Learn / Ask The Landscape Professional
Now that the leaves are off the trees, I notice that my cherry tree has several large, ugly black growths. They concern me; what is causing them and what do I do about them?
Answer
Your cherry tree has a common, but destructive
fungus, Apiosporina morbosa. It is widespread in plants such as
plums, cherries, wild black cherries, and peaches. It was first reported
over 200 years ago in Massachusetts and, although it is found all
over the country, it is most common in New England. Not only does it
look terrible, it can actually kill your trees unless action is taken. The
disease forms various shaped hard, black swellings that can get quite
large (over a foot across) and grow larger year after year. Black knot
can occur on the main trunk, small twigs or any of the tree's branches
(or all of the above). The picture shows a section cut from a diseased
tree that has black knot over 6 inches across. The disease is spread
by spores which are ejected from the fungus and easily spread by
the wind. New infections generally occur in April through June during
rainy, warm periods when the temperatures are in the low 70's.
To save your tree, you must take remedial action before April 1.
Prune out any black knots or swelling wherever they occur and cut back at least 4 inches away from the
diseased pieces you remove. If the disease is on the side of a larger stem of the tree, cut into the healthy
wood at least an inch past the infection all around. Since the removed pieces of a tree may still be actively
infected, burn or bury the debris. If there are many infection sites on your tree, the only practical solution
may be to remove the tree completely and dispose of it. You should inspect your trees annually.
If you need assistance with your cherry or any of your trees, give us a call. We'd be happy to help.
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About Linda Lillie
Linda K. Lillie is the President of Sprigs & Twigs, Inc, the premier
landscape design and maintenance, tree care, lawn care, stonework, and carpentry
service provider in southeastern Connecticut since 1997. She is a graduate of
Connecticut College in Botany, a Connecticut Master Gardener and a national
award winning landscape designer for her landscape design and landscape installation work.
