Ulmus 'Morton Stalwart' (selling name ), is a Morton Arboretum hybrid cultivar arising from a controlled crossing of with the hybrid of a Field Elm U. minor from eastern Russia and a Siberian Elm U. pumila.Cirrus Digital Hybrid Elm - Ulmus (carpinifolia x pumila) Tested in the US National Elm Trial coordinated by Colorado State University, averaged a survival rate of 85% after 10 years.
Description The branches are upright, but the form of the tree is more oval than vase-shaped; the leaves are relatively large. However, examples grown in the warmer climes of the southern United States have not impressed, and it was dismissed, along with its Morton stablemates and , as 'ugly' by Michael Dirr, Professor of Horticulture at the University of Georgia , on account of its 'wild' growth and splaying branches.
Pests and diseases Although resistant to Dutch elm disease in the United States, the tree is moderately susceptible to insects, notably elm leaf beetle Xanthogaleruca luteola,McPherson, G. et al. (2008). National elm trial: Initial report from Northern California. Western Arborist, Fall 2009, 32–36. Japanese beetleBrady, 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. and Gypsy moth.
Cultivation is vigorous and robust, adjudged the third fastest-growing cultivar of 17 assessed by the University of Minnesota and fourth out of 15 in trials at UC Davis. The tree is also extremely tolerant of droughtGiblin, C. P. & Gillman, J. H. (2006). Elms for the Twin Cities: A Guide for Selection and Maintenance. University of Minnesota. and cold; in artificial freezing tests at the Morton ArboretumShirazi, A. M. & Ware, G. H. (2004). Evaluation of New Elms from China for Cold Hardiness in Northern Latitudes. International Symposium on Asian Plant Diversity & Systematics 2004, Sakura, Japan. the tree was found cold-hardy to −40°C.
was introduced by Chicagoland Grows and is currently being evaluated in the National Elm TrialCSU Shade Tree Lab coordinated by Colorado State University. The tree was introduced to the UK in 2014, but is not known (2016) to have been introduced to Australasia.
Accessions North America Arnold Arboretum, US. Acc. no. 131–2002 Bickelhaupt Arboretum, US. Acc. no. 02–018 Brenton Arboretum, US. 5 trees, acquired 2009. Acc. no. not known. Chicago Botanic Garden, US. 1 tree, planted in the Parking Lots; no other details available. Dawes Arboretum, Newark, Ohio, US. 2 trees, accession nos. 2004-0046.001 and 2004-0046.002.'Morton Stalwart', Dawes Arboretum Holden Arboretum, US. Acc. no. 00–124 Morton Arboretum, US. Acc. nos. 274–97, 109–2006. Smith College, US. Acc. no. 36405 University of Idaho Arboretum, US. Two trees. Acc. no. 2000089 Europe Grange Farm Arboretum, Lincolnshire, UK. Acc. no. 1141.
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