Black Knot disease on cherry tree

By Robert L. Anderson [CC BY 3.0], via Wikimedia Commons

Black knot is an ugly looking fungal disease which is found on trees such as cherry and plum. The pathogen is in the affected twig and as it grows it produces a dark swollen “knot” on the twig or branch.  Management of black knot is very difficult.  Infected branches cannot be saved. The best strategy is to try to protect the remainder of the tree through pruning and fungicide application.