Gophers
Photo by Jack Kelly Clark. Four species of pocket gophers are found in Colorado and
distributed
almost entirely in different areas (Figure 1), possibly because of
different ecological requirements or competition. Plains pocket gophers
(Geomys bursarius) are abundant in sandy and silty soils of
the plains but are not abundant in compacted soils. The northern pocket
gopher (Thomomys talpoides)
occurs in deep, sandy soils of the plains to shallow gravel in
mountainous areas. It is the most common species in mountain rangelands
and forests. The Botta's (formerly called valley) pocket gopher (Thomomys
bottae) is found primarily in well-developed soils of warm valleys
in southern Colorado. The yellow-faced pocket gopher (Pappogeomys
castanops)
inhabits a portion of southeastern Colorado where the plains pocket
gopher is found. However, the yellow-faced pocket gopher is confined to
drier sites. Pocket gophers attain the highest densities on
light-textured soils with good herbage production. Shallow soils limit
pocket gophers due to tunnel cave-ins and poor insulation from warm
summer and cold winter temperatures. Distinguishing among the four species of pocket gophers
in Colorado
is moderately easy. The northern and Botta's pocket gophers have smooth
upper incisors with a single indistinct groove near the inner border
and have smaller bodies and proportionately smaller front feet than the
plains and yellow-faced pocket gophers. The northern pocket gopher
usually is dark-colored with a whitish chin and belly whereas the
Botta's pocket gopher is often reddish-brown with a blackish chin and
reddish belly. These two species are often difficult to tell apart. The
plains pocket gopher has two distinct grooves on the front surface of
each upper incisor whereas the yellow-faced pocket gopher has one
distinct groove. Pocket gophers feed on roots they encounter from
digging, from
vegetation they pull into the tunnel from below, and vegetation above
ground near the tunnel. They like above-ground vegetation when it is
green and succulent. Pocket gophers prefer alfalfa. Many trees and
shrubs are clipped just above ground, especially under snow cover. Pocket gophers construct burrow systems by loosening the
soil with
their claws and incisors, then use their forefeet and chest to push the
soil out of the burrow. The soil is deposited in fan-shaped mounds 12
to 18 inches wide and 4 to 6 inches high. Burrow systems consist of a main tunnel, generally 4 to
18 inches
below the soil surface, and a variable number of lateral burrows
extending from the main. Lateral burrows end with a soil mound or only
a soil plug at the surface. Burrows are about 2 to 3 1/2 inches in
diameter, depending on the size of the gopher. A burrow system may be
linear to highly branched, may contain up to 200 yards of tunnels, and
may have a hundred or more mounds. Pocket gophers usually construct one to three mounds per
day
although the rate varies. One gopher brings about 2 1/4 tons of soil to
the surface each year. Mound-building activity usually is greatest in
spring and fall. Pocket gophers usually breed in the spring and produce
one litter of
one to 10 young (typically three to four) after a gestation period of
about 20 days. Usually, only one adult is found in each burrow system
except during breeding and while raising young. Six to eight plains
pocket gophers per acre are considered high densities whereas northern
pocket gophers occasionally reach densities of 20 per acre. Young
pocket gophers usually begin dispersing from the natal burrow in June
when about one-third grown. Pocket gophers are consumed by owls, hawks, badgers,
coyotes, foxes, bobcats, skunks, weasels, bullsnakes and rattlesnakes. Pocket gophers reduce the productivity of alfalfa fields
and native
grasslands on which they are found by 20 to 50 percent. If gophers are
present on 10 percent of a field, they may reduce overall forage
productivity of the field by 2 to 5 percent. Gopher mounds dull and
plug sickle bars when harvesting hay or alfalfa. Gophers sometimes
damage trees by girdling or clipping stems and by pruning roots.
Gophers may, at times, destroy underground utility cables and
irrigation pipes. In retrospect, gophers are beneficial in several ways.
Their
burrowing activities increase soil fertility by adding organic matter
in the form of plant materials and feces. Their burrowing increases
soil aeration, increases water infiltration, reduces compaction, and
increases the rate of soil formation by bringing up subsoil subjecting
it to weatherization. Gophers are not protected by state or federal laws. When
selecting a
damage-control program, consider nonlethal measures such as habitat
modification or appropriate alfalfa varieties, which may be as cost
effective as lethal measures and should minimize adverse environmental
impacts. It is important to maintain biodiversity, or to retain the
existing plants and animals that may later benefit humans and assist in
maintaining ecosystem function. Pocket gophers can be excluded from valuable plots of
ornamental
trees and shrubs with a 1/4 to 1/2-inch mesh hardware cloth fence
buried at least 18 inches. The bottom of the fence should be bent at a
90-degree angle so that a 6-inch apron of wire projects horizontally
toward the gopher. Place the fence in shallow soil at least 2 feet from
the nearest plants to avoid root injury. This method is of limited
practicality because of expense and labor. Cylindrical plastic Vexar
mesh tubes placed over the entire seedling, including bare root, can
reduce damage to newly planted seedlings. Alfalfa varieties with several large roots rather than a
single tap
root suffer less when pocket gophers feed on them and are more
resistant to grazing by grasshoppers. Each cut section of roots from a
multi-rooted variety will send up a new shoot that may compensate for
losses due to gophers. Rotating alfalfa with grain Crops effectively controls
pocket
gophers because annual grains do not produce large enough roots to
support gophers year round. Planting 50-foot wide buffer strips of
grain around a hay field can provide unsuitable habitat and minimize
immigration of pocket gophers. Controlling broad-leaf forbs with 2, 4-D herbicide
treatments can
effectively control northern and Botta's pocket gophers because they
prefer the underground storage structures of the forbs. This method is
less effective for plains pocket gophers because they easily survive on
grasses. In orchards and shelterbelts, forb control will likely limit
gopher damage. Flood irrigation can effectively control gophers,
especially in
fields that are leveled to remove high spots that might serve as
refuges. The wet-flooded soil generally prevents diffusion of gasses in
and out of the burrow and sticks to the pocket gopher's fur and claws
creating an inhospitable environment. Trapping is one of the best methods to reduce pocket
gopher numbers
on small to moderate-sized fields (less than 50 acres) and to remove
remaining animals after a poison control program. Body-gripping traps
(Death Clutch 1, Macabee, Victor, Guardian Gopher Trap), available from
hardware and trapping supply stores, work exceptionally well for
capturing gophers. Traps can be set in the main tunnel or in a lateral,
preferably near the freshest mounds. The lateral tunnel usually can be
located by a circular plug (sometimes a depression) in the fan-shaped
mound (Figure 2). Probe into the depression, usually in the direction
away from the mound, until the direction of the tunnel is determined.
