Tar Spot
LOWRhytisma acerinum / R. americanum
Overview
A very common and distinctive fungal disease of maple leaves. The raised black spots are dramatic in appearance but the disease is almost entirely cosmetic and does not harm tree health. It is most severe in cool, wet years. The fungus overwinters in fallen leaves.
- Type
- Fungus
- Severity
- LOW
- Source
- University of Wisconsin Extension
Symptoms
Raised black tar-like spots on upper surface of maple leaves, spots are roughly circular and up to half an inch in diameter, spots start as light green-yellow areas in early summer then darken to black by late summer, mostly cosmetic with no significant impact on tree health, heavy infections may cause minor early leaf drop
Affected Species
Geographic Spread
Treatments
Fall Leaf Cleanup
Rake and remove fallen maple leaves in autumn to reduce the fungal inoculum for the following spring. Composting or municipal leaf collection are both effective since the fungus does not survive composting.
No Treatment Necessary
Tar spot is cosmetic and does not harm tree health. No fungicide treatment is recommended for landscape trees. Raking leaves is the primary management strategy.
Recommended Products & Tools
Helpful supplies for managing Tar Spot. Always read and follow label directions, and confirm a diagnosis before treating.
Broad-spectrum protectant for many fungal leaf and bark diseases.
Preventive spray for needle cast, leaf spots, and blights.
Sharp, clean cuts to remove affected wood — a tree-care essential.
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Frequently Asked Questions
What is Tar Spot?
A very common and distinctive fungal disease of maple leaves. The raised black spots are dramatic in appearance but the disease is almost entirely cosmetic and does not harm tree health. It is most severe in cool, wet years. The fungus overwinters in fallen leaves.
What are the symptoms of Tar Spot?
Raised black tar-like spots on upper surface of maple leaves, spots are roughly circular and up to half an inch in diameter, spots start as light green-yellow areas in early summer then darken to black by late summer, mostly cosmetic with no significant impact on tree health, heavy infections may cause minor early leaf drop
Where is Tar Spot currently found?
Tar Spot is currently active in Connecticut, Iowa, Illinois, Indiana, Massachusetts, Maryland, Maine, Michigan, Minnesota, Missouri, Nebraska, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, South Dakota, Virginia, Vermont, Wisconsin, West Virginia. It has been reported in 22 total states across the United States.
What plants are affected by Tar Spot?
Tar Spot affects Sugar Maple, Red Maple, Japanese Maple. Susceptibility varies by species.
How do I treat Tar Spot?
Treatment options for Tar Spot include: Fall Leaf Cleanup, No Treatment Necessary. Treatment approaches may include chemical, biological, cultural, and mechanical methods depending on the severity and context.