Wildland Fire Behavior & Forest Structure

Environmental Consequences

Economics

Social Concerns

Root Diseases in Coniferous 

Forests of the Inland West: 

Potential Implications of Fuels 

Treatments

Root Diseases in Coniferous 

Forests of the Inland West: 

Potential Implications of Fuels 

RMRS-GTR-141

August 2005
The Authors _________________________________________

Raini C. Rippy is a Biological Science Technician with the USDA Forest Service, Rocky

Mountain Research Station at the Forestry Sciences Laboratory in Moscow, ID, and is pursuing

a doctorate in plant pathology at Washington State University. She completed a B.S. degree in

forest resources and an M.S. degree in forest products at the University of Idaho.

Jane E. Stewartis a Biological Science Technician with the USDA Forest Service, Rocky Mountain

Research Station at the Forestry Sciences Laboratory in Moscow, ID.

Paul J. Zambino is a Research Plant Pathologist with the USDA Forest Service, Rocky Mountain

Research Station at the Forestry Sciences Laboratory in Moscow, ID.

Ned B. Klopfenstein is a Research Plant Pathologist with the USDA Forest Service, Rocky

Mountain Research Station at the Forestry Sciences Laboratory in Moscow, ID.

Joanne M. Tirocke is a Biological Science Technician with the USDA Forest Service, Rocky

Mountain Research Station at the Forestry Sciences Laboratory in Moscow, ID.

Mee-Sook Kim is a Plant Pathologist with the USDA Forest Service, Rocky Mountain Research

Station at the Forestry Sciences Laboratory in Moscow, ID.

Walter G. Thies is a Research Plant Pathologist with the USDA Forest Service, Pacific

Northwest Research Station in Corvallis, OR.

Abstract ____________________________________________

Rippy, Raini C.; Stewart, Jane E.; Zambino, Paul J.; Klopfenstein, Ned B.; Tirocke, Joanne M.; Kim, Mee-Sook;

Thies, Walter G. 2005. Root diseases in coniferous forests of the Inland West: potential implications

of fuels treatments. Gen. Tech. Rep. RMRS-GTR-141. Fort Collins, CO: U.S. Department of Agriculture,

Forest Service, Rocky Mountain Research Station. 32 p.

After nearly 100 years of fire exclusion, introduced pests, and selective harvesting, a change in forest

composition has occurred in many Inland West forests of North America. This change in forest structure

has frequently been accompanied by increases in root diseases and/or an unprecedented buildup of fuels.

Consequently, many forest managers are implementing plans for fuels treatments to lower the risk of

severe wildfires.

Impacts on root disease should be considered before selecting appropriate fuels treatments. Complex

interactions exist among conifer root diseases, fuels treatments, forest structure, species composition,

stand history, and other environmental factors. As forest managers prescribe fuels treatments, their

success in lowering the risk of severe wildfire will depend in part on the impacts of these treatments on root

disease. Root diseases are one of many factors to be considered when developing plans for fuels

treatments. Choices must be made on a site-by-site basis, with knowledge of the diseases that are present.

This paper provides examples of how fuels treatments may increase or reduce specific diseases and

demonstrates their importance as considerations in the fuels management planning process. Several root

diseases prevalent within Inland West of North America are addressed: Armillaria root disease, annosus

root disease, laminated root rot, black stain root disease, Schweinitzii root and butt rot, Tomentosus root

disease, Rhizina root rot, and stringy butt rot. For each disease, general information is provided on disease

identification, management options, and potential effects of fuels treatments. However, many long-term

studies are needed to assess effects of specific interactions among fuels treatments, root diseases, and

host trees.

Key words: wildfire, forest planning, forest structure, mechanical treatments, prescribed fire,

coniferous hosts, pathogens, disease management
Foreword ______________________

This document is part of the Fuels Planning: Science

Synthesis and Integration Project, a pilot project initiated

by the USDA Forest Service to respond to the need for

tools and information useful for planning site-specific fuel

(vegetation) treatment projects. The information addresses fuel and forest conditions of the dry inland

forests of the Western United States: those dominated by

ponderosa pine, Douglas-fir, dry grand fir/white fir, and

dry lodgepole pine potential vegetation types. Information was developed primarily for application at the stand

level and is intended to be useful within this forest type

regardless of ownership. Portions of the information also

will be directly applicable to the pinyon pine/juniper

potential vegetation types. Many of the concepts and

tools developed by the project may be useful for planning

fuel projects in other forests types. In particular, many of

the social science findings would have direct applicability

to fuel planning activities for forests throughout the United

States. As is the case in the use of all models and

information developed for specific purposes, our tools

should be used with a full understanding of their limitations and applicability.

Root Diseases in Coniferous Forests of the Inland

West: Potential Implications of Fuels Treatments

The science team, although organized functionally,

worked hard at integrating the approaches, analyses,

and tools. It is the collective effort of the team members

that provides the depth and understanding of the work.

The science team leadership included the following USDA

Forest Service personnel:

• Deputy Science Team Leader Sarah McCaffrey,

North Central Research Station

• Forest structure and fire behavior: Dave Peterson

and Morris Johnson, Pacific Northwest Research

Station

• Environmental consequences: Elaine KennedySutherland and Anne Black, Rocky Mountain Research Station

• Economic uses of materials: Jamie Barbour and

Roger Fight, Pacific Northwest Research Station

• Public attitudes and beliefs: Pamela Jakes and

Susan Barro, North Central Research Station

• Technology transfer: John Szymoniak, Pacific

Southwest Research Station

This project would not have been possible were it not

for the vision and financial support of the USDA Forest

Service Washington Office Fire and Aviation Management individuals, Janet Anderson Tyler and Leslie

Sekavec.

Russell T. Graham, Science Team Leader

USDA Forest Service, Rocky Mountain

Research Station
Acknowledgments _________________________

This paper was supported by the USDA Forest Service, Fuels Planning:

Science Synthesis and Integration Project, Rocky Mountain Research Station

RWU-4552 (Microbial Processes as Ecosystem Regulators in Western Forests), and the Sustainable Forestry component of Agenda 2020, a joint effort

of the USDA Forest Service Research and Development and the American

Forest and Paper Association. The authors thank Drs. Deborah S. PageDumroese and Russell T. Graham for their support on this project. We thank

Dr. Gregory M. Filip, Dr. John W. Schwandt, Dr. Susan K. Hagle, Dr. Jack D.

Rogers, Ms. Kris L. N. Fields, Mr. Brennan A. Ferguson, Ms. Jonalea R. Tonn,

Ms. Ann Abbott, and Mr. Bob Atwood for their comments on an earlier version

of this manuscript. We also thank Dr. Jack D. Rogers, Dr. John W. Schwandt,

and Mr. John W. Hanna for their contributed photographs. In addition, we

greatly appreciate the helpful reviews by three anonymous reviewers.
Contents___________________________________

Page

Introduction .................................................................................................. 1

Armillaria Root Disease................................................................................ 6

 Disease Symptoms and Signs ......................................................... 6

 Disease Management .................................................................... 10

 Fuels Treatment Considerations .................................................... 10

Annosus Root Disease............................................................................... 11

 Disease Symptoms and Signs ....................................................... 11

 Disease Management .................................................................... 13

 Fuels Treatment Considerations .................................................... 14

Laminated Root Rot ................................................................................... 15

 Disease Symptoms and Signs ....................................................... 15

 Disease Management .................................................................... 15

 Fuels Treatment Considerations .................................................... 17

Black Stain Root Disease........................................................................... 18

 Disease Symptoms and Signs ....................................................... 18

 Disease Management .................................................................... 20

 Fuels Treatment Considerations .................................................... 20

Schweinitzii Root and Butt Rot ................................................................... 21

 Disease Symptoms and Signs ....................................................... 21

 Disease Management .................................................................... 21

 Fuels Treatment Considerations .................................................... 21

Other Root Diseases of Consideration in the Inland West ......................... 23

 Tomentosus Root Disease ............................................................. 23

 Rhizina Root Rot ............................................................................ 23

 Stringy Butt Rot .............................................................................. 23

 Disease Management and Fuels Considerations .......................... 24

Summary of Fuels Management Considerations ....................................... 25

References ................................................................................................. 26
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USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005 1

Introduction ____________________

The effects of nearly 100 years of fire exclusion, introduced

pests, and selective timber harvesting have caused dramatic

changes in tree species composition across much of the Western landscape. These changes have contributed to an unprecedented buildup of fuels and increased incidence of root

disease (Tiedemann and others 2000). Heavy accumulations of

fuels and ample fuel ladders have put stands at risk for

uncharacteristically severe wildfires. Consequently, many forest managers are implementing plans for fuels treatments to

lower the risk of fire. An understanding of how these fuels

treatments might affect the many complex interactions that

exist within forest ecosystems is critical because even subtle

disturbances can trigger associated responses from many coexisting organisms (Borchers and Perry 1990).

Historically, root diseases have played an important and

beneficial role in ecological processes of succession, decomposition, and fire in forests with moderate- to high-intensity

fire regimes (Hessburg and others 1994; Hansen and Goheen

2000). As with other tree pathogens, native root pathogens are

thought to have coevolved with their hosts and are a natural,

and even necessary, part of forest ecosystems. In most situations, native root diseases do not cause irreplaceable loss of

entire stands over large areas nor threaten the existence of any

host species. However, shifts in stand composition and other

natural and human-caused disturbances have frequently resulted in increased damage from root-rot diseases (Edmonds

and others 2000). In some situations, the change in root rot

dynamics may influence forest growth and succession for

centuries. Thus, careful consideration of future root disease

impacts is critical before implementing any management activities, including fuels treatments.