Remove the several-inch plug of soil with a Garden trowel or a spade.
Insert a trap, secured to a wire and marker stake, with the body
gripping jaws about 6 to 8 inches into the tunnel (Figure 3). Traps also can be set in the main tunnel located about
12 to 18
inches from the mound. After uncovering the main tunnel with a shovel,
set two traps as shown in Figure 3. The tunnels either can be left open
or covered after setting traps. Check traps twice daily since gophers
often visit the traps within a few hours. If a trap is not visited
within 48 hours, move it to a new location. Trapping usually is most
successful in the spring and fall when gophers are actively building
mounds. Four rodenticides are registered for pocket gopher
control in Colorado: Strychnine, formulated on milo, barley or wheat, is a
widely used
toxicant but is highly toxic and potentially hazardous to all wildlife.
It usually is labeled as a Restricted-Use Pesticide. Underground
baiting with strychnine presents minimal hazards to non-target wildlife
but any grain spilled on the surface may be hazardous to ground-feeding
birds. In some studies, zinc (ZP Rodent Bait) phosphide has been less effective
than
strychnine. Diphacinone (
Eaton's Answer) is blended with a water
resistant material and is formulated in bait blocks. The blocks provide
long-term control because the bait remains effective after killing
resident gophers so that invading gophers also are eliminated. Since
chlorophacinone (Rozol) is a multiple dose anticoagulant, more bait is
required to achieve adequate control. To poison pocket gophers, place
the bait in their tunnel systems by hand or with a burrow builder
machine. Place bait into a burrow system by hand after opening
the main
tunnel or with a hand probe. Treat two or three of the freshest mounds
within each burrow system (a circle with about a 100-foot diameter). To
place bait in the burrow system by hand, locate the main tunnel by
digging with a shovel 12 to 18 inches from the plug side of the mound.
Place the recommended amount of bait, following label directions, in
each direction of the opened main tunnel and well into the system.
Close off each tunnel with sod clumps and soil so gophers do not
attempt to close the system and cover the bait with soil. A less time-consuming baiting method involves using a
pointed-rod
hand probe. Locate the main tunnel 12 to 18 inches from the plug side
of the mound by pressing the probe into the ground (Figure 4).
Determine the location of the tunnel by the decreased friction on the
probe. Place bait through the probe hole into the tunnel. A
reservoir-type bait probe dispenser also is available for poisoning
gophers (Figure 4). A button is pushed on the bait probe when it is
pushed in the burrow and a metered dose of bait drops into the burrow.
Place the recommended amount of bait down each of two or three probe
openings and then cover the probe holes with sod. The burrow builder mechanically delivers bait
underground so large
acreages can be economically treated for pocket gopher control. Burrow
builders are available in a standard hydraulically operated unit or a
three-point hitch model. The device consists of a knife and torpedo
assembly that makes an artificial burrow at desired soil depths, a
coulter blade that cuts roots of plants ahead of the knife, a seeder
assembly for bait dispensing, and packer wheel assembly to close the
furrow behind the knife. The seeder box has a metering device for
dispensing various poison baits at desired rates. Burrow builders can
be used successfully in agricultural mountainous areas if the soil is
not extremely rocky. However, operations on steep slopes can result in
poorly constructed tunnels or damage to the torpedo. To achieve good results with a burrow builder: Fumigants, such as aluminum phosphide and gas
cartridges, are not
very successful for controlling pocket gophers because gophers either
sense the poisonous gas and plug the tunnel or the fumigants diffuse
into the soil, particularly when it is dry. Pocket gophers reportedly
can be controlled by injecting exhaust from an old vehicle without
antipollution devices into the burrow for about 3 minutes. Shooting pocket gophers is impractical because they
seldom wander above ground. Protect buried utility cables and irrigation lines by
enclosing with
lead, PVC, or other conduit materials exceeding 2.9 inches in diameter.
Pocket gophers can damage cables armored with soft metals (lead,
aluminum) if the diameters are less than 2.9 inches. Crushed rock or
gravel greater than 1 inch in diameter placed around cables may protect them. Thanks to
W.F. Andelt, Colorado State University Cooperative Extension wildlife specialist and associate professor, fishery and
wildlife biology; and R.M. Case, forestry, fisheries and wildlife, University of Nebraska. 11/95. Reviewed 5/06, for
the above information.
276 ANSWER Gopher Bait Blocks for the Control of Pocket Gophers
Pocket Gophers can be killed with the zinc phosphide bait included in
ZP Rodent Bait is most effective.
Do not apply in wet conditions.
A good thing about zinc phosphide is that there is little danger of poisoning
wildlife by their eating the dead voles, in contrast to anti-coagulant or strychnine
baits. |
cooperseeds.com
|