Source: William M. Brown Jr., Bugwood.org
The causal fungus, Sphaerotheca pannosa, attacks leaves, twigs, and fruit.
On fruit the disease first appears as round, whitish spots 2 to 4 weeks after shuck fall. The spots get bigger until they cover much of the fruit.
The white spots are produced by the fungus mycelium and its spores. About the time of pit-hardening, the skin of the fruit under the spot turns pinkish, and the fungus and its spores disappear. Eventually the skin becomes leathery or hard, turns brown, and may crack.
Diseased leaves often fail to unfold normally, while those of new shoots become narrow, straplike, and distorted. New shoots are shorter than normal and distorted. The white mycelium and spores of the fungus may cover infected leaves and shoots or may appear as whitish patches.
The fungus overwinters on shoots infected the previous season. Quite likely it survives behind leaf bud scales. Flower buds of infected shoots often do not survive the winter. As leaf buds expand in spring, young leaves become infected and the spores produced on the leaves serve to infect young fruit, new shoot growth, and newly expanding leaves.
Routine fungicides adequately control this disease.