Getting rid of ground squirrels in California requires combining multiple control methods rather than relying on any single approach. The California ground squirrel (Otospermophilus beecheyi) is one of the most common vertebrate pests in the state, damaging crops, undermining levees and foundations, and creating tripping hazards across rangelands, orchards, and suburban yards. No single tool eliminates them permanently, but anticoagulant baits, fumigation, trapping, and habitat modification each chip away at the problem, and the evidence on how well each works is more nuanced than the labels on the products suggest.
Know What You Are Dealing With
California ground squirrels live in colonial burrow systems that can extend several feet underground, with multiple entrances and escape routes. A single burrow system may house a few adults or an extended family group. The squirrels are active during the day, hibernate or estivate depending on temperature, and breed once per year in spring, producing litters of five to eight pups on average. Their colonial habits and underground lifestyle make them harder to control than solitary rodents. A poisoned bait that kills a few adults still leaves pups underground, and a fumigated burrow is quickly reoccupied by neighbors expanding their range. Understanding this biology is the reason pest professionals recommend an integrated strategy rather than a one-and-done solution.
Anticoagulant Baits
Anticoagulant baits are the most widely used chemical tool for ground squirrel control in California. The two active ingredients you will encounter most often are diphacinone and chlorophacinone, both first-generation anticoagulants that work by interfering with blood clotting. The squirrel needs to consume bait over multiple feedings before a lethal dose accumulates, which is why baiting programs involve repeated applications rather than a single offering.
A common misconception is that bait stations need to be refreshed every day or two, with no more than 48 hours between feedings. Laboratory research on diphacinone has shown that this tight schedule is unnecessary. Two applications spaced three to five days apart achieved effective control, and reducing the amount of bait per application by about 70 percent did not significantly change mortality rates.
1Crop Protection. Effect of the timing of applications and amount of 0.01% diphacinone consumed on mortality of California ground squirrels (Spermophilus beecheyi)That finding matters practically because it means you can use less bait and visit the site less often without sacrificing results. It also reduces how much toxicant ends up in the environment, which is a real concern in California, where secondary poisoning of raptors and other wildlife has drawn increasing regulatory attention.
Field trials comparing diphacinone and chlorophacinone at two different concentrations (0.005% and 0.01%) found no significant difference in efficacy between the two chemicals, the two concentrations, or broadcast versus spot application methods on rangeland.
2Wildlife Research. Comparison of 0.005% and 0.01% diphacinone and chlorophacinone baits for controlling California ground squirrels (Spermophilus beecheyi)In other words, for open rangeland, you have flexibility in which product you choose and how you apply it. The caveat is that these trials were run on rangeland where alternative food sources were limited. In orchards, gardens, or areas with abundant natural forage, squirrels may be pickier about bait, and a lower-concentration product could underperform. If you are dealing with squirrels in a lush irrigated landscape, going with the higher concentration or supplementing with another method is a reasonable hedge.
How to Bait Effectively
Timing your bait applications matters more than most product labels convey. The best window is late spring through early summer, after young squirrels have emerged from burrows and are actively foraging but before natural seed crops mature and give them plenty of alternatives. Baiting during winter, when many adults are dormant underground, wastes product and effort.
For small properties, tamper-resistant bait stations placed near active burrow entrances are the standard approach. You load them, check them every few days, and replenish until feeding activity drops off. For larger acreage, broadcast application with a seed spreader is legal in California for certain registered products, though you need to follow label directions carefully to avoid scattering bait where non-target animals can reach it. In either case, plan on at least two rounds of bait application spaced a few days apart, based on the research showing that two feedings are the critical threshold for lethal accumulation.
One practical tip: pre-baiting with untreated grain for a few days before switching to toxic bait can dramatically improve acceptance. Ground squirrels are naturally cautious about new food sources. Letting them get comfortable with the grain first means more of them eat a lethal dose once the active ingredient is introduced.
Burrow Fumigation
Fumigation targets squirrels inside their burrows by filling the tunnel system with a lethal gas. The two most common approaches in California are aluminum phosphide tablets (which release phosphine gas on contact with soil moisture) and pressurized exhaust machines that pump carbon monoxide into burrow openings.
Aluminum phosphide is highly effective but restricted to licensed applicators in California. You cannot buy it over the counter. It is also dangerous to the person applying it, so this is genuinely a professional-only tool. If you hire a pest control company for ground squirrel work, aluminum phosphide fumigation is often what they use on large infestations.
