Elm Yellows—The Re-Emergence of an Old Tree Killer: A Brief History of American Elms and DED

American Elm at Spring Grove Cemetery and Arboretum, Cincinnati, Ohio Photo courtesy Joe Boggs

By Joe Boggs and Francesca Peduto Hand, PhD

Dutch Elm Disease (DED) was first diagnosed on American elms in Cleveland, Ohio, in the late 1920s. The disease first appeared in eastern Canada in the 1940s and gradually spread westward into Ontario (1967), Manitoba (1975), and Saskatchewan (1981). DED arrived in North America from Europe; however, it was not native to Europe.

DED was first detected in Europe in 1910 when native European elms began succumbing to a mysterious malady. The causal agent was not known until 1921 when a fungus (Ophiostoma ulmi) associated with the elm die-off was isolated and identified by two Dutch plant pathologists, Dr. Bea Schwarz and Dr. Christine Buisman, who were working in the Netherlands at the University of Utrecht; thus, the ‘Dutch’ in DED. It is now known the originally identified fungus, which produces a slow death, has been largely supplanted in North America and Europe by a closely related, but much more aggressive species, O. novo-ulmi. It is also generally accepted that DED originated in Asia, which accounts for the resistance of most Asian elms to the disease.

Research on elm resistance to DED started in Europe as soon as the causal agent of the disease was identified. Indeed, Buisman spent the remaining years of her short career researching DED, developing methods to test resistance to the fungus, and working with others to identify resistant trees. The first resistant elm selection was named (posthumously) in her honour in 1936; Ulmus ‘Christine Buisman’ is now referred to as Ulmus procera ‘Christine Buisman.’ One of the first elm cultivars found to be resistant to DED in North America was Ulmus Americana ‘Princeton.’ The cultivar was actually first selected in 1922 by Princeton Nurseries in Kingston, NJ, for its landscape value; its resistance to DED was not discovered until years later, however.

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