Elm Phloem Necrosis

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Einar W. Palm
Department of Plant Pathology
Wilfred S. Craig
Department of Entomology
Phloem necrosis of American elm is a disease of unknown origin of many years standing, which is now widespread in the region of the central and lower Ohio River watershed. It extends to northern Mississippi, eastern Oklahoma, Kansas, Nebraska, and is generally distributed throughout Missouri. It damages the tissues which conduct food to all parts of the tree, and it causes wilting and death. Both forest and shade trees are affected, and trees of all ages and all degrees of vigor are susceptible. Trees may be infected for six months to one or more years before symptoms appear. The majority of infected trees usually die from 1 to 1-1/2 years, although some may die in three to four weeks and others may survive for two or more years. Since all infected trees die eventually, this is a serious disease of elms.

Cause

Phloem necrosis is caused by a mycoplasma-like organism (formerly believed to be a virus infection), and is usually spread from diseased to healthy elms by an insect, a leaf hopper, Scaphoideus leuteolus (Van Duzee). The virus may also spread through root grafts in close plantings or dense natural stands of elm. The disease affects only the American and winged elm; other species of elm are resistant.

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