Earlier today I met up with a former colleague from the City of Toronto to check out a couple of forest sites that had been attacked by beech bark disease.
Beech bark disease is caused by the beech scale insect Cryptococcus fagisuga and the canker fungus Neonectria faginata. It attacks American beech, which is a major component of Ontario’s tolerant hardwood forests and a food source for bears, deer, rodents, and birds.
Here are some photos from my day in the forest:
The little white tufts above are a protective covering created by the beech scale and can be observed on trees well before the disease appears. The stage when beech scale is present without the disease is the “advancing front”. The scale can weaken the tree, but doesn’t kill it. Two to ten years later, the fungus attacks and is identified by lemon-shaped cankers and red fruiting bodies on the trunk (shown above). This is called the “killing front” when the fungus colonizes the inner bark and cambium of the tree.
Sometimes the tree can stop the canker fungus from penetrating the bark by compartmentalizing the damage and keeping the cankers inactive. It is thought that 1% of beech trees in North America are resistant to beech scale attack and therefore resistant to beech bark disease since the fungus requires the feeding wounds from the scale to penetrate the bark.
For the remaining 99% of beech trees, the fungus eventually surrounds the whole bole of the tree or the bark begins to peel off in strips. Within 3-6 years of infection by the fungus, the tree dies, the canopy opens and the cankered bark peels off and exposes the dead wood underneath.
Beech bark disease is advancing through the range of beech in Ontario. Although, there is no way to fully protect the trees before or once they become infected, forests can be managed to retain healthy, potentially resistant trees and remove diseased trees.
For more information about beech bark disease in Ontario click here