Tar Spot on Maple Trees in Rochester, NY: What Are Those Black Spots?

If you’ve noticed black, raised spots appearing on the leaves of your maple trees around Rochester and Monroe County, you’re not alone. Tar spot is a common sight on

maples throughout Western New York, particularly as we move through late summer and into fall. Although those black spots can look alarming, the good news is that tar spot is usually more of a cosmetic problem than a serious threat to the health of your maple tree.

What Is Tar Spot?

Tar spot is a fungal leaf disease caused by several species of Rhytisma. It gets its name from the distinctive dark spots that develop on infected maple leaves and eventually look as though drops of black tar have been splattered across the surface.

The infection actually begins much earlier than most homeowners realize. During cool, wet spring weather, something we certainly experience here in the Rochester area, fungal spores can infect newly emerging maple leaves. Early symptoms may appear as small yellow or yellow-green areas on the leaves. As the growing season progresses, those areas become darker and more pronounced. By late summer, they develop into the thick, black spots that make tar spot so easy to recognize.

Why Are We Seeing So Much of It?

Weather plays an important role in the development of many fungal leaf diseases. Extended periods of moisture during the spring give fungal spores an opportunity to infect young leaves. The symptoms then become increasingly obvious as summer progresses. That means a maple tree that appeared perfectly healthy earlier in the season can suddenly look quite different by August or September. Tar spot can affect several types of maple trees, and Norway maples are particularly prone to developing noticeable infections.

Is Tar Spot Killing My Maple Tree?

In most cases, no. Tar spot can make a maple look unhealthy, but on an otherwise vigorous, established tree, it generally does not cause significant long-term damage. Heavily infected trees may begin dropping some leaves earlier than usual, but most will leaf out normally again the following spring. It’s important, however, to look at the entire tree rather than just the leaves. If your maple is also showing significant canopy thinning, dead branches, extensive dieback, peeling or damaged bark, unusual growth, or substantial premature leaf loss, there may be another problem contributing to the tree's decline. Drought stress, root damage, soil conditions, insects, and other diseases can all affect maple health.

What Can Rochester-Area Homeowners Do About Tar Spot?

One of the easiest things homeowners can do is clean up infected leaves in the fall. The fungus responsible for tar spot can overwinter on fallen leaves and produce spores the following spring. Raking and removing infected leaves can help reduce the amount of fungal material around the property. Keeping your maple healthy overall is also important. Proper watering during dry periods, appropriate mulching, and professional pruning when necessary can help reduce stress and maintain a healthy canopy. Good airflow can also help foliage dry more quickly after rain and heavy morning dew.

Fungicide treatment is generally unnecessary for mature landscape trees affected only by tar spot. If treatment is appropriate for a particular tree or situation, it must be timed preventatively in the spring. Once the black spots become visible later in the season, spraying the leaves will not make them disappear.

Black Spots Don’t Always Mean a Sick Tree

One of the most important things to remember about tar spot is that appearance doesn’t always equal severity. A maple covered in black-spotted leaves can look dramatically unhealthy while the tree itself remains structurally and physiologically sound. For most Rochester-area homeowners, tar spot is something to manage rather than fear. Clean up the leaves this fall, continue to care for the tree properly, and chances are good that you’ll see a fresh canopy of green leaves again next spring.

If your maple is showing symptoms beyond the characteristic black spots or you simply aren’t sure whether you’re looking at tar spot or another tree-health problem, the arborists at High Falls Tree Service can evaluate the tree and help determine whether additional care is needed.

High Falls Tree Service proudly cares for trees throughout Rochester,