Beech Bark Disease

Healthy American Beech tree

What is beech bark disease?
Beech bark disease is a fungus that infects and is often lethal to beech trees. The fungus is spread from a soft-bodied scale insect. The scale will eat and deposit its eggs into the bark of the tree. This opens the tree to infection by the nectria fungus. This fungus can kill the wood, blocking the flow of sap in the bark. This blockage can lead to beech snap (infected trees break off in heavy winds before dying). The fungus will be bright red and tiny lemon-shaped bodies that cluster in the cracks or holes of tree bark (dead or alive).

Beech Bark scale insects

Close-up of scale insects


Beech bark disease has 3 stages
“Advancing front” is an area where the scale has been found and is beginning to build populations.
“Killing front” is an area where infestations and high populations of beech scale, nectria attacks, and tree mortality is found.
“Aftermath Zone” is where heavy tree mortality occurred in the past and has a few large trees remaining with many small beech trees sprouting from old tree roots. These young tree sprouts are considered highly defective due to the contact with the scale insects and nectria fungus

About the scale insect:
When the scale insect is mature it has a yellow elliptical shaped body that is 0.5 to 1.0 millimeters long. It’s eyes are a reddish-brown color and it has rudimentary antennae and legs. It has also minute glands that will secrete a white “wool-like” wax. Infested trees will have a white fuzzy look to portions of the bark.

What’s at stake?
American Beech tree mortality is a threat in the Lower Peninsula. Approximately 2.5 million beech trees of 32 million beech trees have been killed by beech bark disease to date. Most of the die off has been reported in the eastern Upper Peninsula.


Tree mortality will begin about 3-6 years after the scales initially infect beech trees. Trees larger than 8 inches in diameter have a larger infestation rate. Some infected trees may be healthy looking (fully leafed-out) but will be considered a hazard due to beech snap.

Studies have shown that 3% of American Beech trees are resistant to the disease. Resistant trees are identified and being studied to produce resistant trees for forest regeneration.

Beech snap

Control methods.
Not many methods of control are known at this point but research is being conducted.

Studies suggest that the scale insect may not be able to withstand air temperatures below -35 degrees fahrenheit, especially when they are not protected by snow cover. The scale insect is preyed upon by a ladybird beetle (Chilocorus stigma) and there is a fungus, Nematogonum ferrugineum (Gonatorrhodiella highlei), that can parasitize the nectria fungi.

On large-scale infestations of forest stands, a salvage cutting can be done to beech trees. Removing the beech trees is a known method to reduce disease losses. This action should be consulted with by a consulting forester. Please see the general forestry page for a link to these qualified individuals.

MISIN has suggested to wash scale infested trees with a soft-brush using a water from a high-pressure nozzle. Sometimes dormant and horticultural oils could be used to cover and suffocate soft-bodied insects like scales, aphids, and spider mites. They have not found any effective insecticides to date.

How can you help?
-DO NOT move infested beech firewood, pulpwood, or sawlogs to un-infested areas from July 1 to snowfall.
-Report beech bark disease as soon as you find it. You can do so by A) Contacting your conservation specialist (Renee Penny, renee.penny[at], or call our office at (231) 258-3307. B) Reporting to Midwest Invasive Species Information Network (MISIN).
-Report resistant trees also.
-Support regeneration research efforts.

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