|Ulmus americana 'Valley Forge'|
'Valley Forge', Delaware, Ohio.
|Origin||Agricultural Research Service, Maryland, US|
The American Elm cultivar Ulmus americana 'Valley Forge' was raised by the Agricultural Research Service in Maryland. The tree was released to wholesale nurseries without patent restrictions by the U. S. National Arboretum in 1995 after proving to have a high resistance to Dutch elm disease. 'Valley Forge' proved only moderately successful in the US National Elm Trial, averaging a survival rate of 66.7% overall, owing largely to environmental factors rather than susceptibility to disease.
The branching is typically upright and arching, creating a broad vase-shaped structure complemented by a dense canopy of leaves. However, Michael A. Dirr, Professor of Horticulture at the University of Georgia criticized the tree's form as 'floppy'. The bark features greyish, flat-topped ridges, separated by roughly diamond-shaped fissures. The dark green leaves are large, < 17 cm (avg. 12 cm) long by < 10 cm (avg. 7.4 cm) broad, typical of the species, turning golden yellow in autumn. In an assessment at U C Davis as part of the National Elm Trial, the tree initially grew comparatively slowly, increasing in height by 0.85 m per annum, although stem development at 2.6 cm d.b.h. was near average.
'Valley Forge' has proven the most resistant of all the American Elm cultivars (although it is not immune) to Dutch elm disease. While also very resistant to the elm leaf beetle, Xanthogaleruca luteolalike all other American Elms it is susceptible to Elm Yellows. In California 'Valley Forge' has also been found to be susceptible to leaf curling aphids ( Eriosoma sp.) which produce honeydew
The cultivar is only moderately preferred for feeding by the Japanese Beetle Popillia japonica ,but the species as a whole is the most susceptible of all the elms to verticillium wilt.
In England, the leaves of 'Valley Forge,' along with those of other American Elm cultivars, remained completely free from Black Spot.
All examples included in 10-year trials at Atherton, California, to evaluate replacements for Californian elms lost to disease were withdrawn after a combination of rapid growth and poor structure condemned the trees as "likely to require more maintenance than most municipalities would find acceptable".However, these verdicts may reflect in large measure the fact that they were grown in warm climates but with minimal weed competition. Trees raised in the nursery of the University of Minnesota also proved very difficult to manage, but "settled down" as they matured, adopting a more manageable form and habit. 'Valley Forge' seems to develop far fewer structural problems in temperate climates further north, where the rate of growth in any given season is much more moderate. Moreover, where grown in the countryside, competing vegetation tends to keep excessively vigorous growth in check .
Interim results from the aforementioned trial at U C Davis confirm the tree's high pruning requirement.'Valley Forge' was introduced to the UK in 2010; it is not known to have been introduced to Australasia.
'Valley Forge' was named for the site near Philadelphia where Washington's forces endured the winter of 1777 during the War of Independence.
Ulmus davidiana var. japonica, the Japanese elm, is one of the larger and more graceful Asiatic elms, endemic to much of continental northeast Asia and Japan, where it grows in swamp forest on young alluvial soils, although much of this habitat has now been lost to intensive rice cultivation.
Ulmus 'New Horizon' is an American hybrid cultivar raised by the Wisconsin Alumni Research Foundation (WARF), from a crossing of the Japanese Elm clone W43-8 = 'Reseda' with Siberian Elm clone W426 grown from seed collected from a street tree at Yankton, South Dakota. Tested in the US National Elm Trial coordinated by Colorado State University, 'New Horizon' averaged a survival rate of 74% after 10 years.'New Horizon' was patented in the US in 1994, while in Europe, it is marketed as one of the 'Resista' elms protected under E U breeders' rights.
Ulmus laciniata(Trautv.) Mayr, known variously as the Manchurian, cut-leaf, or lobed elm, is a deciduous tree native to the humid ravine forests of Japan, Korea, northern China, eastern Siberia and Sakhalin, growing alongside Cerciphyllum japonicum, Aesculus turbinata, and Pterocarya rhoifolia, at elevations of 700–2200 m, though sometimes lower in more northern latitudes, notably in Hokkaido.
Ulmus 'Frontier' is an American hybrid cultivar, a United States National Arboretum introduction derived from a crossing of the European Field Elm Ulmus minor with the Chinese Elm Ulmus parvifolia in 1971. Released in 1990, the tree is a rare example of the hybridization of spring- and autumn-flowering elms. Tested in the US National Elm Trial coordinated by Colorado State University, 'Frontier' averaged a survival rate of 74% after 10 years.
Ulmus 'Homestead' is an American hybrid elm cultivar raised by Alden Townsend of the United States National Arboretum at the Nursery Crops Laboratory in Delaware, Ohio. The cultivar arose from a 1970 crossing of the Siberian Elm Ulmus pumila with the hybrid N 215, the latter grown from seed sent in 1960 to the University of Wisconsin-Madison elm breeding team by Hans Heybroek of the De Dorschkamp Research Institute in the Netherlands. Tested in the US National Elm Trial coordinated by Colorado State University, 'Homestead' averaged a survival rate of 85% after 10 years. 'Homestead' was released to commerce without patent restrictions in 1984.
Ulmus 'Regal' is an American hybrid elm cultivar developed by the University of Wisconsin–Madison and released in 1983. 'Regal' was derived from seeds arising from the crossing of the Dutch hybrid clones 'Commelin' and '215' sent in 1960 by Hans M. Heybroek of the Dorschkamp Research Institute for Forestry & Landscape Planning, Wageningen, Netherlands.
