Meadow Voles and Pocket Gophers: Management in Lawns, Gardens, and Cropland

Erratum for PNW 627 Meadow Voles and Pocket Gophers: Management in Lawns, Gardens, and Cropland

Statements indicating all trapping of voles and gophers is illegal in Washington are incorrect. Some limited trapping is allowed, as follows:

In Washington, the only legal vole or gopher trapping devices are common rat and mouse traps or devices that do not grip or hold the body in any way.

VIEW PDF PNW 627 Meadow Voles and Pocket Gophers: Management in Lawns, Gardens, and Cropland D. Gunn, R. Hirnyck, G. Shewmaker, S. Takatori, L. Ellis

Meadow voles and pocket gophers agency or department of agriculture cause significant damage to range- regarding legal control methods in Voles land, alfalfa, pastures, and other ag- your area. Management options ricultural crops. Combined or alone, depend on the pest, the situation, Vole biology forage losses from gophers and/or cost limitations, and equipment and Several species of voles exist in voles have been estimated at 10 to labor availability. It is important to the Pacific Northwest, and it can be 50 percent in pastures and alfalfa. understand the target pest’s biology difficult to distinguish among them. These rodents also cause significant and habits before implementing The meadow vole, or meadow damage in orchards, nurseries, turf management strategies. mouse (Microtus pennsylvanicus), is farms, ornamental flower plantings, Figure 1. Vole (meadow mouse). Photo by the most common species in pas- landscapes, lawns, and vegetable Danielle Gunn. tures, rangelands, crops, and lawns. gardens. Meadow voles are heavy-bodied, Both voles and gophers dam- small rodents with short legs and age plants by eating roots, trunks, tails; small, rounded ears; and stems, tubers, and leaves. Their coarse, blackish to grayish brown tunneling habits also cause dam- fur with black-tipped hairs and age. Large mounds of soil left by bicolored tails. When fully grown, rodents, particularly gophers, can voles generally average 4½ to 5½ dull knives and discs on harvesting inches long, including the tail (Fig- equipment. Soil from mounds also ures 1 and 2). Under good weather contaminates hay bales. Under- and feeding conditions, voles can ground rodent burrows and tunnels reach 75/8 inches in length. interfere with irrigation practices and equipment. The burrowing and Figure 2. Vole (meadow mouse). Photo by Danielle Gunn. mounding capabilities of gophers encourage weed invasion through ground disturbance and can cause injury to people, horses, and livestock that step into holes. Although voles reproduce more rapidly than gophers, both have remarkable reproductive capacity. Population surges can occur frequently when adequate forage and habitat are available. Voles and gophers are considered non-game mammals in most states and can be legally managed on private property and public lands. Check with your state wildlife

A Pacific Northwest Extension Publication: University of Idaho • Oregon State University • Washington State University Voles can reproduce year-round, by girdling and removing the bark Voles do not hibernate. They are with a peak breeding period in the from the trunk or stems near the active year-round, but are most ac- spring followed by a second, smaller base (Figure 3). Damage to trees and tive in the spring and fall. They are breeding period in the fall. Females shrubs normally occurs in the win- most active at night, but can also be can reach reproductive maturity in ter when voles are foraging under seen during the day. 35 to 40 days. They average one to snow cover. Voles are normally found in areas five litters per year, with three to six of dense ground cover. Vegetation young per litter. Gestation length is greater than 6 inches in height, approximately 21 days. snow cover, brush piles, leaves, and Vole populations are cyclic and low-hanging tree limbs provide pro- can fluctuate dramatically from year tection from predators. Rangeland, to year. During most years, voles alfalfa and grass hayfields, pasture, are not a significant problem, and orchards, and home lawns and gar- populations are partially controlled dens provide ideal habitat and food by predators such as snakes, coy- sources for these pests. otes, foxes, hawks, owls, and domes- Voles do not like crossing bare tic cats. ground and prefer cover when If habitat is abundant and provides feeding. Feeding activity can be adequate protection from preda- easily recognized by the presence tors, weather conditions are ideal, of shallow tunnels and runways and high-protein food sources exist, in vegetation and by underground vole populations can quickly reach nests of grass, stems, and leaves. damaging levels. Minor peak popu- Runways are approximately 1 to 2 lations occur approximately every inches wide, with an entrance hole 4 to 6 years, and epidemic popula- leading underground (Figures 4 and tions occur about every 10 to 12 5). Around frequently used runways, years. However, these cycles are not grass and other vegetation may be regular. Population explosions last clipped very close to the ground. Figure 3. Bark removed by a vole. about a year before the population Photo by Bill Lord, University of New Feces and small pieces of clipped crashes. Population explosions can Hampshire Cooperative Extension vegetation are usually found in run- result in significant economic and Specialist Emeritus. Reproduced by ways. Voles seldom stray from their aesthetic losses. permission from UNH Extension. usual travel routes. Very few references document the Figure 4. Example of vole infestation: feeding area, runways, and entry hole. Photo by cost of vole damage in field crops Danielle Gunn. and nursery stock due to the cyclic nature of vole populations and the potential for explosive epidemics. Economic losses can be severe, but are often not quantified. Vole behavior Most damage caused by voles is Vole Runway the result of feeding activity. Voles weigh 3 to 4½ oz and can eat nearly their own body weight daily. Voles Vole Entry Hole damage crops by feeding on roots and stems, grass, seeds, and un- Vole Entry Hole derground reproductive structures such as bulbs and tubers. They damage and kill trees and shrubs

