The discolored area enlarges slowly, and the older discolored trichomes begin disappearing, leaving a fuzzless, smooth, center spot surrounded by a non-uniform band of orange to tan hairs. Finally, the spots become quite spread out leaving brownish or reddish centers of hard, smooth skin. Powdery mildew is caused by the fungus, Sphaerotheca pannosa , and infects leaves, twigs, and fruit. Powdery mildew on the fruit, however, causes the greatest economic loss. Symptoms Leaves 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 may cover infected leaves and shoots or may appear as whitish patches. On fruit the disease first appears as round, whitish spots 2 to 4 weeks after shuck fall. The spots enlarge until they cover much of the fruit. The fungus mycelium and its spores produce the white spots. Later the mycelium sloughs off and leaves a rusty-colored patch.