We have seen for the past 2 years here in the Cleveland area Viburnum leaf beetle (Pyrrhalta viburni) destroying many Viburnum. So it’s best to be on the alert for the pesky insects this spring. They attack only viburnum, which is a good thing. Viburnum in a shady location are more susceptible to beetle infestation than the same variety planted in the sun.
Inspect your Viburnum for clusters of eggs now to significantly reduce the damage, by destroying the eggs before they hatch into larvae in mid to late spring. The larvae feed for several weeks on viburnums during their vulnerable stage. They often go unnoticed until the damage is already done. Then the larvae pupate in the soil. Adults emerge in early summer and feed on viburnum leaves until late summer. So catch them early!
Treat your viburnum most effectively now with systemic application of Imidacloprid on the soil around the base of the shrub. The chemical will be taken up by the shrub and distributed throughout the foliage. The entire plant will be protected for one year by this application. Zergott Garden Center carries Bayer Advanced 3-in-1 Insect, Disease and Mite Control in ready to use spray bottles for smaller viburnums. There is larger size with a garden hose adapter which is ideal for more mature viburnum. Bayer Advanced Complete Insect Killer is rainproof within one hour. Bayer Advanced 12 Month Tree & Shrub Protect & Feed Dual Action Formula is a concentrated liquid that can be diluted and poured at the base of the shrub. It combines protection and fertilization in a single product. We also have Annual Bonide Tree & Shrub Insect Control and Bonide Systemic Insect Spray, with a hose attachment to shoot up to 25 feet.
If you want an organic approach, you can apply insecticidal soap to control the small larvae. But you must apply this soap very thoroughly to the underside of the leaves where the larvae feed. You may need to do this more than once. This soap will not control larger larvae and adults. This technique may be more difficult on larger varieties and multiple plantings.
According to Cornell University specialists, the varieties that are most resistant to the Viburnum Leaf Beetle which we sell are: V. Carlesii (Korean Spice), V. x Juddi (Judd Viburnum), V. Plicatum (Doublefile Viburnum), V. Plicatum Var. Tomentosum (Doublefile Viburnum). These varieties prefer sun or part shade. Remember that these viburnum can still get eaten by the Viburnum Leaf Beetle but they are the most resistant to the insect.