Tar spot is a fungus that infects mainly maple trees, mostly Norway Maple (Acer platanoides). The black spots that form on the foliage are usually smaller than the size of a loonie and don't tend to affect the overall health of the tree. The presence of tar spot points to excess moisture, so the canopy can be pruned strategically to increase air flow and create a drier environment.
The fungus overwinters on leaves at the base of the tree to re-infect the following spring. Raking and disposing of infected leaves in the autumn is a great way to reduce the presence of the fungus on that particular tree.
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