POCKET GOPHERS (Thomomys spp.)

 

Sign and damage Control methods
• Plugged burrow systems
• Earth mounds
• Girdling of trunks below ground
• Stunted tree or vine growth
• Damage to surface irrigation lines
• Row crop and field crop losses		 • Cultural methods (crop varieties, crop rotation, grain buffer strips, flood irrigation, cover crop selection and management, disking to destroy burrow systems)
• Toxic baits
• Fumigants
• Trapping

 

BIOLOGY
Gophers are burrowing rodents named for the fur-lined pouches that open outside the mouth. These pockets are used for carrying food. Gophers are well adapted for their underground existence: they are powerfully built in the forequarters, the forepaws are large-clawed, and the lips close behind their large incisors. They are highly dependent on their sense of touch.

Pocket gophers breed in response to high availability of green vegetation. In natural habitats, they generally have 2 litters per year however, under irrigated conditions they can breed year-round. Litter size may be as high as 10 but typically averages 3 or 4.

Population densities are highly variable and are dependent on soil type and abundance of food resources. Densities of up to 62 gophers per acre have been reported in California.
Burrow systems consist of a main burrow, generally 4 to 18 inches below the soil surface, with a variable number of lateral burrows off the main one. These end at the surface with a soil mound or sometimes only a soil plug. Deeper branches off the main burrow are used for nests and food caches. The rate of mound building is extremely variable, depending on the soil conditions and time of year. Pocket gophers are extremely territorial – outside of the breeding period there is only one gopher per burrow system.


DAMAGE
Gophers damage trees and vines by girdling roots and stems. This may result in the death of the tree or vine, or a reduction in plant growth or fruit yield. Pocket gophers are also a significant pest in many row and field crops. In addition to direct crop losses, gopher mounds dull sicklebars when harvesting hay or alfalfa. Gopher tunnels can weaken ditch banks and earthen dams, and cause erosion in other areas.
Mature vine killed by a pocket gopher
Erosion due to pocket gopher burrows Girdling damage to a prune tree Gophers cause extensive damage to alfalfa


CONTROL
Pocket gopher problems can be managed effectively using a variety of control techniques. The key to a successful program is having a regular monitoring program to detect and remove gophers invading an area.

Cultural techniques:
Site preparation: Disking a field to a depth of 18 inches, prior to planting will destroy a large part of gophers' burrow systems as well as remove some gophers.
Crop varieties: In alfalfa, multiple rooted varieties suffer less damage than varieties with a single taproot.
Crop rotation: Rotation of alfalfa with grain crops reduces the suitability of the habitat for pocket gophers.
Grain buffer strips:
 Planting a 50-ft buffer strip of grain around alfalfa fields may reduce immigration of gophers into a favored area.
Weed control and cover crop management: Gophers prefer legumes over grasses with fibrous root systems so care should be taken in choosing cover crops in orchards and vineyards. Cover should be kept to a minimum to discourage gophers and to facilitate detection of mounds.
Flood irrigation: Flooding fields will make an area less suitable for gophers.
Lethal techniques:
Toxicants: Strychnine, zinc phosphide, and anticoagulants (diphacinone and chlorophacinone) applied by hand, bait dispenser, or burrow builder.
Fumigants: Aluminum phosphide and gas cartridges are relatively ineffective in controlling gophers.
Trapping: Trapping is labor intensive but can be effective in removing small populations of gophers.