VIBURNUM LEAF BEETLE
Dr. Leonard Perry, Extension Professor
University of Vermont
Viburnum are popular ornamental shrubs with attractive spring or summer flowers, often followed by attractive berries and colorful fall foliage. There are several species and cultivars (cultivated varieties), some of which are native. Many of these landscape plants are being threatened and killed by a recent insect pest, the viburnum leaf beetle.
According to an Extension leaflet from Cornell University containing many details on this non-native invasive pest and its controls, this beetle is originally from Europe. It was first found in North America on the Niagara peninsula of Ontario in 1947, with the first breeding populations reported near Ottawa in 1978. In 1996, the first populations of this pest in our country were reported in upstate New York. Since then the pest has become established in eastern Canada, upper New England, and is spreading into Pennsylvania and Ohio.
What makes this pest such a problem is that it feeds rapidly, and can defoliate a shrub (eat all the leaves) in a few days, leading to death of the plant if this happens for two or three consecutive years. This pest has a fairly simple life cycle, beginning with larvae hatching from eggs in spring. These feed on leaves, then in early summer crawl down the stems to pupate in the soil. The adults emerge in midsummer, feed again on leaves, mate, and lay eggs which overwinter until next spring.
Luckily, not all viburnums are created equal when it comes to feeding preference of this pest. Species that are most resistant to this pest still may become partially infested yet usually have little or no feeding. The most resistant species you should consider for landscapes if this pest is in your area include the Koreanspice (carlesii), Judd (x juddii), doublefile (plicatum), leatherleaf (rhytidophyllum), tea (setigerum), and Siebold (sieboldii) viburnums.
The most susceptible species you should avoid planting, or consider replacing, if this pest is nearby include arrowwood (dentatum), possum-haw (nudum), and cranberrybush (opulus) viburnums. Still susceptible, yet not as much so, are the mapleleaf (acerifolium), wayfaringtree (lantana), Sargent (sargentii), and Wright (wrightii) viburnums. Many of the other species you may find are likely moderately susceptible.
If planting resistant species or replacing susceptible ones isnít an option, consider least toxic control options before reaching for an insecticide. There are several beneficial insects that feed on viburnum leaf beetle larvae, including lady beetle larvae and adults, lacewing larvae, and spined soldier bug nymphs. Adults of both the lady beetle and spined soldier bug also eat viburnum leaf beetle adults. An excellent website from Cornell University (www.nysaes.cornell.edu/ent/biocontrol/) has photos to learn how to spot these helpful garden insects.
Although there are some pesticides you can use to control this viburnum pest, several (including organic pyrethrins) are contact poisons that also kill the beneficial insects. A couple of least toxic organic insecticides that kill many viburnum leaf beetle larvae, yet least harm beneficial insects, are insecticidal soaps and products containing the fungus Saccharopolyspora. Keep in mind insecticides provide little control to eggs, or when you see the adults feeding. The best time to spray such products is in late April or early May when the larvae are emerging. Initital research indicates that horticultural oils applied in mid-April can kill many of the pest eggs.
So if you see feeding this summer by adult leaf beetles, donít instinctively reach for a spray that may only kill beneficial insects. Instead, consider planting resistant species. Also, start checking twigs closely from July through fall and winter for eggs. Look for rows of brownish-black bumps the size of pinheads that contain the eggs. These are easiest seen in fall when leaves drop. Pruning these infested twigs out is perhaps the best way to control the viburnum leaf beetle in future years.
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