How to control moles in your yard

Consumer Reports News: October 09, 2008 12:09 AM

Moles, common in backyards throughout most of the United States, are a frequently cited problem in our Pest Patrol forum. The two most common mole varieties—star-nosed and eastern—measure about 7 inches long from nose to tail. They have broad, outward-facing pads on their front feet, small and narrow hind feet, and tiny pinholes for eyes; their ears are not visible.

Moles are voracious, high-metabolism feeders who use their large front paws to tunnel through the ground searching for ants, earthworms, and grubs; some species consume more than their weight in food daily. "They are pretty well adapted to life underground," says Craig Riekena, a compliance manager for Bell Laboratories, which makes the mole poison Talpirid. "Their fur lies and flexes against their skin in a way that lets them tunnel as if they're swimming."

You'll know you have a mole problem if you spot visible trenches and dug-up soil in your lawn and garden. Look for the raised ridges that characterize mole feeding burrows, along with molehills, which look like miniature volcanoes with plugged holes in the center. These are often located close to the deep permanent burrows where moles nest and reproduce.

Some molehills can be substantial enough to damage mower blades and housings. Flower beds are also at risk. "Since grubs gather around the roots of shrubs and flowers, moles scrape that dirt away and remove the plant's foundation and depriving the flowers of nourishment," says Stephanie VanSyckle, a spokeswoman for mole-trap manufacturer Victor.

Whether you take action against moles will depend on the extent of the damage they cause and your personal threshold for how it looks. Consumers Union Senior Scientist Michael Hansen notes that the ridges and molehills are mainly an aesthetic problem; you can tamp down the ridges and water them to repair damage. Hansen points out that moles' preferred foods include several soil pests, especially grubs, so getting rid of moles could exacerbate other problems.

To prevent moles from burrowing under or climbing into specific sections of your garden, experts recommend burying metal mesh hardware cloth 2 feet vertically below ground with another 6 inches showing above ground. Moles tend to tunnel closer to the surface in spring when soil is moist and go deeper in the summer. "Since moles have trouble burrowing through dense soil, arranging stones or dense claylike soil around a garden to a depth of 2 feet can also help," says Hansen.

Another natural defense—using a castor-oil mixture—has been touted by a poster in the Pest Patrol forum who says he hit on the idea after hearing that moles sometimes avoid fields where castor beans are planted. There's more than a bean of truth to that idea—a series of studies by three Michigan State University researchers revealed that one castor-oil-based spray repellent did keep moles at bay for periods ranging from 30 to 60 days.

However, researchers from Ohio State University and the University of Arkansas disagree with the MSU  findings, citing the short duration and effect of weather on the tests. Marne Titchenell, a professor of wildlife ecology at OSU, also warns that castor oil can harm insects, earthworms and other creatures that populate the soil.

Peter Sawchuk, a program leader in our Technical Department, reports good results using Spectracide's Mole Stop and Bonide's Mole & Gopher Repellent. "Both of these have worked well for me," Sawchuk says, "but keep in mind that you'll be driving the moles into the adjoining property, which might not endear you to your neighbor." Other posters are recommending cats as another natural way to control moles.

More lethal alternatives include trapping and killing moles, which, experts say, is the only way to be sure you're rid of them, and using poison. Consumer Reports has not tested the traps or poisons cited below, and there are safety, health, and/or environmental issues with all of these methods.

Harpoon-type traps like the one shown work best; handling them is risky and requires skill. Locate an active mole runway by pressing down on raised ridges of soil. The next day, note which ridges have been raised again. Then depress the ridge of soil and set the trap over it; the mole will trigger the trap as it moves through the tunnel. "If you're going to use a trap, be very careful, as they are designed to impale or crush animals," Hansen says.

Also check local regulations before you begin trapping. If mole trapping is banned in your state, as it is in Massachusetts and Washington, another alternative is a poison bait such as Talpirid. It comes in a form that resembles an earthworm—another preferred food source of moles—and contains the rodenticide bromethalin, a potent neurotoxin that was developed after rodents began building up resistance to earlier poisons.

The Environmental Protection Agency, concerned about the number of accidental poisonings of children and pets, recently restricted sales of many rodenticides to licensed pest applicators and stipulated that they could be deployed only in sealed bait stations. But since moles are technically insectivores, not rodents, products marketed to control moles are not considered rodenticides and are exempted from those restrictions.

In the wake of an accidental poisoning in New York City, the state of New York has restricted bromethalin's sale and use to licensed pesticide applicators. "Talpirid is a registered pesticide in New York, so it is not banned, but because of the concentration of the specific active ingredient listed—bromethalin—its use is restricted," says Maureen Wren, spokeswoman for the New York State Department of Environmental Conservation.

"Bromethalin is World Health Organizaton Class Ia pesticide—it's highly acutely toxic," says Hansen. "If it's eaten by children, or if the dead moles are dug up and eaten by pets, it can be harmful. It is also toxic to birds and fish." To ensure that you safely and effectively use bromethalin, follow all product instructions and precautions.

But, Hansen says, "There are much better and safer ways to control moles. Controlling grubs is one way, as that's one of their major food sources. You can also use a garden hose and flood out of their tunnels; this is especially effective in the spring when they're breeding and especially effective against moles on the West Coast, who dig their breeding burrows closer to the molehill than other species."

If all else fails, you can hope that raptors will take up residence near your lawn. "A group of hawks did a pretty good job keeping the lawns at our mower-testing facility in Fort Myers, Florida, free of moles," says Sawchuk, who took the photo of the hawk at right.—Gian Trotta and Michael MacCaskey

Essential information: Our Complete Lawn & Yard Guide offers how-to instructions and ratings of a wide array of lawn and garden equipment. You'll also find the expert advice for dealing with weeds, common insects, and lawn diseases—and an interactive guide to the major lawn problems.

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