With the passing of law AB 1322 in 2023 and the recent passing of AB 2552 in September 2024, the options for managing California ground squirrels using lethal methods in urban areas will be more limited. Despite these changes, there are still some viable options available for managing California ground squirrels.

California ground squirrel. Photo by Jack Kelly Clark.

Fumigants

Fumigation can be challenging in urban areas due to the risk of toxic gases leaking into buildings through burrows. However, some burrow fumigants can be used effectively if applied at a safe distance from structures. Be sure to consult the fumigant label for specific usage criteria. Fumigants are lethal to any animal residing within the burrow.

Beginning July 2023, the California Department of Pesticide Regulation (CDPR) has two new fumigation categories available for Qualified Applicator License (QAL) and Qualified Applicator Certificate (QAC) holders. One of these categories, Category M, is required for those who will perform pest control using a pesticide labelled as a fumigant to fumigate pest burrows in sites including, but not limited to: fields, rights of-way, ditches, landscaping, and equipment yards.

There are four types of fumigants available for California ground squirrels.

• Carbon Monoxide Pest Control Devices
  Carbon monoxide (CO) devices are effective but can be costly. These devices cannot be used within 50 feet of inhabited structures. This distance varies depending on the species. Although carbon monoxide is not registered as a pesticide, there are still regulations that must be followed, such as using protective eyewear. Applicators do not need Category M since CO is not registered as a pesticide. In addition, records must be kept for two years for review by CDPR or County Agricultural Commissioners if an employee operates a carbon monoxide pest control device to perform pest control for hire or for a local government, including a city, county, city and county, school district, park district, authority, or any other political subdivision of the state. These records must include the date of use, operator's name, address of treatment location, site where the device was used, and duration of device operation for each treatment.
• Carbon Dioxide
  Carbon dioxide is approved for use on California ground squirrels without proximity restrictions to buildings. However, it cannot be applied to burrows or dens known to house non-target animals.
• Gas Cartridges
  Gas cartridges, made from sodium or potassium nitrate and charcoal (sometimes with sulphur), can be used without a pesticide applicator license. When ignited, they produce carbon monoxide and, if sulphur is present, sulphur dioxide. Use caution with gas cartridges as they pose a fire risk, especially in dry conditions.
• Aluminum Phosphide
  Highly effective (97-100% control in moist soil), aluminum phosphide is a cost-effective choice for controlling ground squirrels. It requires a restricted-use permit and can only be applied by a Qualified Applicator or under supervision. Use is limited to burrow systems located more than 100 feet from buildings and people. 

Table 1. Effectiveness of Fumigation Methods

Trapping

Trapping can effectively control small to moderate populations of California ground squirrels. For larger populations, consider alternative methods.

• Kill Traps: These include box, tunnel, Conibear traps, and the Goodnature® A18 trap. The benefit of kill traps is that the trapper is not responsible for euthanizing live animals.
• Live Trapping: While effective, live trapping requires euthanizing captured squirrels on-site, as relocating them is prohibited under the California Fish and Game Code.

To safely handle carcasses, place the squirrel back in its burrow and cover the opening with soil, or double-bag and dispose of it in a secured garbage container. Be aware that some city ordinances prohibit this practice so it is important to check your local municipal code for guidance.

Live trap set next to a ground squirrel burrow. Photo by Karey Windbiel-Rojas.

Toxic Baits

Zinc phosphide is permitted in limited urban areas (lawns, ornamentals, golf courses, and parks). It is a restricted use material that can only be applied by a licensed pest management professional.

While zinc phosphide can be highly effective and a cheaper option compared to FGARs, efficacy of zinc phosphide is less predictable given its distinctive odor and taste that rodents do not always find palatable; if rodents do not consume the bait, it obviously will not work.

Some labels suggest that zinc phosphide should only be applied once per year, some recommend that applications be separated by 30 days. These recommendations are suggested to limit bait shyness and keep the product effective. Non-toxic prebaiting prior to an application of zinc phosphide is strongly recommended by most rodenticide labels to overcome some of the issues with bait shyness. Because of its acute toxic nature and a lack of an antidote, zinc phosphide is unlikely to be used around homes. Zinc phosphide can be used in a bait station but again not in all areas, and not in all places. It is important to consult the label.

Due to its mode of action, zinc phosphide should not be applied when precipitation, fog, or morning dew are expected. Zinc phosphide should not be applied on top of snow, ice, or wet ground. Do not irrigate for 48 hours after application.

Additional Methods

Other methods such as shooting, repellents, burrow modifications, habitat changes, biological control, and exclusion can also be considered but may have limitations in urban areas. For comprehensive details on these options, visit the Ground Squirrel Best Management Practices Website at www.groundsquirrelbmp.com/.

This article provides a summary of effective control methods for urban California ground squirrel management. Remember to check all labels and follow local regulations to ensure safe and legal use of each control method.

Ground squirrel burrow under a building. Photo by Niamh Quinn.