Voles

Meadow voles (Microtus pennsylvanicus) occur throughout most of the northern  and eastern United States in low wetlands, open grasslands, and orchards. They are most active above the ground but they sometimes live underground where the soil has been cultivated or where a burrow system is already present. Pine voles (Microtus  pinetorum) live throughout the eastern half of the United States and favor open woodlands and orchards.They spend much of their time in underground burrows and usually have an extensive  subsurface trail system that is excavated about 1 to 2 inches deep. Their burrows open to the surface and often connect to above-ground runways. Significant populations of either vole occasionally invade home lawns. Plant injury from vole feeding can be severe enough to cause significant decline and/or death of ornamental or garden plants.

Pine Voles

The pine vole is a stocky little rodent with a blunt nose, short legs, and a tail that  is shorter than the head-and-body length. Adult meadow voles are larger than pine voles, have longer tails, and have dark brown fur. A number of other physical, social, and ecological differences distinguish these two species.

The subterranean habit of pine voles makes controlling these animals difficult.  Occasionally they will come above ground to forage on vegetation. A person may sense a spongy feeling while walking on ground underlain with their numerous subsurface tunnels. The principal foods are bulbs, tubers, seeds, and bark (root bark included), but they have been known to damage roses, fruit trees, bulbs, ornamental trees, shrubs, and flowers as well as vegetable garden plants.

In many cases the damage from pine voles goes unnoticed until the owner discovers the decline or death of a particular plant. In vegetable gardens entire plants may be pulled partially or entirely underground. Wilted plants with chewed roots are commonly observed. In flower and bulb gardens, plants may fail to grow in the spring after underground tubers, roots, and bulbs have been consumed by pine voles. At times the entire root system of smaller ornamental trees, shrubs, and fruit trees are chewed. The plant can actually be pulled out of the soil very easily, or it may fall or lean over. Larger trees and shrubs may have bark girdling on the roots or at the basal area of the trunk which will cause decline and/or the death of the tree.

Meadow Voles

Meadow voles may also be a problem in the home landscape and garden. Their runways can sometimes be observed in lawns or in snow cover. Nests made of interwoven strands of dry grass are baseball-sized food caches. Meadow voles feed on grasses, sedges, seeds, grain, bark, and some insect parts. They also feed on the bark of trees, girdling the trunks at or near the ground surface. The girdling may be higher in the winter months if snow cover exists. Sometimes roots may be damaged.

Management

Early detection and control is important in vole management. Application of toxic bait is the quickest and most effective method for removal. Broadcasting baits across the orchard floor by hand, spreader, or airplane is the most common method of application. However, placing baits directly in runways and burrow openings may be a more effective way to control pine voles, especially when they confine their activity to below a heavy thatch layer or below thick vegetation on the ground. Adherence to safeguards will foster efficacious use of toxic baits for the control of voles in orchards.

Eliminating or reducing vegetation or other cover one reduces voles’ preferred foods, exposes them to predators, and exposes the animals to severe weather. In home grounds, mulch around plants may serve as an excellent cover for the voles. Deep mulch in gardens and plant beds should be reduced and/or avoided where voles are known to be a problem. Certain mulches are more likely to attract voles than others; avoid using mulches with fine or small particle sizes. Large sized crushed-stone mulch and pine bark mulch may reduce vole tunneling. Plastic and landscape fabric mulches may increase vole populations and subsequent damage.

Maintain bare strips of soil under the drip line of trees and shrubs wherever possible. Consider bare soil in gardens and plant beds where possible. If mulch is used, keep it as far away from the trunks of plants as possible. Frequent mowing of grass around trees and shrubs will help to reduce the potential for vole injury.

Tree guards, constructed from 1/4-inch mesh galvanized hardware cloth, can prevent meadow voles from girdling trees. This will not work for pine voles, however, which usually girdle roots. Guards should allow enough room for 5 years of tree growth, and should be driven several inches into the ground (without injuring tree roots.) Be sure to overlap the hardware cloth where it is tied together and do not leave cracks where voles can get in. Check these periodically to be sure they are not restricting the growth of the trunk.

Trapping voles can provide additional population reductions. One trap that is effective is the Sherman Trap, a box-type trap constructed of aluminum and galvanized steel. Snap-back mouse traps baited with small apple pieces can be an economical alternative. Peanut butter can also be effective bait, but will attract more non-target mammals (i.e. shrews and field mice). Snap-back traps can be set above ground directly near vole entrances or in runways. Another method is to make an excavation across a tunnel and place a baited trap at the bottom of this excavation. Cover the exposed portion of the tunnel with a board, shingle, or other suitable material to exclude sunlight and prevent children and non-target animals from disturbing the traps.

Trapping is most successful when done in autumn (late October through November). Trapping can also be effective in spring after snow cover has melted, although winter vole damage has already occurred by this time. It is also necessary to pre-bait the location to be trapped at least 24 hours in advance of trapping. This can be accomplished by placing apple pieces into vole holes and tunnels. You will need to trap voles for at least 4 consecutive days to ensure good success.

The use of dried blood or fox or coyote urine has also been effective in repelling these animal pests. Follow directions carefully with the predator urine. Some formulations may need to be reapplied after a rain.

Adapted from Thomas Kowalsick, Cornell University, 2001