Twig infections occur on new, green, tender growth. Lesions on infected twigs are slightly raised, circular to oval, and become purple to dark brown later in the season. Disease Cycle Peach scab is caused by the fungus Cladosporium carpophilum . The pathogen overwinters in small twig lesions on last season's shoots and on the surface of the bark. Spores, produced in these cankers during the early spring, usually around shuck split, are splashed by rain to young fruits and new shoot growth.
Rain is required for infection.
A very long incubation of 40 to 70 days is needed for symptom development. Although fruit remain susceptible from shuck fall until harvest, usually only infections that occur during the shuck split to pit hardening stage of development have an opportunity to show symptoms before harvest. Twig infections that result in the formation of small overwintering lesions can occur throughout the season. Secondary infections may occur on twigs, but usually do not appear on fruit except on late season cultivars. Disease Management Peach scab is controlled by pruning and fungicidal sprays.