Armillariella mellea and Agrilus bilineatus and Mortality of Defoliated Oak Trees

Dead, recently dead, dying, and living trees in areas defoliated by the gypsy moth, Lymantria dispar , were examined for the presence of the shoe-string fungus Armillariella mellea and the two-lined chestnut borer Agrilus bilineatus . Root systems were excavated with a front-end loader. A. mellea was established in the roots of one-third of the living trees examined. Colonization on trees with healthy crowns was limited to one or several small roots. On trees with half-dead crowns, the fungus had extensively colonized the roots and on many trees was present at the root collar. Both A. mellea and A. bilineatus were present in dead, recently dead, and dying trees. The roots of most of the recently dead or dying trees were extensively colonized by A. mellea , even though the fungus was not visible at the root collar. It is proposed that oak mortality results from an interaction of defoliation, A. mellea , and A. bilineatus . FOREST SCI. 23:485—492.