Ecology, Identification, and Managementof Forest Root Diseases in Oregon

EC 1512 • August 1999 $2.00

G.M. Filip

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ContentsSymptoms and signsof five important root diseases ....... 2

How to identify root diseases ......... 2Laminated root rot ....................... 3Armillaria root disease .................. 3Annosus root disease .................... 5Black stain root disease ................ 6Port-Orford-cedar root disease ........ 6

Host susceptibility ......................... 7

How to manage root diseases ........ 7Managing method of spread .......... 7Managing fungus survival .............. 9Planting and favoringresistant species .......................... 9

Conclusion ................................. 10

For more information .................. 11

Gregory M. Filip, Extension forestprotection specialist, Oregon StateUniversity.

oot diseases are the most difficult type of disease to identify,measure, and manage in Oregon’s trees and forests. The morecommon root diseases are caused by fungi, although root diseasR

also can be associated with abiotic (nonliving) factors such as flooding orsoil compaction.

Root disease fungi attack and destroy the tree’s root system, resultinggrowth loss, decay, death, or windthrow of infected trees. Trees with rootdisease also are more susceptible to pests, especially bark beetles. On tother hand, root diseases are a component of the forest ecosystem and pan important role in creating wildlife habitat and in cycling nutrients.

This publication is for woodland owners and managers interested inidentifying and managing root diseases in trees or forests. It’s intended tohelp identify the common root diseases and to understand the techniquesused to reduce the damage they cause. Related publications are listed opage 11.

Ecologic roles of root diseasesRoot diseases can cause widespread tree death in many forest ecosys

tems and, as a result, create gaps in the forest canopy. These gaps oropenings change the light, moisture, and temperature in the forest and thalter the habitat for plants and animals. Some plants and animals thatrequire more light benefit from these openings; others prefer closedcanopies. Root diseases provide a variety of canopy openings and thuscreate habitat for a wide variety of organisms.

Many animals and birds require dead standing trees (snags) or fallentrees (logs) for their habitat. Because root diseases kill trees of all sizes,snags are formed continually as the disease progresses over many decaSnags that topple because of decayed root systems become logs, providhabitat for a different set of animals and plants than did the snags.

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Many root-disease fungi live in roots anstumps for 50 years or more after trees hadied or been harvested. These fungi continto decay the stump and major roots, thusreturning nutrients to the soil and providinghabitat for a wide variety of animals.

How to identify root diseasesYou can identify root diseases by obser

ing an infected tree’s symptoms and signs(Table 1). Symptoms are the reactions of thhost tree to the disease. Most root diseasecause foliar yellowing and thinning of thecrown due to destruction of the root systemand the subsequent reduced supply of waand nutrients to the foliage. Abundant,undersized cones, called a distress cone coften are produced by trees in advancedstages of decline. Trees with these symptousually die within 1 or 2 years.

Signs are the actual parts of the fungus or near the diseased tree. The most obviosigns of root disease include conks or musrooms on the tree or on the ground near thtree base.

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Root diseases can infect a single tree bumore commonly infect groups of trees. Thegroups of dead, dying, and windthrown treeare called disease patches or centers, orcanopy gaps (Figure 1). Patches grow overtime as the disease-causing fungi spread frtree root to tree root. Patches can range insize from a few trees to hundreds of acres.

Trees in a disease patch show a progression of symptoms; they do not all die at thesame time nor will they be in the same stagof decline. Some trees near the middle of thdisease patch will be dead, while those at tedge might show only a slight reduction inheight growth or a slight yellowing offoliage. By contrast, groups of trees that habeen burned or infected by bark beetlesusually die at about the same time.

Aboveground symptoms can indicate thepresence of root disease but not the type. Ifact, a stand of trees and even a single treecan have two or more different root diseaseOnly by examining the roots can you accu-rately identify specific diseases and deter-mine the best management action.

Specific signs and symptoms of each roodisease are summarized in Table 1 and discussed in more detail in the following pages

Table 1.—Symptoms and signs of five important root diseases in Oregon.

