Forest Insect

& Disease

Leaflet 177

March 2010

U.S. Department of Agriculture • Forest Service

Schweinitzii Root and Butt Rot 

of Western Conifers

Susan K. Hagle1 and Gregory M. Filip2

1

Forest Pathologist, USDA Forest Service, Forest Health Protection, Northern Region, Kooskia, Idaho.

2

Regional Forest Pathologist, USDA Forest Service, Forest Health Protection, Pacific Northwest 

Region, Portland, Oregon.

Schweinitzii root and butt rot also 

has been called brown-cubical 

butt rot, red-brown butt rot, or 

red-brown rot. The disease is 

caused by the fungus Phaeolus 

schweinitzii (Fries) Patouillard 

which is often called the velvettop fungus or cow-pie fungus 

because of the various forms of 

the conks. The species was named 

by the mycologist Fries to honor 

his colleague, Lewis David de 

Schweinitz, who some consider 

the “Father of North American 

Mycology.” His namesake fungus 

causes extensive butt rot in older trees. 

It also can cause a tree-killing root 

disease in young trees. Merchantable 

losses can be extensive in older trees 

because the most valuable part of the 

tree, the butt log, is most seriously 

affected. Schweinitzii root and butt 

rot often is associated with trees also 

affected by Armillaria root disease. 

From a hazard-tree context, failure 

potential can be high because of 

structural weakening at the lower stem 

and roots. Management of older forests 

with Schweinitzii root and butt rot has 

become increasingly important where 

hazard trees need to be removed in 

recreation sites or along roads.

Hosts and Distribution

Schweinitzii root and butt rot has an 

extensive conifer-host distribution 

in western North America (Table 1). 

The fungus occurs in eastern North 

America, Europe and Asia but is 

most damaging in western North 

America, especially in Douglas-fir and 

Sitka spruce. Western larch, western 

hemlock and western white pine can 

Figure 1. Fresh conks have tops with a velvety texture 

and a yellow margin.
2

have considerable damage when they 

are old. Hardwoods affected include 

isolated incidences in Oregon white 

oak (Quercus garryana), Acacia, 

Betula, Liquidambar, Fraxinus, 

Prunus, Ulmus, and Eucalyptus. It 

commonly occurs on hardwoods in 

Hawaii and the South Pacific.

In Montana and northern Idaho, the 

fungus causes the most widespread 

root disease, occurring across a broad 

range of site conditions. In western 

Oregon and Washington and coastal 

British Columbia and Alaska it is one 

of the most common causes of butt 

rot of Douglas-fir and Sitka spruce 

>150-years old. No reliable estimates 

of impact caused by Phaeolus 

schweinitzii are available, in part 

because it is often difficult to detect 

and is often masked by Armillaria root 

disease which is easier to diagnose.

Fungus Biology and Conks

The most obvious sign of the fungus 

is the distinctive conk that is usually 

only found on or near large trees 

(Figure 1). Large (up to 10 inches in 

diameter) annual conks occur on the 

ground near or growing from the base 

of infected trees and stumps. Conks on 

the ground are circular with depressed 

centers and taper to short, thick stalks 

and presumably emerge from infected 

Table 1. Conifer-host distribution for Schweinitzii root and butt rot in western 

North America

Cedar Pine (continued)

Alaska (Chamaecyparis nootkatensis ) Mexican white (P. pseudostrobus )

incense (Calocedrus decurrens ) pinyon (P. edulis)

Port‐Orford (Chamaecyparis lawsoniana ) ponderosa (P. ponderosa )

western red (Thuja plicata ) Scots (P. sylvestris)

singleleaf pinyon (P. monophylla )

Douglas‐fir (Pseudotsuga menziesii ) sugar (P. lambertiana )

western white (P. monticola )

Hemlock whitebark (P. albicaulis )

mountain (Tsuga mertensiana )

western (T. heterophylla ) Spruce

black (Picea mariana )

Larch Engelmann (P. engelmannii )

tamarack (Larix laricina ) Norway (P. abies)

western (L. occidentalis ) Sitka (P. sitchensis )

white (P. glauca )

Pacific Yew (Taxus brevifolia)

True Fir

Pine balsam (Abies balsamea )

Coulter (Pinus coulteri ) California red (A. magnifica )

gray (P. sabiniana ) grand (A. grandis)

jack (P. banksiana ) noble (A. procera )

Jeffrey (P. jeffreyi ) Pacific silver (A. amabilis )

knobcone (P. attenuata ) subalpine (A. lasiocarpa )

limber (P. flexilis) white (A. concolor )

lodgepole (P. contorta )     ‐‐>
3

roots. Conks may also occur on 

infected trunks, appear as thin brackets 

(Figure 2), and often emerge from 

wounds or cracks. Conks appear in 

late summer and fall. When fresh, the 

tops of conks are velvety in texture 

(hence the common name, velvet-top 

fungus) and reddish-brown, greenishbrown, or yellow-brown, often with 

a yellow edge (Figure 1). The conk 

undersurface is poroid and green when 

young and turns brown with age. 

