Damage Prevention and Control Methods
Enact control techniques to reduce damage to crops before 13-lined ground squirrels emerge from hibernation. Deep tilling of soil can destroy dens and disrupt habitat. Repeated filling of entrance holes will not result in the animals abandoning the area. The exact cost of damage caused by 13-lined ground squirrels is difficult to quantify because much of it goes unreported. For a homeowner with 1 or 2 ground squirrels in the garden, or a farmer with a few ground squirrels in a field, the animals may be more of a nuisance than a serious pest. They can cause significant losses, however, when large numbers are present. Thirteen-lined ground squirrels establish colonies in and around borders of minimum-tillage fields of corn and soybeans. Losses of 20 to 80 acres have been reported. The 13-lined ground squirrel is a minor pest in suburban areas and a minor to moderate pest in agricultural situations.
The majority of damage by chipmunks involves minimal economic loss (under $200). Homeowners report that chipmunks are destructive when they burrow around structures. This damage warrants control to protect integrity of stairs, patios, and foundations.
Activity in fields and gardens can be discouraged by deep soil cultivation, which destroys burrows and changes the habitat. Allow grassy areas to grow as tall and as dense as possible if consistent with local land use practices. Such vegetation discourages ground squirrels but may encourage populations of other small mammals, such as voles. Plant crops before squirrels emerge from hibernation to reduce losses to seeds and seedlings.
Deter small mammals from feeding on seeds and seedlings by providing the animals with an alternative source of food. At planting, broadcast 4 bushels of cracked corn per acre over the outside 4 to 8 rows. It also may be necessary to spot-treat fields in areas where burrows are observed and damage is expected, especially if conservation tillage is employed.
Bird feeders should be modified to prevent rodents from accessing them. Use feeders that capture fallen seed to reduce the amount that reaches the ground.
It is difficult to detect burrows that are adjacent to foundations when piles of wood, debris, or ground cover plantings provide aboveground protection. Do not stack firewood against buildings to deter nesting near homes. Landscape features, such as ground cover, trees, and shrubs, should not be planted in a continuous fashion that connects wooded areas with the foundations of homes. Remove or mortar stone walls.
Exclusion is expensive and practical only in limited situations. Thirteen-lined ground squirrels and chipmunks can be kept out of electrical substations or similar installations with hardware cloth topped with sheet metal. Most electrical substations and other secured installations are enclosed by chain-link fences that can be modified to exclude ground squirrels. Dig a trench 18 inches wide and 18 inches deep around the installation next to the outside of the existing fence. Install galvanized ½-inch or smaller mesh hardware cloth (6 feet wide) across the bottom and up the side of the trench nearest the existing fence, continuing 3 feet up the fence. Backfill the trench and securely attach the hardware cloth to the chain-link fence. Attach a piece of sheet metal, 2 to 3 feet wide, to and above the hardware cloth. Adjust all gates to fit within ½ inch of the support post and the ground. It may be necessary to install cement thresholds to keep squirrels from digging under gates.
Use gutter guards and cover downspouts to prevent squirrels and chipmunks from entering a house. For active burrows, wait until the animals are out and away, fill the holes with soil, and cover with a rock or other heavy object. Chipmunks should be excluded from buildings whenever possible. Use hardware cloth with ¼-inch mesh, Copper Stuff-Fit, or Xcluder™ fill fabric to close openings where they can gain entry.
Secure exhaust vents with professionally manufactured screens. Exhaust vents of dryers require particular care due to fire hazards.
Hardware cloth (¼-inch) can be used to exclude chipmunks from flower beds. Cover seeds and bulbs with ¼-inch hardware cloth. The cloth itself should be covered with soil and extend at least a foot past each margin of the planting.
No frightening devices are effective for the control of 13-lined ground squirrels or chipmunks.
Check your state pesticide regulations before applying any repellent.Repellents are expensive and usually do not provide 100% reduction in damage. Effectiveness of active ingredients varies, and most commercial repellents have not been adequately tested.
Thiram (75% concentration) is registered by the US Environmental Protection Agency (EPA) as a seed treatment to reduce damage to seeds by 13-lined ground squirrels. Carefully follow the instructions on the label.
Taste repellents that contain capsaicin, Bitrex®, or ammonium soaps of fatty acids can be used to protect flower bulbs, seeds, and foliage. Multiple applications of repellents are required.
Predator urine (fox or coyote) is the active ingredient in products registered for repelling animals from lawns and gardens. The repellent is to be used as a barrier. Follow the instructions on the label.
For 13-lined ground squirrels, zinc phosphide is formulated as pellets or grain baits, and is most effective in spring and late summer when ground squirrels are gathering seeds. Apply untreated pellets or grain as a prebait to encourage the squirrels to consume the treated bait quickly. Rapid consumption is necessary to decrease the likelihood of bait- shyness. Zinc phosphide is a Restricted Use Pesticides in most states and may be applied only by certified pesticide applicators.Apply prebait on a bright, warm, sunny day when ground squirrels are most active. Do not apply treated bait over bare ground or in areas of scant vegetation, where it can pose a direct threat to grain-eating birds.
Chlorophacinone is registered for the control of chipmunks. Some states may have Special Local Needs 24(c) registrations for site-specific use of baits for the control of chipmunks.
