Elm yellows

Taxonomy

Domain	Bacteria
Phylum	Tenericutes
Class	Mollicutes
Order	Acholeplasmatales
Family	Acholeplasmataceae
Genus	Candidatus Phytoplasma

Scientific Name

Candidatus Phytoplasma ulmi

Common Name

Elm yellows

Elm yellows, formerly called Elm Phloem Necrosis, is caused by a mycoplasma-like organism transmitted by the whitebanded elm leafhopper, Scaphoideus luteolus. The disease affects American elm and its varieties, slipper elm, winged elm, and Buisman elm. Siberian and Scotch elm seem resistant.

The small fibrous roots die before any symptoms appear in the crown. Even the larger roots often are dying and the lower part of the stem becoming discolored by the time the leaves show symptoms. The first foliage symptoms are dropping leaf blades and upward-curling leaf margins. The leaves then turn yellow or brown, or both, and fall from the tree. Usually all branches on a tree show symptoms at the same time, but sometimes the symptoms develop branch by branch. American elms usually die within a year after symptoms appear. Slippery elms normally survive for at least 2 years and usually develop witches' brooms before dying.

The inner bark of large roots and the lower trunk of affected American elms is a yellow to butterscotch color, and has a wintergreen odor when freshly peeled. The odor can be detected after the bark sample has been in a warm, stoppered vial for a few minutes. The dead tissue of infected slippery elm sometimes has an odor similar to that of maple syrup.

Image Gallery

References

• USDA Forest Service. 1979. A guide to common insects and diseases of forest trees in the northeastern United States. Northeast. Area State Priv. For., For. Insect and Disease Management., Broomall, PA. p. 123, illus.