[Reprint of Forest Service unnumbered circular, issued Oct. 21, 1908.] 
EXTENT AND IMPORTANCE OF THE CHESTNUT BARK 
DISEASE, 
By E. R. Hopson. 
InTRODUCTION. 
Three Pb ago a destructive fungous disease of the chestnut first 
attracted attention and almost immediately assumed the character 
of an epidemic. It seems to be one of the most serious diseases 
which has ever attacked an American forest tree, and has done great 
damage locally in and around New York City, and is now spreading 
rapidly in all directions to forest tracts in Connecticut, New York, 
New Jersey, and even into Pennsylvania. 
The disease was first studied by Dr. W. A. Murrill, of New York, 
and during the past 18 months it has been under investigation by 
Dr. Haven Metcalf, of the Bureau of Plant Industry. The tech- 
nical details given in this circular have been derived chiefly from the 
publications of the former and information supplied by the latter. 
Manner or INFECTION. 
The disease is caused by a fungus known as Diaporthe parasitica 
or Valsonectria parasitica, the spores of which enter the tree through 
wounds on branches or trunk. Dead twigs also offer a means of 
entrance, and there are probably other ways, not yet known, by 
which the trees become infected. 
From the point of entrance the fungus spreads in all directions 
throughout ttie cambium and inner bark until it completely girdles 
the branch or trunk it has attacked. It has been found that a few 
of the outer annual rings of the wood are also attacked, and it is very 
likely that the fungus penetrates some of the medullary rays in 
search of the food material which they contain; but the real seat of 
the injury is the inner bark and the growing layer of the wood. 
SYMPTOMS. 
When a tree is first attacked the disease is not noticeable, and is 
likely to be overlooked. In many instances the trees are attacked 
first on the smaller branches. These are soon girdled, and the foliage 
turns yellow and then wilts. By these wilted branches the disease 
can be detected from a distance. The girdled branches or trees do not 
usually die until the second year, except when they are attacked 
very early in the season, or when the infected limbs are small. 
On limbs with smooth bark the diseased patches are sunken and 
discolored, with small brownish or yellow knobs scattered over the 
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