A New Threat: Beech Bark Disease 

What is Beech Bark Disease? 

Beech Bark Disease (BBD) is a new threat affecting American Beech trees (Fagus grandifolia) in Canada’s hardwood and mixed forests. This disease is the result of an insect-fungus complex caused by a non-native insect, beech scale (Cryptococcus fagisuga), coupled with a Neonectria fungus.  

Beech scale comes from Europe and first arrived in Nova Scotia in the 1890s. This insect, and the ensuing disease, is gradually spreading throughout much of the natural range of beech trees and is now found in all the maritime provinces, Quebec, and several eastern US states. In 1999, it was confirmed to be in Ontario. 

How do Beech Trees Contract the Disease? 

The disease begins with healthy trees being attacked by the scale insect. An infestation is easily detected as the nymphs or crawlers secrete a white, waxy covering to protect their body, giving the tree a woolly or snowy appearance. They pierce the living bark, creating puncture wounds as they feed on the tree’s sap. The feeding holes kill the bark cells, causing small cracks to form on its surface.  

While the insect does not move far on its own, they can be carried long distances by wind, mammals, birds, or in firewood. Usually, the larger trees in a stand are attacked first. Although the scales generally do not kill the tree, infestations reduce tree vigour and growth, and lower the tree’s resistance to fungal infections.  

Three to six years after the introduction of beech scale, the causal fungus (Neonectria faginata) enters the tree through the wounds opened by the insects and begins to colonize and destroy the cambial layer. This stage of the disease produces circular or oval shaped cankers that deform the bark surface.   

In the fall, small orange-red fruiting bodies appear in and around the canker, releasing tiny fungal spores that are dispersed to new sites by wind and splashing rain. Branches above large patches of dead bark often show signs of decline, producing yellowing leaves and reduced canopy. As the cankers become progressively worse, the tree is girdled, resulting in 90% of the trees succumbing to the disease within five to 10 years.  

Ecological, Economic, and Social Impacts 

American beech plays an important role in the forests of eastern Canada. BBD causes severe die-back in mature beech trees, negatively impacting wildlife, biodiversity, and sustainable forests in Ontario.   

• The disease typically kills larger trees first, significantly reducing canopy cover and altering the stand structure and forest dynamics.  
• Along with oaks, beech trees are valuable nut-producing trees, providing an important source of mast (food) for many forest-dwelling birds and mammals. The loss of beech trees means a change in food availability for wildlife, including black bears, deer, squirrels, and several bird species. Their demise also results in a loss of habitat for cavity-nesting birds and mammals. 
• While not particularly sought after, beech wood does provide valuable lumber, possessing a beautiful, fine grain for flooring and furniture. BBD may reduce the marketability of infected trees, thus negatively impacting the forest industry. 
• The loss of these beautiful trees decreases the aesthetic value of our hardwood forests. 

Trees that are at Risk 

Trees are more at risk of BBD when there is a nutrient imbalance in the forest soils. Drought and other pests can predispose trees to the disease. Weather conditions, such as winter temperatures that remain above -25° C or continual autumn rainfall, can favour the build-up of beech scale populations and the Neonectria fungus.  

On a positive note, heavy rains can wash crawlers off the trees and delay infestation, and some trees (about 1%) may exhibit resistance to the scale insect or tolerance to the fungus. Trees less than 30 years old also seem to have a natural immunity to attacks.