2014 ASHS Annual Conference

American elms (Ulmus americana L.) once lined Midwestern and New England towns until the late 1950’s. At that time, 80 percent of elms across the country had been diagnosed with Dutch elm disease and were removed. This created a need to find genetically diverse elms, and began many researchers’ work on finding species and/or hybrids that would have increased resistance to Dutch elm disease. As part of their efforts, Colorado State University coordinated a multi-state effort to evaluate elm cultivars in different climates and hardiness zones, also known as the National elm trial. Auburn University joined this trial in 2007, with the purpose to evaluate growth, horticultural tolerance, and insect, disease and stress tolerance. There have been many trials throughout the United States, but those in the Southeast have not been completed or at least reported. These characteristics need to be evaluated before recommendations on specific cultivars most suitable for the region can be reported to producers and the landscape industry. In the Auburn University trial, a total of 19 cultivars were planted. Eighteen cultivars were replicated five times, and one cultivar was replicated ten times, equaling a total of 105 trees. No herbicides, pesticides, or supplemental irrigation were used.

Data collected includes height, trunk diameter (at 12”), crown width, crown shape, fall foliage color, date of fall foliage color onset, duration of fall foliage, disease incidence and severity, and insect incidence and severity. In the fall of 2013, Ulmus ‘Morton Red Tip’ had the greatest height (19.1 ft) and caliper (4.55). U. ‘Patriot’, U. parvifolia ‘BSNUPF’, U. americana ‘Princeton’, and U. ‘Morton Stalwart’ were among the tallest cultivars. U. americana  ‘Homestead’, U. americana ‘Lewis and Clark’, U. parvifolia ‘Emer I’, U. ‘Morton Stalwart’, and U. ‘New Horizon’ were cultivars with a trunk diameter of greater than 3.5 inches. U. propinqua ‘JSF-Bieberich’, U. parvifolia ‘Emer I’, U. ‘Morton Plainsman’, and U. ‘Morton Triumph’ were among the shortest cultivars with heights equal to or less than 12 ft. U. ‘Morton Triumph’, U. americana ‘Princeton’, U. propinqua ‘JFS-Bieberich’, and U.  ‘Morton Plainsman’ had the smallest trunks with diameters less than 2.5 in. This data will be useful in creating recommendations for elm cultivar selection in the Southeastern U.S.