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July/August 1996

Those Villainous Voles!
by Pamela Weil

It's been a rough spring for many Connecticut gardeners. Winter lingered with a late, heavy snowfall in April, and several killing frosts damaged plants in May. In addition to setting new weather records, 1996 may also be remembered as The Year of the Worst Vole Damage.

"I have a very large perennial garden, and by spring a third of it was eaten," says Sylvia Teeuwen (Cheshire). "We've always had a few voles," says Sydney Eddison (Newtown), "but there's been a population explosion this year. It's been devastating. Such a huge volume of roots was eaten that the entire bed sunk four or five inches. I've been gardening for 30 years and nothing like this has ever happened."

Why now? Why this year? "It was a good winter for voles," says Ed Marrotte, the Consumer Horticulturist for the University of Connecticut's Cooperative Extension System. "There was a beautiful snow cover and the ground wasn't frozen too deep, so digging was a lot easier for the voles and the snow layer protected them from predators." Voles damage plants by eating the roots of perennials and gnawing the bark of trees, sometimes girdling and killing the trees.

Two kinds of voles damage Connecticut plants: meadow voles (Microtus pennsylvanicus) and pine voles (Microtus pinetorum). Meadow voles are a little larger (3-1/2 to 5 inches) than pine voles (2-4/5 to 4-1/5 inches) and live primarily above ground or in shallow surface tunnels or runways. Pine voles live in a series of shallow, connecting underground tunnels. The entrance holes to their tunnels are about the size of a broomstick, 1 to 2 inches in diameter. "I call it a blind hole," says Marrotte, "because there's no soil on the outside."

So which kind of vole do you have? For positive identification, you'll need to trap one, but it's really not necessary. Control measures are the same for both, but pine voles are harder to control than meadow voles because they're underground most of the time.

Are any plants "vole resistant"? "They didn't touch either the daffodils or hellebores," says Sydney Eddison. "They also left the snowdrops alone." Hellebores were also spared in Judith D. King's (Farmington) garden, so perhaps there are a few vole resistant plant. But "they've had a go at virtually everything else," says Eddison, including roses, rhododendrons, euonymus, ornamental grasses, and all sorts of daisies. "They've eaten about 80% of my hostas and every single bit of Sedum 'Autumn Joy'. The only place I didn't lose all the hosta was in a bed immediately under a huge maple, where the roots are large and the hosta is jammed in the pockets among the roots."

As with deer, finding the best method for your garden requires some experimentation. A method that works for one gardener might not (and usually doesn't) work for another. Here are some suggestions, some "tried and true," others culled from reference books. Let's hope one will work for you.

Control Measures
"A hungry cat is your best line of defense," says Mary Ann McGourty (Norfolk). The three furry felines at Hillside Gardens keep the display gardens vole and mole free.

If you have moles in your garden, your first priority will be to get rid of the moles. Although the moles aren't eating your plant roots (they eat grubs and other soil insects), their tunnels provide the voles with "existing six-lane super highways to your plant roots," says Ed Marrotte. Control the moles by killing their food source, white grubs. Nematodes are a highly effective grub control for gardeners who don't want to use chemicals.

Some experts suggest you remove your garden mulch before winter, because it won't freeze solid (or freezes rather crumbly) which makes it very easy for voles and field mice to dig in for winter protection. However, if you do remove the mulch late in the season, you're also exposing some roots that are very near the surface that may freeze. Ed Marrotte suggests a compromise. He says, "I would leave the mulch there but I would keep it several inches away from the plant. Voles like to girdle at the crown line and this doesn't give them the opportunity."

During the winter, protect your seedlings and young trees from girdling damage with galvanized hardware cloth cylinders. The mesh should be 1/4 inch or less in size. Make a cylinder around the trunk and bury it 6 inches to keep hungry voles from burrowing under.

Repel the Voles
Will making life difficult for the voles send them off in search of pleasanter conditions in someone else's yard?

