Forest Health Protection, Southern Region

Importance. - Black knot is an important disease of cherry, because it degrades this valuable veneer and lumber species. Except for southern Florida and southern Louisiana, this disease is found throughout the Southeast. Many species of cherry are affected, but black cherry is the only commercially important species. The disease is rarely fatal.

Identifying the Fungus. - Swellings on the branch of the host plant are covered with an irregular, rough, fruiting layer of fungal tissue. Spore bearing fruiting bodies form within this fruiting layer. The fruiting bodies and the spores are easily recognized by a specialist.

Identifying the Injury. - Black knot is a disease that causes irregular black swellings on black cherry stems, branches, and twigs. Often a white fungus is found growing over the swellings. Later, the swellings blacken and appear rough.

Biology. - Infection occurs during the spring, and swellings develop the following spring. These swellings are overgrown by a black irregular mass of fungal fruiting bodies.

Control. - Control is generally achieved by pruning out diseased tissue along with at least 12 inches (30 mm) of uninfected wood. In forest stands, trees with infections on their boles should be removed during improvement thinnings.