Wood rotting fungi cause losses over longer periods of time than most other diseases. Losses are caused mainly by breakage of branches and trunks due to a decline in the structural integrity of the wood. Structural integrity of the wood is altered by the enzymatic digestion of wood cell wall components by the fungal pathogen or pathogens that have colonized the wood. Some of the same fungi that cause wood rot can also cause dieback. The two most common symptoms of wood rot are breakage of the limbs or main trunk and the presence of fruit bodies on the bark or wood surface.
Symptoms vary depending upon the particular wood rotting fungus involved in the rot or dieback.
For example, infection by Trametes versicolor causes a papery bark symptom, in addition to wood rot. The symptoms are usually seen on the portions of large branches where the bark is still smooth. Smaller branches arise at the point where the limb is still healthy, and the infected part of the branch dies back to this point. Wood rotting fungi can also cause dieback from the central leader. When this occurs, infected tissue appears water-soaked and darker than the surrounding tissue.