Black Growths on Plum Tree
There are several black lumpy growths on the stems of my plum tree. Will this kill my tree? How can I keep it from spreading to my other plants?
The black growths on the stems are caused by black knot fungal disease. This disease attacks all Prunus including cherries, ornamental plums, peaches and other stone fruits. Fortunately it will not attack other types of trees. The stem swellings can girdle (stop flow of water and nutrients) limbs and stunt the plant's growth. Prune out and destroy the green knots in spring to reduce the risk of new infections. Unfortunately there may be other disease-infected plants in nearby natural and cultivated landscapes. These serve as sources for future infection for your and other nearby susceptible plants. There is some work on biological controls so there may be some good news in the near future. Look for disease resistant varieties whenever possible. President plum is highly resistant while Methley, Milton, Early Italian, Brodshaw, Fellenberg, Shiro, Santa Rose, and Formosa varieties are moderately resistant.
Related
Upcoming Live Events
& Webinars
April 20, 2024
Pruning Hydrangeas and Other Shrubs
Pasquesi Home & Gardens, Lake Bluff, IL
April 27, 2024
Ridges & Rivers Book Festival
Viroqua, WI
April 28, 2024
Flowering Trees and Shrubs
Ebert's Greenhouse Village, Ixonia, WI
May 1, 2024
FREE WEBINAR
Ornamental Fruits and Vegetables
Register now
May 4, 2024
Garden U 2024
New Richmond, WI
Register now
May 9, 2024
FREE WEBINAR
How to Plant Your Rain Garden
Register now
May 11, 2024
Ask The Plant Doctor Q & A
Ebert's Greenhouse Village, Ixonia, WI
May 12, 2024
Ask The Plant Doctor Q & A
Ebert's Greenhouse Village, Ixonia, WI
May 18, 2024
Ask The Plant Doctor Q & A
Ebert's Greenhouse Village, Ixonia, WI
June 1, 2024
Selecting, Planting, Pruning and Caring for Hydrangeas
Ebert's Greenhouse Village, Ixonia, WI
June 5, 2024
FREE WEBINAR
Under-Appreciated Pollinators
Register now
WATCH ON-DEMAND WEBINARS
Learn More