In the spring spores are produced and dispersed to the new leaves of susceptible trees. Rake up all fallen leaves. Fertilization and watering may help to reduce the disease. Autumn Flame, Tilford and Gerling red maple varieties are relatively resistant to leaf spot. For chemical control use the same fungicides as listed for control of anthracnose.
Spots arise in late spring or early summer after leaves attain full size.
At first the infected tissue is light green or yellow. Then, during late summer, raised, shining black, tarlike dots develop within the yellow spots on the upper leaf surfaces. The lower surface of a leaf beneath a large tar spot turns brown, but the surface beneath speckled tar spots remains yellow. Leaves with multiple spots may wither and drop prematurely, but seldom so early or in such quantities as to threaten the health of the tree. This disease is more common in the forest, but may be seen in some landscape situations.