Damage on American beech: Cankered stem of beech following attack by beech scale and infection by Neonectria (beech bark disease complex) in Ontario.

Beech bark disease is a fungus spread via a scale insect. Specifically, at least two different species of nectria fungus (accidentally introduced to the U.S. via European nursery stock in the late 1800s) is introduced into susceptible beech trees via the beech scale, a tiny sap-feeding insect that pierces the thin bark of the tree.

The beech scale (Cryptococcus fagisuga) was first found in the U.S. in Massachusetts and Maine in the 1930s. The European insect feeds on beech trees by inserting its long, needle-like, piercing-sucking mouthparts through the smooth bark. Persistent feeding can stress the tree, especially during drought conditions, and reduce the beech’s vigor and quality. However, the true danger lies with the disease the scale spreads.

The fungus results in canker development that eventually cuts off the flow of water and nutrients, killing the tree over the course of a few years.

Sources: University of Michigan Extension, University of Tennessee Extension

Photos by Linda Haugen, USDA Forest Service, Bugwood.org and Joseph O’Brien, USDA Forest Service, Bugwood.org