Burrow fumigants are effective for ground squirrels and chipmunks in small areas. Fumigation may be the most humane method from mid-April to mid-June because both female ground squirrels and their young are present in the burrows. Fumigants should never be used in or around buildings, or where people, livestock, or other non-target animals may come into contact with the gases. Treat and plug all burrows, wait 24 to 48 hours, and retreat any burrows that have been reopened. Most burrow fumigants work best when the soil moisture is high and the air temperature is above 50°F.
Aluminum phosphide tablets and pellets can be used to treat burrows of 13-lined ground squirrels and chipmunks in agricultural and non-cropland areas. Use of aluminum phosphide is highly regulated and a fumigation plan must be created prior to use. Carefully read and follow all instructions on the label. Place 1 to 4 tablets, or 5 to 20 pellets, as far down into the burrow as possible. The higher rates are recommended for larger burrow systems when soil moisture is low. Seal the entrance of the burrow by packing it with crumpled newspaper and then shoveling soil over the entrance. Do not cover the tablets or pellets with soil when sealing the burrow.
Gas cartridges produce carbon monoxide (CO) and carbon dioxide (CO2) and consume oxygen when applied to a closed burrow system. Gas cartridges come in different sizes; make sure the cartridge will fit into the burrow before lighting the fuse. Some cartridges include built-in fuses while others must have the fuse inserted by the operator. Check the label of the product for instructions and prepare the cartridge accordingly. Avoid breathing the smoke when using gas cartridges. Do not use them near buildings or other combustible material, or during periods with prolonged dry weather, because of the potential hazard of fire.
Prepare gas cartridges according to label instructions. Cut a clump of sod slightly larger than the opening of the burrow with a spade or shovel. Kneel at the opening, light the fuse, and place the cartridge, fuse end first, as far down the burrow as possible. Do not throw the cartridge. Immediately place the sod, grass side down, over the opening and cover with soil to make a tight seal. Close any openings from which smoke appears.
Check with your state wildlife agency for restrictions or permits required to shoot 13-lined ground squirrels and chipmunks. Shooting ground squirrels and chipmunks may reduce the local population if the shooter is persistent. Air rifles, .22-caliber rifles, and shotguns are ideal.
The use of traps is a practical method for eliminating ground squirrels and chipmunks in areas less than 1 acre.To determine the number of traps for ground squirrels, count the number of dens and divide by 2. For chipmunks, quickly scan the site, count the number of chipmunks and multiply by 3. Follow-up trapping may be needed to remove animals that come from the surrounding area. Set all traps in areas where damage is occurring, next to active burrows, or on active runways.
Cage traps (Figure 7) for 13-lined ground squirrels and chipmunks should be at least 3 x 3 x 10 inches with fine mesh (¼-inch). Cover ½ of the trap to provide additional shelter for the trapped animal and to keep bait out of view of tree squirrels and birds. Ensure the cover does not interfere with operation of the trap.
Peanut butter is an effective bait, and is difficult for animals to remove without springing the trap. Pieces of fruit, vegetables, nut meats, or sunflower seeds also can be used as bait. Seeds may be glued to the trigger of the trap. Place bait in the back of the trap to avoid attracting birds.
Check traps at least every 24 hours, preferably at dusk, and apply fresh bait. If more than 2 or 3 days pass without a sprung trap, move it to a new location. If the bait is taken without the trap being sprung, try using mouse-sized snap traps. Young ground squirrels may not be heavy enough to spring rat-sized traps.
The Bethel ground squirrel trap (12- by 20-inch piece of ½-inch mesh) employs a 1-way door to capture 13-lined ground squirrels (Figure 8). Before setting the trap, spend time observing the animals to determine which burrows are active. Plug holes within 20 feet of active burrows with soil. Place the trap over the main burrow entrance used by ground squirrels. Squirrels may emerge from their burrows after 20 minutes. Gravity will hold the door closed until an animal pushes past it to enter the trap.
Common rat snap traps can be used to kill ground squirrels and chipmunks. Restrict access to traps by non-target animals by placing traps under inverted wooden boxes with a 2-inch hole cut in each end, or use rat-sized bait stations. This will, however, reduce success of trapping. All snap traps should be anchored to prevent squirrels from carrying them away.
To avoid killing songbirds in rat snap traps, enclose traps within a box with openings that allow only rodents access (Figure 9).
The box must allow enough clearance for the trap to operate properly. Conceal snap traps that are set against structures by leaning boards over them. Electronic rat traps also are effective in capturing 13-lined ground squirrels.
Locate snap traps in the same manner as cage traps and secure bait to the triggers. Prebait traps for several days for large jobs or set traps immediately. Set snap traps perpendicular to the pathway of a chipmunk or in pairs along travel routes with the triggers facing away from each other. Set the trigger arm so that it is sensitive and easily springs the trap.
Handling – Relocation
Relocation of 13-lined ground squirrels and chipmunks is not feasible except in rescue situations.
Translocation is not recommended for ground squirrels. Release chipmunks at least 3 miles from the site of capture. Avoid this option for chipmunks in late summer, as translocation will separate the animal from its winter food cache.
Carbon dioxide is an appropriate method of euthanasia for 13-lined grounds squirrels and chipmunks.
Check your state regulations regarding disposal of carcasses.
Other Control Methods
Ground squirrels can be captured by pouring water down their burrow and forcing the squirrel to the surface. Use a gallon milk jug turned upside down so that opening is flush with hole. As water fills the den, the ground squirrel will climb into the container. Turn the container over and seal it with the cap.