Ground Squirrel Control Research Articles

Estimating Reduction in Standing Crop Biomass from California Ground Squirrels in Central California Rangelands

California ground squirrels (Otospermophilus spp.) cause more economic damage to California rangelands than any other rodent. Damage comes in many forms, although forage loss is typically the greatest concern. These losses are believed to be significant for ranchers, particularly given the economically marginal environment in which they exist, yet our understanding of these economic losses is limited. Furthermore, current public opinion is often not supportive toward ground squirrel control on many public grazing lands. Information on the damage that ground squirrels cause to rangelands may be needed to justify management actions in the future. Therefore, we evaluated the amount of standing crop removed by California ground squirrels across 16 sites at four different ground squirrel density categories in central California rangelands from 2019 through 2020. We also included precipitation and livestock grazing intensity to help account for their potential effect on forage production. We found that ground squirrel abundance negatively affected standing crop biomass, with available forage reduced by 27.2 kg ha−1 per individual ground squirrel at the end of the growing season. Likewise, precipitation influenced standing crop, with each cm of precipitation yielding a 16.6 kg ha−1 increase in available forage. We did not observe any effect of livestock grazing intensity, an interaction between livestock grazing intensity and ground squirrel abundance, or an interaction between precipitation and ground squirrel abundance on residual standing crop. Collectively, this information will be useful to ranchers to help determine when control efforts may be needed for California ground squirrels given relative abundance of ground squirrels on their rangeland properties.

Are reports of reduced field efficacy of diphacinone and chlorophacinone in California ground squirrels (Otospermophilus beecheyi) due to elevated rodenticide metabolism?

Anticoagulant rodenticides are commonly used by agricultural producers to control California ground squirrels, Otospermophilus beecheyi, in a variety of crops. With this widespread use, producers are reporting reductions in the efficacy of diphacinone and chlorophacinone for ground squirrel control. Reductions in efficacy have been shown to be related to increased metabolism of compounds to non-toxic metabolites. This study examined liver metabolism of diphacinone and chlorophacinone using microsome isolations from squirrels captured in areas that had never used anticoagulants and areas with a history of prior use. Only male squirrels from anticoagulant exposed areas had a significant reduction in metabolic activity when compared to males from unexposed locations. Based on these data, the cause of the decreased anticoagulant rodenticide efficacy in ground squirrels does not seem to be related to anticoagulant rodenticide metabolism, but may be a result of other physiological (i.e. genetic resistance) or behavioral (bait avoidance) factors.

The Applicability of Burrow Fumigants for Controlling Belding’s Ground Squirrels in Alfalfa

Rodenticides are often used to control burrowing rodents but have not been overly efficacious for Belding’s ground squirrels due to poor bait acceptance. This has left alfalfa growers searching for alternative options for controlling this rodent species. As such, we tested aluminum phosphide and gas cartridge burrow fumigation in an alfalfa field in Butte Valley, CA, to determine if either of these approaches were efficacious and cost effective for controlling Belding’s ground squirrels. A comparison of the number of burrows treated and the number of burrows reopened 48-hours post-treatment indicated that both burrow fumigants were highly effective (aluminum phosphide = 94-98%, gas cartridges = 100%). The average cost per application was $1.05 and $2.92 for aluminum phosphide and gas cartridges, respectively. Given the almost 3-fold difference in cost of application between the two approaches, aluminum phosphide appears to be the more practical approach for Belding’s ground squirrel control. Although we currently lack an approach for estimating the amount of damage that Belding’s ground squirrels are likely to cause to an alfalfa field, it seems plausible that burrow fumigation could be a cost effective approach to reduce damage caused by this species, particularly if long-term control can be obtained. Possible long-term management options for Belding’s ground squirrels are discussed.

Fumigation of California Ground Squirrels Revisited: Are Fumigants an Effective Method for Controlling Ground Squirrels?

