distinguishing characteristic of the disease. Death follows the 
dying of the roots. 
Elm phloem necrosis is an extremely destructive disease. Dur- 
ing epiphytotics such as occurred in the Central States in the late 
thirties and forties, it has killed enormous numbers of valuable 
shade tree elms in many cities and towns (fig. 206). More re- 
cently, however, it has been at a low ebb. 
Beech bark disease.—A destructive disease of American and 
European beeches and all. their varieties is caused by the 
fungus, Nectria coccinea var. faginata Lohman, Watson, and 
Ayres. The pathogen gains entry into the tree through tiny rup- 
tures in the bark caused by the feeding of the beech scale. The 
scale, and probably the fungus, is of foreign origin. The disease, 
which was first recorded at Halifax, Nova Scotia in 1920, now 
occurs throughout the Maritime Provinces of Canada and south 
through the beech-growing areas of New England to Central 
New York and eastern Pennsylvania. 
The fungus may infect large areas on scale-infested trees, com- 
pletely girdling and killing them. Trees only partially girdled may 
remain alive in a weakened state for many years, or they may be 
broken by the wind. On some trees, the fungus may be confined to 
strips or spots on the bole where it produces cankers. Parts of the 
crowns of these trees become chlorotic and die. 
The beech bark disease is destructive. In many stands it has 
killed more than half the beech, and the commercial value of many 
of the survivors has probably been seriously reduced. Shigo 
(646) discussed possible methods of control. 
Oak wilt.—This disease is caused by the fungus, Ceratocystis 
fagacearum (Bretz). It occurs over a wide area, from Nebraska 
and Kansas to the Carolinas and Pennsylvania, and, as far as 
known, attacks all native species of oak regardless of size, age, 
or vigor. The fungus spreads from infected trees to adjacent 
healthy trees through natural root grafts, and there is consider- 
able evidence that insects are responsible for spread over longer 
distances: fungus spores have been recovered from the bodies 
of several species of insects after they fed on fungal mats, and 
some of these are known to feed on sap at fresh wounds on healthy 
trees (116, 170, 314). 
Oak wilt is potentially a very serious disease (fig. 207). Given 
the proper conditions for an epiphytotic, it could cause heavy 
losses in the vast oak forests of eastern United States. It has al- 
ready caused considerable damage in many oak woodlots and 
forest stands in Wisconsin, Minnesota, and Iowa. Methods of con- 
trol are discussed by Fowler (260). 
Persimmon wilt.—This fast-killing disease of common persim- 
mon, Diospyros virginiana L. in the Southeastern States, is 
caused by the fungus, Cephalosporium diospyri Crandall, which 
produces masses of spores beneath the bark of infected trees. In 
smooth-barked trees the spores occur in such large masses that 
the overlying bark is raised in the form of blisters. When these 
blisters break, the spores are released and then blown away by 
the wind. In rough-barked trees the spores are produced in the 
cambium region and are released when the bark begins to disin- 
tegrate or is removed or broken off. 
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