Plum pocket is an unusual disease caused by the fungi Taphrina communis or Taphrina pruni, affecting plums, damsons, and certain ornamental Prunus species. It results in the abnormal growth of fruits, rendering them worthless and distorted within a month or two after bloom. This disease impacts various plum varieties in the U.S., leading to malformations, crop loss, and unsightly fruit. Airborne spores released from the fungal bloom on the fruit can lodge in bark and bud scales, remaining dormant until the following spring when they invade the plant tissues, causing swollen and deformed shoots. In subsequent years, the fungus invades flowers and developing fruit.
Plum Pocket
Signs of damage
- Plum pocket symptoms are characterized by a small blister on the fruit, which quickly grows to cover the entire fruit.
- The infected fruit can grow up to ten times its normal size, becoming spongy and covered in velvety gray fungal spores.
- Eventually, the fruit dries out, turns black, and becomes hollow at the center.
- Leaves may thicken and curl in some cases.
- Infected fruit usually fall to the ground, while some may remain on the tree throughout winter.
- Other symptoms include elongated and hollow fruit without stones, the appearance of white fungus bloom, and the formation of witches' brooms on stems.
How to prevent
To prevent plum pockets, apply a fungicide just before bud break in early spring. Another effective method is to plant disease-resistant cultivars, as most improved varieties are resistant to the disease. If you have wild plum trees nearby, remove them to safeguard your cultivated crop. If your tree has been previously infected, use a plum tree-safe fungicide as a preventative measure in the spring.
Heal
The plum pocket disease doesn't harm the tree's health, so no active management is required. However, reducing the disease's impact can be done by removing infected plums and burying them in a compost pile. Thoroughly removing infected branches, witches' brooms, and fruit before spore production can also help control the disease, although it may not completely eliminate the risk of new infections. If left untreated, it can lead to significant fruit loss, but it can be treated with fungicide sprays labeled for use against the plum pocket. Follow the instructions carefully, including the recommended waiting period before harvest, known as the post-harvest interval (PHI). Store fungicides safely and avoid spraying on windy days.
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