Most towns have an Elm Street, but many towns have no elm trees. Elms once towered over many suburban streets until Dutch Elm Disease (DED) began to decimate this native hardwood. Beginning in the 1920s and continuing through the 1950s, this deadly fungus spread across the United States and killed as many as 95 percent of the existing elm trees. Today, widely scattered populations of American elms still exist, and disease-resistant varieties are available as suitable substitutes.
The American elm (Ulmus americana) is a fast-growing, North American native tree that can grow to 100 feet with a similar spread. Prior to the devastating outbreaks of Dutch Elm Disease, these long-lived trees could obtain trunk widths of nearly 7 feet. The 6-inch long, dark green leaves of the American elm turn yellow in the fall. In spring, small flowers appear. When mature (after approximately 15 years), elm trees produce seedpods that are eaten by birds.
Elm trees produce a hard, durable wood that is used for lumber and furniture making. Early settlers discovered that the wood could be steamed and bent, and elm tree wood was used to make barrels, wheel hoops and rocking chairs. Native Americans used the large, straight trees to construct canoes. Today, fine-grained elm wood is used primarily in the furniture industry.
According to North Dakota State University extension, elm is purported to have some medicinal properties. Robert W. Stack, a professor of plant pathology, states, "Extracts of some Ulmus species have been used as a demulcent, an astringent, a diuretic, and for inflammation, burns, cold sores and wound treatments."
American elm grows best in full sun in rich, well-drained soil---although it can tolerate light shade and compacted soils. Elms are drought resistant, but prolonged dry periods can increase the tree's susceptibility to disease. Hardy from northern Florida into southern Canada (zone 2), elm trees can be pruned extensively. You should monitor elm trees carefully for signs of disease.
Symptoms of DED include wilting and yellowing of the leaves during spring and summer. The first leaves to be affected are those at the end of the infected branches. Eventually, the tree will die.
A fungus introduced by beetles in the 1930s, Dutch Elm Disease is a deadly shade tree disease. The fungus enters the tree and, according to the U.S. Forest Service, "reproduces in the water conducting parts of elm branches and stems. The fungus blocks water movement to tree leaves which causes the leaves to wilt and turn brown." The fungus can kill a mature tree in two to four years. DED can spread to other elms through their shallow root systems.
In addition to Dutch Elm Disease, American elms are vulnerable to gypsy moths, mites and scale.
Control of DED
If caught and treated early, Dutch Elm Disease can be controlled. Trees with less than 10 percent of affected branches can be pruned and treated with a systemic fungicide. Severely infected trees should be removed. Clean up and dispose of all remaining bark, sawdust and leaf litter from the infected tree to prevent further spread.
Disease resistant elm cultivars are available. The USDA Forest Service suggests that communities and homeowners "plant a mixture of suitable cultivars of as many elm genotypes as possible" to prevent widespread losses if "these cultivars are found to be susceptible to tree health problems."