Root Diseases in Coniferous

Forests of the Inland West:

Potential Implications of Fuels

Treatments

Raini C. Rippy

Jane E. Stewart

Paul J. Zambino

Ned B. Klopfenstein

Joanne M. Tirocke

Mee-Sook Kim

Walter G. Thies

Whether specific effects of root diseases are considered to be

beneficial or detrimental depends on social values and management objectives for the site. For some sites, impacts by root

disease in a stand may be viewed as undesirable because of

potential increases in fuels buildup, reduced timber volume,

damage to facilities from wind-thrown trees, and potential

personal injury. At other sites, with different management

objectives, loss of trees as a result of root disease may be

acceptable or even desirable because of benefits attributed to

disease-created openings, scattered mortality (lower density

stand), and increased volume of standing and downed large

woody debris. Such disease-associated changes may provide

forage for large game animals, habitat for small animals and

cavity-nesting birds, sources for specialty forest products,

increased diversity in the plant community, and other changes

in forest structure that reduce the likelihood of catastrophic

wildfire (Thies 1999; Filip 1999; Thies and Goheen 2002).

Fuels treatments range widely in approach and application,

but generally involve mechanical treatments and/or prescribed

fire (Fitzgerald 2002; Graham and others 2004; Peterson and

others 2005). Mechanical treatments, such as thinning, can

remove fuels as usable forest products, which can include

biomass energy. Other types of treatments may involve cutting

trees, reducing the size of fuels, eliminating fuels ladders, and

methods that place fuels on the forest floor to accelerate

decomposition, such as mowing (Fitzgerald 2002). Prescribed

fire is also used to reduce surface fuels and ladder fuels;

however, the effects of prescribed fire on resulting stand

structure are less predictable than mechanical treatments. As

forest managers implement plans for fuels treatments, their

success in lowering risk of severe wildfire will depend in part

on the impacts of management activities on levels of root

disease that contribute to subsequent fuels accumulation. The
2 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005

type of fuels treatment can often be selected to match the

overall objectives for a stand, while addressing root rot dynamics and possible detrimental effects on a site.

Fuels management practices can influence root disease in

complex ways that should be considered at the ecosystem

level. Tree thinning can generate stumps and residual root

systems that are susceptible to colonization by root-rot pathogens. Stumps, roots, and slash can serve as nutrient substrates

that increase the overall growth and distribution of root rot

fungi. Thinning-associated wounds on retained trees can provide opportunities for root disease fungi to cause new infections. When seral tree species—for example, pine and larch—

are removed in thinning operations, the resulting stand may

consist of a higher proportion of tree species that are more

susceptible to root rots, such as grand fir or Douglas-fir. Fuels

treatments can cause physiological stress to remaining trees,

increasing the likelihood that root rot problems will develop.

Although the effects of slash burning may vary, superficial

burning appears to have little impact on the distribution of

pathogens, such as Armillaria species, Phellinus weirii, or

Heterobasidion annosum, which frequently occupy protected

areas within structural roots (Hadfield and others 1986). However, some measures that limit substrate availability for root

pathogens may reduce inoculum and possibly reduce disease

severity. Thus, care must be taken to select appropriate fuels

treatments that will achieve the objective of reducing current

and future fuels levels while avoiding undesirable increases in

root disease. Evaluating the presence and distribution of root

diseases is an essential step in selecting appropriate fuels

treatments. Surveys for root disease include observing signs

and symptoms on living trees, and also examining snags,

stumps, and overturned trees (Thies 1995).

Although fuels reduction has recently emerged as a national

issue, there are few research studies specifically addressing

fuels-treatment effects on root diseases. For this reason, much

of the information applied to fuels treatments in this paper is

based on general principles of plant pathology, knowledge of

pathogen biology, and/or derived from studies conducted for

other purposes. Because the consequences of root disease

resulting from fuels treatments may not be immediately apparent but may continue for decades after treatments, there is an

increased need to conduct and interpret long-term studies that

examine effects of specific fuels treatment on root disease

interactions. Such long-term studies would provide more precise information for understanding these complex relationships.

The objectives of this paper are to (1) provide insights for

consideration regarding potential effects of fuels treatments on

root diseases, (2) identify specific needs for research pertaining to the effects of fuels treatments on root diseases, and (3)

aid field personnel in identification of the primary root diseases. This discussion focuses on the dry, mixed conifer forests

between the crest of the Cascade Mountains and the crest of the

Rocky Mountains in North America, hereafter referred to as

the Inland West. In forests of the Inland West, special attention

is warranted for several root diseases, such as Armillaria root

rot (caused by Armillariaspecies), Annosus root rot (caused by

Heterobasidionspecies), laminated root rot (caused by Phellinus

weirii), black stain root disease (caused by Leptographium

wageneri), and Schweinitzii root rot (caused by Phaeolus

schweinitzii), and other diseases including Tomentosus root

disease (caused by Inonotus tomentosus), Rhizina root rot

(caused by Rhizina undulata), and stringy butt rot (caused by

Perenniporia subacida). Rudimentary information is provided in this paper for identification of these diseases; however, more detailed and definitive field guides with a greater

representation of pathogens are available (Partridge and Miller

1974; Partridge and others 1978; Hadfield and others 1986;

Scharpf 1993; Allen and others 1996; Filip 1999; Hagle and

others 2003). Figures illustrate signs and symptoms of the

more common root diseases. We included factors to be considered in the effects of potential fuels treatments on each root

disease and identify gaps in research information. Three tables

located on the next 3 pages contain general supporting information: table 1 lists common symptoms and signs of each root

disease; table 2 lists common coniferous hosts of each root

disease; and table 3 lists common and scientific names of

pathogens, trees, and insect species.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005 3

Table 1—Symptoms and signs associated with common root diseases of conifers of the Inland West.

Root disease Symptoms Signs

(causal fungus) (the most diagnostic are in bold text) (the most diagnostic are in bold text)

Armillaria root disease Reduced tree growth Mycelial fans within tightly attached bark

 (Armillaria ostoyae) Crown thinning and yellowing Rhizomorphs

Smaller, stress cones Fruiting bodies:

Resinosis (sap on butt/roots) Honey mushrooms in late summer or fall

Wood decay/rot: spongy, yellow, stringy

Annosus root disease Reduced tree growth Ectotrophic mycelium on roots

 (Heterobasidion annosum) Reduced growth of lateral branches Fruiting bodies:

Crown thinning and yellowing Perennial conks:

Smaller, stress cones dark brown (top)

Red staining in the heartwood cream colored, porous (below)

Wood decay: First-year conks

 Spongy, stringy, white with black flecks buff-colored when immature

 Laminated decay

Black stain root disease Reduced tree growth Dark purple-to-black hyphae:

 (Leptographium wageneri) Crown thinning Stain in recent sapwood and cambium

Stress cones Lengthwise stain in lower bole

Rapid crown wilting

Laminated root rot Reduced tree growth Ectotrophic mycelium

 (Phellinus weirii) Crown thinning and yellowing Reddish-brown setal hyphae between

Laminated decay in roots/lower bole layers of decayed wood

Layers of decay contain small pits Fruiting bodies:

Red-brown staining flat, cream-brown

Rhizina root disease Only in recently burned area Masses of white to yellow mycelia form

 (Rhizina undulata) Dead seedlings mats around roots

Sparse foliage Fruiting bodies:

Discolored needles Disklike, with multiple rootlike

Stem resinosis structures scattered across underside

 Groups form along or over infected roots

 Brown to black with age

Schweinitzii root and butt rot Reduced tree growth Fruiting bodies:

(Red-brown butt rot) Crown thinning and yellowing On ground: circular or irregularly lobed

(Phaeolus schweinitzii) Gall-swelling of small roots On trees: shelf-like

Pronounced butt swelling Fresh: Upper surface velvety, usually

Yellow/red-brown staining in heartwood reddish-brown with a yellow margin

Wood decay: Older: brown, resembling cow dung

 Cubical decay, reddish-brown, crumbly

Carpenter ants often occur within decay

Stringy butt rot Wood decay: Yellow mycelial mats between layers of

(Perenniporia subacida) Light brown stain in heartwood decayed wood

 Small white pits in decayed wood, Fruiting bodies:

 Masses of stringy, white spongy fibers On undersides of downed trees and

 with small black flecks branches of living trees

 Laminated wood decay Perennial, flat and leathery to crustlike,

 cream to light yellow, underside covered in

 small circular pores

Tomentosus root rot Resin exuded on infected roots Fruiting bodies:

(Inonotus tomentosus) Wood decay: Annual, circular, on roots or ground, often

 Red stain, small pockets lined with united with multiple stems.

 white fibers Upper surface: velvety, yellow to brown

 Lower surface: light brown pores darken

 when bruised
4 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005

Table 2—Common coniferous hosts of root diseases of the Inland West. Consult text for major and minor hosts for each

pathogen species, form, type, and variety.

Coniferous hosts

Hemlocks, cedars,

 Root disease Pines Douglas-fir and firs Spruce and larch juniper, and yew

Armillaria root disease Jeffrey pine Douglas-fir Engelmann spruce juniper

lodgepole pine grand fir mountain hemlock

ponderosa pine subalpine fir western hemlock

western white pine white fir western redcedar

whitebark pine

Annosus root disease Jeffrey pine Douglas-fir Engelmann spruce incense cedar

ponderosa pine grand fir juniper

white fir mountain hemlock

other true firs western hemlock

Black stain root disease Jeffrey pine Douglas-fir Can be found on a Can be found on

lodgepole pine variety of spruce hemlock species, but

pinyon pine species, but found found only occasionally

ponderosa pine only occasionally

western white pine

Laminated root rot Can be found on Douglas-fir Engelmann spruce mountain hemlock

pines, but not grand fir western larch Pacific yew

common subalpine fir western hemlock

white fir

Rhizina root rot lodgepole pine Douglas-fir Englemann spruce western hemlock

ponderosa pine grand fir spruce species western redcedar

western white pine western larch

other pine species

Schweinitzii root lodgepole pine Douglas-fir western larch western hemlock

 and butt rot ponderosa pine true firs many spruce species western redcedar

western white pine

Stringy butt rot lodgepole pine Douglas-fir Engelmann spruce western hemlock

western white pine true firs western larch western redcedar

white spruce

Tomentosus root rot lodgepole pine Douglas-fir Engelmann spruce

ponderosa pine grand fir white spruce

western white pine white fir
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005 5

Table 3—Common and scientific names for pathogens, tree species, and insect species.

