Maple Tree Diseases: Which Ones Actually Threaten Your Tree

Nine out of ten maple tree “diseases” that send homeowners into panic mode are cosmetic problems that look terrible and do nothing. Black spots on the leaves. Brown patches in spring. Weird bumps. White powder. Your tree handles all of it without help.

The one disease that actually kills maples is verticillium wilt. It has no cure, no effective treatment, and no vaccine. And it lives in the soil of most residential yards. That’s the one you need to know about.

Here’s how to tell the difference between the problems you can ignore and the one that matters.

Tar spot (the black spots everyone panics about)

Tar spot (Rhytisma acerinum) is the most common maple leaf disease in North America, and it’s completely harmless. You’ll see it on Norway maples and silver maples more than anything else. The black spots show up in late summer and look exactly like someone flicked tar at the leaves.

The spots start as small yellow areas in spring, then develop raised black lesions by August. By September, heavily infected leaves look dramatic. People photograph them and post them online asking if their tree is dying. It’s not.

Tar spot does not kill branches, does not spread to the trunk, and does not weaken the tree’s structure. The Morton Arboretum confirms that tar spot is a cosmetic issue that does not warrant fungicide treatment on mature trees.

The only management step worth taking: rake infected leaves in fall. The fungus overwinters on fallen leaves and reinfects the tree from spore splash the following spring. Removing the leaf litter reduces the spore load. That’s it. No spraying, no pruning, no arborist visit.

Anthracnose (the spring scare)

Maple anthracnose (Aureobasidium apocryptum) causes brown, irregular dead spots along leaf veins and between veins. It hits during cool, wet springs when temperatures hover between 50 and 68 degrees. Sugar maples and red maples are the most susceptible.

A bad anthracnose year looks alarming. Leaves curl, brown, and drop in May and June. The tree can lose 30-50% of its early-season foliage. Then it pushes a new set of leaves by July and looks fine for the rest of the summer.

That’s the key distinction: anthracnose is a spring disease that the tree grows out of. Verticillium wilt is a summer disease that gets worse every year.

Treatment is rarely justified on mature maples. If you have a young tree that gets hammered by anthracnose for three consecutive years, a copper fungicide applied at bud break can reduce infection. Cost runs $40-80 for materials on a small tree. For large trees, the spray isn’t practical. Let the tree handle it.

Verticillium wilt (the one that actually kills)

Verticillium wilt (Verticillium dahliae) is the most serious disease of maples in residential landscapes. The fungus lives in the soil, enters through the roots, and clogs the tree’s vascular system. It can survive in soil for a decade or more without a host.

Sugar maples and Japanese maples are the most susceptible. Norway maples show resistance, which is one of the only good things about that species. Red maples fall in the middle.

How to identify verticillium wilt

The classic symptom is wilting and dieback on one side of the tree, often starting in mid to late summer. Leaves on the affected side turn yellow, scorch at the margins, and die while leaves on the other side look fine.

The diagnostic test: scratch the bark on a dying branch with a pocket knife. If you see olive-green or brown streaking in the sapwood underneath, that’s verticillium wilt. Healthy sapwood is white or cream-colored. The green streaking is the fungus growing inside the water-conducting vessels.

Crown dieback gets worse each year. The tree may lose 25% of its canopy the first summer, then 50% the next. Some trees wall off the infection and stabilize. Others decline over 2-5 years and die. According to the Morton Arboretum, there is no chemical cure for verticillium wilt. No fungicide, no injection, no soil treatment eliminates the pathogen.

What you can do

Pruning dead branches removes the unsightly wood and reduces entry points for secondary infections. Sterilize your tools between cuts with a 10% bleach solution or rubbing alcohol. Fertilize the tree to boost vigor. Deep water during dry periods. Mulch the root zone with 2-4 inches of wood chips, keeping mulch 6 inches from the trunk.

These steps won’t cure the disease, but they give the tree the best chance of compartmentalizing the infection and surviving. Trees that are well-watered and not stressed by heat or compaction have the strongest defense response.

