Chestnut Canker

Causal Agent

• The causal agent of chestnut blight was initially identified as Endothia parasitica. After 1978, this name was changed to the presently known Cryphonectria parasitica. As a result of the devastating Asian fungus, to which the American chestnut has no resistance, much like the case of small pox and the native Indian communities, the once tallest trees in the eastern hardwood forests now grow as poorly productive, small trees.

Symptoms

• The disease is characterized by the appearance of a large canker or a sunken or swollen area on the tree trunk. This canker can also appear on branches. Wounds or cracks in the bark are common sites of infection. The fungus gradually grows under the tree bark. In later stages of infection, the canker starts to secrete tiny yellow or orange fruiting bodies referred to as pycnidia.

Damage

• The tree areas around the canker slow start to die. Though the tree may continue to sprout and grow, the younger sprouts also get infected and die gradually. Cankers spread throughout the tree, killing younger trees in less than a year. Older, larger trees may take a few years to die completely. The root system is not damaged by the fungus and new trees sprout from the roots. The younger trees are frequently infected again within five years when they are 25 feet tall. These tree fail to bear flower or fruit.

Management

• There are no control options once the American chestnut tree is infected with the fungus. Management research for the disease is focusing on the development of a hypovirulence or viral disease that may help to weaken and retard the spread of the causal fungus through the trees. Another strategy is the breeding of disease resistant American chestnut trees by creating hybrids with the Asian chestnuts.