Laminated Armillaria Annosus Black stain Port-Orford-cedarSymptoms root rot root disease root disease root disease root disease

Reduced tree height √ √ √ √Crown thinning and yellowing √ √ √ √ √Distress cones √ √ √ √Basal resin (sap) √ √Brown stain in inner bark √Black stain in sapwood √Laminated decay √ √Yellow, stringy decay √

Signs

White mycelial fans √Leathery conks √Mushrooms at base √Setal hyphae √Ectotrophic mycelium √ √

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s,Figure 1.—Root disease patch showing a progression of symptoms such asstumps, snags, recently killed trees, and infected live trees.

Laminated root rotLaminated root rot is the

most damaging root diseasein Oregon from the stand-point of wood fiber produc-tion. Found in western andeastern Oregon, the diseaseis caused by the fungusPhellinus weirii. It affectsall conifer species to somedegree but is most damaginto Douglas-fir, grand andwhite fir, and mountainhemlock (Table 2, page 4).

Hardwoods are immune tothis disease; they neverbecome infected.

The disease decays rootsystems, causing growth losdeath, and windthrow. Oneof the best indicators of

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laminated root rot is the presence of rootballs. Root balls form when decayed rootsbreak near the root collar, leaving an abnomally small “ball” of roots on fallen trees. Bcontrast, healthy trees blown over by windhave a large mat of mostly undecayed roo

Root or stem wood with laminated root rcharacteristically separates into sheets aloannual growth rings, hence the term “lami-nated.” The decayed wood is pale yellow-brown with numerous small oval holes or pon both sides of the sheet. The pits are simto shot holes and are about 1 millimeter indiameter. By using a magnifying lens to

Figure 2.—Ectotrophic mycelium (arrow) of Phethe root of an infected Douglas-fir.

examine the wood sheet, you might see thekey diagnostic indicator of laminated rootrot—setal hyphae. Setal hyphae are small,wiry, reddish brown hairs of the fungus andare positive proof of laminated root rot.

Another good indicator of laminated rootrot, especially on young living trees, growson the surface of roots. Diseased roots arecovered with a white to grayish crust offungal growth called ectotrophic mycelium(Figure 2). It appears only on the outside ofthe root, not in the wood or between the barand wood. Setal hyphae also can be mixedwith ectotrophic mycelium on the root

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.llinus weirii on

surface. The surface ofhealthy conifer roots isreddish brown.

Armillaria root diseaseArmillaria root disease i

caused by the fungusArmillaria ostoyae and is thmost widespread root disein Oregon. It is most prevalent and economicallydamaging in eastern andsouthern Oregon. In westeOregon, the disease com-monly affects small groupsof 10- to 30-year-old trees

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Table 2.—Relative susceptibility of Oregon trees to damage by root diseases.1

Laminated Armillaria Annosus Black stain Port-Orford-cedarHost trees root rot root disease root disease root disease root disease

Douglas-fir (coastal) .......................... 1 ....................... 2 ....................... 3 ......................... 1 .............................. 4

Douglas-fir (inland) ........................... 1 ....................... 1 ....................... 3 ......................... 2 .............................. 4

Ponderosa pine, Jeffrey pine .............. 3 ....................... 2 ....................... 2 ......................... 2 .............................. 4

Lodgepole pine, knobcone pine ......... 3 ....................... 2 ....................... 2 ......................... 3 .............................. 4

Sugar pine .......................................... 3 ....................... 1 ....................... 3 ......................... 4 .............................. 4

Western white pine ............................ 3 ....................... 2 ....................... 3 ......................... 4 .............................. 4

Whitebark pine, limber pine .............. 3 ....................... 2 ....................... 3 ......................... 4 .............................. 4

Grand fir, white fir ............................. 1 ....................... 1 ....................... 1 ......................... 4 .............................. 4

Pacific silver fir ................................. 2 ....................... 2 ....................... 1 ......................... 4 .............................. 4

Noble fir, Shasta fir ........................... 2 ....................... 2 ....................... 2 ......................... 4.............................. 4

Red fir, subalpine fir .......................... 2 ....................... 2 ....................... 2 ......................... 4.............................. 4

Western hemlock ............................... 2 ....................... 2 ....................... 2 ......................... 3 .............................. 4

Mountain hemlock ............................. 1 ....................... 2 ....................... 1 ......................... 3 .............................. 4

Western larch, subalpine larch ........... 2 ....................... 3 ....................... 3 ......................... 4 .............................. 4

Engelmann spruce ............................. 2 ....................... 2 ....................... 3 ......................... 4 .............................. 4

