Pocket plum

What you see

Fruit grows long, flattened, hollow and bladder-like, pale green then greying with a bloom of spores, with no stone inside. Affected fruits shrivel and hang on the twig.

Conditions

Cool, wet spring weather at flowering, exactly like its relative peach leaf curl. Spores overwinter in bud scales and on the bark.

Treatment

Pick off and bin every distorted fruit before it turns grey and sporulates. That is essentially the whole treatment - it is a once-a-year, one-shot infection.

Prevention

A copper spray at bud swell, before the buds open, prevents infection. Prune for airflow. Remove all affected fruit annually to break the cycle.

Months: March, April, May

Plants

Plum, Blackthorn

Remedies

Bordeaux mixture (copper)

The thing people get wrong

It is the same genus as peach leaf curl and it works the same way - a single infection window as the buds open in cold wet weather, and nothing you do after that changes anything. So the timing rule is identical and equally counter-intuitive: the useful spray happens in late winter on bare wood, weeks before any symptom exists.