Photographer: Ptelea Source: www.wikipedia.org Copyright: CC BY 3.0
Ophiostoma ulmi or Dutch elm disease (DED) is one of the most destructive shade tree diseases in North America. Symptoms of DED begin as wilting of leaves and proceed to yellowing and browning. The pattern of symptom progression within the crown varies depending on where the fungus is introduced to the tree. If the fungus enters the tree through roots grafted to infected trees (see disease cycle section), the symptoms may begin in the lower crown on the side nearest the graft and the entire crown may be affected very rapidly. If infection begins in the upper crown, symptoms often first appear at the end of an individual branch. Symptoms begin in late spring or any time later during the growing season. Symptoms may progress throughout the whole tree in a single season, or may take two or more years. Branches and stems of elms infected by the DED fungus typically develop dark streaks of discoloration. To detect discoloration, cut through and peel off the bark of a dying branch to expose the outer rings of wood. In newly infected branches, brown streaks characteristically appear in the sapwood of the current year.
Host Preferences: American, English, Russian and Rock Elm.
The ecological threat of this disease is apparent. It is able to kill elm trees within 1 to 4 years. With elms being an important component of many kinds of natural forests, and Dutch Elm disease affecting most species of elm, it can severely impact forest ecosystems all over North America.
This fungal pathogen is spread by elm bark beetles like the native elm bark beetle (Hylurgopinus rufipes Eich), the smaller European elm bark beetle (Scolytus multistriatus Marsh) and the banded elm bark beetle (Scolytus schevyrewi). The beetles are attracted to stressed, dying or dead elm wood to complete the breeding stage of their life cycle. The adult beetles tunnel into the bark and lay their eggs in tunnels (called galleries) in the inner bark. The eggs hatch and the larvae feed in the inner bark and sapwood. Once the DED fungus is introduced into the upper crown of healthy elms by bark beetles, it slowly moves downward, killing the branch as it goes. Disease progression may occur rapidly, killing the tree by the end of the growing season, or may progress gradually over a period of two or more years. It is also possible that the tree may recover. The success and rate of progression within the tree depends on tree size, time and location of infection in the tree, climatic conditions, and response of the host tree.
For more information on the Banded Elm Bark Beetle click here
Although believed to be originally native to Asia, the disease has been accidentally introduced into America and Europe, where it has devastated native populations of elms which had not had the opportunity to evolve resistance to the disease. The name "Dutch elm disease" refers to its identification in 1921 and later in the Netherlands by Dutch phytopathologists. Since even the native elm bark beetles are able to carry this fungus DED has been present in the United States for over a century but has been documented since the late 1930s.
Native Origin: Asia
U.S. Habitat: Elm trees in any setting, forested or residential.
U.S. Present: Wherever elm trees are present, especially the American elm. All states are at risk of this aggressive fungal pathogen spread by 3 different beetle species. Infection confirmed in Northeastern and Midwestern United States, over to Washington, and down to California.
Control options are greater for trees infected with Dutch elm disease. A diseased tree of low value should be removed and the roots killed by chemical or mechanical means to prevent the spread to adjacent higher value trees. Affected portions of high value trees can be pruned and a fungicide can be injected into the trunk or branches, or both, to retard the infection rate. Specific information on chemical and mechanical control is available in the following publications:
Text References
Buth, J.L and R.A. Ellis. 1981. Trapping elm bark beetles in the City of Winnipeg, with a new record for Scolytus multistriatus, (Coleoptera: Scolytidae) in Manitoba. The Canadian Entomologist 113: 263-264.
Strobel, G.A. and G.N. Lanier. 1981. Dutch elm disease. Scientific American 245: 56-66.
Woodward, Susan L., and Joyce Ann. Quinn. 2011. Dutch Elm Disease Fungi. Encyclopedia of Invasive Species: From Africanized Honey Bees to Zebra Mussels. Santa Barbara, CA: Greenwood. 21-24. Print.
Internet Sources
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