Sitka spruce ....................................... 3 ....................... 2 ....................... 3 ......................... 4 .............................. 4

Western redcedar ............................... 3 ....................... 2 ....................... 3 ......................... 4 .............................. 4

Alaska-cedar ...................................... 3 ....................... 2 ....................... 3 ......................... 4 .............................. 3

Port-Orford-cedar .............................. 4 ....................... 3 ....................... 3 ......................... 4 .............................. 1

Pacific yew ........................................ 4 ....................... 3 ....................... ? ......................... 4 .............................. 2

Juniper ............................................... 4 ....................... 2 ....................... 3 ......................... 4 .............................. 4

Coast redwood ................................... 4 ....................... 3 ....................... 3 ......................... 4.............................. 4

Incense-cedar ..................................... 4 ....................... 3 ....................... 3 ......................... 4 .............................. 4

Birch .................................................. 4 ....................... 3 ....................... ? ......................... 4 .............................. 4

Buckthorn .......................................... 4 ....................... ? ....................... ? ......................... 4 .............................. 4

Cherry ................................................ 4 ....................... 3 ....................... ? ......................... 4 .............................. 4

Pacific dogwood ................................ 4 ....................... 3 ....................... ? ......................... 4 .............................. 4

Willow ............................................... 4 ....................... 3 ....................... ? ......................... 4 .............................. 4

Giant chinkapin ................................. 4 ....................... 3 ....................... ? ......................... 4.............................. 4

Bigleaf maple..................................... 4 ....................... 3 ....................... 3 ......................... 4 .............................. 4

Red alder ............................................ 4 ....................... 3 ....................... 3 ......................... 4 .............................. 4

White alder ........................................ 4 ....................... ? ....................... ? ......................... 4 .............................. 4

Pacific madrone ................................. 4 ....................... 3 ....................... 2 ......................... 4.............................. 4

Oregon ash ......................................... 4 ....................... ? ....................... ? ......................... 4 .............................. 4

Tanoak ............................................... 4 ....................... 2 ....................... ? ......................... 4 .............................. 4

Quaking aspen ................................... 4 ....................... 2 ....................... ? ......................... 4.............................. 4

Black cottonwood .............................. 4 ....................... 2 ....................... 3 ......................... 4 .............................. 4

Oregon white oak .............................. 4 ....................... 2 ....................... ? ......................... 4 .............................. 4

California black oak .......................... 4 ....................... 3 ....................... 3 ......................... 4 .............................. 4

California laurel ................................. 4 ....................... ? ....................... ? ......................... 4 .............................. 4

1Classes: 1 = severely damaged; 2 = moderately damaged; 3 = seldom damaged; 4 = not damaged

4 THE WOODLAND WORKBOOK

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The disease affects all conifer species tosome degree (Table 2) and can be damagito hardwoods, especially white oak. Armil-laria has a history of affecting conifers,hardwoods, and fruit trees throughout theworld.

Infected conifers usually produce a flow pitch or sap just above ground level. Thisflow is the tree’s response to the fungusgrowing beneath the bark. Extensive growtof the fungus eventually girdles and kills thtree.

Chopping into the bark reveals white tocream-colored sheets of fungus called myclial fans (Figure 3). These fans are inside thbark in the lower main stem of the tree or inroots. Mycelial fans have a rubbery textureand sometimes can be peeled from the wolike latex paint. They are a positive indicatoof Armillaria root disease. Mycelial fans arecloser to the ground in younger trees than older trees.

Armillaria mushrooms occasionally appein autumn, are edible to humans and wildlifand can be a useful indicator of the disease

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Annosus root diseaseAnnosus root disease,

caused by the fungusHeterobasidion annosum, isone of the more difficult roodiseases to diagnose becauoften the only symptom isbutt rot, and the disease sigare difficult to detect. InOregon, the disease has twstrains, one that affectsprimarily fir, hemlock, andspruce, and another thataffects primarily pine. Thisfact is important to knowwhen planting or favoringresistant tree species.

Besides causing rootdisease, Heterobasidionannosum also causes stemdecay. The decayed woodcontains silvery-whitemycelium and small blackflecks about the size of ricegrains. In western Oregon,

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the fungus causes serious degrade in westehemlock and grand fir due to decay and stain the valuable butt log.

