Hello,

The plum tree that you have is a cultivar of the purple-leafed plum, Prunus cerasifera, a non-native tree from Asia. In the article from the University of Connecticut (link listed below), it lists cankers and borers as liabilities associated with the species. The disease, black knot, is also a fungal infection of trees common to the Prunus genus.

Bacterial canker, discussed in the second article below is very common to Prunus. This disease can sometimes but not always be lethal to a tree. Gummy liquid tree sap will drip from a lesion in a branch or trunk which explains the term,"gummosis", as one name for bacterial canker. Many times cankers form where there has been an injury to the tree or where a limb has been removed. This disease would be difficult to diagnose, and the most accurate diagnosis should be done by a university plant diagnostic lab.

Black Knot is a fungal disease in which large black galls or growths form on the tree. These are very identifiable and therefore easier to diagnose. It is not always a problem or deadly for a tree. It would certainly depend on the overall tree health and environmental conditions.

Shothole borer, American plum borer, and ambrosia beetle are damaging insects which can cause dripping sap and other issues in plum trees. In the case of borers and beetles, the sap would ooze from the entry and exit holes in the trunk. These holes would be easy to see if this is the problem with your tree.

From the pictures that you have sent, I'm not getting a clear view of the places from where the sap is dripping. I do not see growths but again, the pictures are not quite close enough to tell. Also, is there any limb or twig dieback, holes in leaves, or issues with the flowers or fruit? These would be indications that the disease/pest is becoming a problem for the tree.

In order to treat or manage a disease or pest, the correct diagnosis must be made. The next step for you would be to read the articles listed below and then look closely at the areas from where the sap is dripping. By the process of elimination, you may get a general idea of what the problem might be. You may send more detailed pictures to me but the most accurate diagnosis should be done by a lab.

To get a diagnosis from a lab, you must send send a sample of a diseased branch or other diseased part of the tree to a lab. The C. Wayne Ellett Plant and Pest Diagnostic Clinic (PPDC) run by OSU in Wooster accepts plant samples by mail and walk-ins. I've listed their website link below. This website explains sampling instructions and how to submit it to the PPDC. After examining the sample they will send you the information needed to guide you in determining the necessary treatment or management for the plum tree.

 Please write back if you should have more questions about any of the information that I've sent you.

Thanks for asking Ask Extension.

Betsy B. - MGV





https://plantdatabase.uconn.edu/detail.php?pid=349

https://hort.extension.wisc.edu/articles/bacterial-canker/

https://extension.umn.edu/plant-diseases/black-knot

https://treefruit.wsu.edu/crop-protection/opm/shothole-borers/

https://content.ces.ncsu.edu/american-plum-borer-in-ornamentals

https://ppdc.osu.edu/