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Beech Tree bark disease

Beech bark cankers Photo: Kevin McKeon

Editor’s note: Did you see something unusual last time you were out in the woods? Were you puzzled or surprised by something you saw? Ask our “Out in the Woods” columnist Kevin McKeon. He’ll be happy to investigate and try to answer your questions. Email him directly at:

Insidious Disease Stunts and Kills Beech

By Kevin McKeon, Director, Mousam Way Land Trust

While walking Sanford’s wonderful trail system, many interesting forces of nature can be seen. A common sight along the wooded trails are beech trees whose normally smooth, gray bark is pockmarked and very rough looking. You’re looking at the work of a tag-team composed of very small insects called scales and fungi.

The beech scale was accidentally introduced from some European beech products shipped to Halifax, Nova Scotia, in 1890. By the 1930s, the scale and an associated Neonectria fungus were found to be killing trees in eastern Canada and Maine. The disease has continued to spread and is now found as far south as Tennessee and North Carolina. It was discovered in Michigan in 2000 and in Wisconsin in 2009. Natural movements of infestations via wind, birds, and people average about six miles per year.

Beech scales are tiny, aphid-like insects, smaller than the tip of a pencil, and they’re all females, reproducing without mating. Their long, tube-like mouthpart (stylet) is inserted into the tree to suck the sap. Eggs are laid during the summer, hatching in the fall. Once a suitable location is found and they begin feeding, they lose their legs and become covered with a visible, woolly wax, remaining on the bark for the rest of their lives. They overwinter and become egg-laying adults in the spring.

Next come the fungi. After two years or so, an orange color on the tree’s bark reveals the fungi entry area through the scales’ feeding wounds. The fungi grow, killing the tree’s inner bark — the cambium layer — which feeds the tree. Sometimes a visible brown sap is produced. The tree responds by creating a rough, woody growth on the bark called a canker. Eventually, the inner bark becomes damaged to the point of strangling the tree, killing it. Sometimes large trees may live but remain disfigured. One such tree is on the Carpenter Trail at Deering Pond.

The insidiousness of beech bark disease is that trees are usually killed before the highly nutritious beechnuts can be produced. And beech trees are noted for their production of “suckers”— trees sprouting from the mother tree’s roots. This adaptation means beech can become invasive in some areas, keeping other vegetation from colonizing and resulting in a local monoculture of beech, causing a lack of wildlife diversity and “dramatic shifts toward smaller, denser forests over time,” said New Hampshire Agricultural Experiment Station researcher Jeff Garnas, associate professor of forest ecosystem health at the UNH College of Life Sciences and Agriculture.

“Given beech’s dominance through much of its range, this demographic shift from larger to smaller beech trees results in major reductions in carbon storage capacity, nut crop production, and the availability of cavity nesting habitat, and generally alters the look and feel of the forest,” he said.

Because the disease requires both the insect and fungus, killing the scales will prevent the disease from happening. The scales can be controlled on ornamental beech trees with insecticides, dormant oils and insecticidal soaps. A soft brush or strong stream of water can be used to remove the scales on small trees. But in the forest, there is no practical control option. A small percentage of trees are resistant to the scale and do not develop disease symptoms, even in heavily infected stands. Therefore, breeding resistant trees is a possible long-term management option.

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