1

The black stain fungus—Leptographium wageneri (Kendrick)

Wingfield*—infects and kills several

species of western conifers. The fungus colonizes water-conducting tissues of the host's roots, root collars,

and lower stems, ultimately blocking

the movement of water to foliage.

Severely infected trees exhibit wilting

symptoms characteristic of vascular

wilt diseases. Black stain kills young

trees within a year or two of infection.

Older infected trees decline more

slowly (over 2 to 8 years) and are often

predisposed to bark beetle infestation.

Distribution

Black stain root disease is thought to

be native to western coniferous

forests. Although the disease was first

discovered in 1938, further spread

went virtually undetected until the

1970s. Tree mortality associated with

Black Stain Root Disease of Conifers

Paul F. Hessburg, Donald J. Goheen, and Robert V. Bega

the disease was often mistakenly attributed to other, more easily identified root diseases or to bark beetles,

which are commonly associated with

the rapid decline and death of black

stain-infected trees.

Black stain occurs in many locations

throughout the western United States.

At present, the greatest development of

the disease occurs in southeastern and

northwestern California, southwestern

and east-central Oregon, the central

Sierra Nevada, and southern Colorado.

In recent years, reports of black stain in

young, intensively managed stands

have increased dramatically, especially in Oregon and California. The

disease affects trees in high-use recreation areas and areas important for

wildlife management as well as those

on lands dedicated to timber production.

—————————————

Paul Hessberg is research plant pathologist at the USDA Forest Service's Pacific Northwest Research Station, Forestry Sciences Laboratory, Wenatchee, Washington; Donald Goheen is plant pathologist/entomologist at the USDA Forest Service's Southwest Oregon Forest Insect and Disease Technical Center, Rogue

River National Forest, Medford, Oregon; and Robert Bega retired as a research plant pathologist from the

USDA Forest Service's Pacific Southwest Forest and Range Experiment Station, Berkeley, California.

*Other names have been given to the fungus that causes black stain root disease: Ophiostonia wagneri

(Goheen and Cobb) Harrington is the name of the sexual stage; Ceratocystis wageneri, and Verticicladiella

wageneri are no longer considered taxonomically correct.
2

Hosts

The principal hosts of L. wageneri are Douglas-fir, ponderosa

pine, Jeffrey pine, pinyon, and singleleaf pinyon. Seldom-damaged

hosts in the United States include

lodgepole pine, western hemlock,

mountain hemlock, sugar pine, western white pine, and knob-cone pine.

Tree species highly resistant or immune to infection are "cedars" (Alaska

yellow-cedar, Port-Orford-cedar,

western redcedar, and incense-cedar),

spruce, larch, junipers, and true firs.

Recent research indicates that there

are three distinct variants of L. wageneri, each with specific host preferences. One (var. wageneri) attacks

pinyon, another (var. pseudotsugae)

attacks Douglas-fir, and the third (var.

ponderosum) attacks hard pines and

occasionally hemlocks. Although limited cross-over has been shown experimentally with the Douglas-fir and hard

pine variants, natural occurrences have

not been detected. For purposes of

resource management, each of the

variants can be considered host specific.

Black stain root disease occurs over a

wide range of environmental conditions, from the hot and semi-arid

Southwest to cool Pacific coastal areas. Soil type does not appear to be a

major factor in the distribution of the

disease. Soil moisture and temperature, however, may influence disease

distribution significantly. Cool, moist

soil conditions in spring and early

summer are ideal for infection,

Figure 1 — Crown symptoms of black stain

root on young Douglas-fir.

Figure 2 — Faded, sparse crown of ponderosa pine with black stain root disease.
3

growth, and tree-to-tree spread of the

pathogen.

Symptoms and Damage

Trees infected by the black stain fungus

usually exhibit symptoms of gradual decline before they die (figures 1 and 2). In

early stages of decline, terminal growth is

reduced and older needles become

chlorotic. As the disease progresses, older

needles are shed prematurely, new needles

are somewhat stunted and yellow, and reduced internodal growth is evident on lateral branches. In advanced stages,

new growth is compact and chlorotic, with

a tufted appearance, and tree crowns exhibit

very sparse foliage. They also bear

"distress" cone crops. Very small trees, or

those affected by other significant stress factors, may succumb quickly without exhibit- Figure 3 — Typical dark sapwood stain associated with black stain root disease.

