If you have a cherry or mayday tree; it’s important to inspect the canopy carefully each fall (with the leaves gone the growths are easy to spot).
If caught early, black knot can be kept at bay quite well with just some light pruning, easily done by a handy homeowner with a pole saw, or a professional.
If let to metastasize for too long; a severely infected tree is generally not worth saving. At this point removing, and replacing the tree with a species not susceptible to the fungus, is advisable.