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Tree Fungus Identification: What's Growing on Your Tree and What to Do About It

Michael Kahn, Sacramento homeowner and lifelong gardener
Michael Kahn
12 min read
Cluster of wild mushrooms growing on a tree trunk in a forest setting

You walk outside one morning and there’s a shelf of mushrooms growing out of your oak tree. Your first thought: is my tree dying?

Maybe. Maybe not. Fungi show up on trees for all kinds of reasons, and most of the time, the mushroom you’re looking at is just the fruiting body of a fungus that’s been living in or on the tree for years. The real question isn’t whether there’s fungus. It’s which fungus, where it’s growing, and whether your tree can handle it.

Here’s how to figure out what you’re dealing with and whether you need to do anything about it.

The two categories that matter: cosmetic vs structural

Before you panic about any fungus on your tree, understand this: some fungi attack living tissue and will kill your tree. Others just feed on dead wood and are basically recyclers. The location of the fungus tells you a lot.

Fungi on living branches or trunk bark are more concerning. These are usually parasitic and actively harming the tree.

Fungi on dead wood, stumps, or fallen branches are saprophytic (decomposers). They’re doing their job. Leave them alone.

Fungi at the base of the tree or on roots are the most dangerous. Root rot fungi can topple a tree that looks perfectly healthy above ground.

Ganoderma bracket fungus growing on a tree trunk, indicating internal wood decay

Bracket and shelf fungi (the most common)

Those hard, semicircular shelves growing out of your tree trunk? Those are bracket fungi, also called shelf fungi or conks. They’re the most visible sign of internal wood decay, and they’re extremely common. For the structural-safety side, when a decaying tree becomes a hazard and how to judge it, see our tree rot and decay guide.

What you’re looking at

The shelf or bracket is just the reproductive structure. The actual fungus is a network of threads (mycelium) inside the wood, slowly breaking down the heartwood. By the time you see a conk on the outside, the internal decay has been progressing for years.

Turkey tail fungi growing in colorful bands on a fallen tree log in a forest

Common species homeowners encounter:

  • Artist’s conk (Ganoderma applanatum): flat, brown-topped shelf with a white underside. Scratch the white surface and it turns brown (hence the name). Found on oaks, maples, elms. Indicates significant heartwood decay.
  • Turkey tail (Trametes versicolor): thin, colorful bands of brown, tan, and cream. Very common on dead wood and stumps. Rarely attacks living trees. Mostly cosmetic.
  • Reishi (Ganoderma lucidum complex): shiny, reddish-brown, kidney-shaped. Found at the base of oaks and other hardwoods. Indicates root and butt rot. Take this one seriously.
  • Sulfur shelf / Chicken of the woods (Laetiporus sulphureus): bright orange and yellow shelves, sometimes massive. Found on oaks, cherries, willows. Causes brown cubical rot inside the trunk.

Should you worry?

If a bracket fungus is growing on a dead stump or fallen log, no. If it’s on a living tree’s trunk, yes. The visible conk means internal decay has already advanced enough for the fungus to reproduce. An arborist can assess how much structural wood remains with a resistograph test ($200-400) or a simple sounding test.

Don’t try to remove the conks. Breaking them off does nothing to stop the internal decay and just removes the evidence your arborist needs to see.

Armillaria root rot (the hidden killer)

Armillaria (Armillaria mellea and related species) is the most widespread tree-killing fungus in North America. It lives in the soil, attacks roots, and can spread from tree to tree through root contact and underground structures called rhizomorphs, black, shoestring-like cords that grow through soil.

How to identify it

The above-ground symptoms are frustratingly generic: yellowing leaves, thinning canopy, branch dieback. These symptoms look like drought stress, which is why Armillaria goes undiagnosed for years.

The telltale sign: peel back the bark at the base of a declining tree. If you see white, fan-shaped sheets of fungal tissue (mycelial fans) between the bark and wood, that’s Armillaria. The tissue smells distinctly mushroomy.

In fall, clusters of honey-colored mushrooms may appear at the base of infected trees. These honey mushrooms are the reproductive stage and confirm the diagnosis.

Cluster of honey-colored Armillaria mushrooms growing at the base of a tree in autumn

Treatment

There is no chemical cure for Armillaria root rot once a tree is infected. The University of California IPM program recommends:

  • Remove dead and dying trees, including as much of the root system as possible
  • Expose the root crown by pulling soil back 9-12 inches (solar heating slows the fungus)
  • Avoid replanting susceptible species in the same spot for several years
  • Choose resistant species for replacement: most oaks, coast redwood, and many conifers tolerate Armillaria better than stone fruits, maples, and birches

If you’ve lost a tree to Armillaria and plan to replant, that’s a good time to consult our guide on how to plant a tree correctly. Proper planting depth helps prevent future root issues.

Single mushroom growing on decaying tree bark in a forest setting

Anthracnose (the leaf spotting fungus)

Anthracnose is probably the most common fungal disease homeowners notice because it hits the leaves. Brown or black irregular spots, curled leaf edges, and premature leaf drop in spring and early summer. Sycamores, dogwoods, oaks, and maples get hit the hardest.

