federal Barberry Eradication program, including detailed maps of barberry eradication sites in Washington is titled “Protecting Cereal Grains from Stem Rust“.