Root diseases Scientific name of causal fungus

Armillaria root disease Armillaria ostoyae

Annosus root disease Heterobasidion annosum

Black stain root disease Leptographium wageneri

Laminated root rot Phellinus weirii

Rhizina root rot Rhizina undulata

Schweinitzii root and butt root (Red-brown butt rot) Phaeolus schweinitzii

Stringy butt rot (Yellow root rot) Perenniporia subacida

Tomentosus root rot Inonotus tomentosus

Trees Scientific name

Aspens, Cottonwoods Populus spp.

Douglas-fir Pseudotsuga menziesii

Engelmann spruce Picea engelmannii

Grand fir Abies grandis

Incense cedar Calocedrus decurrens

Jeffrey pine Pinus jeffreyi

Juniper Juniperus spp.

Larch Larix spp.

Lodgepole pine Pinus contorta

Mountain hemlock Tsuga mertensiana

Oaks Quercus spp.

Pacific yew Taxus brevifolia

Ponderosa pine Pinus ponderosa

Singleleaf pinyon Pinus monophylla

Spruce Picea spp.

Subalpine fir Abies lasiocarpa

Sugar pine Pinus lambertiana

Western hemlock Tsuga heterophylla

Western larch Larix occidentalis

Western redcedar Thuja plicata

Western white pine Pinus monticola

Whitebark pine Pinus albicaulis

White fir Abies concolor

Insects Scientific name

Douglas-fir beetle Dendroctonus pseudotsugae

Douglas-fir pole beetle Pseudohylesinus nebulosus

Fir engraver beetle Scolytus ventralis

Mountain pine beetle Dendroctonus ponderosae

Western pine beetle Dendroctonus brevicomis
6 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005

Armillaria Root Disease __________

Armillaria root disease, also known as shoestring root rot, is

caused by a variety of Armillaria species that are widely

distributed throughout the Western United States, Europe,

Asia, Africa, and Australia (Watling and others 1991). In

North America, Armillaria ostoyae (Romagn.) Herink predominantly infects conifers; whereas other species of Armillaria

primarily infect hardwoods or are primarily saprophytic (Gregory and others 1991). Ecological roles of Armillaria species

include those of primary pathogen, secondary invader, and

saprophyte. As a primary pathogen, Armillaria is capable of

killing vigorous hosts, while as a secondary invader it only

colonizes hosts predisposed to disease. Armillaria ostoyae is

the most widespread and aggressive species of Armillaria on

conifers in forests of the Inland West (Kile and others 1991).

It can survive up to several decades in previously infected

stumps (Goheen and Otrosina 1998). A recent study estimated

that a single pathogenic A. ostoyae individual occupied an area

of 965 ha (2,385 acres) in a mixed-conifer forest of northeastern Oregon and estimated its age to be between 1,900 and 8,560

years old (Ferguson and others 2003). Thus, Armillaria root

disease can be a persistent, long-term influence within forest

ecosystems. Armillaria root disease causes significant mortality, wood decay, and growth reduction in infected conifers

(Williams and others 1989).

The host range for A. ostoyae includes several western

conifer species in North America; however, susceptibility of

individual tree species may vary depending on site factors and

location (Goheen and Otrosina 1998). Armillaria ostoyae

causes more mortality in forests of the Inland West than in

coastal forests (Goheen and Otrosina 1998), but Armillaria

root disease is a serious problem in both regions (Morrison

1981; Hadfield and others 1986). Highly susceptible hosts

include Douglas-fir, grand fir, and white fir. Other species

damaged or killed by A. ostoyae include ponderosa pine,

Jeffrey pine, lodgepole pine, whitebark pine, western white

pine, Engelmann spruce, subalpine fir, western and mountain

hemlock, western redcedar, and juniper. Some hardwoods

including species of oak, cottonwood, and aspen are damaged

or killed by other species of Armillaria, such as A. mellea

(Morrison 1981; Hadfield and others 1986; Filip 1999; Filip

and Ganio 2004).

Host range, virulence, and other aspects of the ecological

behavior of Armillaria species vary with geographic location.

It can be difficult to predict where Armillaria root disease

might occur (McDonald and others 1987a,b; Kile and others

1991; Mallett and Maynard 1998). On some sites, pines and

other species are tolerant to A. ostoyae, but on other sites

almost all tree species are killed (Goheen and Otrosina 1998).

Locations where trees are stressed—such as sites with drainage problems, soil compaction, or those on the outer limits of

geographic range for the host—have increased mortality (Close

1988; Gregory and others 1991; Goheen and Otrosina 1998).

Occurrence of Armillaria root disease appears to be associated

with groups of habitat types called vegetation subseries

(McDonald and others 2000). Pathogenic Armillaria is rare or

absent in hot-dry, cold-dry, and frost-pocket habitat types

(McDonald 1998, 1999). Conifers growing on coarse-textured

soils are typically at greater risk of developing Armillaria root

disease than those growing on fine-textured soils (Mallett and

Maynard 1998).

Armillaria root disease is commonly associated with other

root diseases, and it may be difficult to tell which disease

occurred first or which disease has caused the most damage.

Additionally, Armillaria root disease may predispose conifers

to bark beetle attacks (Partridge and Miller 1972; Lane and

Goheen 1979; Schmitt and others 1984; Schowalter and Filip

1993).

Disease Symptoms and Signs

Most symptoms of Armillaria root disease (reduced height

growth, thinning and yellowing of foliage, and/or abundant

crops of smaller stress cones) are common to many root

diseases. Although not always present, pitch flow just above

the ground is a fairly diagnostic symptom on resinous conifer

species (fig. 1). Signs that are indicative of Armillaria root

disease can be found at the base, roots, and beneath the bark of

an infected tree or stump. Signs include:

• Mycelial mats or fans (white, thick, fan-like shapes that

can be found under the bark) (fig. 2).

• Rhizomorphs (reddish-black, flat, shoestring-like mycelial cords that are commonly present on or beneath the

bark of roots and lower stems and in the soil near infected

trees or stumps).

• Presence of honey-colored mushrooms (the fruiting bodies of the pathogen) produced in late summer or fall after

rain (fig. 3) (Morrison 1981; Hadfield and others 1986;

Williams and others 1989).

Fans and rhizomorphs do not always indicate that mortality

has been caused by Armillaria root disease. Pathogenic

Armillaria is diagnosed if mycelial fans are found within bark

that is tightly attached to living wood, especially if resinosis is

present at the root crown. Extensive growth of the fungus

eventually girdles and kills the tree. As mycelial fans age, they

become yellow and begin to disintegrate, but a fan-shaped

imprint is left behind in the wood and bark (Goheen and

Otrosina 1998). Pitch flow is an indication of the living tree’s

response to the pathogenic fungus, and the amount of resin

flow may be indicative of the amount of A. ostoyae-caused

colonization in the roots (Omdal and others 2004). In contrast,

fans of saprophytic species of Armillaria often invade between

loosened bark and wood of dead trees or trees dying from other

causes. Trees invaded by saprophytic Armillaria spp. exhibit

little or no evidence of resinosis or wound callus formation

(Robinson and others 2004).

As the disease progresses, stands affected by Armillaria root

disease display increased mortality, often with uprooted trees

with roots broken at some distance from the bole (fig. 4 through

6). Also, as infected trees decay, the cambial tissues and wood
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005 7

Figure 1—Abundant resin flow at the base and roots of a

conifer is a common symptom indicating infection by Armillaria

ostoyae. (Photo courtesy of R.C. Rippy)

Figure 2—Mycelial fans are present within roots of this grand fir infected

with Armillaria ostoyae. (Photo courtesy of J.W. Hanna)
8 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005

Figure 3—Fruiting bodies of Armillaria species. Armillaria ostoyae

commonly fruits in large clusters; however, mushrooms of other Armillaria

species also grow in clusters. (Photo courtesy of R.C. Rippy)

Figure 4—In this Armillaria-caused mortality center, mushrooms

from a species of Armillaria can be seen in the foreground.

(Photo courtesy of J.W. Hanna)
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005 9

Figure 5—Armillaria-caused mortality

centers as they appear in mixed conifer

stands. (Photos courtesy of J.D. Rogers)

Figure 6—An uprooted ponderosa pine showing

decayed roots that have broken at some distance

from the bole. These root wad characteristics, with

other signs and symptoms, indicate mortality from

Armillaria root disease. (Photo courtesy of R.C.

Rippy)
10 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005

become yellowish, moist, stringy, and sometimes have a

pungent odor (Goheen and Otrosina 1998). In the later stages

of decay, wood becomes spongy, light yellow, and may be

marked with numerous black lines, called “zone lines”

(Morrison and others 1992). Decayed wood becomes hard and

fibrous as it dries, as can be seen in wind-blown trees. Mushrooms produced by Armillaria species are often called honey

mushrooms because of the honey-colored caps produced by

some species (fig. 3). The mushrooms have white spores, gills

attached to the stem, minute peg-like hairs at the center of the

upper cap, and a cottony ring around the upper stem (stipe).

These mushrooms are often found growing in clusters near the

bases of infected trees or stumps (fig. 4). Although, mushrooms are typically produced during moist conditions in the

late summer and fall, they are sometimes difficult to find, and

they are not produced every year. Other species of Armillaria

produce similar mushrooms, which can make field identification unreliable.

