Chapter 1 Pocket Gophers
Application Techniques, Chemicals and Control
The pocket gopher is one of the most serious and difficult to control vertebrate pests that the landscaper or pest control operator may encounter. There are at least 5 species of pocket gophers in the west, with Thomomys bottae having the widest distribution, occurring throughout this area except in the northernmost extremes. The remaining species are confined to the Northwest. Within their ranges, these species are found in most situations, except for very rocky areas, parts of the dry desert and the highest mountain ranges.
DAMAGE
Damage from these pests is multifold. In agricultural and urban situations they commonly attack a variety of crops and landscaping plants by feeding on roots, stems, foliage and bark. They have been known to kill young trees by entirely girdling the bark. Their burrowing activity and removal of vegetation adds to the possibility of slope failure in landscape situations.
In turf they kill the grass, leave unsightly above ground mounds and cut below ground irrigation wires. Their earthen mounds dull or destroy the blades of lawnmowers. There have been many lawsuits due to someone’s tripping on a gopher hole in a yard, park or athletic field.
Typical pocket gopher damage in turf. All this damage is due to one gopher.
ANATOMY AND SENSES
The pocket gopher is named for its external fur-lined pouches on both sides of the head. These pouches are used exclusively for either carrying or temporarily storing food. Because they live an almost entirely subterranean life and rely little on vision, they have very poor eyesight. Gophers have a keen sense of smell and are extremely sensitive in the perception of ground vibrations. This is a sense that comes in quite handy when being stalked by a cat or overly zealous pest control technician. Vibrations are sensed by their oral vibrissae (whiskers) and elongated tactile hairs on the body. Pocket gophers have narrow hips and well-developed shoulders. The narrow hips allow them to maneuver and turn easily in their small burrows while their strong shoulders enhance their digging ability.
An adult pocket gopher, Thomomys bottae.
Baits Used for Gopher Control
Strychnine Bait
Strychnine is a white crystalline powder with a characteristic bitter taste and mild aroma. The bitter taste is significant. Although this apparently does not affect the acceptance of the bait to gophers the taste is a warning to applicators of exposure to the chemical. Humans can taste very small quantities of this chemical. Strychnine is one of the most toxic pesticides with an Acute oral LD50 0f a little less than 2 (Category 1 material). Since strychnine is not water soluble and the baits are very dry there is little danger from exposure through the skin.
There are a number of formulations of strychnine baits but most depend on the impregnation of this highly toxic material on grain bait. The baits vary considerably in percent strychnine of the final formulation ranging from .3 percent to 3 percent. Generally speaking the higher the concentration, the more effective the bait. For the purpose of detection and possibly making them less attractive to nontarget organisms (e.g. birds) baits containing strychnine are marked with a green dye.
Human poisoning due to strychnine in adults is usually a result of suicide attempts or accidental ingestion by children. Again absorption through the skin when formulated as a bait and inhalation potential is very low; however, a certain amount of dust residue accumulates at the bottom of packaging that should be avoided when pouring from the original container.
Strychnine is extremely toxic when ingested and acts very rapidly with the onset of symptoms within 30 minutes or sooner. Symptoms begin as stiffness in the knees and muscle spasms in the arms and legs followed by muscle spasms, which eventually can lead to death due to respiratory failure. In the case of poisoning, once symptoms begin to appear, attempts to induce vomiting should be avoided as this in itself can result in convulsions. Bright light, excessive moving of the victim and loud noises may also increase the chances of convulsions.
Poisoning of domestic animals most frequently occurs when strychnine baits are added to meats (e.g. hamburger) and intentionally used to poison someone pet or pets. Because strychnine use for commercial and homeowner control is confined to gophers the chance of a non-target organism consuming a poisoned animal is quite low. Since strychnine is so fast acting almost all poisoned gophers die below ground. If a large number of gophers are killed in a short period of time this possibility still does exist.
Protective Equipment Required.
Long sleeve shirt and long pants.
Cotton gloves.
Shoes and socks.
Application and Equipment. Application of the highest concentration (3%) is restricted to gopher burrow building machines. Baits containing a 1.8% concentration or lower can legally be applied with a long-handled spoon or hand held mechanically dispensing gopher probe.
