Elm phloem necrosis phytoplasma - Elm Phloem Necrosis

Synonyms

elm yellows phytoplasma

Plant hosts

The only known hosts are elms (Ulmus spp.) including the American species U. americana, U. rubra, U. alata, U. serotina, U. crassifolia, and the natural hybrid U. pumila x rubra.

Symptoms

The first foliar symptoms usually develop between mid-July and mid-September in the northeastern USA and include yellowing, epinasty (drooping or downward bending of turgid leaves), and premature casting. Usually all branches on a tree show symptoms at once. Sometimes, however, symptoms develop in just one branch system of a tree, while other parts remain normal for a brief period of time. Bright-yellow leaves may occur together with green ones on a single small branch, but more often all leaves on a branch assume the same yellowish-green to yellow color. Once foliar symptoms appear, root mortality and degeneration of phloem in the roots and base of the tree are extensive. As the disease progresses, the phloem tissue will turn from a very light color to dark brown. Most infected trees die within 1-year after foliar symptoms appear.

ODA Commodity Inspection Division, Plant Health