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Damage Control
Natural Controls: Hawks, owls, snakes, weasels, raccoons, foxes, opossums, and house cats all feed on voles. These predators are beneficial in orchards because they help keep vole populations under control. Whenever possible, growers should encourage these predators, or at least not harass or kill them. When natural controls are inadequate, artificial methods must be used to control vole populations. The fall is the best time for initiating control programs. A number of different control methods are listed below. The greatest success is usually achieved by using a variety of techniques at once.
Habitat Modification: In orchards, the major food sources for voles are normally not the fruit trees, but roots and stems of grasses and other groundcover. As a result, habitat modification (e.g., reducing or eliminating grasses and cover) is one of the best long-term methods of controlling voles. Repeated mowings that maintain groundcover at a height of 3 to 6 inches serve to limit both food and cover and expose voles to predators. Where possible, mow both between trees in a row as well as along tree rows. Delays between mowings result in excessive vegetation, which, when cut (especially with a sickle-bar mower) forms a thatch layer that protects voles. A flail or rotary mower is preferred to reduce thatch.
Establishing vegetation-free zones that extend at least 2 feet from tree trunks will discourage voles from living near the bases of trees, where they cause the most damage. Vegetation-free zones can be established by mowing, applying herbicides, cultivating, or placing a layer of crushed stone or gravel 1 to 2 inches deep extending 15 to 18 inches from the trunk. Do not allow mulch, prunings, or decaying vegetation to accumulate around the bases of trees or in tree rows.
Exclusion: Hardware cloth barriers can be used to keep voles from girdling small trees. Wrap a strip of 0.25- inch or smaller mesh hardware cloth around the base of each small tree. The hardware cloth should be set 4 to 6 inches into the ground and be approximately 18 to 24 inches high. Use higher guards where snow might be deep. Tree guards should be large enough to allow for 5 years of growth. This method is very effective but extremely labor intensive and expensive when a large number of trees need protection.
Repellents: Several repellents are registered for voles. The primary active ingredient in these products is capsaicin (the "hot" in hot peppers). It is not clear how effective these products are at deterring voles. If you need to protect a large number of plants, repellents could become too expensive. As with most repellants, they should be applied before damage is significant, and always follow label directions.
Trapping: Trapping is not an efficient way of controlling voles in large orchards, but it is an effective and safe control method in small orchards or around selected trees. Use standard wooden-base snap traps (mouse size) and bait them with peanut butter, oatmeal, or apple slices. For meadow voles, place the traps in runways, flush with the ground and perpendicular to the runway. Place the trigger end directly in the runway. For pine voles, locate a tunnel and place the trap within the tunnel and perpendicular to it.
Summary: Keep the grass mowed as if it were your front lawn. This is an excellent way to control rodents. Rodents require lots of cover to keep their natural predators--hawks and cats--from finding them. If the cover is removed, voles won't stay in the area. Use snap traps to help maintain populations at low levels.