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Pocket Gophers | Pocket Gopher Overview | Pocket Gopher Damage Assessment | Pocket Gopher Damage Management | Pocket Gopher Resources | Pocket Gopher Acknowledgments | ICWDM | Wildlife Species Information |
Damage Prevention and Control Methods
Contents |
Exclusion
Because of the expense and limited practicality, exclusion is of little use. Fencing of highly valued ornamental shrubs or landscape trees may be justified. The fence should be buried at least 18 inches (46 cm). The mesh should be small enough to exclude gophers: 1/4-inch or 1/2-inch (6- to 13-mm) hardware cloth will suffice. Cylindrical plastic netting placed over the entire seedling, including the bare root, reduces damage to newly planted forest seedlings significantly.
Cultural Methods and Habitat Modification
These methods take advantage of knowledge of the habitat requirements of pocket gophers or their feeding behavior to reduce or eliminate damage.
Crop Varieties. In alfalfa, large tap-rooted plants may be killed or the vigor of the plant greatly reduced by pocket gophers feeding on the roots. Varieties with several large roots rather than a single taproot suffer less when gophers feed on them. Additionally, pocket gophers in alfalfa fields with fibrous root systems may have smaller ranges. This would reduce gopher impact on yield.
Crop Rotation. There are many good reasons for using a crop rotation scheme, not the least of which is minimizing problems with pocket gophers. When alfalfa is rotated with grain crops, the resultant habitat is incapable of supporting pocket gophers. The annual grains do not establish large underground storage structures and thus there is insufficient food for pocket gophers to survive year-round.
Grain Buffer Strips. Planting 50-foot (15-m) buffer strips of grain around hay fields provides unsuitable habitat around the fields and can minimize immigration of gophers.
Weed Control. Chemical or mechanical control of forbs, which frequently have large underground storage structures, can be an effective method of minimizing damage by Thomomys to rangelands. It may also be effective in making orchards and shelterbelts less suitable for pocket gophers. The method is less effective for plains pocket gophers as they survive quite nicely on grasses. The warm-season prairie grasses have large root-to-stem ratios and these food sources are adequate for Geomys.
Flood Irrigation. Irrigating fields by flooding can greatly reduce habitat suitability for pocket gophers. Water can fill a gopher’s tunnel, thus causing the occupant to drown or flee to the surface, making it vulnerable to predation. The soil may be so damp that it becomes sticky. This will foul the pocket gopher’s fur and claws. As the soil becomes saturated with water, the diffusion of gases into and out of the gopher’s burrow is inhibited, creating an inhospitable environment. The effectiveness of this method can be enhanced by removing high spots in fields that may serve as refuges during irrigation.
Damage-Resistant Plant Varieties. Tests of several provenances of ponderosa pine showed that some have natural resistance to gopher damage.
Repellents
There are a few repellents registered by EPA for gopher control that contain castor oil. Some predator odors have been tested as gopher repellents, but cannot be currently recommended. Commercially-available sonic devises are claimed to repel pocket gophers. There is, however, no scientific supporting evidence. The plants known as caper spurge, gopher purge, or mole plant (Euphorbia lathyrus) and the castor-oil plant (Ricinus communis) have been promoted as gopher repellents, but there is no evidence of their effectiveness. In addition, these are not recommended as they are both poisonous to humans and pets.
Toxicants
Several rodenticides currently are federally registered and available for pocket gopher control. The most widely used and evaluated is zinc phosphide (2%)on grain baits. There is some concern that pocket gophers may consume sublethal doses of zinc phosphide and then develop bait shyness. Zinc phosphide acts very rapidly and gophers sometimes die within hours after consuming a lethal dose. It is registered for use for Geomys spp. and Thomomys spp. If the label has directions for use with a burrow builder machine, then it is a Restricted Use Pesticide. A few anticoagulants now are available for pocket gopher control. Currently, the only federally registered products are chlorophacinone and diphacinone.
To poison pocket gophers, the bait must be placed in their tunnel systems by hand or by a special machine known as a burrow builder. Underground baiting for pocket gopher control with zinc phosphide presents minimal hazards to nontarget wildlife, either by direct consumption of bait, or by eating poisoned gophers. Poison bait spilled on the surface of the ground may be hazardous to ground-feeding birds such as mourning doves.
The main drawback to grain baits is their high susceptibility to decomposition in the damp burrows. A new product that contains a grain mixture plus the anticoagulant, diphacinone, in a paraffin block not only increases the bait’s effective life, but also makes it possible for more than one gopher to be killed with the same bait. Once the resident gopher ingests the toxicant and dies, it is typical for a neighboring gopher to take over the tunnel system and thus to ingest the still-toxic bait.
Hand Baiting. Bait can be placed in a burrow system by hand, using a special hand-operated bait dispenser probe, or by making an opening to the burrow system with a probe. Placing bait in the burrow by hand is more time-consuming than either of the probing methods, but there is no doubt that the bait is delivered to the tunnel system.
