Maple Leaves With Black Spots in Rochester: Is It Tar Spot or Something Worse?

By Linda Marsh, Pests & Diseases. Last updated: June 25, 2026

If you walk a Rochester sidewalk in late summer and see Norway maples studded with shiny black blotches, your first instinct is usually panic. In the vast majority of yards across Monroe County, those black spots are tar spot, a fungal disease that is more eyesore than emergency. But not every black-on-leaf symptom is tar spot, and a few of the look-alikes are genuinely worth worrying about. This guide walks through how to tell the difference here in Upstate New York.

What does maple tar spot actually look like?

Tar spot is caused by fungi in the genus Rhytisma. On local maples that usually means Rhytisma acerinum on Norway maple, with the speckled Rhytisma punctatum and Rhytisma americanum turning up on native species. The pattern is distinctive once you know it. Spots start in early summer as faint, pale-yellow or light-green flecks. By August and September they thicken into raised, glossy black masses that genuinely look like someone flicked roofing tar onto the foliage. A single spot can grow from pinhead-sized to the diameter of a quarter or larger.

Norway maple (Acer platanoides), planted up and down Rochester streets for decades, is the single most affected tree in the area. Silver and red maples get it too, just less dramatically. If your spots are big, raised, and tar-black on a Norway maple, you are almost certainly looking at textbook tar spot.

Is tar spot harmful to maple trees?

For an established, otherwise healthy maple, tar spot is essentially cosmetic. The fungus colonizes leaf tissue late in the season, when the leaves have already done most of their summer photosynthesis. It does not invade the wood, the branches, or the roots. Even in a heavy year, an established tree will leaf out normally the following spring.

The two real downsides are visual, plus a touch of early leaf drop. Trees with a severe infection may shed leaves a few weeks ahead of schedule. That can look like trouble, but if the rest of the canopy is full and the twigs are flexible and green underneath the bark, the tree is fine. Premature defoliation matters far more when it stacks on top of other stress, which is exactly when an arborist evaluation is worth it.

When are black spots NOT just tar spot?

This is the part most homeowners miss. Several other problems produce dark leaf symptoms, and some of them affect the tree's health far more than tar spot does. Watch for these patterns:

• Anthracnose. Instead of discrete round black dots, you see irregular brown-to-black blotches that follow the leaf veins, often with crinkling, curling, and leaf drop starting on the lower interior canopy. Cool, wet Rochester springs drive it hard. This is a different management conversation, covered in our guide to anthracnose in Rochester shade trees.
• Verticillium wilt. This soilborne fungus does not really make leaf spots, but it is the heavyweight to rule out because it can kill a maple. The tells are sudden wilting or scorch on one side or one branch, sometimes with olive-green streaking in the sapwood. If a maple is dropping a whole limb's worth of leaves while the rest looks normal, read our explainer on verticillium wilt in Rochester maples and get eyes on it fast.
• General decline. Black or blackened leaves combined with widespread yellowing, thinning, and dieback can point to root or vascular problems rather than a leaf fungus at all. When the whole tree looks off, our overview of why leaves curl, yellow, and die helps you sort cosmetic from serious.

The quick rule: round, raised, glossy black dots scattered across green leaves favor tar spot. Irregular vein-following blotches, one-sided wilting, or canopy-wide thinning favor something that deserves a closer look.

Why is tar spot so common on Rochester's Norway maples?

Two things stack up. Norway maple was massively over-planted as a street and yard tree across Monroe County, so the host is everywhere, often in dense rows that let the fungus spread leaf to leaf. And our climate cooperates: lake-effect moisture, humid summers, and wet springs give Rhytisma the leaf-wetness it needs to infect.

The fungus overwinters on fallen leaves, then releases spores in spring that land on newly emerging foliage. That life cycle is the key to control, because it means the leaves on the ground this fall are the source of next year's spots.

How do you manage maple tar spot in your yard?

Because tar spot is cosmetic, most arborists do not recommend spraying established trees for it. Fungicide timing is narrow (it has to hit emerging spring leaves) and full coverage of a large maple is impractical and rarely worth the cost. The far more effective, lower-impact approach is sanitation:

• Rake and remove fallen leaves in autumn rather than letting them sit under the tree. Bag them or hot-compost them; do not leave them as mulch beneath the canopy.
• Improve air circulation where practical so leaves dry faster after rain.
• Keep the tree generally vigorous. A well-watered, properly mulched maple shrugs off cosmetic disease easily, while a stressed one is more vulnerable to the things that actually matter.

If you are unsure whether you are dealing with harmless tar spot or one of the serious look-alikes, that is the moment to bring in a professional. Schedule an arborist evaluation with Monster Tree Service rather than guessing, especially if more than one symptom is showing up at once.

FAQ

Is tar spot harmful to maple trees? For an established, healthy maple it is essentially cosmetic. The fungus arrives late in the season after the leaves have done most of their work, and it does not invade the wood or roots. It only becomes a concern when it stacks on top of other stress.

Will tar spot spread to my other trees or my vegetable garden? Tar spot is host-specific to maples (and a few close relatives), so it will not jump to oaks, evergreens, or your vegetables. It can spread maple to maple, which is why dense rows of Norway maple show it most.

Should I spray my maple with fungicide for tar spot? Usually no. Effective fungicide timing is narrow and full coverage of a large tree is impractical and costly for a problem that does not threaten the tree. Raking and removing fallen leaves each autumn is the more effective control.

How do I know if it is tar spot or something serious like verticillium wilt? Tar spot makes round, raised, glossy black dots on green leaves. Verticillium wilt instead causes sudden one-sided wilting or branch dieback, sometimes with streaking in the wood, and it can kill the tree, so it is worth a professional look if you see those signs.

Does raking leaves really reduce next year's tar spot? Yes. The fungus overwinters on fallen leaves and releases spores in spring onto new foliage, so removing the leaves removes much of next season's spore source.

Sources

• Cornell Garden-Based Learning
• USDA Forest Service: Urban Forests
• Michigan State University Extension: Tar Spot on Maple Trees
• International Society of Arboriculture: Trees Are Good (Find an Arborist)
• Monster Tree Service of Rochester