[Illustration: Stem canker caused by chestnut blight organism.]
Chestnut blight is caused by the fungus _Endothia parasitica_. It can be
found on American chestnut throughout its range where it has virtually
eliminated this valuable species from eastern hardwood forests. The
chestnut blight fungus is also parasitic on other hosts including common
chinkapin, Spanish chestnut, and post oak. Japanese and Chinese
chestnuts are resistant.
Stem cankers are either swollen or sunken and the sunken type may be
grown over with bark. The fungus forms fruiting bodies some distance
back from the advancing cankers, and the spores may exude from bark
crevices as orange curl-like masses during moist weather. Young cankers
are yellow-brown in sharp contrast to the normal olive-green color of
the bark. The chestnut is a vigorous sprouting species but the fungus
survives in previously killed stumps and later kills the new sprout
growth.
No effective control has been developed for chestnut blight, even after
several decades of intensive research. The most promising control
involves the development of a blight-resistant species. Research is
presently underway on this matter but results are inconclusive.
[Illustration: Fruiting bodies on surface of canker.]