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.