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Development of disease and pest resistant cultivars in elm and ash

Introduced diseases affect the health of our trees and shrubs, and breeders are always seeking to find new sources of resistance.

Development of disease and pest resistant cultivars in elm and ash
Developed at The Morton Arboretum by Dr. George Ware, Ulmus ‘Morton Glossy’ Triumph(™) has excellent resistance to Dutch elm disease. This particular selection was developed through controlled crosses using Ulmus ‘Morton Plainsman’ Vanguard(™) and Ulmus


Here at The Morton Arboretum, Dr. George Ware worked toward the acquisition of one of the largest and most extensive elm collections in the world in order to identify potential germplasm for breeding elms resistant to Dutch elm disease (DED).  In his time at the arboretum, Ware identified chance seedlings in the collections that exhibited disease resistance.  Some of this material was introduced into the trade (Accolade(™) elm) through Chicagoland Grows(R), and they were also used as parents in the arboretum’s Elm Improvement Program.

While these selections continue to prove resistant to DED, pathogens evolve much more rapidly than their hosts, and genetic diversity in the urban landscape is necessary to prevent future devastation of our urban forests.  In order to diversify the material available for DED resistant elm plantings, the New Plant Development Program will continue the legacy elm breeding program of Dr. Ware using the elm collection planted here at The Morton Arboretum.  Other pests that the arboretum releases are resistant to or tolerant of include elm leaf beetle, Japanese beetle, gypsy moth, and elm yellows.

The Emerald Ash Borer is an introduced pest that has decimated the native ash forests of eastern North America and the Midwest.  The devastation is evident in the forest canopy of the Chicago region from the forest preserves to the developed landscapes of the suburbs.  In an effort to develop ash trees that can function as street trees, the New Plant Development Program will join efforts with researchers in the Center for Tree Science and the University of Notre Dame.  Native green ashes (Fraxinus pennsylvanica) with EAB tolerance have been identified by researchers at the US Forest Service in Delaware, OH.  These ashes are referred to as lingering ashes due to their lone presence in stands of dead trees.  Cloned material from these populations will be used in an ash breeding program at The Morton Arboretum in order to identify F1 hybrids with both EAB tolerance and good overall form.  In addition to the green ash breeding project, the New Plant Development Program will be focused on developing Asian ash hybrids with improved form and EAB resistance for use as street trees.

Funding sources

The Morton Arboretum, Haerther Charitable Trust

Project status