EC 1117 / Revised October 1990 ,>

Controlling pocket gopherdamage to agricultural cropsW.D. Edge

Pocket gophers cause considerable dam-age to hay and grain crops as well as tocherry, apple, pear, and filbert or-chards. Some of the losses are a directresult of feeding activities of gophers:Root-clipping apple and cherry trees,eating alfalfa hay and filbert nuts.Other losses result from tunneling andmound-building activities: Soil androcks from mounds damage harvestingmachinery and degrade quality of crops.This publication describes activitiesdesigned to reduce damages by pocketgophers to hay, grain, and orchardcrops.

Pocket gophers are also a seriousproblem to homeowners and gardeners:Controls for gophers under these cir-cumstances are outlined in EC 1115.Damages to hay, grain, and orchardsusually occur over larger acreages,calling for control methods that differfrom those used by the homeowner andgardener.

Identify the pestAs with any control program, your

first step is to ensure that you haveproperly indentified the pest. Damagesby other pests such as moles and micemay closely approximate those of go-phers, but control methods for thesepests are different and don't work forthe pocket gopher.

Because the mole is also a burrowerand mound builder, it's easy to make amistake in identification.

Pocket gophers extend lateral (side)tunnels to the surface from their deepermain tunnels and push out the excess

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Figure 1 .Pocket gopher mound

soil in flattened or fan-shaped mounds.These vary from 12 to 24 inches indiameter and 4 or more inches in height.The gophers then plug the surfaceopening through which this soil ispushed, leaving a noticeable dent orplug at one end of the pile (figure 1).The entire lateral may be backfilled tothe main tunnel.

Moles. Mole mounds are the result ofrepeated eruptions from below andsimply continue to grow or enlarge untilthe mole has disposed of the excess soiland moved on. Mole mounds are higher

and generally rounder in shape thangopher mounds and look more likeminiature volcanoes.

No hole at the side of the mound isevident. However, if you place yourfinger in the middle of the mound andpush it down in a circular fashion,you'll discover the mole's hole is in the

W. Daniel Edge, Extension wildlife special-ist, Oregon State University, prepared thisrevision. The original author was David S.deCalesta, former Extension wildlife spe-cialist, Oregon State University.

OREGON STATE UNIVERSITY EXTENSION SERVICE

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Figure 2.Mound patterns, mole and pocket gopher

middle rather than on the edge of themound.

The pattern of mounds helps todistinguish gopher from mole activity.Gopher mounds tend to be clumped intight groups; the mole's tend to bespaced in a line as single mounds (figure2).

Meadow mice (voles). Another pestcommonly misidentified with the pocketgopher is the meadow mouse or vole.These small animals girdle the base ofcherry and apple trees, often killing thetrees.

A good clue is the presence of smalltunnel systems at or just below thesurface of the ground in the shelter ofgrass or weedy cover. Meadow micehave no mounds at the entrance of theiropen burrows, which are about the sizeof a 5O piece. The tooth marks of volesare very small and leave a fuzzy appear-ance on the bark of damaged trees.

Pocket gophers will girdle but moreoften tend to clip off roots and rootlets.When the root system of damaged treesis exposed, the loss of roots and rootletsis very typical (figure 3).

Voles will use pocket gopher burrowsystems but may make their own exca-vations as well. Any area with pocketgopher burrows and mounds that alsohas small open holes with intercon-necting surface tunnels can be suspected

of harboring both voles and pocketgophers.

Tree squirrels have been known tostrip bark from the base of filbert andother orchard trees. This type of dam-age is totally different from that causedby pocket gophers or voles, so there

Figure 3.Rootdamage by

pocket gophers

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should be little confusion. Also, thereare no burrow openings or mounds; treesquirrels make their homes in hollowopenings in trees as well as in large,bulky leaf nests. Almost always there isan adjacent hardwood woodlot fromwhich squirrels forage.

Other species, such as porcupines,cottontail, and jackrabbits, will alsogirdle fruit, nut, and ornamental trees.However, their damage is usually quiteextensive around the base of trees.Pocket gopher damage will be muchlower on the tree.

