Determining the Efficacy of Pocket Gopher Control Practices

Determining the Efficacy of
Pocket Gopher Control
Practices
Steve Orloff
University of California Cooperative Extension,
Siskiyou County
Roger Baldwin, IPM Vertebrate Advisor, KAC
Pocket Gopher
Most common and most
destructive vertebrate pest of
alfalfa
• Burrowing rodent about 6-8 in long; rarely seen above
ground.
• Pair of external fur-lined pouches to carry food and nesting
material
• Large claws for digging
• Lips that close behind incisors so can keep soil out of
mouth while burrowing
• More active excavating soil in spring and fall than summer
• Average litter size 5 or 6
• Max life span 5 years
• Gopher mounds are plugged and often fanshaped.
• Burrow system can cover from a few hundred
sq. ft. to over 1,000 sq. ft.
• Antisocial. As soon as young weaned leave to
establish their own territory
Gopher Damage
• Feed primarily on roots
weakening and/or killing plants.
• Burrow systems cause loss of
irrigation water and erosion.
• Mounds may kill the alfalfa
plants they cover
• Mounds serve as weed seed
beds
• Permanent stand decline so
cause long-term yield reduction
• Generally feed inside burrow
(several inches to foot below soil
surface
• Soil in bales
Assessing Options
• How bad is the
infestation?
• Is it bad enough to
warrant control?
• Or is it so bad that
control is not costeffective
Biology information
• Concentrate control
efforts in late winter to
early spring when
alfalfa is breaking
dormancy and before
gophers give birth.
• Rotation to annual
crops greatly reduces
population
What Control Options are Available?
Pocket
gopher
Habitat
modification
Exclusion
Baiting
Burrow
fumigation
Trapping
X
X
X
X
X
Repellent
Frightening
Shooting
Control Options—Biocontrol
• Natural predators have
been used to control
gopher populations.
• Owl boxes are
inconclusive at best.
• Gopher snakes kill a few
but are unlikely to control
populations.
Control Options—Habitat Modification
• Involves altering habitat or soil to reduce the desirability for pests.
• Example:
- deep ripping to remove gopher burrow systems.
- control weeds to reduce food sources for gophers.
Deep ripping to destroy gopher burrow systems.
Control Options—Repellents
• Repellents rely on
objectionable odors,
unpleasant tastes, or
ground vibration to
deter gophers.
• Examples include
chemical repellents
and sonic stakes.
• These do not work.
Control Options—Exclusion
Pocket gophers
Protected side
Above ground 1’
• Wire boundaries can be
laid 3 feet below
ground.
• Recommend ¾ inch
galvanized wire.
Below ground 3’
• Not typically practical
for large areas.
Perpendicular bend 6”
Control Options—Other Strategies
Gas Explosive Device
• Involves combustion of propane and oxygen.
• Kills gopher through concussive force and will destroy burrow
system.
• May not be overly effective and has potential hazards.
Control Options—Baiting
Pocket gophers
• Best and most widely used bait is
strychnine
• Anticoagulant baits generally less
effective
• Use probe to find tunnel.
• Dispense bait in tunnel.
Control Options—Baiting
100%
Limited training
90%
Thorough training
80%
Efficacy
70%
60%
50%
40%
30%
20%
10%
0%
Field 4
Field 6
Field 7
Mean
Current Control Strategies
•
•
•
•
•
Create artificial burrow at same
depth as created by gophers
Parallel rows 20 – 25 ft. intervals
so intercept gopher runways
(1.8% strychnine better than
0.5%)
Proper soil moisture critical
Only use in areas where gophers
are present
Lancaster experience
The most common source is from the
seeds of the Strychnos nux vomica tree
The Strychnine tree (Strychnos nux-vomica L.) also
known as Nux vomica, Poison Nut, Semen strychnos
and Quaker Buttons, is a deciduous tree native to
India, southeast Asia.
India is the primary place where produced.
Improvement in status of poor people difficult to find labor
force to harvest the strychnine.
Control Options—Fumigation
• Involves use of poison
gas in burrows to
control vertebrate
pests.
• Works best when soil
moisture is high (late
winter early spring for
gophers).
• Fumigants should not
be used around
buildings.
Control Options—Fumigation
Gas cartridges
• Not effective for gophers.
Aluminum phosphide
• Tablets can be used for
gophers.
• Usually apply around 4
tablets per gopher burrow
system. 8 cents per tablet.
• Is a restricted use
pesticide.
Control Options—Trapping
Pocket gophers
• Locate the main tunnel of
a fresh burrow using a
probe.
• Dig down to the burrow
and place the traps. Be
sure the traps are wired to
a stake.
• If nothing captured in 1-2
days move to another
location.
Control Options—Trapping
Pocket gophers
Capture Rate
• Has many positive attributes
including:
90%
80%
Mean capture rate
– knowledge that you’ve
removed the target animal.
– no use of toxic chemicals.
– available for use in organic
setting.
– can be efficient and
economical once user
becomes proficient at
trapping.
