Pocket gophers (Figure 1), commonly called moles, are a problem in pastures and hayland throughout much of Alberta. They also eat garden crops and kill woody plants and shrubs by feeding on the roots.
Pocket gophers tend to feed above ground in late spring and early summer, when stems and leaves are most nutritious. As the nutritional quality of stems and leaves declines, pocket gophers turn to feeding below ground on roots and other plant parts. These gophers create extensive burrow systems in search of food.
Soil from the burrows is deposited in mounds above ground. Increased mounding by gophers coincides with the haying season. One animal may make up to 50 mounds per year through its burrowing activity.
The mounds cause wear on farm machinery and necessitate slower operating speeds. Mounds also smother desirable vegetation, provide a seedbed for annual weeds and reduce stand density, particularly in legumes.
Figure 1. Pocket gopher
Unlike ground squirrels that hibernate, pocket gophers are active throughout the winter, feeding and burrowing beneath the snow.
Females have one litter of four to six young during late May or June. The young mature quickly and move out into surrounding areas during late summer and fall. They tend to be solitary with one occupant per burrow system, except during the breeding season and when females are raising young. However, gophers seem to know when their neighbors disappear. Empty burrows may be re-occupied within two to three days.
Problems with pocket gophers are often made worse because many farmers do not try to control them until gopher populations are very high and damage is severe. In addition, gophers on roadsides, headlands and other uncultivated areas are frequently ignored even though these areas serve as reservoirs for gophers, which re-infest newly-seeded legume fields.
The best time to start pocket gopher control on legume fields and pastures is two to three years before seeding, when fields are in cereals or other annual crops and when gopher populations are low. This approach requires long-term planning with the objective of removing all gophers that might re-infest newly-seeded legume fields.
Crops should be rotated so that legumes are not seeded immediately adjacent to pastures and hayfields that are already infested with gophers. Control must be started when gopher populations are at their lowest level, and gopher numbers must be maintained at near zero. In other words, one gopher is too many.
Pocket gophers are forb or broadleaf eaters (for example, dandelions and alfalfa are broadleaf plants); the gophers cannot obtain enough energy to raise young on a diet composed strictly of grasses. Thus, pocket gopher numbers can be considerably reduced from roadsides, headlands and other uncultivated areas with a herbicide that eliminates broadleaf plants (2,4-D for example). Similarly, gophers can be eliminated from cereals and other annual crops by cultivation and effective weed control.
Headlands and roadsides should be treated with a herbicide when adjacent fields are in annual crops, preferably cereals, two to three years before legumes are seeded. If legumes are adjacent to headlands and roadsides, then gophers can obtain an adequate diet by moving into the legumes. Consequently, the herbicide treatment will be less effective. An effective herbicide treatment in early spring should reduce gopher populations by 85 to 90 per cent by the following year.
The remaining gophers should be removed with traps or poison, and infested areas should be spot-treated with herbicide. Brushy or wooded areas need not be treated with herbicide because these are not prime gopher habitat. The few individuals that live within or along the edges of brushy or wooded areas can best be controlled using traps.
Removing all gophers from headlands and uncultivated areas will not totally eliminate gophers from newly-established legume fields because some do move overland. However, most gophers either move in from the headlands or are raised within the field. Removal of all gophers from annual crops, headlands and other uncultivated areas should lead to manageable gopher control or at least delay serious damage on haylands by one or two years.
Strychnine alkaloid and zinc phosphide are registered for pocket gopher control in Alberta. Strychnine is probably more effective than zinc phosphide. Toxicants are usually applied to grain baits, which become less effective after vegetation becomes green in the spring.
Timing is most important; control should be conducted as early as possible in the spring after snow melt and before vegetation begins to grow. Further, it must be emphasized that effective control will probably be achieved only when populations are low, before serious damage occurs.
Underground baiting of pocket gophers is of minimal hazard to other wildlife that might consume bait or eat poisoned gophers. However, poisoned bait spilled on the ground is a hazard to other animals, particularly ground-feeding birds.
Regardless of the method used, bait must be placed within the burrow system. The key to baiting by hand is locating the burrow system.
Gophers tend to throw soil downhill, so the burrow will be located up slope from the mound. Gophers also throw soil away from the burrow entrance creating a fan-shaped or horseshoe-shaped mound. After the mound is built, the gopher plugs the burrow entrance with several centimetres of soil, so the entrance may not be conspicuous. However, the burrow will be located up slope from the mound and at the base of fan-shaped mounds or in the indentation of horseshoe-shaped mounds. The burrow will be 2 to 20 cm below ground level and can be located with a probe.
A long screwdriver or a 1 cm-diameter rod sharpened at one end will make a satisfactory probe. For best results, begin to probe 1 to 2 cm from the edge of the mound. You will know you have located the burrow by the decreased friction on the probe.
Open the burrow system with a shovel and place a tablespoon of bait in each direction in the burrow. Bait should be placed well into the burrow, and the opening should be blocked with soil. If the burrow is left open, the gopher will plug the burrow with soil and may cover the bait before it is eaten.
As an alternative to the method just described, an opening can be made with a probe from the surface of the ground to the burrow. A tablespoon of bait should be dropped into each of two or three probe openings. The openings should then be plugged with soil.
Hand-operated bait-dispensing probes are commercially available although they seem to be unduly heavy. Dispensing bait through a hole made with a probe is faster than opening burrows with a shovel, but you cannot be certain the bait is always placed in a burrow actively being used by gophers.
Mechanical burrow builder
In the late 1950s, a burrow builder was developed to mechanically deliver bait underground so that large areas could be treated for pocket gopher control. The burrow builder is tractor drawn and looks vaguely like a plow. The device consists of a knife and torpedo assembly that makes an artificial burrow at desired soil depths, a coulter that cuts the soil ahead of the knife and a seeder assembly for bait dispensing.
The burrow builder has been used throughout Alberta with mixed results. It does not work well in soil that is sandy, rocky, dry or shallow. However, some farmers have used the burrow builder very effectively. Contact your local municipal agricultural fieldman to determine if the burrow builder has been effectively used in your area.
Gophers can be controlled by trapping, although the method is somewhat time consuming. Probably the best trap on the market today is the box-type gopher trap. These traps are set by removing the fresh mound and placing the trap in the entrance of the lateral tunnel. As many as 20 to 40 traps may be required to remove gophers from fields larger than 16 ha (40 acres).
Traps are most effective in early spring when gopher populations are at their lowest level and mounds are more conspicuous. However, traps can be used in late summer and fall, after forage has been removed and the gophers are building mounds. Traps are set in the burrows. A method for locating gopher burrows was described in the hand baiting section.
Pocket gophers and grazing intensity
Pocket gopher numbers have been shown to increase as grazing intensity increases on native fescue grassland in southern Alberta. Changes in gopher numbers seem to be associated with changes in the physical characteristics of the soil. This means that prolonged overgrazing may cause changes in soil condition that may favor high gopher populations for many years after overgrazing ceases.
(SOURCE: Alberta Agriculture and Forestry)