Winter injury is frequently an important predisposing factor to infection. Once established in dead or weakened tissue, the Cytospora fungi will invade adjacent healthy tissue, causing dieback and stem cankers. These structures produce millions of spores, called conidia. During wet weather, spores ooze out of the spore-producing structures in reddish to orange colored gelatinous masses. These spores are not adapted to wind dispersal.
Spores germinate at wound sites, resulting in infection and eventual cankering.
Spore-producing structures ultimately form in the new cankers, producing more spores for subsequent infections. The spore-producing structures generally form 4 to 6 weeks after a cankered branch dies. The fungus overwinters in diseased tissue of living hosts and in stem debris on the ground. If cankers are allowed to remain for several years, a second spore-producing structure, the perithecium, develops in the diseased tissue and produces ascospores. Infection can occur anytime during the year, except during very hot and dry, or cold weather.