Controlling burrowing rodents
Rodents like prairie dogs, ground squirrels and pocket gophers can damage fields, pastures and crops. When these critters move into your barnyards or pastures they may need to be controlled.
Robert M. Timm, PhD, Extension Wildlife Specialist Emeritus, University of California Hopland Research & Extension Center, said some geographic regions have different rodent problems. Sometimes the best advice on dealing with your specific type of rodent wildlife will be from local sources of expertise. Some burrowing rodents are more of a problem in crops or hayfields than out on rangeland.
“In my experience — working mostly in California and the Midwest — ground squirrels, pocket gophers and prairie dogs can have a serious impact,” Timm said. Some species of ground squirrels cause losses in forage and other crops, while pocket gophers can be a major problem in perennial plantings such as alfalfa, orchards and vineyards. Even on pasture and rangeland, they can reduce forage productivity.
In a hayfield or crops, rodent mounds can damage implements when harvesting, and burrows may interfere with flood irrigation. “Water may go down the burrows rather than where it’s intended,” Timm said. Rodent burrows can also create erosion problems, and damage ditches, irrigation canals and roads.
Sarah Baker, University of Idaho Extension, said forage loss in a field or pasture from gophers may be 10% to 50%. In hayfields, mounds left by gophers can dull the blades on cutting machinery, and dirt may end up in hay bales.
“When I get calls about burrowing rodents, the first thing I ask is what animal they are dealing with. Eradication methods differ, so we need to know if it’s pocket gophers, prairie dogs or ground squirrels. Many people confuse pocket gophers with ground squirrels,” she said.
“The ground squirrels’ activity is more above ground and they make larger holes. Since they feed above ground our control measures are focused more above ground. Pocket gophers tend to stay underground, with extensive burrow systems. All control measures with pocket gophers must be inside their tunnels because they don’t come above ground very often,” she said.
“The best way to identify pocket gophers is by their horseshoe-shaped mounds. As they dig burrows they push the soil above ground and create many mounds in that area of the pasture,” Baker said. The mounds may be 12 to 18 inches wide and 4 to 6 inches high. These gophers can create several mounds a day and a single burrow system may cover 200 to 2,000 square feet.
“The main control methods are trapping, rodent baits placed within the burrow system or fumigating the burrows,” Timm said. “Historically, fumigation does not work well for pocket gophers, except for aluminum phosphide, which comes as a tablet or pellets that are placed within the sealed burrow. This fumigant is highly restricted, and only used by trained, licensed professionals. It can’t be used for rodent control near structures, because the phosphine gas generated could seep out through cracks in the ground or through the burrow system itself into structures that might be occupied by animals or people; it’s fatal to anything that breathes it,” Timm said. Most other types of fumigants don’t work well for pocket gophers; they smell it coming and quickly wall up dirt to protect themselves.
Some producers hire licensed pest control professionals to use aluminum phosphide. Trapping also works if a person is diligent. “There are several good pocket gopher traps on the market and once you learn to use them, they can be very effective. Ranchers trying to eliminate gophers usually carry gopher traps in their pickup. As soon as they see a fresh mound they try to trap the gopher before it reproduces or causes major damage.”
Trapping and poison grain baits within the burrow system are the most common methods of control. “Strychnine used to be the most effective and most readily available product but it’s become hard to get,” Timm said. Zinc phosphide and anticoagulant baits are also registered for pocket gopher control, but are generally less effective.
“A few companies do burrow fumigation for pocket gophers and ground squirrels using pressurized carbon monoxide machines. These devices use a four-cycle gasoline engine to produce carbon monoxide in the exhaust, which is piped into an air compressor driven by the engine. The machines are expensive, so producers usually hire operators to come treat rodent burrows. Recent research indicates this technique provides moderate to good success in killing pocket gophers, depending on the location, time of year, soil type and who is doing the operation,” he said. To achieve complete control may require a second treatment, or follow-up using traps or rodenticide baits.
If there was a large infestation and your pasture is riddled with old tunnels and dotted with holes or mounds, you may have to disk it up and reseed it. “The important thing when you see rodent activity or mounds is to take control early,” Baker said. “Once the population gets going, it becomes more difficult to eradicate them all. Pocket gophers breed in spring and can have one or two litters per year, averaging three to six babies per litter. They can produce a lot of young ones and really get out of hand and seriously damage a pasture,” she said.
