Tar Spot Of maple

Disease Information

Tar Spot

 Symptoms and damage

Tar spot is caused by the fungus Rhytisma acerinum. 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, tar-like 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.


The fungus survives the winter in fallen leaves. Rake up and discard the leaves in fall. Spraying three times at two-week intervals with a copper-based fungicide, mancozeb, or triadimefon starting when the leaves begin to unfurl in spring will provide control .


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