The spots eventually turn dark-green to brown and develop a rough texture. Some leaf distortion may accompany infection of expanding foliage. Numerous leaf or petiole infections will cause leaf yellowing and premature defoliation. The fungus also may attack the fruit at any stage of development. Early infection results in blossom blight and dropping of young fruit.
Later infections produce dark- green to black, circular lesions on the fruit.
These rough, scaly spots cause surface blemishes to the fruit but do not extend deeply into the flesh. The scab fungus overwinters as immature fruiting structures in partially decayed leaves on the orchard floor. In Kansas, primary spore release begins in early to mid-April and continues for a period of five to nine weeks. Windblown spores are deposited on expanding leaves where they germinate and penetrate the leaf surface. Germination and infection of the host requires that the leaf surface remain wet for a period of time, the length of which varies according to the ambient temperature.