Disease Management

Armillaria root disease is difficult to control because the

disease inoculum (mycelium and rhizomorphs that have colonized woody substrates) is nearly impossible to eliminate from

a site. In timber-growing areas, management decisions should

consider site characteristics (habitat type, soil type, and associated conditions), stand structure, host species composition,

stand management history, and Armillaria species present to

minimize impacts of this disease (Morrison 1981; Hadfield

and others 1986; Williams and others 1989; Fox 2000). Impacts of Armillaria root disease can be reduced by:

• Favoring more resistant/tolerant tree species.

• Maintaining tree species diversity.

• Reforesting stands with locally adapted species suitable

to the site.

• Promoting tree vigor by minimizing stress and avoiding

wounds.

• Reducing inoculum sources through the uprooting of

stumps and removal of woody debris (Williams and

others 1989; Hagle and Shaw 1991; Roth and others

2000).

These management considerations are especially critical for

sites with high levels of inoculum and/or conditions favorable

for disease development (Hagle and Shaw 1991). Thinning has

also been examined as a possible management option for

reducing Armillaria root disease within a stand. Some studies,

outside of the Inland West, in the Cascade Range of western

Oregon and Washington have shown that precommercial thinning either decreases or does not impact mortality caused by

Armillaria root disease (Filip and others 1989; Filip and Ganio

2004). Precommercial thinning may improve tree vigor by

decreasing tree stress, thereby reducing infection. In contrast,

thinning increased the mortality caused by the disease in

several Inland West locations, such as northern Idaho and parts

of Canada (Cruickshank and others 1997). Stumps that remain

after thinning treatments are a potential inoculum source that

could increase new infections (Cruickshank and others 1997).

Differences in the results from these studies highlight that site

location and plant association can potentially affect outcomes

of management choices, and suggest that these factors be

considered in planning fuels treatments. More research information about Armillaria root disease has been compiled in

Shaw and Kile (1991).

Fuels Treatment Considerations

Because Armillaria species can reside deep in the soil and

within large woody roots, superficial slash burning or prescribed fire is unlikely to eliminate the pathogen, although

these treatments may reduce infection potential indirectly by

removing highly susceptible host species that are readily killed

by fire (Hadfield and others 1986; Filip and Yang-Erve 1997;

Ferguson and others 2003). Mortality caused by Armillaria

increases fuel loads (Fields 2003). Prescribed fire may be used

to reduce fuel loads, which may also reduce inoculum levels

above ground by eliminating nutritional substrates for growth

of Armillaria. However, fire may have minimal direct effects

on the pathogen below ground (Filip and Yang-Erve 1997).

Yet, fire may have indirect effects on Armillaria inoculum by

increasing populations of antagonistic soil fungi such as Trichoderma (Reaves and others 1990). Studies have demonstrated that Armillaria species survive intense fires (Ferguson

and others 2003) and can readily colonize roots of trees killed

by fire (Blodgett and Lundquist 2004). Fire may increase or

decrease the susceptibility of a stand through its influence on

species composition, stand structure, and tree vigor. Thinning

treatments that favor climax or late-successional host trees will

likely aggravate Armillaria root disease. However, thinning

that favors early seral species may reduce root disease over the

long term. Also, greater spacing can improve tree vigor of seral

species, which may increase tolerance to Armillaria root disease.

Recently, a Web-based tool (Armillaria Response Tool:

ART) has been developed that can estimate risk of Armillaria

root disease caused by A. ostoyae in dry forests of the Western

United States (McDonald and others, in press). This tool uses

habitat types to identify sites where A. ostoyae may occur, and

the tool indicates how some fire reduction activities (fuels

management) may exacerbate Armillaria disease within highrisk stands.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005 11

Annosus Root Disease ___________

Annosus root disease, caused by Heterobasidion annosum

(Fr.) Bref., is found in many temperate coniferous forests

around the world. It is an endemic pathogen that is common

and widely distributed in North America. Although this disease has existed for millennia within coniferous forest ecosystems, harvesting practices have increased its incidence and

impacts, especially in Western and Southeastern North America.

In many forest stands, annosus root disease has reached epidemic levels (Otrosina and Ferrell 1995).

Within the Inland West, annosus root disease is of most

concern on true firs and pines (Schmitt and others 2000).

Heterobasidion annosum is a genetically diverse organism

that is composed of at least three intersterility groups (ISGs),

termed S-, P-, and F-types. These groups cannot be distinguished based on appearance, but they differ in pathogenicity

and host range and are intersterile (cannot mate) when paired

with each other (Goheen and Otrosina 1998; Sullivan and

others 2001). Only the S-type (which affects mainly true firs,

hemlock, spruce, and Douglas-fir) and the P-type (which

affects mostly pines, larch, incense cedar, and juniper) are

found in the Inland West (Otrosina and Ferrell 1995; Goheen

and Otrosina 1998). Disease-induced mortality of ponderosa

pine, in the Inland West, is often observed on dry sites of poor

quality (Goheen and Goheen 1989; Lockman 1993). Mortality

can also be quite high in natural grand and white fir stands,

especially stands that have experienced selective harvesting

(Schmitt and others 1984; Chase 1989; Goheen and Goheen

1989). Annosus root disease is often associated with mortality

of ponderosa pine or Jeffrey pine in second-generation or

partially harvested stands (Schmitt and others 2000). Specificity of the P- and S-types only applies to living hosts; both types

will colonize dead wood of almost all coniferous species

(Otrosina and Scharpf 1989; Goheen and Otrosina 1998).

Because of differences within and among H. annosum ISGs

and their interaction with host tree species and environmental

factors, the behavior of annosus root disease is highly variable

(Goheen and Otrosina 1998; Garbelotto and others 1999).

Recent research information about annosus root disease has

been compiled in Woodward and others (1998).

The fungus spreads primarily in two ways: aerial spread, and

local underground tree-to-tree spread (Schmitt and others

2000). Basidiospores released from fruiting bodies of the

fungus can travel up to 161 km (100 miles) (Goheen and

Otrosina 1998). Heterobasidion annosum readily colonizes

fresh stumps and stem wounds of all coniferous species except

red and yellow cedar (Wallis and Reynolds 1970; Filip and

Morrison 1998), and spread from colonized stumps can cause

subsequent infections of residual trees via root contacts after

thinning operations (Morrison and Johnson 1978; Sullivan and

others 2001). Stump surfaces are vulnerable to colonization for

up to 4 weeks after harvesting or thinning (Otrosina and Ferrell

1995). However, stump vulnerability to H. annosum basidiospores significantly decreases after a period of 2 weeks, as

stumps become colonized by competing fungi. Hyphae from

germinating basidiospores colonize the wood of the stump and

lateral roots. Root grafts or contacts, where roots from two or

more trees touch, can provide contact between infected and

healthy trees and are a source of asexual spread of H. annosum.

Infection centers can often be traced to larger stumps that were

colonized soon after harvest. Stumps greater than 36 cm (14

inches) in diameter are more likely than smaller stumps to

serve as foci of infection centers (Goheen and Otrosina 1998).

Incidence and severity of annosus root disease varies considerably, depending on site location and history of forest stands.

In general, annosus root disease represents a more serious

problem in managed forests than in natural forests (Shaw and

others 1994). Previous studies have shown that higher levels of

mortality are typically found in stands that have been partially

cut and stands that have experienced multiple thinnings (Schmitt

and others 1984). In one survey in Oregon, 89 percent of true

fir stumps were colonized 5 to 9 years after harvest (Filip and

others 2000). In the Inland West, this disease can cause

substantial tree mortality, especially when associated with

drought stress or insect attack (Filip and Morrison 1998). Trees

infected with annosus root disease are frequently subject to

attack by insects, such as the fir engraver beetle on true firs

(Cobb and others 1974; Hertert and others 1975; Lane and

Goheen 1979; James and Goheen 1981; Schowalter and Filip

1993) and mountain pine beetle or western pine beetle on pines

(Cobb and others 1974). In northern Idaho and northeastern

Washington, stands that are dominated by Douglas-fir can

have large amounts of mortality, especially on dry sites

(Lockman 1993; Schmitt and others 2000). Heterobasidion

annosum can persist on a site and within stumps for long

periods. In larger stumps, H. annosum can survive up to 60

years (Goheen and Otrosina 1998).

Disease Symptoms and Signs

Common symptoms of annosus root disease are the same as

for many other root diseases and include yellowing or thinning

of crowns, reduction in tree height and lateral branches, and

stress cone crops. In firs, heartwood in butts and lower stems

of infected trees are often stained red (fig. 7). Advanced decay

includes stringy, spongy, and white-streaked areas that often

have scattered black flecks (fig. 8). Decayed wood can also

become laminated (separated along spring wood of growth

rings) as it dries out.

Fruiting bodies occur in hollow stumps, on root crotches, or

on root collars of dead and dying trees. Although rare or

inconspicuous, fruiting bodies can be used for positive identification of the fungus. Conks are perennial and may appear to

have several layers or furrows. In the early stages of development, these conks appear as small buff-colored cushions. In

later stages, the conks are shelf-shaped, the upper surface is

smooth and a darker brown than the cream-colored margin,

and the undersides are cream-colored with tiny-pores (fig. 9).

A layer of white fungal mycelium (ectotrophic mycelium) is

occasionally seen growing on the exterior of infected roots. In

the absence of other identification methods, wood samples

held at high humidity produce distinctive asexual fruiting

bodies (conidiophores and conidia). DNA-based methods are
12 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005

Figure 7—Common staining and decay caused by Heterobasidion

annosum as it appears in a cross section of hemlock. (Photo

courtesy of W.G.Thies)

Figure 8—White pocket rot characteristic of wood decay caused by

Heterobasidion annosum. White mycelium with black specks is a common sign

of this disease. (Photo courtesy of J. W. Schwandt)
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005 13

Figure 9—Fruiting bodies of Heterobasidion annosum,

the cause of annosus root disease, are perennial and

often found in recessed hollows of stumps and roots.

These were observed on an uprooted grand fir. (Photo

courtesy of R.C. Rippy)

also available to help identify H. annosum to species (Garbelotto

and others 1999; Bahnweg and others 2002).

