Dutch elm disease.—This disease is caused by the introduced 
fungus, Ceratocystis ulmi (Buisman) C. Moreau. It was first re- 
corded in North America in Ohio in 1930. Three years later it 
was found in the New York City area. It is now known to occur 
on the east coast from New England south to the Carolinas, Ala- 
bama, and Mississippi and west to the Rocky Mountains (763). 
Its hosts are listed as both native and exotic species of elm, 
American elm especially. Its principal insect vectors are the 
smaller European elm bark beetle and the native elm bark beetle 
(150). Root grafting may also account for local tree-to-tree 
spread, particularly among closely spaced street trees. 
The first symptoms of Dutch elm disease are the wilting and 
yellowing or drying of the foliage. This is followed immediately 
by defoliation and death of the affected branches. Diseased trees 
commonly die within a single growing season, but some may die 
gradually, branch by branch, over a period of several years. Dis- 
eased trees develop a brown discoloration in the water-conducting 
vessels in the wood. In early spring, this occurs as brown streaks 
in the wood just under the bark of diseased branches (fig. 204). 
Later in the growing season, it appears as brown spots or as a 
partial or complete brown circle in one or more outer rings of the 
wood. 
Dutch elm disease is one of the most destructive tree diseases 
known. It kills both wild and planted elms but is best known as a 
killer of valuable shade tree elms. Since its discovery, it has killed 
too many of these trees to count. Currently, the value of trees 
killed and the cost of their removal is estimated at $100 million 
each year. A considerable amount of research has been devoted to 
the control of the bark beetles responsible for its spread (763). 
F-519563 
FIGURE 204.—Cross-section of an elm branch affected with Dutch elm 
disease, showing brownish discoloration in outer ring of sapwood. 
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