Fumigation with either gas cartridges or aluminum phosphide is often considered to be an effective method for controlling California ground squirrel populations, although few studies have corroborated their effectiveness. Additionally, utilizing aluminum phosphide in combination with gas cartridges could increase effectiveness of both fumigants by indicating additional burrow openings through escaping smoke from gas cartridges and allowing for treatment of these additional openings with aluminum phosphide, which is a cheaper and potentially more effective material. Therefore, we compared the efficacy of gas cartridges, aluminum phosphide, and a combined treatment on ground squirrel populations from mid-April through early May 2009 to determine which was most effective. We established 4 plots (3 treatments plus control) at each of 2 treatment sites in Madera County, California. All plots were between 1 and 2 ha in size with survey areas of 0.3 - 0.5 ha centrally located within the plot. Ground squirrels were visually counted within survey areas for 3 consecutive days prior to treatment. Following counting, treatments were applied. Forty-eight hours post-treatment, squirrels were again counted within survey areas to determine percent control. These counts were repeated the following 2 days. All treatments were then reapplied for the same plots, with similar surveys again following 48 hours post-treatment. We found that all fumigation methods resulted in marginal to exceptional control of ground squirrels (percent control: gas cartridges = 62 - 86%, aluminum phosphide = 97 - 100%, gas cartridges + aluminum phosphide = 59 - 71%). We suggest aluminum phosphide use could be expanded to increase ground squirrel control in California, given its high efficacy combined with its relatively cheap material cost.

Ground Squirrel Control Training and Certification using an Interactive Computer Kiosk System

Author(s): Newman, Peter; Salmon, Terrell P. | Abstract: This study was undertaken to demonstrate and assess the efficacy of a new outreach education tool, an interactive touch-screen computer (kiosk) for ground squirrel control education. The target audience for the concept is the California agricultural industry and urban members of the public who are dealing with ground squirrel problems. Users of the computer kiosk are able to access various learning tools: a learning library, a quiz, video learning, an interactive decision-making tool, and they are able to print information and certificates. The computer kiosks are available at select California County Agricultural Commissioner offices. They are networked (computer linked) so that the education content is capable of being added to or amended from remote locations. In addition, the kiosks seamlessly gather statistical data and also collect voluntary information from users (i.e. email addresses and comments). The success of the computer kiosks demonstrated their potential for use in statewide continuing education and pesticide applicator certification efforts related to vertebrate pest control.

Evaluation of Irrigation Valve Boxes as Underground Bait Stations for California Ground Squirrel Control

Author(s): Ellis, Tracy; Salmon, Terrell P.; Wilen, Cheryl | Abstract: The anticoagulants chlorophacinone and diphacinone are registered in California to control ground squirrels. Since multiple feedings on these anticoagulants are necessary, bait stations are often used. Several bait station designs have been suggested and used to reduce tampering and also to minimize bait exposure to non-target animals. Potential options to reduced exposure risk strategies are to use a modified-T bait station, underground bait station, or in-burrow baiting. This study evaluated the behavior of ground squirrels with regard to modified-T and underground bait station compared to the standard-T bait station that is commonly used for ground squirrel control.

Grower Evaluation of California Ground Squirrel (Spermophilus beecheyi) Control using Anticoagulant Baits

Author(s): Kowalski, Victor J.; Long, Rachel; Sullins, Jim; Garcia, Sergio; Salmon, Terrell P. | Abstract: California ground squirrels continue to present a significant problem for many facets of California agriculture. The use of diphacinone- and chlorophacinone-treated baits remains the most frequent control method for ground squirrels in agricultural settings. Research suggests no difference in efficacy between the two bait types or between broadcast and spot baiting strategies or bait stations. However, these studies were limited in scope and were conducted exclusively on rangeland sites where there is limited availability of alternate food sources. Studies also suggest that a reduced baiting strategy may be as effective as current label recommendations, but this has received only limited attention in field research. We utilized a new approach in conducting field evaluations of anticoagulant baiting efficacy in different agricultural settings and locations throughout the state. We solicited agricultural producers as cooperators to participate in a field-based evaluation to determine if the reduced baiting strategies are effective under specific agricultural operating conditions. Cooperators were trained in a simple research design and monitored to ensure consistent data collection. The training program included a comprehensive manual on squirrel biology, behavior, and control, as well as information on toxicants and legal measures regarding endangered species. An informal survey was sent to cooperators at the end of the project to evaluate their opinions on the efficacy of control methods. We found no difference in efficacy between baiting methods or strategies. Differences in efficacy were found between chlorophacinone and diphacinone and efficacy was lower in nut orchards than in other settings. Despite no difference in efficacy between baiting methods, more cooperators indicated they would use bait stations than other methods in future ground squirrel control operations.