Disease Management

Protective measures have focused primarily on preventing

the colonization of stumps by germinating basidiospores

(Morrison and others 1989; Schmitt and others 2000; Johansson

and others 2002). Chemical and biological treatments of stumps

have been tested with varying levels of success (Driver 1963a,b;

Edmonds and others 1969; Weir 1969; Driver and others 1970;

Russell and others 1973a; Nelson and Li 1980; Woodward and

others 1998). One boron-containing compound (sodium

tetraborate decahydrate) has been widely used and can be

successful for preventing colonization if applied within 48

hours after harvesting (Otrosina and Ferrell 1995; Schmitt and

others 2000). Alternatively, in Europe, freshly cut stumps may

be treated with urea, as this increases the pH of the stump

surface to a level where basidiospores cannot survive (Brantberg

and others 1996; Johansson and others 2002).

The potential for biological control of H. annosum has been

the subject of limited investigations in Western North America

(Filip and Morrison 1998). A fungal species, Phlebiopsis

gigantea (=Peniophora gigantea), has been documented to

out-compete H. annosum when applied to freshly-cut stumps

(Rishbeth 1963; Woodward and others 1998). In Europe, use

of this biological agent for controlling H. annosum is widespread, commercially available, and effective (Vainio and

others 1998).

Stump removal can be effective for reducing buildup of rootrot fungi after tree removal; however, this method is expensive

and can be disruptive to the site (Thies and others 1994; Roth

and others 2000). Because H. annosum can behave as a wound

parasite, wound prevention, especially during harvest, is a
14 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005

primary method of disease management (Goheen and others

1980; Aho and others 1983; Filip and others 1992b; Sullivan

and others 2001). Heterobasidion annosum populations vary

in their pathogenicity and host ranges, and hosts also vary in

their ability to resist strains of the pathogen (Worrall and others

1983). This pathogen can be extremely damaging on sites

planted with a single species. Thus, one approach used to

manage annosus root rot is favoring mixed stands that include

hardwoods or a mixture of conifers (Schmitt and others 2000).

Timing of management activities may be important, but

results from different studies are in conflict. Thinning in

summer or winter may be preferred over spring or fall. Thinning under warm temperatures may allow other fungi such as

Trichoderma viride to out-compete H. annosum for establishment within the substrate of newly created stumps (Driver and

Ginns 1969). Alternatively, if thinning occurs during winter

when snow cover is present or temperatures are at or below

freezing, the rate of stump colonization by H. annosum may be

reduced and may favor colonization by other microorganisms

(Chernykh and Belyi 1978). Studies in northeastern Oregon,

however, found no difference in stump colonization by H.

annosum among different harvesting seasons (Filip and others

1992a).

Fuels Treatment Considerations

Thinning may be one of the most important management

practices that encourages the spread of H. annosum because it

opens infection routes, creates fresh stumps for colonization by

H. annosum, and creates logging wounds on standing trees that

serve as infection sites for H. annosum (Aho and others 1983;

Korhonen and others 1998; Sullivan and others 2001). On the

other hand, one study showed that thinning in western hemlock

stands increased sound-wood volume in residual trees despite

minor logging wounds and H. annosum-caused decay (Goheen

and others 1980). Also, wound prevention and stump treatments

have been shown to greatly reduce H. annosum infection.

In pine stands in the Southeastern United States, annosus

root disease has been reduced by prescribed burning prior to

thinning operations. This burning reduces the duff layer that

favors sporophore production, thus reducing the spore loads in

the stand at the time of thinning (Froelich and others 1978;

Otrosina and others 1995). However, successful tests of

underburning for control of annosus root disease have not been

reported for forests in the Inland West, perhaps because this

treatment is typically considered impractical under the stand

and soil conditions in this region. Research on the effects of

prescribed fire on the incidence of stump-surface infection is

needed in the Inland West.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005 15

Laminated Root Rot _____________

Laminated root rot, caused by Phellinusweirii(Murr.) Gilb.,

is prevalent in British Columbia, Washington, Oregon, northern California, northern Idaho, and western Montana (Nelson

and others 1981; Sturrock and Garbutt 1994; Thies and Sturrock

1995). Phellinus weirii is considered a “disease of the site”

because it persists across tree generations (Hadfield and others

1986; Thies and Sturrock 1995). This disease can cause extensive growth loss and mortality that is often associated with

windthrows within disease centers involving several conifer

species of diverse age classes. The pathogen appears to spread

by contact of susceptible tree roots with stumps or roots of

previously infected trees. Laminated root rot is most destructive in stands 25 to 125 years old, and damage increases in

subsequent stands (Tkacz and Hansen 1982).

In Western forests, highly susceptible species include Douglas-fir, grand fir, mountain hemlock, and white fir. Intermediately susceptible species include Engelmann spruce, Pacific

yew, subalpine fir, western hemlock, and western larch. Species that are tolerant or resistant to laminated root rot include

lodgepole pine, sugar pine, western white pine, ponderosa

pine, and western redcedar; all hardwoods are immune (Filip

and Schmitt 1979; Hadfield and others 1986; Nelson and

Sturrock 1993; Thies and Sturrock 1995). Fire exclusion

increases the proportion of shade-tolerant conifers, which are

generally more susceptible to laminated root rot.

Phellinus weirii has two basic forms: one that produces a

butt rot in western redcedar, and another that causes root

disease in Douglas-fir and several other conifer species (Thies

and Sturrock 1995). A proposal to change the scientific name

of the form of P. weiriiaffecting Douglas-fir to P. sulphurascens

(Larsen and Cobb-Poulle 1990) or Inonotus sulphurascens

(Larsen and others 1994) has not been universally accepted.

Phellinus weirii often occurs with other root diseases, such as

Armillaria root disease and black stain root disease (Sinclair

and others 1987). More than 4.4 million cubic meters (154

million cubic feet) of timber volume are estimated to be lost

annually to laminated root rot (Nelson and others 1981).

Associations have been found between the occurrence of P.

weirii and aspect, elevation, timber type, habitat type, and soil

type. Soil characteristics, such as pH, temperature, and moisture content, may also affect the occurrence and extent of

damage from laminated root rot (Thies and Sturrock 1995).

Mortality due to this disease is generally higher on wetter than

on drier habitat types.

Trees infected with P. weirii are sometimes killed by bark

beetles in combination with other root diseases. The Douglasfir beetle, Douglas-fir pole beetle, and fir engraver are commonly associated with laminated root rot (Schowalter and Filip

1993). Laminated root rot, as with other root diseases, provides

a continuous source of suitable material for maintaining endemic bark beetle populations when conditions are not favorable for epidemics (Thies and Sturrock 1995).

Disease Symptoms and Signs

Infected trees exhibit crown symptoms typical of many root

diseases: chlorosis, reduction in growth, gradual crown thinning, and a crop of stress cones. In wind-thrown trees, decayed

roots are typically broken at the root collar; roots do not usually

lift from the soil as the tree falls (fig. 10). This is especially

noticeable in infection centers, where fallen trees may occur as

a random pattern of crossed stems. Incipient decay in the roots

and lower bole of infected trees usually gives a red-brown stain

to the outer heartwood (fig. 11). Advanced decay separates

easily into sheets at the annual rings; sheets contain small pits

and are covered with reddish-brown to pinkish setal hyphae

that can be seen with a hand lens (fig. 12). Gray-white to buffcolored mycelia may be found on the outer surface of infected

roots. Fruiting bodies of P. weirii typically form near or in

contact with the forest floor on the underside of downed trees

and uprooted stumps. They have light gray-brown pore surfaces and margins that are white to cream-colored when young

but later turn a uniform chocolate brown. However, fruiting

bodies are of little diagnostic value, as they are uncommon and

inconspicuous (Hadfield and others 1986; Sinclair and others

1987).

Disease Management

Identifying areas containing laminated root rot is the essential first step to successfully managing for this disease. After

disease has been assessed, acceptable levels of disease must be

determined before deciding upon a management response. To

reduce disease impacts, thinning treatments can:

• Avoid areas with the disease.

• Selectively remove the most susceptible species.

• Favor root-disease resistant or tolerant species.

• Make openings in which to plant or regenerate root

disease-resistant or tolerant species.

• Use push-felling to extract root systems from the soil

(Bloomberg and Reynolds 1988; Morrison and others

1988).

• Include stump removal to reduce inoculum levels

(Hadfield 1985; Hadfield and others 1986; Thies and

Sturrock 1995).

• Include a combination of these treatments.

However, the potential adverse effects of soil compaction

and tree wounding caused by heavy equipment must also be

considered (Lull 1959; Froehlich and McNabb 1984; Smith

and Wass 1991). Thus far, effects of treatments such as

fertilization have supported increased growth of trees but

produced no apparent reduction in disease-caused tree mortality (Thies and Nelson 1988). Eradication of P. weirii from

infected stumps with fumigants (Thies and Nelson 1987) in

conjunction with antagonistic Trichoderma (Nelson and Thies

1985, 1986; Nelson and others 1987) has been successful

under experimental conditions but has not been used operationally in the United States. Increasing species diversity to
16 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005

Figure 10—Laminated root rot mortality center showing characteristic root

wads with roots broken near the root collar, leaving only stubs. (Photo

courtesy of W.G. Thies)

Figure 11—Incipient decay from laminated root rot in the roots and lower bole of infected trees is frequently

observed as a red-brown stain in the outer heartwood. (Photos courtesy of W.G. Thies)
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005 17

reduce losses associated with P. weirii is a preferred strategy

in northern Idaho, western Montana, Oregon, and Washington

(Hadfield and others 1986; Thies and Sturrock 1995; Filip

1999).

For additional information pertaining to P. weirii and its

management, see Morrison and others (1992), Thies and

Sturrock (1995), and Hansen and Goheen (2000).

