Dutch elm disease A devastating disease which can affect all species of elm (Ulmus). The causal agent is Ceratocystis ulmi, a fungus originating in Asia but first identified in Holland. The fungus develops and spreads in the xylem vessels; tyloses are formed. Symptoms include wilting, with curling and yellowing of foliage, followed by the rapid death of branches or the whole tree. The fungus is spread from tree to tree by elm-bark beetles (commonly Scolytus species). In the 1960s a new and more virulent strain of the pathogen was introduced into Britain on logs imported from Canada; since then many millions of elms have been killed, dramatically changing the landscape in many regions of Britain. The disease has also been proposed as the cause of the elm decline.

Dutch Elm Disease

Dutch elm disease is a fungal infection of the vascular system of elm trees. The fungus, Ophiostoma ulmi, is spread from diseased to healthy trees by elm bark beetles. Fungal spores adhering to the beetles are introduced to the tree through feeding wounds in young branches. In nonresistant elms, large portions of the vascular system are infected before the tree can defend itself against the invading pathogen . Water transport within the tree is blocked by the fungus and the tree eventually wilts and dies.

The fungus first appeared in the Netherlands about 1912; from there it spread across Europe, reaching the United States in 1930. At the time, the American elm, Ulmus americana, was the premier urban tree, planted for its beauty, shade, and durability. Across the Midwest, this hardy, quick-growing tree was used for windbreaks as well as on the streets of new towns. As the disease spread across the nation, streets once shaded by majestic, arching elms were soon barren of trees. It is estimated that over one hundred million trees have been lost to the disease.

Early attempts at controlling the disease concentrated on killing the fungus and its vector . As tree spraying became frowned upon and injection of fungicides more costly, more effort has been made to breed disease-resistant elms. Several European cultivars that have been developed are not completely resistant to the disease or sufficiently cold-hardy for North America. Hybrid crosses of resistant Asian species with American species lack the height and characteristic form of the American elm. Selective breeding and testing of American elms has led to promising varieties such as American Liberty, Princeton, and Valley Forge, but whether any of these will be resistant to the disease as the fungus itself evolves remains to be seen.

see also Breeding; Interactions, Plant-Fungal; Interactions, Plant-Insect; Pathogens.

Craig Steely

Bibliography

Stipes, R. Jay, and Richard J. Campana, eds. Compendium of Elm Diseases. St. Paul, MN: American Phytopathological Society, 1981.

Dutch elm disease A devastating disease which can affect all species of elm (Ulmus). The causal agent is Ceratocystis ulmi, a fungus which appears to have originated in Asia, not Holland. The fungus develops and spreads in the xylem vessels; tyloses are formed. Symptoms include wilting, with curling and yellowing of foliage, followed by rapid death of branches or the whole tree. The fungus is spread from tree to tree by elm-bark beetles (commonly Scolytus species). In the 1960s a new and more virulent strain of the pathogen was introduced into Britain on logs imported from Canada; many millions of elms were killed, dramatically changing the landscape in many regions of Britain.

Dutch elm dis·ease • n. a disease of elm trees caused by the fungus Ceratocystis ulmi (phylum Ascomycota) and spread by bark beetles. A virulent strain of the fungus that arose in North America in the early 20th century has destroyed the majority of American elms in many areas.

Dutch elm disease Highly infective fungus infection that attacks the bark of elm trees, and spreads inwards until it kills the tree. It is spread by beetles whose grubs make a series of linked tunnels in the wood below the bark.

Dutch elm disease: see diseases of plants; elm.