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Identifying and Preventing Vole Damage

Introduction As the deep snows in our yards or on our properties recede, you may be greeted by one or more pathways in the snow (see photo). If you’re lucky, these paths only run from one burrow opening to another. Unfortunately, some of the trails probably lead to some of your favorite trees and the damage caused by the animals girdling (gnawing the bark off all the way around the plant) the tree will kill it. The furry culprit in this destruction? The vole. Also known as meadow mice, these small, stocky short-tailed rodents can cause severe damage in landscape, orchard, windbreak or timber plantings. They measure from 4 to 8.5 inches long and vary in color from brown to gray. They are pudgy, with blunt faces and small eyes, small and sometimes inconspicuous ears, short legs, and a short and scantily haired tail (the long-tailed vole is an exception). Voles are active day and night throughout the year. They usually live 2 to 16 months. Voles construct many surface runways and underground tunnels with many burrow entrances. Voles are extremely prolific, having three to six young per litter and three to 12 litters per year. Females may become pregnant at three weeks of age and voles breed almost year round. Large population fluctuations ranging from 14 to 500 voles per acre are common. Most vole damage occurs in the winter when voles move through their grass runways under protection of snow or where there are thick, tall grasses and weeds. Heaviest vole damage seems to coincide with years of heavy snowfall.

Damage and Control Vole damage to trees and shrubs is characterized by girdling and patches of irregular gnaw marks about 1/16 to 1/8-inch wide. Gnawed stems have a pointed tip. Do not confuse vole damage with damage by rabbits, which includes stems clipped at a smooth 45-degree angle and wider gnaw marks. Stems browsed by deer usually have a rough jagged edge. Voles also girdle the roots of trees and shrubs. Other signs of voles being present include: 1) 1- to 2-inch wide runways through matted grass and burrows; 2) visual sightings; 3) hawks circling overhead and diving into fields; and 4) spongy soil from burrowing activity. Trees that appear to be suffer from disease or insect infestation may be suffering from unseen vole damage. Methods to prevent and control vole damage are habitat management, exclusion, repellents, trapping and poison baits. Voles are non-game animals in Colorado and may be captured or killed when they create a nuisance or damage property.

Habitat Management Elimination of ground cover including weeds and tall grasses by frequent close mowing, tilling or herbicide application is the most successful and longest lasting method to reduce vole damage. Other methods include: Plant short grasses that do not mat or lodge such as buffalograss or blue grama. These will provide little protective cover and may reduce vole numbers. Summer removal of vegetation around fruit trees provides some protection because voles avoid exposed areas. Remove tall grassy cover near plantings voles may damage. Plant crown vetch (a legume unpalatable to voles) in areas bordering orchards and field boundaries to limit vole populations. Important predators of voles include short-tailed shrews, badgers, coyotes, foxes, bobcats, barn owls, great horned owls, long-eared owls, short-eared owls, barred owls, screech owls, and some snakes. Predators can help significantly reduce vole populations. Landowners should protect and encourage predators if they do not constitute a pest problem. Exclusion To protect trees and shrubs from vole damage, encircle them with 1/4-inch mesh hardware cloth or 3-inch diameter (young trees) Vexar plastic mesh cylinders. This barrier should project 18 inches above the ground and 3 to 6 inches below the surface.

Repellents Little data are available on effectiveness of repellents to deter vole damage. There are a variety of commercial repellents labeled for protecting tree seedlings, shrubs, ornamental plantings, nursery stock, and fruit trees from voles. Check with nursery supply stores Capsaicin (Hot Sauce Animal Repellent, Miller Chemical and Fertilizer Corp.) is labeled to protect various woody plantings from voles. The following home made repellent has also proven to be quite effective in keeping most animals away from given areas and plants. It must be reapplied after three to five days. Hot Pepper Repellent Recipe • One chopped yellow onion • One chopped jalapeno pepper • One tablespoon cayenne pepper Boil ingredients for 20 minutes in two quarts of water. Let the solution cool and then strain through cheesecloth. You can apply this with a tank-type sprayer or a spray bottle. Another home made repellent that has been shown to be effective in reducing deer and elk browsing and may reduce vole damage. 20% Chicken Egg Repellent A spray of 20% whole eggs and 80% water is effective, but to keep the sprayer from clogging, remove the chalaza or white membrane attached to the yolk before mixing the eggs. The egg mixture is weather resistant but must be reapplied in about 30 days.

Trapping Use mouse snap traps to remove small populations of voles from lawns. Place traps perpendicular to runways with the trigger mechanism in the runway and bait the trap with small amounts of peanut butter or a mixture of peanut butter and rolled oats. Set traps in the fall before most damage occurs.

Toxic Baits Rodenticides are a short-term solution to damage by voles. Habitat management usually is more successful than rodenticides for eliminating damage, particularly in orchards. Two percent zinc phosphide is the only legal grain bait in Colorado. It is a restricted use pesticide, so only certified applicators can use this material. Another toxic bait, Kaput©, has been labeled for vole control in placement packets. In this product, the active ingredient, Warfarin, is metabolized in about 42 hours according to the manufacturer, meaning the vole may not even be dead yet before the chemical is out of its system. This means a very small chance of secondary poisoning of non-target species that might eat voles killed by this product. This product is not a restricted use pesticide. Always use products labeled for use on voles and follow label directions. If you have other questions regarding vole management, contact your county’s Colorado State University Extension Office. Article modified from information in “Managing voles in Colorado”, W.F. Andelt and S. Ahmed, Colorado State University Extension, Fort Collins, CO. Fact Sheet No. 6.507

 

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