Conks die after a few weeks, become 

dark brown and brittle, and resemble 

cow feces; hence the other common 

name, cow-pie fungus (Figure 3). 

Conks are less common on dry sites, 

although the disease may be present. 

Dead conks will persist for a year or 

two on or around affected trees and 

are often the sole indicator of infection 

and decay.

Conks produce microscopic 

basidiospores when conditions are 

optimum in the fall. The spores 

are deposited on and subsequently 

percolate into the soil. Fine roots 

are the main infection court for 

basidiospores. Fresh trunk wounds 

caused by mechanical injury or fire 

probably are not infected directly 

by spores but instead the wounds 

exacerbate decay in previously 

infected roots and butts (Figure 4). 

Infection of Douglas-fir and possibly 

other species results from direct 

invasion of root tips. Once in the 

xylem, the fungus can grow axially 

within the roots. Adventitious root 

production is stimulated in infected 

roots. Subsequent infections of 

adventitious roots by the fungus result 

in gall-like swellings that eventually 

become stubbed and often infected 

by Armillaria spp. In northern 

Idaho and Montana, Armillaria spp. 

probably often kills Douglas-fir that 

has been infected by P. schweinitzii. 

The converse also appears to occur: 

research in Europe has shown that 

P. schweinitzii readily infects wood 

previously colonized by Armillaria.

Spread of P. schweinitzii within the 

forest is not significantly facilitated 

by root contacts as are other root 

pathogens. Douglas-fir and grand fir 

are tolerant of extensive root infection 

by the fungus. Ponderosa pine and 

western larch are more resistant to 

infection than the firs. The fungus 

probably can persist for decades in 

dead or cut trees and infect roots of 

adjacent developing trees. Although 

the fungus has been reported to 

Figure 2. Conks are most frequently found 

on the ground but may also occur on lower 

tree boles.

Figure 3. As conks age, they become dark brown 

and brittle, and resemble “cow-pies.”
4

persist for decades in stumps of slash 

pine (Pinus elliottii) and longleaf 

pine (P. palustris) in Florida and 

spread to plantation trees, this has 

not been reported in other species or 

areas, and P. schweinitzii-infected 

stumps are considered unimportant 

sources of inoculum.

Root disease caused by P. schweinitzii

in forest stands or plantations does 

not resemble infection by other rootdisease-causing fungi. Instead, P. 

schweinitzii-killed or windthrown trees 

more often are scattered throughout 

a stand rather than located in discrete 

pockets or centers as is Armillaria 

root disease or laminated root rot. 

Scattered diseased or decayed trees 

imply spore infections of roots rather 

than mycelial spread via root contacts 

or grafts with adjacent infected trees 

or stumps. This is further supported 

by observations that adjacent infected 

trees often are colonized by a different 

strain of the fungus via infection 

from a single basidiospore. There 

also is some evidence that the fungus 

can live saprophytically in the duff 

and subsequently infect fine roots. 

Similar to other root pathogens, P. 

schweinitzii-infected trees often are 

attacked by bark beetles, at least in 

Idaho and Montana. P. schweinitzii 

root infections in young trees cause 

root decay and death with loss of 

tree increment proportional to the 

percentage of root infection.

After initial infection, there may be 

no signs of early root decay, or it may 

show as a yellow to reddish-brown 

discoloration of the wood a few inches 

to several feet ahead of advanced 

decay (Figure 5). Small roots near 

decay in the root collar often develop 

dark reddish-brown and resinous 

heartwood (Figure 6). These roots are 

useful for diagnosing the disease in 

large trees where extensive excavation 

is difficult. Wood becomes soft just 

before the advanced stage is reached. 

Advanced decay is a distinctive dry, 

crumbly, brown-cubical rot (Figure 

5). Thin, resinous, crust-like mycelial 

layers often are found in shrinkage 

cracks of the decayed wood. Decay 

in living trees appears limited to the 

heartwood and normally confined to 

roots and butts. The fungus, however, 

has been found in wood surrounding 

bird cavities in western larch 30 feet 

above the ground.

Crown symptoms seen in trees with 

extensive root decay include shortened 

terminal growth which gives the crown 

a rounded appearance, a thin crown 

with scattered dead branches, slight 

chlorosis, and an overall unthrifty 

appearance. Diseased trees often have 

Figure 4. Fresh wounds probably exacerbate 

decay in previously infected roots and butts as 

shown in this grand fir. Note the old Schweinitzii 

conks at lower right of tree base.
5

pronounced enlarged bases or butt 

swell (Figure 7). Roots often become 

truncated, and thick callous tissue 

gives the roots a club-like appearance 

(Figure 8). Severe decay and truncated 

roots can result in tree breakage or 

windthrow. After decayed butts and 

roots disintegrate, the brown-rot 

residues are very stable and provide 

important properties to the organic 

component of forest floors where they 

may comprise up to 30% of the soil 

volume in the upper layers. Conks are 

presumed to be produced after trees 

have developed considerable decay. 

