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FS ShieldForest Health Protection, Southern Region

ELM PHLOEM NECROSIS,

caused by Mycoplasma

Importance. - This disease kills more elms than Dutch elm disease in many urban areas. It is prevalent in the eastern half of the nation. The disease is common on winged and American elms, but attacks all elms.

Identifying the Cause. - Mycoplasma, which are microscopic plants, cannot be field identified. Consult a specialist.

Identifying the Injury. - Symptoms appear initially on one branch or a small portion of the crown. Leaves wilt, become chlorotic, and their margins curl upwards. Defoliation follows, and the crown appears bushy. Defoliation and death can occur in a few weeks. Some of the brown, wilted leaves persist, separating these symptoms from Dutch elm disease. This disease is identified by the butterscotch discoloration of the inner bark of the host tree. A wintergreen odor can sometimes be smelled after placing the affected bark in a vial or plastic bag.


Butterscotch discoloration of inner bark

Butterscotch discoloration of inner bark. (Click for detail. JPG 37K)


Biology. - Leafhoppers that have previously fed on infected elms transmit the mycoplasma to healthy elms.

Control. - Removal of dying or dead trees will reduce the spread of this disease by reducing the source of the mycoplasma.