The black rot fungus covers a wide geographical range and can infect many hosts other than apple. The role these hosts play in the spread and development of the disease is not known. In the spring, spores are released during rainfall. The amount and duration of rainfall, as well as temperature, are the main factors influencing spore release, germination, and infection. Conidia are primarily waterborne and continue to be produced during wet periods throughout the summer.
Ascospores are primarily airborne and are most common during the petal fall period.
At this temperature, four and a half hours are necessary for infection. During rain, conidia ooze out by the thousands and are disseminated by splashing rain, wind, and insects. Spores attach themselves to the plant, germinate in a film of moisture within five to six hours and penetrate the leaf surface through stomata. Early season infection of fruit also occurs through stomata. Later in the season, infection of fruit occurs through cracks in the cuticle or via wounds and possibly lenticels.