Early symptoms of tar spot fungal infection are now appearing on maple leaves. Leaves are infected in late spring when wind-borne spores land on leaves. Infected tissue turns light green or yellowish-green. As the infection progresses, the yellowish spots turn dark and eventually develop a black, shiny, tar-like tissue on the surface of the leaf.
This disease is unsightly, but usually does not affect the long-term health of the tree. Leaves should be raked and burned in the fall, to prevent the fungus from wintering over and re-infecting the tree the following year.