If you’re replacing a tree killed by verticillium wilt, don’t plant another maple in the same spot. The fungus persists in the soil. Plant a resistant species instead: oaks, conifers, birch, beech, or willows are all resistant. Our guide to types of maple trees notes which species have some tolerance.

Powdery mildew

White powdery coating on maple leaves, usually showing up in late summer when warm days and cool nights create ideal conditions. It looks like someone dusted the leaves with flour. Norway maples and big-leaf maples get it most.

Powdery mildew on maples is cosmetic. The tree looks rough for a few weeks, then the leaves drop normally in fall. No treatment needed on mature trees. Good air circulation (don’t crowd the tree with other plantings) helps prevent it.

Leaf scorch: disease or just stress?

Brown, crispy leaf edges on a maple in July can mean one of two things, and the distinction matters.

Environmental leaf scorch is caused by hot, dry weather, especially when combined with wind and reflected heat from pavement. The browning is uniform across the tree and follows the same pattern every summer. It’s not a disease. It’s the tree telling you it needs more water. Deep soak the root zone once a week during heat waves. Red maples and sugar maples planted in full-sun parking strips are the usual victims.

Bacterial leaf scorch is caused by Xylella fastidiosa, the same bacterium behind Pierce’s disease in grapevines. Leafhoppers spread it from tree to tree. The key difference: bacterial leaf scorch produces a distinct yellow or reddish band between the green tissue and the dead brown margins. Environmental scorch doesn’t produce that band.

Bacterial leaf scorch worsens every year. Symptoms appear earlier each season and affect more of the canopy. If your maple shows the yellow-banded scorch pattern and it’s getting worse annually, lab testing ($50-150) confirms the diagnosis. There is no cure. An arborist can manage symptoms with trunk injections, but the disease progresses regardless. Plan for eventual removal.

Pests that look like diseases

Three maple pests produce symptoms that homeowners often mistake for diseases.

Cottony maple scale (Pulvinaria innumerabilis) shows up as white, cottony masses on twigs and branches. It looks like a fungal infection but it’s an insect. Heavy infestations produce honeydew (sticky sap that coats everything under the tree) and black sooty mold on the leaves. Silver maples are the primary target. In most years, natural predators like twice-stabbed lady beetles keep populations in check. Treatment with horticultural oil in early spring before bud break controls overwintering nymphs. If you’re also dealing with aphid problems, the honeydew and sooty mold look similar because the mechanism is the same.

Maple galls are weird bumps, raised spots, and fuzzy patches on leaves caused by eriophyid mites. Bladder galls appear as bright red bead-like growths on silver and red maples. Spindle galls look like tiny green spikes standing up from the leaf surface. Erineum galls create velvety red or green patches. Every one of them is cosmetic. The Penn State Extension and University of Minnesota Extension both confirm that leaf galls do not seriously affect tree health. Treatment is almost never warranted.

Asian longhorned beetle (ALB) is the existential threat. This invasive beetle from Asia creates perfectly round, dime-sized exit holes in maple trunks and branches. The larvae tunnel through the heartwood, destroying the tree’s structure from the inside out. ALB has been found in New York, Massachusetts, Ohio, and South Carolina. If it spreads unchecked, it could kill 12-61% of urban street trees in North America. There is no treatment. Infested trees must be cut down and chipped. If you see a large (0.75-1.5 inch), glossy black beetle with white spots and banded antennae on your maple, collect it in a jar, freeze it, and call USDA at 1-866-702-9938. Don’t move firewood.

Lichen is not a disease

The crusty gray-green patches growing on your maple’s bark are lichen, and they’re harmless. Lichen is a combination of algae and fungus living together on the bark surface. It doesn’t penetrate the bark, doesn’t steal nutrients from the tree, and doesn’t need treatment.

Lichen is more visible on older trees and on the north side of trunks where moisture lingers. You tend to notice it more when the tree loses leaves in winter. It’s been there all along. Leave it alone.

How to keep your maples healthy

Most maple problems in residential yards come down to stress. A stressed tree gets diseases. A healthy tree fights them off.

