Fig. 7. White streaks and black flecks throughout wet

spongy advanced decay most often found on

H. annosum-infected grand fir, Douglas-fir or hemlock.

Fig. 8. Spiniger meineckellus conidiophores characteris-
tic of the asexual form of H. annosum. These are pro-
duced on incubated infected material and provide posi-
tive diagnosis and identification of infection. 50X mag-
nification.

lateral branch growth. In recent root exca-
vations of annosus-infected live ponderosa
pine in the southern Blue Mountains, at
least 90 percent of the root systems were
killed by the pathogen before crown symp-
toms were noticeable. Crown symptoms
are also produced by other root diseases,
such as black stain root disease, caused by
Leptographium wageneri var. ponderosum
(Harrington & Cobb).

Because conks are not always found,
decay is highly variable, and crown symp-
toms may be caused by other agents, posi-
tive identification of H. annosum infection
by finding definite signs and symptoms is
not always assured. Frequently, other
more readily identifiable fungal pathogens
are found and mistakenly identified as
being the sole or primary cause of tree
decline or mortality. Because of this, mask-
ing of annosus symptoms by those of other

pathogens is common. Additional
techniques for positive diagnosis of
H. annosum are frequently needed.
When H. annosum infected wood is
incubated at high humidity in a
plastic bag, wrapped in wet paper,
or cultured on nutrient media, the
fungus produces characteristic
asexual fruiting structures (conidia
and conidiophore) of its Imperfect
state, Spiniger meineckellus
(Olson) Stalpers (~Oedocephalum
lineatum Bakshi) (fig. 8). These
are diagnostic and confirm the
identity of the fungus.

Life Cycle

Heterobasidion annosum is a
wood decay fungus. The micro-
scopic fungal threads (hyphae) that
comprise the vegetative state of the
pathogen grow through woody tis-
sues by secreting enzymes that
break down the cellulose and lignin
of the wood cells to simple carbo-
hydrates that the fungus uses for
food. While decay is often in
“dead” heartwood, in some species
(notably pines), living cells of the cambi-
um and phloem are attacked and killed.

In true firs, the inner sapwood is com-
monly attacked and the fungus may grad-
ually invade and kill the outer sapwood.
Trees so attacked can be girdled and
killed or rendered susceptible to bark bee-
tles or to toppling because of extensive
root decay.

Two kinds of spread are impor-
tant in the life cycle of H. annosum: local,
underground tree-to-tree spread within a
center and long distance, aerial spread that
establishes new centers. Most local
spread involves hyphal growth within and
along the surface of roots. When there is
contact between an infected root and a
healthy root, H. annosum hyphae can
grow across the contact to the healthy root
and begin growing on the surface and
through the phloem and xylem. By this
means, the fungus spreads from tree to


Pesticides used improperly can be injurious to
humans, animals, and plants. Follow direc-
tions and read all precautions on the labels.
Consult your local forest pathologist, county
agricultural agent, or State extension agent
about restrictions and registered uses of partic-
ular pesticides.

The United States Department of Agriculture (USDA) prohibits discrimination in

its programs and activities on the basis of race, color, national origin, gender, reli-

gion, age, disability, political beliefs, sexual orientation, and marital or family sta-

tus. (Not all prohibited bases apply to all programs.) Persons with disabilities who

require alternative means of communication of program information (Braille, large

print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600
(voice and TDD).

To file a complaint of discrimination, write USDA, Director, Office of Civil
Rights, Room 326-W, Whitten Building, 14th and Independence Avenue, SW,
Washington, DC 20250-9410 or call (202) 720- 5964 (voice or TDD). USDA is an
equal opportunity provider and employer.

R6-NR-FID-PR-002-00


stands on poor, dry sites suffer the greatest
impacts (fig. 11). There is some indica-
tion from root excavations and stump
investigations that infection rates are actu-
ally rather high throughout the pine type

Fig. 9. A small annosus root disease center with
several toppled grand fir.

