Viburnum Leaf Beetle Info
Viburnum Leaf Beetle are invasive insects which feed on the leaves of many popular types of viburnum. Even many of the Illinois native viburnum are susceptible to damage from Viburnum Leaf Beetle. The insects larvae will chew holes in the leaves in spring (typically early to mid-May). After this, the larvae will change form (pupate) in the soil. In early summer (typically late June or early July), the adult insect will emerge from the soil and chew pill-shaped holes in the leaves. Throughout the summer and into early fall, the female insect will drill small holes into the branches of the plant, lay eggs inside, and then cover the holes with a saw-dust like material for protection. Each female can deposit up to 500 eggs.
It is important to treat your viburnum if you start to see damage, since infestations of Viburnum Leaf Beetle can grow very quickly. Left untreated, Viburnum Leaf Beetle can completely defoliate a plant and can lead to the plants overall death.
When selecting viburnum, it is important to choose ones that are resistant to Viburnum Leaf Beetle, especially if you have already had previous infestations close by. The most susceptible species of viburnum are American cranberrybush viburnum (V. opulus var. americanum) and arrowwood viburnum (V. dentatum). The most resistant species of viburnum are Judd viburnum (V. x juddii), Koreanspice viburnum (V. carlesii) and doublefile viburnum (V. plicatum x tomentosum)
Treatment & Control Methods
Once you have identified that you have Viburnum Leaf Beetle, there are a few methods to fully control the insect. In spring, spray a contact insecticide on the leaves of the plant to kill the larvae while they are feeding. Wasco Nursery’s preferred contact insecticide is Hi-Yield’s Bug Blaster (Bifenthrin). In late-spring / summer, apply a systemic drench to the soil around the plant to target the adult insect. Systemic drenches need to be applied AFTER flowering to reduce risk of harming pollinators. Wasco Nursery’s preferred systemic drench is Bonide’s Annual Tree & Shrub Insect Control (Imidacloprid) In late fall, winter or early spring, apply a horticultural oil to the branches where the females laid eggs. This will help to prevent some of the eggs from hatching to reduce the amount of larvae that feed on the plant. Wasco Nursery’s preferred horticultural oil is Bonide’s All Seasons Horticultural Spray Oil.