Dutch Elm Disease Resistant Elm Trees

A healthy, DED-free elm leaf

Dutch elm disease (DED) is a devastating tree fungus that seriously damages and kills elm trees of many kinds. America has had its taste of the damage: Dutch elm disease all but wiped out American elms starting in the 1930s, killing 200 million trees in the United States alone. New hybrid DED-resistant trees are available around the world and are making a comeback, though it should be remembered that trees are susceptible to several other diseases and pests.

Effects

The devastating effects of Dutch elm disease start at the roots and work their way up. DED is a fungus that attacks the vascular system, or water circulatory system, housed within the tree's roots. The fungus essentially blocks up the roots, keeping water from making its way to the crest (everything above ground) of the tree. The tree wilts and dehydrates. Without early treatment of the disease, the tree will surely die. DED is transmitted by beetles and underground root contact with infected roots.

Types

Instead of pursuing fungicides and killing off disease-carrying beetles, scientists have gone ahead to develop DED-resistant elms, which are cultivars (variants) of the American elm tree. The Valley Forge and New Harmony cultivars are the most DED-resistant of them all. These cultivars, much like standard elm trees, have gray bark and a vase-shaped crest and grow 26 to 60 feet tall. Other types include the Accolade, Independence, Cathedral, Frontier, Homestead, New Horizon, Patriot, Pioneer, Prospector and Regal, all of which vary only slightly from the American elm. These trees are most hardy in USDA zones 4-6.

Geography

The University of Wisconsin and the National Arboretum are America's leading research institutions in the treatment of infected trees and creation of new DED-resistant hybrids. The American elm is native to the eastern half of North America and grows in many climates. The DED-resistant cultivars do not require special treatment or care. They grow well in urban and rural settings.

Significance

Dutch elm disease took out most American elm trees over a period of 50 years. DED-resistant trees are the result of rigorous effort and costly research that has evolved from finding a cure for the disease to engineering trees that resist infection in the first place. Without the development of DED-resistant trees, the elm tree would be in danger of eradication.

Considerations

DED-resistant trees are still susceptible to other tree disease and pests, such as moths, mites, borers and various types of root rot. It is a good idea to regularly look over an elm tree for any symptoms of illness.

References

• USDA Forest Service Northwestern Area: How to Identify and Manage Dutch Elm Disease
• Iowa State University: Dutch Elm Disease and Disease-Resistant Elms
• USA Today: American elm makes slow return
• University of Florida: American Elm

Resources

• North Dakota State University Department of Agriculture: Profile of Dutch Elm Disease