Pressurized exhaust machines, sometimes called carbon monoxide delivery devices, are available for purchase and increasingly popular with ranchers and landowners. Research on one such device found it was effective against California ground squirrels, achieving roughly 83% reduction in activity, though results varied considerably between study sites, ranging from about two-thirds to complete elimination. The researchers noted that differences in soil moisture and injection time likely drove that variability.
3Wildlife Society Bulletin. Is pressurized exhaust an effective tool against burrowing rodents?Soil conditions are the make-or-break factor for any fumigation method. If the soil is dry and cracked, gas escapes through fissures before it reaches the squirrels. If the burrow system has many open exits, the gas disperses too quickly. Fumigation works best in spring when soils are still moist and compact, which helps seal the gas inside the tunnels. Before fumigating, walk the area and plug any secondary burrow openings you can find with soil or wadded newspaper, leaving only the main entrance open for gas injection. After injecting, seal that entrance too and check back the next day for reopened holes, which tell you survivors are still present.
The practical takeaway: fumigation is a good complement to baiting but not a perfect standalone tool. An 83% reduction sounds impressive until you realize the remaining squirrels can repopulate the colony within a season. Fumigation works best as a follow-up to knock down survivors after a baiting program has reduced the population, or as a targeted treatment for small, isolated colonies.
Trapping
Trapping is the most labor-intensive method, but it is the only option that involves zero toxicants, which matters if you have pets, children, or livestock on the property, or if you are near waterways where chemical runoff is a concern. Kill traps designed for ground squirrels (Conibear-style body-grip traps or modified rat snap traps) are placed at burrow entrances and checked at least once daily. Live-catch traps are also available, but California law requires that captured ground squirrels be killed humanely on site. Relocating them is illegal because they can carry plague and other diseases, and releasing them elsewhere just moves the problem.
Trapping is most practical for small infestations: a handful of burrows in a yard or garden. For a rancher dealing with hundreds of burrow systems across dozens of acres, trapping alone is not realistic. But for suburban homeowners or small-acreage farmers, it can be surprisingly effective. Set traps in the morning when squirrels are most active, bait them with walnuts, peanut butter, or oats, and expect to catch the boldest individuals first. You will notice diminishing returns after a week or two as the remaining squirrels become trap-shy, at which point switching to a different method helps maintain pressure.
Habitat Modification and Exclusion
Ground squirrels prefer areas with short vegetation, loose soil for burrowing, and nearby cover like rock piles, brush, or equipment. Removing cover and maintaining taller, denser vegetation around the perimeter of a property can make it less attractive to colonizers. This is not going to eliminate an existing colony, but it slows reinvasion after you have knocked the population down with other methods.
Exclusion fencing works for small, high-value areas like gardens or individual tree trunks but is impractical for large acreage. Hardware cloth buried at least 18 inches deep and extending a foot above ground will keep squirrels from burrowing into a garden bed. For individual fruit or nut trees, a sheet-metal band around the trunk prevents climbing, though it does nothing about tunneling damage to roots.
Flood irrigation, where it is still practiced, can force squirrels out of burrows and discourage them from settling in irrigated fields. Conversely, drip irrigation that keeps soil surface dry can make a property more attractive to burrowing because the soil at the surface stays loose and workable. This is one of those details that surprises people: switching irrigation methods can inadvertently create or solve a ground squirrel problem.
Why Raptors Alone Will Not Solve the Problem
Installing raptor perches and owl nest boxes has become a popular “natural” approach to rodent control, and it sounds elegant: attract the predators, let them eat the pests. The reality is more complicated. A comparative field study that tested hunting perches against rodenticide treatments and untreated control plots found that perches successfully attracted far more raptors, with barn owls and diurnal raptors spending nearly 98% more time on perch plots compared to rodenticide or control areas. But rodent activity increased across all three treatments over the study period, and vegetation damage worsened regardless of whether raptors were present.
4PubMed Central. Assessing Birds of Prey as Biological Pest Control: A Comparative Study with Hunting Perches and Rodenticides on Rodent Activity and Crop HealthThe study suggested that raptor predation on its own cannot keep pace with a reproducing rodent population. Barn owls, in particular, showed a bottom-up relationship with rodent numbers, meaning the owls tracked where prey was abundant rather than suppressing it. That is a classic ecological pattern: predators follow prey, but rarely regulate prey populations when those populations are booming. Hawks and owls certainly eat ground squirrels, and encouraging their presence is a net positive for the landscape. Just do not expect them to replace active management. Think of raptors as a helpful background pressure, not a solution.
