Ulmus 'Frontier'

Ulmus 'Frontier' is an American hybrid cultivar , a United States National Arboretum introduction (NA 55393) derived from a crossing of the European Field Elm Ulmus minor (female parent) 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.[1]

Ulmus 'Frontier'
'Frontier', Grange Farm Arboretum, UK.
GenusUlmus
Hybrid parentageU. minor × U. parvifolia
Cultivar'Frontier'
OriginUS

Description

'Frontier' develops a vase or pyramidal shape, with glossy green foliage turning, unusually for elms, to burgundy in autumn.[2] The twigs are pubescent.[3] Slow growing,[4] the ultimate height of the tree has yet to be determined, but should be > 15 m. The tree is autumn-flowering [5] but rarely does so, and has not produced seed.[6][7]

  • Fall foliage
    Fall foliage
  • Flowers and foliage
    Flowers and foliage
  • Fall color
    Fall color

Pests and diseases

'Frontier' has a good resistance to Dutch elm disease, rated 4 out of 5,[8] but tolerance of Elm Yellows from grafts in the United States was found to be poor.[9] However, no mortalities are known to have occurred from the latter disease in the field, the cultivar not known to be vulnerable to infection through natural means.[9] The tree can be heavily to severely damaged by the Elm Leaf Beetle Xanthogaleruca luteola, although it fared better than most of the cultivars assessed at U C Davis, suffering little more than 10% foliar damage.[4] Although susceptible to attack by Japanese Beetle, it is far less seriously affected than most hybrid cultivars available in the United States.[10]

Cultivation

In trials in eastern Arizona , 'Frontier' and another American hybrid, 'Regal', were found to have the highest tolerance of the hot and arid climate, notably exhibiting minimal leaf scorch. However, 'Frontier' is known to have sustained winter damage where planted in the Great Plains . This failing was repeated in the elm trials conducted by the University of Minnesota, although the tree often recovered the following year. It was also criticized for its form and integrity, considered "unsuitable" for urban forestry.[11] 'Frontier' fared better in 10-year trials at Atherton, California, to evaluate replacements for Californian elms lost to disease: "Strong structure, rapid growth rate, attractive leaf color in spring and fall, and relatively low pruning requirement suggest that Frontier has promise...",[12] although the tree again proved only moderately tolerant of elm leaf beetles.

'Frontier' has had a limited introduction to Europe,[13] where it is largely restricted to arboreta and elm collections; it also featured in trials in New Zealand during the 1990s at the Hortresearch station, Palmerston North.

Accessions
North America
Europe

Nurseries
North America
Europe

References
  1. Griffin, J.; et al. (2017). "Ten-Year Performance of the United States National Elm Trial" (PDF). Arboriculture & Urban Forestry. International Society of Arboriculture, Atlanta, US. 43(3):107–120.
  2. Photographs of burgundy colouring of 'Frontier' elm leaves in autumn: Arthur Lee Jacobson, 'Plant of the Month, 2008', photos 3 to 6
  3. Jacobson, Arthur Lee, 'Plant of the Month, 2008': arthurleej.com/p-o-m-Oct08.html.
  4. McPherson, G. et al. (2008). National elm trial: Initial report from Northern California. Western Arborist, Fall 2009, 32–36.
  5. Jacobson, Arthur Lee, 'Plant of the Month, 2008' arthurleej.com/p-o-m-Oct08.html
  6. Santamour, J., Frank, S. & Bentz, S. (1995). Updated checklist of elm (Ulmus) cultivars for use in North America. Journal of Arboriculture, 21:3 (May 1995), 121–131. International Society of Arboriculture, Champaign, Illinois, US.
  7. Townsend, A. M., Schreiber, L. R., Masters, W. O. and Bentz, S. E. HortScience, 26: 80–81, 1991.
  8. Heybroek, H. M., Goudzwaard, L, Kaljee, H. (2009). Iep of olm, karakterboom van de Lage Landen (:Elm, a tree with character of the Low Countries). KNNV, Uitgeverij. ISBN 9789050112819
  9. Sinclair, W. A., Townsend, A. M., Griffiths, H. M., & Whitlow, T. H. (2000). Responses of six Eurasian Ulmus cultivars to a North American elm yellows phytoplasma. Plant disease, Vol. 84, No.12, 1266–1270. American Phytopathological Society, St. Paul, MN
  10. Brady, C., Condra, J., & Potter, D. (2008) Resistance of Landscape-suitable Elm (Ulmus spp.) Cultivars to Japanese Beetle, Leaf Miners, and Gall Makers. 2008 Research Report, Nursery & Landscape Program, 15–16. University of Kentucky.
  11. Giblin, C. P. & Gillman, J. H. (2006). Elms for the Twin Cities: A Guide for Selection and Maintenance. University of Minnesota.
  12. Costello, L. R. (2004). A 10-year evaluation of the performance of four elm cultivars in California, U. S. Journal of Arboriculture, March 2004.
  13. Burdekin, D.A.; Rushforth, K.D. (November 1996). Revised by J.F. Webber. "Elms resistant to Dutch elm disease" (PDF). Arboriculture Research Note. Alice Holt Lodge, Farnham: Arboricultural Advisory & Information Service. 2/96: 1–9. ISSN 1362-5128. Archived from the original (PDF) on 26 October 2017. Retrieved 26 October 2017.
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