Chestnut blight is a disease which affects American chestnut trees. From the time the disease was first observed in the early 1900s, it took around 50 years for the blight to wipe out much of the American chestnut population. Although the disease devastated American chestnuts, chestnuts from other regions of the world do not appear to be as vulnerable to it.
The blight is caused by a fungus, Endothia parasitica, which gets into the stems and trunks of the chestnut tree, causing a canker which first splits the bark and eventually girdles it, killing everything above the height of the canker. Despite this, the chestnut is a very resilient tree, and shoots and leaves will often grow below the canker. These grow for only a short time before they too are eliminated by chestnut blight, in a cycle which continues until the tree dies.
It is believed that chestnut blight entered the United States on Asian chestnuts introduced for ornamental gardens. By 1904, botanists were noting that chestnut trees in New York City appeared to be dying of a blight and the fungus spread like wildfire across the chestnut's range. At one point, these iconic trees were found widely distributed throughout the Appalachian mountains and they were an important source of timber as well as forest habitat. By the 1950s, they were increasingly difficult to find.
In 1912, the Plant Quarantine Act was passed in an attempt to halt the spread of chestnut blight. However, the fungus was too well established at this point. Today, a few trees exist in regions which have not been touched by blight but the American chestnut is no longer a viable commercial tree species. Botanists have tried breeding resistant species, in addition to cultivating trees in blight-free areas with the goal of eventually reintroducing the American chestnut. In addition, they have experimented with hypovirulence, in which the fungus is manipulated to make it less virulent, giving trees a chance of resisting the blight.
The spread of the chestnut blight fungus across the United States was unfortunate for the American chestnut and it also served as a sobering illustration of the danger of introduced organisms. American chestnuts had never been exposed to the fungus before and thus had no resistance. Other fungal blights have swept through plant populations such as oak trees and grapevines, dealing out similar damage to plants which were simply not prepared. The destruction of American chestnut populations also changed the American landscape and contributed to the development of phytopathology, a scientific discipline which focuses on the study of plant diseases, in America.