Dutch elm disease is caused by an Ascomycete fungus that kills elm trees, and is spread by elm bark beetles. Believed to be originally native to Asia, the disease was accidentally introduced into America, Europe, and New Zealand. In these regions it has devastated native and exotic populations of elms that did not have resistance to the disease. The name "Dutch elm disease" refers to its identification from 1921 onwards in the Netherlands by the Dutch phytopathologists Bea Schwarz and Christine Buisman, who both worked with Johanna Westerdijk. The disease affects multiple species in the genera Ulmus and Zelkova, and is carried from tree to tree by any of several species of beetle, especially bark beetles of the genus Scolytus.
Multiple types of treatment or prevention have been attempted. The use of insecticides against the beetle vectors was tried in America in the 1940s and 1950s, causing significant harm to other organisms including insects and birds. Several fungicides are effective at protecting individual trees by injection every two or three years, as long as the root system has not been infected. A vaccine, Dutch Trig, uses a different fungus, Verticillium albo-atrum, to induce an immune response in individual trees. Breeding of elms resistant to Dutch elm disease has been attempted in the Netherlands, America, and Italy.