Brown leathery conks with white under-sides occasionally are found in rotten stump(Figure 4, page 6) and among roots ofwindthrown trees. The conks produce sporethat are the chief means of disease spread.The airborne spores need freshly cut stumpsurfaces or fresh tree wounds to infect andcolonize the wood. After stumps are infectedthe fungus grows through the root system acan infect living trees through root contacts.

In eastern Oregon, annosus root diseasemost damaging to true fir and ponderosapine. Stands that have been partially cut ovemany years show the most disease. In manareas, groups of pines die without showingsubstantial decay, especially on very drysites. A progression of symptoms usually isevident—old dead trees near the center of topening and recent kills near the perimeter.

Annosus root disease has been reported bigleaf maple, red alder, and Pacific madronbut not on other hardwoods. Extensive sur-veys are needed to determine accurate hosranges.

Figure 3.—Mycelial fans of Armillaria ostoyae under the bark of an infectedpine.

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Figure 4.—A conk of Heterobasidion annosum in the hollow of an oldinfected fir stump.

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Black stain root diseaseBlack stain root disease, caused by the

fungus Leptographium wageneri, is uniqueamong the root diseases affecting Oregon’forests because it is spread primarily byinsects, mostly root-feeding bark beetles anweevils. Fungal spores form in the insecttunnels, stick to the insects, and are spreadwhen the insects fly or walk to other trees.

These insects are attracted to low-vigortrees and freshly cut stumps where they feand breed. Once the insects have introducthe fungus into a tree, it can spread to othetrees across root grafts or by growing shortdistances through the soil. The fungus doenot live long after the tree dies.

In Oregon, one form of black stain rootdisease attacks firs, mainly young (10- to 3year-old) Douglas-fir, and the other attackspines. In eastern Oregon, ponderosa pine iaffected at any age. Other conifers seldomaffected (Table 2).

Similar to Dutch elm disease, black staina wilt disease that kills trees rapidly by plugging the water-conducting tubes of the rootwood. Black stain is most severe in parts osouthwestern Oregon, where it is considereepidemic; 25 to 50 percent of 10- to 30-yeaold Douglas-fir stands in this region have thdisease to some extent. In western Oregonblack stain is most common along roadsidein stands that have been precommercially

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thinned, and in stands with history of soil disturbancefrom tractor logging. Factorsassociated with black stainroot disease in easternOregon are not well known.

As in Armillaria rootdisease, a black-stain-affected tree often producesresin at the base of its trunkHowever, it does not havewhite mycelium on the rootsurface or inside the barkunless other root diseasesalso are present.

You can diagnose blackstain by chopping into thewood of roots or the rootcollar of dying or recentlykilled trees to look for blackto brown streaks in the mos

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trecent growth rings (Figure 5). This stain isthe result of the dark fungus growing in thewater-conducting tubes of the sapwood.

Port-Orford-cedar root diseasePort-Orford-cedar root disease, caused b

the fungus Phytophthora lateralis, mighthave been introduced to Oregon around 19on ornamental cedars from Asia.

In southwestern Oregon, the disease isvery damaging to Port-Orford-cedars, and insome areas the commercial status of the treis threatened. Pacific yew and Alaska-cedaralso are infected when growing with Port-Orford-cedar. The disease affects ornamenPort-Orford-cedars throughout Oregon.

Port-Orford-cedar root disease destroysthe root system and discolors foliage, whichturns from light green to yellow, red, andfinally to brown. Look for a brown innerbark that abruptly joins white, healthy innerbark at the base of infected trees (Figure 6)This symptom is most apparent on trees wityellow foliage.

Roots are infected by special swimmingspores, called zoospores, produced by thefungus. Zoospores spread downslope ordownstream in water. Consequently, treemortality often is apparent along water-courses or roadsides, especially on thedownhill side (Figure 7, page 8).

Figure 5.—Black stain root disease causedby Leptographium wageneri in the wood ofan infected ponderosa pine.

Figure 6.—Port-Orford-cedar killed by Port-Orford-cedar root disease. Note the darker,infected wood under lighter, healthy wood.

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Animals and humans also can spread thdisease. Machinery, tires, or transplantedseedlings can move infested soil and thusspread the fungus from one site to anotherThe disease also can spread upslope throuroot contacts.