Legal statusPocket gophers are classified as

nongame wildlife under the OregonWildlife Codes, and they're not affordedany specific protection. Furthermore,the wildlife codes permit a landowner oragent to control noxious animals on hisor her property. Pocket gophers inOregon are not protected under Federalregulations.

Control methodsFlood irrigation. Years ago, farmers

flooded hay and grain crops requiringirrigation with a thin sheet of water inspring and at intervals throughout earlysummer. This forced pocket gophers toleave their burrow systems or drownand resulted in nearly 100% control.Invasion from adjacent nonirrigatedlands or reinvasion by animals forcedto nearby higher ground is often aproblem.

The advent of sprinkler irrigationincreased acreages where irrigated cropscould be grown, such as on hillsides anduneven lands, but pocket gophers aren'tflooded out under sprinkler irrigation,so this form of cheap control isn'tgenerally available.

In situations where you can use floodirrigation and pocket gophers are a se-rious problem, consider this method butgive careful attention to control in sur-rounding areas, to prevent reinvasion.

Vegetation management. Studieshave indicated that pocket gopher dam-ages can be reduced by about 50% byapplying herbicides that remove vegeta-tion pocket gophers require for food.This option is limited to orchards and tononcrop areas close to hay and graincrops.

Other studies have indicated thatremoving existing crops (such as al-falfa), followed by deep tilling, willdisrupt burrow systems, remove food,and result in a significant reduction inpocket gopher numbers in fields sotreated.

When alfalfa fields begin to decline inproductivity for one reason or another,plow them up and plant some alternatecrop rather than keep them in alfalfafor a few additional years at greatlyreduced yields.

Trapping. Techniques for trappingpocket gophers are outlined in EC 1115.In situations where infestations arelimited to 5 or fewer acres, trappingmight be an option. You could also trapas a followup to larger-scale poisoning

operations, to remove pocket gophersthat escaped or avoided the poisonbaiting.

Trapping is not recommended as theprimary control method on large acre-ages because of labor requirements andthe high potential for pocket gopherreinvasion.

Poison baiting. Because of constantlychanging labels, laws, and regulations,Oregon State University can assume noliability for the consequences of use ofchemicals suggested here. In all cases,read and follow the directions andprecautionary statements on the spe-cific pesticide product label.

The application of toxicants to con-trol pocket gopher damage is generallyrecommended when larger agriculturalareas (10 + acres) are heavily infested.A variety of toxicants are available inthe form of poison baits, such as oatsand wheat seeds, alfalfa pellets, seedmixtures, and dried fruits.

Toxicants currently registered bythe U.S. Environmental ProtectionAgency and the Oregon Department ofAgriculture include strychnine, zincphosphide, and acute anticoagulantssuch as chiorophacinone.

Most commercially available baitshave a seed base, but the pelletized

Use pesticides safely!Wear protective clothing and safetydevices as recommended on the label.Bathe or shower after each use.Read the pesticide labeleven ifyou've used the pesticide before.Follow closely the instructions on thelabel (and any other directions youhave).Be cautious when you apply pesti-cides. Know your legal responsibilityas a pesticide applicator. You may beliable for injury or damage.

alfalfa and grain-raisin-apple mixtureshave been highly effective under somecircumstances.

Pocket gophers are active year-round,but the best times for baiting coincidewith the best soil conditions for apply-ing baits. Gopher burrowing activityseems to increase in late winter andearly spring when the soil softens, andthis is a good time to begin baiting, justbefore the pocket gophers reproduceand have young. Eliminating one fe-male pocket gopher at this time willprevent several little pocket gophersfrom developing into problems later.

During summer, the soil generallyhardens as it dries. There is less burrow-ing activity, and baits are more difficultto apply. With the rains in early fall, thesoil begins to soften again, and burrow-ing activity of pocket gophers increases.Then you can once more apply baitseffectively, now against adults plus theyoung that were produced earlier in thebreeding season.

