There are black growths on the branches of my chokecherry. What should I do?

FAQ
Question: 

There are black growths on the branches of my chokecherry. What should I do?

Answer: 

The black growths are probably black knot.  Black knot is a fungal disease that occurs on chokecherry, European birdcherry, and several other wild and cultivated cherries and plums.  The black growths (galls) can vary from a few inches to a foot or more in length. 

Black knot is caused by the fungus Apiosporina morbosa.  Fungal spores produced on one-year-old and older galls initiate new infections.  The knots are soft when newly formed and later become hard and black with age. 

Black knot is difficult to control.  If only a few galls are present, prune out the infected branches in late winter.  When pruning, make the cut at least three to four inches below the gall.  The pruned material should be removed from the area and destroyed.  Several fungicide applications may help prevent future infections.  The fungicide applications should begin just before bud break and continue until after fruit set.  Attempts to control black knot in badly infested trees are likely to be unsuccessful.  When dealing with severe black knot infections, the best options are to do nothing or remove the tree and replace it with a black knot resistant tree.