Tree Killers: Chestnut Blight

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  • Common English name: Chestnut Blight
  • Other names:
  • Latin (scientific) name: Cryphonectria parasitica

Threat type

150x150 diseases

History in Canada

  • American Chestnut only occurs in Canada in southern Ontario in the Carolinian Forest zone
  • Chestnut blight probably arrived in North America in the late 1800’s
    by the 1950’s, virtually all mature Chestnuts in North America had been killed by the blight
  • today, American Chestnut occurs primarily as sprouts from stumps and roots, and occasional saplings and larger trees
  • in Ontario, there are a small number of large seed-producing trees that do not appear to be affected by the blight
  • these apparently-resistant trees may be very important to the recovery of the species


  • a fungus disease that infects and kills American Chestnut (Castanea dentata)
  • the disease was brought to North America on imported Japanese Chestnut
    Chestnut blight attacks twigs, branches, and the trunk
  • the blight causes cankers that eventually girdle and kill the tree
  • infected trees show disfigured bark and often areas of small orange bumps growing through the dead bark
  • the fungus has killed most mature trees in North America but they often resprout from the base
  • Can live a number of years and may produce some viable seeds

Impact on Trees

  • the American Chestnut tree was an important forest species in southern Ontario that provided valuable wood for furniture and nut crops that were used by wildlife, Native Americans, and early settlers
  • in much of the eastern US, American Chestnut was the dominant forest tree and its loss had a profound impact on deciduous forests
  • American Chestnut is considered Endangered in Canada due to the impact of the disease

What can be done to control this tree killer?

  • there is no known cure for Chestnut trees infected with blight
    early studies in the US focused on a search for trees with natural resistance to the blight
  • none were found that had sufficient resistance
  • more recent studies have involved hybridization with Chinese Chestnuts that are not affected by the blight
  • such hybrids may allow reforestation of ‘American-like’ Chestnuts, but they will not be true American Chestnuts

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