Wood Decay in Trees

Wood decay is one of the most common problems in urban trees, and because decayed wood could threaten people or property, it is one of the most serious. The presence of a conk or a mushroom on a living tree is a positive indicator of decay, and therefore represents an increased likelihood for a tree or its parts to break or fail. Some fungi will decay the wood faster than others, and some species of trees rot faster than others. It is possible to generalize about the amount of wood decay when certain wood decay fungi are found fruiting on a tree. Decay caused by some fungi is usually limited in extent, whereas when others spread it can mean extensive decay. Decay of living trees is a disease, and therefore spreads. Depending on the decay fungus present, and tree health, the amount of decay may increase to a point where the tree may become hazardous. Most decay in urban trees is found without the presence of any wood decay fruiting structures. In the absence of fruiting bodies, we rely on other indicators to warn us of the presence of internal decay. These signs, cavities, carpenter ants, cracks, stem or trunk swellings, seams, and others suggest decay is present but usually do not indicate the extent.

Ganoderma applanatumzoom

Common Wood Decay Fungi:

Ganoderma applanatum, Artist’s conk
Common hosts - Maples, oaks, most hardwoods
Habitat - At the base or trunk of living trees
Mode of action - An aggressive decay fungus that decays heartwood and can kill and decay sapwood
Notes - Almost always associated with extensive internal decay



Polyprus squamosus


Polyprus squamosus, Dryad’s Saddle

Common hosts - Maples, elms, horsechestnut, and most hardwoods
Habitat - Usually from old wounds or old pruning sites on stems and larger branches
Mode of action - Slow progressing white rot
Notes - Decay is usually restricted to the area around the wound and fruiting body, seldom a cause for removal, but branches may have be tested for decay




Schizophyllum commune


Schizophyllum commune, Split gill fungus
Common hosts - Maples, lindens, crabapples, most hardwoods
Habitat - On wounds and dead areas of bark and cambium on the trunk or larger branches
Mode of action - Slow sap rot and cambium killer on weakened trees
Notes - Common on trees that have thin bark that have sun scald or that have done poorly after transplanting, once established on wounded tissues, it can also attack healthy bark and cambium adjacent to infected tissues.




What should you do if your trees have fungi fruiting bodies?
Property owners and managers should work with a certified arborist to develop an annual inspection and maintenance plan for the trees that will alert the property owner to structurally unstable trees and set forth how they will be dealt with! This forward-looking planning can avoid damage to people and property.

Fred Hoppe
Board Certified Master Arborist WI-0556B
Hoppe Tree Service


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