Chestnut Blight

Common Name: Chestnut blight fungus, or Chestnut bark disease 
Scientific Name: Cryphonectria parasitica (Murrill) Barr

Classification:

Phylum or Division: Ascomycota 
Class: Sordariomycetes
Order: Diaporthales 
Family: Cryphonectriaceae

swollen blight canker on a chinquapin

The disease attacks the cambium region of the tree which forms a canker. The canker housing the fungus can be either swollen or sunken, with the latter being the lethal type that kills the tree. At first, the tree dies above the canker, killing the top completely but allowing trunk suckers to regrow from the base. These suckers often reach the diameter of a man’s leg when they are again killed back to the ground. After several cycles of this kind of attack, the tree that used to coexist with oaks and hickories as an equal now is little more than a shrub in the under-story of the forest.  Although young trees may succumb to the disease within a year, mature trees may take years to succumb to the fungus.

Site and Date of Introduction: Chestnut blight was first described in the Bronx Zoo in 1904 but had probably been killing American chestnut trees in scattered pockets across the eastern seaboard for several years prior to that date. Nut bearing Japanese chestnut cultivars, with fruits larger than their native cousin, were widely available in the nursery trade of the day. Parsons Nursery in Flushing, N.Y. was the first to offer grafted trees in 1876, but by the end of the century several other selections had been imported by different nurseries.

By 1912, the epidemic had swept across most of New England and Pennsylvania, leaving 100-foot tall skeletons of American chestnuts in its wake. By 1940, the fungus had spread throughout the range of the American chestnut and jumped to the Ozark Chinquapin (castanea Ozarkensis) where it continued its destructive ways.  When the blight was first identified in the early 1900’s, scientists knew very little about this new disease. Today, much more is known about the chestnut blight and the fungus pathogen that causes it, Cryphonectria parasitica.  Cryphonectria parasitica is a member of the Ascomycetes group of fungi, many of which are parasitic, including Dutch elm disease and oak wilt fungi. The same fungus that attacks American chestnuts also devastated Ozark chinquapin and is mildly pathogenic on Allegheny chinkapin and scarlet oaks.

Original Distribution: The first study that looked into the source of the blight fungus disease was commissioned in 1913 by the USDA. Frank Meyer, who led the study for the USDA, reported in that year that the disease was found on chestnut trees in mountainous uplands of China. Two years later, in 1915, Meyer also discovered the blight fungus disease in Japan, in mountainous ranges where chestnut trees were growing. It has since been established that both Japanese chestnut trees, (C. crenata Siebold and Zuccarini), as well as some Chinese chestnut trees (C. mollissima), are resistant to the fungus. While they may become infected, they seldom are killed by the fungus. 

Current Distribution: The figure below shows the natural range of chestnuts as presented by Saucier in 1973: eastern North America, from Mississippi to Maine, mostly on mountainous uplands that slope in an upwards, northeasterly direction. The disease has spread through out the native range, killing trees planted outside the range.