Conks are produced on or near living 

trees but will continue to fruit on or 

near dead trees, stumps, and logs.

Young conks of Phaeolus schweinitzii

resemble the conks of another root and 

butt rot fungus, Inonotus tomentosus, 

once called the false velvet-top 

fungus. Conks of I. tomentosus usually 

are much smaller (1 to 3 inches in 

diameter) than conks of P. schweinitzii

(up to 10 inches in diameter). Even 

when fresh, conks of P. schweinitzii

usually are much darker than conks of 

I. tomentosus.

Estimating Extent of Decay

The amount of decay caused by 

P. schweinitzii is quite variable in 

Figure 5. Advanced decay caused by P. 

schweinitzii is a brown cubical rot.

Figure 6. Small-diameter roots with a dark 

red resinous heart can help diagnose disease 

caused by P. schweinitzii.

Figure 7. Decayed trees often have pronounced 

butt swell as seen in this Douglas-fir.

Figure 8. Roots with Schweintzii rot commonly 

are truncated with ends covered by thick callus, 

producing a club-like appearance.
6

infected trees, even if butt swell, 

wounds, or conks are present. If 

conks alone are found on the ground 

near the base of a tree, or on the tree 

at the base, decay length averages 8 

feet above ground in older trees. If 

both conks and wounds/cracks are 

present at the base of a tree, decay 

length averages 16 feet above ground 

in older trees and 8 feet above ground 

in younger trees. If both conks and 

wounds/cracks are present 8 feet or 

more above the ground, decay length 

averages 32 feet. Without conks, as 

is common on dry sites, amount of 

decay can be estimated in suspect trees 

by drilling at the root collar or butt 

(see management section). If infected 

trees are dead, add 4 feet to the above 

estimates. Decay columns are conical, 

tapering upward from the ground level. 

Management

Managing stands and sites with 

P. schweinitzii requires careful 

consideration of the disease 

expression. Although other tree species 

may become infected and die or decay, 

Douglas-fir, Sitka spruce, and perhaps 

larch, are most seriously affected 

by Schweinitzii root and butt rot. 

Consequently, the following are some 

common situations for these species 

and recommended management:

Douglas-fir <150-years old with 

mortality >1 tree/acre

Young stands with mortality caused by 

Schweinitzii root and butt rot usually 

are found on harsh sites for Douglasfir and may be only marginally 

productive for timber. It is difficult to 

manage young forests with potential 

infection and decay caused by P. 

schweinitzii because there are usually 

no above-ground signs or symptoms 

of the disease. The presence of large 

residual trees or stumps with typical 

decay or conks may be an indication 

that infection is present in young 

surrounding trees. Younger or smallerdiameter stands generally will not have 

sufficient butt decay to cause impact; 

however, volume lost to growth loss 

and mortality may be excessive. Such 

stands often have a history of insectcaused defoliation or bark-beetle 

activity that will further weaken or kill 

trees. Partial-harvest methods should 

be avoided where Douglas-fir is a 

major component. If Douglas-fir seed 

trees are used, they usually windthrow 

and should be readily salvable or 

expendable. If adapted, other species 

should be encouraged as well. 

Ponderosa pine and lodgepole pine 

are more resistant to Schweinitzii root 

and butt rot and should be managed 

with Douglas-fir. Maintaining 

good stand growth through density 

management may be difficult on these 

sites, but it is essential to minimize 

root-disease impact. 

A more serious situation occurs 

where young Douglas-fir with notable 

mortality also has Armillaria root 

disease. Phaeolus schweinitzii and 

Armillaria ostoyae are commonly 

found together damaging stands 

in northern Idaho and Montana 

and possibly other areas. Stands or 

plantations with both root diseases 

should be managed as Armillaria root 

disease problems. Planting or favoring 

the more Armillaria-resistant pines or 

larch is recommended.

Douglas-fir or Sitka spruce 

>150-years old with butt rot but 

low mortality

Commercial forests: Concern for 

infection and mortality of Douglasfir or spruce regeneration following 

harvest of older trees is probably 
7

unwarranted if the replacement stand 

is intended for harvest before reaching 

150 years of age. However, butt rot in 

the older trees probably is associated 

with considerable root rot. Seed tree 

or shelterwood regeneration methods 

may result in windthrow of leave 

trees. If the trees are readily salvable 

or expendable, this may be of little 

consequence unless they fall before 

sufficient seeding has taken place.

