Forest Insect & Disease Leaflet 177 March 2010

U.S. Department of Agriculture • Forest Service Schweinitzii Root and Butt Rot of Western Susan K. Hagle1 and Gregory M. Filip2

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 schweinitzii (Fries) Patouillard which is often called the velvet- top 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 Figure 1. Fresh conks have tops with a velvety texture Schweinitz, who some consider and a yellow margin. the “Father of North American with Schweinitzii root and butt rot has .” His namesake fungus become increasingly important where causes extensive butt rot in older trees. hazard trees need to be removed in It also can cause a tree-killing root recreation sites or along roads. disease in young trees. Merchantable losses can be extensive in older trees Hosts and Distribution because the most valuable part of the Schweinitzii root and butt rot has an tree, the butt log, is most seriously extensive -host distribution affected. Schweinitzii root and butt in western North America (Table 1). rot often is associated with trees also The fungus occurs in eastern North affected by Armillaria root disease. America, Europe and Asia but is From a hazard-tree context, failure most damaging in western North potential can be high because of America, especially in Douglas- and structural weakening at the lower stem Sitka . Western , western and roots. Management of older forests hemlock and western white can

1Forest Pathologist, USDA Forest Service, Forest Health Protection, Northern Region, Kooskia, Idaho. 2Regional Forest Pathologist, USDA Forest Service, Forest Health Protection, Pacific Northwest Region, Portland, Oregon. have considerable damage when they of impact caused by Phaeolus are old. Hardwoods affected include schweinitzii are available, in part isolated incidences in Oregon white because it is often difficult to detect oak (Quercus garryana), Acacia, and is often masked by Armillaria root Betula, Liquidambar, Fraxinus, disease which is easier to diagnose. Prunus, Ulmus, and Eucalyptus. It commonly occurs on hardwoods in Fungus Biology and Conks Hawaii and the South Pacific. The most obvious sign of the fungus In Montana and northern Idaho, the is the distinctive conk that is usually fungus causes the most widespread only found on or near large trees root disease, occurring across a broad (Figure 1). Large (up to 10 inches in range of site conditions. In western diameter) annual conks occur on the Oregon and Washington and coastal ground near or growing from the base and Alaska it is one of infected trees and stumps. Conks on of the most common causes of butt the ground are circular with depressed rot of Douglas-fir and Sitka spruce centers and taper to short, thick stalks >150-years old. No reliable estimates 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 ( ) Scots (P. sylvestris ) singleleaf pinyon (P. monophylla ) Douglas‐fir ( menziesii ) sugar (P. lambertiana ) western white (P. monticola ) Hemlock whitebark (P. albicaulis ) mountain ( 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 ) ‐‐> 2 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, greenish- brown, 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). Figure 2. Conks are most frequently found Conks are less common on dry sites, on the ground but may also occur on lower although the disease may be present. tree boles. Dead conks will persist for a year or has been infected by P. schweinitzii. two on or around affected trees and The converse also appears to occur: are often the sole indicator of infection research in Europe has shown that and decay. P. schweinitzii readily infects wood previously colonized by Armillaria. Conks produce microscopic when conditions are Spread of P. schweinitzii within the optimum in the fall. The spores forest is not significantly facilitated are deposited on and subsequently by root contacts as are other root percolate into the soil. Fine roots pathogens. Douglas-fir and grand fir are the main infection court for are tolerant of extensive root infection basidiospores. Fresh trunk wounds by the fungus. Ponderosa pine and caused by mechanical injury or fire western larch are more resistant to probably are not infected directly infection than the . The fungus by spores but instead the wounds probably can persist for decades in exacerbate decay in previously dead or cut trees and infect roots of infected roots and butts (Figure 4). adjacent developing trees. Although Infection of Douglas-fir and possibly the fungus has been reported to 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. Figure 3. As conks age, they become dark brown probably often kills Douglas-fir that and brittle, and resemble “cow-pies.” 3 by observations that adjacent infected trees often are colonized by a different strain of the fungus via infection from a single . 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 Figure 4. Fresh wounds probably exacerbate decay in previously infected roots and butts as decay in the root collar often develop shown in this grand fir. Note the old Schweinitzii dark reddish-brown and resinous conks at lower right of tree base. heartwood (Figure 6). These roots are persist for decades in stumps of slash useful for diagnosing the disease in pine (Pinus elliottii) and longleaf large trees where extensive excavation pine (P. palustris) in Florida and is difficult. Wood becomes soft just spread to plantation trees, this has before the advanced stage is reached. not been reported in other species or Advanced decay is a distinctive dry, areas, and P. schweinitzii-infected crumbly, brown-cubical rot (Figure stumps are considered unimportant 5). Thin, resinous, crust-like mycelial sources of inoculum. layers often are found in shrinkage cracks of the decayed wood. Decay Root disease caused by P. schweinitzii in living trees appears limited to the in forest stands or plantations does heartwood and normally confined to not resemble infection by other root- roots and butts. The fungus, however, disease-causing fungi. Instead, P. has been found in wood surrounding schweinitzii-killed or windthrown trees bird cavities in western larch 30 feet more often are scattered throughout above the ground. a stand rather than located in discrete pockets or centers as is Armillaria Crown symptoms seen in trees with root disease or laminated root rot. extensive root decay include shortened Scattered diseased or decayed trees terminal growth which gives the crown imply spore infections of roots rather a rounded appearance, a thin crown than mycelial spread via root contacts with scattered dead branches, slight or grafts with adjacent infected trees chlorosis, and an overall unthrifty or stumps. This is further supported appearance. Diseased trees often have