Most companies that specialize in gopher control do not use hand held mechanically dispensing gopher probes but prefer non-mechanical probes for locating the gopher’s tunnels and long handled spoons for application. The reason for this preference is that the mechanical probes typically rely on dispensing the bait though a small opening located at the end of a rather large diameter probe. Two problems can occur when using this type of a probe. First of all, as indicated, the diameter of the probe is quite large (up to 1 inch or more). This large size makes it difficult to locate the gopher’s tunnel which can occur a foot or more below the ground. Secondly the small opening at the end of the probe frequently becomes plugged with earth thus preventing release of the chemical into the gopher’s tunnel.
A Non-Mechanical Gopher Probe.
A Mechanical Gopher Probe.
The advantage of a non-mechanical probe is that the diameter of the probe is quite small thus making it more sensitive in finding the gopher’s tunnel. Once the tunnel is located the probe can be withdrawn, flipped around 180 degrees and used to expand the opening with the large end of the probe. This enlarged opening to the tunnel allows accurate spooning of the bait into the tunnel. It is extremely important that all the bait be placed into the gopher’s tunnel and that none is left above ground. Leaving and strychnine bail above ground is considered a serious violation by the California Department of Pesticide Regulations.
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The normal suggested application of strychnine baits is several teaspoons per burrow system. In cases of very heavy infestations it is almost impossible to tell where one gopher system ends and another one begins. In this case where there are mounds “everywhere” it is suggest placing treatments in a grid-like fashion, namely treat every 10 feet at each corner of the subsections of the grid.
Pocket gophers lead an almost completely subterranean existence, venturing above ground only to push dirt out of their burrows, seek new territory, or to graze on plants immediately adjacent to the burrow entrance. The burrow system typically consists of 2-to-4 inch diameter tunnels and can be quite extensive. Depending on the time of year, the main tunnel (run) is situated from 3 to 18 inches (or more) below and parallel to the soil surface.
During the winter, gopher tunnels are typically found at shallow depths (4 to 8 inches). During the summer months when soils tend to dry out and temperatures rise, these critters dig deeper. Lateral runs are dug at varying angles to the surface from the main run and are used to push out loose dirt accumulated by burrowing. Once removed from the tunnel, soil appears as the large mounds (Figure 4) that are characteristic of gopher activity.
These mounds are normally horseshoe in shape, with the high side of the mound furthest away from the plugged opening of the lateral run and the lowest side nearest the plug. The shape of the mound becomes important when attempting to locate the main run (discussed later in control). The number of above ground mounds produced by an individual gopher varies with the season. During the winter gophers produce a daily average of 3 to 4 mounds, while during the summer they produce an average of 1 mound every 2 days. Of course in irrigated areas or areas nearly barren of plants, these figures can change drastically. For example, gophers tend to dig more when looking for food in areas with few plants and, as a consequence, many above ground mounds may be produced in one day.
A Diagrammatic Representation of a Mature Gopher Tunneling System.
Pop holes lead straight up to the surface from the main run and are used as access to foliage growing closely to the opening. Pop holes and lateral runs are nearly always filled with loose dirt, but appear at the surface as small, circular plugs surrounded by denuded foliage. If a gopher dies, irrigation or rain can wash the loose soil plugs from lateral runs and pop holes, which leaves open tunnels. Keeping the pop holes and lateral runs plugged excludes potential predators such as snakes and weasels.
Drainage tunnels, as the name implies, are used for water run-off, which is mandatory during heavy rains or excessive irrigation. There may be one or more drainage tunnels extending downward many feet off the main run and there may be one or more “potty holes” which extend a few inches below the main run. Other parts of the system typically include food storage areas and a nesting area for sleeping and/or rearing of young.
The length and complexity of any one-gopher burrow system depends on a number of factors. First of all these systems are not static but instead they change daily. In well-irrigated areas a gopher may not need to dig much in search of food; but when food is sparse, a gopher is likely to dig considerably, moving into new areas and filling the old tunnels with the earth that it uncovers in doing so.
Because gophers are extremely territorial and the regions of any 2 rarely overlap, it follows that in heavily infested areas the tunneling system of a mature gopher is much shorter than the same-aged gopher in a lightly infested area. Of course it is quite logical that newly formed burrow systems are much shorter and less developed than older more established systems. While a newly formed burrow system may be only several feet in length, it is not uncommon to find well-developed systems beginning in one lawn and extending under a street and continuing a few hundred feet into several other properties on the block.