Fig. 10. A recently toppled #1. annosum infected grand
ively rotied roots showing the characteris-

fir with extensivel
tic laminated decay.

Fig. 11. An annosus root disease center in
young ponderosa pine.

but mortality is manifested mainly on the
poorer sites. There are indications that H.
annosum readily infects pines on better

sites but causes mainly growth loss rather

than mortality in such situations. In some
cases, planted pine have had high rates of
infection. High levels of damage have
occurred where off-site planting stock had
been used. Loss of site productivity, loss
of vegetation cover, and the risk
of tree failure in campgrounds and
other recreation facilities are
effects of annosus root disease in
pine.

Western and Mountain Hemlock

Infected hemlocks are seldom
killed outright by annosus root
disease unless they are broken or
windthrown. Most damage to
hemlocks occurs as decay in roots
and the lower butt, though rot also
may be substantial in the stems of
older trees. Decay is usually asso-
ciated with wounds. Decay is
almost always confined to the
cylinder of woody tissue present
when the tree was wounded, a
condition known as compartmen-
talization.

Incidence of decay is higher in
older trees and stands more than
120 years old. Younger hemlocks
seldom have appreciable decay
even if there is a high incidence of
wounds associated with a history
of partial cutting. While some
infection occurs from stump colo-
nization, minor amounts of decay
result when rotations are short.
Direction to maintain stands over
longer rotations and to use more
frequent entries will increase the
incidence of annosus root disease
and associated decay in hemlock
stands.

Disturbances associated with
high use areas such as campgrounds and
other recreation areas in hemlock types
will predispose trees to large amounts of
H. annosum infection. Hazard tree poten-
tial will likely be a major concern, espe-
cially in older trees.


tree, creating an enlarging disease center
in the stand.

Rates of center enlargement depend on
stand and site conditions and generally are
estimated to be between 1.6 and 5 feet
(0.5-1.5 m) per year. Some centers even-
tually cease enlarging, but others continue
to spread for years. All the factors affect-
ing rate of spread are not fully understood.
Numerous field observations indicate that
the disease in seedling and sapling size
pine trees around large stumps will spread
to the limit of the rooting zone for the
stump and then stop. In similar stands of
poles or larger size trees, the root disease
will continue to spread, moving beyond
the rooting zone of the original stump that
served as the source of the infection.

Long distance spread occurs when air-
borne sporidia produced from H. annosum
conks disperse and infect freshly-exposed
stump surfaces or woody tissues at
wounds. Wounds can be colonized and
result in decay anywhere on the roots,
butt, or upper bole. While infections
resulting from wound colonization usually
result in decay of the scarred tree, they
rarely cause root disease since the decay is
usually compartmentalized within the bole
and the infection does not extend to the
exterior of roots where it can spread
between trees.

Sporidia on tree wounds or freshly cut
stump surfaces germinate, produce hyphae
that colonize exposed wood, and initiate
new infections. Spores also can percolate
down through soil and infect wounded
roots. The fungus has been isolated from
insects that feed on lower stems and roots,
but insect transmission of the pathogen has
not been verified. Another spore type, the
asexual conidia, is also produced, but its
role in the life cycle is uncertain.

Sporulation, spore germination, and
colonization of wounds or stumps are
affected by temperature and humidity.
Spores are produced throughout the year,
except in extreme cold, very high heat, or

during prolonged drought. Stump colo-
nization is unlikely when stump tempera-
tures are high and relative humidity is
low. Stumps are susceptible to infection
for 2 to 4 weeks following cutting.
Colonized stumps less then 6 inches in
diameter may heat sufficiently during hot
summer days to kill H. annosum myceli-
um in the wood.

Once established in roots, the fungus
may persist for several decades in resinous
tree species. In non-resinous species such
as firs and hemlocks, persistence may not
be as long, but good data are wanting. As
long as viable hyphae remain in old roots
they can infect roots of susceptible trees
that become established in old centers,
thus regenerated trees may be damaged or
die prematurely.

