Taphrina pruni being larger than the healthy one. As a fungus, cool and wet weather conditions promote the germination of spores, whilst warm and dry weather results in infection rarely taking place. Colonisation can become extensive and eradication very difficult. The disease can to some degree be controlled by carefully removing infected branches, witch's brooms and fruit before the infective air borne spores are produced. Applications of copper-containing fungicides have a degree of control over the fungus. Taphrina pruni Taphrina pruni is a fungal plant pathogen of blackthorn (Prunus spinosa) that causes the Pocket or bladder Plum gall, a chemically induced distortion
Prunus americana Prunus americana Prunus americana, commonly called the American plum, wild plum, or Marshall's large yellow sweet plum, is a species of "Prunus" native to North America from Saskatchewan and Idaho south to New Mexico and east to Québec, Maine and Florida. "Prunus americana" has often been planted outside its native range and sometimes escapes cultivation. It is commonly confused with the Canada plum ("Prunus nigra"), although the fruit is smaller and rounder and bright red as opposed to yellow. Many cultivated varieties have been derived from this species. It forms an excellent stock upon which to graft the domestic plum.