DUTCH ELM DISEASE RESISTANT ELM CULTIVARS
Kathryn J. Bevacqua
Dutch elm disease (DED), one of the most widely-known diseases, affects elms world-wide. DED was first isolated in the Netherlands in 1920. In 1930, it was reported in Cleveland and Cincinnati, Ohio. A serious outbreak occurred in 1933 in the New York City region, followed by another serious outbreak in the Midwest several years later. The first confirmed case of DED in Minnesota was recorded in 1961.
So many trees have been lost that people are now wondering if DED has run its course and if it is time to replant elms. No, DED has not run its course, but it is time to replant with DED resistant cultivars. These resistant cultivars should be planted in an area with an active DED program. Resistance has been studied in the U.S. since about 1938, with much of the work being done at the University of Wisconsin since 1957.
Unfortunately, the native American elm has very little resistance to DED. Although the Asian species are more resistant, they do not have the classic elm vase-shape. These Asian species may be less hardy than our native American elms. Plant breeding has focused on three areas of research: development of resistant American elms, development of Asian species with desirable characteristics, and development of various elm hybrids. Crossing various species of elm shows the most promise.
The search for DED resistant elms has been a slow process, complicated by a number of factors. Nevertheless, much research has been completed and DED resistant elm trees have been developed. It is a good idea to keep in mind that all trees are subject to problems of one sort or another. Other diseases, insects, and environmental injury may also create problems in tree health. Although resistant elms have been developed, it is important to remember that they are not immune. However, resistance combined with proper care ensures the best chance for success.
The table which follows has been adapted from an article which summarizes some of the most current elm research. Cultivars were included in this list if they were developed in a more northerly latitude (for example, Canada, Wisconsin, Maryland) and were generally available. Before purchasing or planting a DED resistant cultivar, ask your retailer about the hardiness of a particular selection.
We've learned how devastating a disease can be to a monoculture. Careful selection of hardy, disease- resistant varieties suited for that particular site, along with proper care, will ensure a healthy, diverse landscape. Reintroducing DED resistant elm trees is part of that attempt.
|American Elm--Ulmus americana|
|Brandon||More pyramidal than vase-shaped||Alberta, Canada introduction; may be same cultivar as 'Patmore'|
|Delaware||USDA introduction; susceptible to elm yellows|
(not yet available)
|Upright, vase-shaped; vigorous||Elm Research Institute (New Hampshire) introduction with research carried out at U. of Wisconsin; one of the 'American Liberty' elms clonally derived from resistant surviving elms|
|Vase-shaped||US National Arboretum introduction. Better form but less resistant than Valley Forge|
|Princeton||Vase-shaped||Some resistance to elm leaf beetle|
|Valley Forge |
|Vase-shaped||US National Arboretum introduction. Shows excellent disease resistance.|
|Washington||Not clear whether this tree is truly an American elm|
|Japanese Elm -- Ulmus japonica (sometimes listed as U. davidiana)|
|Jacan||Manitoba, Canada introduction|
|Chinese Elm -- Ulmus parvifolia|
|Dynasty||Small, vase-shaped||Cross of 2 Korean trees; for plantings under power lines|
|King's Choice||Upright crown; yellow autumn color||Zone 5|
|Ohio||Reddish autumn color||USDA introduction|
|Siberian Elm -- Ulmus pumila|
|Dropmore||Manchurian introduction; replaces 'Chinkota', and 'Harbin', and 'Manchu'.|
|Park Royal||Fast growing||Ontario, Canada introduction|
|North American Hybrids|
|Accolade||Vase-shaped; deep glossy green leaves||Morton Arboretum (Illinois) introduction; U. japonica x U. wilsoniana; resistant to elm leaf beetle and leaf miner|
|Cathedral||Broad, vase-shaped; medium to light green foliage.||University of Wisconsin introduction; U. pumila x U. japonica from Hokkaido University botanical garden; somewhat less resistant to DED than 'Sapporo Autumn Gold'; highly tolerant of Verticillium wilt; resistant to elm leaf miner|
|Frontier||Pyramidal; red-purple autumn color||U. carpinifolia x U. parvifolia; moderately resistant to elm leaf beetle; probable resistance to elm yellows|
|Homestead||Pyramidal; fast growing||Netherlands introduction; U. pumila x other hybrids|
|New Horizon||Upright; dark green large leaves; gray bark||University of Wisconsin introduction; U. japonica x U. pumila; resistance to elm leaf miner; high tolerance to Verticillium wilt.|
|Patriot||USDA introduction; 'Urban' x U. wilsoniana; highly tolerant to elm leaf beetle|
|Pioneer||Globe-shaped; very vigorous; fast growing||U. glabra x U. carpinifolia|
|Regal||Columnar; large, dark green, glossy leaves||University of Wisconsin introduction; U. hollandica and U. pumila x U. carpinifolia|
|Sapporo Autumn Gold||Upright, somewhat vase-shaped; immature tree has vigorous side shoots which need to be pruned||University of Wisconsin introduction; U. pumila x U. japonica from Hokkaido University botanical garden; tolerance to Verticillium wilt|
Santamour, Jr., Frank S., and Bentz, Susan E. "Updated Checklist of Elm (Ulmus) Cultivars for Use in North America," Journal of Arboriculture, 21:3 (May 1995), 122-131.
Smalley, E.B, and Guries, R.P. "Breeding Elms for Resistance to Dutch Elm Disease," Annual Review Phytopathology, 31 (1993), 325-52.
Stipes, R. Jay and Campana, Richard J., eds. Compendium of Elm Diseases. St. Paul: The American Phytopathological Society, 1981.
Chad Behrendt, Crystal Floyd