Viburnum shrubs have always been considered among the best options for pest-free landscape plants, but unfortunately, a sneaky little insect newer to North America seeks to change all that. Native to both Europe and Asia, viburnum leaf beetles were first spotted in North America in 1978, in the Ottawa-Hull region of Canada. Since then, the pests have made their way south from Canada into the United States, beginning first in New York state where they were spotted in 1996, and eventually spreading throughout the northeast (though there have also been viburnum leaf beetle sightings in Wisconsin and Illinois). They're a close relative of the more commonly-seen elm leaf beetle and can very quickly strip the leaves from viburnums plants thanks to their large numbers and voracious appetites.
Viburnum Leaf Beetle Appearance
Viburnum leaf beetles are rather bland looking for an exotic pest, making them easy to miss on your plants if you don't know what you're looking for. When fully matured, viburnum leaf beetles are about a quarter-inch long and a dull brown, while their larva measure about one-third an inch long and are a yellow-brown shade, allowing them to blend into the foliage better for protection.
Viburnum Leaf Beetle Feeding
Both the larva and the adult viburnum leaf beetles feed on viburnum leaves, chewing a lace-like pattern into the foliage and skeletonizing the plant in a relatively short amount of time. Feeding typically begins in the early summer months and, while initial infestations will not kill the plants, defoliation for two or three consecutive years can be fatal to the viburnum.
While all viburnum plants are susceptible to a beetle infestation, there are certain varietals that are more at-risk than others. The viburnum leaf beetle has three known favorite varieties of viburnum plants—it's wise to avoid planting these specific types if you want to lower your chances of an issue. They include:
- European highbush cranberry (Viburnum opulus)
- Wayfaring tree viburnum (Viburnum lantana)
- Rafinesque viburnum (Viburnum rafinesquianum)
Viburnum Leaf Beetle Lifecycle
Viburnum leaf beetles overwinter as eggs deposited onto the branches of the viburnum plant. They hatch in May, and the larvae begin to feed on the leaves that are emerging for spring. Since the newly hatched larvae are so small, the first signs of injury to the plant may very easily be missed, as the damage can appear as holes no larger than a pinprick, almost invisible to the naked eye.
Sometime in June, the larvae will make their way into the nearby ground, where they will pupate in the soil. The adult viburnum leaf beetles will emerge in the latter part of July, where they will continue to feed on the viburnums—within a month, the skeletonizing of the plant's leaves will be hard to miss.
Female viburnum leaf beetles can lay eggs from late summer to the first frost, which can sometimes mean as many as 500 eggs per season. The female will chew holes in the new growth of viburnum and lay eggs in each hole—the holes are then covered with a mix of chewed twig and excrement, making them harder to notice. One sure sign eggs have been laid on your plant: The holes will form a straight line on the underside of the twig and the eggs will overwinter there until they hatch in spring. Altogether, it takes about eight to 10 weeks for the viburnum leaf beetle to go from egg to adult.
How to Control Viburnum Leaf Beetles
The best protection against viburnum leaf beetles is to plant resistant varieties of the viburnum plant. Just like there are some varietals that the beetles prefer to eat, so too are there ones that they typically steer clear of, allowing to you get the beauty of the shrub without the added hassle of having to worry about bugs. Luckily, beetle "resistant" varietals include some of the most popular landscape viburnums, like:
- Doublefile viburnum (Viburnum plicatum)
- Korean Spice viburnum (Viburnum carlesii)
- Leatherleaf viburnum (Viburnum rhytidophyllum)
If you already have viburnum shrubs in your landscape, keep a close watch on them throughout the year for signs of an infestation. In the early spring (before the eggs hatch) this means carefully examining the small twigs from the previous year’s growth for any evidence of egg-laying holes and scars. Increasing temperatures can cause those holes to swell, allowing the "caps" to fall off and eggs or larva to emerge. If present on your plant, you will need to prune out and destroy all infested wood before the eggs have a chance to hatch.
As new leaves begin to open on your viburnum throughout the summer, continue to check both sides of the leaves for larvae and again prune and destroy any obviously infected plant parts. If necessary, chemical pesticides are most effective when applied while the larvae are young. Adult viburnum leaf beetles tend to fly away or drop to the ground when disturbed and are often not eradicated completely with spraying. For the most effective treatment of a severe infestation, check with your local extension service for recommended pesticides.