Water correctly. Newly planted maples need 15 gallons per week per inch of trunk diameter for the first two to three years. Established maples rarely need supplemental irrigation except during extended drought. Water deeply at the drip line, not at the trunk. Avoid frequent shallow watering, which keeps roots near the surface. Our spring tree care checklist covers the full seasonal care routine.

Mulch the root zone. Two to four inches of wood chip mulch from the trunk flare out to the drip line. Keep mulch 6 inches from the bark. No mulch volcanoes. Good mulch conserves moisture, suppresses weeds, and supports beneficial soil fungi.

Prune correctly. Remove dead branches any time. Prune for structure in late winter (January-February) when the tree is dormant. Never prune maples in spring when sap is flowing heavily. Our tree trimming tips cover the three-cut method. Don’t top your maple. Ever. Topping creates dozens of weak, poorly attached sprouts that break in storms and provide entry points for decay fungi.

Don’t damage the roots. Construction, trenching, soil compaction from heavy equipment, and grade changes over the root zone all cause slow-motion death. Symptoms from root damage take 2-5 years to appear. By then the damage is done. Protect the soil within the drip line during any construction project.

Choose the right species for your site. Sugar maples planted in full sun parking strips with salt exposure and compacted soil will always struggle. Red maples handle tougher conditions. Japanese maples need afternoon shade in hot climates. Matching the tree to the site prevents most disease problems before they start. For more on identifying whether a struggling tree can be saved, our guide covers the scratch test, bud check, and when to call a professional.

What does it cost to treat a diseased maple?

Arborist diagnosis: $75-250 for a visual assessment. Add $50-150 for lab testing if verticillium wilt or bacterial leaf scorch is suspected.

Fungicide treatment (anthracnose prevention): $200-500 per application for a professional spray on a large tree. DIY copper fungicide for a small tree runs $15-40 in materials.

Scale insect treatment: $150-400 for professional horticultural oil application. DIY dormant oil spray costs $15-30.

Verticillium wilt management: No cure. Budget for ongoing care (deep watering, mulch, pruning) at $100-300 per year through an arborist, or do it yourself for the cost of mulch and water. If the tree dies, removal runs $500-3,500 depending on size and access.

ALB response: Zero cost to the homeowner. USDA handles quarantine, removal, and chipping at federal expense. Your only job is to report the beetle and not move firewood from the area.

For professional tree care and arborist services, knowing which species you’re dealing with helps narrow down the likely problems.

Frequently asked questions

What is the most common maple tree disease?

Tar spot is the most common. You’ll see black spots on maple leaves in late summer across most of the eastern and midwestern United States. It’s cosmetic and does not harm the tree. The most dangerous maple disease is verticillium wilt, which clogs the vascular system and has no cure.

Can you save a maple tree with verticillium wilt?

Sometimes. Trees can compartmentalize the infection if they’re otherwise healthy. Prune dead branches, deep water during dry periods, mulch the root zone, and fertilize to boost vigor. Some maples stabilize and live for decades with verticillium wilt. Others decline and die within 2-5 years. There is no chemical cure.

Why does my maple tree have black spots on its leaves?

That’s tar spot fungus (Rhytisma acerinum). It’s cosmetic and harmless. The spots appear in late summer, mostly on Norway maples and silver maples. Rake fallen leaves in autumn to reduce spore load next spring. No spraying or treatment is needed.

Should I worry about weird bumps on my maple leaves?

No. Leaf galls caused by eriophyid mites are cosmetic. Bladder galls (red bumps), spindle galls (green spikes), and erineum galls (velvety patches) do not harm the tree. Natural predators keep populations in check. Treatment is almost never needed.

When should I call an arborist for my maple?

Call an arborist when you see wilting on one side of the tree (possible verticillium wilt), progressive crown dieback that worsens each year, large dead branches hanging in the canopy, or dime-sized exit holes in the trunk (possible ALB). A consultation runs $75-250 and is far cheaper than emergency removal later. Find an ISA-certified arborist at treesaregood.org.