Efficacy of Strychnine and Zinc Phosphide Cabbage Baits in Controlling Ground Squirrels in Diamond Valley, Nevada

Author(s): Balliette, John; O’Brien, John M.; Eisemann, John D. | Abstract: A field trial was conducted to determine the efficacy of strychnine and zinc phosphide cabbage baits for controlling ground squirrels in Diamond Valley, Nevada. The reduction in aboveground ground squirrel activity was 83% for strychnine and 70% for zinc phosphide. Similar results were found for reductions in burrow activity: 88% for strychnine and 70% for zinc phosphide. Strychnine appeared to be slightly more effective than zinc phosphide, but both appeared to be effective for ground squirrel control.

Considerations Related to Richardson's Ground Squirrel (Spermophilus richardsonii) Control in Montana

Alfalfa (Medicago sativa L.) production is limited in Montana due to activities associated with Richardson's ground squirrels (Spermophilus richardsonii), and control is often considered to be cost prohibitive. This study was conducted to document the economic impact of ground squirrel activities on alfalfa yield and demonstrate field efficacy of available toxicants. Montana alfalfa producers completed a survey to determine perceived severity and losses due to ground squirrels. Actual first‐harvest forage yield losses were determined at two locations in southwest Montana in 2003 and 2004 using cage exclosures. Chlorophacinone (Rozol), diphacinone (Ramik‐Green), and zinc phosphide were administered at two locations to determine the efficacy of each treatment. Survey results across Montana indicate alfalfa producers estimate a 24% average reduction in forage yield in areas known to be infested with ground squirrels. First‐cut forage yields were reduced by 31% in southwest Montana. Rozol was the most effective control agent (84% efficacy) while Ramik‐Green was the least effective control agent in our trials (29% efficacy). Landowner perceptions of ground squirrel damage are similar to actual yield reduction and possibly underestimated. The costs associated with the control of ground squirrels can be quite high, and caution must be exercised when implementing a new control program to assure these costs are offset by forage gained.

EXIT™/VARGON™ -- a new reduced-risk rodenticide for the control of burrowing rodents

