Comparative Test of Six Ded-Tolerant Elms: A Preliminary Report on Nursery Performance

Abstract

American elm (Ulmus americana) was the most popular street tree in the United States until the introduction of Dutch elm disease (DED) (Ophiostoma uimi). Now, several DED-tolerant clones have been identified, and there is hope that tolerant cultivars of the American elm will soon again be on the list of preferred urban forest species. But before the rush to plant, it is important to consider which clones are most tolerant, not only to DED but to other diseases, insects, and various environmental stressors. Local site adaptation as well as form and utility in the landscape also need to be evaluated. We have established several long-term comparison plots of clones of American elm that have shown DED tolerance. Plots are at the following U.S. locations: Rutgers University, New Brunswick, New Jersey; Pennsylvania State University, State College, Pennsylvania; EA. Bartlett Tree Expert Co., Charlotte, North Carolina; Shaker Heights, Ohio; and other sites. The plots will serve to demonstrate clonal differences in the following characteristics: field tolerance to DED; tolerance to elm yellows (phloem necrosis; samples tested by Rutgers University's Plant Diagnostic Laboratory), elm leaf beetle, any other pests or diseases and abiotic factors such as salt, drought, and air pollution; rate of growth, shape, and size of tree; appearance of general health and vigor, fullness of crown, leaf size and color; and possible G x E interaction (one clone better at one site, another somewhere else).