Black knot is a common fungal disease of
Prunus trees including ornamental, edible, and native plum and cherry trees.
Hard swollen black galls (tumor like growths) form on branches and occasionally on trunks. Many Prunus
trees tolerate black knot. Tolerant trees have many galls throughout the tree with few negative effects on the health of the tree. Some Prunus trees are more severely affected by black knot. In these trees, leaves and shoots wilt and die on branches with galls.
Management will vary depending on how severely the tree is affected by black knot.