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-flowering and autumn-flowering elms.

Description

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

Pests and diseases

'Frontier' has a good resistance to Dutch elm disease, rated 4 out of 5, but tolerance of Elm Yellows in the USA was found to be poor. No mortalities are known to have occurred from the latter disease, however, and the cultivar is not known to be vulnerable to infection through natural means. 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. Although susceptible to attack by Japanese Beetle, it is far less seriously affected than most hybrid cultivars available in the USA.