Author(s): McCulloch, Wally | Abstract: EXIT™/VARGON™ is a new, reduced risk, non-toxic, environmentally friendly rodenticide developed in Canada. The product will be marketed as EXIT™ in Canada and VARGON™ in the United States. United States, Canadian and international patents have been applied for. The product was given reduced risk status for the control of burrowing rodents in May 1999 and has been accepted for joint review by the PMRA and EPA under the North American Free Trade Agreement. Laboratory and field research trials conducted within both the United States and Canada to determine efficacy for control of ground squirrels (Spermophilus spp.) showed 100% efficacy in the laboratory and 94% to 98% efficacy when used in the field according to label directions. Laboratory trials conducted in Canada to determine efficacy for control of Norway rats (Rattus norvegicus) showed 100% efficacy in the laboratory. Preliminary field trials have been carried out with promising results. EXIT™/VARGON™ is a concentrated mixture of alpha-olefin sulfonate and mustard seed powder (Brassica hirta) in water. Prior to application, the concentrate is diluted 1 part concentrate to 24 parts water to form the field solution. The field solution is applied as a foam to individual burrows through an air-aspirating nozzle. All treated animals become unconscious due to anoxia within 1 minute and death by asphyxiation occurs in less than 3 minutes from the start of application. Application equipment consists of a water tank, 12-volt 3.6-gpm Shur Flow pump, a hose reel, and 100 feet of ½-inch garden hose. The nozzle is a 3-gallon per minute aspirating nozzle with a 12-inch to 16-inch extension tube to create foam. The foam expands 3 to 4 times as it exits the nozzle and fills most burrows in 15 to 20 seconds. Prior to application, burrow entrances are blocked with a wire basket or perforated plastic cones to prevent escape of target animals. Foam is applied through the basket or cone into the burrow. The product can be applied at any time and does not depend on the feeding patterns of the target species for efficacy. Application can be made in early spring prior to emergence, throughout the summer when the animals are active, or in late fall after the rodents begin to hibernate. Burrows must be examined and certified free of threatened or endangered species prior to using EXIT™/VARGON™. The product is very site specific, and selected areas such as playing fields, grazing areas, parks, etc. can be targeted for treatment while wildland areas can be left as habitat for the ground squirrels. Periodic treatments will keep the selected areas free of target species. The product is biodegradable, environmentally friendly, and essentially non-toxic. It is safe to handle and easy to apply. Treated animals die and remain in their burrows. As the product has no systemic toxicity, there is no secondary poisoning risk to humans or other species.

Fresh cabbage bait for ground squirrel control

Author(s): O'Brien, John M. | Abstract: The Nevada Department of Agriculture acquired the authority to control vertebrate pests of agriculture and public health in 1975. Prior to the Department becoming involved in vertebrate pest control, agricultural producers did not have ground squirrel baits which were very effective. The Department examined products used in surrounding states and due to the effectiveness of sodium monofluoroacetate fresh cabbage baits used in Modoc County, California, began using strychnine cabbage baits. Strychnine was chosen as a toxicant rather than sodium monofluoroacetate because it was thought to be less “toxic” politically. Fresh chopped cabbage baits were initially broadcast above ground in swaths or near active ground squirrel burrow openings. Due to the prohibition of above-ground uses of strychnine which resulted from a 1988 U. S. District Court ruling, the Department changed the labeling of its strychnine paste concentrate. Ground Squirrel (and yellow-bellied marmot) baiting directions now require bait to be placed 6 inches or more into burrow openings. The change in application procedure reduced the effectiveness of chopped cabbage bait, however it still surpasses the effectiveness of grain based baits due to the attractiveness of the cabbage to ground squirrels in Nevada. Baits are usually prepared on site by the producers who apply it immediately after formulation. One application in early spring prior to the emergence of juveniles is the optimum time for baiting. Follow-up applications may be made on surviving ground squirrels or when ground squirrels migrate in from other areas later in the season.

Weatherability of a steam-rolled oat groat chlorophacinone ground squirrel bait under field and laboratory conditions

Investigations of the weatherability of spot-baiting for ground squirrel control in northern CA field studies were conducted with a registered bait consisting of 0.01% chlorophacinone (an anticoagulant rodenticide) on steam-rolled oat groats. For reference purposes, a laboratory test was later conducted in an environmental chamber simulating some of the observed weather conditions. Three weathering plots were established in alfalfa for field tests. Each was baited with rodenticide fortified bait that was handled the same as for a simultaneous control project. Test areas were protected with wire mesh to prevent bait consumption by birds and mammals. Bait samples were collected daily over 7 days, then frozen, and shipped for analysis. Test No. 1 conducted under wet conditions showed a 71% loss of chlorophacinone after 1 week. Test No. 2 demonstrated a 57% loss of chlorophacinone under drier conditions. Test No. 3, a 24 h test under very wet conditions within the alfalfa field irrigated by overhead sprinklers, had a 92% loss of chlorophacinone. Laboratory studies using controlled environmental conditions: light (16 h light:8 h dark), with a mean relative humidity of 98%, and a range of temperature 11.1–27.8°C (52–82°F) showed ≈50% loss of the chlorophacinone. The magnitude was less (37% at 7 days) in the environmental chamber when corrected for water weight gain.