4 Figure 5. Advanced decay caused by P. Figure 6. Small-diameter roots with a dark schweinitzii is a brown cubical rot. red resinous heart can help diagnose disease caused by P. schweinitzii. pronounced enlarged bases or butt swell (Figure 7). Roots often become Young conks of Phaeolus schweinitzii truncated, and thick callous tissue resemble the conks of another root and gives the roots a club-like appearance butt rot fungus, Inonotus tomentosus, (Figure 8). Severe decay and truncated once called the false velvet-top roots can result in tree breakage or fungus. Conks of I. tomentosus usually windthrow. After decayed butts and are much smaller (1 to 3 inches in roots disintegrate, the brown-rot diameter) than conks of P. schweinitzii residues are very stable and provide (up to 10 inches in diameter). Even important properties to the organic when fresh, conks of P. schweinitzii component of forest floors where they usually are much darker than conks of may comprise up to 30% of the soil I. tomentosus. volume in the upper layers. Conks are presumed to be produced after trees Estimating Extent of Decay have developed considerable decay. The amount of decay caused by Conks are produced on or near living P. schweinitzii is quite variable in trees but will continue to fruit on or near dead trees, stumps, and logs.

Figure 8. Roots with Schweintzii rot commonly Figure 7. Decayed trees often have pronounced are truncated with ends covered by thick callus, butt swell as seen in this Douglas-fir. producing a club-like appearance. 5 infected trees, even if butt swell, residual trees or stumps with typical wounds, or conks are present. If decay or conks may be an indication conks alone are found on the ground that infection is present in young near the base of a tree, or on the tree surrounding trees. Younger or smaller- at the base, decay length averages 8 diameter stands generally will not have feet above ground in older trees. If sufficient butt decay to cause impact; both conks and wounds/cracks are however, volume lost to growth loss present at the base of a tree, decay and mortality may be excessive. Such length averages 16 feet above ground stands often have a history of insect- in older trees and 8 feet above ground caused defoliation or bark-beetle in younger trees. If both conks and activity that will further weaken or kill wounds/cracks are present 8 feet or trees. Partial-harvest methods should more above the ground, decay length be avoided where Douglas-fir is a averages 32 feet. Without conks, as major component. If Douglas-fir seed is common on dry sites, amount of trees are used, they usually windthrow decay can be estimated in suspect trees and should be readily salvable or by drilling at the root collar or butt expendable. If adapted, other species (see management section). If infected should be encouraged as well. trees are dead, add 4 feet to the above Ponderosa pine and lodgepole pine estimates. Decay columns are conical, are more resistant to Schweinitzii root tapering upward from the ground level. and butt rot and should be managed with Douglas-fir. Maintaining Management good stand growth through density Managing stands and sites with management may be difficult on these P. schweinitzii requires careful sites, but it is essential to minimize consideration of the disease root-disease impact. expression. Although other tree species A more serious situation occurs may become infected and die or decay, where young Douglas-fir with notable Douglas-fir, Sitka spruce, and perhaps mortality also has Armillaria root larch, are most seriously affected disease. Phaeolus schweinitzii and by Schweinitzii root and butt rot. Armillaria ostoyae are commonly Consequently, the following are some found together damaging stands common situations for these species in northern Idaho and Montana and recommended management: and possibly other areas. Stands or Douglas-fir <150-years old with plantations with both root diseases mortality >1 tree/acre should be managed as Armillaria root disease problems. Planting or favoring Young stands with mortality caused by the more Armillaria-resistant or Schweinitzii root and butt rot usually larch is recommended. are found on harsh sites for Douglas- fir and may be only marginally Douglas-fir or Sitka spruce productive for timber. It is difficult to >150-years old with butt rot but manage young forests with potential low mortality infection and decay caused by P. Commercial forests: Concern for schweinitzii because there are usually infection and mortality of Douglas- no above-ground signs or symptoms fir or spruce regeneration following of the disease. The presence of large harvest of older trees is probably 6 unwarranted if the replacement stand depending on frequency and duration is intended for harvest before reaching of road traffic or work activity. 