(Scaphoideus luteolus)
Elm leafhoppers by themselves cause only minor damage to elms. However, they carry mycoplasmas (microscopic organisms similar to bacteria) within their bodies that cause the very serious disease phloem necrosis. The leafhoppers spend the winter as eggs in the bark of twigs. Slits made by the egg-laying organ of the female leafhopper may injure or kill twigs. When the weather warms in spring, the young leafhoppers emerge and settle on the undersides of the leaves. They suck the plant sap, causing stippling. The leafhoppers that are carrying phloem necrosis transmit it as they feed. Infected trees often die. Several other leafhoppers that infest elms may also transmit phloem necrosis.
Control leafhoppers with an insecticide containing acephate in late May or early June. A second application may be necessary if a flush of new growth occurs during July or August. Insects carrying the phloem necrosis organism are difficult to control because it takes only one to infect the tree. (For more information about controlling disease-carrying insects, see Vectors of Plant Diseases.)
Plant Care for Ulmus