Moles are not harmful to plants, since they eat insects, not roots, but they do cause unsightly ridges in your lawn where they push up earth above them. They are particularly difficult to combat. Moles can figure out to avoid traps, digging around them. They also don't easily eat poisoned bait because of their mouth structure. Carbon monoxide poisoning can be an especially humane way of treating them, as kind as you can get without resorting to a catch-and-release program.
Determine which raised ridges over the mole tunnels are active. This can be done by stepping on a stretch of raised earth above the tunnel to flatten it, and seeing if it stays flat for several days.
Flatten the ridges of the whole run of active tunnels where the lawn has been pushed up (just by stepping on them). These raised ridges aren't airtight, and would let the gas seep out and be less effective.
Attach a garden hose to your car tailpipe. Seal it, using duct tape.
Insert the other end of the hose in the middle, not the end, of a flattened ridge. Seal around the hose with dirt to prevent gas escaping.
Pump the carbon monoxide from the exhaust directly into the tunnel. Run your car engine for an hour to fill the tunnel.
Make sure to treat all tunnels in your yard by filling each with carbon monoxide multiple times.
Contact a pest exterminator for application of a fumigant, if the above does not work. Fumigants need to be applied by a licensed exterminator.
- Consider a catch-and-release program as well. This is just a matter of digging up a tunnel, inserting a double-door trap in the tunnel, and closing up the tunnel so no sunlight gets in. The two doors close simultaneously on the mole and you can release it in the woods where lawn cosmetics are not an issue.
- Offer the service to your neighbours, so the moles in their lawn don't "re-infest" your own.
- Use sulphur sticks, or "mole smokes," which are another way of gassing the tunnel. They are lit and inserted into the tunnel in multiple places.
- Treat your grass for grubs, the mole's food supply.
Don't insert the hose into a hole at the end of a tunnel. The tunnel will not fill up with gas quickly and can escape out the hole. Exercise caution, as carbon monoxide is poisonous to humans as well as the moles you are trying to exterminate.