Just as the name indicates, this plant fungus disease appears as black spots on the leaves. It’s as if someone flung paint or tar all over the tree leaves. Occasionally, the tree also develops lesions, or wounds on the leaves that appear more yellow or rust colored. Several varieties of Maple trees are affected, but Norway and Silver Maples are often the most susceptible to Maple Tar Spot. The good news is the damage caused by Maple Tar Spot is usually minimal. Primarily, the disease affects the appearance of the tree and not its structure. If the infection is severe, the tree may drop leaves earlier in the fall, but it’s not believed the disease impacts tree growth or development.

This year is a particularly bad year for Maple Tar Spot in our area, due to the wet weather we experienced this spring. While infection occurs during the spring, symptoms don’t appear until the summer or fall season. Maple Tar Spot is most commonly found in wet areas when leaves remain around the trees, after the leaves have fallen. This disease thrives in moist conditions. The fungus overwinters in the fallen leaves and re-infects the tree the following spring, by producing fungal spores that attack new tree growth.

There are solutions to combat Maple Tar Spot. Most importantly, eliminate leaves from the landscape, as they fall from the trees. Fall clean-up reduces the incident of re-infection the following growing season. Maple Tar Spot primarily causes cosmetic damage. Because of this, chemical action may not be required. If the infection is severe and bothersome, contact the Plant Health Care Department at KTS for more information on Maple Tar Spot or to have it properly identified by a Certified Arborist. Characteristics of many fungal diseases appear similar. It often takes a trained individual to properly identify the problem and find a solution.

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