A couple years ago, I went on a tirade about the Viburnum Leaf Beetle attacking the shrub just outside my bedroom window.
The reason for my rant was not because of the insect itself, but because I didn't feel I had been give fair warning by those in the know about this newly-introduced pest and the damage it could do to one of the most of beloved flowering garden shrubs.
My plant, which was defoliated three times by this little monster only to bounce back each time because it refused to be defeated, is still living and thriving just where I planted it several years ago. I'm glad to see it is still plugging along, which I attribute to my ability to save it before it became weakened from the insects' constant attacks. I saved my shrub by learning the life cycle of this voracious pest and worked diligently to keep ahead of it. This meant near constant examination of the shrub, heavy pruning and lots of patience.
I like to think of my garden as a haven for birds and pretty much any other wildlife that wants to visit. Squirrels run around the trees and share in the birdseed we put out, and chipmunks frolic on the landscaping ties that line the front sidewalk. I suspect they are the reason I don't have crocus blooming any longer in early spring, but to be honest, I'd rather watch the chipmunks play.
The viburnum is an important part of the shrubs and trees that provide shelter and protection for the wildlife, not to mention that I love the way the white, snowball-size flowers cascade in front of the house.
When the insect invaded my garden, it wasn't widely known in this area. I spoke with other gardeners who had similar attacks, and some went to the extreme and culled all viburnum from their landscapes. I thought this was a bit harsh, but not everyone has the time or the desire to keep constant vigil over a plant when there are so many others that aren't bothered by this invasive pest.
It is nice to know that some birds will feast on the larvae, but even a flock of hungry birds can't keep up with a large infestation. These voracious eaters can strip a plant clean in 24 hours. Once the plant is defoliated, the larvae crawl down to the ground where they pupate and return as adult beetles. Just as the shrub has recovered from the first defoliation and has regrown many of those lost leaves, the adult beetles mount their own attack and once again the shrub is stripped clean.
After eating until there's nothing left, the beetles mate and deposit their eggs in individual chambers excavated in fairly straight lines on the undersides of new growth. Several eggs can be stowed in each cavity. After depositing eggs, the female beetle will cover the cavity with chewed bark and other nasty stuff she has secreted to protect the eggs over winter. According to information from Cornell University's Department of Entomology, the cover is spongy and porous, allowing water to seep into the cavities to provide humidity for the eggs.
I'm writing about this now to warn those who have viburnum and want to keep them, if you haven't already checked your shrubs for signs of insect larvae, now is the time before they hatch.
On the undersides of the branches, you will notice sewing stitch-like markings that are the egg cavities. Prune away those stems and destroy the clippings. Don't add them to the compost pile. Pruning actually can be done anytime from October to April, preferably before the larvae hatch, right around the time the plant is opening its leaves.
Fortunately, Viburnum Leaf Beetles only have one generation per year, but the entire process from egg hatch to adult beetle can take eight to 10 weeks. In addition, when there is nothing to feast on where they are, adult beetles can travel to the next available shrubs, which is how they came to visit me in the first place.
To keep viburnum healthy and beetle-free, beetle-watch must take place every year.