The good news

Anthracnose is almost never fatal. It’s cosmetic. Trees that lose leaves to anthracnose in spring will push out a second flush of leaves within weeks. The tree looks rough for a month and then recovers.

When it happens

Anthracnose thrives in cool, wet spring weather (60-70F with rain). Dry, hot summers stop it cold. This is why you’ll see it in April and May but not July.

Treatment

For most homeowners, the answer is: do nothing. Rake up fallen infected leaves in autumn to reduce spore load next spring. Prune for better air circulation.

Fungicide sprays (chlorothalonil or copper-based products) can help on small, high-value trees like dogwoods. Application timing is critical: you need to spray as buds break in spring, then repeat twice at 10-14 day intervals. I keep a bottle of Monterey Liqui-Cop in the garage for exactly this reason. It’s a ready-to-mix copper fungicide that works on anthracnose and most other fungal leaf diseases, and our fungicide for trees guide breaks down copper versus neem versus sulfur and when to use each. Cost: $15-30 for the product, or $150-300 for professional application per tree.

For the full cross-species breakdown, including which trees shrug it off and why dogwood anthracnose is the dangerous exception, see our anthracnose on trees deep-dive.

Colorful bracket fungus with concentric bands growing on a tree in a forest setting

Powdery mildew (the white coating)

That white, powdery coating on your tree’s leaves? Powdery mildew. It’s one of the easiest fungal diseases to identify and one of the least dangerous.

Crape myrtles, dogwoods, and oaks are frequent targets. The fungus grows on the leaf surface, not inside the tissue, which is why it rarely causes serious harm. Leaves may curl slightly and drop early, but the tree’s health isn’t threatened.

Close-up of a leaf showing powdery mildew fungal infection on the surface

Prevention beats treatment: Plant resistant cultivars (many newer crape myrtle varieties are bred for mildew resistance). Improve air circulation by pruning dense interiors. Avoid overhead irrigation that keeps leaves wet.

If you want to spray, neem oil or potassium bicarbonate (1 tablespoon per gallon of water) work as organic options. Apply at first sign of the white coating.

Our powdery mildew on trees guide covers the full host list, why it shows up even without wet leaves, and the complete treatment ladder.

Pine-specific fungal problems

Pines get their own category because they have a unique set of fungal issues that don’t affect hardwoods.

Diplodia tip blight

Diplodia (Diplodia sapinea) is the most common pine disease in residential landscapes. New candles (spring growth) emerge stunted, with needles only half their normal length. The stunted shoots turn brown and die, making the tree look like it’s dying from the tips back.

Austrian pines and Scotch pines are extremely susceptible. Evergreen trees in the white pine group tend to resist it better.

Treatment: Prune out infected tips during dry weather. Fungicide sprays (thiophanate-methyl or copper) applied when buds begin to swell in spring can prevent new infections. Two applications, 10-14 days apart. A Chapin 1-gallon sprayer is all you need for a small ornamental pine. No hauling around a big tank.

Dothistroma needle blight

Red-brown bands across pine needles, followed by needle drop starting from the bottom of the tree and working upward. Austrian and Ponderosa pines are most susceptible. The tree gradually thins from the bottom up over several years.

Treatment: Bonide Copper Fungicide sprays in mid-May and again 4-6 weeks later. Penn State Extension reports good control with consistent annual treatment.

Pine needle rust

Orange pustules on needles in spring. The rust fungi need two hosts (pine and an alternate plant like goldenrod or aster) to complete their life cycle. Usually cosmetic. Remove the alternate host if possible, otherwise ignore it.

Sooty mold (the black coating)

Black, sooty coating on leaves and branches. Looks terrible but is actually growing on honeydew (the sticky excrement from aphids, scale insects, or whiteflies), not on the tree itself. Sooty mold doesn’t infect the tree.

The fix is controlling the insects, not the mold. Once the honeydew stops, the mold weathers away on its own. Check our guide on getting rid of aphids if you’re seeing sticky leaves with a black coating.

Bracket fungus growing on a birch tree trunk in a forest setting

Tree trunk with visible bark damage and wound in a winter forest

Canker diseases

Cankers are dead, sunken areas on branches or trunks caused by various fungi (and some bacteria). They look like wounds that won’t heal: darkened bark, sometimes with oozing sap or visible fungal growth at the edges.

Common canker fungi include Cytospora (hits spruces and stone fruits), Nectria (targets maples, oaks, and birches), and Botryosphaeria (attacks stressed trees of many species).

What to do

Prune out branches with cankers, cutting at least 6 inches below the visible damage. Sterilize pruning tools between cuts with 70% rubbing alcohol or a 10% bleach solution.

Cankers on main trunks can’t be pruned out. An arborist can assess whether the tree can wall off the canker or whether it’s a long-term structural risk. Professional assessment runs $75-200 for a single-tree consultation.

Trees get canker diseases when they’re stressed by drought, poor soil, or mechanical damage. The best prevention is keeping your trees healthy with proper watering, appropriate fertilization, and avoiding trunk wounds from mowers and string trimmers.