X
A Typical Horseshoe Shaped Gopher Mound. Top of Image is High Side of Mound. Note the Circular Plug of Earth that Fills the Entrance of Lateral Run. Large x Indicates Where Main Run is Likely to Occur below Ground.
A diagrammatic illustration of how to find the main run. Also note the slightly expanded tip of the mechanical gopher probe. This tip in fact makes the probe very sensitive in find the run.
Considering the previous description the main run in the above diagram would likely occur approximately 1 foot out from the earthen plug or in the location marked by the big x. This would be the location where probing should begin and once found where bait should be placed.
Biology
Mature gophers normally are solitary except at mating time or before the females wean their young. If 2 adult gophers encounter each other at any time other than the above 2 situations, they will fight, occasionally to the death of one.
In warmer areas (e.g., Southern California), these pests remain active throughout the year in irrigated landscaping. Under these conditions, they have a tremendous reproductive capacity, with females capable of bearing 3 broods per year (an average-size brood is 6 to 7 young). In non-irrigated areas, (e.g. natural fields), their reproductive cycles correlate with rainfall; hence, under these conditions, there is typically only one generation per year (during the spring months). Many authorities believe that gophers do not hibernate, but may have a dormant period in non-irrigated areas during the hot, dry summer months.
Even though gophers are typically found underground, they are capable (much to the landscaper’s or homeowner’s disgust) of traveling above ground to new areas. Excavation connected with construction projects or disking of fields is commonly believed to uproot large numbers of gophers that subsequently move into adjacent areas. However, in the authors’ opinion, the opposite is true and that most are likely killed by these operations, especially with deep plowing.
We once had a 40-acre control project that was heavily infested with gophers and squirrels. It was surrounded by homes and there was considerable controversy as to what would happen to the gophers once the property was plowed in order to develop an auto center. As a result our bid included monitoring and controlling any gophers that moved out of the field into the surrounding lawns once it was plowed. We successfully controlled the squirrels prior to plowing, but because the soil in the field was bone dry and there was little rain that year, we had little success in controlling the estimated 3,000+ gopher population. It was quite surprising that after plowing, less than a half dozen of these gophers migrated into the surrounding lawns and an adjacent park and the deep plowing left none in the 40-acre field.
Heavy rains may force gophers from their tunnels. Finally, because these animals are territorial, a mother will force weaned young from her burrow, which then may move above ground up to 1000 feet or more to new territories.
A number of factors determine potential infestation of a given area. Again, unsettled areas are more likely to have more gopher problems than settled areas. Slopes, also, are more prone to infestation than are flat areas. This undoubtedly is associated with better drainage and possibly with the looser soil in filled areas.
Finally, and most importantly, the types of plants used in landscaping are closely linked to potential gopher infestations. Most ornamental trees and shrubs do not readily support large gopher populations and there is a tremendous variation in the attractiveness of various other plants to these pests. Based on several years of gopher control, we find most major gopher problems in areas planted with, gazanias, alfalfa and other legumes such as O’Connor’s legume. In landscaping those ground covers not commonly infested include honeysuckle, ice plant, red apple and ivy to mention a few.
All ground covers have advantages and disadvantages. However if plants such as O’Connor’s legume or gazanias are planted on slopes near undeveloped areas, the landscaper can expect a gopher problem to develop and should be well versed in control techniques.
There have been various studies trying to determine what is the maximum capacity or the largest number of gophers a given area can support. Of course this would be dependent on a number of factors (e.g., slope versus flat ground, type of plants present, soil type, amount of moisture). Indeed this is difficult to determine as these animal live below the ground. However a few hundred per acre would be a conservative figure. I once saw a worker empty a large watering truck into one area trying to drown the gophers out at a school where the gopher population had to be at nearly peak capacity (a mound every 2 feet or so). Several gophers surfaced from the soil in about a 30-foot square area in an attempt to avoid drowning.
