What does that mean?

• Some fungi can attack and weaken the wood in living trees under certain conditions.
• 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 harm.
• 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

• 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 loss.
• 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 trees.

• 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 and evaluation.

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 "Tree 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.