Voles, often called Meadow Mice or Field Mice, are common throughout the United States. These small, short-tailed/short-eared rodents will sometimes feed upon and damage plants in our gardens and orchards . Washington has six species but most damage in N.W. Washington is done by the Oregon Meadow Vole, Microtus oregoni (A.K.A. Creeping Meadow Vole), and Townsend's Meadow Vole, Microtus townsendii.
In the Winter of 1988, these little animals were responsible for an unusual amount of damage in local apple orchards by feeding on the roots and girdling trunks. Meadow Voles will also tunnel through vegetable and flower gardens, feeding on juicy roots, tubers and bulbs - damage that is often blamed on our poor, insect-eating Moles! Voles will even use the mole's tunnels when making these raids!
Leonard Askham with vole-damaged tree
How can you tell if you have a vole problem? Obvious signs include gnawed roots and root crops (note the small grooves left by the 2 large front teeth). In badly infested orchards, you can locate the dead trees during the dormant period by reaching out and giving them a wiggle. If they move very much, the entire root system is probably gone. In the growing season, damaged trees are leggy and thinly leafed with a reddish tinge to the foliage. If you pull the tree up, the underground part often looks like it was run through a pencil sharpener. Girdling of tree trunks extending to just above soil line (rabbits usually damage trunks and twigs higher up and leave larger tooth marks at 45° angles while Mountain Beavers generally clip the branches, leaving 2 inch stubs) and well-used tunnels through the soil and/or in the grass or thatch are other signs of infestation. Finally, voles often leave open, 1 inch holes in areas of heavy activity (moles always seal up their holes).
Vegetation management is a key issue in keeping vole populations low. In orchards, keep the tree rows free of vegetation at least 36 inches on both sides of the trunk. This can be done by weeding or by using a registered herbicide. If you are using a string weeder (Weedeater, Weed Whacker, etc,) be sure not to hit trunks. despite assurances that they are safe, they can injure the thin bark of young trees. Be very careful if you use mulches! Voles are often encouraged by a nice, loose mulch. Mow the grass in between rows and keep it short. Avoid thatch which the voles can hide under. (see EB1117, and EB0924). Finally, be sure to pick up all fallen fruit so the voles can not feed on it.
In gardens, try to keep surrounding areas free of tall grass and thatch and don't leave root vegetables in the ground over winter.
Biological: Almost all small meat-eaters love to feed on voles. By encouraging hawks, owls, coyotes, foxes,weasels and shrews you can help keep vole populations from exploding.
Mechanical: For small populations, trapping may be sufficient. Although use of body-gripping traps became illegal in Washington State in the 2000 elections, "common rat and mouse traps" were exempted so ordinary mouse-traps can be baited with peanut butter or apple and set IN the runs. Dig into the underground tunnels to place the traps and then cover with a board for the most effective set. Check traps daily and re-set as needed. Multiple-catch mousetraps (e.g. "Victor Tin Cat") will also work on the smaller species. Trapping is a very time-consuming method but useful where poisoned baits are not wanted or allowed. Tree guards, which are effective in controlling rabbit damage, will NOT discourage voles since they feed largely underground. In fact, voles have been known to nest under loose-fitting guards!Pitfall traps can also be used. These are simply tall cans or jars that are sunk into the ground so that the lip is even with the floor of the vole tunnel and covered with a board. These should be checked twice a day and the voles either released elsewhere on the property or euthanized.
trapped under apple tree
Chemical: There are few rodenticides registered for homeowner use against voles in Washington State. Mole/Gopher baits registered for home use may kill voles when applied to underground mole tunnels, according to the label directions for moles but they are not registered for use on voles so they can not be recommended specifically for controlling these animals.
Several rodenticides ARE registered for professional use on voles. Some are more water-resistant and acceptable to the mice than others. Parafinized anticoagulant baits applied according to label directions are probably the safest to use. ALWAYS READ THE LABEL BEFORE USING ANY PESTICIDE!!! Some of the chemicals registered include zinc phosphide (VERY toxic - decomposes quickly in damp situations), chlorophacinone and diphacinone (anticoagulants). Keep the bait as dry a possible to encourage feeding. Bait pellets MUST be placed into the burrows to be most effective and to minimize hazard to other wildlife.
How do you know where to place the baits? Damaged areas, tunnels and runways are always likely areas. However, since vole populations fluctuate wildly, it's a good idea to first place apple or carrot pieces in your various target areas and cover with a shingle or 12"x12" piece of cardboard (be sure the cover doesn't blow away). If there is no feeding on these materials within 24-48 hours, there are probably no voles in the immediate few square yards. You can save time and effort by working only where the rodents show feeding activity.
A week after you place the bait, put out some more apple or carrot pieces. If there is no feeding within a couple days, your baiting program was successful.
In order to discourage voles, it is most important to remove as much of the mouse's shelter as possible (grass, thatch, etc.). Locate the areas of feeding by setting out food and checking for feeding signs. Finally, the population can be reduced by trapping (for small areas) or using registered rodenticides according to label directions.
For more information contact your WSU Extension office.