Several types of beetles damage elm leaves, but one invasive pest is a severe threat to elm trees. Known as the elm leaf beetle, this pest feeds heavily on elm leaves in both its adult and larval forms. Even large, mature trees can be completely defoliated. Elm leaf beetles don't transmit the fungi responsible for Dutch Elm disease — that's done by elm bark beetles. However, extensive leaf loss severely weakens trees, which increases their attractiveness to elm bark beetles. Elm leaf beetles are also significant nuisance pests when they try to enter homes and overwinter.
Identification: Adult elm leaf beetles are greenish-yellow insects about 1/4 inch long. Two black stripes run along the outer edges of their wing covers, and a thin stripe runs down their center back. They lay yellow-white, football-shaped eggs on the underside of elm leaves in distinctive double rows. Newly hatched, worm-like larvae are black, but they mature to yellow-green. Dark bumps run down the sides of their 1/3-inch-long bodies.
Signs/Damage: Elm leaf beetle damage may look like Dutch Elm disease at first. Closer inspection reveals the chewing damage. Adult beetles chew through foliage, leaving holes. Larvae feed on leaf undersides, skeletonizing leaves and creating a windowpane look. Leaves turn yellow and brown, and then drop prematurely.
Control: Effective treatment of elm leaf beetles involves treating foliage and tree surfaces. After feeding on foliage, larvae crawl down trees and pupate around tree bases. GardenTech® brand offers highly effective options to kill elm leaf beetles. These products treat foliage on trees less than 10 feet tall (seek a professional for foliage treatment on larger trees) and tree trunks where larvae crawl:
- Sevin® Insect Killer Ready to Spray provides thorough coverage of elm tree surfaces. Attached the container to a regular garden hose, and it measures and mixes automatically as you spray. Cover all leaf surfaces, both upper and lower, and lower trunks thoroughly to kill elm leaf beetles and reduce future populations
- Sevin® Insect Killer Concentrate, used with a pump-style sprayer, allows for precision and large-scale coverage. Use the easy-to-use measuring cap to add the concentrate to your sprayer, add the corresponding amount of water, and mix well. Spray all leaf and lower trunk surfaces thoroughly, with special attention to the tree base.
Tip: Elm leaf beetles overwinter in protected locations, such as wood piles, leaves or other debris. Keep areas near elm trees free of these potential winter hideaways.
Always read product labels and follow the instructions carefully.
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Sevin is a registered trademark of Tessenderlo Kerley, Inc.