Fuels Treatment Considerations

The effect of wildfire on P. weirii has been speculated to be

more indirect than direct, as fire acts by changing stand species

composition and forest successional patterns involving susceptible and resistant hosts (McCauley and Cook 1980). Because

fire has little direct influence on the survival of P. weirii

Figure 12—White mycelium on the outer bark of infected root underneath the duff is a common characteristic of laminated root rot

(upper left). Advanced decay from laminated root rot causes wood to separate easily along growth rings of spring-wood. Each layer

of decayed wood has small pits and often displays cinnamon-brown mycelium with hairlike pegs that project away from the layer

(upper right). The underside of this Douglas-fir log shows the appressed habit of the young fruiting bodies of Phellinus weirii

(lower). (Photos courtesy of W.G. Thies and R.C. Rippy).

inoculum, fuels reduction by burn treatments, such as prescribed burning, are not likely to directly influence the

occurrence of laminated root rot (Thies and Sturrock 1995).

However, fuels treatments that would use prescribed burning

at intervals that approximate historic fire frequencies, with the

aim of converting stand composition back to an early successional stage, are strategies for management of this disease.

From a production standpoint, thinning is generally not recommended in stands with a major component of susceptible trees

and moderate to high levels of disease. In disease centers,

thinning treatments without stump removal may increase disease severity. This approach is generally only considered when

either a final harvest is scheduled within 15 years, or severe

losses are deemed acceptable (Thies and Sturrock 1995).
18 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005

Black Stain Root Disease _________

Black stain root disease is caused by three host-specialized,

genetically isolated varieties of the pathogen Leptographium

wageneri (Kendrick) Wingfield (Harrington and Cobb 1984,

1986, 1987; Zambino and Harrington 1989, 1990). The hard

pine variety (var. ponderosum) is prevalent from the Pacific

Coast States to the Northern Rockies, including all States and

Provinces of the Inland West south and west of the Bitterroot

Mountain range. This variety infects ponderosa, lodgepole,

and Jeffrey pine and can also occasionally be found in hemlocks, white and Engelmann spruce, and white pines (Morrison

and Hunt 1988; Allen and others 1996). The Douglas-fir

variety (var. pseudotsugae) is broadly adapted to Douglas-fir

from moist coastal to arid situations, from California to British

Columbia to southern Colorado and New Mexico. The pinyon

variety (var. wageneri) occurs on pinyon species, primarily

singleleaf pinyon, throughout the Southwest to the southern

edge of Idaho.

Stands affected by black stain root disease are generally

moist to mesic. Disease incidence may be higher in areas with

soil compaction, poor drainage (Hadfield and others 1986), or

coarse-textured soils and shallow soils prone to summer drought

(Morrison and Hunt 1988). The pinyon and hard pine varieties

are limited to areas with cool soil temperatures, whereas the

Douglas-fir variety can survive and infect at higher soil and

bole temperatures. Black stain root disease occurs as persistent

infection centers or as scattered infections after disturbances

such as road building, construction, and thinning (Hansen

1978; Harrington and others 1983). Within infection centers,

the pathogen spreads by growth in and along roots, by root

grafting or root contact, and by limited hyphal growth (up to 15

cm) through the soil between roots (Cobb 1988). Infection can

occur through natural openings in small roots, such as splits at

root forks and sites where lateral roots emerge, or at the site of

root injuries, such as caused by abrasion against rocks (Hessburg

and Hansen 2000). Root lesions from Armillaria infections on

adjacent trees can also allow transfer of the black stain root

disease pathogen from host to host (Hessburg and Hansen

2000). Root damage caused by equipment can provide an

abundance of infection courts. Experiments with inoculated

Douglas-fir seedlings indicate that most minor root wounds no

longer act as infection courts after 1 month, because wound

closure prevents infection. The pathogen does not penetrate

either intact parenchyma or callus (Hessburg and Hansen

2000).

Expansion of infection centers in the various hosts averages

around 1 m/year (3.3 feet/year) (Hessburg and others 1995),

with rates of up to 7 m/year (23 feet/year) reported in some

pinyon stands (Cobb 1988). Even the slower rate is substantially (three to five times) faster than most other root diseases

(Hessburg and others 1995). It appears that the black stain

pathogen may be active in stumps for only 3 years after harvest,

as it dies rapidly after the death of host tissues (Cobb 1988).

Severity and rates of spread are positively related to density of

hosts (Cobb 1988). In Douglas-fir, rates of infection center

expansion decrease markedly after stands reach an age of 30 to

35 years (Hessburg and others 1995).

Unlike many root pathogens, infection centers of black stain

root disease are established from initial infections vectored by

root-feeding bark beetles and weevils (Goheen and Cobb

1980; Harrington and others 1985; Witcosky and Hansen;

1985; Witcosky and others 1986; Cobb 1988; Hansen and

others 1988; Harrington 1988). Insect vectors are attracted to

stressed trees (Harrington and others 1985; Morrison and Hunt

1988). Trees in decline due to black stain root disease are also

predisposed to infestation by both root-inhabiting and boleinhabiting species of bark beetles (Goheen and Cobb 1980;

Cobb 1988; Hessburg and others 1995, 2001; Negron and

Wilson 2003). Bark beetle species that vector the disease are

attracted to volatiles given off by living roots of dying trees

(Witcosky and others 1987; Kelsey and Joseph 1998). Once an

insect has caused a tree to become infected, recent layers of

xylem in the root system are colonized. Presence of persistent

black stain root disease infection centers can maintain local

populations of bark beetles, initiating bark beetle mortality

centers (Cobb 1988).

Disease Symptoms and Signs

Crown symptoms that occur if black stain root disease is

present in a stand include many typical above ground symptoms of root disease, such as reduced growth and fading of

crowns, slow or rapid decline (slower in old trees and faster in

young trees), distress cones, and crown wilt. Pines will usually

succumb to bark beetle attacks before the latter symptom can

be expressed (Cobb 1988). Because mortality can be hastened

by bark beetles, and the crown symptoms of black stain root

disease are similar to those of other root diseases, mortality

caused by black stain root disease is sometimes mistakenly

attributed to other causes (Cobb 1988; Hessburg and others

1995). However, stands with black stain root disease will have

trees in different stages of mortality, typical of root disease

infection centers, instead of a uniform onset of mortality,

typical of mass attacks by bark beetles (Cobb 1988).

The most diagnostic sign of black stain root disease is the

microscopic mycelium that is visible as dark purple to black

staining in younger layers of sapwood in roots and the lower

trunk of an affected tree (fig. 13). Unlike blue stain fungi,

which are also vectored by insects, these streaks of intense

staining in the bole strictly follow the path of xylem upward

from the roots where the initial infection point occurred. In

cross-sections of stems and roots, the staining has an arclike

appearance, as it lies primarily within early wood of recently

infected growth rings. This staining pattern further differentiates black stain root disease from blue stain, which develops in

parenchyma rays at the time of mortality and extends in wedgeshaped patterns into heartwood (fig. 14). The restriction of

black stain to recent rings results from fungal colonization of

the tracheids of active xylem (Cobb 1988). These symptoms

and the development of disease are similar to the vascular wilts

of hardwoods (Joseph and others 1998).
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005 19

Figure 13—Dark purple to black streaks of stain within the outer one to two annual rings of

sapwood in the lower bole and roots of an affected tree indicate black stain root disease caused

by Leptographium wageneri. (Photos courtesy of W.G. Thies and R.C. Rippy)

Figure 14—Arcs of stain (left) are typical of black stain root disease and are caused by Leptographium

wageneri colonizing the tracheids of the most active growth rings. In contrast (right), fungi that cause blue

stain colonize parenchyma rays to form wedgelike sections that penetrate to the limits of the sapwood.

(Photos courtesy of W.G. Thies and R.C. Rippy)
20 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005

Disease Management

Few long-term field studies have been conducted to assess

the behavior of this disease over time in stands under different

types of management. Nonetheless, indications from existing

studies suggest that the disease may be minimized by maintaining stand vigor while avoiding disturbance and injury, especially during times of peak beetle activity (Hadfield and others

1986; Hessburg and others 1995). Maintaining trees in vigorous condition with adequate spacing has been suggested as the

most useful long-term strategy for minimizing losses to black

stain root disease (Cobb 1988).

Because black stain root disease is vectored by beetles, any

activities that increase the numbers of vectors in an area have

the potential to increase disease, if disease is already present in

stands within flight distances of its vectors. The distance for

concern is 1.6 km (1 mile) for insect vectors of Douglas-fir

(Hansen and others 1988; Hessburg and others 1995). Black

stain root disease has long been associated with road building

(Goheen and Hansen 1978; Hansen 1978; Hessburg and others

2001) and thinning-associated disturbance (Harrington and

others 1983; Hessburg and others 2001). Thinning of affected

species can trigger increases in vector population and establishment of many new infection centers. Dramatic 20- to 100-

fold increases in the most important of the three insect species

that act as vectors in Douglas-fir have occurred following

springtime precommercial thinning (Harrington and others

1985; Hansen and others 1988). Thinning and clearcutting in

ponderosa pine in winter and spring also cause dramatic

increases in vector beetles (Otrosina and Ferrell 1995). Management strategies for Douglas-fir have included preventing

tree wounds, avoiding tractor logging within 1.6 km (1 mile) of

an infection center, favoring a diverse stand composition that

includes tree species that are not susceptible to the pathogen,

and restricting thinning to summer after spring beetle flights

(Hansen and others 1988; Filip 1999; Hessburg and others

1995, 2001). This ensures that vectors will be established in

other dead or dying trees prior to thinning. Summer thinning

also allows roots and stumps of newly cut trees time to dry out

before fall (Witcosky and others 1986; Hessburg and others

1995; Filip 1999). Fall thinning is not recommended because

stumps may still attract insects the following spring. A specific

recommendation for minimizing disease by the hard pine

variety of the pathogen is to maintain mixed conifer type

forests where indicated by habitat, but limit susceptible pine

species to 25 percent of the mix when disease is present (Cobb

1988). If stands of susceptible tree hosts have adequate spacing

and are intermixed with nonsusceptible species, these stands

will be at lower risk of becoming permanent infection centers

and will have reduced tree-to-tree spread through roots. Because the pathogen has low persistence, healthy but susceptible

trees outside the margins of infection centers have been felled

to limit further expansion (Tainter and Baker 1996).

