Fall is a good time to control viburnum leaf beetles
Control viburnum leaf beetles in fall and winter to lessen damage in spring.
Viburnum leaf beetle, Pyrrhalta viburni, a relative newcomer to Michigan landscapes, has quickly affected the health of many viburnums in southern and central areas of the Lower Peninsula. First seen in Michigan in 2003, it attacks many of our native viburnums, including arrowwood viburnum (Viburnum dentatum), American cranberrybush viburnum (Viburnum opulus var. americana), mapleleaf viburnum (Viburnum acerifolium) and downy arrowwood viburnum (Viburnum rafinesquianum). Cornell University has a list of susceptible and resistant viburnums available online, or you can call the Michigan State University Extension Lawn and Garden Hotline at 888-678-3464 for more information on susceptible varieties.
Viburnums are loved for their flowers and some for incredible fragrances, and are abundant in landscapes across Michigan. This large group of shrubs fits almost any landscape, with varying shapes and sizes. It is incredible to think this small insect can have such a serious impact on plants that are hardy and easy to grow.
At first, viburnum leaf beetle feeding may not be noticeable, leaving small, oval-shaped holes in leaves. After just a couple of seasons, viburnum leaf beetle populations can swell to the point where plants are being defoliated. Continued defoliation from year-to-year will stunt plants and may even kill them.
Viburnum leaf beetles impact viburnum shrubs through all stages of their life cycle. Leaves are fed upon by the larval and adult stages of the beetle. Small twigs are damaged as the females chew holes into twigs to deposit her eggs.
From mid-summer into early fall, female beetles lay eggs into twigs. These excavated holes are about 1 millimeter in diameter and are mostly found on the current season’s growth. The female viburnum leaf beetle can lay up to 500 eggs annually, resulting in a surge in the viburnum leaf beetle population in just a few years. After laying about eight eggs per hole, she then covers the hole with chewed bark. These egglaying sites are usually found in rows on the underside of twigs and branches.
As leaves drop this autumn, scout viburnum plants in the landscape for twigs and branches where eggs have been laid. Egglaying sites that are found can easily be pruned out during the dormant season. Removed twigs should then be destroyed or disposed of to prevent hatching larvae from feeding on the plants next spring.
Be proactive! Removal of just a few small branches may prevent hundreds of leaf beetles from damaging viburnums next spring.