Another invasive insect has arrived in our region, the viburnum leaf beetle. It has been moving westward and this is the farthest west it has been detected.
The larvae and adults can severely defoliate the leaves from viburnums. Viburnums are a very common landscape shrub around homes and commercial buildings.
Most insecticides are quite effective in controlling the insect, but lack of treatment over time will often result in the death of the shrub.
The viburnum leaf beetle, Pyrrhalta viburni (Paykull), is from Europe. It arrived in the United States in 1996 in western New York. It spread south and west and reached northeastern Ohio in 2002.
Mansfield had been its farthest western movement.
The beetles are golden-brown and will have a metallic luster in full sun. They are easily seen, being one-quarter to three-eighths-inch long. Mature larvae are worm-like, white to beige, and about a half-inch long.
Viburnum leaf beetles spend the winter on stems in the egg stage. Larvae will emerge in early to mid-May and feed on the underside of leaves. They will skeletonize the leaves, consuming tissue between the veins and leaving only the major veins and midrib intact.
Larvae will mature by early to mid-June, drop to the ground, and pupate in the soil. Adults will emerge in early July and feed on the leaves.
Feeding will leave irregular circular holes in the leaves. Generally, it takes eight to 10 weeks from egg hatch to adult emergence.
Adults will feed, mate, and lay eggs on terminal twigs until the first killing frost. Female beetles will chew holes on the under-surface of terminal twigs, or new growth, as egg sites.
Egg sites are about one-eighth-inch in diameter and arranged in a straight row. Each site will contain around five eggs.
Females will place a protective cap over each egg site made from excrement, chewed bark, and glandular insect glue. One female can lay up to 500 eggs.
Viburnum leaf beetles only feed on viburnums. Landscapers selected viburnums for excellent foliage, striking and fragrant flowers, attractive fruit and interesting winter appearance.
Viburnums all have opposite leafing or branching arrangements, that is, a pair of leaves at the same point on the stem opposite of each other.
They are generally known for clusters of white flowers in the spring and attractive fall foliage. Different species range in height from two to 30 feet.
Several species are native to Ohio such as arrowwood viburnum (Viburnum dentatum), American cranberrybush (Viburnum trilobum), and blackhaw (Viburnum prunifolium).
Some viburnums are more susceptible to the viburnum leaf beetles than others. Arrowwood viburnum is the most susceptible and Koreanspice viburnum the least.
Viburnum leaf beetles are easily controlled with insecticides, but applications should be avoided during flowering to protect bees and other pollinators. Systemic insecticides also work, but should not be applied until after flowering for the same reason.
For individual plants and small viburnum plantings, the most effective control measure is to remove infested twigs after egg laying has ended in the fall and before hatch the following spring.
Until now, viburnums have had few pest problems. Individuals will need to inspect viburnums in the future for viburnum leaf beetle. However, this pest is manageable.
Additional information on the viburnum leaf beetle may be found at http://ohioline.osu.edu/sc195/013.html; at http://www.hort.cornell.edu/vlb/manage.html; and at http://www.hort.cornell.edu/vlb/suscept.html.
If you are not sure if shrubs are viburnum, bring plant samples, that is, a stem with leaves, to the Hancock County Extension Office. Ohio State University Extension Master Gardener volunteers can assist in shrub identification.
Lentz is extension educator for agriculture and natural resources for The Ohio State University Extension Service in Hancock County. He can be reached at 419-422-3851 or via email at lentz.38@osu.edu.
Lentz can be heard with Vaun Wickerham on weekdays at 6:35 a.m. on WFIN, at 5:43 a.m. on WKXA-FM, and at 5:28 a.m. at 106.3 The Fox.

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