Apply baits only to fresh burrowsystems. You can identify these byleveling mounds with a hard iron rakeor by foot and then returning in a day ortwo to determine where fresh activity isoccurring. Revisit areas 2 to 3 days afterbaiting to search for fresh mounds,which indicate where pocket gophersavoided control. Such areas requireadditional baiting or trapping.

Because pocket gophers will rapidlyreinvade areas that have been cleared bypoison baiting, survey such areas peri-odically so that you can control anyinvading pocket gophers quickly.

Applying poison baits undergroundto pocket gophers results in low hazardto nontarget wildlife. Studies haveshown that some mice and voles may beaccidentally poisoned in the burrowsystems, but relatively few other non-target animals contact the baits directly.

Poisoned pocket gophers almostalways die belowground, so their car-casses are rarely available on the surfaceto nontarget scavengers such as hawksand owls. Avoid bait spillage, but if

it occurs, bury baits promptly toavoid hazard to nontarget birds andmammals.

Hand-baiting. Hand-baiting is de-scribed in EC 1115 and is recommendedonly where infestations are localized onsmall (2 to 5 acres) areas. Hand-baitingis slow, requiring 7 to 20 hours to treat 1acre.

Probe-bait dispensers. Probe-bait dis-pensers (figure 4) allow you to probe forrunways and dispense the poison bait inone step. Their use is about twice as fastas hand-baiting. The probe-bait dispen-sers generally can operate only withgrain baits. (Pelleted baits and baitscontaining raisins and dried fruits usu-ally won't pass through the dispensingmechanism.)

Push the probe-bait dispensers intothe ground in a circular pattern aroundfresh mounds as you seek the runways.Once you find a runway (the dispensersuddenly sinks 2 to 4 inches deeper inthe ground), a twist of a lever dispensesa measured amount of bait into therunway. Place three to five baits inrunways around each cluster of freshgopher mounds.

Burrow builder. For situations wherepocket gopher infestations are severe on10 or more acres, the burrow builder(figure 5) is the most effective way todispense baits.

The burrow builder is designed foruse with a tractor of at least 25 horse-power and having a conventional three-point hitch. The device consists of asupporting frame, a depth-adjustable,burrow-forming torpedo at the end of ashank, a rolling coulter to cut surfacetrash and shallow roots ahead of theshank, a bait-metering device, and presswheels to drive the metering unit andclose the knifelike slit made by theupper portion of the shank. The bait isdropped into the artificial burrowthrough a tube built into the shank.

The torpedo is pulled 6 to 10 inchesbelow ground level, forming an artifi-cial burrow. Baits are dispensed every18 to 48 inches. Pocket gophers use theartificial burrows, where they intercepttheir own burrow system. When theydiscover and eat the machine-placedbaits, they're poisoned.

Pull the burrow builder at a speed of2½ to 3½ miles per hour. You can treatan acre in 6 to 12 minutes, a markedimprovement over baiting by hand orwith the probe-bait dispenser.

For maximum effectiveness, the arti-ficial burrow must be at the sameapproximate depth as natural gopherburrows. You can determine this bydigging into a burrow system, measur-ing the depth, and adjusting the depthof the torpedo.

The torpedo must be level underground. If it is angled downward, it willbe hard for the tractor to pull. If thetorpedo is angled upward, it will notstay below ground. Build these artificialburrows 20 to 25 feet apart.

BAIT RELEASE LEVER

HANDLE1

BAITCANISTER

PROBE

HPROBE H ( IEND

Figure 4.Probe-bait dispenser

Figure 5.Burrow builder

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Extension Service, Oregon State University, Corvallis, O.E. Smith, director. Thispublication was produced and distributed in furtherance of the Acts of Congress of May 8and June 30, 1914. Extension work is a cooperative program of Oregon State University, theU.S. Department of Agriculture, and Oregon counties.

OOregon State University Extension Service offers educational programs, activities,andmaterialswithout regard to race, color, national origin, se age, or disabilityas requiredby Title VI of the Civil Rights Act of 1964, Title IX of the EducationAmendments of 1972,and Section 504 of the Rehabilitation Act of 1973. Oregon State University ExtensionService is an Equal Opportunity Employer.