Species-specific disease guides

For tree-by-tree disease deep-dives covering symptoms, treatment, spray timing, and resistant cultivars, see the species guides below. Each one covers the 5-7 most important diseases for that species, with sanitation protocols and arborist callout thresholds.

Fruit trees:

Shade and ornamental trees:

By disease (cross-species deep-dives):

  • Anthracnose on trees: the leaf-blotch fungus across sycamore, oak, ash, maple, and dogwood
  • Powdery mildew on trees: the white coating on crape myrtle, dogwood, oak, and maple
  • Verticillium wilt: the soil-borne wilt that has no cure, on maple, ash, catalpa, and redbud
  • Oak wilt: the fungus that kills red oaks in weeks, and why pruning timing is everything
  • Dutch elm disease: the beetle-borne fungus that took out the American elm, and the resistant elms that survive it
  • Fire blight: the bacterial disease that scorches apple, pear, and crabapple, controlled mostly by pruning
  • Root rot in trees: Phytophthora and Armillaria in waterlogged soil, a drainage problem more than a spray problem
  • Apple scab: the olive-black leaf and fruit spots on apples and crabapples, controlled by sanitation and resistant cultivars
  • Cedar-apple rust: the two-host rust that bounces between apples and junipers
  • Peach leaf curl: the puckered red peach leaves that only a dormant-season spray prevents
  • Sooty mold on trees: the black film that grows on insect honeydew, a pest problem in disguise
  • Sudden oak death: the coastal-California water mold that kills oaks with bleeding cankers

Not sure it’s even a fungus? Start with is my tree dying? to rule out water stress, pests, and old age before you go chasing a disease.

When to call an arborist vs handle it yourself

Call an arborist ($150-500 for assessment and treatment plan):

  • Bracket fungi or conks on the trunk of a large tree near your house, driveway, or where people gather
  • Mushrooms at the base of any tree (possible root rot)
  • Large cankers on the main trunk
  • Rapid canopy decline with no obvious cause
  • Any tree that could hit a structure if it fails

Handle it yourself:

  • Leaf spots and anthracnose on otherwise healthy trees
  • Powdery mildew on leaves
  • Sooty mold (treat the insects causing it)
  • Small cankers on branches you can safely prune
  • Fungi growing on dead wood, stumps, or mulch

The bottom line: fungus on dead wood is nature doing its thing. Fungus on living wood deserves attention. And mushrooms at the base of your tree mean you should get a professional opinion before that tree drops a branch on your car.

How to prevent fungal problems

Most tree fungi exploit stress. A healthy, well-maintained tree fights off fungal infections that would kill a stressed one. The prevention checklist is straightforward:

  • Water deeply during drought (especially the first two years after planting)
  • Mulch with 2-4 inches of organic material, but keep it away from the trunk
  • Avoid wounding the trunk with mowers, string trimmers, or construction equipment
  • Prune for air circulation in dense canopies. Follow our tree trimming guidelines for timing
  • Don’t pile soil against the trunk or bury root flares
  • Choose disease-resistant species and cultivars when planting new trees

A $50 bag of mulch and a $20 soaker hose do more to prevent tree fungus than any fungicide on the market. Start with the basics. Your trees will thank you with decades of healthy growth, and you can check tree health tips at mklibrary.com’s landscaping guide for more property maintenance advice.

Frequently asked questions

Are mushrooms growing on my tree a bad sign?

It depends on where they’re growing. Fungi on dead wood, stumps, or fallen branches are decomposers doing their job, so leave them alone. Fungi on living branches or trunk bark are usually parasitic and actively harming the tree. Fungi at the base of the tree or on the roots are the most dangerous, because root rot can topple a tree that looks perfectly healthy above ground.

Should I remove bracket fungus or conks from my tree?

No. Breaking off the conks does nothing to stop the internal decay, and it just removes the evidence your arborist needs to see. The visible shelf is only the reproductive structure. The actual fungus is a network of threads inside the wood that has been breaking down the heartwood for years by the time a conk appears on the outside.

Will tree fungus kill my tree?

Some will, most won’t. Armillaria root rot and the bracket fungi that signal internal decay are structural threats that can kill or topple a tree. But anthracnose, powdery mildew, and sooty mold are mostly cosmetic. Anthracnose trees push out a second flush of leaves within weeks, and powdery mildew grows on the leaf surface without threatening the tree’s health.

Is there a cure for Armillaria root rot?

There is no chemical cure once a tree is infected. The University of California IPM program recommends removing dead and dying trees along with as much of the root system as possible, exposing the root crown by pulling soil back 9 to 12 inches, and avoiding susceptible species in that spot for several years. Replant with resistant species like most oaks, coast redwood, and many conifers.

What is the black coating on my tree’s leaves?

That’s sooty mold, and it looks worse than it is. It grows on honeydew, the sticky excrement from aphids, scale insects, or whiteflies, not on the tree itself. The fix is controlling the insects, not the mold. Once the honeydew stops, the mold weathers away on its own.

tree fungus tree diseases fungus identification tree care armillaria bracket fungus root rot