A product called MoleMed is derived from castor oil. It's diluted and used to water your gardens. King says, "I tried it this spring, but didn't have outstanding success. Although I do know of one nursery that has used it very successfully." There is a version of this product you can make yourself (see Homemade Methods).

The Mole Mover II, available in both a battery or solar power model, is another possibility. This device emits intermittent vibrations that "sound like a badger growling," according to Anita Ballek (East Haddam). "But, I don't even notice it anymore, and it's worked well for me for two years."

Ballek only recommends it for gardens under 75 square feet, and thinks that a key to its success may be the location of your garden. Ballek's garden is surrounded on three sides by driveways and on the fourth side with her house. If your garden is open on all four sides to vole infested grass or woods the Mole Mover II may not be as effective.

Protect the Bulbs
Ballek suggests planting some bulbs deeper (10 to 12 inches) to discourage the voles. "Lilies, large hyacinths and tall tulips will benefit from deep planting. Also, strategically placing sharp pea stone around the fleshy roots will make it harder for the rodents to dig to get at the roots."

A new product called Bulb Insurance claims to protect your tulips, hyacinths and crocuses. It's made of crushed oyster shells that are added to the soil at planting. The Gardener's Supply Company catalogue claims, "The first year (of use), bulb damage was reduced by over 90%."

Mary Jo Bridge Palmer (Greenwich) soaks crocus and tulip bulbs in Ro-Pel before planting them in the fall. She soaks them for at least one hour (you can leave them in the solution overnight), and lets them dry off before planting. "Squirrels will still dig them up but they won't eat or store them. Voles and moles don't bother them at all." She thinks that any product that repels by smell would probably work. If you're using a concentrate, dilute it according to the manufacturer's directions before soaking your bulbs.

Mesh Your Plants
Judith D. King says, "I have never lost a plant protected by quarter-inch hardware cloth. I cut lengths of the stuff into nine-inch strips and use it to encircle the planting holes of choice plants." Currently, King favors aluminum Gutter Guard mesh. It's inexpensive ($3.49 for a roll 6 by 20 inches) and because the edges are finished it's easier to install. "It's not as heavy duty as the hardware cloth. And so far, I haven't lost a plant."

Helen Sykes (Sudbury, MA) doesn't use the hardware cloth much anymore because it's expensive and hard to work with. Instead, she uses a fairly heavy-duty plastic mesh, which she orders by the roll (National Netting, 1-800-233-7896). It costs about $36 including shipping for a 3 by 100 foot roll. "When you order, just ask for the green plastic, 1/4 inch x 1/2 inch netting. I use galvanized nails to pin it together exactly like pinning something prior to sewing it."

Instead of surrounding one plant, Sykes digs a whole chunk, usually about 8 by 8 feet, and lines the bottom and sides with plastic mesh. "Not only is it much more economical and not as hard on my hands, it also makes it easier to move plants around. I usually leave a bit sticking up but even where it's flush with the ground the voles don't seem to cross it."

In three years, the voles have never chewed through the plastic (although they could) and Sykes hasn't lost one plant. The voles bump into it and would rather go around it. She has a very long garden area. "Each time I put a new bed in, the voles quickly dig tunnels all the way around it. In fact, at the edge of the protected beds is a very good place for trapping them."

Trap the Voles
Before setting your traps, identify the active tunnels. Look for a straight, not meandering, ridge just below the soil surface. Mash down part of the ridge with your foot and flag it. If the tunnel is rebuilt in a day or two, you know it's active.

Sykes has trapped over a hundred voles using ordinary mouse snap traps baited with peanut butter. She places a trap next to a hole and covers both the hole and the trap with an upturned large flowerpot secured with a large rock. She believes that the key to success is to use a lot of traps in an area where there are many entrance tunnel holes. She says, "We didn't have much luck trapping the voles in areas where there were few surface holes." And you must keep trying. Sykes found that summer was not a good time to trap voles; she was more successful in the spring and fall.

