Hi Judy,

I am looking forward to helping you learn what is affecting your Plum tree and what can be done to eradicate the problem.

Before I consult with the team's plant pathologist, is it possible for you to send a few pictures? One showing the entire tree and a few closeups.

Have you had a successful plum production in the past from the affected tree? Have you considered having the soil analyzed to determine how suited it is for plum/peach trees and what nutrients are needed?

Please let me know if you are unable to send along pictures and I will research further. Your correspondence will be forwarded to me until the inquiry is closed.  I look forward to helping you produce plums and peaches.

Jeff Nummelin

Extension Master Gardener Volunteer

Hi Judy,

Based on your pictures and consulting with EMG colleagues, you have Black Knot. All stone fruits (genus Prunus) including Peaches and Plums are susceptible. I wasn’t able to find if the Brilliance Peach Tree is a resistant variety, you may want to check with your supplier. The UNH Extension link below recommends pruning in February or March, 3-4” below the affected area. Burn the pruned branches. It also points out the fungus is spread from wild sources, here in Vermont we have Black Cherry trees. It advises removing wild sources from within 600 feet.  Instead of removing, you may want to consider pruning nearby affected Black Cherry trees if any exist, we have so few.

I enjoyed researching your question, my daughter has a wild black cherry tree near a cultivated red cherry tree and I’m curious if either have Black Knot. If you have any other questions regarding improving the soil to benefit your plum and peach trees health, please do not hesitate.

Enjoy Gardening

Jeff Nummelin

Extension Master Gardener Hotline Volunteer

The following excerpt is from: https://extension.unh.edu/blog/my-plum-tree-has-black-fungus-growing-branches-what-can-i-do-treat-it

Trees in the genus Prunus, which includes plum and peaches, are susceptible to a fungal disease called black knot. Trees infected with black knot have swollen, hard, black knots on their branches. The disease is common on both wild and landscape trees and is easily diagnosed by the swollen, black galls that appear on infected branches. The fungus produces spores in the spring and early summer that are dispersed by splashing or windblown rain. When the spores land on the branches of susceptible trees, they enter straight through the bark on the current season’s growth or through wounds. Infected branches gradually swell throughout the growing season, progressively growing into obvious hard, black knots by the fall. The knots, which can grow to over six inches long, will continue to enlarge until they girdle the affected branches. The fungus overwinters in the knots on the stem, beginning growth again in the spring and producing more spores to start the disease cycle all over again.

Control of black knot requires both prevention and sanitation. Prune out all infected branches in late winter (late February through the end of March) and destroy them by burning, burying, or throwing them away. Remove at least 3-4 inches of healthy tissue below each knot to ensure elimination of the fungus. Heavily infected trees should be removed completely, including wild host trees such as black cherry (Prunus serotina). However, the most effective way to avoid issues with black knot in the future is to plant resistant varieties of plum.