Why Are My Plums Turning into Hollow Pouches?

Pocket plum disease is one of the stranger sights in the kitchen garden — plums that swell to an exaggerated, elongated shape but remain pale, hollow and inedible, with no stone inside and a wrinkled, bag-like texture. It is caused by the fungus Taphrina pruni and is related to the peach leaf curl organism, though on plums it attacks the developing fruitlets rather than the leaves.

What happens to the fruit

The Taphrina pruni fungus infects the young ovaries as the flowers are opening, or even earlier. As the fruitlet develops, the fungal infection prevents normal stone formation — the stone fails to develop and the fruit wall expands into an elongated, flattened or bladder-like shape. Affected fruits are several times longer than normal, soft, pale yellowish-green or later purplish, and completely hollow in the centre where the stone should be. They are inedible and should be removed immediately. In late summer, affected fruits may turn grey-white and powdery as the fungus sporulates on the surface before dropping.

How widespread is pocket plum?

Pocket plum can affect a proportion or, in severe years, the majority of fruit on a susceptible tree. Damsons and wild plums are particularly prone; many modern cultivated varieties show some resistance. In most years only a small proportion of fruits are affected, but in cold, wet springs with extended blossom periods the infection window is longer and damage can be substantial.

Prevention — the key intervention

Because infection occurs at or around flowering, post-symptom spraying has no effect. Prevention requires applying a copper-based fungicide (copper hydroxide, copper oxychloride) as a winter wash before the buds begin to swell in late January or February. A second application at green-tip (when buds first show green tissue) provides additional protection. Timing is critical — the spray must be in place before the flowers open.

Removing affected fruit promptly

Pick off all pocket plums as soon as they are identified and destroy them — do not compost them. Leaving them on the tree allows the fungus to sporulate and potentially infect the following year's buds. After harvest, collect fallen fruits from the ground for the same reason.

Long-term management

In gardens where pocket plum recurs annually, the copper winter wash should become a routine part of the annual programme. Trees with good air circulation and reduced ambient moisture around the blossom are less severely affected.