Beech bark disease is a new threat affecting beech (Fagus grandifolia) trees in Canada’s hardwood and mixed forests. This disease is caused by a combination of an introduced beech scale insect (Cryptococcus fagisuga) from Europe, coupled with a nectria fungus. While the nectria fungus was likely native to North America, the introduced scale insect provides an opening to a new host tree for the fungus. The disease begins with many scales feeding on beech tree sap while they form a covering of white wooly wax over their body. Once the scales have opened wounds in the bark, the nectria fungus begins to colonize the bark, cambial layer, and sapwood of the tree. This stage of the disease produces cankers sometimes resulting in isolated tarry spots oozing from the bark and /or raised blisters and calluses on the outer bark covering much of the trunk.
Beech bark disease results in severe die-back in mature Beech trees, potentially creating a significant threat to wildlife, biodiversity, and sustainable forestry in Ontario. While this new disease poses a significant threat to Ontario’s majestic beech stands, not all beech are killed by the disease, and prevention on individual beech trees is possible.
After introduction of the beech scale insect to Nova Scotia in 1890, the nectria fungus began infecting wounds opened up by the insect. Beech bark disease is marching from east to west through the maritimes, Quebec, and throughout the northeastern United States including New York, Pennsylvania, Ohio, and Michigan. Recently, the disease has been identified in southern Ontario
Impacts of Beech Bark Disease
- Beech bark disease attacks mature trees over 8 inches in diameter, rather than small, more vigorous stems.
- Decreases the amount of forage trees for wildlife. The beechnuts are an important food source for wildlife, especially black bears.
- Severely weakens trees, exposing them to other stresses.
- Reduces the marketability or use in wood products.
How to Identify Beech Bark Disease
- Mature beech scales are a soft bodied, wingless insect, 0.5 – 1.0 mm long.
- After feeding on the sap under the smooth beech bark, the scale is easily recognized by the covering of white wooly wax on their outer body.
- In fall, the fungal fruiting bodies can be seen as deep-red, lemon-shaped structures in the bark.
- Infection by the nectria fungus may also result in oozing from the bark.
- Tree crowns appear yellow and die back.
What You Can Do
- Learn how to properly identify the signs and symptoms of beech bark disease.
- Individual high-value ornamental beech trees can be controlled with commercially available products.
- Look for large, healthy individuals with no signs of disease within areas of high infection. These mature trees may be immune to the disease and can provide an excellent seed source for the next generation of beech bark disease resistant trees.
- If you’ve seen Beech Bark Disease or any other invasive species in the wild, please contact the toll-free Invading Species Hotline at 1-800-563-7711 or visit EDDMapS to report a sighting.
Forest Pests and Pathogens - A Quick Reference Guide
OFAH/OMNRF Invading Species Awareness Program. (2021). Beech Bark Disease. Retrieved from: www.invadingspecies.com.
This factsheet may be reproduced for non-commercial purposes.
Header photo by Patrick Hodge, MNRF.