The key to efficient and effective use of these methods is locating the burrow system. The main burrow generally is found 12 to 18 inches (30 to 46 cm) away from the plug on the fan-shaped mounds (Fig. 6). If you use a trowel or shovel to locate the main burrow, dig 12 to 18 inches (30 to 46 cm) away from the plug. When the main burrow is located, place a rounded tablespoon (15 ml) of bait in each direction. Place the bait well into each tunnel system with a long-handled spoon and then block off each tunnel with sod clumps and soil. Bait blocks are also applied in this manner. The reason for closing the burrow is that pocket gophers are attracted to openings in their system with the intent of closing them with soil. Thus, if there is a detectable opening near the placement of poison, the pocket gopher may cover the bait with soil as it plugs the opening. Pocket gophers normally travel all portions of their burrow system during a day.
For extensive use in relatively soft soil, a durable probe may be made of 3/4-inch gas pipe— 1 piece 30 inches long. The 30-inch piece is threaded at both ends and the other pieces at one end only. A piece of 1/2-inch round iron about 2 inches long is welded into the unthreaded end of the 14-inch pipe and bluntly pointed. The pieces are then arranged and fitted together with two 3/4-inch T-joints as shown here.
Lower image. For use in hard soil, the probe may be made of the following materials:
- 1 piece of 1/2-inch galvanized pipe, 34 inches long
- 1 piece of 1/2-inch galvanized pipe, 5 inches long
- 1 1/2-inch galvanized T-joint
- 1 piece of 1/2-inch round iron, 2 inches long
- 1 piece of highly temperatured steel, 3/8-inch in diameter and 28 inches long
- 1 3/8-inch set screw, 1 inch long
- 1 3/8-inch nut
- 1 reducer, 1/2 inch to 3/8 inch
The two pieces of pipe are each threaded at one end. The piece of round iron is welded into the unthreaded end of the 34-inch pipe and bluntly pointed. A 3/8-inch hole is bored in the T-joint, and the 3/8-inch nut is brazed over this hole to accommodate the set screw. The piece of highly tempered steel is sharply pointed on one or both ends and held in place by the set screw. The pointed end of a hay-rake tooth cut 28 inches long would serve well for this piece. These materials are then assembled as shown here.
Place a probe for pocket gopher tunnels where you expect to locate the main burrow as described above (plans for making a probe and instructions for use are presented in Fig. 7). You will know you have located a burrow by the decreased friction on the probe. With a reservoir-type bait probe dispenser (Fig. 8), a button is pushed when the probe is in a burrow and a metered dose of bait drops into the burrow. With the burrow probe (without a bait reservoir), make an opening from the surface of the ground to the burrow. Place about a tablespoon (15 ml) of bait down the probe opening. This method is much quicker than digging open the burrow tunnel. For best control, dose each burrow system in two or three places. Be sure to cover the probe hole with a sod clump so that the pocket gopher does not cover the bait when attracted to the opening in its burrow. Greater doses of chlorophacinone or other locally-registered anticoagulants are recommended (1/2 cup [120 ml]) at each of two or three locations in each burrow. Also, since some gophers poisoned in this manner die aboveground, the area should be checked periodically for 10 to 14 days after treatment. Any dead gophers found should be buried or incinerated.
The device consists of a knife and torpedo assembly that makes the artificial burrow at desired soil depths, a coulter blade that cuts roots of plants ahead of the knife, a seeder assembly for bait dispensing, and the packer wheel assembly to close the burrow behind the knife. The seeder box has a metering device for dispensing various toxic baits at desired rates.
Mechanical Burrow Builder. The burrow builder (Fig. 9) delivers bait underground mechanically, so large areas can be economically treated for pocket gopher control. It is tractor-drawn and is available in hydraulically operated units or three-point hitch models.
The artificial burrows should be constructed at a depth similar to those constructed by gophers in your area. The artificial burrows may intercept the gopher burrows, or the gophers may inquisitively enter the artificial runways, gather bait in their cheek pouches, and return to their burrow system to consume the bait. Recommended application rates of 1 to 2 pounds per acre (1.1 to 2.2 kg/ha) of 2% zinc phosphide grain should provide an 85% to 95% reduction in the gopher population (Table 1 demonstrates how to calculate bait delivery rates).
The burrows should be spaced at 20-to 25-foot (6- to 8-m) intervals. To assure success:
(1) Operate the burrow builder parallel to the ground surface, at a depth where gophers are active. It is essential to check the artificial burrow. If the soil is too dry, a good burrow will not be formed; if the soil is too wet and sticky, soil will accumulate on packer wheels or even on the knife shank and the slot may not close adequately.
(2) Check periodically to note whether bait is being dispensed. Sometimes the tube gets clogged with soil.
(3) Encircle the perimeter of the field with artificial burrows to deter reinvasions.
(4) Follow directions provided with the burrow builder machine. It is especially important to scour the torpedo assembly by pulling it through sandy soils so that smooth burrows will be constructed.
Fumigants
Federally registered fumigants include aluminum phosphide and gas cartridges with various active ingredients. These fumigants usually are not very successful in treating pocket gophers because the gas moves too slowly through the tunnel system. Unless the soil is moist, the fumigant will diffuse through the soil out of the gopher’s tunnel.
