Tree fungus or bag worms?

Asked February 6, 2017, 10:02 PM EST

I have an ornamental plum which is breaking open at spots (one place a lot more than others) and seeping sap. The biggest area is blackened. (See pic) There was a cherry tree in this lication before, and it had the same problem. Last spring, I cleared bag worms away from this branch that is the worst. Is that what I am dealing with, or is a fungus involved?

Jefferson County Kentucky trees and shrubs tree diseases bag worms tree fungus

1 Response


This is a disease called 'Black Knot" that affects members of the Prunus family (includes cherries, plums, and other pit fruit). The most effective control is to prune out the branches below the 'knots'. Be sure to wipe the pruners with alcohol or a 10% bleach solution so that the disease is not spread by your equipment.

Cut down wild cherries on your property as they can harbor the disease.

For more information on Black Knot click here:http://plantpathology.ca.uky.edu/files/ppfs-fr-t-04.pdf

Feel free to contact our office if you have other questions.

Let me know if I can help you further!


Carol Wilder
Horticulture Technician
Jefferson County Cooperative Extension Service
502-569-2344
200 Juneau Drive
Louisville KY 40243