. Eastern forest insects. Forest insects. 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 bee
. Eastern forest insects. Forest insects. 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. 499. Please note t
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Keywords: ., bookcentury1900, bookcollectionbiodive, booksubjectforestinsects
