EC 1256August 1992$1.00

Reforestation

Controlling Vole Damageto Conifer Seedlings

R.E. Duddles and D.S. DeCalesta OF D

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adow mice as they’red, can cause signifi-

damage to coniferforestation sites and

plantations (figure l).ge occurs wheredant cover of grassesll, broadleaved plants).l for vole damage iser plantations estab-ass fields or pasturesestablished voleis publication helpse damage and conductam, if you need one.

gyo voles that damage in Oregon, Townsend’sd the Oregon vole

Both are reddish toon top and light grey toerneath. They havel eyes, and ears so smallden in the fur.gh reproductive rates.le of breeding at 3 weeks

Figure 1.—Vole or common meadow mouse.

s, Extension agentand Curry Counties, andsta, former Extension Oregon State University.

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Voles, or me

commonly callecant economicseedlings on reChristmas treeTypically, damathere’s an abunand forbs (sma

The potentiahighest in coniflished in old grthat have well-populations. Thyou identify vola control progr

Vole bioloThere are tw

conifer seedlingsvole (bog rat) an(creeping vole).blackish brown light brown undshort tails, smalthe ears are hid

Both have hiThey are capab

Ralph E. Duddle(forestry), Coos David S. DeCalewildlife specialist,

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of age, and can produce up to 13 littersof four to eight young a year.

Both species of voles constructwell-used runways through and undervegetation, and they both buildextensive underground burrowsystems with many entrances. They’refound in meadows, marshy areas,pastures, and riparian areas wherethere’s dense ground cover forsecurity from predators.

You can tell the two voles apartbased on size and distribution.Townsend’s vole is 6 to 9 inches longwith a 1- to 3-inch tail, and it’s foundprimarily on the coast and in the CoastRange. The smaller Oregon vole is 5 to6 inches long and is found from thecoast to the Cascade Mountains.

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Identifying the pestConifer seedlings damaged by

voles have distinctive characteristics.Bark is removed from ground level toabout 5 inches up the stem and has atypically fuzzy appearance. Voles canremove only small portions of barkwith each bite because their teeth areso small. So they chew bark off insmall pieces (figure 2).

Close inspection of the exposedwood reveals minute tooth marks andsmall gashes. Feeding starts on oneside of a seedling and progressesupward, so seedlings tend to bepeeled only on one side at first. Withlater and more extensive girdling, allbark may be removed up to the lowerlateral branches.

Voles girdle only small seedlings(less than 2 inches in diameter) atground level, but occasionally they’lldamage conifers of sapling or pole size.Damage is always less than 12 inchesabove the ground.

Voles must always have dense,overhead grassy cover, so thepresence of this cover, coupled withfuzzy girdling, is a strong indicatorof voles. Voles defecate where theyeat, so you may find piles ofdroppings at the base of damagedseedlings. These droppings are darkbrown, oval, and l⁄8 to l⁄4 inch long.

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Figure 2.—Because of their small teeth, voles typically girdle young seedlings in stages.

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Damage byother pests

Insects. Damage by large, burrow-ing insect larvae, such as the straw-berry root weevil, looks identical tovole damage. Unlike voles, however,these insects also remove bark fromunderground rootlets, so examiningrootlets will provide positive identifi-cation of the pest.

Another positive way to separateinsect from vole damage is todetermine if vole burrows are presentInsects don’t produce burrows orburrow entrances.

Rabbits and mountain beaver clipseedlings at ground level or removeupper branches and the leader ratherthan girdle at the base.

Pocket gophers girdle seedlings,ut their much larger tooth marks are clear indicator of their damage.T O

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Gophers pull small seedlingsunderground or clip them at groundlevel. Unlike moles or pocketgophers, voles don’t mound dirt attheir tunnel entrances, so smallburrow openings that are intercon-nected by trails and lack soil moundsare a sure sign of voles.

Deer and elk. When the bark issoft in spring, deer and elk damage toconifer seedlings may resemble thatof voles. They cause this damage bygrasping the seedling at ground levelbetween their lower front teeth andtheir upper palate. They strip the barkof stem and lateral branches frombottom to top and often remove smallneedles in this process.

Voles typically don’t eat needles,and their damage doesn’t extend asfar up the main stem or includeremoval of lateral branches.

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Damage control techniques

Manipulating habitat

Voles are so dependent onprotective cover from predators thatone of the most effective means ofreducing or eliminating voledamage is to remove this cover.

Two techniques often used toprepare regeneration sites forplanting of conifer seedlings areburning and/or scarifying the slash

that results from clearcut logging. Inareas where grasses and forbsquickly invade clearcut sites, slashburning and/or scarifying willreduce or eliminate vole cover andprevent damage by these pests toplanted conifer seedlings.

Several herbicides—includingAtrazine, Velpar, and Accord—areregistered for ground cover control.Herbicides may be applied by ground

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or aerial equipment. They’re aneffective tool when proper labelrecommendations are followed.

