Japanese Maple Diseases: How to Identify and Treat Common Problems

Japanese maples (Acer palmatum) are among the toughest ornamental trees you can plant. They resist most pests, tolerate a range of soils, and live over 100 years. But they’re not invincible. When something goes wrong with a Japanese maple, homeowners panic because these are often the most expensive and beloved tree in the yard.

Before you panic: most “disease” symptoms on Japanese maples are actually environmental stress, not infection. Leaf scorch from hot sun, wind burn from dry air, and winter damage are far more common than actual diseases. Knowing the difference saves you from unnecessary treatments and misplaced worry.

When it’s NOT a disease

Leaf scorch (the most common “problem”)

Brown, crispy edges on leaves, especially in mid-to-late summer. This is the #1 complaint Japanese maple owners have, and it’s almost never a disease. Leaf scorch happens when the tree loses water through its leaves faster than roots can replace it.

Causes: Hot afternoon sun (above 90F), dry wind, reflected heat from pavement, inconsistent watering, shallow roots in compacted soil.

Fix: Move the tree to morning sun with afternoon shade if possible (easy for container trees, obviously harder for planted ones). Water deeply once per week during hot weather. Add 3-4 inches of organic mulch over the root zone to hold soil moisture. Protect from drying winds. These watering techniques apply to Japanese maples just as they do to any new tree.

Leaf scorch is cosmetic. The tree is stressed but not dying. Consistent watering and proper siting prevent it entirely.

Winter damage

Symptoms appear in spring: dead branch tips, delayed or patchy leaf-out, distorted new leaves. Caused by temperatures dropping below the variety’s tolerance or by late spring frost hitting new growth.

Which varieties are vulnerable: Laceleaf (dissectum) types, variegated cultivars, and any Japanese maple planted at the cold edge of its zone range. ‘Bloodgood’ and ‘Emperor One’ are among the hardiest. Weeping varieties like ‘Crimson Queen’ and ‘Tamukeyama’ are more cold-sensitive.

Fix: Wait. Japanese maples often push new growth from buds lower on the branch after tip damage. Don’t prune “dead” branches until June, when you can see what’s truly dead vs. what’s recovering. Cut dead wood back to the first point of living tissue.

Normal spring leaf unfurling

New Japanese maple leaves emerge crinkled, curled, and sometimes reddish even on green-leaved varieties. This is normal. The leaves smooth out and flatten within 1-2 weeks. Don’t treat it.

Fall color change

Japanese maples change color in fall. This is the point. If your green-leaved Japanese maple turns orange and red in October, that’s success, not disease.

Actual diseases

Verticillium Wilt

The most serious disease affecting Japanese maples. Caused by the soil-borne fungus Verticillium dahliae, which blocks the tree’s water-conducting vessels. Japanese maples are the most susceptible maple species to this fungus.

Symptoms:

• Sudden wilting and die-back of individual branches, often one side of the tree
• Green leaves that wilt and turn brown while still attached (they don’t fall off right away)
• Sapwood streaking: cut into a wilting branch and look for dark brown or olive-green streaks in the wood. This is the most reliable diagnostic sign
• Progressive branch die-back over weeks or months
• Sometimes affects the whole tree at once in severe cases

Treatment: There is no chemical cure for verticillium wilt. Management is the only option:

• Prune dead branches back to healthy wood with no sapwood streaking. Sanitize tools between cuts.
• Water consistently. A well-hydrated tree can sometimes wall off the infection.
• Fertilize with a low-nitrogen, high-potassium formula to support the tree’s defense response.
• Mulch to reduce soil temperature stress on roots.
• Avoid planting susceptible plants (tomatoes, strawberries, potatoes, other maples) in the same soil.

Prognosis: Some trees recover and live for years with reduced vigor. Others decline over 1-3 seasons. Young trees die faster than established ones. If you lose a Japanese maple to verticillium, don’t replant another maple in the same spot. The fungus persists in soil for 10+ years.

Prevention: Plant in well-drained soil that hasn’t recently grown tomatoes, potatoes, or other Solanaceae family crops (these amplify Verticillium in the soil). Buy from reputable nurseries that grow in clean media.

Anthracnose

A fungal disease that causes brown to tan irregular blotches on leaves, usually along veins and leaf edges. More common in cool, wet springs. Looks similar to leaf scorch but appears earlier in the season (May-June vs. July-August for scorch).

Symptoms: Brown blotches on leaves, often following leaf veins. Distorted, curled leaves. Premature leaf drop in severe cases. Lower canopy usually affected first.

Treatment: Anthracnose rarely kills Japanese maples. It’s cosmetic in most years.