2 Voles Table 1. Meadow vole management options. Control method Rodenticide Legal constraints* Timing Comments Habitat modification n/a n/a Early spring through Mow, graze, or burn vegetation. late fall Remove weeds and other debris. Exclusions: 3/8-inch n/a n/a Year-round Excellent for protecting trees, netted wire extending 6 shrubs, and flowers. inches below and above desired vegetation. Trapping n/a Trapping is not legal in Anytime Begin in early spring. Place Washington. May be used only traps at right angles in surface in Idaho and Oregon. runways. Hand and mechanical Zinc phosphide Check individual product labels; Early spring through Apply by hand or mechanically. baiting some allow use on cropland. late fall Bait stations are useful for larger Some formulations are populations. restricted-use products. Oregon Do not apply when moisture is has additional restrictions on anticipated. zinc phosphide use. General-use Available for purchase and use Anytime Requires multiple applications. anticoagulants: without an applicator license. chlorophacinone, For noncrop use only. Generally warfarin for use around homes and buildings.

Restricted-use A pesticide applicator license Early spring through Requires multiple applications. anticoagulants: is required to purchase and late fall Diphacinone apply these products. For use (Ramik Brown, in orchards, nurseries, turf, Kaput-D) and lawn, golf courses, tree and chlorophacinone forestry plantations, and other (Rozol Vole Bait) noncrop areas. May be applied to dormant alfalfa. *Pesticide license requirements for baits and fumigants: Note that some baits and all aluminum phosphide fumigants are restricted-use pesticides (RUP) and can be purchased and applied only by a licensed pesticide applicator. Oregon has additional restrictions on zinc phosphide use. Contact your state department of agriculture for more information concerning pesticide licensing for rodent control. Vole management Where voles are likely to be a problem, routinely monitor for signs of Vole Runway feeding activity from early spring until late fall. Runways, clipped forage, gnawed stems, bark, and roots are signs of possible vole activity. Table 1 provides a summary of various measures to help manage damaging vole populations.

Habitat modification Habitat modification and/or population reduction strategies can prevent large population increases. Methods include the following: • Mowing or burning ditch banks, Figure 5. Vole runway. Photo by Danielle Gunn. barrow pits, and fence lines

Voles 3 • Clearing weeds and debris from Do not apply bait when moisture Note: Trapping is not allowed in windbreaks and other affected is anticipated. Place bait stations in Washington State. Residents in areas runways or next to burrows so voles Washington cannot utilize trapping will find them while traveling their • If practical, developing weed-free to manage vole populations. cultivated buffer strips around normal routes. Bait stations can cropland. For large acreages, this be prebaited with vegetables and the ground and at a right angle to is an effective method. peanut butter to attract voles, but surface runways (Figure 6). Use a this practice generally is not neces- • Grazing or mowing alfalfa and small chain to attach the trap to a sary unless voles are not consuming pasture in the late fall when stake to prevent raptors or other bait. If voles are not consuming bait plants are not actively growing predators from dragging away the products, prebaiting with nontoxic • Light tillage of field perimeters vole and trap. bait that is the same size, shape, and and fields Bait is generally not needed formulation as the toxic bait may • Aluminum flashing or other ma- because voles will trip traps during increase consumption. Once voles terials constructed around areas normal activity. If desired, traps are used to consuming the nontoxic of concern to serve as entry can be baited with peanut butter, bait on a regular basis, change to the barriers oatmeal, or apple slices. Voles toxic bait. occasionally learn to take bait with- Always use fresh bait products. Old Plant protection out tripping the trap. To avoid bait bait products may have an off odor You can protect trees, shrubs, and loss, mix peanut butter with cotton or could be moldy or damaged and flower beds by surrounding plants wool or cotton balls and clamp the not effective. cotton into the tripping mechanism with netted wire. Install 3/8-inch When using bait stations in turf, of the trap. netted wire from approximately 6 place them on the edges of turf inches below soil level to approxi- Examine traps daily and remove where the most activity is apparent. mately 6 inches above ground. and bury dead voles. Like all ro- Move bait stations regularly so that dents, voles can carry diseases, turf under the cover is not signifi- Trapping bacteria, and other organisms that cantly damaged. can be harmful to humans, so do In Idaho and Oregon, homeown- For range and pastures, bait can not handle voles without gloves. ers with small infestations can trap be placed around field perimeters. voles with wooden mousetraps. Trapping is best utilized in small Lengthen the feeding tube to at Trap placement is crucial for opti- areas, such as lawns, and is not ef- least 12 inches and stake the bait mum success. Place traps flush with fective or practical for large infesta- station to the ground. The longer tions. tube holds more bait since these stations cannot be monitored as Baiting often as those in lawns and gardens. Toxic bait can successfully control The longer tube also reduces bait voles in gardens, turf, rangeland, spillage. In these areas, bait stations and cropland perimeters. Many of do not need to be covered, since these baits must be placed in bait pets and children are not likely to be stations. Figure 7 illustrates a simple present and good vegetative cover PVC pipe bait station. The plywood will encourage voles to visit. How- cover provides protection from ever, if safety is a concern, use a du- predators or raptors, keeps bait dry rable covering over the bait station. so it does not lose effectiveness, and The cover will prevent non-target prevents access by children, birds, poisoning and deter other animals pets, and other animals. Although from damaging the bait station. Figure 6. Proper trap placement using Figure 7 suggests a quarter sheet of Carefully read and follow all label a right angle to intercept voles using plywood, any sturdy covering, such instructions when applying bait. runways. (Note: Trapping is legal only in as a tarp, canvas, or metal roofing Use caution when applying baits Idaho and Oregon, not in Washington.) material will suffice. where children, pets, and other Photo by Danielle Gunn.

