A number of diseases of stone fruit are caused by fungi similar to the leaf curl fungus. In the northeastern United States, the most important disease affecting the American-type plum is known as plum pockets, or bladder plum. It is caused by the fungus, Taphrina pruni. This fungus occurs wild or on abandoned plum trees and its occurrence is rare.

Symptoms

First signs of the disease on fruit are small, white blisters. These enlarge rapidly and soon cover the entire fruit. The fruit becomes spongy and tissues of the seed cavity wither and die. Fruit become bladder-like, abnormally large, and misshapen with thick, spongy flesh. As their spongy interiors dry up, the plums turn velvety gray as spores grow on their surfaces. Infected fruit become hollow in the center, turn brown, wither and fall from the tree.

New shoots and leaves are usually infected as well as fruit. Shoots thicken and are often curled or twisted. Diseased leaves are thickened and curled as in leaf curl.

Disease Cycle

pores of the fungus overwinter on twigs. During cool, wet periods in early bloom, these spores may be splashed onto the opening buds, where infection takes place. Developing spores give the infected fruit a velvety gray appearance.

Disease Management

A spray program similar to the one for peach leaf curl may also control plum pockets.