Beech Bark Disease (Cryptococcus fagisuga and Neonectria faginat)


Beech Bark Disease results from the combined actions of the Woolly Beech Scale (Cryptococcus fagisuga), a non-native sap-feeding scale insect and certain types of fungi, mainly Neonectria faginata1. The disease arrived around 1890 in Nova Scotia on an imported European Beech, and by the 1930s it was causing significant beech mortality across the Maritime Provinces2. The disease (both the insect and the fungus) has since spread outward, killing beech trees across north-eastern North America. By 2004, Beech Scale had been detected in Ontario as far north as the north shore of Lake Huron and southwest to London. The disease has since been detected in areas to the east and across the GTA and the Golden Horseshoe. Beech Bark Disease is found throughout the Credit River Watershed. Within CVC’s terrestrial monitoring plots, 100% of mature beech trees are infected.


The Woolly Beech Scale, spread by wind, is tiny and often goes unnoticed until its adult stage when it produces a white woolly wax that can cover large areas of bark1. The fungus usually arrives within 2-10 years after the tree becomes colonized by scale3 at which time the scale may disappear, indicating the underlying bark has been killed by the fungus. Other symptoms include crown die-back, leaf wilting, smaller leaves (that are typically yellow in colour), black or brown tarry spots on the bark, and warty cankers3.

The fruiting bodies of the fungus appear as small red or light orange coloured nodules at the site of the cankers, and spores are released during moist conditions1. Spores are normally spread by wind and rain, but can also be spread by contact.

Bark cracking from extensive infection

Ecological Threat

The possibility of disease arises when Woolly Beech Scale colonizes beech trees, puncturing the bark during feeding. This leaves the trees susceptible to infection by the fungus; the spores of which enter the tree through these puncture wounds. The fungus then grows inside the wound, killing the inner bark of the tree and creating a canker of dead and dying tissue. If too many wounds develop around the trunk, the tree can become girdled and die. If the fungus does not kill the tree directly, the cankers may enable other fatal pathogens and parasites to attack, or severely weakened trees may snap in the wind1. Beech Bark Disease tends to kill larger trees first3.

The loss of healthy beech trees negatively impacts species that use them, such as White-tailed Deer, Wild Turkey, Black Bear, and other small mammals such as Eastern Chipmunk. Beech Bark Disease can also lead to reduced biodiversity and major changes to forests3.

Preventative Strategies

To prevent accidentally spreading the disease, firewood should not be moved from infested stands. Ornamental trees can be monitored seasonally and treated for the scale insect to prevent infection by the fungus. For more information, please contact CVC via email.


1. Ayres, M.P., Evans, C., Garnas, J.R., and A.M. Liebhold. 2011. “Subcontinental Impacts of an Invasive Tree Diesease on Forest Structure and Dynamics”. Journal of Ecology 99, 532-541. Web. 14 August 2018.

2. Houston, D.R. and J.T. O’Brien. 1998. “Beech Bark Disease”. U.S. Department of Agriculture and Forest Service. Web. 15 June 2012.

3. Ontario Ministry of Natural Resources and Forestry. 2018. “Beech bark disease”. Web. 27 June 2018.

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