4 Voles Materials Needed: Other zinc phosphide products 3 - 2” PVC pipe cut to 8” lengths are general-use pesticides and do 3 – 2” PVC pipe end caps (two Instructions: partially cut, see diagram) not require a pesticide applicator 1 – 2” T-connection for PVC pipe Assemble all of the pieces as seen in 1 – 12” metal stake (rebar works) the diagram below, making sure that license. These products can be used 1 – Hose clamp you cement all of the pipes to the in turf, lawns, and other non-crop PVC pipe prep and cement T-connection and the two partially cut ¼ sheet of plywood or smaller end caps. Do not cement the end cap areas. They can be placed in run- Feed 6-8” that will be used to fill the bait station. ways, in or next to burrows, or Tube Drill or cut a hole larger than 2” in the mechanically broadcast in infested Hose middle of the plywood. The hole must Clamp accommodate the PVC pipe and the areas. In many areas, spreaders are stake. available for rental from farm or garden supply stores. However, it is 2” 2” always a good practice to place zinc phosphide in a bait station to keep 8” 8” it out of reach of children and non- Stake target animals. Place the bait station in a vole runway and secure to the ground using the Be sure to keep zinc phosphide stake and hose clamp. Place the from getting wet. Moisture activates Leave at least ¾ inch plywood over the bait station making lip on the end cap – sure that the tube and stake fit through the chemical, rendering it ineffec- this will prevent the the hole. Fill the feed tube with bait bait from spilling out and place end cap on top. Place weight tive very quickly. of the bait tube. such as bricks on top of the plywood to Zinc phosphide acts rapidly, and a make sure larger animals cannot get access to the bait. single feeding is generally lethal to voles within 12 hours. In rare cases, voles may survive and become bait Fill tube for the bait station shy. For this reason, zinc phosphide 1/4 sheet of plywood should not be used in the same field more than once in a 6-month period. Note: Place heavy object (bricks, weights) on top of the plywood to prevent larger animals (dogs, foxes, etc.) from disturbing the bait station. Zinc phosphide converts to phosphine gas when it is ingested by a vole, causing death. It does not ac- Figure 7. Bait station construction. Diagrams by Sherman Takatori. cumulate in the vole’s body tissues. non-target animals are likely to be potatoes, sugar beets, grape vine- Therefore, predators or scavengers present. Dispose of dead voles and yards, orchards, and nursery stock. such as dogs or cats are not likely bait that may spill from the trap These products can be broadcast on to be affected by eating poisoned so there is no chance of poisoning the target site. Before purchasing, rodents. However, children, pets, pets, livestock, or wildlife. check the label to be sure the prod- birds, and other animals can be uct can be used on the target crop. Zinc phosphide baits: Zinc phosphide is sold under trade names Oregon restrictions on zinc phosphide use such as Prozap and ZP AG. Some zinc phosphide products are com- In order to prevent exposure to geese from zinc phosphide applied on bined with grains, while others are grass grown for seed, Oregon has issued Special Local Need (SLN) regis- in pellet form. trations with specific application restrictions and timing of applications. Additionally, there are several other Oregon SLN labels for zinc phos- Some zinc phosphide products are phide use that prohibit any use in Gilliam, Morrow, and Umatilla coun- restricted-use pesticides and require ties. Some Oregon SLN labels restrict uses to below-ground applications a pesticide applicator license to pur- only. Be sure to check with the Oregon Department of Agriculture or chase and use. These products in- their website (http://www.oregon.gov/ODA/PEST/index.shtml) before clude those labeled for agricultural purchasing or applying any zinc phosphide in Oregon, and read and fol- crops such as wheat, barley, alfalfa, low all zinc phosphide use directions on the Oregon SLN labels.

