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Ground Squirrels
General Information
Ground squirrels (Spermophilus spp.) can be serious problems. California ground squirrels have a flecked coat and a long bushy tail. In contrast, Belding ground squirrels are slightly smaller, have a short flat tail, and are solid brown. California ground squirrels are generally more of a nuisance than a serious problem because they prefer to stay on field edges, along fence rows or roadsides. However, Belding ground squirrels are a very serious problem. They consume large amounts of crops and inhabit the interior of fields, constructing massive mounds that can damage hay-harvesting equipment. One study estimated that 123 squirrels per acre removed about 1,800 pounds of crop per acre in 44 days. This section pertains primarily to Belding ground squirrels, not California ground squirrels.

Unlike pocket gophers, ground squirrels are frequently visible in the field. they spend much of their time out the burrow, sunning, feeding, or socializing. The burrows provide protection and a place to rear young, store food, and rest and sleep. Their burrow system is not as extensive as that of pocket gophers, but it can be as deep as 6 feet. Ground squirrel burrow systems are much larger in diameter than are gopher systems, and their burrow entrances are always unplugged.

Belding ground squirrels come out of hibernation and are first visible from mid-January to mid-February. They breed in late February and in March. The breeding season lasts 3 to 6 weeks. Young are born in the spring. About 4 weeks after birth, the young squirrels emerge from the burrow. Females have only one litter per year. They may appear to have more litters because the young squirrels are visible for a long period, but this is not the case. The fact is that older females breed first and then the younger females breed, thus giving the impression of multiple litters. Litter size ranges from 3 to 12 young and averages about 7 young. Females may live 10 years or more and have a life span twice that of males.

When they first emerge after hibernation, the squirrels may eat nothing at all, surviving on stored fats, or they may subsist on foliage. They prefer green foliage in early spring and will not eat seed like grain until later in the season. About June 15 to July 1 some of the adult males go into hibernation for the winter. The adult females begin to hibernate later, and then, as fall approaches, the young born that year begin. Although squirrels are not active for much of the year, they are very energetic and nearly double their body weight in a few months.We have worked to get rid of and exterminate our problem ground squirrels, damaging gophers, destructive voles, prairie dogs, ground hogs, chipmunks, rats, badgers and moles out of our property. They kill our trees, grape vines, damage our houses, levees and cause millions of dollars of damage a year. We explain our experience of how to control or eliminate these rodent pests on your property. We have tried to kill these rodents with many types of traps, poisons, bait stations, .22 rifle, and even a propane rodent blaster to explode them in their underground tunnels.


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Control Methods
Deep Tillage
Preventing excessive populations is much easier than bringing high populations under control. Therefore, the first step in squirrel management--deep tillage--should occur when a field is taken out of production. Deep tillage is thought to be effective for controlling squirrels because it disrupts burrow systems. It is believed to be more effective when done in fall than in spring.

Shooting
As a means of controlling large squirrel populations, shooting is seldom effective when used by itself. Shooting is time-consuming, and squirrels become gun-shy. Shooting is best used for fields with low populations or to control survivors that remain following other control operations. Do not approach shooting haphazardly. Section off the field and systematically concentrate efforts in 1-to 2-acre grids.


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Fumigants
Acrolein
Registered in California for the control of burrowing rodents in the spring of 1993, Acrolein (Magnacide) is the most effective method currently available to control ground squirrels. If has achieved up to 95-percent control of both California and Belding ground squirrels in the field trials and commercial applications. A dispensing rod, with nitrogen gas as the propellant, injects Magnacide into squirrel holes. A Restricted Use Permit from the Agricultural Commissioner's Office is required. Other notification requirements may exist as well; if so, they will be stated on the permit. Magnacide can be very hazardous. Those who use it must receive training from company representatives or other qualified persons.

Before using this fumigant, drag the fields to determine which holes are part of active burrow systems. Treat every hole, because distinguishing active burrows by looking at the location of the holes is impossible. Do not treat burrows until aboveground squirrel activity is apparent. The best time for treatment is early in the season, after the squirrels become active but before significant crop growth has occurred. Applying the fumigant before the young are born in the spring is best. Cover holes after treatment. Reopened holes indicate that squirrels were not controlled or that the burrow system was invaded by neighboring squirrels. Revisit treated areas to retreat and open burrow systems. If squirrels remain active burrow systems can be treated after the first cutting. Do not treat holes in the summer or fall; at that time squirrels start going into hibernation and plug off their tunnels--rendering Magnacide ineffective.

The fumigant is too costly and time-consuming to be used on older fields with squirrel populations. Keep squirrel populations at manageable levels by concentrating control efforts on young fields or fields with low infestations.

Gas cartridges and aluminum phosphide
Smoke bombs and aluminum phosphide (such as Phostoxin and Fumitoxin) have been used with limited success. Although Phostoxin has been effective for control of California ground squirrels, it is only 30 to 40 percent effective for control of Belding ground squirrels. Cold dry soils, which prevent the toxicant from penetrating far, may partially explain the poor results. Also, the burrow system of the Belding ground squirrel is so extensive that perhaps not enough toxicant is released to be lethal.

If you use Phostoxin before March, cold soil will reduce its effectiveness. To determine which holes are active, drag the field before using gas cartridges or Phostoxin. Gas cartridges are often preferred over Phostoxin because they help the user determine which holes are part of the same burrow system--smoke escapes from holes in the same system. Seal the hole from which smoke escapes by stomping in it. Determining which holes belong to the same burrow system is difficult when using Phostoxin. Two holes that are next to each other are not necessarily part of the same burrow system, but two holes 25 feet apart may be. Therefore, you must place Phostoxin tablets or pellets in every hole.


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Baits
Anticoagulant baits (chlorophacinone or diphacinone) have been used in some areas. Do not use them before May, because squirrels will not feed on grain early in the season. For baits to be effective, squirrels must feed on them for at least 5 days, with interruptions of no longer than 48 hours between feedings. Greater than 90-percent control has been achieved when anticoagulant baits have been used properly. Grain baits can no longer be broadcast on fields; they must be used in bait stations. Place bait stations around the perimeter of the field and within the field at spacings no larger than 100 feet.

Squirrel management requires the integration of several control practices, each employed at the correct time. These practices include deep cultivation in the fall, fumigation with Magnacide, shooting, and anticoagulant baits.