150 years of age. However, butt rot in Trees with one or more conks and the older trees probably is associated considerable decay (<15% sound-rind with considerable root rot. Seed tree thickness) indicate imminent-failure or shelterwood regeneration methods potential and should be removed may result in windthrow of leave within one year of evaluation. trees. If the trees are readily salvable Wildlife habitat: Although wildlife or expendable, this may be of little values related to Schweinitzii root consequence unless they fall before and butt rot have not been reported, sufficient seeding has taken place. hollows in infected butts created Developed sites and roadsides: by the fungus probably provide Schweinitzii root and butt rot is a major safety concern in older Douglas- fir 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 Figure 9. Decayed trees with a poor sound- rind thickness may have a high-failure if within striking distance of valuable potential and should be removed if within targets (Figure 9). If butt wounds are striking distance of valuable targets. present, a 25% or greater sound-rind thickness is required. Because of the good habitat for a variety of living high variability in the location of organisms both in standing trees decay in butts and roots, it is important and in down logs. Infected trees can to drill these trees at multiple locations be retained in thinned or partially to determine if decay is present. Trees harvested stands if enhancing with decay but with adequate sound- wildlife habitat is the primary forest- rind thickness should be monitored management objective, especially if frequently depending on decay extent. mostly down wood is desired. 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 7 References Hennon, P.E. 1995. Are heart rot fungi major factors of disturbance in Aho, P.E. 1982. Indicators of cull gap-dynamic forests? Northwest Sci. in western Oregon conifers. USDA 69(4):284-293. Forest Service Gen. Tech. Rep. PNW- GTR-144. 17 p. Toupin, R., G. Filip, T. Erkert, and M. Barger. 2008. Field guide for danger tree Boyce, J.S. 1966. Forest Pathology. identification and response. USDA Forest Third Edition, McGraw-Hill Book Co., Service, R6-NR-FP-PR-01-08. 64 p. New York. 572 p. Dubreuil , S.H. 1981. Occurrence, symptoms, and interactions of Phaeolus Assistance schweinitzii and associated fungi Private landowners can get more causing decay and mortality of conifers. information from County Extension Ph.D. diss., Univ. of Idaho, Moscow. Agents, State Forestry Departments, 157 p. or State Agriculture Departments. Goheen, E.M., and E.A. Willhite. 2006. Federal resource managers should Field guide to the common diseases and contact USFS Forest Health Protection insect pests of Oregon and Washington (www.fs.fed.us/foresthealth/). This conifers. USDA Forest Service, R6-NR- publication and other Forest Insect and FID-PR-01-06. 327 p. Disease Leaflets can be found at www.fs.fed.us/r6/nr/fid/wo-fidls/. Hagle, S.K., K.E. Gibson, and S. Tunnock. 2003. Field guide to diseases and insect pests of northern and central Acknowledgements Rocky Mountain conifers. USDA Forest Critical reviews were provided by Service, R1-03-08. 197 p. USDA Forest Service pathologists: Hansen, E.M., and K.J. Lewis. 1997. James Hadfield, Wenatchee, WA; Craig Compendium of conifer diseases. APS Schmitt, La Grande, OR; Paul Hennon, Press, The American Phytopathological Juneau, AK; and James Hoffman, Society, St. Paul, MN. 101 p. Boise, ID. David Shaw, pathologist Harvey, R.D., Jr., and P.F. Hessburg, Sr. from Oregon State University, 1992. Long-range planning for developed Corvallis, also provided a review. sites in the Pacific Northwest: the context Photos: USDA Forest Service, of hazard tree management. USDA Forest Pacific Northwest Region and Service, FPM-TP039-92. 120 p. Northern Region.

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