Forestry experts typically claim that Dutch elm disease, caused by a vascular wilt fungus, has been the most destructive tree disease to ever strike our woodlands. Introduced to North America more than 80 years ago by a Cleveland, Ohio, furniture company, that unwittingly purchased infected logs from France, DED was assisted in rapidly spreading across the country from tree to tree by the introduction of the European elm bark beetle to North America about the same time.

RESISTANT ELMS: This Princeton American elm tree is one of several selections identified by UM researchers that shows resistance to Dutch elm disease. (Courtesy of Department of Forest Resources, University of Minnesota)

DED has decimated millions of American elm trees, including a dozen trees on our own farmstead.  It also strikes other native elms in the upper Midwest like rock elm and red elm. The result is that elms have been almost completely removed from rural tree planting lists. However, that stigma may be about to change.

Thanks to research on DED-resistant elm varieties conducted over the years at first at Cornell University, the Boyce Thompson Institute in New York, the Bureau of Plant Industry in New Jersey, the University of Wisconsin, the National Arboretum and more recently at the University of Minnesota, resistant varieties have been identified that could bring the elm back to the farmstead forest.

Even after almost 80 years of research, DED is still not understood very well. No American elms have been identified as completely resistant, and even tolerant trees can become infected. UM Extension recently revised their DED-resistant varieties list to include several tolerant hybrid Asian elms, along with American elms that show tolerance to DED.

Among the UM American elm list is Princeton, a cultivar selected in 1922, with vigorous growth, an upright form and some availability commercially. Prairie Expedition is a more recent selection, coming out of North Dakota State University in 2004, with the classic, vase-shaped American elm form with outstanding autumn gold color. New Harmony is a USDA selection, which appears to have superior form compared to Princeton, for instance, but limited availability commercially.

St. Croix was selected by Mark Stennes from a gigantic parent tree in Afton, Minn. Finally, Valley Forge is another USDA resistant selection, but doesn’t have the form of New Harmony, for instance, and requires heavy pruning.

Typically, many of these resistant varieties require more pruning during their early formative years than the old American elms that were a favorite in rural landscapes decades ago. According to Gary Wyatt, UM Extension agroforestry educator, diversity in rural landscapes is still the key to beating disease and insect issues. “We are telling farmers and rural landowners they can plant other tree species that have been used in the past and maybe trying other varieties like Kentucky coffeetree, catalpa, hackberry, swamp white oak, buckeye, linden and DED-resistant elm,” Wyatt says. “People can also plant shrubs that will produce edible nuts and berries like hazelnut, elderberry, juneberry, black chokecherry, Aronia berry and others.”

Thanks to long-term research and the identification of resistant varieties, it is possible that stately American elm and Asian elm trees may once again play a major role in rural tree plantings, helping improve the diversity of rural woodlands. You can learn more by contacting UM Extension DED-resistant elm researcher Chad Giblin at [email protected].