We are seeing a huge increase in the amount of viburnum bushes affected with the viburnum leaf beetle. The damage from these pests can be quick and devastating. The beetles “skeletonize” the leaves of the viburnums with damage looking strikingly similar to Japanese beetle feeding, but of course we will not have the pleasure of those pests for another month or so. The larvae feed on the leaves of the shrubs and in some cases can nearly completely defoliate them.
Later this spring the larvae will drop off the leaves into the soil below. At this point they will pupate and emerge sometime in July as adult beetles. The adults will also feed on the viburnum leaves. The adults will then fly (and they fly very well, which allows the pest to spread quickly) and find a viburnum suitable to be the host for their eggs over winter. The adults lay the eggs in pits that are chewed into the stems of the bushes and they will remain there until the next spring.
Pyrethroids as well as insecticidal soaps and horticulture oils have shown varied control in studies. We have found the best results from a once per year treatment of imidacloprid. We now feel we can control these pests with no problems if they are found before too much damage has been done. This has halted and prevented new damage from occurring in our customers’ landscapes.
Overall, this is a very aggressive pest that can devastate viburnums. I recommend an inspection of all viburnum shrubs whether or not damage is yet to be seen. If the beetles and/or damage is found, I highly recommended to quickly find the treatment option that best suits you.