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Thursday, July 12, 2012
Viburnum Leaf Beetle
There's a New Pest in Town: Viburnum leaf beetle
The Viburnum leaf beetle (Pyrrhalta viburni) is native to Europe. In the United States it hasbeen found in only a few states, including New York, Ohio, Pennsylvania, Maine, Vermont and Massachusetts. The first confirmed occurrence of the beetle in Illinois was documented in 2009 in Cook County. A second occurrence was confirmed last week in DuPage County. Should we panic? No. Should we be alert and looking for this pest? Definitely! Early detection is important for management of any pest.
Egg laying damage
This is a pest of concern because it has the potential to be a serious defoliator of viburnums. The beetle overwinters as eggs in the tips of stems. The egg-laying damage usually occurs in rows. The eggs are laid in holes chewed by the adult. The holes are then covered by a cap of chewed bark. These caps are fairly easy to see as they are darker than the stem.
The eggs hatch into larvae in the spring, usually in May. The larvae vary in color. They may be pale green, pale orange or yellow. They do have a distinctive pattern of black spots along their sides and a row of black dashes running down their backs. At maturity, the larvae are a little less than half an inch long. The larvae chew on the undersides of new foliage, skeletonizing it.
Viburnum leaf beetle
When mature, the larvae crawl to the ground, usually in mid-June, and pupate in the soil. Adults emerge from the soil (early July) and also chew on the leaves. Their feeding damage forms irregular round holes in the leaves. The beetles are about ¼ inch long and generally brown in color. On close inspection golden hairs can be seen on the wing covers of the adult beetle (figure 5). The adult beetles will be mating and laying eggs from summer into fall. There is one generation of the beetle each year.
Viburnum leaf beetle feeds only on viburnums. Several viburnums are susceptible, including arrowwood viburnum (Viburnum dentatum),
European cranberrybush viburnum (V. opulus), American cranberrybush viburnum (V. trilobum), and Rafinesque viburnum (V.rafinesquianum). Other hosts include Sargent viburnum (V. sargentii), wayfaring tree (V. lantana), nannyberry (V. lentago), and blackhaw viburnum (V. prunifolium). Resistant viburnums include Korean spice viburnum (V. carlesii), Burkwood viburnum (V. burkwoodii), doublefile viburnum (V. plicatum var. tomentosum), Judd viburnum (V. × juddii), lantanaphyllum viburnum (V. × rhytidiophylloides), and leatherleaf viburnum (V.rhytidiophyllum).
Heavy and repeated defoliation by the viburnum leaf beetle can lead to death of the shrubs. Management of this pest can include several practices depending on the time of year. From October through April twigs with eggs in them can be pruned out and destroyed. Insecticides can be used on the larvae in May when they are feeding, and on the adults in summer when they are feeding. University of Illinois Extension suggests the insecticides containing one of the following ingredients: carbaryl, cyfluthrin and permethrin.
To report this pest:Illinois Cooperative Agricultural Pest Survey is interested in monitoring where this pest is found. To report the viburnum leaf beetle at your location go to their websitehttp://www.inhs.illinois.edu/research/CAPS/ for instructions on reporting the beetle.
Help with identifying viburnum leaf beetle:Trees "R" Us, Inc. can help you identify this pest and provide a treatment for it. If you are not in the Trees "R" Us, Inc. service area, there are some agencies that can help you with identification of the beetle. They include:
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Trees "R" Us, Inc. services the north shore, north suburbs, and northwest suburbs of Chicago. We are a full service tree company providing quality tree care, tree trimming, pruning, stump grinding, and plant health care by certified arborists.