Voles 5 Diphacinone bait products Additional cautions regarding rodenticide use (Ramik Brown and Kaput-D) are Rodenticide baits may pose a hazard to federally designated endan- restricted-use pesticides available gered and/or threatened species and may not be used in any manner only to those who have a current that results in harm or death of these species. It is the responsibility of pesticide applicator license. These the pesticide applicator to perform any application correctly so that it products can be used in fruit and will not harm and/or kill any threatened and/or endangered species. nut orchards, tree nurseries, and Always follow the rodenticide (pesticide) label directions, especially the tree farms, but cannot be applied “Environmental Hazards” section of the label. The label may contain directly to food or feed crops. additional web-distributed information that will be the responsibility of Another restricted-use pesticide is the pesticide applicator to obtain and follow. If you have any questions Rozol Vole Bait (chlorophacinone). or concerns regarding species that may be affected by the application, It can be used in noncrop areas, contact your local extension office, state department of agriculture, or lawns, turf, ornamental flower and local fish and wildlife agency. shrub plantings, orchards, nurseries, Rodenticide (pesticide) labels and uses are constantly changing. Spe- and tree and forestry plantations. cific product names and rates are not provided in this publication, due General-use anticoagulant pesti- to the nature of changing labels and product availability. The following cides include another formulation websites may be useful for checking on locally registered rodenticide of chlorophacinone (Rozol pellets) products. Be sure you select a product that is allowed for your applica- and warfarin (Kaput, Rodex). These tion site and target rodent pest. products can be used by the general • In Idaho, the University of Idaho Pest Management Center maintains public. They are intended for use an annually updated table of rodenticides labeled for use to control around homes and buildings. meadow voles and pocket gophers in a variety of sites. The web ad- All anticoagulant baits are toxic to dress is http://www.uihome.uidaho.edu/ipm. other animals, so take precautions • In Oregon and Washington, a searchable pesticide database, Pesticide to prevent nontarget animals from Information Center Online (PICOL), is available online at http:// consuming the bait. Carefully read cru66.cahe.wsu.edu/LabelTolerance.html. This is a very detailed and follow the precautionary state- search engine and requires some additional knowledge. It is recom- ments on the pesticide label. Bait mended that you seek advice from extension personnel the first time must be used at the specific target you access information from PICOL. site as indicated on the label. • In Oregon, also be sure to check the Oregon Department of Agricul- Predators ture website for a list of zinc phosphide SLN registrations: http://oda. state.or.us/dbs/pest_productsL2K/search.lasso Owls, hawks, snakes, cats, dogs, and other predators utilize voles as a food source. However, predators affected by direct contact with the are useful around ditches and other alone will not eliminate damage to bait. Store bait out of reach and use areas where moisture may cause fields, rangeland, trees, or lawns, it carefully to minimize unintended other types of baits to spoil and lose and often do not keep vole popula- access. potency. tions at an acceptable level. Anticoagulant baits cannot be ap- Anticoagulant baits: Anticoagu- plied directly to food or feed crops. lants require multiple feedings by To avoid contact with a growing the rodent before a lethal dose is in- crop, these baits are used in areas gested. Anticoagulant baits are for- adjacent to crop fields or during mulated using grain or other food crop dormancy. Before purchasing sources that will attract rodents. any product, check the label to be These baits are usually in the form sure it can be used on the target of pellets and blocks, and some are site. coated in paraffin to provide moisture resistance. Paraffin-coated baits

6 Voles Pocket gophers Pocket gopher biology Pocket gophers (Figure 8) are one of the most prevalent and destructive vertebrate pests in the Pacific Northwest. There are three genera of pocket gophers in the United States, Thomomys, Geomys, and Pappogeomys, representing 18 different species. Genus classification is based on the size of the forefeet, claws, and front surfaces of the incisors. Identification of species can be difficult. Generally, only one species is found in a defined area. Pocket gophers are burrowing rodents that get their name from the fur-lined, external cheek pouches they use for carrying food and nest- ing materials. Pouches are located outside the mouth on both sides of the face. Pocket gophers are 5 to 14 inches long and have soft fur, rang- Figure 8. Pocket gopher. Photo by Glenn Shewmaker. ing in color from black to varying shades of brown. Some species can and produce one or two litters per those that do not diffuse air for be yellow to almost white. year, averaging three to six young breathing (high-moisture, clay- per litter. In irrigated alfalfa fields, based soil textures) limit popula- Pocket gophers are well equipped it is not uncommon for gophers to tions. Deep soils are also important for digging and tunneling. They have up to three litters per year. The for insulating gophers from extreme have powerfully built forequarters; gestation period is 20 days for most temperatures. Vegetation with large, large-clawed front paws; fine, short species. Births occur from March fleshy roots or tubers creates ideal fur that does not cake in wet soils; through June. habitat. small eyes and ears; and flat heads and short necks. Gopher lips close Burrows consist of a main tunnel behind four large incisor teeth to Pocket gopher behavior and several lateral tunnels, which keep soil out of their mouths while Gophers do not hibernate and are are linear or branched (Figures 9 digging, leaving their big, yellow active year-round. They are territo- and 10). Tunnels are about 2½ to 3½ incisors visible. Highly sensitive rial and antisocial. There is nor- inches in diameter. Tunnels always facial whiskers and tails help go- mally only one gopher per burrow slope toward the ground surface be- phers move in the dark. The tail is system, unless the gopher is mating cause gophers do not make straight sparsely covered with hair and has or is a female raising a litter. vertical tunnels. the unique function of helping to Gophers reside in varying geo- A gopher’s burrow system can regulate body temperature. Gophers graphical elevations, soils, and cover an area that is 200 to 2,000 have a keen sense of smell, which conditions. They will occupy rocky square feet. Typically, most feeding enables them to find food. areas, but prefer fine-textured, deep, burrows are 6 inches or less below Gophers become sexually mature porous soils that are conducive to the soil surface. The nest and food at 1 year of age and can live for 3 to digging and feeding. Soils that do storage chambers can be as deep as 5 years. Gophers breed in the spring not hold tunnels (sandy soils) and 6 feet.

