Key Features
- Blotch and snake-like leaf mines
- Holes in leaves
- Small, oval-shaped beetle
Symptoms
Infested leaves have either one or more brown areas produced by leaf mines feeding inside the leaves. Leaves may also be peppered with holes in early spring and in late summer. From a distance, the accumulation of chewed holes can give a tree a faded appearance. If mines are present in the absence skeletonized leaves, the culprit could be a species of sawfly wasp (elm leaf mining sawfly, Fenusa ulmi).
Biology
Adult beetles overwinter in the leaf litter and begin flying in search of elm leaves that have just emerged from their buds. Eggs laid in leaves produce the grubs which make June mines. Adults emerge from leaves and feed on leaves until they overwinter. There is one generation per year. This insect is more of a problem on newly planted trees where foliage is low enough to the ground for injury to be noticed. As trees get older and larger the small holes in the leaves and leaf mines are difficult to detect in the vigorously growing trees. This pest is unlikely to harm the health of larger trees.
Management Recommendations
Light infestations do not threaten tree health. Cosmetic injury can be reduced, but not eliminated with soil-applied systemic insecticides (dinotefuran, imidacloprid) applied in the fall to kill leaf miners during the following spring. Foliar sprays of broad-spectrum insecticides like bifenthrin or carbaryl directed against adult weevils in spring can also reduce mine formation. These insecticides have the potential to cause late-season outbreaks of spider mites. Elm pollen is commonly used by pollinators in the spring.
Effective Pesticides
Active Ingredients include: Bifenthrin, Carbaryl, Cyfluthrin, Dinotefuran, Imidacloprid, Lambda- cyhalothrin
Resources
- Not satisfied with ID? Contact the Purdue Plant and Pest Diagnostic Lab
- Sign Up for the Purdue Landscape Report