Developed sites and roadsides: 

Schweinitzii root and butt rot is a 

major safety concern in older Douglasfir or Sitka spruce forests in developed 

sites. Trees near conks, whether on 

the ground or on the tree, should 

be examined closely for obvious 

additional defect indicators such as 

leans, ground heaving or root lifting 

within 2-3 feet of the butt, butt swell 

and wounds, shake or cracking of the 

butt, or evidence of carpenter ant or 

woodpecker activity in the butt.

The butt and major roots should be 

drilled to determine the extent of 

internal decay. Trees with a sound-rind 

thickness <15% of the butt diameter 

are considered high-failure potential 

and should be removed immediately 

if within striking distance of valuable 

targets (Figure 9). If butt wounds are 

present, a 25% or greater sound-rind 

thickness is required. Because of the 

high variability in the location of 

decay in butts and roots, it is important 

to drill these trees at multiple locations 

to determine if decay is present. Trees 

with decay but with adequate soundrind thickness should be monitored 

frequently depending on decay extent. 

From a danger-tree context along 

roadsides or in the workplace, one or 

more conks on or near a tree indicate 

likely failure potential, and such trees 

should be removed within 1 to 3 years 

depending on frequency and duration 

of road traffic or work activity. 

Trees with one or more conks and 

considerable decay (<15% sound-rind 

thickness) indicate imminent-failure 

potential and should be removed 

within one year of evaluation.

Wildlife habitat: Although wildlife 

values related to Schweinitzii root 

and butt rot have not been reported, 

hollows in infected butts created 

by the fungus probably provide 

good habitat for a variety of living 

organisms both in standing trees 

and in down logs. Infected trees can 

be retained in thinned or partially 

harvested stands if enhancing 

wildlife habitat is the primary forestmanagement objective, especially if 

mostly down wood is desired.

Figure 9. Decayed trees with a poor soundrind thickness may have a high-failure 

potential and should be removed if within 

striking distance of valuable targets.
8

References

Aho, P.E. 1982. Indicators of cull 

in western Oregon conifers. USDA 

Forest Service Gen. Tech. Rep. PNWGTR-144. 17 p. 

Boyce, J.S. 1966. Forest Pathology. 

Third Edition, McGraw-Hill Book Co., 

New York. 572 p. 

Dubreuil , S.H. 1981. Occurrence, 

symptoms, and interactions of Phaeolus 

schweinitzii and associated fungi 

causing decay and mortality of conifers. 

Ph.D. diss., Univ. of Idaho, Moscow. 

157 p. 

Goheen, E.M., and E.A. Willhite. 2006. 

Field guide to the common diseases and 

insect pests of Oregon and Washington 

conifers. USDA Forest Service, R6-NRFID-PR-01-06. 327 p.

Hagle, S.K., K.E. Gibson, and S. 

Tunnock. 2003. Field guide to diseases 

and insect pests of northern and central 

Rocky Mountain conifers. USDA Forest 

Service, R1-03-08. 197 p. 

Hansen, E.M., and K.J. Lewis. 1997. 

Compendium of conifer diseases. APS 

Press, The American Phytopathological 

Society, St. Paul, MN. 101 p. 

Harvey, R.D., Jr., and P.F. Hessburg, Sr. 

1992. Long-range planning for developed 

sites in the Pacific Northwest: the context 

of hazard tree management. USDA Forest 

Service, FPM-TP039-92. 120 p.

Hennon, P.E. 1995. Are heart rot 

fungi major factors of disturbance in 

gap-dynamic forests? Northwest Sci. 

69(4):284-293.

Toupin, R., G. Filip, T. Erkert, and M. 

Barger. 2008. Field guide for danger tree 

identification and response. USDA Forest 

Service, R6-NR-FP-PR-01-08. 64 p.

Assistance

Private landowners can get more 

information from County Extension 

Agents, State Forestry Departments, 

or State Agriculture Departments. 

Federal resource managers should 

contact USFS Forest Health Protection 

(www.fs.fed.us/foresthealth/). This 

publication and other Forest Insect and 

Disease Leaflets can be found at 

www.fs.fed.us/r6/nr/fid/wo-fidls/.

Acknowledgements

Critical reviews were provided by 

USDA Forest Service pathologists: 

James Hadfield, Wenatchee, WA; Craig 

Schmitt, La Grande, OR; Paul Hennon, 

Juneau, AK; and James Hoffman, 

Boise, ID. David Shaw, pathologist 

from Oregon State University, 

Corvallis, also provided a review.

Photos: USDA Forest Service, 

Pacific Northwest Region and 

Northern Region.

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Published by USDA Forest Service, Pacific Northwest Region (R6), Portland, Oregon

FS/R6/RO/FIDL#177-10/002