• Rake and destroy fallen leaves in fall (they harbor spores).
• Improve air circulation by thinning interior branches per our pruning timing guide.
• In severe cases, a copper-based fungicide applied at bud break and again two weeks later can reduce infection. Chlorothalonil is also effective.
• Don’t overhead water. Wet foliage promotes spore germination.

Phyllosticta Leaf Spot

Small, round tan spots (1/8 to 1/4 inch) with dark borders on leaves. Caused by Phyllosticta fungi. More common in wet years. Usually cosmetic and doesn’t affect tree health.

Treatment: Same as anthracnose: clean up fallen leaves, improve air circulation, avoid overhead watering. Fungicide rarely justified.

Powdery Mildew

White powdery coating on leaf surfaces, usually in late summer and fall. More common in shaded, humid conditions with poor air circulation. Rarely serious on Japanese maples but unsightly.

Treatment: Improve air circulation. Avoid watering foliage. If persistent, spray with horticultural oil or a potassium bicarbonate fungicide.

Tar Spot

Black spots or raised black patches on leaves in late summer and fall. Caused by Rhytisma fungi. Looks alarming but is almost entirely cosmetic. See our maple tree diseases guide for details on this and other maple-specific conditions.

Treatment: Rake and destroy fallen leaves. No fungicide treatment necessary.

Root and trunk problems

Phytophthora Root Rot

A water mold that attacks roots in consistently wet, poorly drained soil. Japanese maple roots turn dark brown and mushy. The tree wilts despite wet soil, because the rotted roots can’t absorb water. Often fatal.

Symptoms: General decline, yellowing leaves, wilting despite adequate soil moisture, dark discolored roots, sometimes oozing cankers at the soil line.

Causes: Over-watering, poor drainage, heavy clay soil, planting too deep, volcano mulching that holds moisture against the trunk.

Treatment: Improve drainage. Reduce watering frequency. Remove mulch from direct contact with the trunk (keep it 3-6 inches away). In severe cases, there’s no saving the tree.

Prevention: Plant in well-drained soil. Never plant Japanese maples in spots where water pools after rain. Don’t over-water established trees. Proper landscaping around the base prevents most trunk-moisture problems.

Sunscald and Bark Damage

Japanese maple bark is thin and vulnerable. Southwest winter sun (sunny afternoons on cold days) can heat one side of the trunk, causing cells to break dormancy, then freezing kills them at night. The result: vertical cracks or dead patches on the south or west side of the trunk.

Prevention: Wrap young tree trunks with white tree wrap for the first 3-5 winters. Position the tree where buildings or other trees shade the trunk from intense afternoon winter sun. Our tree sapling protection guide covers wrapping technique.

Pests that mimic disease

Scale insects

Waxy bumps on branches and twigs. Heavy infestations cause branch die-back and general decline that looks like disease. Check branches closely. If the “disease” rubs off and leaves a colored smear, it’s scale, not a fungus.

Treatment: Dormant oil spray in late winter kills overwintering scale. Horticultural oil in summer for active crawlers.

Japanese beetle

Skeletonized leaves (veins remaining, tissue eaten away) in June through August. Not a disease but the damage pattern looks alarming. Japanese beetles are especially fond of Japanese maples (the irony).

Treatment: Hand-pick beetles in the morning when they’re sluggish. Neem oil or carbaryl spray for severe infestations. Avoid Japanese beetle traps (they attract more beetles to your yard than they catch).

Aphids

Curled, distorted new growth, sticky honeydew on leaves, sooty mold on lower leaves. More of an annoyance than a threat on mature trees. See our aphid treatment guide for options ranging from garden hose to pesticides.

Keeping your Japanese maple healthy

Most Japanese maple problems are preventable with proper siting and care:

Right location: Morning sun, afternoon shade in zones 7+. Full sun is fine in zones 5-6. Protection from hot, dry wind. Well-drained soil.

Right watering: Deep, infrequent watering (once per week in summer, more during heat waves). Avoid constantly wet soil. Japanese maples want moisture, not saturation.

Right mulch: 3-4 inches of organic mulch over the root zone, kept 4-6 inches away from the trunk. Mulch moderates soil temperature, retains moisture, and prevents trunk damage from mowers.

Minimal pruning: Prune in late winter for structure and to remove dead wood. Never top a Japanese maple. The natural form is the whole reason you planted it. Light thinning of interior branches improves air circulation and disease resistance.

A healthy, properly sited Japanese maple rarely gets sick. If yours has recurring problems, the issue is almost always environmental (too much sun, too much or too little water, poor drainage) rather than pathological. Fix the environment and the “disease” usually disappears.

For the full picture on maple health across all species, see our maple tree diseases guide, and for tips on showcasing these trees in your yard, check our trees with red leaves guide and mklibrary.com’s curb appeal tips.