Mushrooms growing on a tree: what Northwest tree fungi mean

What mushrooms growing on a tree mean

The mushroom is only the reproductive part. The fungus itself lives in the wood and digests it. The Forest Service’s urban tree risk manual lists mushrooms, conks and brackets among the indicators of advanced decay, and notes that decay fungi produce fruiting bodies only in advanced stages.

Oregon State University Extension gives homeowners the same reading: mushrooms on a trunk mean a decay fungus is already growing inside the tree. Picking the mushroom off removes the evidence, not the fungus.

Decay does not automatically mean a tree is about to fall. Trees wall off wounds, and the Forest Service describes how that compartmentalization lets a decaying tree keep its strength as long as a thick enough shell of sound wood surrounds the rot. So the real questions are how much sound wood is left, where the decay sits, and what the tree would hit.

Timing matters when you look. Hard, perennial conks such as artist’s conk stay on the tree all year, but many fruiting bodies are seasonal: the Forest Service says Armillaria’s honey mushrooms come up in autumn, especially in wetter places, and velvet-top conks appear in late summer and fall. An OSU mycologist puts it plainly: in Oregon, mushrooms come and go with the rainy times. In Seattle and Portland the rain returns in earnest in October, so October and November are the months to walk around the base of your big trees. A bare trunk in July proves little; the velvet-top leaflet notes that conks are often missing on dry sites.

Source: NOAA NCEI 1991–2020 monthly normals, Seattle-Tacoma International Airport (USW00024233) and Portland International Airport (USW00024229); checked 2026-10-02.

Where the fungus grows tells you the risk

Before anyone names the species, the location gives a first read. The four zones below run from the most serious to the least.

At the base or root flare: highest risk. The Forest Service lists fruiting bodies at the root collar among the symptoms of root problems, and the International Society of Arboriculture’s tree-risk checklist asks whether mushrooms are present at the base of or under the tree. Root and butt rots weaken the part that anchors the tree, so a failure tends to be the whole tree rather than one limb.

On the trunk: depends on the shell. A conk on the trunk marks a decay column. The Forest Service rates a stem as a high risk of failure when advanced decay covers more than 40% of its circumference, or when the sound shell is thinner than 1 inch per 6 inches of diameter.

On a branch: that limb. A conk on a limb means the limb is decayed. The same manual counts any large branch with decay as a high risk of failure, but the fix is often pruning that limb out rather than losing the tree.

On a cut stump: usually low. A stump has no living wood left to protect, and decay fungi are what eventually rot it away. The exceptions are root-disease fungi that use stumps as a base to reach living trees, covered in the stump section below.

Which tree fungus is it? Common Washington and Oregon species

This table lists only fungi whose Northwest hosts and meaning are documented by the Forest Service’s Forest Insect and Disease Leaflets, Washington State University or Oregon State University Extension, or the Pacific Northwest Plant Disease Management Handbook. Treat a match as a lead to confirm, not a diagnosis.

Sources: USDA Forest Service FIDLs 177 and 188 and Region 6 notes; WSU Hortsense; PNW Plant Disease Management Handbook; UC IPM (turkey tail appearance); checked 2026-10-02.

Laminated root rot gets its own page on this site, laminated root rot in Douglas fir, because it is the Northwest root disease you are least likely to spot from a mushroom. The species pages for Douglas fir and bigleaf maple cover what else goes wrong with those two trees.

Orange mushrooms on a tree

Bright orange shelves with yellow undersides, stacked in a cluster on a trunk or stump, match the handbook’s description of sulphur shelf. The Forest Service manual groups it with the velvet-top fungus and the red-belt fungus as brown rotters that do not make the tree lay down extra wood, so there is no bulge or swelling to warn you. On a living trunk, especially low down, treat it as a decay column that needs measuring.

Mushrooms on a tree stump: usually harmless, with exceptions

Most mushrooms on a stump are doing exactly what you would want, turning dead wood back into soil. If you are trying to get rid of the stump anyway, decay fungi are on your side; how to kill a tree stump covers speeding that up, and stump grinding is the fast route.

Three Northwest root diseases are the exception, because a stump can feed them and pass them to living trees nearby:

For those three, extension and Forest Service guidance points the same way: dig out infected stumps and larger roots where it is practical, and replant with species the fungus leaves alone. WSU’s Armillaria sheet says to remove infected stumps and roots larger than 1 inch in diameter, which grinding the stump top does not do; stump removal vs. grinding explains the difference. If you see honey mushrooms on a stump with living conifers close by, watch those trees for thinning, yellowing crowns.

Is there a treatment or cure for tree fungus?

No spray cures wood decay. WSU’s Hortsense fact sheets list “None recommended” under chemical management for Armillaria root rot, laminated root rot and annosus root rot, and the PNW handbook’s decay entries for bigleaf maple, oak and hemlock offer only cultural controls. The Forest Service’s Armillaria leaflet notes that soil fumigants have been tested experimentally, but their use is severely restricted because of environmental concerns.

Wound paint does not help either. OSU Extension advises against wound paints and sealants because they can trap moisture and often make decay worse.

What an arborist does instead is measure, then decide. The Forest Service’s San Dimas Technology and Development Center evaluated the tools: resistance microdrills, which read how hard the wood pushes back against a fine bit, and sonic or stress-wave timers, which work because decay slows sound moving through wood. Its conclusion was that expensive equipment “cannot offset inexperienced users,” so the person matters as much as the device.

1. Note the location and the targetBase, trunk, branch or stump, and what the tree would hit if it fell: house, driveway, play area, power line.
2. Photograph the fungus and the treeShoot the top and underside of the conk and note the tree species. As the table shows, the host tree narrows the list fast.
3. Leave it aloneDo not scrape, paint or drill the spot yourself. The fungus is inside the wood either way.
4. Get a tree risk assessmentAn arborist checks the root collar, sounds the trunk, and drills or uses a sonic device if the extent of decay matters for the decision. See tree risk assessment.
5. Act on the resultISA lists the options: prune out the defective limb, cable or brace weak stems (not a guarantee against failure), keep up routine care, or remove the tree when its risk is unacceptable.

If the crown has already died back, how to tell if a tree is dead covers the other signs to check, and an arborist can tell you whether a decayed tree is worth keeping.

How to keep decay out of a healthy tree

The Forest Service manual puts it simply: wounds start the decay process. That is why the PNW handbook’s cultural controls read like a list of things not to do to a tree:

Tip: Keep soil and mulch off the root flare. The Forest Service manual calls planting too deeply a primary cause of lower stem decay, and a buried flare hides the root collar that any risk inspection needs to see.