Cherry-plum, infected with pocket plum disease

I had been hoping for a good cherry-plum harvest this summer - the fruits make excellent jam - but the hedgerow trees that I had my eye on are infected with pocket plum disease, caused by the fungus Taphrina pruni. In the first picture you can see one uninfected developing fruit, green, and then the rest are red, swollen and deformed so that they are flattened, resembling pockets. Soon spores will erupt from their surface.

In previous years I've seen infections on sloes and on bird cherry. This is the first year I've seen a severe infection on cherry-plum.

 

Pocket plum disease

 This summer there have been some spectacular local outbreaks of pocket plum disease, affecting sloes on blackthorn on the Durham coast near Hawthorn dene  and bird cherry fruits in Weardale. It's caused by the fungus Taphrina pruni, which induces the fruits to swell, become spongy and fill with watery fluid. In bird cherry (bottom picture) the normally spherical, shiny black fruits become banana-shaped. No seeds are formed inside these deformed fruits, instead there is an empty 'pocket'.