Gophers 7 As they dig tunnels, gophers push loose soil to the surface, forming mounds that are 12 to 18 inches wide and 4 to 6 inches high. Typically, mounds are crescent- or horseshoe-shaped when viewed from above. These soil deposits are plugged lateral tunnels. A slight depression will be present on the plug side of the mound (Figure 11). Gophers can create several mounds in one day. Fresh soil mounds are evidence of recent activity. For the most part, gophers re- main underground, although they are sometimes seen feeding at the edge of an open burrow, pushing soil out of a burrow, or moving to a new area. Gophers rarely venture more than 2½ feet from a burrow entrance. Figure 9. Gopher burrow system—top (above) and side (below) views. Drawing by Betsy Gophers feed underground on Morishita. roots and tubers, and they cut plant stems below ground to pull plants into the burrow (Figure 12). They acquire water from the vegetation they feed on and do not need to leave the burrow to drink. Gophers will consume any edible plant material, including green, succu- lent vegetation; roots; bulbs and tubers; grasses and seeds; forbs; tree roots and bark; and legumes with palatable roots, such as alfalfa and clovers. Annual crops, such as grains and annual grasses, are not ideal habitat for gophers because their shallow, fibrous root system does not provide a good food source. Alfalfa is one of the best food sources and habitat for pocket gophers. Gophers are very destructive to alfalfa fields, feeding on alfalfa taproots and killing the plants. Gopher damage to alfalfa is perma- nent and will continue to affect field productivity throughout the life of the stand. Figure 10. Underground view of a pocket gopher system. © Regents of the University of California. Reproduced by permission from Orloff, S., et al., eds. 1997. Intermountain Alfalfa Management. Publication 3366, University of California Division of Agriculture and Natural Resources. 8 Gophers In irrigated cropping systems, Gophers can also be very destruc- there is snow cover. This damage gophers can damage irrigation lines, tive to tree nurseries, orchards, and will reduce plant health and may kill divert water by burrowing through vineyards, especially during the the plant. ditches and dikes, degrade canals winter, when food sources are lim- The level of infestation required to and levees, and cause soil erosion ited. Gophers will gnaw and feed on produce economic damage depends problems and various structural the bark around the base of trees, on growing conditions, irrigation failures. shrubs, and vines, especially when practices, and the type and economic value of the crop. In a high-value crop, as few as two gophers per acre can decrease yield and plant viability. Pocket gopher management Understanding pocket gopher habits, especially the burrow system, is the key to effective control. Man- agement methods include trapping, hand or mechanical baiting, fumigation, combustion, cultivation, and crop rotation. For most effective control, use a combination of methods. In cases of heavy infestations, drag or harrow the field to eliminate mounds of soil and identify active burrows. See Table 2 for a summary of control measures. Figure 11. Fresh gopher mound. The depression in the mound indicates a plugged hole. Photo by Danielle Gunn Trapping In Idaho and Oregon, trapping is legal and is a safe and effective control method for small areas or light infestations. It may not be practical or economical for large acreages or for heavy infestations. Trapping can be done year-round, but is difficult when the ground is frozen. The most common type of trap is a two-pronged pincher trap. The trap is triggered when the gopher pushes against a flat, vertical pan. Examples include the Cinch, Macabee, and Gophinator (Figures 13–15) style traps.

Note: Trapping is not allowed in Washington State. Residents in Washington cannot utilize trapping to manage pocket gopher populations. Figure 12. Gopher cache of beans. Photo by Glenn Shewmaker.

Gophers 9 Table 2. Pocket gopher management options. Control method Rodenticide Legal constraints* Timing Comments Vegetation modification n/a n/a Early spring through Mow, graze, or burn vegetation. late fall Remove weeds and other debris. Cultivation n/a n/a Early spring through Cultivation destroys burrows and late fall mounds. Crop rotation to small n/a n/a When possible Gophers do not prefer the shallow grains roots of small grain crops. Trapping n/a Trapping is not legal in Year-round Time-consuming but effective. Washington. May be used only Use traps in pairs, facing in Idaho and Oregon. opposite directions in the main burrow. Hand and mechanical Strychnine Cannot be used above ground. Early spring through Very effective. baiting late fall

Zinc phosphide Check product labels for Early spring through Apply by hand for small usage information. Some late fall infestations or mechanically for formulations are restricted- large infestations. Do not apply use products. Oregon has when moisture is anticipated. additional restrictions. Hand baiting Rozol For noncrop use only. Early spring and late Can be effective for small fall infestations. Mechanical baiting Rozol Gopher Bait Restricted-use pesticide. Can be Early spring and late For use with artificial burrow Burrow Builder used in alfalfa. fall builders. Can be very effective. Formula Exclusions: gravel, ½- to n/a n/a Year-round Helps protect ornamentals and 3/8-inch wire mesh, metal, underground structures. wires, and underground plastic pipes Fumigation n/a Aluminum phosphide is a Spring through late Works best when soil is moist restricted-use product. Carbon- fall enough to maintain tunnel monoxide-producing devices structure. are not restricted-use products. Combustion n/a n/a Early spring through Use extreme caution with this late fall method. *Pesticide license requirements for baits and fumigants: Note that some baits and all aluminum phosphide fumigants are restricted-use pesticides (RUP) and can be purchased and applied only by a licensed pesticide applicator. Oregon has additional restrictions on zinc phosphide use. Contact your state department of agriculture for more information concerning pesticide licensing for rodent control.

