What is Viburnum Leaf Beetle?
The Viburnum Leaf Beetle (Pyrrhalta viburni) first arrived in southeastern Wisconsin around 2015 and, unfortunately, has established itself as a major pest on susceptible species of Viburnum. This imported pest is native to Europe and Asia and, as such, our native Viburnums have not had a chance to establish resistance and are especially vulnerable.
Viburnum Leaf Beetle Damage
Viburnum Leaf Beetle feeds only on certain species of Viburnum. They can quickly skeletonize leaves and defoliate entire plantings. Most damage is done by the larval stage in spring and early summer, but the adult beetles will also feed on foliage from mid-summer through fall.
Life Cycle: Larvae Stages
These beetles produce one generation per year. They overwinter as eggs in the Viburnum’s twigs and hatch in early May as tiny, light green/yellow larvae marked with rows of black dots. They begin feeding immediately on leaves. Due to their small size, you may notice damage before you see the insects. They grow through three developmental stages as larvae, molting, and growing larger at each stage.
Life Cycle: Adult/Beetle Stage
They reach the final stage of larval development in June, crawl down the stems and burrow into the soil. They remain in the soil for 10-14 days and then emerge as adult beetles. The adult beetles are light brown in color and approximately ¼” to ½” in length. They will continue feeding on leaves through the summer months, causing skeletonization.
The female beetles will chew holes into the slender stems, lay their eggs in these crevices, and then seal the holes with a mixture of the chewed wood fiber. A single female can lay up to 500 eggs in a season. These sealed cavities protect the eggs overwinter. Then they emerge in spring to begin the cycle again.
A healthy Viburnum plant may survive significant defoliation for one season; however, severe beetle damage will likely weaken or kill the plant after several seasons.