Blumeriella jaapii

This fungus overwinters in dead leaves on the ground. In early spring (at the time of petal fall), fungal fruiting bodies called apothecia develop in these leaves. Ascospores produced in the apothecia are forcibly discharged into the air starting at petal fall. They can start new infections in new, green leaves and serve as the primary inoculum in each new growing season. The ascospores can stick to the leaf and, given a film of water and optimal temperature, germinate within hours of adhesion. Upon germination, hyphae can grow into the leaf via stomata (natural openings) on the underside of the leaf. Hyphae cannot invade immature stomata very effectively. After invasion, the hyphae grow in the intercellular spaces in the leaf, killing and feeding on leaf tissues. Incubation times vary with available moisture and temperature. The small purple lesions can appear within 5 days if there are damp conditions and the temperature remains steady between 60–68 °F (16–20 °C), or up to 15 days in lower temperatures and drier conditions. Leaves become less susceptible to infection as they age. The first sign of disease may be on the suckers close to the ground. Sexual reproduction is associated with the primary infection cycle of cherry leaf spot. Infection levels in this primary cycle are low, but essential for the success of the pathogen. …