Eastern Forest Threat Center - Beech Bark Disease

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Cankered stem of American beech

Cankered stem of American beech

Linda Haugen, USDA Forest Service, Bugwood.org

Beech Bark Disease
Neonectria coccinea var. faginata

Beech bark disease causes significant mortality and defect in American beech, Fagus grandifolia. The disease results when bark, attacked and altered by the beech scale, Cryptococcus fagisuga, is invaded and killed by fungi, primarily Nectria species.

Keywords: fungus, beech scale, Cryptococcus fagisuga, white wax, cankers, American beech, Fagus grandifolia, Nectria fungi, BBD

Distribution Map Distribution Source Image

Threat Description

C. fagisuga is a soft-bodied scale insect. At maturity, it is yellow, elliptical, and 0.5 to 1.0 mm long. It has reddish-brown eyes, a 2-mm stylet, rudimentary antennae and legs, and numerous minute glands that secrete a white "woollike" wax. The white wax secreted by the beech scale is the first sign of beech bark disease. Isolated dots of white "wool" appear on the bole of the tree on roughened areas of bark, beneath mosses and lichens, and below large branches. Eventually the entire bole of the tree may be covered by the waxy secretion as the insect population increases. It is probable that great numbers of scales feeding on the liquids of bark cells can materially weaken a tree. But serious damage results only after the later invasion of the bark by Nectria, presumably through injuries made by scale feeding activity. In North America, two species of the Nectria fungi are associated with beech bark disease. On some trees, a red-brown exudate, called a slime flux or "tarry spot," oozes from dead spots. These dead spots are often the first symptom of Nectria infection, and frequently perithecia of Nectria later appear around them. The dead areas may extend into the sapwood.