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Elm Leaf Beetle |
By Judy Sedbrook, Colorado Master GardenerSM, Colorado State University Cooperative Extension, Denver County
The elm leaf beetle is a serious pest of elm trees in Colorado and also a nuisance in houses. They feed on elm tree leaves, causing them to dry up and die and giving the affected trees a general brown color. Trees weakened by repeated damage may be prone to limb dieback and wind injury. The elm leaf beetle during an outbreak may damage all elm species but prefers the Siberian elm.
The adult elm leaf beetle is about 1/4 inch long, yellowish to olive green, with a black stripe along its back on each side of the wing cover.
Adults overwinter in protected locations such as homes, garages, and woodpiles and under yard debris. They will not infest the house, but simply spend the winter there. They do not reproduce or cause damage and are often overlooked during the winter months. They are noticed in the spring when it warms up and they begin to move about and leave the house. By mid-spring they will have all gone outdoors or died.
In spring they fly to elm trees, depositing yellow, lemon-shaped eggs in groups of 25 or more on the undersides of leaves.
Elm leave beetle larva
Both larvae and adults feed on the leaves, skeletonizing them if the attack is severe. Most trees will not be killed unless the defoliation is severe for two or three consecutive years. Elm leaf beetles do not transmit Dutch elm disease.
CONTROL:
Biological:
- Natural enemies that feed on elm leaf beetle pupae include predacious stinkbugs and plant bugs. A small wasp that develops in the insects may also kill pupae and a fungus disease may also kill some.
- Bt (Bacillus thuringiensis) insecticides that are effective against elm leaf beetle include M-One and Novodor.
Prevention:
- Preventing invasion of elm leaf beetles into the home in the fall will forestall nuisance problems in the winter. Prior to mid-August through September, when beetles move into homes, seal all cracks and have window and door screens in place.
Chemical:
- Control of these insects should be directed toward the larvae and adults on the trees. To minimize leaf injury to elms, apply an insecticide after the eggs have hatched and while the larvae are small.
- Insecticides useful for control of elm leaf beetle when applied as foliar sprays are acephate (Orthene), bifenthrin (Talstar), carbaryl (Sevin), cyfluthrin (Tempo), deltamethrin (Deltaguard), spinosad (Conserve), neem (Azatin) or permethrin (Astro).
- A commercial aerosol of pyrethrins or propoxur (Baygon) can be used indoors. Follow label instructions.
- If all entry points cannot be identified, an insecticide can be applied around the outside of the building.
- Large numbers indoors can also be controlled with a household aerosol spray containing pyrethrins.
- Some control of elm leaf beetle populations is possible by banding trunks with an insecticide that has been registered for use on elm or shade trees. Larvae that crawl across the band are killed. The advantages of trunk banding include ease of application, reduction of pesticide drift, and reduction of pesticide quantity used. This should be done before larvae start to crawl down trunks in search of pupation sites, usually in mid to late June.
- Systemic insecticides injected into the tree trunk are effective against the elm leaf beetle but are limited to commercial applicators. They move through the sap of the elm and are ingested by the insect when they feed on the leaves.
Physical:
- Insects found inside can be removed by hand, with a vacuum cleaner or by other physical means.
- During warm periods the beetles congregate on windows and walls in the home. At this time they can be controlled best by vacuuming.
- Periodic sweeping or a shop vacuum can destroy larvae and pupae that gather at the base of a tree.
For more information of elm leaf beetles, see CSU Fact Sheet 5.521.
Photos: Judy Sedbrook
