Stem Decay Fungi of Hardwoods and Conifers
Compiled by Ned Tisserat, Colorado State University:
Stem Decay Fungi of Hardwoods and Conifers
A wide array of fungi attack and decay living and dead trees. Fungi that decay dead trees and wood are, in general, beneficial organisms that recycle carbon by breaking down wood cell wall components. This process returns billions of tons of carbon to the atmosphere and allows new plants to utilize the carbon as carbon dioxide. Decay fungi also play an important role in soil fertility by adding organic matter and contributing to aeration of the soil by decaying roots.
Recognition of decay in trees is not always easy in the Western U.S. because fruiting bodies (conks or mushrooms) do not always form. Decay recognition is best done by looking for other indicators of possible decay such as, open wounds, animal nests in the trees, broken branches, and swollen areas on the stem or branches. On living trees it is not always necessary to identify the fungus decaying the tree since it is the recognition of the decayed wood that is the main objective. Trees weakened by decay are prone to windthrow or breakage and are thus called hazard trees. Infected trees which are situated such that they may cause property damage or potentially injure people should be evaluated by a professional arborist to determine the extent of damage, and should be removed if there is any question regarding the stability of the affected parts.
Infection by decay fungi is usually accomplished through wind-borne spores, which enter the tree through wounds on the trunk, branches, root crown, or roots. Older trees are generally considered to be more susceptible to infection by decay fungi than younger, more vigorous trees. In the majority of decays, the disease is not treatable once it is established in the host tree. The most effective preventive measures are promoting tree health, keeping younger trees when removing trees, and avoidance of wounding.
Decay fungi are often classified by the type of decay they cause. Brown rots are those in which the fungus breaks down the cellulose and hemicellulose components of the wood’s cell walls leaving the brownish lignin component. Brown rotted wood tends to be dry and fragile, readily breaking into cubes or crumbling. Brown rots cause structural weakness with little visible change in the wood so are considerable more dangerous than white rots. White rot fungi are able to breakdown both the lignin and cellulose components leaving behind white to yellow, spongy, stringy, laminated, or crumbly material.
Select one of the links below for additional information about a few of the decay fungi common to the High Plains IPM region.
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