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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

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? 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.

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