Figure 13. Cinch Trap. (Note: Trapping is legal only in Idaho and Oregon, not in Washington.) Photo by Sherman Figure 15. Macabee gopher trap. (Note: Takatori. Trapping is legal only in Idaho and Oregon, not in Washington.) Photo by Figure 14. Improved Cinch Trap. (Note: Sherman Takatori. Trapping is legal only in Idaho and Oregon, not in Washington.) Photo by Sherman Takatori. 10 Gophers Another popular type is the chok- in the main burrow. Beginning with Although the main tunnel is er-style box trap (Figure 16). Box a fresh mound, probe on the plug generally the best place to trap, traps are often easier to set, particu- side of the mound with a gopher trapping in lateral tunnels may be larly for the beginning trapper. The probe or by digging with a shovel. effective if traps are placed where Black Hole Trap is similar to a box If using a shovel, dig into the lateral there is evidence of very recent trap, but is made with a plastic tube tunnel plug until it can be opened. activity. In fact, experienced gopher the same diameter as a gopher bur- Then follow this lateral to the main trappers report more success trap- row. It uses a spring-loaded noose tunnel; it will intersect with the ping in actively used laterals than instead of the box trap’s spring- lateral burrow approximately 8 to 12 in main burrows. Laterals are used loaded ridged wire mechanism to inches from the soil plug and will be for maintenance of the main bur- catch the gopher. 6 to 12 inches deep. Often, the main row system, and gophers generally Generally, open-trigger style traps burrow goes between two lateral revisit a lateral a number of times to (box, Cinch, Gophinator) are better tunnels. move soil and other materials to the for lateral tunnels, and closed- Gopher probes (Figure 17) can surface. trigger style traps (Macabee and make it easier to locate the main One advantage of trapping in the Victor Ring) are better for main tunnel. Probes can be purchased laterals is that less digging is burrows. from farm supply stores or con- needed. Trapping in main tunnels To begin trapping, locate areas structed with pipe. It takes some takes more time and significantly of recent gopher activity based on practice to recognize when the disturbs the burrow system. The the presence of fresh mounds of probe enters the main burrow. gopher may become aware of this moist, dark soil. Mounds have a When it drops approximately 2 disturbance and shy away from the small, circular depression on one inches, you have located the main trap. Also, when trapping an active side, which is the plugged opening tunnel (Figure 18). of a lateral tunnel. Gophers may not revisit lateral tunnels, so trapping and baiting may be more successful

Figure 16. Box trap. (Note: Trapping is legal only in Idaho and Oregon, not in Washington.) Photo by Sherman Takatori. Figure 18. Gopher probe in burrow. Photo by Glenn Shewmaker.

Figure 17. Gopher probe. Photo by Danielle Gunn.

Gophers 11 lateral, there is no need to cover the opening, since gophers usually leave laterals unplugged. Regardless of whether you trap in the main tunnel or in a lateral, use a shovel to open the tunnel wide enough to set traps. Place traps in pairs with their openings facing opposite directions (Figure 19) in order to intercept a gopher coming from either end of the burrow. Attach traps to stakes with wire to prevent gophers from moving them deep into the burrow system. If trapping in main burrows, cover openings with plywood, soil clods, or other materials to exclude light. Gophers do not like openings in Figure 19. Proper trap placement in gopher tunnels. Note stakes for the traps. (Note: the main burrow system and will Trapping is legal only in Idaho and Oregon, not in Washington.) Drawing by Betsy promptly cover the source of light Morishita. or leave, thereby avoiding the trap. voir (Figure 20). Use the device to If trapping in lateral tunnels, it is probe for the gopher burrow and not necessary to cover the opening. place a premeasured amount of bait Move traps approximately every 3 in the burrow by turning or de- days. pressing a lever. Hand baiting Place the bait in the main tunnel in two or three locations. Close the Bait must be placed in the main probe holes with plywood, rocks, burrow where gophers are active. soil clods, or any other material that If bait is placed in lateral burrows, will exclude light and protect the the gopher is more likely to push bait. Make sure to prevent dirt from it up to the surface, increasing the falling on the bait. Do not reuse the chance of nontarget poisoning. bait placement device for any other After locating the main gopher purpose. tunnel as described on page 11, After placing bait, use a shovel or enlarge the opening by rotating the spade to knock down or level exist- probe or inserting a rod or stick into ing gopher mounds. This will make the opening. Place the bait carefully it easier to identify new gopher in the opening using a long-handled activity and retreat as necessary. spoon or other suitable device. Take care not to spill bait onto the Rodenticide bait rates vary de- ground. Hand-held gopher-baiting pending on the product type, loca- equipment can be purchased from tion of use, and application method. farm supply stores. These devices Check the product label for rates. consist of a probe and a bait reser- Strychnine: Strychnine is the most common type of toxic bait utilized Note: See sidebar on page 6 for for control of small gopher infes- more information about using tations in lawns and agricultural fields. It can be used only below rodenticides. Figure 20. Hand-held gopher baiting ground. Strychnine baits are sold apparatus. Photo by Danielle Gunn.