Zinc Phosphide Baits
Zinc phosphide reacts with atmospheric moisture to slowly release phosphine (not phosgene), a toxic and flammable gas with an odor similar to garlic or onions. This is again a Category 1 material with an LD50 of around 30.When formulated as grain bait and exposed to normal atmospheric conditions the gas that is produced presents little hazard. However when exposed to acidic conditions (as in the stomach) the gas is released quickly accounting for the toxic nature of the chemical. Although zinc phosphide baits have a strong pungent odor this seems to attract rodents, especially rats, and apparently makes the bait unattractive to some other animals. Bait shyness is a problem if rodents are exposed to sub lethal amounts of the toxicant.
Under normal conditions there is only a small amount of deterioration of zinc phosphide baits due to the loss of phosphine gas. Under field conditions, zinc phosphide baits can remain active for several months until the grain rots or is carried of by harvester ants or other insects. Mineral oil is sometimes added to the grain baits, which gives a considerable amount of protection from moisture.
Animals that consume lethal amounts of zinc phosphide typically die within 30 hours. Early symptoms include nausea, tightness of the chest, excitement and an overall feeling of cold and vomiting of a black colored stomach contents and the garlic smell of phosphine gas. Advanced symptoms include convulsions, paralysis, coma and death due to respiratory failure. If symptoms extend for several days intoxication occurs with resultant heavy liver damage. Typically if an individual lives for 3-day recovery is complete. The odor and color of zinc phoshide baits (gray) are a supposed safety factor in some situations. However as little as a teaspoon of bait can cause toxic symptoms in a child who of course might not be deterred by the color odor.
The dust at the bottom of zinc phosphide container creates a potential hazard and every precaution should be maintained to inhaling this material when pouring from the original packaging. Zinc phosphide bait should not be handled without gloves. Oils and other liquid are used in the preparation of some bait. As a result repeated handling can results in small amount being absorbed through the skin.
Zinc phosphide is not stored in muscles or other tissues so true secondary poisoning (poisoning of non-target animals-dogs, cats) does not seem to be a problem with this chemical. However, if a non-target animal consumed enough poisoned rodent with bait in their stomachs problems could occur. I am aware of a least one situation where a very large number of gophers were poisoned with zinc phosphide and 2 foxes died the following day supposedly due to consuming a number of poisoned gophers. Since this is a slower acting than strychnine it is more probable that some of the animals would die above ground. Still zinc phosphide is considered one of the safest rodeticides from the standpoint of secondary kills. It has the additional safety factor of being an emetic and consequently will be regurgitated if consumed by non-target organisms.
The main formulation that is used as gopher bait is 2% zinc phosphide in an alfalfa pellet. Based on the authors experience this bait is far less effective for gopher control than the strychnine baits. On advantage is that is safer to use than strychnine.
Application. The same techniques used to apply strychnine baits apply to zinc phosphide bait.
Multiple Dose Anticoagulant Baits
Formulation and Toxicity. Chlorophacinone and diphacinone are the most commonly used of the multiple dose anticoagulants with diphacinone being the most commonly used of the 2. Anticoagulant baits are typically dyed blue, which serves as a marker for identification and supposedly makes them less attractive to seed feeding birds and other non-target organisms. As previously mentioned, these materials work by preventing clotting of the blood, rupturing capillary blood vessels and subsequently causing the animal to bleed to death internally. They are referred as multiple dose anticoagulants because in order to be effective an animal typically has to feed on them over a several day period. This is considered to be a slow, but painless death. In the uncommon instance of accidental poisoning there is an antidote, vitamin K.
Application. The same techniques outline for strychnine can be used for these baits. These baits are relatively safe to use and have little if any effect on nontarget organisms (when used below ground for gopher control). Generally speaking they are not that effective for control of these pests when compared to strychnine baits. The problem that exists is that in order to be effective a gopher must feed on them for several consecutive days. Under most conditions it is unlikely that grain based baits will remain attractive to these past for more than a few days. Under moist condition grain baits mold within a few day. This problem can be partially eliminated by treating in a dozen or more locations
daily within the tunneling system. There are also formulations of anticoagulant baits that are imbedded in a wax-like material. Of course in this case the idea is to prevent molding. The author is not aware of how attractive these wax coated baits are to gophers.
Factors Effecting Success with Baits.