Fuels Treatment Considerations

Factors to consider prior to choosing a fuels treatment are

whether black stain root disease occurs within the vicinity of

the treatment area, which hosts are being affected, the ratio and

spacing of host and nonhost trees, and the choice of season for

fuels management treatments. In general, if a fuels treatment is

necessary, the key for minimizing subsequent black stain root

disease is to reduce wounding of residual trees, minimize

compaction, and time activities in relation to insect dispersal

activities. Little published information is available on the

effects of prescribed fire in different seasons on host vigor and

root diseases (Thies and others 2001). Research is needed to

determine the degree to which insect vectors of black stain root

disease are attracted to roots damaged by prescribed fire,

whether the damage or attraction differs with the season during

which the fire treatment is applied, and how long insect

attraction persists. Thus, answers are likely to be complex, and

must weigh the direct detrimental effects on hosts against the

potential effects on disease and fire behavior. A study of

ponderosa pine/juniper stands in the Blue Mountains of southeastern Oregon showed that all root- and lower bole-feeding

insect species that could potentially act as vectors of black stain

root disease were greater in abundance following prescribed

burns than in unburned controls. Fall burning caused greater

direct and delayed mortality than spring burning, but mortality

was not due to black stain root disease (Thies and others 2001;

Thies and others in press). Different species of root- and lower

bole-feeding insects were favored by spring or fall burns, and

no clear relationships between time-of-burn or transmission of

black stain root disease had been identified at these sites (Thies

and others 2001). Another study in the same location showed

that fall burning caused significant reductions in both fine root

biomass and ectomycorrhizal fungus species richness in stands

of ponderosa pine, both important for tree health, whereas

spring underburning had little effect (Smith and others 2004).
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005 21

Schweinitzii Root and

Butt Rot _______________________

Phaeolusschweinitzii(Fr.) Pat., also known as the velvet top

fungus, causes Schweinitzii root and butt rot, a decay in the

roots and lower stem that affects most mature coniferous tree

species in Western forests (Hadfield and others 1986). It is the

most common cause of brown-cubical rot in Douglas-fir and

other commercial timber species (Gilbertson and Ryvarden

1987). Douglas-fir is the most common species infected, but

ponderosa pine, lodgepole pine, western white pine, western

redcedar, western larch, western hemlock, spruces, and true

firs are also known hosts (Allen and others 1996; Hagle and

others 2003). Phaeolus schweinitzii is regarded as the most

serious butt-rot pathogen of conifers in old-growth forests in

the United States (Sinclair and others 1987).

Windborne spores of P. schweinitzii colonize trees through

basal scars caused by fire, wounds from logging, or through

wounded roots. The pathogen might also spread between trees

with root contact, but little direct evidence is available to

support this theory (Sinclair and others 1987). This fungus

usually infects and kills root tips, resulting in “stubbed” roots

with blunt ends (Hagle and others 2003). Soil compaction,

drought, and flooding may predispose roots to damage (Tainter

and Baker 1996). Trees growing on sites with shallow soils or

soils with low water-holding capacity are more likely to be

damaged by P. schweinitzii (Beckman and others 1998).

Phaeolus schweinitzii can grow through wood colonized by

Armillaria species and may predispose trees to Armillaria root

disease and bark beetles (Hadfield and others 1986; Sinclair

and others 1987). Alternatively, Armillaria species may be a

secondary pathogen that follows P. schweinitzii in Douglas-fir

and grand fir in Idaho (Dubreuil 1981).

Decay is usually confined to the roots and lower 3 m (9.8

feet) of the bole. Trees with advanced Schweinitzii rot are

predisposed to windthrow and breakage. Valuable butt logs are

extensively decayed, causing serious losses in timber volume.

Decay caused by P. schweinitzii may be confused with decay

caused by Fomitopsis pinicola, Fomes officinalis, Laetiporus

conifericola, and Postia sericeomollis (Partridge and others

1978; Allen and others 1996; Hagle and others 2003).

Disease Symptoms and Signs

Trees infected with P. schweinitzii rarely exhibit root-disease crown symptoms (Partridge and others 1978; Hadfield

and others 1986; Hagle and others 2003). Carpenter ant infestation and/or bark beetle attacks may occur on trees weakened

by this disease. Small-diameter roots that are infected may be

“stubbed” with gall-like swellings and may have dark, resinous

heartwood (Hagle and others 2003). Infected trees may also

have pronounced swelling at the butt (Scharpf 1993).

Fruiting bodies are annual, developing in the late summer

and fall, but may persist for a year or more (fig. 15). These

fruiting bodies are found on the ground near infected trees or

occasionally emerge directly from the stem of an infected tree

(Hadfield and others 1986; Hagle and others 2003). Those that

form on the ground are circular or irregularly lobed in form

with a sunken center and short, central stalk; those forming on

infected trees are shelflike. The upper surface is velvety, up to

25 cm (10 inches) in diameter, and usually reddish brown with

a yellowish margin when fresh. The lower surface has large

angular pores and is yellow-green when young, turning brown

with age. Older fruiting bodies can resemble cow dung in

appearance (Scharpf 1993; Hagle and others 2003). Incipient

decay, though sometimes inconspicuous, often produces a

yellow to red-brown discoloration in the heartwood. With

advanced decay, wood becomes reddish brown, crumbly, and

may crack into large cubical pieces. Decayed wood can be

easily crumbled into fine powder. Thin, white mycelial mats

are sometimes present in shrinkage cracks (Gilbertson and

Ryvarden 1987; Hagle and others 2003).

Disease Management

To reduce infection by P. schweinitzii, care should be taken

to avoid wounding of trees and minimize soil compaction

during harvesting operations. Because Schweinitzii rot primarily impacts older trees, economic losses might be reduced by

harvesting trees before they are overmature (Hadfield and

others 1986). Because of possible windthrow (fig. 16), trees

infected with P. schweinitzii in recreation areas and around

buildings should be considered hazardous. Increment boring

of the lower bole and roots of trees can be used to detect brown

rot. At other sites, the degree of care used to prevent new

disease may be less. However, the beneficial ecological roles

of brown-rots should also be considered before selecting

management activities. For example, brown-rotted logs once

incorporated into the forest floor or mineral soil can act as

moisture reserves for ectomycorrhizal root development in

periods of drought, provide a source of N fixation, and/or

improve soil physical properties (Harvey and others 1987;

Page-Dumroese and others 1994; Jurgensen and others 1997).

Fuels Treatment Considerations

Prescribed fire hot enough to cause basal wounds on trees

should be avoided. Infections can be reduced by minimizing

tree wounding during thinning operations. Information is

unavailable for other potential interactions of fuels treatments

with Schweinitzii root and butt rot.
22 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005

Figure 16—Trees infected with Phaeolus schweinitzii may break off above ground

level, exhibiting characteristic brown cubical butt rot (left). Phaeolus schweinitzii

decay 30.5 cm (12 inches) above ground level in fire scar (right). (Photos courtesy

of R.C. Rippy and J.D. Rogers).

Figure 15—Fruiting bodies of Phaeolus schweinitzii form on the

ground or cut stumps of affected trees. They are circular or

irregularly lobed in form, with a sunken center and short, central

stalk. Older fruiting bodies, such as in the lower photo, dry up and

closely resemble cow dung—hence the common name “cow-pie

fungus.” (Photos courtesy of J.E. Stewart and W.G. Thies)
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005 23

Other Root Diseases of

Consideration in the

Inland West ____________________

Other notable root diseases present in the Inland West are

Tomentosus root disease, Rhizina root rot, and stringy butt rot.

While Tomentosus root disease, also known as stand-opening

disease, has been the subject of numerous studies in British

Columbia and Ontario, less information has been reported on

it for the Inland West. Published information is also quite

limited for Rhizina root disease and stringy butt rot.

Tomentosus Root Disease

Tomentosus root disease is found throughout the temperate

region of the northern hemisphere (Hunt and Unger 1994). In

Oregon and Washington, Engelmann spruce is the most common host (Hadfield and others 1986). Lodgepole pine is an

important host in other parts of the range, while true firs,

western white pine, and Douglas-fir are occasional hosts

(Hagle and others 2003). The fungal pathogen, Inonotus

tomentosus(Fr.) Teng., primarily spreads slowly from host-tohost by root-to-root contact but it also spreads by spores

(Lewis 1997). Because of the slow rate of spread, infection

centers occur as clumps of dead trees in the landscape, with

standing dead or windthrown trees surrounded by trees in

various stages of disease progression (Lewis 1997).

The likelihood that Tomentosus root disease will occur on a

site depends on species composition, stem density, and site

characteristics, such as soil moisture and nutrient regime

(Lewis 1997; Bernier and Lewis 1999). Tomentosus root

disease is difficult to control once I. tomentosus has become

established at a site. The fungus can utilize root and stump

resources well after bole removal, allowing it to persist at least

30 years after timber harvest. In a study in Utah, I. tomentosus

was isolated from 75 percent of stumps 20 years after cutting.

It was also isolated from dead roots as small as 1.3 cm (0.5

inches) in diameter 9 years after cutting and up to 5.5 m (18

feet) away from an infected stump 20 years after cutting (Tkacz

and Baker 1991). Postharvest burning did not reduce the

incidence of I. tomentosus, as the fungus was recovered in the

same proportion of stumps from burned and unburned areas.

