Question
Sir;  I live in Divide, Colorado (http://www.parks.state.co.us/parks/mueller/Pages/MuellerHome.aspx) elevation 9000, USDA zone 4-ish and am an avid organic vegetable gardener. My soil has neutral pH, comparatively little natural nutrient (the native grasses suck it all up), and lots of gravel (I joke that I don't harvest my vegetables -- I mine them).  That said, with lots of grass clippings, rabbit droppings and other organic fertilizers, we do pretty well with it.  My trouble this year is with meadow voles.  They are really going after my peas and lettuces (and, to a slightly lesser extent, beans and other leaf vegetables).  I've got potatoes, onions and turnips and they seem to leave those alone.  I use traps (metal and glue), the granular mole/vole repellant, sonic repellants and a Golden Retriever to fight them, but the voles are definately winning this year.  Not one has been caught in a trap.  I would welcome any suggestion you may have to get rid of or otherwise stop them.  Thanks a lot.

Answer
Curtis, since you have followed every measure and precaution I take against moles and voles, I am sending you an article I found very beneficial in controlling these pests. This article is credited to The Internet Control of Wildlife Damage Management and written by John M. O'Brien.

Damage Prevention and Control Methods
Exclusion

Hardware cloth cylinders exclude voles from seedlings and young trees. The mesh should be 1/4 inch (0.6 cm) or less in size. Bury the wire 6 inches (15 cm) to keep voles from burrowing under the cylinder. Large scale fencing of areas is probably not cost-effective. Drift fences with pit traps may be used to monitor populations and can indicate when voles are immigrating to crops, orchards, or other cultivated areas.

Cultural Methods and Habitat Modification

Cultural and habitat modification practices can reduce the likelihood and severity of vole damage. Eliminate weeds, ground cover, and litter in and around crops, lawns, and cultivated areas to reduce the capacity of these areas to support voles. Lawn and turf should be mowed regularly. Mulch should be cleared 3 feet (1 m) or more from the bases of trees.

Voles can live in dense populations in ditch banks, rights-of-way, and water ways that are unmanaged. Adjacent crop fields can be cost-effectively protected by controlling vegetation through mowing, spraying, or grazing.

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

Frightening

Frightening agents are not effective in reducing vole damage.

Repellents

Repellents utilizing thiram (also a fungicide) or capsaicin (the 揾ot?in chilis) as an active ingredient are registered for meadow voles (see Supplies and Materials). These products (or repellents registered for other species) may afford short-term protection, but this has not been demonstrated. Check with your state pesticide regulatory agency for availability.

Toxicants

Zinc phosphide is the most commonly used toxicant for vole control. It is a single-dose toxicant available in pelleted and grain bait formulations and as a concentrate. Zinc phosphide baits generally are broadcast at rates of 6 to 10 pounds per acre (7 to 11 kg/ ha), or are placed by hand in runways and burrow openings. Although prebaiting (application of similar nontreated 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. Zinc phosphide baits are potentially hazardous to ground-feeding birds, especially waterfowl. Placing bait into burrow openings may reduce this hazard.

Anticoagulant baits are also effective in controlling voles. Anticoagulants are slow-acting toxicants requiring from 5 to 15 days to take effect. Multiple feedings are needed for most anticoagulants to be effective. In many states, one or more anticoagulant baits are registered for controlling voles.

In addition to broadcast and hand placement, anticoagulant baits also can be placed in various types of bait containers (Byers and Merson 1982, Radvanyi 1980). Water repellent paper tubes with an anticoagulant bait glued to the inside surface make effective, disposable bait containers. Tube size is about 5 inches (12 cm) long by 1 1/2 inches (4 cm) in diameter (Libby and Abrams 1966, Marsh et al. 1967). Bait containers protect bait from moisture and reduce the likelihood of nontarget animals and small children consuming bait.
Fumigants

Fumigants usually are not effective because the complexity and shallowness of vole burrow systems allow the fumigant to escape. They may work in new, small burrow systems with only one or two entrances.
Trapping

Trapping is not effective in controlling large vole populations because time and labor costs are prohibitive. Mouse snap traps can be used 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. Fall and late winter are periods when many vole species are easiest to trap.

Although voles rarely invade houses, in the event that they do, they can be controlled by setting snap traps or live traps (Sherman or box-type) as you would for house mice (see Trapping in the House Mice chapter).

Shooting

Shooting is not practical or effective in controlling voles.

Other Methods

A wide variety of predators feed on voles. Voles are relatively easy for most predators to catch and are active, and therefore available, day and night year-round. Despite their vulnerability and availability, voles are not usually 揷ontrolled?by predators. This is because voles have a high reproductive potential. Postpartum breeding is common and females may breed as early as 2 weeks of age. Synchronous breeding also occurs. These factors enable voles to increase at a faster rate than predators (Pearson 1985).

I hope this information helps. Please feel free to write again if you ever need assistance.

Regards,

Mike