Figure 4 — Cross section through affected root showing arc-shaped pattern of black stain.
4

hibiting gradual decline symptoms; foliage may change rapidly from green

to yellow or reddish brown.

Crown symptoms of trees affected by

black stain root disease are very similar usually a lighter color and typically

are wedge-shaped in cross-section or

they discolor the entire sapwood radius.

Black stain root disease affects groups

of trees in distinct infection centers

(figures 5-7). Typical infection centers

have trees in various stages of decline

near the perimeter and dead trees in

the interior nearer the origin of initial

infection. Infection centers usually occur in well-stocked stands where a

preferred host predominates or occurs

in unmixed clumps. In stands where

species composition is well mixed,

Figure 5 — Black stain root disease center in

a second-growth ponderosa pine plantation.

Figure 6 — Typical black stain root disease center in a Douglas-fir plantation.
5

Figure 7 — Black stain root disease center in singleleaf pinyon.

Figure 8 — Insect vectors of the black stain root disease fungus on Douglas-fir: Hylastes nigrinus, Steremnius carinatus, and Pissodes fasciatus.
6

infection and mortality are less common, but isolated trees or tree clusters

can be infected.

Disease Cycle

Long-distance spread of the black

stain fungus involves insect vectors

(figure 8). The root-feeding barkbeetles Hylastes macer LeConte and H.

nigrinus (Mannerheim) are believed to

be the primary vectors of the fungus

on ponderosa pine and Douglas-fir,

respectively. Two weevils—Steremnius carinatus (Boheman) and Pissodes fasciatus LeConte—have also

been implicated as vectors in Douglasfir, but their involvement in local and

long-distance spread of the pathogen

is still poorly understood.

Vector insects commonly breed in

roots of recently dead or dying host

trees including those infected by L.

wageneri. Several vector species—H.

nigrinus, P. fasciatus, and S. carinatus—also breed in Douglas-fir stumps,

which are susceptible to infection by

L. wageneri for up to 7 months after

stems have been severed.

Leptographium wageneri sporulates

readily inside insect galleries in infected roots and root collars. Stalked,

microscopic fruiting bodies

(conidiophores) form on gallery

walls, each bearing a sticky spore

droplet that protrudes into the gallery.

These sticky spore droplets are well

suited to insect dispersal (figure 9).

During emergence, some young adult

beetles are contaminated with spores

as they brush against spore droplets in

galleries or pupal chambers. ContamiFigure 9 — Enlargement (25x) of fruiting bodies of the black stain root disease fungus in an

insect gallery, showing sticky spore masses.
7

-nated beetles fly (or walk) from brood

trees, burrow through the duff and soil,

visit roots of healthy, recently dead, or

dying trees, and deposit spores on root

sapwood exposed during feeding.

Wounds that expose sapwood xylem

are required for infection, because L.

wageneri hyphae are unable to penetrate live bark and cambial tissues.

Once established, the black stain fungus colonizes root and stem sapwood

xylem, reducing water uptake and the

vertical ascent of xylem sap by clogging water conducting vessels with hyphae and host reaction compounds. In

live trees, the fungus is confined to

tracheids; parenchymatous tissues are

not invaded. Infected trees die (usually

in summer, when soil moisture is depleted) because of inability to take up

water.

Black stain infection centers are most

prevalent in areas where substantial

tree damage or site disturbance has

occurred, especially along roads and

skid trails, in areas having a history of

tractor logging and resultant soil compaction, and in areas that have been

precommercially thinned. The appearance of infection centers in areas of

disturbance reflects vector insect preference for stressed trees.

Once a new infection center is

established, spread of the infection

from tree to tree occurs through

root grafts between healthy and

diseased trees and through intimately associated roots via limited

growth (< 15 cm, or about 6 in) of

the pathogen through soil. Small

rootlets (< 5 mm., or .2 in diameter) serve as infection courts where

roots are not grafted. Infection

centers in ponderosa pines and

pinyons enlarge on the margin at

an average annual rate of 1.0 m/yr

(3.2 ft/yr). Infection centers in

Douglas-fir enlarge at a rate of 0.8

to 1.5 m/yr (31.5 to 59.1 in/yr), but

enlargement of infection centers

with this host often decreases

markedly when stands reach 30 to

35 years of age. The rate of enlargement of black stain infection

centers is 3 to 5 times faster than

that of other common root diseases.

