Tar Spot on Maples: Atlanta Identification & Management Guide

What Is Tar Spot?

Tar spot is a foliar fungal disease of maples caused by fungi in the genus Rhytisma, most commonly Rhytisma acerinum, Rhytisma americanum, and Rhytisma punctatum. Infected leaves develop yellow patches in late spring and early summer that gradually turn into raised, shiny, black blotches that look like dabs of tar.

How to Recognize It

• Small (roughly 1/8 inch) pale yellow or yellow-green spots appear on leaves in late spring or early summer after the leaves are fully expanded.
• Through summer, the yellow patches enlarge and a raised, shiny black, tar-like spot develops in the center, sometimes reaching about 3/4 inch across.
• On Norway maple, multiple small black flecks often cluster together. On silver and red maple, spots tend to be larger and more solitary, with fingerprint-like ridges.
• Heavily spotted leaves may turn yellow and drop earlier than normal in late summer, especially on shaded, low-airflow branches.
• The disease only affects leaves. The bark, branches, and trunk look normal.
• Symptoms are usually most obvious by August.

Infection happens in spring as new leaves expand. Yellow spotting becomes visible in May and June, and the dark, tar-like blotches develop and darken through summer. The fungus then overwinters in fallen leaves and produces fresh spores the following spring.

Why It Matters for Atlanta Trees

Tar spot is generally considered a cosmetic disease. Extension specialists agree it rarely threatens the long-term health of an otherwise healthy maple, even when the leaves look badly disfigured. In heavy infection years it can cause some early leaf drop, but it does not by itself kill trees or create a falling-limb hazard. Around Atlanta, the maples most likely to show tar spot are red maple, silver maple, sugar maple, Norway maple, and occasionally Japanese maple, all of which are common in local yards and street plantings.

General Prevention

• Rake and remove fallen leaves from under affected maples each autumn, then bag, bury, or hot-compost them so overwintering spores cannot infect next year's leaves.
• Improve air movement around the canopy through proper structural pruning (done at the right time of year for maples) so leaves dry faster after rain.
• Water at the base of the tree rather than overhead, and avoid wetting the foliage when possible.
• Keep maples generally vigorous with appropriate mulch rings, room for roots, and consistent watering during Atlanta's summer dry spells, since stressed trees tend to show damage more dramatically.

What NOT to Do

• Do not self-diagnose. Many tree problems look alike, and treating the wrong one wastes time and can harm the tree.
• Do not apply fungicides, insecticides, or other chemicals without an arborist's specific recommendation. The wrong product or wrong timing makes things worse.
• Do not leave fallen, spotted maple leaves in place over winter or add them to a passive backyard leaf pile near the same trees, because the fungus overwinters in that leaf litter and reinfects the canopy the next spring.

Related Services

For most diagnosis and treatment questions, the right starting point is one of our services:

• ISA-Certified Arborist Services: diagnosis, consultation, second opinion
• Plant Health Care (PHC): ongoing tree health management
• TRAQ Tree Risk Assessment: when the tree may be a safety hazard

Sources

This page summarizes general information from: University of Wisconsin-Madison Division of Extension, UMass Extension Center for Agriculture, Food, and the Environment, and Michigan State University Extension.