Effects

• Rhytisma acerinum, the most common of the tar spot fungi to infect the maple, is spread from tree to tree in the spring by the wind, according to the Maine Forest Service's website. The fungus overwinters in the leaf litter beneath the tree.
  
  

Identification

• Infected leaves develop yellow spotting first before the characteristic black, raised spots occur. The black spots split to release reproductive spores into the environment.
  
  

Prevention

• Rake all fallen leaves up from the infected maple tree and promptly dispose of them. Do not allow leaves to overwinter on the ground. Apply liquid copper or other fungicides if the infection is severe, but the treatment is rarely completely successful because the entire leaf must be saturated in the fungicide to achieve adequate control, according to the Charter Township of Waterford Michigan's and Michigan State University's website.