| FOR IMMEDIATE RELEASE | CONTACT: Patricia Denke |
| May 12, 2004 | (406) 444-3790
TTY (406) 444-4687 |
EDITORS: A photo of an elm leaf beetle can be downloaded here.
Elm Leaf Beetles Mostly Nuisance, May Threaten Trees
HELENA, Mont. — Warmer weather and open windows have brought an invasion of tiny beetles to some Montana homes, particularly those situated near elm trees.
Elm leaf beetles are mostly a nuisance but can threaten stately elms that are already stressed by recurring drought, says Patricia Denke, entomologist at the Montana Department of Agriculture. Beetles are about one-quarter inch long and olive green to black in color. Adults overwinter in attics, windowsills, and other protected areas.
Both the adult and larval stages of the elm leaf beetle feed on elm leaves. Two or more generations of the insect occur each summer, Denke says. The second generation is more numerous, more noticeable and more damaging. When damage is severe, leaves may be skeletonized or curl and fall off prematurely.
Overwintering adults start laying eggs on leaves as soon as they emerge on the trees. Larvae mature in two to three weeks and fall from the trees or crawl down the trunk in search of crevices or sheltered ground areas in which to pupate.
Elm leaf beetles should not be confused with elm bark beetles, which transmit Dutch elm disease and kill large trees. Leaf beetles are mostly aesthetic pests, except where trees are already stressed by other causes.
Full-tree spraying of insecticides for elm leaf beetle is not advised for several reasons, says Will Lanier, entomologist at Montana State University. Even professional landscape services may have difficulty getting adequate spray coverage on large trees. Insecticides also kill beneficial insects such as parasitic wasps, which may worsen the problem.
A band application of pesticide or a sticky substance such as Tanglefoot Pest Barrier can be applied to tree trunks before larvae begin to migrate down the trunks to pupate. Sticky barriers can leave a stain on tree trunks and may need to be reapplied during the season for maximum effectiveness. One way to minimize staining, Lanier says, is wrap duct tape around the tree and apply the sticky barrier over it, taking care to adhere the tape tightly to avoid gaps through which the insects can pass without contacting the material.
Using a shop vacuum to periodically remove larvae from around the base of the tree also can help reduce future generations without the use of pesticides, he says.
Thorough watering of trees may help minimize stresses related to defoliation.
For more information on landscape pests, contact Patricia Denke, entomologist at the Montana Department of Agriculture at (406) 444-3730 or by e-mail at agr@mt.gov, or Will Lanier at the Montana State University Insect Diagnostic Lab at (406) 994-5690. A Colorado State University fact sheet on elm leaf beetles is available online at: http://www.ext.colostate.edu/PUBS/INSECT/05521.html.
