The Q&A Archives: Cankers on Ornamental Cherry Branches

Question: My mother has a diseased ornamental weeping cherry tree. This year all of the branches have small patches where the leaves have died and what seems to be sap exuding out from them. We tried insectidal sprays but that hasn't help. Could it be Fire Blight?

Answer: Fortunately, it's not fire blight, which doesn't attach stone fruits such as cherry. It could well be another bacterial disease, though - bacterial canker, also known as gummosis. Dark, sunken lesions on the trunk and branches form and gummy sap oozes from them. Unfortunately, there's nothing you can do to reverse the damage that has been done, and the affected branches should be removed as soon as possible. Use clean pruners and/or saw that have been sterilized with rubbing alcohol, and make cuts 1-2" below the affected tissues. Clean tools with alcohol between cuts to avoid spreading the disease to healthy wood. The best way to protect trees from the disease is to grow resistant varieties, remove wild cherry trees that are infected from the vicinity of your favored trees, and in the cooling humidity of fall, spray the tree with a copper sulfate based product, such as Bordeaux Mixture (available at many garden centeres). Follow label instructions carefully, since misuse of the product can have bad effects on the tree. Also, in the future, before you spray any plant, find out what the source of the problem is - freely spraying insecticides does much more harm than good. We're happy to help anytime you have a question - hope you'll visit again!

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