Historically, stem rust of wheat and barley has been one of the most important diseases human civilization has confronted.
This disease occurs worldwide and is probably most important on wheat. In the United States, stem rust has been most important in the Midwest and Great Plains states. Stem rust has occurred sporadically in the Pacific Northwest USA over the past 60 years, but weather patterns since 2007 have been more conducive to its appearance in eastern Washington, northern Idaho, and western Oregon. Unlike most diseases, stem rust requires two plants to complete the entire cycle. The common barberry (Berberis vulgaris) is the alternate host to the stem rust fungus, and is crucial to the pathogen completing its life cycle. Note that common barberry is a different species than the Japanese baberry (Berberis thunbergii), which is a common, decorative landscape plant in the U.S. Damage to the host plant results from destruction of photosynthetic leaf area, as well as an increase in evaporative water loss due to breakage of the epidermis and cuticle of the plant.
This website is an educational tool produced by the scientists working on this problem.
The stem rust fungus produces several different structures during its life cycle. The most obvious of these on wheat are the reddish-colored urediniospores that form on leaves, stems, and heads during the growing season. These spores are spread by wind and infect wheat or barley plants. The black-colored teliospores are produced toward the end of the growing season and are structures specialized for survival. These spores enable the fungus to survive on straw over winter and only spread with the straw. On barberry, orange- to salmon-colored aecia are produced on the lower leaf surfaces early in the spring. Aeciospores are produced in the aecia and are spread to wheat by wind.
When stem rust is severe, lodging of infected plants may occur, but disease is seldom that severe in the PNW.