Leptographium wageneri is relatively nonpersistent in infected

root systems, remaining active

usually no more than 1 year after

its host dies.

Management and Cultural

Controls

In recent years, black stain root disease

has been detected in many new areas,

often causing locally severe damage.

Incidence appears to be steadily increasing. At the present time, there is

no effective cure for already diseased

trees, and genetically resistant host

genotypes have not been identified.

Current management strategies for

control of black stain root disease are

either preventive or corrective.
8

Preventive Management

Black stain root disease is favored by

several traditional management and

road maintenance activities that are

used throughout the range of its hosts.

By modifying or eliminating some of

these influences and by minimizing

site disturbances, tree injuries, and the

opportunity for successful insect vectoring, further spread of the pathogen

can be reduced.

Minimizing site disturbance:

Management treatments for diseaseprone areas should be those that cause

the least site disturbance, particularly

avoiding soil compaction and disruption of the soil profile. Where timber

is being harvested, high-lead and skyline yarding are preferable to tractor

logging and should be selected when

an option exists. When tractorlogging, the area covered by skid trails

should be minimized, and yarding

should be restricted to the dry season

(mid to late summer), when the risk of

serious soil compaction is reduced.

Skid trails should be designated on the

ground before beginning falling activities, and tree falling should be done to

the yarding lead. Soils particularly

prone to compaction by heavy equipment should not be tractor-logged.

New road construction through established young Douglas-fir plantations

(<30 years old) or second-growth

stands of ponderosa pine should be

avoided, especially within 1.6 km (1

mile) of known black stain disease

centers. If new roads must be established or old roads re-opened, injured

trees and those with root collars partially covered by fill or side cast from

the right-of-way after construction

should be removed. Damaged and partially buried trees are often weakened

and have been shown to be attractive

to insect vectors of black stain. Many

new infection centers begin in rightsof-way cut for roads. Special care

should be exercised in road and site

construction when developing new

recreation sites.

Minimizing tree injury: During road

building and maintenance, recreation

site development, and timber harvest

activities, creating flooded or poorly

drained areas in or around Douglas-fir

plantations or second-growth stands of

ponderosa pine should be avoided.

Vectors of black stain root disease

often visit trees with roots in flooded

or poorly drained soils. Using rotaryblade brush-cutting machinery to clear

roadsides adjacent to Douglas-fir plantations is another practice to avoid, for

newly created tree stumps and trees

that are damaged but not severed by

the blades are attractive to vectors.

Special care should also be taken to

avoid damaging young plantation trees

when harvesting sawtimber in adjacent stands.

Modifying silvicultural practices:

Precommercial thinning in Douglas-fir

plantations should be done after the

vectors of black stain have emerged

and established themselves for breeding in other dead, dying, or down materials. Vectors usually emerge in the

spring or early summer. In areas where

black stain is a potential probem, precommercial thinning should be sched-
9

uled between the last of June and the

first of September to ensure that thinning slash will be red and dry by fall.

This will limit opportunities for insect

vector population build-up. In areas

where summer months are often dry

and droughty, the period of precommercial thinning may be extended into

late September.

Corrective Management

Where black stain root disease is already established, a few silvicultural

remedies are available. Cultural controls should be incorporated into silvicultural prescriptions and should not

disrupt the normal management schedule unless incidence in stands is moderate or worse (more than 5% of trees

affected).

When establishing new plantations

near areas where black stain is a

known management concern, a mix of

species should be planted to provide

future options for species manipulation. Where black stain is already

causing significant mortality in young

Douglas-fir stands, resistant or immune tree species should be favored

over Douglas-fir in precommercial

thinning or cleaning operations, especially in active infection centers and in

buffer zones immediately adjacent to

them. The width of buffer zones

should be based on the number of

years before the next scheduled entry

and a potential pathogen spread rate of

1.5 m/yr (4.9 ft/yr). Buffer zones are

typically two to five normal tree spacings wide, depending on the tree

species, size class, and stocking control guidelines for that species.

