What has been a perennial problem in commercial orchards has also become a significant problem on many home grounds. Significant populations of either meadow voles, Microtus pennsylvanicus, or pine voles, Microtus pinetorum, have invaded home grounds in locations on Long Island. Plant injury from vole feeding can be severe enough to cause significant decline and/or death of ornamental or garden plants.
Pine voles prefer a light loamy soil. They live primarily in a series of connecting underground tunnels that are usually less than 1 foot deep. Entrance holes 1-2 inches in diameter may be noticed in gardens, home orchards, near trees and shrubs, or in plant beds. The subterranean habits of pine voles makes controlling these animals difficult. Occasionally they will come above ground to forage on vegetation. You may sense a spongy feeling while walking on ground underlaid with numerous subsurface tunnels. The principal foods are listed as bulbs, tubers, seeds and bark (root bark included). On Long Island, we have seen them damage roses, fruit trees, bulbs, ornamental trees, shrubs, and flowers as well as vegetable garden plants.
The total length (head and body) of the pine vole is from 3 to 4 inches. They have a relatively short tail, less than 1 inch in length, and it is less than or equal to the length of the hind foot. The adults' fur is smooth, soft, chestnut brown in color, and lacks guard hairs. Their eyes are small, and ears are inconspicuous.
Pine voles produce several litters of young per year, usually from March to November. Litters average about 3 offspring each. The young are ready to breed in 2 or 3 months. Pine voles can have a high survival rate because their underground habits help protect them from predators. Family units maintain year-round exclusive territories.
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 which have had their roots chewed is another common observation. 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 (Microtus pennsylvanicus) may also be a problem in the home landscape and garden. The total length (head and body) of the meadow vole is 3 1/2 - 5 inches. The tail is much longer than that of the pine vole, and is one of the characteristics that can be used to distinguish between the two species. The tail is 1 1/2 - 2 1/2 inches in length, and at least twice the length of the hind foot. The adults’ fur is coarse, and a dark brown color mixed with black. Their eyes and ears are larger than those of pine voles, but still much smaller than those of field mice (Peromyscus spp.).
Meadow voles live primarily above ground or in shallow surface tunnels or runways. These runways can sometimes be observed in lawns or in snow cover. Nests made of interwoven strands of dry grass are baseball-sized food caches. The females maintain exclusive territories during the breeding season, and the males are mobile. Meadow voles are listed as feeding on grasses, sedges, seeds, grain, bark and some insect parts. These voles will 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.
Voles require vegetation or other cover in order to survive. By eliminating or reducing this cover one reduces their 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 problems. Certain mulches are more likely to attract voles than others. Avoid using mulches which have 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 the grass growing 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, 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 you tie it 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 which is effective is the SHERMAN TRAP*. It is a box type trap constructed of aluminum and galvanized steel. Researchers have been able to eliminate a high percentage (90+% in some research trials) of voles per acre using these traps baited with apple pieces. The SHERMAN TRAP used in research plots is model SNG and it's dimensions are 2 x 2.5 x 6 inches.
Snap-back mouse traps baited with small apple pieces can be an economical alternative. Peanut butter can also be an effective bait, but will attract more non-target mammals (i.e. shrews, and field mice).
Trapping is most successful when done in autumn (late October through November). Trapping can also be effective in spring after snow cover has melted, however, winter vole damage has already occurred by this time. Trapping during the summer may not prove as successful because there is plenty of food available for voles at that 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.SHERMAN TRAPS are set primarily above ground. You should select sites near entrance holes and in grass runways used by voles. Dig the soil away slightly so the trap will lay on the bottom surface of the runway. Next cover the trap with an asphalt roofing shingle by draping it over the trap to exclude sunlight. Voles are more likely to enter traps covered in this manner and the shingle also keeps non-target animals from disturbing the trap.
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.
Currently the only rodenticides** labeled for vole control in non-crop areas, (i.e., lawns and ornamentals) are restricted-use pesticides. For this reason they can only be purchased and used by a professional pesticide applicator who is licensed with the New York State Department of Environmental Conservation. It is recommended that these only be used in locked, tamper-proof bait stations and according to label directions.
* SHERMAN TRAPS are available from H.B. Sherman Traps, Inc., P.O. Box 20267, Tallahassee, Florida, 32316. Telephone (850) 575-8727. FAX (850) 575-4864. At this time the company is not supplying retail stores. You can order directly from the company. If possible try to have a local garden supply or hardware store order a quantity of the traps for you and your neighbors. This could be a more economical way to purchase the traps.
** Rodenticide - a pesticide used to control rats, mice, rabbits, and their relatives (from: Pesticide Applicator Training Manual, 2nd Edition).
12/94 Prepared by: Thomas Kowalsick, Horticulture Consultant, Cornell Cooperative Extension - Suffolk County and Dr. Paul Curtis, IPM Wildlife Specialist Department of Natural Resources, Cornell University.
9/99 Slight Revision: TK