PEST ALERT: Keep an eye out for the Viburnum Leaf Beetle
The viburnum leaf beetle (VLB) is an invasive insect that feeds exclusively on and can significantly damage Viburnum species. VLB is native to Europe and has first been spotted in Milwaukee in 2014. The pest is now found scattered across much of Wisconsin. Over the last four years, VLB has rapidly grown to epidemic proportions.
Severe VLB infestations can cause complete defoliation of a viburnum shrub, as the beetles feed in both adult and larval stages. In spring, the VLB larvae chew holes in viburnum leaves creating a lace-like pattern. In late June and early July, VLB adults continue eating the tissue between the veins which skeletonize the leaves. If left unchecked, two or three years of heavy feeding will weaken the plant over time and can eventually lead to the death of the plant. Adult beetles are active until frost, and females will lay their eggs in the cavities they chew into the stems. Egg laying occurs from late summer into autumn, with each female laying as many as 500 eggs. Eggs remain in place through winter until they hatch the following spring.
What can you do? One of the easiest ways to reduce the population of beetles is to remove and destroy the twigs that bear the eggs. Egg infested twigs can easily be seen once the leaves have fallen. They can be removed from October through the following spring. Once twigs have been pruned, destroy them by burning (where permitted) chipping, composting or burying. There are also some beneficial insects that will attack the viburnum leaf beetle, such as lady beetles, lacewings, assassin bugs, and spined soldier bugs.
When necessary, a number of pesticides are effective in controlling VLB. Products containing carbaryl (Sevin) as the active ingredient or one of the pyrethroid insecticides (cyfluthrin, permethrin, resmethrin) are highly effective as foliar sprays. Only spray infested viburnum plants and try to avoid drift onto other plants to preserve beneficial insects in the yard and garden. Systemic products, such as Merit which contains imidacloprid, applied as soil drenches can also help. You should apply these products after flowering to minimize risks to pollinators, but before VLB damage occurs to achieve the best protection.