Many factors influence the success of control with baits. Dry, sandy soil collapses easily, burying the baits so it’s difficult for the gopher to find. Also in dry soil, gophers may not show signs of activity until moisture is available. On the other hand, excessive moisture can cause the bait to mildew quickly, making it unpalatable to gophers. In our experience, the types of available plants affect how quickly gophers accept bait. For example, gophers are controlled more easily with baits in turf than in O’Connor’s legume (a favored gopher food), as the latter is a preferred host.
Finally, gophers may become “bait shy” if they ingest sub-lethal amounts of bait and become sick. Because the animal associates the sickness with the taste of the bait, it will no longer feed on it. Once this occurs, other types of bait or alternative control method should be used. Bait shyness may develop rapidly in a few gophers; however, typically it takes many months, or even years, of repeated applications to occur in many individuals of a large population.
Fumigants
Gas Cartridges
There are a number of different types of gas cartridges on the market that can be used for gopher control. These range in size from the small cartridges that can be purchased from home and garden center to the large commercial size that are available from The Department of Agriculture.
A commercial gas bomb.
These typically come with a fuse. Once ignited the cartridges are placed in the tunneling system. The subsequent combustion produces a toxic gas-carbon monoxide primarily. Generally speaking these type devices are considered the least effective of the various gopher control techniques. The reason being is it is that gophers have a well-developed sense of smell and can quickly sense the presence of a burning bomb and simply shut off that end of the tunnel where it occurs.
There are two possible situations where control might be achieved with these devices. One would be where a gopher has recently moved into and formed a new tunnel. In this case the tunnel is very short (a few to several feet) and of course more chance of the gas quickly filling the entire tunnel. The other might be where a gopher is trapped between two or more bombs that have been placed in the tunnel.
Aluminum Phosphide
Formulation-Toxicity. Other than this material fumigants are relatively ineffective for gopher control. The most popular formulation of this material for use in outdoor vertebrate pest control is tablets, which are marble like in size. This material is a highly toxic fumigant (Category 1) but as it currently stands a gas mask is not required when used in an outdoor location for vertebrate pest control. To there author’s knowledge there are no cases of human death from the use of this highly toxic material when properly used outdoor for vertebrate pest control. Aluminum phosphide is also used indoor for grain fumigation and clearly presents more of a potential hazard in this situation.
These materials are packaged in an airtight aluminum canister. Once aluminum phosphide tablets are removed from their canister containers and come in contact with atmospheric or any type of moisture the highly toxic phosphine gas begins to be released. This gas is clear and odorless but due to certain contaminants normally has garlic-like smell. It is important to limit how long an individual canister is left open, as atmospheric moisture will react with the tablets in the canister and release gas. Once the canister is tightly closed available moisture is quickly used up and the additional pressure produced by the small amount of gas produced in the canister essentially stops any further release from the tablets.
Protective Equipment Required.
Cotton gloves only when used outdoor for vertebrate pest control.
A canister of Fumitoxin.
Application. Aluminum phosphide may be applied to underground burrow systems located in noncrop or crop areas occupied by woodchucks, yellowbelly marmots, prairie dogs, (except Utah prairie dogs), Norway rats, roof rats, house mice, ground squirrels, moles, voles or chipmunks. All applications must be made outside and not within 15 feet of inhabited structures and under no conditions can applications be made when a burrow system opens under an occupied building.
When opening an aluminum phosphide canister, one should do so with the opening pointed away from face and body and, if possible, in a crosswind. This will not only limit applicator exposure but will serve to protect in the unlikely event of a flash ignition. If large amounts of aluminum phosphide dust accumulate in the bottom of a canister, heat may be generated with a resultant flash when exposed to air. I have been working with this material for almost 20 years and this has never happened. The label also advises not to open canisters in a flammable situation. Because the amount of gas released from tablet or other formulation increases with available moisture (atmospheric or otherwise) some operators have attempted to add water to a treated area (e.g. adding water to a ground squirrel burrow). This is generally considered an unadvisable practice as it increases applicator exposure and the chance of ignition.
When properly used aluminum phosphide (Phostoxin, Gastoxin, Fumitoxin) is by far the most superior rodenticide used for gopher control. It is advisable to only remove the number of tablets that are going to be used within a short period, as this will limit applicator exposure. Cotton or leather gloves should be used when handling aluminum phosphide tablets. Recent experiments indicate that leather gloves (as opposed to cotton) may reduce applicator exposure.