Host susceptibilitySusceptibility to infection and to associ-

ated damage by root disease fungi varies wtree species (Table 2). Susceptibility is thelikelihood that a tree species will be damagif it contacts the root disease fungus. Damasusceptibility is rated on a scale of 1 to 4,based on field observations in Oregon.

Susceptibility of some tree species, hardwoods especially, is unknown for somefungi. Hardwoods are not affected by lami-nated root rot, black stain root disease, orPort-Orford-cedar root disease, three of themost important root diseases in Oregon. Fothis reason, hardwoods are recommended planting or favoring in many areas affectedby root disease.

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How to manage root diseasesManagement of root diseases is based on

two important traits—the method of spreadand fungus survival. All root diseases spreadby root contact when the fungus grows froman infected tree or stump root to a healthytree (Figure 8, page 9, and Table 3, page 8)In general, disease patches expand radiallyabout 1 to 2 feet a year from root contacts.

Managing method of spreadOne strategy to stop the spread of disease

between healthy trees and infected trees is tbreak the connection of root contacts bycutting the “bridge tree.” The bridge tree isthe first healthy tree next to the infected treeHowever, it is difficult to determine whethera tree is healthy or infected if it has noaboveground symptoms.

A better strategy to break the connectionbetween root systems is to interplant or favodisease-tolerant tree species. Root diseasefungi cannot spread as well on the roots ofresistant or tolerant trees.

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Figure 7.—Port-Orford-cedars killed by Photophthora lateralis as a result ofwaterborne spores along roadways.

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Thinning, either precommercial or com-mercial, can affect the severity of rootdiseases. In the Cascade Range, pre-commercial thinning reduces mortality froArmillaria root disease in ponderosa pine(Figure 9) but has no effect on mortality inDouglas-fir, true fir, or hemlock.

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Precommercial thinning inDouglas-fir stands canincrease black stain rootdisease, especially if done inlate winter or spring (beforeinsect flight in July).

Annosus root disease canincrease in stands that havebeen thinned, especially incommercially thinned true firstands, because windbornespores spread to freshly cutstumps. Treatments such asborax application to stumptops are recommended toprevent annosus spores frominfecting stump surfaces andsubsequently spreading toadjacent live trees. Salvagelogging, especially of dyingtrees, can increase annosus

and Armillaria root diseases in susceptibleresidual trees. For more information onthinning, see the publications list on page 1

The effects of other silvicultural tools(pruning, fertilizing, and prescribed fire) onroot disease are mostly unknown, but studiare underway.

Table 3.—Method of spread, major hosts, and management strategiesfor the major root diseases in the Pacific Northwest.

Root disease Method of spread Major hosts Management strategies

Armillaria root disease Roots All species Prevent soil compaction.Prevent tree wounding.Favor resistant species.

Laminated root rot Roots All species Favor resistant species.(especially firs)

Annosus root disease Air, roots True firs Treat stump surfaces.Hemlocks Prevent tree wounding.Pines Favor resistant species.

Black stain root disease Insects, roots Douglas-fir Prevent tree wounding.Pines Thin after July.

Favor resistant species.

Port-Orford-cedar Water, mud, roots Port-Orford-cedar Avoid infested areas.root disease Clean logging equipment.

Favor resistant species.

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Figure 8.—Infected trees and stumps spread root disease to healthytrees through root contacts and grafts.

Managing fungus survivalFungus survival is the

second trait that provides abasis for management. Manroot disease fungi cansurvive in roots for decadesafter infected trees have dieIf you harvest and replant adiseased stand withoutconsidering the disease,seedlings eventually willbecome infected. Damage inthe new stand can be worsethan in the preceding stand.Black stain root disease isone exception to long-termsurvival in roots; this fungusdies within 1 to 2 years aftertree death.

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Researchers and forest managers have

excavated infected stumps and roots or hatreated them with chemical fumigants in anattempt to control root disease. Stumpexcavation can be effective if done properlybut costs and potential soil damage must bconsidered. Stump fumigation requiresspecial equipment and licensing and has battempted only experimentally.

Figure 9.—Thinning decreases mortality from Armillaria root disease inponderosa pine.

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Planting and favoringresistant species

Based on our understanding of spread and long-termsurvival of root diseasefungi, we recommendplanting resistant species(Table 2) or favoring themduring thinning or partialcutting as the preferredmethod of reducing rootdisease.

