Chestnut blight fungus attacks and kills the American chestnut tree (Castenea dentata). It also infects oak trees but does not kill them.

The fungus enters wounds on American chestnut trees and then grows under the bark, circling the twig branch or trunk. The fungus blocks the flow of water and nutrients between the circled parts and kills the tree.

In less than 50 years the fungus killed 3.5 billion chestnut trees, which made up 25 to 50% of the eastern forests. The loss of these trees permanently changed the composition of the forest landscape.

Chestnuts were used extensively for food by Native Americans and wildlife. Replacement oaks and hickories do not provide the same resource.

Loss of chestnut trees caused severe economic losses because American chestnut produced excellent timber and wood products. Many houses and barns were built with chestnut because of its straight grain and rot resistance.