[1][2][3] In North America, the disease occurs after extensive bark invasion by Xylococculus betulae and the beech scale insect, Cryptococcus fagisuga.

[4] Through a presently unknown mechanism, excessive feeding by this insect causes two different fungi (Neonectria faginata (previously Nectria coccinea var.

faginata) and Neonectria ditissima (previously Nectria galligena)) to produce annual cankers on the bark of the tree.

The woolly, white tufts and broad strips are the colonies of the beech scale insect that are formed in tiny crevices along the bark.

[3] An adult beech scale insect has a soft body, is yellow in color, ranges from 0.5 to 1.0 millimeter long, and has an elliptical shape.

[1] They have short antennae and legs, and move around until they find a suitable and safe place to settle down and force their stylet into the bark to begin feeding.

[1][3] A second type of scale insect, Xylococcus betulae, which is non-host-specific, is native to North America and causes beech bark disease to a lesser degree than Cryptococcus fagisuga.

[1] These fungi infect the tree through the wounds caused by the beech scale insect and then begin to produce spores.

Spores are contained in perithecia, which are red, lemon-shaped fruiting bodies that form in clusters on the bark.

These perithecia mature in the fall, and once they have become sufficiently moist, they each release eight spores that are carried by the wind to other beech trees.

The amount of waxy material observed depends on the population of the beech scale insect on that tree.

One important management strategy is prohibiting the movement of nursery stock, firewood,[6] or other materials that may harbor the beech scale insect.