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' (female parent) 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 EU breeders' rights (EU council decision 2100/94). Description Unlike its elder stablemate 'Sapporo Autumn Gold', 'New Horizon' initially has a compact, pyramidal form, with comparatively dense foliage comprising glabrous, dark-green, elliptical leaves < 12 cm long by 7 cm broad, occasionally without the asymmetric bases typical of the genus. The perfect, apetalous wind-pollinated flowers appear in March, followed by the seeds in April; flowering, and consequent fruiting, is sparse, in common with its female parent Japanese Elm, and usually begins when the tree is aged 8 years. The tree's growth habit is unusual; in an assessment at U C Davis as part of the National Elm Trial, its stem diameter increased faster than any other of the 15 cultivars, but increase in height, averaging 0.9 m per annum, made it one of the slowest growing, vertically. In commerce in the US, the tree is occasionally propagated by grafting onto an Ulmus pumila rootstock, rather than simply rooting cuttings as normally practiced in North America and Europe. Pests and diseases 'New Horizon' has a very high resistance to Dutch elm disease, rated 5 out of 5 in Europe; it is also resistant to elm leaf miner, and verticillium wilt. However, it has proven susceptible to attack by elm leaf beetle Xanthogaleruca luteola and Japanese Beetle in the United States. Up until its patenting in 1993, no Coral Spot fungus infection had been observed in the US. Cultivation The tree has not been an unqualified success. In the elm trials conducted by the University of Minnesota, 'New Horizon' was found to need relatively high levels of maintenance, largely owing to its predilection for co-dominant leaders and heavy side branches. In the Netherlands, removal of sideshoots from the lower trunk was found to be necessary twice a year. In trials in eastern Arizona it often exhibited > 25% crown dieback over winter