This fungus has a complex life cycle with up to eight different spore types observed in the field and under laboratory conditions. Most stages are not readily observed in the field. The most visible spore stages likely to be observed in a natural setting are the single-celled urediniospores which propagate the fungus within the growing season, and two-celled teliospores which are the overwintering stage of the fungus. Spores are microscopic, but the brown pustules that bear them are readily visible on both the upper and lower leaf surfaces of infected plants.