Control of destructive ground squirrels in demands high kill ratio?

David Wheeler, the wildlife management specialist, outlined the best practices to deal with ground squirrels. 

In vineyards, squirrels can kill young vines by stripping the bark and damage older vines by burrowing through root systems causing moisture loss in the root ball.

Ground squirrels eat shoots and fruit and their constant gnawing, to condition their teeth, on irrigation lines causes significant losses in drip irrigation lines and emitters. Their burrowing weakens ditches and levee banks and can damage foundations of buildings.C

After hibernation during the winter, they start breeding during February and March, producing litters of six to eight that emerge in April.

In describing controls, David said “your goal for control should be a minimum of 90 percent. All you need is for one female to survive and you have the beginning of a problem for the year.”

Once breeding is complete, David said, the females prefer a diet of plants such with high protein levels to support lactation.

“That becomes important because if you try to use treated grain baits, you have to remember they do not readily go to eat grain in spring. So, you’ll need to pre-bait the areas you plan to bait to get them away from what they naturally want to eat.”

Using that example of best practices in Temecula and Murrieta, David said in about April young squirrels may need several weeks to get off their diet of vegetation shoots and switch to foraging for grains. 

Timing is everything to get the most effective control, whether with bait stations, traps, or fumigants, and varies with the season. The animal’s life-stage, population density, and location, although there can be some overlap of the three methods during April and May.

“Before you do anything, try to get rid of brush or debris piles that are shelter for squirrels,” David said. Ground squirrels will travel a quarter-mile from such protection to feed in vineyards and orchards.

 “We use a pre-bait of just rolled oats without any dye or anything added to it. If they eat this, we know they will eat the treated grain,” David said.

Common baits for squirrels are two anticoagulants, diphacinone and chlorophacinone, and zinc phosphide (a restricted material requiring a permit for purchase and use). At Wheeler’s Pest Control we use diphacinone because it has a half life of 21 days. What that means is it take 21 days for ½ of the digested diphacinone to leave the body. ½ of the remaining ½ is expelled in 21 days, so on until it all out of the body of the pest. 

We use two types of bait stations, one of the bait stations we make is of piping made to exclude non-target species and plans prevent the bait from spilling out the ends.                                                                                               Anticoagulants require multiple feedings over a period of about 15 days. Although relatively large amounts need to be consumed for these compounds to be effective.

The T-STATIONS should be placed about every 100 feet near runways and burrows or at the perimeter of the vineyard. They should be anchored to a fence post or stake to keep the bait from spilling out. The smaller “Wilco Stations” would be places on or near burrows. They should be monitored weekly and repeat applications can be made if necessary.

Spot treatments by hand (using anticoagulants only) can be made near burrows. Bait should be scattered and not clumped, since scavenging squirrels will naturally forage and find the bait.

After the bait applications are made and the population is reduced, Fumitoxin can be used on surviving pests that are still burrowing on your property. This product can be used any time of year, but treatment is most successful in late winter to early spring when hibernation has ended and the soil has a higher moisture content which retains the gas best. Soil must be shoveled into the burrow opening to seal it.                                                 Although trapping works well against squirrels, they are time-consuming for preparation and monitoring and are most suited to control of low levels of populations. 

Conibear traps should be placed directly in the opening of the burrow. Traps should be secured to a stake so they can be monitored and retrieved and to prevent them being carried off by predators.

Most useful during early morning and late afternoon, Conibear traps have to be sprung during the evening to avoid non-target animals. Traps need to be monitored and reset as necessary.

Use of modified gopher traps involves baiting for several days at the unset traps to encourage squirrels to forage near them. Afterward, traps can be set and monitored daily.

To avoid catching non-target animals, Rinder recommends setting a larger box over traps with a 3-inch opening 6 inches above the soil line, allowing squirrels to gain access.

Regardless of which method of control is used, it is best for the grower or rancher to become thoroughly familiar with regulations available at respective county agricultural commissioners’ offices before carrying out a control program.

The California ground squirrel, Spermophilus beecheyi, also feeds on almonds, pistachios, walnuts, applies, apricots, peaches, prunes, oranges, tomatoes and alfalfa. It consumes certain vegetable crops at the seedling stage.

A study done several years ago estimated that, in spite of controls, the species inflicts $30 million to $50 million in agricultural and other damage each year in California.

Another study calculated that 200 ground squirrels consumed the same amount of forage as a 1,000-pound steer.