Disease Symptoms and Signs—Classic root rot symptoms,

including thinning crown, chlorotic foliage, and reduced height

growth, are displayed by trees infected with I. tomentosus

(Bernier and Lewis 1999). Crown symptoms may not develop

until 50 percent of a tree’s roots are infected, so it is difficult to

recognize Tomentosus root disease until after it is well established (Filip 1986; Lewis 1997). Characteristics of the decay in

the root and butt heartwood are diagnostic. Appearance ranges

from a reddish-brown stain in the early stages of decay, to

elongate, spindle-shaped white pockets separated by firm

reddish-brown wood in advanced decay (Tkacz and Baker

1991; Hagle and others 2003). In spruce, disease caused by I.

tomentosus can be differentiated from annosus root rot, because wood decayed by the former is firm, instead of spongy.

Also, the annual conks of I. tomentosus, which are produced on

the ground near infected trees, are readily distinguished from

the perennial conks of H. annosum. Fruiting bodies of I.

tomentosus are 5 to 12.7 cm (2 to 5 inches) in diameter, with

velvety caps and short stems. The pore surface on the underside

of the cap is yellow and cream-colored, and darkens with age

(Hagle and others 2003).

Rhizina Root Rot

Rhizina root rot is a disease of burned sites that affects

conifer seedlings. This disease is not responsible for large

volume losses, but it can impact plantings and natural regeneration after fire (Ginns 1968; Morgan and Driver 1972).

Spores of Rhizina undulata Fr.:Fr. are viable for up to 2 years,

and spore germination is stimulated by fire (Gremmen 1971).

After underlying or adjacent soils have been warmed by fire,

pathogen spores will germinate quickly and colonize the

recently sterilized soil. The pathogen may infect susceptible

conifer seedlings and cause mortality within a growing season.

Infection occurs when a susceptible conifer root contacts

mycelium or strandlike rhizoids. Losses of up to 80 percent of

planted stock have occurred (Callan 1993); however, an extensive survey of 277 burned clearcuts in western Washington and

Oregon found that Rhizina root rot caused little damage (Thies

and others 1979). Rhizina root rot does not occur at all sites

exposed to fire. For this disease to occur, sites must have the

pathogen (usually from past infections), acidic soils, and

susceptible conifer roots. In a laboratory study, young seedlings of lodgepole pine, a fire-successional conifer species,

displayed strong disease symptoms when exposed to an isolate

of Rhizina undulata from British Columbia (Egger and Paden

1986). While the pathogenicity of this fungus was consistent

and intense, field occurrences either go unrecognized or occur

infrequently.

Disease Symptoms and Signs—Seedling symptoms are

nonspecific and may be easily misidentified as other root

diseases or drought. The presence of Rhizina fruiting bodies in

the vicinity of a dead conifer seedling is reliable evidence of the

pathogen’s presence on the site. Fruiting bodies of this fungus

are brown to black, crustlike and fleshy, slightly convex, and

often have an undulating margin. The undersides of the fruiting

bodies have root-like rhizoids at multiple locations, which

attach them to the soil, host roots, and occasionally to other

substrates in the soil. They can occur in groups or lines that

follow buried substrates or parasitized roots (Ginns 1974).

Stringy Butt Rot

Perenniporia subacida(Peck) Donk. produces a white stringy

butt rot in infected trees and may also be known as yellow root

rot because of its distinctively colored mycelium (Hadfield and

others 1986). It is most commonly associated with mature trees

that are either suppressed or weakened (Hadfield and others

1986). True firs, western hemlock, western redcedar, Engelmann spruce, and white spruce are among the most susceptible

of its many coniferous and deciduous hosts. Perenniporia
24 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005

subacida has been classified as a wound parasite, although it is

unclear whether infection by spores or mycelium is primarily

responsible for disease initiation (Zeglen 1997). Trees infected

by P. subacida are subject to windthrow and mortality. Significant volume loss from stringy butt rot is not an important issue

in the Inland West (Hadfield and others 1986).

Disease Symptoms and Signs—Initially, the decay appears

as a light-brown heartwood stain. Distinctive yellow mycelial

mats may be observed when sheets separate along the annual

rings; these mycelial mats help identify the fungus as P.

subacida. Progression of the decay leads to small white pits in

the sheets of annual wood, but eventually only white spongy

fibers with black flecks remain. Leathery, perennial fruiting

bodies that are cream to yellow in color may occupy the

underside of downed wood or the basal region of standing dead

trees. Small, circular pores mark their surface (Gilbertson and

Ryvarden 1987).

Disease Management and Fuels Treatment

Considerations

Tomentosus Root Disease—The ability of I. tomentosusto

colonize organic debris and remain on site for decades is an

important characteristic of this root disease. The survival and

spread of I. tomentosusin an infected stand may be exacerbated

by stumps and dead roots created by thinning practices. These

reservoirs of inoculum may never contact susceptible trees if

susceptible spruce and pine species are not planted. By delaying the regrowth of susceptible species for 20 years after tree

removal, roots and stumps may decay to a water-soaked

condition that reduces the likelihood of new infections. At least

one study indicates that I. tomentosus cannot be recovered

from such material (Tkacz and Baker 1991). In some situations, stump removal may be a viable option. Thinning methods that minimize wounding of residual trees would also limit

the establishment of new infections. Prescribed burning to

reduce woody substrate would not likely kill all of the fungus

that resides within root heartwood.

Standing or windthrown trees dead from or having

Tomentosus root disease contribute to fuel loading and may

provide substrate for spruce beetles. One study reported that

diseased trees were not predisposed to attack and may have

helped to maintain spruce beetle populations at low levels

(Lewis and Lindgren 2002). Infected trees can live 15 to 20

years before mortality occurs. The gradual decay of the roots

makes infected trees subject to windthrow and a hazard concern for recreation areas.

Rhizina Root Rot—Even without seedlings to infect and

parasitize, Rhizina undulata has the ability to use woody debris

as a nutrient source. The fungus Rhizina may actually aid the

decomposition of some smaller organic debris (Callan 1993).

Described as only weakly saprotrophic, it is not known how

long the fungus can remain on site without a living host.

In the past 15 years, no new research has been published on

Rhizina root rot in the Inland West, so little is known about the

interaction of fuels treatments, fire, and Rhizina root rot. If

susceptible conifer seedlings were to be planted, it would be

important to reduce spore germination by minimizing the areas

of soil subject to warming. One possible strategy would be the

use of “pile and burn” practices for removing hazardous fuels.

More studies are needed to determine the scope of this disease

in the Inland West and appropriate fuels treatments on sites

with this disease.

Stringy Butt Rot—With so many hosts susceptible to

infection by P. subacida, the best methods to manage stands

infected with stringy butt rot are to prevent the creation of

wounds that facilitate new infections on healthy trees and to

remove diseased trees during thinning. The effects of fuels

treatments and fire on stringy butt rot have not been well

studied. Not enough is known about the distribution of this

disease and the extent of its impact on the Inland West.

Additional research studies are needed to determine impacts of

fuels treatments on this disease.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005 25

Summary of Fuels Management

Considerations _________________

Before prescribing fuels treatments, managers should

know whether root diseases are present and where they are

located on a site. For conifer forests of the Inland West, root

diseases caused by A. ostoyae, H. annosum, Phellinus weirii,

L.wageneri, and Phaeolus schweinitzii are of special concern

because of the extreme damage and mortality they can cause.

The interactions between trees, root pathogens, and environment are complex and vary by forest structure, stand history,

habitat type, species composition, soil characteristics, bark

beetle populations, and activity of other forest insects and

pathogens. It is not uncommon to have more than one root

disease present in a stand.

Fuels treatment options should consider past management

practices and their effects on current stand conditions. Seral

species tend to be tolerant of root diseases but have declined in

many areas of the Inland West. In northern Idaho, the combined effects of blister rust, selective harvesting, planting

practices, and fire exclusion have reduced stand representation

of white pine, western larch, and ponderosa pine but increased

those of root disease-susceptible Douglas-fir and true firs

(Beckman and others 1998; Filip 2002). On sites with mixed

species composition—where seral and climax species cooccur with root disease organisms—infection and mortality of

susceptible species have the potential to prolong the seral

phase. This can favor the seral species that are tolerant to root

disease unless late seral or climax species have been favored by

management (Meyer 2004).

Use of a single type of treatment will not be appropriate for

all forest conditions and root diseases. Some fuels treatments

may increase root disease incidence, so managers should

decide at the outset of planning what levels of mortality and

growth loss will be acceptable. Estimates of treatment effects

on mortality will be important for making subsequent estimates of changes in surface and ladder fuels. Tree mortality

may be attributed directly to the root disease or to indirect

consequences of infection, such as susceptibility to bark beetle

attack. Killed trees can persist as standing snags or as

windthrows, and may increase the overall amount of woody

debris. Thus, fuels reduction treatments that cause increases in

root disease mortality will likely increase the accumulation of

fuels.

Acceptable options for fuels treatments differed among the

diseases included in this paper. Thinning may increase damage

from some root diseases, such as Armillaria root rot, laminated

root rot, and annosus root disease. Incidence of black stain root

disease and Schweinitzii root and butt rot may be less affected

by this management practice if specific guidelines are followed. For all root diseases, care should be taken to avoid

wounding of trees during timber harvesting or prescribed fire

to reduce future impacts on stand health. Thinning treatments

should also favor the species most tolerant to root disease and

be timed to avoid problems with bark beetles. For example,

regarding annosus root disease, biological and chemical control applied at the time of thinning could be effective for

preventing new infections. Little information is available on

the effects of prescribed fire and when it should be applied

(seasonally) to decrease the effect of most root diseases.

Despite the importance of these issues, research regarding

interactions of fuels treatments with root diseases has been

limited. For this reason, much of the information presented

here has been based on general principles of forest pathology.

More precise information for specific sites, diseases, and host

trees would be desirable to optimize fuels treatments with

stand conditions and locations. To determine the most suitable

forest management practices for the Inland West, more studies

are needed on the interactions among fuels treatments, fire, and

root diseases.
26 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-141. 2005

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