The recommended rate for gophers is 2 to 3 tablets per burrow system. However, in cases of very heavy infestations it is almost impossible to tell where one gopher system ends and another one begins. In this case where there are mounds “everywhere” it is suggest placing treatments in a grid-like fashion, namely treat every 10 feet at each corner of the subsections of the grid.
This is an extremely effective material when used properly in certain environmental conditions. Ideal conditions for effective control include adequate soil moisture, heavy clay soil and access to the entire length of a gopher’s tunneling system.
Aluminum phosphide and gas bombs are generally less effective in sandy soil. The logical reason for this is that in this type of soil, a certain amount of gas escapes from the runs. If sandy soil exists, this problem can be partially alleviated if there is a high level of moisture in the soil, presumably sealing the runs and releasing the gas at a faster rate.
If the entire length of a gopher’s run is not treated, the gopher may escape the gas by plugging off one end of the tunneling system with soil. Best results are achieved by first placing a tablet at each end of the system and then as many as needed at intermittent intervals in between. For effective control, tablets should be applied at the rate of 2 to 4 per burrow system. With very heavily infestations (e.g. a mound ever 3 or 4 feet) the applicator really doesn’t know how many gopher systems there are in a given area. In this situation we have found treating the burrows with one tablet every 15 feet in a grid-like fashion typically will give good control.
Treatment consists of opening up the main runs with a metal probe and dropping a tablet into the tunnel and then closing off the opening. Some county Departments of Agriculture or other regulatory agencies insist that the tunnel be reclosed with a wad of paper and then a barrier of soil. It should be noted that aluminum phosphide use in rodent control has recently been severely limited in recent years. Applicators should check with the appropriate governmental agencies in their area as to these changes.
The possibility exists that endangered species may be found in or around the burrows of target pests. The applicator must always be aware that this possibility exists and take every step necessary to protect these federally and state protected animals when using this or any other pesticide. Generally speaking, information on endangered species can be obtained from a county or state department of agriculture office or from local, state or federal game offices.
Traps.
Trapping, although effective, is time consuming and best used for small areas with light populations of gophers. In heavy infestations there may be hundreds of gophers per acre. Considering the reproductive capacity of these pests, it would be difficult (if not impossible) to control large populations with traps alone. A good trapper typically can set and later check 8 or 9 in an hour. An average catch rate would possibly be 50 %. Assuming there is a large area (10 acres) with a heavy gopher population and taking into account that the average female will produce 6 to 7 young every 4 months who within a few months will also begin reproducing, the numbers become astounding. In this type of situation it would take (according to my math) 3 people trapping 8 hours a day, 30 days a month to stay even with the population. Maybe my math isn’t that good but the point should be made. Traps do not give effective control with big populations of gophers!
One of our studies compared the effectiveness of several models of box and snap traps-the 2 basic trap types. As can be seen from the results in Figure 9, there was a large variation in the degree of effectiveness from model to model.
The Two Commonly Used Types of Gopher Traps. Image Courtesy of California Department of Agriculture.
Normally traps are not baited with any food to attract the gopher. Gophers are normally attracted by light or run into the traps randomly. Typically, snap-type traps (Macabee, Victor) are best set in the main run while box traps are set in the lateral run or in the main run, if there is room.
Snap Traps* No. of sets Percentage Catch
Macabee 263 48.7
Victor Gopher 292 62.2
Newhouse 260 36.7
Box Traps **
Cook Box 294 42.2
Baitless Gopher 267 31.3
Go For Steel 292 16.1
Guardian 278 59.3
California Box 261 44.3
* One set of a snap traps is defined as one trap set in both directions of
the main run.
**One set of a box trap is defined as a single trap set in the lateral run.
Comparative Efficiency of Various Commercially Available Gopher Traps
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Typical locations when setting snap or box type gopher traps and proper placement of baits=bait should be placed in the main run (right). Image Courtesy of California Department of Agriculture.
