Plum Pocket

Plum Pocket is a fungus that infects all species of native plum but does not infect commercially cultivated plums from Europe and Asia. It occurs across the United States and in southern Ontario Canada. It is uncommon in Minnesota. It causes deformation and underdevelopment of fruit but is not fatal to the plant.

Plum pocket spores overwinter on twigs and buds of the host. The spores germinate in early spring and infect young developing fruit 6 to 8 weeks after the buds open. The infection first appears as small white blisters on the fruit. The vegetative part of the fungus (mycelium) grows between the cells of the fruit, causing the cells to expand and divide abnormally. The blisters enlarge as the fruit grows, and eventually envelop the entire fruit. Spore-bearing cells (asci) eventually break through the skin (epidermis) of the fruit.

The result is an enlarged, misshapen fruit with a grayish velvety coating. Seeds do not develop in infected fruits, and the hollow plums are called “pockets”. When the asci mature they release their spores which are spread by wind and splashed by rain to new plants and new parts of the same plant. These spores do not germinate until the following spring. Eventually the pockets turn brown or black and fall from the plant.

American plum, Canadian plum

Spring

Sources

4, 7, 26, 29, 30, 77.

Jake Strange
5/25/2024

Location:Ramsey, Anoka county. Observed on my plum trees ar 15346 Okapi St nw, Ramsey 

I have observed plum pocket on my fruit trees the last 3 or 4 years and just now figured out what it is. Any help treating it would also be appreciated.

The University of Minnesota Extension has information on managing Plum Pocket.

How to manage plum pocket

Location: North East Corner of Dowling School, Minneapolis property.

The tree is contaminated with the Plum Pocket.