Some root diseasesseriously affect only certaintree species—Port-Orford-cedar root disease on Port-Orford-cedar, and differentforms of black stain rootdisease on Douglas-fir andon pines. Armillaria root

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disease, laminated root rot, and annosus rootdisease can cause severe mortality, especiallfor grand fir, white fir, and Douglas-fir.

You can favor disease-tolerant anddisease-resistant species (classes 3 and 4,Table 2) during a variety of forest operationsincluding planting, thinning, and partialharvesting. If tolerant or resistant tree speciesare planted or regenerated for 50 years or

FOREST PROTECTION 9

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more, and you periodically remove newseedlings of more susceptible species (cla1 and 2), root disease fungi should die ovemost of the infected area.

If tree species in damage class 2 are usmany trees will become infected but at lowlevels than if tree species in damage classhad been grown.

By planting or favoring hardwood specieespecially on sites affected by laminated rorot, potentially you can sanitize sites.

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ConclusionRoot diseases generally are much easier

prevent than to correct. By maintaining ahealthy forest with mixtures of tree species,you can prevent economic damage from rodisease.

If root disease is present, identify the typof disease and take appropriate steps durintree and stand maintenance to minimize thedamaging effects of disease. These stepsinclude favoring more resistant species wheregenerating or thinning infested stands.

,

For more informationOSU Extension Service publicationsEmmingham, W.H. and N. Elwood. Thin-

ning: An Important Timber ManagementTool, PNW 184 (reprinted 1992). 50¢

Filip, G.M., A. Kanaskie, and A. CampbellIII. Forest Disease Ecology and Manage-ment in Oregon, Manual 9 (1995). $14.50

Jensen, E.C. and C.R. Ross. Trees to Know inOregon, EC 1450 (reprinted 1999). $5.00

Oester, P.T. and W.H. Emmingham. UsingPrecommercial Thinning to EnhanceWoodland Productivity, EC 1189(reprinted 1997). $2.00

Oester, P.T., S.A. Fitzgerald, W.H. Emming-ham, A. Campbell III, and G.M. Filip.Forest Health in Eastern Oregon, EC 1413(1992). 75¢

Pscheidt, J.W. and C.M. Ocamb, eds. PacificNorthwest Plant Disease Control Hand-book (published and revised annually bythe Extension services of Oregon StateUniversity, Washington State University,and University of Idaho). $25.00

To order copies of the above publications,or additional copies of this publication, sendthe complete title and series number, alongwith a check or money order (payable toOregon State University) to:

Publication OrdersExtension & Station CommunicationsOregon State University422 Kerr AdministrationCorvallis, OR 97331-2119Fax 541-737-0817

We offer a 25-percent discount on ordersof 100 copies or more of a single title.

You can view our Educational Materialscatalog and many of our publications on theWeb at eesc.orst.edu

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ther publicationsamm, P.B., S.J. Campbell, and E.M.Hansen. Growing Healthy Seedlings:Identification and Management of Pests inNorthwest Forest Nurseries, Special Pub-lication 19 (Forest Research Laboratory,Oregon State University, Corvallis, OR,1990).

haw, C.G. III and G.A. Kile, eds. ArmillariaRoot Disease, USDA Forest ServiceAgriculture Handbook No. 691 (USDAForest Service, Washington, DC, 1991).Contact: C.G. Shaw, PNW ResearchStation, 2770 Sherwood Lane, Suite 2A,Juneau, AK 99801-8545.

hies, W.G. and R.N. Sturrock. LaminatedRoot Rot in Western North America,USDA Forest Service/Canadian ForestService, Resource Bulletin PNW-GTR-349(USDA Forest Service, Portland, OR,1995). Contact: W.G. Thies, PNWResearch Station, 3700 SW Jefferson WayCorvallis, OR 97331.

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12 THE WOODLAND WORKBOOK

The Woodland Workbook is a collection of publications prepared by the Oregon StateUniversity Extension Service specifically for owners and managers of private, nonindus-trial woodlands. The Workbook is organized into separate sections, containing informa-tion of long-range and day-to-day value for anyone interested in wise management,conservation, and use of woodland properties. It’s available in a 3-ring binder withtabbed dividers for each section.

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

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© 1999 Oregon State University

Published August 1999 (replaces publication EM 8717).