Controlling Burrowing Rodents on Large Properties in Temecula and Murrieta ?

You walk out to your horse’s pasture one morning and notice something’s amiss: Small mounds of fresh soil dot the even terrain you’ve worked hard to establish and maintain. You’ve been invaded by pocket gophers seemingly overnight. And unless you eliminate these pesky rodents, they will continue to create dangerous gaps in the ground all over your property.

Burrowing animals—ground squirrels, gophers, voles, can destroy pastures and leave behind holes just begging to ensnare horse limbs. Two of the most damaging animals to set up shop in fields and pastures are pocket gophers and ground squirrels.

Aside from the danger they pose to horses, gopher-infested fields or pastures can see forage losses anywhere from 10-50%. Gopher mounds will dull the blades on cutting machinery their tunnels will even interfere with irrigation by draining off water or damaging irrigation piping.  

Identify the Pest

Sure, you can eliminate burrowing pests, but first you must identify them, says Sarah Baker, extension educator at the University of Idaho, in Moscow.

“Eradication methods differ, so you need to know if it’s pocket gophers, voles, or ground squirrels,” she says. Ground squirrels, which typically live in colonies, make larger holes—which can be detrimental in horse pastures—and feed aboveground. They leave these holes uncovered. Pocket gophers, on the other hand, are primarily solitary creatures (aside from breeding season) and stay underground within extensive burrow systems, snacking on grubs, earthworms, and plant roots. They plug the holes they make, but horses can step through into these systems if they are are shallow enough. You can identify a pocket gopher infestation by the crescent or horseshoe-shaped mounds they create as they push soil aboveground.  

These mounds can be 12-18 inches wide and 4-6 inches high. Gophers can create several mounds in one day, and a single burrow system might cover 200 to 2,000 square feet. Gophers don’t hibernate and are active year-round.

“Pocket gophers have one or two litters per year, averaging three to six babies per litter,” Baker says. “They can quickly get out of hand and seriously damage a pasture.”

Control Strategies

Control methods include do-it-yourself trapping underground, setting poison or anticoagulant baits underground, burrow fumigation, or hiring a pest-control professional.

“For a large infestation you might consider plowing that field to destroy the burrows/mounds and force the rodents to come above ground, where they are vulnerable to predators,” says Baker. “One way to eliminate them in a field is crop rotation. Gophers love alfalfa because they feed on the large taproots. If you have a serious infestation in an alfalfa field, you could plow it out and plant an annual grain like oats. Gophers don’t like the shallow roots of small grain crops.”

This method, of course, might not be practical for many farm owners, especially those not growing a crop for harvest.  

The important thing when you see rodent activity or mounds is to take action early, because the longer a population has been established, the more difficult it is to eradicate.  

“Depending on severity of the damage, you may decide to renovate the pasture after you get rid of the rodents,” Baker says. “If it’s just a small area, you might smooth it up with a rake and shovel so horses won’t step in the burrows. We actually recommend doing this while you are trying to get rid of them, because if you’ve smoothed it and then see new mounds, you know where the gophers are. If there’s no new activity you know you got them all or they’ve moved somewhere else.”  

Matt Brechwald, who operates a control service in Kuna, Idaho, says ground squirrels estivate (go into a dormant or inactive state) and seal their tunnels while sleeping. “But they seal them off down deep, and it’s harder to exterminate them at that point. It’s easier when they are active and you see them on the surface.”

He advises his clients to rake over the affected area with a disk or harrow four or five days before his farm visit so he can see where they’re active and knows where to treat.

Here’s a breakdown of the commonly used rodent control methods.

Traps are a feasible option for removing small gopher or ground squirrel populations, but they might be too time-consuming for large infestations. Trapping is not legal in some states, so check the laws. Several kinds of traps work, says Baker, including cinch traps (that grasp the animal mid-body) and box traps set at the end of the tunnel to catch the animal as it surfaces.

Set traps in the main tunnel or in any of the lateral tunnels (the main tunnel runs parallel to the ground; lateral tunnels are linear or branched and slope toward the ground surface, evident where the gophers have pushed all the dirt out onto the surface into mounds). “Gophers may not revisit lateral tunnels, however, so trapping may be more successful in the main burrow,” says Baker. “When you locate fresh mounds, find the plug (a small, circular depression on one side of the mound that leads to the opening of the tunnel), and insert a stick or probe to find the lateral tunnel. Dig it out with a shovel or your hand, following the lateral tunnel until you reach the main tunnel.”  

Place traps in the main tunnel in pairs, facing opposite directions (see diagram at left). Farm supply stores sell a variety of traps, which can be set according to manufacturers’ directions. Anchor traps to stakes with wire to keep gophers from moving them deeper into the burrow system and to keep predators from making off with the gopher and trap, advises Baker.

Brechwald cautions against opening up rodent holes for trap use in horse-occupied pastures. If a hoof lands in a gut-clench trap, for instance, the device might injure or spook the horse when it snaps. Or, the horse might simply step in the hole and foul the trap. For these reasons remove horses from the pasture until the rodents and traps are gone and the holes refilled. The benefit to trapping is that you know when you’ve captured the animal and can eliminate it.  

