Beetles a threat to viburnums

It has been two years since the first viburnum leaf beetle was found in Hancock County. This invasive insect has the ability to cause severe defoliation in viburnums, a very popular landscape plant grown 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. Knowing the viburnum leaf beetle’s life cycle and the history of its movement across Ohio will assist in keeping this destructive pest in check.
The viburnum leaf beetle, Pyrrhalta viburni (Paykull), is a native of Europe. Documentation of its arrival to the U.S. was in 1996, being detected in western New York. It continued to spread south and west and reached northeastern Ohio in 2002. Mansfield was it furthest western movement until detected in Findlay.
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 one-half inch long.
Viburnum leaf beetles overwinter 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, 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. It generally takes eight to 10 weeks from egg hatch to adult emergence.
Adults will feed, mate, and lay eggs on terminal twigs (new growth) until the first killing frost. Female beetles will chew holes on the under-surface of terminal twigs 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, which are common landscape plants. Landscapers selected viburnums for excellent foliage, striking and fragrant flowers, attractive fruit and interesting winter appearance.
Viburnums, Viburnum ssp., all have opposite leafing or branching arrangements (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 pests. Individuals will need to inspect viburnums in the future for viburnum leaf beetles. Adult beetles will be feeding at this time through August.
Additional information on the viburnum leaf beetle may be found at the following websites:
http://ohioline.osu.edu/
factsheet/anr-39
http://www.hort.cornell.edu/vlb/manage.html
http://www.hort.cornell.edu/vlb/suscept.html
If you are not sure if shrubs are viburnum, bring plant samples (stem with leaves) to the Hancock County Extension Office. Ohio State University Extension Master Gardener volunteers can assist in shrub identification. They can also confirm identification of viburnum leaf beetles.
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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