Monitoring Whether Your Efforts Are Working
After any control effort, you need a way to tell whether it actually worked. The simplest method is visual counting: sit at a fixed observation point at a consistent time of day and count the number of squirrels you see above ground over a set time period, say 15 to 30 minutes. Repeat the count at the same time and place before treatment and again a week or two after. The percentage drop in your count gives you a rough measure of how much you reduced the active population.
Research on monitoring methods for California ground squirrels has validated visual counts as an effective tool for assessing control outcomes, comparable to more labor-intensive methods. One practical recommendation from that work is to maintain a buffer of at least about 60 meters around your census area, because squirrels from outside the treated zone can wander in and inflate your post-treatment counts if the observation area is too close to untreated ground.
5DigitalCommons@USU / Human–Wildlife Interactions. Utility of Visual Counts for Determining Efficacy of Management Tools for California Ground SquirrelsIf your counts drop by 70% or more, the treatment was reasonably successful. If they drop less than 50%, something went wrong: poor bait acceptance, leaky fumigation, bad timing, or reinvasion from neighboring properties. That feedback loop is what turns pest control from guesswork into a process you can actually improve on.
Legal Considerations Specific to California
California regulates ground squirrel control more tightly than most states. A few things to know before you start:
- Second-generation anticoagulants are banned: Products containing brodifacoum, bromadiolone, difenacoum, and difethialone cannot be used in California. Only first-generation anticoagulants like diphacinone and chlorophacinone are legal for ground squirrel control, and they must be used according to label directions.
- Aluminum phosphide requires a license: You need a Restricted Materials Permit from your county agricultural commissioner’s office to purchase and apply aluminum phosphide. Homeowners cannot legally buy or use it themselves.
- Strychnine is no longer available: Once a mainstay of ground squirrel control, strychnine-treated grain bait was pulled from the California market. It is not a legal option.
- Relocation is illegal: California classifies ground squirrels as nongame mammals. You may trap and kill them, but releasing them alive elsewhere is prohibited due to disease transmission risk.
- County ag commissioners are a free resource: Every county in California has an agricultural commissioner’s office that can advise on legal control methods, issue permits for restricted materials, and sometimes loan equipment like bait applicators. Contacting them before starting a control program can save you from buying the wrong product or running afoul of regulations.
Putting a Seasonal Plan Together
The most effective approach follows the squirrels’ annual cycle. In late winter, while some adults are still emerging from hibernation, scout your property to identify active burrow clusters. Mark them with flags or GPS so you know where to focus. In early spring, when soils are moist, fumigate isolated or hard-to-reach burrow systems. As spring progresses and juvenile squirrels emerge, begin a baiting program with diphacinone or chlorophacinone, applying bait in two rounds spaced three to five days apart. Through summer, supplement with trapping in areas where bait stations are impractical, and monitor results with visual counts. In fall, before squirrels begin hibernation, do a final round of fumigation or baiting to knock down any remaining population before they retreat underground for winter.
Expect to repeat some version of this cycle annually. Ground squirrels from neighboring properties will eventually recolonize treated areas, and a few survivors from each treatment cycle will rebuild. The goal is not eradication, which is almost never achievable for a colonial rodent living in a landscape full of suitable habitat. The goal is suppression below the level where they cause meaningful damage. Over time, consistent pressure keeps colonies small and manageable, and that is the realistic victory most California landowners should aim for.
When to Call a Professional
For a backyard with a few burrows, a homeowner armed with bait stations and snap traps can handle things. But there are situations where professional help makes sense. Large agricultural properties with hundreds of active burrows are better served by a licensed pest control operator who can use aluminum phosphide or large-scale broadcast baiting legally and efficiently. Properties near waterways or endangered species habitat face additional regulatory constraints that a professional will navigate more easily. And if your initial efforts produce minimal results after two rounds of treatment, a professional can assess whether the issue is bait resistance, reinvasion pressure from neighboring land, or a burrow system so extensive that stronger tools are needed. County agricultural commissioners can also refer you to qualified operators in your area, making them a good first call regardless of the scale of your problem.