Sunday, October 18, 2009

Organic gardening Control of voles and Meadow Mice

The following information was gathered from several sources on the internet.

Cultural Methods and Habitat Modifications
Weeds, ground cover and litter provide food and cover for voles. Eliminating them in and around crops, lawns and cultivated areas will reduce the capacity of these areas to support voles. Lawn and turf should be mowed
regularly, and mulch, if used in orchards, cleared 3 feet or more from the base of trees.

Soil tillage is effective in reducing vole damage since it removes cover, destroys existing runway burrow systems and kills a percentage of the existing vole population. Because of tillage, annual crops tend to have
lower vole population levels than perennial crops. Voles nevertheless are capable of invading and damaging annual crops, especially those that provide them with cover for extended periods of time.

Repellents containing Thiram or a "hot sauce" type of ingredient are registered for meadow voles. These products (as well as products registered for other vole species) may afford short-term protection, but this has not been demonstrated in many areas of the country.

Toxic Baits
Toxicants have been a mainstay in vole damage control. Zinc Phosphide has been the toxicant most frequently used. It is a single-dose toxicant available in pelleted formulation. Zinc Phosphide baits generally are broadcast at rates of 6 to 10 pounds per acre., or placed by hand in runways and burrow openings. Although pre-baiting (application of a non-toxic bait prior to applying toxic bait) is not usually needed to obtain good control, it may be required in some situations such as when a population has been baited several times and bait shyness has developed. ZP Gopher Bait is the best zinc Phosphide bait to kill voles.

When voles are numerous or when damage occurs over large areas, toxic baits may be the quickest and most practical means of control. Take necessary measures to ensure the safety of children, pets, and non-target animals; follow all product label instructions carefully.

Anticoagulants, often referred to as multiple-feeding baits, interfere with an animal's blood-clotting mechanisms, eventually leading to death. They are probably the safest type of rodent bait for use around homes and gardens because they are slow acting, must be consumed over a period of 5 or more days to be effective, and there is an effective antidote, vitamin K1. Anticoagulant baits are available at many county agriculture commissioners' offices as well as at retail stores.

Some anticoagulants such as brodifacoum and bromadiolone cannot be used for voles because of the potential risk they pose to predators such as cats and dogs; check the label carefully to ensure that the bait has voles or meadow mice listed.

Because the pest must feed on anticoagulant baits over a period of 5 days, the bait must be available until the vole population is controlled. Usually baiting every other day for three applications is effective. As with trapping, bait placement is very important. Place the recommended amount of bait in runways or next to burrows so voles will find it during their normal travels. Generally, spot treating (placing bait in a specific place, such as a runway) is the preferred method of baiting, but if there is a heavy ground cover or if the area to be treated is quite large, broadcasting might be a better option if the label allows it. When broadcasting bait, be sure to spread it evenly over the infested area. If you use this technique, you will probably have to broadcast every other day for a total of three or four applications.

When voles are not numerous or when the population is concentrated in a small area, trapping may be effective. Use a sufficient number of traps to control the population: for a small garden a dozen traps is probably the minimum number required, and for larger areas at least 50 or more may be needed. A simple, wooden mouse trap baited with a peanut butter-oatmeal mixture or apple slices is commonly used. Often, no bait is needed because voles will trigger the trap as they pass over it.

Trap placement is crucial. Voles seldom stray from their runways, so set traps along these routes. Look for burrows and runways in grass or mulch in or near the garden. Place baited traps at right angles to the runways with the trigger end in the runway. Examine traps daily and remove dead voles or reset sprung traps as needed. Continue to trap in one location until no further voles are caught, then move the trap to a new location 15 to 20 feet away. Destroy old runways or burrows to deter immigration of new voles to the site.

Bury dead voles or place them in plastic bags in the trash. Because voles may carry infectious pathogens or parasites, do not handle them without rubber gloves; you can use a plastic bag slipped over your hand and arm as a glove. Once the vole is removed from the trap, hold it with your "bagged" hand and turn the bag inside out while slipping it off your arm and hand. Be sure to keep small children and pets out of the area where you have set traps.

Though voles rarely invade houses, when they do they can be controlled by setting snap traps (see Victor Snap Traps with expanded trigger) or live traps (the Tin Cat is best) as you would for house mice. To protect
non-target wildlife from injury, you can use a combination of snap traps and Tin Cats. Simply place two snap traps inside your Tin Cat, with triggers facing the entry holes. This prevents birds and other wildlife from being
hurt by the snap traps. Only mice and voles will be able to enter the Tin Cat.

Trapping is not effective in controlling large vole populations because time and labor costs are prohibitive. Mouse snap traps can be use to control a small population by placing the trap perpendicular to the runway with the trigger end in the runway. A peanut butter-oatmeal mixture or apple slices make good baits for trapping voles

Wire fences at least 12 inches above the ground with a mesh size of 1/4 inch or less will help to exclude voles from entire gardens. These fences can either stand alone or be attached to the bottom of an existing fence. Bury the bottom edge of the fence 6 to 10 inches to prevent voles from tunneling beneath it. A weed-free barrier on the outside of the fence will increase its effectiveness.

Young trees, vines, and ornamentals can also be protected from girdling with cylinders made from hardware cloth, sheet metal, or heavy plastic that surround the trunk. Support or brace these devices so that they cannot be pushed over or pressed against the trunk. Also, make sure they are wide enough to allow for tree growth and, in areas with snow, are tall enough to extend above snow level. Bury the bottom of the protective device below the soil surface to prevent voles from digging under it. Individual milk cartons, tin cans, or plastic soda bottles can also be cut at both ends to fit over small plants. Be sure to frequently check protective devices to
make sure meadow mice have not gnawed through or dug under cylinders and are hidden by the tree guard while they feed on the tree.

Commercial repellents are available for protecting plants from voles but their effectiveness is questionable and their use is often not practical. They must be applied before damage occurs. Voles usually damage plants at or just beneath the soil surface, making adequate coverage difficult or impossible. Do not apply repellents to food crops unless such use is specified on the product label.

Biological Control
Many predators, including coyotes, foxes, badgers, weasels, cats, gulls, and especially hawks and owls, eat voles. However, in most cases predators cannot keep vole populations below damaging levels. Many predators simply do not hunt close to homes and gardens where control is needed. Most predators have a broad-based diet and readily shift to alternative prey when the number of voles declines. Predators rarely, if ever, take every last vole thus, a residual population remains. With their extremely high reproductive potential, any remaining voles could repopulate an area in a short period. With this potential for severe damage, a homeowner or gardener cannot afford to wait for a predator to appear, but must take immediate action to prevent the loss of valuable plantings. Effective, immediate action usually involves baiting or trapping and habitat modification.

As with all animals, natural constraints limit vole numbers. Because populations will not increase indefinitely, one alternative is to do nothing and let nature limit the voles. Experience has shown, however, that around
homes and gardens the natural population peak is too high and damage will be above tolerable limits.

Other Control Methods
Burrow fumigants are not effective for the control of voles because the vole's burrow system is shallow and has numerous open holes. Electromagnetic or ultrasonic devices and flooding are also ineffective against voles.

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