“It’s important to level the gopher mounds, because then if you see fresh mounds you know you still have gophers left. As a kid trapping gophers I always knocked over the mounds and then if I saw some new ones pop up I’d know where to put my traps. If there’s no new activity you know you got them all or they’ve moved somewhere else,” she said. Gophers don’t hibernate and are active year round.
GROUND SQUIRRELS AND PRAIRIE DOGS
Prairie dogs and ground squirrels are similar in the damage they cause and the control methods commonly employed. “These burrowing rodents can be a problem on rangeland, pastures, alfalfa and other crops,” Timm said. Some species of ground squirrels are colonial, with large numbers living in groups and spreading out from their main burrows. Prairie dogs are scattered across the landscape and live more solitarily,” he said.
Ground squirrels and prairie dogs are active above ground, feeding during the day on green plants when available, and on seeds and grains when green forage is not present. “They tend to dislike tall vegetation. Management strategies that avoid grazing, mowing, or burning tend to discourage these rodents. Unlike pocket gophers, ground squirrels and prairie dogs tend to hibernate during winter. Control options depend on their seasonal behaviors, particularly in regard to rodenticide baits and burrow fumigants.”
Of the many species called “ground squirrels,” fewer than half are pests. “Some are troublesome only in particular situations and locals. Problems with ground squirrels are most severe west of the Rocky Mountains. Typical damage involves crops and livestock forage. Their burrowing can damage earthen structures, irrigation systems and agricultural machinery. Plastic drip irrigation systems are damaged by their gnawing. Ground squirrels may serve as reservoirs of disease that can affect humans, which may be transmitted by their fleas and ticks. These diseases include plague, tularemia, spotted fever, relapsing fever and Colorado tick fever,” Timm said.
Control of prairie dogs and ground squirrels can be complicated in habitats where there are endangered or protected species living in and around their burrows. The black-footed ferret lives in prairie dog towns, and various species of endangered kangaroo rats share habitats with California ground squirrels. Burrowing owls may also use rodents’ burrows. Pesticides (baits and fumigants) registered for use against ground squirrels and prairie dogs have specific instructions on where such materials are prohibited, and how to survey for endangered species in other areas where rodent control may be permitted. Appropriate federal and state agencies should be contacted for current recommendations.
Control of ground squirrels and prairie dogs is typically done using poison bait or by burrow fumigation. Trapping or shooting, which are more labor intensive, are sometimes employed on a smaller scale or as a follow-up to rodenticide application.
Various grain and grain-pellet rodenticide baits are registered for ground squirrel or prairie dog control. Check product labels for target species, and follow application procedures described. “Some products are restricted-use pesticides. Many products now require pre-baiting or verification that the rodents will accept that form of bait prior to toxic bait application. Some species of ground squirrels and prairie dogs won’t consume grain bait when green forage is available, so timing is critical for success,” Timm said.
“Some ground squirrel baits having anticoagulants as the active ingredient and are registered for use in bait stations, which if established around the field perimeter may reduce ground squirrel numbers or dissuade re-invasion,” he said.
Burrow fumigation can work well, but is often more expensive than grain bait in terms of materials and labor. “Aluminum phosphide is a very effective burrow fumigant, but highly restricted. Incendiary gas cartridges, which burn and produce carbon monoxide as well as smoke, can be very effective for ground squirrels and prairie dogs, but do not work in porous dry soils or in winter when the rodents are hibernating, or during the heat of summer when they may be in summer estivation and sealed off in their burrows. Fumigants may be used as a follow-up to grain bait application,” he said.
On small acreages, or where only a few ground squirrels or prairie dogs are present, some people try to control them by shooting with small caliber rifles, or using appropriate traps set in burrow entrances or along travel-ways. “With persistent shooting, however, the rodents become wary of human presence. Control of prairie dogs or ground squirrels can be tricky. Seek local advice, and plan a strategy. You might be able to control 60% to 70% of the population with grain bait and then remove remaining rodents by burrow fumigation. The goal should be to eliminate 85% or more of the population. If you do a good job you may only need to do a control program once every three to five years.” ❖
— Smith Thomas is a cattle rancher, horseman, freelance writer and book author, ranching with her husband near Salmon, Idaho. She can be reached at firstname.lastname@example.org.