Whenever fungal conks (also called fruiting bodies or basidiocarps) are found growing out of the trunk or at the base of a tree, it is an indication that the tree is decaying inside. There are many different kinds of wood decay fungi that can cause heart, root, and butt rot of living trees. Some wood decay fungi may form hard, leathery, permanent conks, while others produce soft, temporary mushrooms. Infection by these wood decay fungi are almost always associated with stress to the tree and wounding.
The decay process is typically slow. By the time the conks are visible, internal decay is extensive, and trees are subject to falling or breaking in wind storms. Trees with multiple trunks are often weaker and more susceptible to internal decay. When conks are noticed anywhere on a tree, have it checked by a certified arborist or other tree care professional to make sure it is not posing a safety hazard.