It may be necessary to reapplyherbicides yearly for the first 2 to 3years after planting or until theseedlings have grown large enoughnot to be vulnerable any longer tovole damage.

Important note: Most atrazineproducts are now listed as restrictedchemicals that require a licensedapplicator.

Mowing to remove vole cover isan option used mainly in Christmastree plantations. Mowing must beconducted on a schedule that keepsgrass and forb cover from growingover 6 inches.

In pastures being converted toconifer plantations, you must controlpreexisting grass cover the first yearto get rid of voles. Sometimes, treegrowers place seedlings in themiddle of 2- to 3-foot squares ofblack plastic or kraft paper to reducecompetition for nutrients, light, andwater with grasses and forbs onthese old pastures.

Unfortunately, the squares provideexcellent vole cover—they concen-trate vole activity around the seed-lings, resulting in girdling by voles.

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PredationHawks and owls are major predators

of voles. You can encourage them tohunt on clearcut sites by leavingstanding snags (figure 3). A study inCalifornia indicated that hawks andowls made high use of artificial perchesconstructed of l7-inch-long, 2 x 2 inchpine blocks screwed on top of l5-foot-high, galvanized, 3⁄4-inch pipe.

Likely, one snag or perch pole peracre would provide an adequatenumber of hunting sites for hawksand owls.

Predation by hawks and owls ismore effective with reduced cover, sosnags or artificial perches will be mosteffective when you combine themwith methods for reducing vole cover.

Figure 3.—You can encourage predation by hawks and owls by leaving snags for perches.

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Seedling protectorsHabitat manipulation isn’t

always possible. There will be siteswhere vole damage occurs. If otherpests are present—such as deer, elkor mountain beaver—using rigidplastic tubes (figure 4) to controldamage by these animals will alsocontrol damage by voles.

However, on sites where voles arethe only vertebrate pest, you couldmake cheaper but effective barriers togirdling from tinfoil. Cut 12-inchrolls of tinfoil in half with a hacksaw,producing two 6-inch rolls. Wrap thebase of a seedling twice with 4 to 5inches of the foil and loosely crimp it(figure 5 on page 5).

You can achieve nearly 100 percenreduction in vole damage at low costwith the foil, which lasts about 2 years.There’s no evidence that the foilcauses any scalding or encouragesattack by pathogens.

However, don’t use foil on seed-lings less than 10 inches high—it cancatch the wind and whip the seedlings,rubbing all the bark off at the base.

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Poison baits

Poison baits have been used tocontrol vole damage to coniferseedlings in the past, but there’s littldocumentation of actual effective-ness. Commercial vole baits, consising of wheat seeds treated with zincphosphide, have been recommendefor years.

A difficulty with poison baits isthat mouse damage occurs generallin winter, and applying baits at thistime is usually ineffective. Baits arerapidly degraded by the constantmoisture, and they may becomeunpalatable before voles encounterthem.

Attempts to protect baits from rainor snow by placing them in baitstations have been unsuccessful.Voles don’t enter the bait stations, brain does—which means rapid loss obait acceptance by voles.

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Figure 4.—Rigid tubes made of a plastic-like netting not only prevent vole damage butalso protect against deer and elk browsing.

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SummarySuccessful management of vole

damage is greatly enhanced if youeliminate grasses and forbs fromregeneration sites, or manage so thatresulting vegetation doesn’t providerequired overhead cover.

You can also protect coniferseedlings from vole attack by tubing,netting, or tinfoil. Baits haven’tgenerally proven effective.

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Figure 5.—Aluminum foil provides inexpensive protection.BLIC

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Use pesticides safely!• Wear protective clothing and safety devices as recommende

on the label. Bathe or shower after each use.• Read the pesticide label—even if you’ve used the pesticide

before. Follow closely the instructions on the label (and anyother directions you have).

• Be cautious when you apply pesticides. Know your legalresponsibility as a pesticide applicator. You may be liable forinjury or damage resulting from pesticide use.N IS

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The Woodland Workbook is a collection of publications prepared by the OregoState University Extension Service specifically for owners and managers ofprivate, nonindustrial woodlands. The Workbook is organized into separatesections, containing information of long-range and day-to-day value for anyointerested in wise management, conservation, and use of woodland propertIt’s available in a 3-ring binder with tabbed dividers for each section.

For information about how to order, and for a current list of titles and prices,inquire at the office of the OSU Extension Service that serves your county.

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

Oregon State University Extension Service offers educational programs, actties, and materials—without regard to race, color, national origin, sex, age, ordisability—as required by Title VI of the Civil Rights Act of 1964, Title IX of thEducation Amendments of 1972, and Section 504 of the Rehabilitation Act o1973. Oregon State University Extension Service is an Equal OpportunityEmployer.

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