Damage
rue firs

True firs infected by H. annosum suffer
direct mortality, butt rot (and associated
reduction in merchantable volume), pre-
disposition to bark beetles, and wind-
throw. Impacts are observed in both
enlarging centers (fig. 9) and as isolated
single diseased trees (fig. 10). Losses are
greatest in stands of pure fir or where fir
basal area exceeds 26 square ft./acre (20
square m/ hectare), where total stand basal
area exceeds 100 square ft./acre (75
square m/hectare), where stand age
exceeds 120 years, and in stands that have
been partially cut. Surveys in the
Rockies, the Northwest, and the
Southwest indicate that H. annosum is
widespread and prevalent in true firs.
Except during droughts, activity of fir
engraver beetles (Scolytus ventralis
LeConte) is closely associated with occur-
rence of root disease in firs.

Pines
Annosus root disease has been serious

on pines in some localities and under cer-
tain site and stand conditions. Generally,


Stump size recommendations have var-
ied in the past, especially between differ-
ent USDA Forest Service Regions and
states. However, differences in stump
sizes for effective treatments are not
believed to be substantial between similar
stand types in different areas.

Borate stump treatment is not effective
on stumps of trees that are already infect-
ed. In stands with numerous already-
infected stumps, silvicultural treatments
should be employed to deal with the dis-
ease. Where possible, stands should be
managed by conversion to full stocking of
site-adapted, less susceptible species.

Stump treatment should be standard
procedure when cutting conifers in recre-
ation and other high-use areas. In
California, treatment of all conifer stumps
in recreation areas is required. It is strong-
ly recommended that stumps of highly
susceptible species be treated in Oregon
and Washington. Treatment is also recom-
mended for pine and true fir seed orchards,
progeny test plantations, and other stands
of high value trees.

Assistance

If you need assistance in recognizing
and controlling annosus root disease, con-
tact your local State Forester or your local
USDA Forest Service Forest Health
Protection office.

References

Bega, R.V.; Smith, R.S., Jr. 1966.
Distribution of Fomes annosus in the nat-
ural forests of California. Plant Disease
Reporter 50: 832-836.

Driver, C.H.; Wood, R.E. 1968.
Occurrence of Fomes annosus in inten-
sively managed young-growth western
hemlock stands. Plant Disease Reporter
52: 370-372.

Goheen, D.J.; Filip, G.M.; Schmitt
C.L.; Gregg, T.F. 1980. Losses from
decay in 40- 120 year old Oregon and
Washington western hemlock stands.
Portland, OR: USDA Forest Service,
Forest Pest Management; Pacific
Northwest Region. 19 p.

Otrosina, W.J., and R.F. Scharpf (tech-
nical coordinators). 1989. Proceedings of
the Symposium on Research and
Management of Annosus Root Disease
(Heterobasidion annosum) in Western
North America. April 18-21, 1989;
Monterey, CA: USDA Forest Service,
General Technical Report PSW-116. 117 p.

Russel, K.W.; Thompson, J.H.; Stewart,
J.L.; Driver, CH. 1973. Evaluation of
chemicals to control infection of stumps
by Fomes annosus in precommercially
thinned western hemlock stands. Wash.
Dept. of Nat. Res. Rpt. No. 33, 17 p.

Schmitt, C.L.; Goheen, D.J.; Goheen,
E.M.; Frankel, S.J. 1984. Effects of man-
agement activity and dominant species
type on pest-caused mortality losses in
true fir on the Fremont and Ochoco
National Forests. Portland, OR: USDA
Forest Service, Forest Pest Management,
Pacific Northwest Region, 34 p.



