Elm Yellows

Elm yellows or elm phloem necrosis is a lethal disease affecting elm trees (Ulmus spp.) in the eastern U.S. and Canada.
Photographer: Flickr user William Yurasko
Elm yellows is caused by a bacteria that is spread by a sap-sucking insect, the leaf hopper. Unlike Dutch elm disease, elm yellows typically affects the entire crown of an elm tree all at once, turning the leaves yellow in late summer and causing them to drop prematurely.1 Trees may develop witch's broom—dense sprouts in tiny patches in the crown.

By the time symptoms have appeared, the tree is infected systemically, and may die right away, or within a year or two. When infected, the inner bark of several species of elms develops the odor of wintergreen; that of slippery elm acquires the smell of maple syrup.2