Trapping
Figure 10. Common pocket gopher traps. a. Macabbee b. Victor Gopher Getter c. DK-1 (formerly Death-Clutch trap d. Guardian (California box-type) gopher trap.
Trapping is extremely effective for pocket gopher control in small areas and for removal of remaining animals after a poisoning control program. Some representative traps are illustrated above (Fig. 10) with instructions for setting them below (Figs. 11 and 12).
Figure 11. Instructions for setting Macabee®. Step 1. Hold trap exactly as shown. Be sure left index finger holds trigger (1) in upright position. Step 2. Press thumbs down, and with left index finger guide hook on trigger (2) over end of frame of trap. Step 3. Still holding frame down, place other end of
trigger (3) into small hole in plate.
Figure. 12. Instructions for setting the D-K 1 gopher trap.Step 1. Pull thumb latch away from body shaft counterclockwise (putting tension on spring), releasing from shipping position. Twist thumb clockwise until thumb latch stops. Step 2. With jaws in open position (as shown), hook crooked end of trip lever over top of left jaw with long end under jaw. Push top of trip lever toward spring. Step 3. Slide flat metal piece toward jaws with points up. Put trip lever through large hole and move flat metal piece up about 1 inch.Step 4. To apply spring tension, hold body shaft in right hand, catch thumb latch with left fore and middle fingers under spring. Hold firm and crank body shaft clockwise one turn, and hook thumb latch back to body shaft. Caution: wear gloves as finger may touch end of trip lever. If this becomes a problem, trim tail of trip lever slightly.Step 5. Move flat metal piece to ear (away from jaws) near tip end of trip lever. Trap is now ready to place into burrow.
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Vulnerability to trapping differs among species of pocket gophers and sometimes within the same species in different areas and at different times of the year. For effective trapping, the first requisite is to find the tunnel. The procedure will vary depending on whether traps are set in the main tunnel or in the lateral tunnels (Fig. 13). To locate traps in the main tunnel, refer to the section on hand baiting. To locate the lateral tunnels, find a fresh mound and with a trowel or shovel, dig several inches away from the mound on the plug side. The lateral may be plugged with soil for several inches (cm) or several feet (m). However, fresh mounds are usually plugged only a few inches.
You may have to experiment with trap type and placement. Some trappers have success leaving tunnels completely open when they set their traps; others, when they place traps in the main, close off the tunnel completely, and when trapping the lateral, close most of the tunnel with sod. Traps can be marked above ground with engineering flags and should be anchored with a stake and wire or chain so a predator does not carry off the catch and the trap.
Trapping can be done year-round because gophers are always active, but a formidable effort is required for trapping when the soil is frozen. Trapping is most effective when gophers are pushing up new mounds, generally in spring and fall. If a trap is not visited within 48 hours, move it to a new location. Leave traps set in a tunnel system even if you have trapped a gopher in spring and early summer, when gophers are most likely to share their quarters.
Shooting
Since pocket gophers spend essentially all their time below ground, this method is impractical.
Other Methods
Buried utility cables and irrigation lines can be protected by enclosing them in various materials, as long as the outside diameter exceeds 2.9 inches (7.4 cm). Gophers can open their mouths only wide enough to allow about a 1-inch (2.5-cm) span between the upper and lower incisors. Thus, the recommended diameter presents an essentially flat surface to most pocket gophers. Cables can be protected in this manner whether they are armored or not. Soft metals such as lead and aluminum used for armoring cables are readily damaged by pocket gophers if the diameters are less than the suggested sizes.
Buried cables may be protected from gopher damage by surrounding the cable with 6 to 8 inches (15 to 20 cm) of coarse gravel. Pocket gophers usually burrow around gravel 1 inch (2.5 cm) in diameter, whereas smaller pebbles may be pushed to the surface.
Summary of Damage Prevention and Control Methods
Exclusion
Generally not practical.
Small mesh wire fence may provide protection for ornamental trees and shrubs or flower beds.
Plastic netting protects seedlings.
Cultural Methods
Damage resistant varieties of alfalfa. Crop rotation. Grain buffer strips. Control of tap-rooted forbs. Flood irrigation. Plant naturally resistant varieties of seedlings.
Repellents
Synthetic predator odors are all of questionable benefit.
Toxicants
Baits: Strychnine alkaloid. Zinc phosphide. Chlorophacinone. Diphacinone.
Fumigants
Carbon monoxide from engine exhaust. Others are not considered very
effective, but some are used: Aluminum phosphide. Gas cartridges.
Trapping
Various specialized gopher kill traps. Common spring or pan trap (sizes No. 0 and No. 1).
Shooting
Not practical.
Other
Buried irrigation pipe or electrical cables can be protected with cylindrical pipe having an outside diameter of at least 2.9 inches (7.4 cm).
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Pocket Gophers | Pocket Gopher Overview | Pocket Gopher Damage Assessment | Pocket Gopher Damage Management | Pocket Gopher Resources | Pocket Gopher Acknowledgments | ICWDM | Wildlife Species Information |