Ulmus 'Sapporo Autumn Gold' is one of the most commercially successful hybrid elm cultivars ever marketed, widely planted across North America and western Europe, although it has now been largely supplanted by more recent introductions. Arising from a chance crossing of the Japanese elm and Siberian elm, seed was sent in 1958 by Prof. Nobuku Takahashi and his colleagues at the Sapporo Botanical Garden of Hokkaido University, Sapporo, to Eugene Smalley at the University of Wisconsin–Madison. The patent issued in 1975 has expired, and there are now no propagation restrictions.
Ulmus gausseniiW. C. Cheng, the Anhui, or hairy, elm, is a medium size deciduous tree whose natural range is restricted to the valleys of the Langya limestone mountains of Chu Xian in Anhui Province, eastern China. The tree was most commonly found on the flood plains, indicating a tolerance of periodic inundation. However, U. gaussenii is now possibly the rarest and most endangered elm species, with only approximately 30 trees known to survive in the wild in 2009. The tree was introduced to the West in 1995, at the Morton Arboretum, Illinois, as part of an evaluation of Chinese elms for landscape use.
Ulmus 'Morton' is an elm cultivar cloned from a putative intraspecific hybrid planted at the Morton Arboretum in 1924, which itself originated as seed collected from a tree at the Arnold Arboretum in Massachusetts. Although this tree was originally identified as Ulmus crassifolia, it is now believed to have been a hybrid of the Japanese elm and Wilson's elm. Accolade has proven to be the most successful cultivar tested in the US National Elm Trial, averaging a survival rate of 92.5% overall.
Ulmus 'Morton Glossy' is a hybrid cultivar raised by the Morton Arboretum, Illinois. Originally named 'Charisma' until it was realized that name had already been registered for another plant, the tree was derived from a crossing of two other hybrid cultivars grown at the Morton: Accolade and Vanguard. Tested in the US National Elm Trial coordinated by Colorado State University, Triumph averaged a survival rate of 86% after 10 years. Triumph was introduced to the UK in 2006 by the Frank P. Matthews nursery in Worcestershire.
Ulmus 'Morton Plainsman' is a hybrid cultivar raised by the Morton Arboretum from a crossing of Siberian Elm and a Japanese Elm grown from openly pollinated seed donated by the Agriculture Canada Research Station at Morden, Manitoba. Tested in the US National Elm Trial coordinated by Colorado State University, Vanguard averaged a survival rate of 78% after 10 years.
Ulmus 'Morton Red Tip' is a hybrid cultivar raised by the Morton Arboretum from an open pollination of Accolade. The tree has occasionally been reported as a hybrid of Accolade with the Siberian Elm Ulmus pumila, an error probably owing to the commercial propagation of the tree by grafting onto U. pumila rootstocks. Tested in the US National Elm Trial coordinated by Colorado State University, Danada Charm averaged a survival rate of 77.5% after 10 years.
Ulmus 'Morton Stalwart', is a Morton Arboretum hybrid cultivar arising from a controlled crossing of Accolade with the hybrid of a Field Elm U. minor from eastern Russia and a Siberian Elm U. pumila. Tested in the US National Elm Trial coordinated by Colorado State University, Commendation averaged a survival rate of 85% after 10 years.
The American Elm cultivar Ulmus americana 'Princeton' was originally selected in 1922 by New Jersey nurseryman William Flemer of Princeton Nurseries for its aesthetic merit. 'Princeton' was later found to have a moderate resistance to Dutch elm disease (DED).
The American Elm cultivar Ulmus americana 'New Harmony' was raised by the Maryland Agricultural Research Service and released by the United States National Arboretum in 1995, along with 'Valley Forge'. 'New Harmony' proved the most successful U. americana cultivar in the US National Elm Trial, averaging a survival rate of 85.5% overall.
The American Elm cultivar Ulmus americana 'Jefferson' was cloned from a tree growing near a path in front of the Freer Gallery of Art, close to the Smithsonian Institution Building on the National Mall in Washington, D.C. The United States National Park Service, which had planted the tree during the 1930s, cloned it in 1993 after screening tests showed that it possessed an outstanding level of tolerance to Dutch elm disease (DED).
The Japanese Elm cultivar Ulmus davidianavar.japonica 'Jacan' is a cold-resistant selection from Canada. The tree was raised by the Morden Research Station, Morden, Manitoba in the 1980s.
The American elm cultivar Ulmus americana 'Lewis & Clark' is a development from the North Dakota State University (NDSU) Research Foundation breeding programme, released in 2004 to commemorate the 200th anniversary of the eponymous expedition. The cultivar was cloned from a tree discovered in 1994 along the Wild Rice River south west of Fargo, ND., where all those around it had succumbed to Dutch elm disease; the tree remains in perfect health (2008). Prairie Expedition proved only moderately successful in the US National Elm Trial, averaging a survival rate of 62.6% overall, owing largely to environmental factors rather than susceptibility to Dutch elm disease.
The Japanese elm cultivar Ulmus davidianavar.japonica 'Prospector' was originally treated as a cultivar of Wilson's elm U. wilsonianaSchneid., a species sunk as Ulmus davidiana var. japonica by Fu. A U.S. National Arboretum introduction, it was selected in 1975 from a batch of 1965 seedlings in Delaware, Ohio, and released without patent restrictions in 1990. 'Prospector' proved moderately successful in the US National Elm Trial, averaging a survival rate of 76% overall.
Ulmus 'Patriot' is a hybrid cultivar raised by the United States National Arboretum in 1980. Derived from a crossing of the American hybrid 'Urban' with the Wilson's Elm cultivar 'Prospector', 'Patriot' was released to commerce, free of patent restrictions, in 1993. Tested in the US National Elm Trial coordinated by Colorado State University, 'Patriot' averaged a survival rate of 85% after 10 years.