12 Gophers under many trade names, and most plication than single-feed baits such Mechanical baiting contain 0.5 percent strychnine. as strychnine. Burrow builders (Figures 21 and 22) Contact your local extension office Anticoagulant baits contain are an effective, time-saving method for information on these products. diphacinone (Kaput D, Gopher of baiting in large areas with signifi- Strychnine is lethal in a single Whacker, and Answer) or chloro- cant numbers of gophers. Burrow feeding. Strychnine accumulates phacinone (Rozol). Diphacinone builders can be connected to a in body tissues; therefore, if a pet bait products can be used only on three-point tractor hitch. With this or other animal ingests a gopher lawns, golf courses, rangeland, and system, a tube or “torpedo” and poisoned with strychnine, immedi- other noncrop areas. colter cuts the soil and makes arti- ate death can result. Pick up and ficial burrows, a seeder or granular dispose of spilled bait according to Note: See sidebar on page 6 for applicator dispenses bait into the label instructions. more information about using artificial burrow at specific intervals, Zinc phosphide: Several zinc rodenticides. and a packer wheel closes the fur- phosphide products are available. row. Gophers will explore the new Check labels to be sure you select a product suitable for your needs. Figure 21. Burrow builder applicator. Photo by Glenn Shewmaker. ZP Rodent Bait is labeled only for underground applications in rangeland, cropland, forest areas, parks, nurseries, lawns, golf courses, and around homes. Other zinc phosphide products can be used only on lawns, golf courses, and other noncrop areas. The State of Oregon may have additional restrictions on the use of zinc phosphide for pocket gopher control. Oregon has several Special Local Need (SLN) labels for the use of zinc phosphide. (See the sidebar on page 5 for more information.) Be sure to check with the Oregon State Department of Agriculture or their website (http:// www.oregon.gov/ODA/PEST/index. Figure 22. Burrow builder applicator. Photo by Glenn Shewmaker. shtml) before purchasing or applying any zinc phosphide in Oregon, and read and follow all zinc phosphide use directions on the Oregon SLN labels. Anticoagulants: Anticoagulant baits are generally less effective than strychnine baits but are less toxic. Their lower toxicity makes them a better choice in areas where pets or other domestic animals might uncover the bait through digging. These products are multiple-feed baits and require more bait per ap-

Gophers 13 burrows, increasing their potential uninfested area to explore artificial Fumigation for bait consumption. burrows. Fumigation with lethal gases, Baiting artificial burrows will not When applying bait, check fre- such as aluminum phosphide and prevent gopher infestations. Use quently to ensure that tunnels are carbon monoxide, can be a cost- the machine only where gophers developing properly and that the effective method of gopher control. are present. Treat the perimeters of bait dispenser is working properly. Machines are available that make fields to delay reinvasion. Strychnine is the most common and distribute gases throughout the Use of a burrow builder requires type of bait used with burrow burrow system. significant knowledge. Consult the builders. Rozol Pocket Gopher Carbon monoxide-producing manufacturer or a knowledgeable Bait-Burrow Builder Formula devices do not require a pesticide person about proper use. (chlorophacinone) is also approved applicator license to purchase and Before using a burrow builder, dig for use on alfalfa and rangeland, in use. Aluminum phosphide is a around fresh gopher mounds to orchards and groves, and noncrop restricted-use product and requires determine the depth of the main areas in Idaho, Oregon, and Wash- a pesticide applicator license to tunnels and the soil conditions ington (EPA Reg. No. 7173-244) with purchase and use. in the field. The burrow builder burrow builders. It is a restricted- Carbon monoxide is odorless, must be set at the same depth and use pesticide, requiring a pesticide but the methods used to produce perpendicular to existing burrows. applicator license to purchase and it sometimes give off odors. None- Dig burrows 20 to 30 feet apart. Soil apply. Apply this product when soil theless, these odors do not seem moisture must be adequate so the conditions allow formation of good to alert gophers to danger, so they soil will hold the burrows. When artificial burrows. do not attempt to seal holes in the crossing uninfested areas, raise the Always read label instructions tunnel or try to escape. Aluminum shank to avoid making burrows; when applying any bait. Be sure to phosphide emits an odor, but it gophers will invade a previously pick up spilled bait and dispose of it does not seem to alarm gophers. according to label instructions.

Figure 23. Gopher control in a large infestation using the Rodenator. The Rodenator uses a mixture of oxygen and propane to kill gophers and collapse tunnel systems. Photo reproduced courtesy of Meyer Industries, Emmett, Idaho.

14 Gophers When using aluminum phosphide, it is very important to treat each burrow system at three different locations. This will provide adequate gas dispersion throughout the burrow system. DO NOT add water to aluminum phosphide tablets or pellets in order to liberate the phosphine gas faster. The rapid release of gas could create a hazardous situation for the applicator.

