The death of long strips of bark results in serious defect when underlying wood is invaded by insects and decay fungi. The craterlike scars indicate where small, isolated nectria cankers were walled off by callus tissue. Since most of the cankers did not penetrate to the sapwood, little damage has occurred. Associated Organisms Other insects and wood-rooting fungi quickly invade the wood beneath bark killed by beech bark disease. Species of Hypoxylon that decay sapwood are among the first to invade.
Ambrosia beetles make holes that allow other fungi to enter.
The shoestring root rot fungus, Armillariella mellea , sometimes invades weakened trees and hastens their death. Attacks by these organisms make it difficult to judge when trees will succumb to beech bark disease. Many trees that are partially girdled remain alive, in a weakened state, for years. In the aftermath zone, attacks of a second scale insect, Xylococculus betulae , create severe defects on young beech stems. Roughened areas resulting from X. betulae attack are, in turn, infested by beech scale and then by Nectria .