Forest Insect
& Disease
Leaflet 172

Revised February 2000

U.S. Department of Agriculture ° Forest Service

Annosus Root Disease of Western Conifers
Craig L. Schmitt!, John R. Parmeter”, and John T. Kliejunas*

Annosus root disease, caused by While annosus root disease is a normal
Heterobasidion annosum (Fr.) Bref. part of most forest ecosystems in the West
(=Fomes annosus (Fr.) Karst.), occurs in contributing to structural and composition-

temperate zones throughout the Northern al diversity, incidence and impacts have
Hemisphere, and is common on conifers in _ increased in recent decades due to man-
the western United States. Infected trees agement practices that favor the disease

suffer root and butt decay, and root mor- and changes in stand compositions that
tality, resulting in reduced vigor, wind- have increased numbers of susceptible
throw, predisposition to bark beetles and hosts. In many situations, the disease has
outright mortality. attained epidemic proportions. Various

'Service Center Pathologist, U.S. Department of Agriculture, Forest Service, Wallowa-
Whitman National Forest, Forestry Range and Sciences Laboratory, La Grande, OR

2Professor of Plant Pathology, retired. College of Natural Resources, University of
California, Berkeley, Calif.

3Pathology Group leader, U.S. Department of Agriculture, Forest Service, Pacific
Southwest Region, San Francisco, Calif.


Prevention/Control-Silvicultural
True fir

True firs seem to be especially suscepti-
ble to annosus root disease as well as sev-
eral other common root diseases and stem
decays. In mixed-conifer stands with a
substantial true fir component, partial cut-
ting should be avoided or minimized.
When intermediate entries are done and fir
will continue to be managed on the site,
care needs to be taken to minimize both
wounding of residuals and site distur-
bance.

Reducing rotation length to less than
120 years will usually limit losses where
other root diseases and stem decays are
not a concern. Restricting cutting to sum-
mer months may reduce potential of stump
and wound colonization by H. annosum in
some warm, dry localities. It has been
suggested that thinning overstocked true
fir stands having annosus root disease will
reduce disease impacts by increasing vigor
of residuals. The success of this strategy
has not been well supported by research.

Mixed Conifer

In many mixed-conifer stands that have
been partially cut, annosus root disease
may have already developed to levels con-
sidered excessive. Because of past cutting
practices and the absence of fire, many
stands previously dominated by pine have
become dominated by less fire resistant
species, especially true firs. Where such a
trend has occurred and root disease affects
are impacting management goals, it is rec-
ommended to reverse the pine-to-fir trend.
Regeneration-type cultural systems and
use of prescribed fire can both be effective
in discriminating against the shade-tolerant
true firs and restoring the stand to a state
more similar to its historic condition.

‘estern hemlock

Western hemlock stands will not devel-
op significant levels of decay unless man-
aged to ages beyond 120 years. Impacts

can be further minimized by requiring log-
ging techniques that minimize damage to
residuals during intermediate entries.
Injured trees should be removed during
entries since they are most susceptible to
decay. Thinning of overstocked stands
should not be avoided since increases in
growth and yield of residuals resulting
from stocking control are usually many
times greater than the increased amount of
decay. Managers should strive for a mix-
ture of other species such as Douglas-fir
and western redcedar in stands where
hemlocks are affected by annosus root dis-
ease.

Prevention/Control-Chemical

Stump infection by H. annosum can be
largely prevented by treating freshly cut
stump surfaces with a light coating of
granular Sodium Tetraborate Decahydrate
or Disodium Octaborate Tetrahydrate.
Currently, the only borate products regis-
tered for annosus control are Sporax® and
Tim-Bor®. Properly treated stumps are
protected at an efficacy level of at least 90
percent from colonization by airborne
spores of H. annosum. Currently, the
Pacific Northwest and Southwest Regions
of the USDA Forest Service have provi-
sions that can be specified in timber sale
contracts requiring purchasers to treat
stumps.

