Symptoms of chestnut blight
Linda Haugen, USDA Forest Service, Bugwood.org
The chestnut blight fungus, Cryphonectria parasitica, has virtually eliminated the American chestnut as a commercial species from eastern hardwood forests. Although roots from trees cut or killed many years ago continue to produce sprouts that survive to the sapling stage before being killed, there is no indication that a cure for this disease will be found.
Keywords: fungus, American chestnut, Castanea dentata, fruiting bodies, pycnidia, stem cankers, girdling, sprouting
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Host infection occurs when fresh wounds in the bark become infected with fungal spores disseminated by wind, birds, rain, and insects. The fungus forms yellowish or orange fruiting bodies (pycnidia) about the size of a pin head on the older portion of stem cankers, which may be sunken or swollen. Sunken stem cankers may be grown over with bark that is usually loose at the ends of the canker. Cankers kill the cambium and girdle the stem. Trees die back above the canker and may sprout below it. Multiple cankers on infected trees are common. No effective control has been developed for chestnut blight, even after decades of intensive research. Current research is targeted toward finding a blight resistant species and the further development of the hypovirulent strains of the fungus. These strains tend to inactivate the pathogen and promote healing, but only when applied directly to developing cankers. Cryphonectria parasitica is widespread and continues to survive as a non-lethal parasite on chinkapin, Spanish chestnut, and post oak.