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.