Stump treatment with borate is current-
ly recommended only for those timber
production sites with known annosus root
disease potential where cultural control is
not viable. Such situations include treat-
ment on dry pine sites, mixed conifer sites
where true firs will be managed in the
future, and all true fir sites. The recom-
mended minimum stump treatment size is
12 inches diameter for pine and true fir
felled using chainsaws. Where mechani-
cal shearers are used, the minimum diame-
ter should be reduced to 8 inches. High
elevation true fir stumps should be treated
down to 8 inches regardless of type of
felling.


Fig. 3. Mature H, annosum conk in the interior of a pon-

derosa pine stump

Toot,

Fig. 5. Characteristic red stain in the interior of a live

H. annosum-infected grand fir root.

Fig. 6. Typical laminated advanced decay caused by
H. annosum.

Fig, 4, Ectotrophic mycelia on the exterior of an infected

A light, tawny-brown colored
fungal growth may be found on
the exteriors of infected roots of
pines, true firs, and Douglas-fir
(fig. 4). This serves as the pri-
mary mechanism for root to root
spread, growing along the sur-
face of roots and moving onto
the roots of adjacent trees across
contacts and grafts. Some other
toot disease fungi form similar
mycelia, and its occurrence
alone cannot be used to diagnose
the disease.

Wood decay and stain caused
by H. annosum are variable. In
true firs and hemlocks, wood of
infected roots and lower boles
usually develops a red-brown to
purple stain in the heartwood
with an irregular margin (fig. 5).
Stain is less common in pines.
Decay in pines and true firs is
initially laminated, meaning the
deteriorating wood comes apart
at the annual rings (fig. 6).
Small, elongated pits, roughly
one-twenty-fourth by one-six-
teenth of an inch (1 mm by 2
mm) may be found, but only on
one side of delaminated sheets.
Commonly in hemlock, true firs,
and Douglas-fir and less com-
monly in pine, advanced decay
will be wet, spongy, and stringy
with large white streaks and
scattered small black flecks (fig.
7). This decay is often found in
the interior of roots.

Crown symptoms are seen in
some live infected trees, most
often pines, Douglas-fir, and
juniper, and less frequently in
other hosts. Infected trees with a
substantial proportion of the root
system infected may have fading
thinning crowns, chlorotic
foliage, and reduced height and


Upon encountering such centers, look for
evidence of gradual, periodic tree death at
the perimeter of the center. Symptomatic
trees may have thin, chlorotic foliage and
reduced height and lateral branch growth.
This indicates that infected roots are
dying, which will eventually lead to death
of the tree. Frequently, infected trees will
be attacked and killed quickly by bark
beetles that infest weakened trees.
In centers, old infected stumps,
stubs, or scarred trees may be
found.

In hemlock stands, annosus
root disease often does not pro-
duce readily identifiable evidence
of infestation. Mortality is infre-
quent to rare in standing trees, but
trees with extensive root and butt
rot may be broken or windthrown.
Usually, the presence of H. anno-
sum is discovered when the stand
is thinned or harvested and decay
and stain at stump height is
observed. In some true fir stands,
similar conditions may be
observed, although mortality is
more frequent, often resulting
from bark beetle attacks.

s_ an

Heterobasidion annosum read-
ily produces fruiting bodies, or
conks, on infected host tissues.
Determining occurrence of H.
annosum conks is a highly reli-
able method of diagnosing anno-

tered on the surface of dead infected roots
(fig. 2). More mature conks, two to three
inches (5.0 to 7.6 cm) across, may be
found in crevices of the root collars of
infected hemlocks, or in or just under the
soil duff layer on the root collars of pines.

Large conks often grow in the interiors
of hollow or extensively decayed hemlock,

Fig. 1. Small button conks of Heterobasidion annosum on
the root collar of a ponderosa pine. Note: these were
formed below the duff layer, which was removed for this
photograph.

Fig. 2. Characteristic buff-colored pustules that form on

sus root disease. Dead and dying the exterior of H. annosum-infected roots.

trees will frequently have fruiting

bodies on their roots and/or root collars.
On pines, small leathery buff-colored
conks, one-eighth to one-fourth inch (0.3
to 0.6 cm) in diameter, and sometimes
larger, are produced on the outer bark at
the root collar, under the bark of dead.
trees, and in the duff layer (fig. 1).

