Dutch elm disease
Widespread disease that kills elms, originally described in the Netherlands. The disease is caused by the fungus Ophiostoma ulmi (also known as Ceratocystis ulmi). It was first identified in the U.S. in 1930, and an eradication campaign could not stop its spread into regions wherever the very susceptible American elm (Ulmus americana) grew. The leaves on one or more branches of a stricken tree suddenly wilt, turn dull green to yellow or brown, curl, and may drop early. Because symptoms are easily confused with other diseases, positive diagnosis is possible only through laboratory culturing. The fungus can spread up to 50 ft (15 m) from diseased to healthy trees by natural root grafts. Overland, the fungus normally is spread by the European elm bark beetle (Scolytus multistriatus; see bark beetle), less commonly by the American elm bark beetle (Hylurgopinus rufipes). Control involves exclusion of the beetles, usually by use of an insecticidal spray applied to the tree.
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