Combustion A mixture of propane (or other explosive gas) and oxygen (Figures 23 and 24) can be very effective. The gases are forced into the burrow system and ignited. The combustion kills the gopher and collapses the burrow. Collapsing the burrow or a portion of the burrow reduces Figure 24. Use of the Rodenator to control gophers. Photo reproduced courtesy of Meyer the chance that another gopher will Industries, Emmett, Idaho. re-inhabit the burrow system. The explosive gas is used in a very Crop rotation particularly high, temporary buffer low concentration relative to the Rotating alfalfa and pasture to strips might be an economically vi- oxygen mix, but gophers do seem able option. to avoid the gas mixture due to the small grains can be a very effective odor. control measure. Small grains have Predators small, fibrous root systems that Gas cartridges are available, but do not sustain gophers as well as Predators that feed on gophers in- they are costly and time-consuming fleshy, tap-rooted vegetation such as clude owls, hawks, badgers, coyotes, to use and give varying results. alfalfa. foxes, bobcats, skunks, weasels, bull Because gopher tunnels are exten- snakes, and rattlesnakes. However, Growing a buffer strip of small sive, gas may not disperse through these predators do not effectively grains around alfalfa and pastures the entire system. Gophers may control large populations. smell the gas and plug the tunnel can discourage large gopher popula- before it can reach them. Wet soils tions. Buffer strips are particularly Other options beneficial if the field is adjacent to inhibit gas dispersal. Because of Fences can protect ornamental an area with a known infestation their higher cost and inconsistent shrubs and trees. To protect flower or to land where gophers can’t be effectiveness, gas cartridges are not beds and vegetable gardens, bury controlled, such as state or federal recommended. ½- to 3/8-inch mesh wire 2 feet land. Buffer strips should be ap- deep, leaving 1 foot extending above Using combustion for gopher con- proximately 50 feet wide. trol can be hazardous to the applica- ground. Lay gravel around cables tor and must be done with extreme Some growers feel that buffer and encase sprinkler lines in metal caution. strips this large are not practical for for protection. perennial crop protection since they Cultivation take land out of production. How- ever, the purpose of the buffer is to Tilling, disking, and plowing can protect the crop from heavy infesta- inhibit gopher activity. Cultivation tions that could be economically destroys burrows and mounds and damaging. If gopher infestations are may drive gophers to other locations.

Gophers 15 Further readings Vantassel, S.M., S.W. Hygnstrom, The Authors D.M. Ferraro, and B.E. Anderson. Andelt, W.F. and R.M. Case. 2006. 2009. Publication G1509, Control- Danielle Gunn, University of Idaho Managing Pocket Gophers. Natural ling Pocket Gophers in Nebraska. Agricultural Extension Educator, Fort Hall Resources Series No. 6.515, Colo- University of Nebraska Lincoln— rado State University Extension. Extension. http://www.ianrpubs. Ronda Hirnyck, University of Idaho http://www.ext.colostate.edu/ unl.edu/sendIt/g1509.pdf Extension Pesticide Coordinator pubs/natres/06515.html Whitaker, J.O. 1996. National Audu- Glenn Shewmaker, University of Case, R.M. and B.A. Jasch. 1994. bon Society Field Guide to North Idaho Extension Forage Specialist Pocket Gophers: Prevention and American Mammals. Alfred A. Sherman Takatori, Program Man- Control of Wildlife Damage. Uni- Knopf, Inc., New York (11th print- ager, Idaho State Department of versity of Nebraska Lincoln—Ex- ing, 2007). Agriculture tension. http://icwdm.org/handbook/rodents/pocketgophers.asp Lance T. Ellis, University of Idaho Extension Educator, Fremont O’Brien, J.M. 1994. Voles: Prevention County and Control of Wildlife Damage. University of Nebraska Lincoln— ALWAYS read and follow the instructions printed on the pesti- Extension. http://icwdm.org/ cide label. The pesticide recommendations in this publication do handbook/rodents/voles.asp not substitute for instructions on the label. Pesticide laws and Orloff, S.B., T.P. Salmon, and W.P. labels change frequently and may have changed since this pub- Gorenzel. 1997. Vertebrate Pests lication was written. Some pesticides may have been withdrawn (Chapter 10), pp. 85–92. In: Inter- or had certain uses prohibited. Use pesticides with care. Do not mountain Alfalfa Management, use a pesticide unless the specific plant, animal, or other applica- S.B Orloff, H.L. Carlson, and L.R. tion site is specifically listed on the label. Store pesticides in their Teuber (eds.), Publication 3366, original containers and keep them out of the reach of children, University of California, Divi- pets, and livestock. sion of Agriculture and Natural Resources. Trade Names—To simplify information, trade names have been Salmon, T.P. and W.P. Gorenzel. used. No endorsement of named products is intended nor is 2010. Voles (Meadow Mice). Pest criticism implied of similar products not mentioned. Notes Publication 7439, Uni- versity of California, Division of Groundwater—To protect groundwater, when there is a choice Agriculture and Natural Resourc- of pesticides, the applicator should use the product least likely to es. http://www.ipm.ucdavis.edu leach. Takatori, S. 2010. Idaho State De- partment of Agriculture Pesticide Updates. Pacific Northwest extension publications are produced cooperatively by the three Pacific Northwest land-grant universities: Washington State University, Oregon State University, Thaemert, R. 2006. Rodent Control. and the University of Idaho. Similar crops, climate, and topography create a natural pp. 63–65. In: Proceedings, Idaho geographic unit that crosses state lines. Since 1949, the PNW program has published more Alfalfa and Forage Conference, than 600 titles, preventing duplication of effort, broadening the availability of faculty February 27–28. Twin Falls, Idaho. specialists, and substantially reducing costs for the participating states. University of Idaho Cooperative Published and distributed in furtherance of the Acts of Congress of May 8 and June 30, Extension. http://www.exten- 1914, by University of Idaho Extension, the Oregon State University Extension Service, sion.uidaho.edu/forage/Proceed- Washington State University Extension, and the U.S. Department of Agriculture cooperating. ings/2006%20PDF/Thaemert%20 rodent%20control%20.pdf The three participating extension services offer educational programs, activities, and materials without regard to race, color, national origin, religion, sex, sexual orientation, age, disability, or status as a disabled veteran or Vietnam-era veteran, as required by state and federal laws. University of Idaho Extension, Oregon State University Extension Service, and Washington State University Extension are Equal Opportunity Employers.