How to Set a Trap. If possible it is best to set a trap or traps in the main run. In some cases this may not be possible because available space (especially with larger box traps. Once the main run is exposed the trap or traps should be placed as far as possible into the tunnel. Any loose soil should be removed from the tunnel prior to placement. It’s best to work the trap down a little into the soil whenever possible. Snap traps should be secured to a stake with a small chain or wire. If not, a trapped gopher will likely drag the unsecured trap deep into its tunnel before dying. Once in place, soil should be used to close off the tunnel behind the traps. Gophers readily close off any light entering their tunnel system. . In the case of snap-type traps it is preferable to leave a pinpoint of light shining through this earthen closure. The theory is that if too much light (behind the trap) enters the tunnel, the gopher pushes dirt to close off the tunnel and merely sets off the trap with this soil. On the other hand, if a pinpoint of light is left behind the trap, the gopher will think (?) the opening is further down the tunnel and thus more readily blunder to the trap in its attempt to reach the distant opening.
Most box traps already have a hole in them to allow a certain amount of light into the tunnel. In the case of the Guardian box trap, there is a baffle at the back of the trap that covers the hole and permits a minimum amount of light into the tunnel but which supposedly allows a draft to enter. The theory behind this trap is that the draft attracts the gopher.
A trap that recently caught a gopher can be reused without cleaning provided the previous occupant did not rot in the trap and leave an obvious odor. There is no need to use gloves when setting traps as human odor does not repel gophers.
Exclusion. Although not a means of controlling a gopher population, exclusion, as the name implies, is a technique that can be used to prevent gophers from reaching a property or plants in the first place. The use of this technique is typically limited to small-scale locations of relative high value. The most commonly used method of excluding gophers from a property is burying ¼-inch mesh hardware cloth to the depth of 2 feet around the entire perimeter of the property. A 6-inch high wall of the cloth should extend above ground to prevent gophers attaining access via this route. Of course the amount of screening necessary will vary tremendously depending of block fencing or other barriers. The bottom of the hardware cloth should be bent at 135-degree angle away from the property to be protected to reduce the possibility of a gopher working around the barrier. This is not a permanent solution but such a barrier will last several years or more depending on environmental conditions.
Factors that May Lead to Unsuccessful Gopher Control.
Probes. Mechanical handheld probes are most commonly used for injecting poison baits into the gophers’ burrows. Most mechanical probes have a large-diameter injecting end that can clog readily with damp soil. A plugged tip may go unnoticed, resulting in non-baited applications. The large tip can also make it more difficult to determine the location of an open tunnel as opposed to a tunnel that has been refilled with soil. Many commercial vertebrate pest control companies use a non-mechanical gopher probe with a narrow, more sensitive end to find the tunnel (Figure 1, 5). Once it is located, the tunnel can be opened wider with the opposite end of the probe and bait can be poured into it with a long handled spoon or then injected by mechanical probe.
Proper Placement of Bait or Aluminum Phosphide. It is essential to place bait or aluminum phosphide in a main run rather than in a lateral run. This normally can be accomplished by probing 10 to 12 inches in front of the earthen plug of the large mounds. The lateral runs are partially filled with loose soil and placement here (in the soil) will prevent the gopher from finding the bait or prevent the gas from being released into the tunnel.
Dry Soil. Adequate soil moisture is essential for effective gopher control. If there is not enough irrigation or rain, an attempt to control any sizable population of gophers is usually worthless. Without moisture the runs do not maintain their integrity, quickly collapse and cover baits and fumigant pellets. Gophers under these conditions also burrow deeper and make it difficult to find active systems.
Soil Type. It is harder to control gophers in very sandy soil. Aluminum phosphide and other fumigants typically do not work as well as they do in clay types of soil. Tunnels also collapse easily covering baits. In cases where there is not plenty of soil moisture, strychnine bait is preferable to aluminum phosphide.
Competitive Plants. In situations where the preferred host plants such as O’Connor’s legume and gazanias are present, baits may be less effective than when used in other types of ground cover. In these cases the gophers may prefer to eat the plants rather than the baits. In such situations aluminum phospide is by far the preferred product for control.
Workers. Undoubtly one of the major reasons why many gopher control programs fail is due to the personnel who are performing the work. In very large projects gopher control can be very hard work and unless one is especially motivated, the work is performed incorrectly or not at all. It is especially worthwhile to spend the extra money to hire someone who will do a good job.
