Excerpt from Landscape Plant News, Vol. 15, No. 3, 2004, published by Landscape Plant Development Center, Box 444, Mound MN 55364

Viburnum Leaf Beetle, a Formidable New Pest in the Landscape

By Paul A. Weston, Sr. Research Associate, Cornell University

Viburnums, those diverse mainstays of the landscape, have long been considered to be relatively free from pests. Aside from the occasional aphid or looper, most insects native to North America don't bother these sturdy plants. A recent arrival from Europe is changing all that. The viburnum leaf beetle, Pyrrhalta viburni (Paykull), specializes on plants in the genus Viburnum, and the most susceptible species are killed after being attacked for a few seasons. Fortunately, not all species of Viburnum are susceptible. * * *

The viburnum leaf beetle is endemic to Europe and western Asia, and likely made its way to North America on infested nursery stock. * * *

It was found in the northeast corner of Ohio in 2002. * * *

What makes it such a damaging pest is the ability of both larvae and adults to feed on foliage of the same plants. Larvae, which emerge at the time the leaves bud out, skeletonize the young leaves, and adults attack any second flush leaves that may come out later in the season. This repeated defoliation quickly depletes the nutrient reserves of susceptible plants, leading to death in as few as 2-3 years following the start of an infestation.

Viburnum leaf beetles have one generation per year. They spend a good part of the year as eggs, which are laid throughout the summer months and into early fall. These eggs require a significant chilling period before they can hatch, which means that eggs laid in one season will not hatch until the following spring. * * *

Their feeding damage is quite distinctive in that they feed on leaf tissue between the veins, leaving "skeletons" of leaves. The fully grown larvae, which are about 1 cm in length, then crawl down stems of the host plant to the soil, where they search for a suitable site and then burrow into the soil. * * *

Viburnum leaf beetles feed only on members of the genus Viburnum, but not all species are attacked. Based on our observations, the most susceptible species are V. dentatum, V. opulus, V. opulus var. americana (formerly known as V. trilobum). * * *

Other species of Viburnum are eventually killed by viburnum leaf beetle, but these species generally are not attacked significantly until the most susceptible species are destroyed. This group includes V. lantana. * * *

Small-scale infestations can be managed by pruning out egg-infested twigs anytime between October and April, but larger scale infestations will likely require the use of pesticides. * * *

Viburnum leaf beetle is in North America to stay. Plant propagators, nursery operators, and landscape managers will all need to adjust the way they do business with viburnums to adapt to this most unwelcome guest in the landscape.