Again, this method doesn't work for everyone. Eddison says that with twelve traps, she caught just one vole this year. She says, "You have to be very fortunate and very vigilant with your traps. Also, it's a little bit hard to know which holes are the working holes. Even when you know where they're active, our voles seem to like the roots better than they like the peanut butter"

Here's a good suggestion from Landscape Problem Solver (Rodale Press, 1989). "The most effective way to reduce mice through trapping is to buy a large number of snap traps and plan a one or two-night massacre. Buying a few traps to catch mice over a long period of time does not work as well. A good technique is to bait the traps for two or three nights without setting them. Then when you finally do set the traps, you'll catch the mice by surprise."

Poison the Voles
If you choose this method, you want to be sure to poison the voles and not your dog, cat or toddler. Unfortunately, there isn't any way to guarantee that this won't happen. There are ways to package the poison bait to discourage curious children and pets, but they are not foolproof.

The directions on the product's box may advise you to drop the poison pellets or poison block directly into the vole hole, but one reader wrote about what happened after she did this: "Within ten minutes, a squirrel had dug one up, and to my horror ran next door! Where they have a dog and two small children."

Instead of dropping it into a hole, you can put the poison bait in a bait station. Bait stations can be purchased from catalogues, garden centers and hardware stores. Ed Marrotte recommends a bait station that you can make yourself for chunk bait (not pellet bait) from an 18 inch long piece of 1-1/2 to 2 inch diameter PVC plastic pipe. Lay the pipe flat on the ground and put the chunk bait inside. "The voles will go inside and eat it," says Marrotte, "and where I've recommended it to people there was a definite decrease in the population."

Connecticut gardeners have been successful with several poisonous rat and mouse baits including castor beans and commercial poisons. Castor beans look like beetles and are extremely toxic to moles, shrews and voles (and cats, dogs and humans). Marrotte says, "I don't recommend castor beans, because they are very ornamental and little kids might pick them up and want to eat them."

A vitamin D bait, offered by several companies, is toxic to rodents. The vitamin D causes a calcium imbalance in the vole's blood. The vole stops feeding after eating the bait and dies in two to four days. See the Homemade Methods for a version of this product that you can make yourself.

John Marchacos (Berlin) uses a combination of Enforcer Rat Kill for bait and mouse glue traps for bait situations. He fills the middle of the glue board with the bait (which resembles cat food), put sit next to a hole, and covers it with a big black flowerpot secured with a rock on top. "It seems to be working. I've been doing it awhile and usually the food is gone in three days. Then I refill the tray. But the last time I put it out they didn't touch it."

The glue board is supposed to trap the animal, but the voles are so dirty that they don't stick to the glue on the traps. Marchacos thinks that you could probably use something else to hold the bait pellets. But he hasn't used anything else. "For some reason the voles are attracted to the mouse glue traps. Sometimes they even eat part of it."

Remember to wear gloves whenever you're working with traps and bait. Voles are sensitive to human scent. And good luck with your efforts! Let us know what works well for you. We'll publish any tips from our readers.

Pamela Weil, the editor and publisher of Connecticut Gardener, is a Master Gardener certified by UConn's Cooperative Extension System.

Homemade Methods

1 tablespoon castor oil
2 tablespoons liquid detergent
One gallon warm water
Whisk or blend the castor oil and liquid detergent together until foamy, then add to the warm water. Soak the active tunnels when the ground is wet. According to the author, "The animals will find the smell offensive and will abandon your yard."
Source: No-Fail Flower Garden (Rodale Press, Inc., 1994).

1/2 cup peanut butter
3 crushed vitamin D tablets
Roll in oats, place inside a 2 inch cardboard tube and bury in a tunnel or where damage is occurring. This creates a calcium deficiency and so our unfavorable rodents perish!
Source: NOFA/CT NEWS (Summer 1996)

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