GIMMICKS AND FOLKLORE
Electrical Devices and Whirling Yellow Pansies. There is and have been a number of probe-like electrical devices that produce a sound or beep and when inserted into the ground, are supposed to drive away or eliminate gophers. We are not aware of any scientific evidence that any of these work. I once walked into a customer’s backyard that had 8 of these devices placed in various locations in her backyard. The whole yard was beeping and the gopher was doing quite well, thank you. It should be mentioned that there are similar devices that can be used in the home for control of any of a variety of insects and vertebrates. Again, in the authors’ opinion and that of many other scientists, these devices are of little, if any, value. Whirling yellow daisies, sunflowers and happy faces, although attractive in the yard, pretty much have the same result.
One of Many Electrical Devices for Control of Gophers and Moles.
Other Remedies. Gopher purge is a plant that is commonly planted in yards with the idea it will drive gophers away. Undoubtedly gophers do not prefer or will not eat these plants, but as far as driving gophers from a property, this seems very unlikely.
There are a number of home remedies that, again, have no validity but are at least interesting. One is that if a person catches a gopher, kills it and then puts it back into its tunnel, it will drive others away or keep gophers from reinfesting the same tunnel. It is true that gophers do reinfest abandoned tunnels. Generally speaking this occurs but typically it takes months. Also, as we know, there is normally only one gopher in each tunnel system. As a consequence, if you kill the only gopher in the tunnel and put its dead body back in, this will not drive away the other gophers, as there are none there in the first place. Additionally a dead gopher in a tunnel rots and is eaten by ants and other insects within less that 2 weeks.
Other remedies include putting a bottle in the tunnels. The theory here is that if a gopher sees its own reflection it will run away. Wrigley’s spearmint chewing gum, banana peels, mothballs and ground glass placed into the tunnel are equally worthless for control.
Placing a water hose in a gopher tunneling system may or may not produce results. If it is a new gopher with a relatively short tunneling system, this may drive the gopher above ground. If it has a well-developed tunneling system with drainage tunnels this typically has no effect as the water merely sinks into the soil, drains down the tunnel while the gopher may retreat to its nest, which is located above the main run and the water. Because excess water has to go somewhere, as it washes out at the other end of the tunnel, it carries dirt with it. This can undermine the tunnel, which sometimes collapses. This can lead to sunken areas on flat ground and devastating slope loss on hillsides.
Placing several road flares in the tunnel has been used for many years and is fairly effective when favorable conditions are present for the use of fumigants. Unlike the small incendiary gas bombs that are available at many garden centers, road flares produce a large amount of gas. These smaller gas bombs are typically only effective on newly established gophers with small runs. Of course the use of road flares over a large area is would be very costly.
Finally the authors are aware of more than one situation where a homeowner has poured gasoline down a gopher tunnel and then igniting its. In one situation the result was setting a field and a neighbor’s fence on fire and in another case (4 gallons were used in this case) the individual basically blew up his backyard and ended up in the hospital. I don’t know if the gopher survived or not but my guess is it did just fine (i.e.-Caddy shack).
Questions,
1. Gophers may become “bait shy” if they ingest sub-lethal amounts of bait and become sick.
2. Gas bombs and aluminum phosphide are less effective for gopher control in dry or “sandy soil”.
3. Other than aluminum phosphide the currently registered fumigants are not generally considered “ineffective” for gopher control.
4. Baits containing single dose toxicants such as strychnine tend to be more effective for gopher control than baits containing multiple dose anticoagulants while the latter is considered safer from the standpoint of possible toxic effects on human and other non-target organisms.
5. 5. It should be noted that aluminum phosphide use in rodent control has recently been “severely limited” in recent years. Applicators should check with
6. the appropriate governmental agencies in their area as to these changes.
7. 6. Experts in the field consider “whirling” yellow daises and electrical devices that produce a beeping sound in the gopher tunnel ineffective for gopher
control.
7. “O’Connor’s legume” and “gazanias” are two host plants that are very attractive to gophers.
8. Strychnine baits left above ground are considered a “serious violation”.
9. Gophers are drawn to a trap by light or run into it “randomly”.
10. It is important to use gloves when setting traps as human odor does “repel” gophers.
11. Gopher traps are a good way to “control large population” of gophers.
12. The “theory” is that if too much light (behind the trap) enters the tunnel, the gopher pushes dirt to close off the tunnel and merely sets off the trap with this soil.