Chestnut blight

Chestnut blight is a destructive plant disease caused by the fungus Cryphonectria parasitica. This pathogen is a significant threat to various chestnut species, particularly the American chestnut, and has caused widespread ecological changes in native forests throughout its range of infestation.

The fungus acts as a wound parasite, infecting the host through bark fissures, pruning cuts, or insect-damaged sites. Once inside, the fungus invades the inner bark, cambium, and xylem. Through the secretion of oxalic acid, it kills host tissues and creates a rapidly expanding canker that eventually girdles the stem or branch, killing everything above the infection point.

Symptoms begin as small, discolored, slightly sunken areas on the bark. As the infection progresses, the bark becomes reddish-brown and may split longitudinally. Under moist conditions, the pathogen produces orange-colored, flask-shaped fruiting bodies known as pycnidia and perithecia, which are indicative of an active infection stage.

• Visible sunken or swollen bark cankers.
• Yellowing and wilting of leaves during the growing season.
• Characteristic orange pustules on the bark surface.
• Development of adventitious sprouts below the canker.
• Progressive crown dieback leading to tree death.

Effective management remains challenging, as chemical fungicides are rarely effective on a forest scale. Current strategies emphasize the breeding of resistant chestnut varieties and the application of biological control using hypovirulent strains—viruses that weaken the fungus's ability to cause fatal damage. Integrated pest management, including the removal of infected wood and strict quarantine, remains essential for disease containment.