Hard, black galls caused by black knot Ohio Cooperative Extension	Black knot swellings on cherry US Forest Service

Black knot is visible as soft greenish knots or elongated swellings which form on the twigs and branches. The knots develop into black, corky, cylindrical galls that range from about 1/2 to 1 1/2 inches in diameter and may be more than 12 inches long. Branches beyond the galls are often stunted or dead.

Black knot is caused by a fungus that multiplies during wet spring weather. The visual symptoms are often seen 6 to 12 months after initial infection.

To control black knot, prune out an destroy infected twigs and branches in the fall and winter. Be sure to cut at least 4 inches below the visible signs of the knot. After each twig branch cut, be sure to sanitize your pruning tool in a mixture of 1 part bleach and 6 parts water as this helps to reduce the spread of the fungus. Large knots or cankers on main branches or the trunk should be cut out to a depth of at least 1/2 inch beyond the infection. In the spring spray the tree with either Captan Fungicide for Fruit & Ornamental Trees or the Fruit Tree, Vegetable & Ornamental Fungicide. Two or three more sprays at intervals of 7 to 10 days are required during the spring season.

Since an affected tree is under immense stress, it is also important to give the tree a good fertilizing. For general tree maintenance, proper fertilization and to improve the overall health of the tree, applying a TreeHelp Annual Care Kit is recommended. These kits contain appropriate fertilizer, mycorrhizal fungi and biostimulant, promoting root development and long-term vitality.

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