Baits come in grain or pellet form. Find out which options are legal in your state. “A common type of toxic bait contains strychnine,” says Baker. “One restriction is that it can’t be used above-ground and must be placed in the burrows. Strychnine is very effective for gophers but accumulates in body tissues. If a pet or some other animal eats a gopher that was poisoned with strychnine, it might die.” So don’t use strychnine in areas where pets roam.

Another legal poison is zinc phosphide, but it’s a restricted-use pesticide, Baker says, meaning you must have an applicator’s license to purchase and use it. This requires learning how to handle it, taking a test, and becoming certified with the state Department of Agriculture. There are some zinc phosphide (2% or less) products available over the counter at garden supply stores, but they are only sold in quantities of one pound or less. Don’t use zinc phosphide pellets if you are expecting rain. Moisture will cause the product to form a phosphine gas, making it ineffective, Baker notes.

“One problem with these products is that in recent years the EPA reduced the level of active ingredients that can be used in over-the-counter baits by about 50% so they are not as lethal as they used to be,” says Brechwald. “If a gopher or ground squirrel samples the bait and doesn’t consume enough to kill them, it just makes them sick for a while—and then they won’t touch it again.”

Then there’s the issue of inadvertently poisoning other wildlife on the surface. “There are restrictions in some states on using poison bait for ground squirrels (remember, they leave their tunnels open) because other animals, such as burrowing owls, may go into the holes and eat the bait,” he explains. Therefore, always read labels because there might be different provisions for ground squirrels for this reason.  

Baits containing anticoagulants (similar to rat poison) are not as effective as strychnine or zinc phosphide, says Baker. “Because of their lower toxicity, however, they may be a better choice in situations where pets or other animals might dig up and eat the dead gopher. Most of these products are multiple-feed baits and require more bait per application than single-feed baits like strychnine.”

You can purchase probes to place bait into the burrows. “Most extension offices have probes that can be borrowed or rented,” Baker says. Place the bait in a small container attached to the probe. To locate the main tunnel, probe around the gopher mound in an 8-to-12-inch radius, poking into the ground about 4 inches. When the probe goes into the main tunnel it readily drops about 2 more inches. Open the container to dispense the correct amount of bait into the tunnel and close the hole afterward.  

“Farmers sometimes use an implement pulled behind a tractor, making a tunnel and dropping bait in that tunnel,” says Brechwald. “Burrowing gophers come across that tunnel, explore it, and eat the bait. This is a way to cover a wide area in less time.”

Poison gas is generally produced in pellet form that creates a lethal vapor on exposure to air or the rodent’s stomach acid, depending on the type of poison. Thomas Barnes, wildlife extension specialist at the University of Kentucky, says you must obtain a restricted use permit from the county Extension office to purchase and get trained/certified in utilizing a fumigant to kill burrowing animals. “With ground squirrels, make sure all (burrow) air escapes are covered,” he says. “Then after the animal goes into the burrow (you’ll know because the burrow has been uncovered), put the toxin into the hole and tightly cover that entrance.   

“Unless they dig out through the covered hole, you know you’ve killed them,” says Barnes. “In my 20-plus years here at the University of Kentucky, I’ve never had anyone say this was not effective for killing rodents.”

“The best toxin available for gophers or voles is aluminum phosphide,” Barnes says, which is most useful when soil is moist. “This triggers a chemical reaction that produces an extremely lethal gas. It works really well, but there have been a few human fatalities using this.”  

Only certified individuals with an applicator’s license can use aluminum phosphide for agricultural purposes. Even then, it can’t be used within 100 feet of any building that might be occupied by people or domestic animals.  

Ignited propane can be used as a DIY approach, or property owners can hire an operator to do the job for them. “These put a combination of propane and oxygen into the tunnel,” Brechwald says. “This is ignited, creating an explosion to kill rodents with the concussion and cave in the tunnel to prevent re-infestation.” If other rodents are digging along and break into a tunnel system that is already there, they might move into it.

One drawback to this method is the noise. “I was a police officer for 12 years, and we got calls whenever someone was igniting these,” Brechwald adds. “Neighbors thought someone was shooting a gun. The explosions may also scare horses, and there are issues with fire danger. We worry about sparks from the explosion setting fires in dry weeds, hay stacks, etc.”

Smoke bombs are available for purchase at farm supply stores. “The disadvantage to these is that you have to open up the tunnel system, light the smoke bomb, get it down into the tunnel, then seal the tunnel,” says Brechwald. “There’s also some risk for fire danger when everything is dry.”

Carbon monoxide poisoning via a PERC (pressurized exhaust rodent control) machine can be useful for getting rid of gophers, voles, and ground squirrels, says Brechwald. The unit he uses has a 14-horsepower motor that powers an air compressor. Exhaust from the motor goes through the cooling coil into the air compressor. Brechwald then injects the carbon monoxide into the tunnel using a probe. He believes this is the most humane way to kill rodents.  

DIY Disclaimers

Barnes does not recommend property owners use home concoctions to try to get rid of pests. “People sometimes pour bleach or gasoline down the holes,” he says. “Even if these methods are effective, they are dangerous—to the person doing it and to the environment. For example, pouring gasoline down a burrow could set off an explosion if there is any spark. One person lost his barn doing that.”

Instead, check with your local Cooperative Extension Agent or state Department of Agriculture for listings of legal or recommended control methods.  

Take-Home Message

Identify the pest, then choose an appropriate method for eliminating that animal. “The