About the Disease
Tar spot is caused by a fungus that infects the leaves of maple trees and causes raised black spots to form on the upper leaf surface. The diseases are caused "tar spots" because their appearance so closely resembles droplets of tar on the leaf surfaces.
Tar spot is rarely serious enough to threaten the health of the trees but sometimes there can be so many spots that the trees becomes unsightly. Heavy infections can also cause early leaf drop, a circumstance that causes the greatest concern to property owners. However, the tar spot fungus is not known to cause long term damage to the trees.