How to Manage Pests
UC Pest Management Guidelines
Scientific Name: Thomomys spp.
(Reviewed 9/08, updated 9/08)
In this Guideline:
Description of the Pest
Adult pocket gophers are 6 to 8 inches long with stout brown, gray, or yellowish bodies and small ears and eyes. They rarely are seen above ground, spending most of their time in a tunnel system they construct 6 to 18 inches beneath the soil surface. A single burrow system can cover several hundred square feet. It consists of main tunnels with lateral branches used for feeding or for pushing excavated soil to the surface. Gophers are extremely territorial; except for females with young, you rarely find more than one gopher per burrow system.
The conspicuous, fan-shaped soil mounds over tunnel openings are the most obvious sign of gopher infestation. These tunnel openings are almost always closed with a soil plug. Gophers feed primarily on the roots of herbaceous plants. They may also come aboveground to clip small plants within a few inches of their burrow and pull vegetation into the burrow for feeding.
Gophers breed throughout the year on irrigated land, with a peak in late winter or early spring. Females bear as many as three litters each year. Once weaned, the young travel to a favorable location to establish their own burrow system. Some take over previously vacated burrows. The buildup of gopher populations in the orchard is favored by extensive weed growth or the presence of most cover crops, especially perennial clovers and legumes.
Pocket gophers can be serious pests, primarily in young orchards. While herbaceous cover crops are their preferred food, pocket gophers will also feed on the bark of tree crowns and roots. When cover crops or weeds dry up, gophers bark feeding may become extensive enough to girdle and kill young trees or reduce the vigor of older trees. Damage to trees is always underground and usually not evident until the trees show signs of stress. Gophers sometimes gnaw on plastic irrigation lines.
Take action as soon as you see any signs of gopher activity in the orchard. For infestations that cover a limited area, use traps or hand-applied poison bait. Trapping and hand-baiting can be used at any time of year, but they are easier when the soil is moist and not dry and hard. In addition to control within orchard, consider controlling gophers in adjacent areas, thus reducing the potential for further gopher problems.
The best times to monitor for gophers are after irrigation and when mound building peaks in the fall and spring. Monitor monthly in spring, paying close attention to orchard perimeters to determine whether gophers are invading the orchard. Monitor more closely in weedy areas such as roadsides and in young orchards with extensive weed growth or ground covers. This type of vegetation is more likely to support gophers, and low-growing vegetation makes signs of burrowing activity harder to see. Look for darker-colored mounds, which indicate newly removed soil.
Treatment options for pocket gophers include the use of baiting with multiple-dose anticoagulants, strychnine, or zinc phosphide, trapping, or fumigating with aluminum phosphide. Strychnine, zinc phosphide, and aluminum phosphide are restricted use materials that require a permit from the County Agricultural Commissioner for purchase or use.
While multi-dose anticoagulants are available for gopher control, single-dose acute baits are generally the most effective.
Bait must be applied below ground. For small infestations or where the use of a mechanical burrow builder is not feasible, use a probe to find the main tunnel next to a fresh mound or between two fresh mounds. Once you find the main tunnel, drop bait into the burrow and then put a board, dirt clod, stone, or other cover over the hole to keep out light and prevent soil from falling onto the bait. Place bait in two or three places along the tunnel.
This hand-application method can be used for single-dose or multiple-dose baits. Reservoir-type hand probes designed to deposit single-dose baits are available. Bait application is faster with these devices because they eliminate the need to stop and place the bait by hand.
For infestations that cover a large area, a mechanical burrow builder is effective and economical. This device is pulled behind a tractor to make artificial gopher tunnels into which it places bait. Use of a mechanical burrow builder may be feasible in situations such as unplanted borders or between widely spaced young trees, if the terrain is relatively level and the soil is not too rocky.
Traps are effective against small numbers of gophers but are labor intensive and therefore relatively expensive to use. You can use either a pincer-type or a box-type kill trap.
To place traps, probe near a fresh mound to find the main tunnel, which usually is on the lower side of the mound. The main tunnel usually is 8 to 12 inches deep, and the probe will drop quickly about 2 inches when you find it. Place two traps in the main tunnel, one facing each direction. Be sure to anchor the traps to a stake with wire. After placing the traps, cover the hole to keep light out of the tunnel. If there is no evidence that a gopher has visited the trap within 48 hours, move it to a new location.
Fumigants such as gas cartridges are not effective because gophers quickly seal off their tunnels when they detect the smoke or poison gases. Aluminum phosphide* can be effective if applied underground into tunnels during a time of year when soil is moist enough to retain the toxic gas, typically in late winter to early spring. Carefully follow all label directions and safety instructions.
UC IPM Pest Management Guidelines:
Acknowledgment for contributions to Vertebrates: