Since the drought ground squirrels have taken over my yard. They have built burrows in my orchard and now this spring they are chewing on all the new vegetable starts that I have set out. I notice that they have even stripped some of the bark off the fruit trees I planted this winter. What can I do to rid my yard of these pests?
California ground squirrels (Spermophilus beecheyi) are indeed a formidable garden pest that can be hard to control. They will, as you point out, eat virtually any growing plant, and their burrowing can also be very destructive to trees and hazardous to livestock. According to the UC IPM website “ground squirrels live in a burrow system where they sleep, rest, rear young, store food, and avoid danger. The burrow openings are about 4 inches in diameter but can vary considerably. The burrows can be 5 to 30 feet or more in length and can extend 2 to 4 feet below the soil surface. Often there is more than one opening in a burrow system. Ground squirrels live in colonies that can include several dozen animals in a complex of burrows.”
To discourage population buildups, remove brush piles and debris, and destroy old burrows at least 20 inches down. Since the California Fish and Game Code classifies them as nongame animals, property owners can use any method to remove them. The main methods of control are trapping, fumigation and baiting.
Trapping can work during all seasons except winter. The best trap I have found for catching ground squirrels is the Squirrelinator trap. However you have to be prepared to then dispose of the live squirrels. Touching trapped animals, is not recommended since ground squirrels can harbor bubonic plague and other diseases.
This time of year fumigation can be a better means of control then trapping. Since ground squirrels breed only once a year in the spring time fumigation can work well to control populations. Timing of breeding varies with location but in the Central Valley ground squirrels breed February through April. Aboveground activity by adults is at a maximum at the height of the breeding season. The young are born in the burrow and grow rapidly. When they are about 6 weeks old, they usually start to emerge from the burrow. Fumigation works from early spring to early summer as long as the soil is still damp. When using fumigants read and follow all label instructions. Some fumigants can produce flames, or have fumes accumulate that may leak into a building if burrows are to close, so use cation when using this method of control.
Later in the summer baiting may work to remove the ground squirrels as this is when they’re eating seeds and will be more drawn to the baits. If you do bait make sure to use bait stations that do not allow pets to gain access to the bait.
For more detailed information on ground squirrels and the different methods of control or to see plans for an easy to build bait station visit the UC IPM website at http://ipm.ucanr.edu/PMG/PESTNOTES/pn7438.html