Wood Decay Fungi on Living Trees
What does that mean?
Why is this topic important?
- Some fungi can attack and weaken the wood in living trees under
- Vigorously growing trees are usually able to resist decay fungi
by outgrowing them or by stopping them with barriers, but wounded or weakened
trees are susceptible to invasion.
- Decay fungi can create hazard trees with a great potential for
- Many older trees that fail during storms have had their strength
sharply reduced or even eliminated by decay fungi. Mushrooms or bracket
fungi on trunk or butt are warnings!
- Strength loss is difficult for amateurs to detect, and even for
professionals to evaluate.
Artist's conk (Ganoderma
applanatum) on European beech
Which decay fungi are common and dangerous in an urban
What can I do about it?
- Climacodon septentrionalis. This fleshy fungus is
made up of multiple cream-colored shelves, each shelf underlain with many
spore-bearing "teeth", and it fruits in August and September. Especially
common on sugar maple.
- Fomes fomentarius. The top portion of the fruiting
structure is hard, gray in color, and takes on a hoof-shaped appearance,
up to 6-8" across. Maple, beech, and birch are most often infected, commonly
at older pruning wounds.
- Artist conk (Ganoderma applanatum). Woody
shelf-type fruiting body up to 2' wide is found on the lower part of trunk
or tree butt. Top brown to reddish-brown with a creamy white margin, may
be shiny. Wide host range includes oaks, maples, and beech.
- Daedalea quercina. Fungus with woody, perennial,
shelf-like fruiting body growing from old pruning wounds. Underside is
maze-like. Common on red oak and other oaks.
- Chicken-of-the-woods (Laetiporus sulfureus).
Lemon-yellow/orange shelf-type fruiting body. Found singly or in overlapping
fans on trunks and butts of many deciduous trees. This is a "brown
rot" that takes the cellulose our first, and it leads to rapid strength
- Cerrena unicolor. This fungus fruits as multiple,
thin, leathery shelves, with green moss on top of younger shelves. It is
especially threatening to stressed trees because it easily outraces efforts
at containment. Produces an ever-expanding elongate canker on many deciduous
Where can I get more information?
- Prevention is the best defense, because you can't "save" a tree
that has decay.
- Promote reasonable growth of young trees: water well
during dry spells, aerate the soil, maintain 2-6" organic mulch, and apply
slow-release fertilizer in early fall or spring.
- Avoid injuring or smothering the roots during construction
or other activity.
- Minimize entry of decay fungi: protect the young trunk from
injury, and use proper pruning technique, timing, and management.
- Provide supplemental water to trees with decay when needed
so the tree can outgrow or contain the spread of decay.
- Call a tree professional trained in the area of decay detection
Detailed descriptions and pictures of these fungi (except Daedalea
quercina) can be found in Wayne A. Sinclair, Howard H. Lyon, and Warren
T. Johnson, 1987, Diseases of Trees and Shrubs (Ithaca NY: Cornell
University Press). Images are available on the web at Gary Morman's
diseases that create hazards" and Flemming Larsen's "Fungi
images on the net". For other information, advice and help on this
topic, call offices of your State Urban Forestry Coordinator or University
Extension service, or visit urban forestry web sites.