Voles are small rodents that commonly referred to as meadow mice or field mice. Voles are often referred to as pests as they can be troublesome in the garden, but they are an important food source for many local predators including coyotes, snakes, foxes, and owls. They are most easily recognized by their short tail (about 1" long, with the long tale vole as the exception). They are 4" to 8.5" in length with gray to brown fur. Voles have short lifespans - 8 weeks to 16 months - but have a very high reproduction rate. It can be common to have large population fluctuations that range from 14 to 500 voles per acre. An individual's surface range is usually less than 1/4 acre. Voles prefer shelter with heavy ground cover of grasses, grass-like plants, or litter. They are active day & night and year-round. Voles construct tunnels and surface runways with many burrow openings to find food and for protection. This intricate network of tunnels and burrows provide them with excellent shelter from the weather and protection from predators.
DO I HAVE A VOLE PROBLEM?
It's fairly easy to spot if you have a vole problem - there will be a well-traveled, above-ground runway system that connects the burrow openings; This system of runways leads to multiple burrow openings that are each about 1 - 1/2" to 2" in diameter. The runways are usually hidden beneath a protective layer of grass or other ground cover and will be easily found by pulling back any overhanging vegetation.
DAMAGE CAUSED BY VOLES
Voles can cause extensive damage. Most damage occurs in the winter when voles move through their grass runways under the protection of snow. The greatest damage seems to coincide with years of heavy snowfall.
Signs of vole damage*:
Trees & shrubs have has girdling and patches of irregular patterns of gnaw marks about 1/16" to 1/8" wide
Stems that are gnawed may have a pointed tip
Roots of trees and shrubs have girdling
Fortunately, voles pose no major public health problems because of their infrequent contact with humans. However, they can harbor diseases, such as plague and tularemia. For this reason, voles should never be handled. If you have to handle a vole, or any other species of wildlife, you should wear the appropriate protective clothing (e.g., leather gloves).
* Damage by rabbits: browsed stems clipped at a smooth 45-degree angle and wider gnaw marks.
* Damage by deer: browsed stems with a rough and jagged edge.
CONTROL METHODS (bullet points expanded below)
Voles are classified as non-game wildlife in Colorado and may be captured or killed if they create a nuisance or cause property damage. Destroying old runways or burrows to deter immigration of new voles to the site is one of the most important components to vole control.
Method options include:
Habitat management (best long-term solution)
This is the best long-term solution for vole control. To do this effectively:
Clean-up with the elimination of weeds, ground cover, and litter around lawns and ornamental plantings can reduce habitat suitability for voles and lead to a decreased vole population.
Destroy vole runway-systems with soil cultivation. This may kill voles outright. This also makes annual plantings less susceptible to vole damage than perennial plantings. Consider planting annuals over perennials for a season or every planting season if the problem persists.
Mow your lawn in the fall before the snow arrives. Damage to lawns can be reduced by a close trim and by mowing & removing tall grassy cover near lawns. To repair damage to lawns from vole runways: rake, fertilize, and water the affected area (see a nursery associate for lawn care & fertilizing timetable).
Exclusion is done by using 1/4" hardware cloth or mesh cylinders (available at most hardware stores) to keep voles away from an individual plants. Bury the cylinder 6 inches or more below the ground surface and rise 18" above the ground. This ensures that voles will not burrow under the hardware cloth and gain access to the plant. This is an effective method of mitigation.
Repellents include: Thiram™, capsaicin/hot sauce, castor oil, and predator odors (like urine). These will require regular reapplication. These can help, but limited data is available for the effectiveness of repellents. As with habitat management, destroy old runways to prevent other voles from moving in.
When voles numbers are small or when the population is concentrated in a small area, trapping is effective. You will need to use a sufficient number of traps to control the population. For a small garden, a dozen traps will suffice. For larger areas, 50 or more may be needed. Traps can be a simple, wooden mousetrap with bait like a peanut butter-oatmeal mixture or an apple slice. Voles rarely stray from their runways, so set traps along these routes. Look for burrows and runways in grass or mulch in or near the garden or flowerbeds. Place baited traps at right angles to the runways with trigger end in the runway. Bait can be unnecessary needed because voles will trigger the trap as they pass over it.
Examine traps daily and remove dead voles and/or reset traps as needed. Trap in one general location until no further voles are caught, then move the traps to a new location 15' to 20' away. As with habitat management, destroy old runways to prevent other voles from moving in.
Rodenticides are usually a short-term solution to damage by voles, especially when compared to the method of habitat management, which is usually long-term. Doing this should only be supplemental to other methods - do not rely on this management technique alone.
If you decide to use a chemical pesticide for vole control, you will be reapplying toxic chemicals to your yard multiple times per season. These chemicals also affect other ecosystems, so please read, fully understand, and follow all of the label guidelines.
2% zinc phosphide (ZP) bait is used for vole management. ZP can be found in pellet form. Fall (before snow cover) is the best time of year to use ZP baits on lawns. Application of bait in the spring (after snow melt) is usually ineffective.
POISON BAIT RULES:
Be cautious when applying pesticide. Birds, other wildlife, pets, and the greater ecosystems can inadvertently be harmed
To avoid harm to birds, do not apply ZP bait on the bare ground, areas without vegetation, or in piles
Do not apply ZP to crops destined for use as food or feed, it is toxic
Wear rubber gloves to avoid contact with the ZP - small amounts can be absorbed through skin
Wear the proper protective clothing and equipment (a mask, goggles, gloves, etc.) and take extra care to avoid breathing or contact with ZP particles
Apply with care and follow all guidelines on the label
Predators like hawks, owls, coyotes, foxes, and badgers eat voles. However, predators often cannot keep vole populations low. Predators rarely, if ever, can hunt every last vole; so a residual population will remain and can repopulate quickly. This will not be the most effective method in managing a vole problem. Like all animals, populations can not increase indefinitely, one alternative is to passively let nature limit the voles.
Electromagnetic or ultrasonic devices (to scare them), flooding, and fumigants are alternative methods, but they have all been shown to be ineffective for reducing specifically voles.
* Resources: The City of Denver, Colorado State University.