Black Knot On Plum And Cherry Trees

Black Knot On Plum And Cherry Trees

Black knot, caused by the fungus Dibotryon morbosum, is a common disease of plum and cherry trees throughout the United States. The fungus attacks twigs and branches forming large, cylindrical, black swellings. The disease becomes more severe on infected trees each growing season and will eventually kill the tree unless effective control measures are used.
Symptoms. The disease first appears in the fall as small, olive-green swellings on twigs, fruit spurs, and branches. In the spring, the swellings turn light brown and rupture as they enlarge. In May or June, elongated swellings become larger and more gall-like. Young gall surfaces have a pulpy texture and are covered with a velvety, olive-green fungal growth. During the summer, the knots or galls turn darker in color and continue to expand. By the following fall, the galls turn dark black and harden-off. Knots continue to expand each year resulting in galls that can be as large as a foot long and over an inch thick.

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