Dead wood produced by fire blight provides areas for secondary fungus infection by other fruit rotting organisms. Fire blight of apple. On the leaf, scab causes an olive green spot somewhat darker than the leaf tissue. Spots later become dark, thicken and cause leaves to curl. On the fruit, grayish, scabby-like spots develop causing fruit to become disfigured and crack.
Spots are always hard and never turn into a soft rot.
Primary leaf and fruit infection occurs very early in the season as soon as the first green tissue is present. The fungus responsible for bitter rot can infect the fruit anytime after petal fall. The disease is severest as fruit reaches maturity. Small, brown, circular areas develop anywhere on the fruit surface. Spots later become sunken, forming a saucer-shaped depression.