Voles may be tiny, but they can do serious damage to shrubs during the winter by stripping off their bark.
By Larry Hodgson
Question: One of my 6 ft (1.8 m) tall lilacs had the bark at its base stripped away by field mice. They had been sheltering there in the winter. Is there a technical way like silicone spray or something else to protect the shrub from bacteria? I don’t want to lose it.
Answer: This kind of damage is indeed often caused by voles, commonly called field mice. They are short-tailed rodents barely any bigger than a mouse. There are more than 150 species of voles found throughout the northern hemisphere. In North America, the most common species is the meadow vole (Microtus pennsylvanicus); in Europe, the common vole (M. arvalis).
During the summer, voles, being small and nocturnal, are rarely noticed. In addition, they feed discreetly on seeds, leaves, insects, etc., rarely doing any noticeable damage. Therefore, they go under the radar of most gardeners.
They’re no more visible in winter, but are nonetheless very active under the snow. They dig tunnels into it so they can move around, safe from predators. However, when the ground is frozen and they run out of their favorite foods, they look for subsitutes. That includes the bark of our shrubs and young trees. Also, they sometimes eat tulip bulbs and chew on the roots of our perennials.
And this is all done “under cover of snow!” You have no inkling that anything is wrong until the snow melts and reveals the damage. And by then, it’s too late to react!
A secondary effect is also seen on lawns. When the snow melts, you discover vole trails 1 to 2 inches (2.5 to 5 cm) wide carved into lawns where the grass has been trampled and gnawed back and which lead to shallow burrows. Usually, a lawn will recover from this damage fairly quickly, but it still drives lovers of perfect lawns crazy.
What Can You Do to Save Your Shrub?
When voles strip the bark off the lower parts of a shrub, this leaves a circle without bark all around the stem. This is called girdling. And when this happens, there is essentially nothing you can do to save the upper part of the branch. Without bark to carry sap, the flow of nutrients, water and other materials to and from the shrub’s root system will stop. Then the girdled stem will die.
Painting or spraying the exposed wood with pruning paint or paste (I really wouldn’t recommend silicone) has no advantages. If no sap can cross the gap, you’d just be wasting your time. The upper part will die anyway.
What you can do is to cut the shrub back. Cut off the girdled stems (there may be more than one) just below the wound. A new stem will soon sprout and grow to replace the old one. Within 2 or 3 years, your lilac will likely have fully recovered.
This is sort of a forced version of renewal pruning (also called rejuvenation pruning). It’s a well-known technique gardeners use to give aging shrubs new vim and vigor.
Most multiple-stemmed shrubs readily produce new branches from below the wound and soon recover fully. In fact, many recover within a year of pruning. The lilac is actually slower to react than most shrubs.
Trees Are More Difficult
So much for multi-stemmed shrubs, such as your lilac. But what about single-trunked trees?
If a tree is girdled, it’s much more serious. Most will not resprout from their base. So, it’s essentially game over. (There is still no need to spray anything.)
Even trees that have the capacity to resprout from the base (cottonwoods, willows, elms, etc.) won’t always give you the results you want. Certainly not if they are grafted trees. Yes, many grafted trees will grow back from the base if you cut off the top, but won’t give you the tree you wanted.
That will be the case with most fruit trees. Nurseries generally graft these onto a rootstock, a fruit tree of unknown value and almost always producing fruits of inferior quality. If such a tree regrows from its base after girdling, it won’t be the original cultivar, but something resembling the wild tree. An eating apple, for example, like ‘Liberty’ or ‘Macfree’, will give something like a wild crabapple. A ‘Crimson King’ Norway maple, grown for its dark red leaves, will produce a plain green Norway maple. There is no use in even trying to save such a tree.
If there is still some bark connected, that’s a different situation. In other words, voles removed some bark, not without fully girdling the stem. This is a situation where you might try to save the tree.
Normally, if the trunk still has bark going halfway around the trunk or more, it can recover and produce new bark to cover the wound. Even trunks with less than a 50% covering sometimes survive, but the chances decrease. And it will take years for complete healing to take place. In most cases, it would still be wise to remove even a partially girdled tree and replace it with an intact one.
If you do decide to try and save a partially girdled tree, it’s certainly easy enough to do! Just clean up the wound and remove any shards or extraneous material. Then let it be. Do not apply silicone (I must admit that’s the first time I’d heard of anyone using that product on plants!). And there is no need to apply tree wound dressings, pruning paints, latex paints, wrappings and other alleged protective barriers either. They were once popular, but arborists no longer use or recommend such protective coatings. They tend to trap diseases on the trunk and then lead to serious fungal infestations.
Just leave the wound open to the air. Ma Nature will take care of it!
One Last-Ditch Treatment
There is a solution to saving a fully girdled tree, though, but not one usually employed by home gardeners. Or even nurseries. More something you that specialist orchards might use.
What you could do is to carry out a “bridge graft.” This a graft of strips of live bark placed so that they reach from the bark below, then over the wound and join the living bark above. If bridge grafting works, it will allow sap to flow again to reform. The tree can then recover.
You can find information on bridge grafting here: Restorative grafting.
Don’t Let Voles Strip Bark From Shrubs
The best treatment for voles is prevention.
In the fall, you can protect sensitive stems from damage with an anti-rodent spiral, wire mesh, traps or other means. I suggest you read For Vole Control, Act Early.
On the other hand, if you discovered damage this spring, be aware that the vole population has undoubtedly dropped significantly since winter. And will rebound massively only in 3 to 4 years. That’s because vole populations vary a lot. So, after a winter when voles attack the bark of shrubs (a sign that the population was overabundant), it tends to drop drastically. So, it’s not next winter that you need to act, but rather in fall 3 or 4 years from now.
Voles: be prepared in the fall if you don’t want to have to take care of their damage the following spring!