Chestnut disease is caused by

Chestnut disease is caused by Cryphonectria parasitica.
The pathogenic fungus Cryphonectria parasitica is a member of the Ascomycota. The fungus spread rapidly and caused significant tree loss in both regions.
It is a parasitic fungus of chestnut trees. This disease came to be known as chestnut blight. The American chestnut and American chinquapin are highly susceptible to chestnut blight.