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College of Food, Agricultural, and Environmental Sciences


Viburnum Chewer Makes Its Way Into Ohio

November 6, 2002

WOOSTER, Ohio -- Ohio landscapers, nursery managers and home gardeners should begin examining their viburnums a little closer. A new exotic pest has just arrived in town --and it’s hungry for the popular woody ornamentals. The viburnum leaf beetle, Pyrrhalta viburni, was recently discovered in the extreme northeastern corner of Ohio in Ashtabula County. A European import, the voracious insect was first found in North America in 1947 in the Niagara peninsula of Ontario, Canada. The first sighting of the pest in U.S. territory occurred in 1996 in New York state. Since then, the beetle has spread into a number of northeastern states, including Pennsylvania. "We are concerned because the viburnum leaf beetle is a very damaging, invasive pest," said Dan Herms, an entomologist with Ohio State University’s Ohio Agricultural Research and Development Center (OARDC). "Unlike most leaf beetles, it will kill plants after only a couple of years. It’s a threat for both the landscaping industry and native populations of viburnum." The viburnum leaf beetle can cause severe defoliation. Both the adult and the larva feed on leaves between the midrib and larger veins, which gives the foliage a lace-like, or skeleton, appearance. Plants that have been defoliated for two or three consecutive years may die. In addition, the beetles’ egg-laying activity damages stems. Females chew deep, round holes in small twigs and deposit their eggs in them. The orifices are then covered with a mixture of excrement, chewed wood, and a special cement secreted for such purpose. These dark-colored "caps" are very evident and unsightly, sharply contrasting with the light-colored bark. The economic impact of this intruder on Ohio’s landscape and nursery industry could be significant if the pest gets out of control. "Viburnums are one of the top ornamental crops produced by Ohio nurseries," Herms pointed out. "And the leaf beetle is just a county away from Lake County, where one third of the state’s nursery industry is located." Viburnum leaf beetles overwinter as eggs, which are laid from late summer to the first frost. At that time of year, monitoring should be done by looking for the brownish egg-covering caps, which are found in a straight line on the underside of the twigs. The eggs hatch in May, and the larvae begin feeding on developing leaves. Very small and dark-colored when they first emerge, the larvae reach 10 to 11 mm when mature. The first signs of feeding injury appear as small pin pricks or holes in the leaves. By June, the skeletonizing becomes quite apparent. In June, larvae drop or migrate to the ground to pupate in the soil. Adult beetles emerge in late July. They are about 4.5 to 6.5 mm in length and brown in color. Adult feeding damage consists of irregular circular holes, and severe feeding can nearly defoliate shrubs once again. This leaf beetle is restricted to feeding on species of viburnum. It exhibits a strong preference for the popular arrowwood viburnum, European cranberrybush viburnum, American cranberrybush viburnum and mapleleaf viburnum. Resistant species are the Koreanspice viburnum and burkwood viburnum. "Sooner or later, this pest is going to spread throughout Ohio," Herms said. "The good news is that the beetles are fairly easy to control if you are diligent in monitoring. The best way to keep this potentially destructive pest from causing major damage is to isolate and eradicate populations as they develop. Early detection is essential." Beetles associated with leaf damage should be positively identified through assistance from Ohio State University Extension or the Ohio Department of Agriculture. For more information, contact county offices of OSU Extension. Both OARDC and OSU Extension are part of Ohio State University’s College of Food, Agricultural, and Environmental Sciences.

Mauricio Espinoza
Dan Herms