Chemical control of ground squirrels consists of burrow fumigants and treated baits. Gas cartridges are one of the burrow fumigants which are relatively easy and safe to use. In order for them to be effective, there must be some soil moisture. Since they are like a pyrotechnic device, they should NOT be used in dry conditions or around dry vegetation or other flammable materials.
Remember, gas cartridges are also a pesticide so any employee using them must first be fully trained according to the requirements outlined in Appendix B. In addition, the pre-application checklist is required. The other burrow fumigant is aluminum phosphide which is a highly effective but potentially dangerous Category 1 pesticide requiring special licensing and permits to apply.
Baits treated with diphacinone or zinc phosphide are also extremely effective, but most, like aluminum phosphide, are restricted-use materials. It is illegal and totally inappropriate to use most of the commercially available “rat” poisons in an attempt to control ground squirrels. ACWM is the principal regulatory agency for all pesticide use in Los Angeles County. In that capacity, it is ACWM’s experience that some pest control companies do not always seem to fully understand this nuance. For this reason, it is recommended that an ACWM biologist review any program for chemical control of ground squirrels by a County employee or a vendor.
Meadow Mice (Voles)
Meadow mice (Microtus spp.) are small grayish-brown rodents that look very similar to “regular” mice (house mice) except for the characteristic short tail. They are an intermittent pest in Los Angeles County usually associated with dense ground covers. They can damage a wide variety of plants by feeding and gnawing on trunks, stems, and leaves. Meadow mice need fairly dense and continuous plant cover to move around from their burrows to feeding areas and back. For this reason, habitat modification is particularly effective in deterring them. Removal of weeds, heavy mulch and thick vegetation will help make an area much less suitable for meadow mice. Meadow mice will often use old gopher burrow systems so filling them in after the gophers have been controlled can be helpful.
Small or localized populations of meadow mice can be controlled by trapping. The most common trap used is the standard mouse “snap” trap baited with peanut butter, apple or oatmeal. Be careful, traps can kill non-target animals including native birds. Chemical control of meadow mice includes treated baits and burrow fumigants. Before any of these are employed, an ACWM biologist should be consulted for advice.