Similar conks are found, but less frequent-
ly, on true firs. On most species of
conifers, early stages of fruiting bodies
appear as small buff-colored pustules scat-

true fir, and ponderosa pine stumps and
roots (fig. 3) or under the bark of decaying
pine stumps. Fully mature fruiting bodies
may be 10 inches (25 cm) across or larger.
HH. annosum conks have a buff to dark
brown-colored upper surface with concen-
tric furrows and a smooth, cream-colored
under surface that has tiny pores and a
narrow sterile (non-pored) margin. Conks
are perennial and may have more than one
tube layer.


resource values are compromised by these
high levels of annosus root disease,
prompting use of management strategies
to restore a more natural level of disease
activity.

Distribution and Hosts

Annosus root disease is found on all
western conifer species but is of most con-
cern on true firs, hemlocks, and pines.
Incense cedar, coast redwood and sequoia
are sometimes infected in California.
Western juniper is infected throughout its
range. Annosus is common and causes
extensive decay in old-growth western and
mountain hemlock stands. Many mixed
conifer stands throughout the inland west
and California have high levels of infec-
tion, resulting in extensive mortality, espe-
cially of true firs.

Pine communities also have high levels
of disease and exhibit varying levels of
impact. Douglas-fir-dominated stands in
northern and central Idaho and to a lesser
extent, northeastern Washington have sub-
stantial amounts of annosus-caused mor-
tality, especially on dry sites where
Douglas-fir grows with ponderosa pine,
but Douglas-fir in California, Oregon and
most of Washington are not seriously
affected. Hardwoods are generally resis-
tant or immune, although madrone and a
few shrub species are occasional hosts.

Incidence and severity of annosus root
disease varies by locality, stand type, and
management history. Generally, stands
having a history of logging-related distur-
bance are most severely affected. Stands
that were partially-cut, especially those
with multiple removals, will have the
highest level of annosus root disease.

Partially cut grand fir- and white fir-
dominated mixed conifer stands in south-
em and central Oregon and northern
California have especially high incidences
of annosus root disease. Incidence is also
particularly high on Jeffrey pine in south-
ern California recreation sites and on

Jeffrey and ponderosa pine in dry Eastside
pine types. In Oregon, annosus root dis-
ease has mostly been associated with
occurrence of large stumps — usually 18”
and larger in diameter. Subalpine fir
stands show evidence of root disease asso-
ciated with stumps much smaller — as
small as 6 to 8” diameter.

In the western United States there are
two different intersterility groups, or bio-
logical species of H. annosum. These two
biological species have distinct host pref-
erences. The P-group infects pines,
incense-cedar, western juniper, pinyon,
and manzanita; the S-group infects true
firs, giant sequoia, Douglas-fir and hem-
locks. The fungus very rarely spreads
between host species of these two groups,
either between trees or stumps and trees.
However, saprophytic stump colonization
can involve either strain. Thus, P-group
H. annosum may colonize grand fir
stumps but root disease will not develop in
pines or firs surrounding these stumps.

Evidence of Annosus Root
Disease

In The Stand

The typical pattern of annosus root dis-
ease in stands involves scattered small
groups of dead trees centered around large
old stumps. There are often old dead
snags and downed trees with rotten roots
near the center of pockets, adjacent to the
old stumps. At the perimeter of centers,
more recent mortality may be found, along
with symptomatic trees. Mortality usually
does not start to occur around stumps until
15 or more years after they are created.

In stands of susceptible species, anno-
sus root disease usually occurs in discrete
centers. The presence of H. annosum in
these centers may be verified by observing
several common characteristics. In stands
of resinous species such as pine, dead and
or dying trees or understocked areas are
identified readily and may be suspect.