Ground Squirrels

February 5, 2005

By Jiordana Stark, Master Gardener

Q: I don’t know how many other people have this problem, but the ground squirrels in my area are driving me nuts. I have tried different methods of control, but cannot get a handle on them. Is there anything else I can be doing?
Judie M.

SLO

A: You are not alone, Judie, and timing is everything. California ground squirrels are sometimes considered one of the most troublesome pests to homeowners, gardeners, and farmers. They are found in nearly every region of our fair state. They can wreak havoc on grains, nut and fruit trees, and vegetable seedlings in gardens. They can gnaw the bark off young plants, vines, and trees, eat the twigs and leaves, and then destroy the roots by burrowing through them. They can harbor diseases harmful to humans, yet they look so cute and innocent.

While ground squirrels look similar to tree squirrels and may climb trees, when frightened they will always retreat to their burrows, whereas tree squirrels will climb a tree or tall structure and never use a burrow. Ground squirrels live in a burrow system where they sleep, eat, rear young, store food, and avoid danger. They are active during the day, mainly from mid-morning through late afternoon, especially on warm sunny days. During our mild winter months the adults usually hibernate, but the young may remain active. During the hot summer months, most adults go into a period of inactivity, call estivation, lasting a few days to a week or more. During these periods, the burrow appears open at the entrance, but the squirrel plugs it with soil near the nest.

Ground squirrels are mainly herbivorous, their diets changing with the seasons. Timing is the key to controlling them. During summer and fall, squirrels primarily feed on seeds. During this period, baiting with treated grain may be most effective. Fumigation is most effective in spring when soil is moist, which helps seal gasses in the burrow system, and when they can be removed before reproducing.

Trapping can be done spring through fall and is practical when squirrel numbers are low to moderate. Live-catch traps are not recommended because the problem of how to dispose of the live animals arises. They carry diseases and are an agricultural pest, making it illegal to release them elsewhere without a written permit from the California Department of Fish and Game. There are several types of traps available that kill ground squirrels, including box traps, Conibear traps, and tunnel traps. Any trap should be used according to the instructions accompanying the trap.

When fumigating, baiting, or baiting the traps, be aware to minimize hazards to children, pets, poultry, and nontarget wildlife. Only fumigate active ground squirrel burrows. Many nontarget species will inhabit inactive burrows. Ground squirrels can reinvade a site by moving into vacant burrows. Therefore, destroy old burrows by deep ripping them to a depth of at least 20 inches. Simply filling in the burrows with soil does not prevent reinvasion as the squirrels can easily find and reopen old burrows.

Lastly, there is natural control. Many predators, including hawks, eagles, rattlesnakes, and coyotes, eat ground squirrels. Owls are not one of their predators, unfortunately, because they hunt at night and ground squirrels are out during the day. In most cases, predators are not able to keep ground squirrel populations below the level of becoming pests.

Once ground squirrels have been controlled, periodically monitor for reinfestation, check for new burrows, and start control actions as soon as new burrows are noticed. It is far easier and cheaper to control just a few rather than whole colonies.

University of California Cooperative Extension Master Gardener Volunteers can provide additional gardening information upon request .Call the San Luis Obispo office at 781-5939 on Mondays and Thursdays from 1 to 5 PM. You may also call the Paso Robles office at 237-3100 on Wednesdays from 9 AM to 12 PM. The San Luis Obispo Master Gardeners website is at http://groups.ucanr.org/slomg/. Questions can be e-mailed to: mgsanluisobispo@ucdavis.edu.