When resistant species selections are

lacking and precommercial thinning is

necessary, avoid thinning in active infection centers and in buffer zones

adjacent to them. Thinning in active

infection centers should be avoided, because odors from freshly cut stump

surfaces of infected trees are more

attractive to vectors than odors from

cut surfaces of healthy trees. This

leads to increasing disease in crop

trees adjacent to active infection centers.

In the central Sierra Nevada of California, mixed conifer stands of ponderosa pine, incense-cedar, and firs

often progress to a more advanced

seral stage when black stain root disease is active in the pine, because

death of the pines favors the other resistant species. When ponderosa pine

is the dominant species in such stands,

a mixture of resistant tree species

should be favored in and around black

stain centers during precommercial

and commercial thinnings. Patch cutting and creation of 15.2-m (50-ft)

buffers around disease centers is often

recommended during intermediate or

selective harvest entries in ponderosa

pine stands to prevent the continued

spread of the pathogen. Patch cutting in

infected pinyon in recreation areas has

also been recommended but does not

appear to be effective unless buffers

much wider than 15.2 m (50 ft) are

used.
10

Assistance

Technical assistance in recognizing

black stain root disease and developing vegetation management prescriptions to reduce or eliminate losses is

available from USDA Forest Service,

Forest Pest Management (FPM), or

other extension, municipal, or State

forestry offices.

Rcferences

Cobb FW Jr, Slaughter GW,

Rowney DL, Dernars CJ. 1982.

Rate of spread of Ceratocystis wageneri in ponderosa pine stands in

the central Sierra Nevada. Phytopathology 72:1359-1362.

Goheen DJ, Hansen EM. 1978.

Black stain root disease in Oregon

and Washington. Plant Disease Reporter 62:1098-1102.

Harrington TC, Cobb FW Jr. 1988.

Leptographium root diseases of

conifers. St. Paul, MN: American

Phytopathogical Society. 149 p.

Harrington TC, Reinhart C, Thornburgh DA, Cobb FW Jr. 1983.

Association of black-stain root disease with precommercial thinning

of Douglas-fir. Forest Science

29:12-14.

Hessburg PF, Hansen EM. 1986.

Mechanisms of intertree transmission of Verticicladiella wageneri in

young Douglas-fir. Canadian Journal of Forest Research 16:1250-

1254.

Hessburg PF, Hansen EM. 1987.

Pathological anatomy of black stain

root disease on Douglas-fir. Canadian Journal of Botany 65:962-971.

Landis TD, Helburg LB. 1976. Black

stain root disease on pinyon pine in

Colorado. Plant Disease Reporter

60:713-717.

Wagener WW, Mielke JL. 1961. A

staining fungus root disease of ponderosa, Jeffrey, and pinyon pines.

Plant Disease Reporter 45:831-835.

Witcosky JJ, Schowalter TD,

Hansen EM. 1986. Influence of

time of precommercial thinning on

the colonization of Douglas-fir by

three species of root-colonizing insects. Canadian Journal of Forest

Research 16:745-749.

Witcosky JJ, Schowalter TD,

Hansen EM. 1986. Hylastes nigrinus, (Coleoptera: Scolytidae), Pissodes fasciatus, and Steremnius carinatus (Coleoptera: Curculionidae)

as vectors of black stain root disease

of Douglas-fir. Environmental Entomology 15:1090-1095.
11

The U.S. Department of Agriculture (USDA) prohibits discrimination in its programs on the basis

of race, color, national origin, sex, religion, age, disability, political beliefs, and marital or familial

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

alternative means for communication of program information (braille, large print, audiotape, etc.)

should contact the USDA Office of Communications at (202) 720-5881 (voice) or (202) 720-7808

(TDD).

To file a complaint, write the Secretary of Agriculture, U.S. Department of Agriculture, Washington, DC 20250, or call (202) 720-7327 (voice) or (202) 720-1127 (TDD). USDA is an equal

employment opportunity employer.

Pesticides used improperly can be injurious to humans, animals, and plants.

Follow directions 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 particular pesticides.

Revised March 1995

Formatted for the Internet April 2000 by

Gloria Perez