Protection Against Voles
Voles are small short-tailed mice of the genus Microtus and are found throughout the Northern Hemisphere. These little creatures rarely cause problems during the summer. In winter, however, they burrow under the snow or forest litter, and hungrily eat away at the bark of trees (especially fruit trees) and shrubs. More rarely, they may also nibble the crowns of perennials and perennial vegetables. When the number of voles is limited, damage is usually minor, but when they reach the top of their population cycle (about every four years), voles can do an incredible amount damage, leaving many shrubs and young trees dead or dying and killing perennials (they seem to especially love Baptisia).
Cats allowed to wander outdoors are quite effective in keeping voles under control in regions there is little or no snow. Unfortunately, they are of little use in winter in areas where snow is abundant, as voles burrow into the snow and can then travel wherever they want undisturbed.
One control technique that works when the population is relatively low is to apply blood meal around susceptible plants: it helps to deter voles, because the smell of blood convinces them there is a predator in the sector. Unfortunately, blood meal alone is rarely enough during a year of population boom, as starving voles will overcome their fears and cross the olfactory barrier.
Spiral tree guards are widely available and can be placed around a the trunk of a sapling before the arrival of winter. Push the bottom end slightly into the ground or voles may work their way under the barrier.
While tree guards work well, they can be expensive if you need a lot of them. It is often cheaper to use a length of plastic drainpipe as a barrier. Cut the pipe to height required (from the ground to the lowest branches), then . slice pipe down one side so that it can be slipped around the trunk of the tree. Install your “sheath anti-vole” in late fall and remove it in early spring. You can also use chicken wire or hardware cloth to create a barrier around the trunk… but make sure this type of barrier stands on it’s own, as if it touches the trunk, the little critters will often manage to nibble off a bit of trunk through holes in the chicken wire.
While it is easy to protect young trees with a barrier of some sort, that isn’t the case with shrubs, as most branch abundantly at ground level. In their case, try spraying or brushing the stems with a bitter tasting rodent repellent (one containing thiram or capsaicin). This is often very effective. Wear gloves and cover your mouth and eyes: you won’t want physical any contact with these products, as they are very irritating to mucous membranes and even, in some people, to the skin.
Treatments to protect against voles are usually somewhat to very effective against other animals that eat the bark or eat the buds of young trees and shrubs during the winter, such as hares and rabbits.