This easy to identify disease is the result of a fungal infection.
It primarily infects fruit trees, especially cherry and plum. The fungus produces spores in the Spring that are spread by the wind. The spores infect a tree by entering through wounds or young green shoots.
Fortunately, infected branches are isolated and won’t kill a tree, but if the trunk becomes infected then the tree will surely die. The best way to control this disease is through pruning. Any infected branches should be removed and disposed of to prevent any further contamination.