Use of zinc phosphide for California ground squirrel control

Zinc phosphide (ZnP) is the only acute rodenticide currently registered for control of the California ground squirrel (Spermophilus beecheyi). Research has shown ZnP to give excellent control of sciurid rodents, but operational control programs in California have reported poor and inconsistent control. We examined the literature and conducted 34 field trials between 1996 and 1999 in order to identify factors affecting the field efficacy of ZnP. Important factors identified from the literature include bait acceptance, prebaiting, and timing of control operations in relation to ground squirrel and vegetation phenology. We used ground squirrel counts or active burrow counts to assess the efficacy of ZnP in the field trials. Treatments were either mechanical broadcast or spot baiting of 2% ZnP-treated oat groats. The first field trials in 1996 and 1997 were conducted without bait acceptance tests and prebaiting, and control was inconsistent, ranging from none on one plot, poor on three plots (45% to 63%), to good on two plots (84% to 87%). Field trials in 1998 and 1999 were conducted with bait acceptance tests and pre-baiting. In 1998 control was excellent (88% to 100%) on all plots. However, control was variable in 1999 trials with good control (80% to 90%) on five plots, but poor control (60% to 79%) on two plots, and no control on one plot. In our studies, pre-baiting had little effect on the efficacy of the ZnP for controlling California ground squirrels.

Modified bait stations for California ground squirrel control in engangered kangaroo rat habitat

California ground squirrels are a major problem in areas that also support populations of endangered kangaroo rats. Traditional bait stations can be easily modified to exclude kangaroo rats, thereby providing landowners with a method of controlling ground squirrels that mitigates hazards to endangered kangaroo rats. Specifications for the design and use of modified bait stations are discussed.

Effectiveness of two anticoagulant rodenticides (chlorophacinone and bromadiolone) for Columbian ground squirrel ( Spermophilus columbianus) control in eastern Washington

Over the years a number of techniques for control of ground squirrels have been developed and used with varying degrees of success. Some have used bait stations, others the broadcast application of chopped vegetable matter and cereal grains. No data were found on the broadcast application of pelletized materials. Two toxicants, chlorophacinone and bromadiolone, were mechanically broadcast over six plots during the summer of 1983. Results were good (70–80% mortality) with the mid-season application, and excellent (100%) with the late-season treatment. Problems of migration compounded part of the study which points out the need for complete coverage to achieve control.

Control of Ground Squirrels with Ground Sprays of Dieldrin

Control of Ground Squirrels with Ground Sprays of Dieldrin

Poison Control and its Effect upon Wild Life

IN California the control of the ground squirrel (Citellus beecheyi) by poison has given rise to strong protests in journals devoted to ornithology and bird protection, on account of the death by poisoning of numbers of wild creatures which are not injurious. We have already referred to some of these articles, and in fairness, it ought to be stated that the California Department of Agriculture, which is responsible for the organisation of the poisoning measures, accepts neither the “facts” nor the conclusions of the writers. In a summary of “The California Ground Squirrel Control Program”, Eugene S. Kellogg states that those in charge of rodent operations were anxious to know what effect thallium, exposed on bait for ground squirrels, might have on other species of wild life, or how it might act as a secondary poison on predatory animals and birds. To check this point, the Biological Survey made a careful census of the wild life, then exposed baits far heavier than necessary for existing ground squirrel population in order to learn wild life tolerances. Careful checking by several observers during thirty days failed to show an appreciable effect on the beneficial animal life of the area. Hawks, quail and mourning doves, the species watched most carefully, appeared to be as numerous at the conclusion of the test as before (California Dept. Agr. Special Pub. No. 109). In this clash of opinion it is impossible for the outsider to discover exactly where the truth lies; our impression is that there is a certain amount of bias on each side and an absence of the scientific detachment which would carry conviction. A basic fact which cannot be ignored is that ground squirrels are an economic pest which somehow must be controlled.