Aptly named Maple Tar Spot (Rhytisma acerinum) is a common fungus that is very common to Norway Maple,  Silver Maple, Red Maple and sometimes Sugar Maple and Sycamore.   The disease resembles spots of black  tar on the leaves of the Tree.   It starts as yellow spots on the leaves usually in July/August,  The spots are about the size of  shirt buttons and slowly transition to black with the black spore units by late August to September.

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 The presence of the fungus is a combination of factors including the genetic predisposition of the tree, the health of the tree  (stressed trees are more susceptible) and, favorable weather conditions to spread and establish the spores. The good news is this is predominately a cosmetic disease of the leaves and does not cause any significant injury. Generally, no spraying of fungicides is recommended. Historically, older texts would recommend raking and removing fallen leaves to limit the recurrence of the disease, but the abundance of reservoir trees (trees nearby that also have the disease) and weather conditions have more a bearing on the spread of the disease than raking as a control method. In other words, raking may help but probable isn't worth the effort.

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