Knowledgebase

Identifying a plum pest #907725

Asked June 29, 2025, 4:51 PM EDT

I have two plum trees in my front yard (Waneta and Toka) that are losing a lot of fruit. The Waneta fruits have small scars on them that are oozing syrup. The Toka fruits are damaged too though not in the same pattern. The leaves look good, there’s no dying off, yellowing or discoloration I see. Is this from a pest, disease, or environmental conditions? Pictures are attached. Extra info: The trees were planted from bare root six years ago, I pruned it this year during the coldest week of the winter, I pruned it again after the buds were done and the leaves were fully out to cut down the water sprouts and reduce the weight on the branches. We usually have a lot of aphids in the early summer (and lots of ants that eat the honeydew) but we didn’t have noticeable numbers of aphids this year, or at least it didn’t visibly affect the new growth on the tree. The ants are still everywhere though. Thank you!

Hennepin County Minnesota

Expert Response

Based on the symptoms you've described—small scars oozing syrup on the Waneta fruit—it is likely that you are experiencing damage from plum curculio, a key pest of plum trees that causes injury to the fruit and can lead to symptoms like these. This pest leaves characteristic scars on the fruit where it has fed or laid eggs, and the oozing sap could be a reaction to the wound on the fruit. These web pages have additional information. 

https://apps.extension.umn.edu/garden/diagnose/insect/garden/beetles/medium/plumcurculio.html

https://www.canr.msu.edu/news/effectively_controlling_plum_curculio_in_stone_and_pome_fruits

The fact that your Toka fruits are also damaged, though with a different pattern, suggests there might be additional factors at play. Plum trees can also be affected by diseases such as shot-hole disease, which can cause leaf and fruit symptoms as well, though your description does not indicate significant leaf damage.

https://ipm.ucanr.edu/PMG/GARDEN/FRUIT/DISEASE/shothole.html

https://ask.extension.org/kb/faq.php?id=870671

https://ask.extension.org/kb/faq.php?id=747772

Your pruning practices sound appropriate, as correct pruning helps improve air circulation and fruit production. Late frosts could also potentially affect fruit set if they occurred during the stage when the blossoms were open. However, since you mentioned that the leaves look good and there are no significant signs of stress, it seems like a localized pest issue, primarily affecting the fruit.

Since you mentioned a history of aphids, while this year has seen fewer visible populations, it's important to continue monitoring as fluctuating populations can occur. The presence of ants is also common when aphids are around because they are attracted to the honeydew produced by the aphids.

To address these issues, consider monitoring the trees for the presence of plum curculio and other pests, and you can use insecticidal soaps or oils for control. Also, removing any damaged or infested fruit and debris from around the trees can help mitigate further pest problems.

https://edis.ifas.ufl.edu/publication/HS250

Linda G Tenneson, Benton County Extension Master Gardener & Tree Care Advisor Replied June 29, 2025, 7:02 PM EDT

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