| Ulmus davidiana var. japonica | |
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'Prospector' Photo: Susan Bentz, USDA National Arboretum, Washington, DC. |
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| Details | |
| Cultivar | 'Prospector' |
| Origin | National Arboretum, USA |
'Prospector' was originally treated as a cultivar of Wilson's Elm U. wilsoniana Schneid., a species sunk as Ulmus davidiana var.japonica by Fu [1]. A U.S. National Arboretum introduction (NA 55398), it was selected in 1975 from a batch of 1965 seedlings in Delaware, Ohio, and released in 1990 [2].
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'Prospector' is a medium tree with a light-grey bark, attaining a height of approximately 14 m and developing a vase shape broadly similar to the American Elm but with lower-drooping branches [4] [5]. The deep-green, glossy obovate leaves are < 11 cm long by 8 cm wide, emerging orange-red and turning yellow in autumn. The perfect, apetalous wind-pollinated flowers emerge in early spring, before the leaves. The samara, <15 mm long, is obovate to orbicular.
The tree grows at a comparatively modest pace; specimens planted at UC Davis as part of the National Elm Trial increased in height by 0.85 m and d.b.h. by 2 cm in the first few years after establishment [3] [6]
'Prospector' has been featured in several elm trials in the USA, notably those conducted by the Northern Arizona University at Holbrook, eastern Arizona[7], and Townsend & Douglass [4] which established that the tree's survival rate after inoculation with the Dutch elm disease fungus was 100%. In trials in California, the tree exhibited a singular sensitivity to boron concentrations of > 200 ppm in the soil, causing marginal necrosis on the leaves [5]. Moreover, although also highly resistant to elm leaf beetle Xanthogaleruca luteola [8] (no damage whatsoever was recorded in the aforementioned trials at U C Davis [3]) and Elm Yellows, 'Prospector' is a favoured food of leaf hoppers which can seriously disfigure foliage by midsummer, and is moderately susceptible to the Japanese Beetle [6].
'Prospector' performed well in California, although it "needed substantial training in the first two to three years"[5]. In Arizona, the tree proved unsuited to the hot, arid climate and suffered > 50 % leaf scorch. In trials conducted by the University of Minnesota, 'Prospector' was appreciated for its extraordinary vigour but faulted for the weakness of its wood, notably stem breakage owing to bark inclusion [7]. Nonetheless, it is considered by the U.S. Department of Agriculture (USDA) as suitable for Zones 4 - 7. The tree is currently being evaluated in the National Elm Trial [9] coordinated by Colorado State University.
'Prospector' was introduced to Europe by Butterfly Conservation in 2009 as part of its elm trials programme in Hampshire [8]. The tree was also included in trials in New Zealand undertaken by Hortresearch at Palmerston North in the 1990s.
Ulmus wilsoniana C. K. Schneid. 'Prospector'.
(Widely available)