100%
70%
60%
50%
40%
30%
20%
10%
0%
Day 1
Day 2
Day 3
Day 4
Trap Comparison Study
Objectives
• Compare capture success of Gophinator and
Macabee traps.
• Compare capture success of covered vs.
uncovered sets.
• Determine if weight or sex of gopher influenced
capture success.
Study Locations
• 4 sites in
Northern CA
• 6 sites in Central
Valley
• 2 sites in
Southern CA
Methods
• Set 20 traps per site of
each combination of:
- Gophinator covered
- Gophinator uncovered
- Macabee covered
- Macabee uncovered
• Traps were set one day
and checked the next.
Methods
• Captured gophers
were weighed and
frozen in plastic bags.
• Sex of gophers was
identified in lab.
Results–Demographics
Spring/Early Summer
Autumn
• Males = 139 (52%)
• Females = 127 (48%)
• Males = 84 (42%)
• Females = 118 (58%)
• Mean Weight:
- Males = 136 grams
- Females = 113 grams
• Mean Weight:
- Males = 171 grams
- Females = 119 grams
Results
Gophinator vs. Macabee Weight Comparison--Autumn
Gophinator vs. Macabee Weight Comparison--Spring/Summer
70
70
Gophinator
Gophinator
Macabee
60
60
50
50
Number of gophers.
Number of gophers.
Macabee
40
30
40
30
20
20
10
10
0
0
60-100
105-145
150-190
195-235
240-280
60-100
105-145
Weight (g)
No difference covered vs. uncovered
150-190
Weight (g)
195-235
240-280
Exhaust from tractor has been used for decades.
• Partially effective but slow and had to open up the
burrow system.
• The back pressure on the exhaust valves can burn up
the valves.
Development of PERC Machine
• Concern that while digging out the burrow gophers would sense
the atmospheric change and block the burrow.
• Developed a probe that would inject the gas into the burrow.
• Pressure from exhaust pipe (a few pounds) inadequate to deliver
sufficient exhaust quickly enough to bring the CO levels in the
burrow to a lethal level.
• Compressor used to pressurize CO.
• Exhaust directly from the engine too hot for the compressor. In
addition, the compressor added about 200 degrees to the
compressed gas stream.
• Components:
– A gas engine, a method to capture and cool the exhaust gasses, a
compressor, a pressure tank and air hoses, hand probes with valves to
inject the gas into the burrow.
An internal combustion engine is used
to generate carbon monoxide and then
pressurize it to 110 PSI. Using multiple
probes, burrows are detected and
carbon monoxide is injected into the
burrow system..
Percentage of Holes Open (Not Plugged)
Gopher Trial #1
100
90
80
70
60
50
40
30
20
10
0
Treated
Control
Percentage of Holes Open (Not Plugged)
Gopher Trial #2
100
90
80
70
60
50
40
30
20
10
0
Treated
Control
Gopher Control With PERC
Tulelake 10/28/11
Belding’s Ground Squirrel Control with
Pressurized Exhaust Device
Klamath Basin and Butte Valley, 2006
100
Efficacy = 81%
Efficacy = 71%
90
Holes Remained Closed (%)
80
70
60
Treated
50
Untreated
40
30
20
10
0
Location 1
Location 2
Cost
20 HP KOHLER ENGINE
6 REELS & PROBES
$12,950
14 HP KOHLER ENGINE
4 REELS & PROBES
$7,695
7 HP ENGINE
2 REELS & PROBES
$5,295
Interest Level in Pressurized
Carbon Monoxide Device
• 400 units in the field and selling about 10
units a month
• Gross sales over the last six years is over $3
million.
• Sales to date approximately 150 percent over
year ago largely due to signing of AB634 in
California
Applied Treatments
• Came back 2 days later
excavated two locations
• Came back day later to
determine percent open
Gopher Study 2012
• Three alfalfa fields Tulelake
• 5 Treatments
1.
2.
3.
4.
5.
Untreated
Gophinator Trap
Carbon monoxide exhaust
injection (PERC)
Aluminum phosphide
Strychnine bait gopher
machine
• Twenty 30 x 30 ft. observation
plots for each treatment
• 80 survey plots x 3 fields (80
acre fields)
• Burrow system excavated at two
locations/plot
• Entry hole left open
• Determined percent open the
following day
PERC Machine
Open
Burrow
Closed
Burrow
Efficacy of Gopher Control Measures
100%
90%
Presence/absence
80%
Plugged burrow counts
Efficacy
70%
60%
50%
40%
30%
20%
10%
0%
Control
Al Ph
Trapping
PERC
Treatment Time Required for Each
Gopher Control Measure
Cheetah Rodent Control Machine
-7% control
Means there were more squirrels after
treatment than before
Conclusions/
Recommendations
• Alfalfa ideal habitat for gophers
• Rip before planting alfalfa or before rotation crop to destroy
burrow system
• Zero tolerance in seedling field
• Trap, bait or aluminum phosphide in seedling field
• Monitor and retreat as needed
• Use integrated approach using variety of control measures
• Older thin stands I would use burrow builder
• Eventually, if population gets out of control may not be worth
treated and time to rotate out of alfalfa