Short answer
Black bark or black leaves on a maple can have several causes, from harmless to serious. Dark, wet-looking bark after rain is common and normal. Black spots on leaves are often a leaf disease such as tar spot. A sooty coating on leaves usually points to insects and sooty mold. The most serious bark cause is sooty bark disease, where bark peels away to reveal black, dusty spores. Because these can look alike, an arborist or local extension office is the best source for a firm diagnosis.
What does black bark on a maple mean?
- Rain-darkened bark. Many trunks look nearly black when wet and lighter when dry.
- Sooty bark disease. A fungus (Cryptostroma corticale) forms black tissue under the bark. Bark may crack and peel, exposing a brown-black powdery mass of spores. It is most often reported on sycamore maple in Europe and has been found on some other maples, including red maple and Japanese maple, in the Pacific Northwest.
- Sooty mold. A black film on bark and leaves that grows on sugary honeydew left by sap-feeding insects such as aphids or scale. It sits on the surface and can often be wiped or washed off.
- Sap flow or cankers. Dark staining from wounds, bleeding sap, or other cankers.
- Lichens or algae. Dark or gray patches that generally do not harm the tree.
Sooty bark disease and safety
Sooty bark disease tends to be associated with hot, dry summers and stressed trees, and it can kill branches or whole trees. The spores can be released in large amounts. They are a known concern for people who work around infected wood, and breathing them in has been linked to a lung condition in some cases. If you suspect it:
- Do not scrape, brush, chip, or burn the bark yourself.
- Keep children and pets away from the area.
- Contact a certified arborist or your local extension or forestry service for diagnosis and for how to handle removal, which may require protective equipment and careful disposal.
Why are the leaves turning black and falling off?
- Tar spot. Raised black spots on leaves in summer, common on some maples. It is mostly cosmetic and rarely threatens a healthy tree, though raking up fallen leaves can reduce its return.
- Anthracnose. Brown to dark blotches, often after cool, wet spring weather, sometimes with early leaf drop.
- Sooty mold. A black film on leaves below insect-infested branches.
- Leaf scorch or drought stress. Dried, browning or blackened edges, especially in heat or wind.
- Frost damage. Blackened new growth after a late cold snap.
- Verticillium wilt or other vascular disease. Sudden wilting and dieback with no clear spots; these need professional diagnosis.
Dark leaves on a Japanese maple may be natural for purple varieties, so compare with healthy leaves on the same tree. For color changes, see growing a Japanese maple in shade.
What does an overwatered maple look like?
Overwatering and poor drainage can cause yellowing or wilting leaves, leaf drop, soft or dark roots, and branch dieback, which can be mistaken for disease. Check the soil a few inches down. If it stays soggy, cut back on watering, improve drainage, and keep mulch off the trunk. Drought has similar-looking symptoms, so check soil moisture before changing your routine. Our guide to what an overwatered tree looks like has a fuller checklist.
Is fungus on trees harmful?
Not always. Many fungi, lichens, and molds are harmless or only cosmetic, while others signal decay or disease. Harm depends on the type and the tree’s overall health. Mushrooms or conks on the trunk, spreading dark patches, peeling bark, or dieback deserve a professional look.
What to do now
- Take clear photos of the bark, leaves, and whole tree.
- Note when it started, recent weather, watering, and any construction near the roots.
- If you see black powder under peeling bark, treat it with caution as above.
- For sooty mold, deal with the insects first. A strong spray of water or horticultural oil may help, but follow label directions. The sticky stuff falling from trees article explains honeydew and the insects behind it.
- Water deeply during dry spells and mulch to reduce stress.
Prevention
Healthy trees resist problems better. Plant at the right depth, give the tree room, avoid root damage, water during drought, and avoid wounding the trunk with mowers and trimmers. Choosing species suited to your climate also helps. For the practical side of choosing and siting maples, read are maple trees messy.
When to call an arborist
Call a certified arborist if bark is peeling with black powder, large limbs are dying, the trunk is cracked or decayed, or the tree stands near your home or a path. They can confirm the cause and advise whether the tree can be saved.