Forest Insect & Disease Leaflet

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Forest Insect & Disease Leaflet 172 Revised February 2000

U.S. Department of Agriculture • Forest Service Annosus Root Disease of Western Conifers Craig L. Schmitt1, John R. Parmeter2, and John T. Kliejunas3

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

1Service 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. #172 Annosus no spreads 4/20/00 9:52 AM Page 2

resource values are compromised by these Jeffrey and ponderosa pine in dry Eastside high levels of annosus root disease, pine types. In Oregon, annosus root dis- prompting use of management strategies ease has mostly been associated with to restore a more natural level of disease occurrence of large stumps — usually 18” activity. and larger in diameter. Subalpine fir stands show evidence of root disease asso- Distribution and Hosts ciated with stumps much smaller — as Annosus root disease is found on all small as 6 to 8” diameter. western conifer species but is of most con- In the western United States there are cern on true firs, hemlocks, and pines. two different intersterility groups, or bio- Incense cedar, coast redwood and sequoia logical species of H. annosum. These two are sometimes infected in California. biological species have distinct host pref- Western juniper is infected throughout its erences. The P-group infects pines, range. Annosus is common and causes incense-cedar, western juniper, pinyon, extensive decay in old-growth western and and manzanita; the S-group infects true mountain hemlock stands. Many mixed firs, giant sequoia, Douglas-fir and hem- conifer stands throughout the inland west locks. The fungus very rarely spreads and California have high levels of infec- between host species of these two groups, tion, resulting in extensive mortality, espe- either between trees or stumps and trees. cially of true firs. However, saprophytic stump colonization Pine communities also have high levels can involve either strain. Thus, P-group of disease and exhibit varying levels of H. annosum may colonize grand fir impact. Douglas-fir-dominated stands in stumps but root disease will not develop in northern and central Idaho and to a lesser pines or firs surrounding these stumps. extent, northeastern Washington have substantial amounts of annosus-caused mor- Evidence of Annosus Root tality, especially on dry sites where Disease Douglas-fir grows with ponderosa pine, but Douglas-fir in California, Oregon and In The Stand most of Washington are not seriously affected. Hardwoods are generally resis- The typical pattern of annosus root dis- tant or immune, although madrone and a ease in stands involves scattered small few shrub species are occasional hosts. groups of dead trees centered around large old stumps. There are often old dead Incidence and severity of annosus root snags and downed trees with rotten roots disease varies by locality, stand type, and near the center of pockets, adjacent to the management history. Generally, stands old stumps. At the perimeter of centers, having a history of logging-related distur- more recent mortality may be found, along bance are most severely affected. Stands with symptomatic trees. Mortality usually that were partially-cut, especially those does not start to occur around stumps until with multiple removals, will have the 15 or more years after they are created. highest level of annosus root disease. In stands of susceptible species, anno- Partially cut grand fir- and white fir- sus root disease usually occurs in discrete dominated mixed conifer stands in south- centers. The presence of H. annosum in ern and central Oregon and northern these centers may be verified by observing California have especially high incidences several common characteristics. In stands of annosus root disease. Incidence is also of resinous species such as pine, dead and particularly high on Jeffrey pine in south- or dying trees or understocked areas are ern California recreation sites and on identified readily and may be suspect.

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Upon encountering such centers, look for tered on the surface of dead infected roots evidence of gradual, periodic tree death at (fig. 2). More mature conks, two to three the perimeter of the center. Symptomatic inches (5.0 to 7.6 cm) across, may be trees may have thin, chlorotic foliage and found in crevices of the root collars of reduced height and lateral branch growth. infected hemlocks, or in or just under the This indicates that infected roots are soil duff layer on the root collars of pines. dying, which will eventually lead to death of the tree. Frequently, infected trees will Large conks often grow in the interiors be attacked and killed quickly by bark of hollow or extensively decayed hemlock, 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 produce 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- Fig. 1. Small button conks of Heterobasidion annosum on sum is discovered when the stand the root collar of a ponderosa pine. Note: these were is thinned or harvested and decay formed below the duff layer, which was removed for this and stain at stump height is photograph. observed. In some true fir stands, similar conditions may be observed, although mortality is more frequent, often resulting from bark beetle attacks. Signs and Symptoms Heterobasidion annosum readily produces fruiting bodies, or conks, on infected host tissues. Determining occurrence of H. annosum conks is a highly reli- able method of diagnosing anno- 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 true fir, and ponderosa pine stumps and bodies on their roots and/or root collars. roots (fig. 3) or under the bark of decaying On pines, small leathery buff-colored pine stumps. Fully mature fruiting bodies conks, one-eighth to one-fourth inch (0.3 may be 10 inches (25 cm) across or larger. to 0.6 cm) in diameter, and sometimes H. annosum conks have a buff to dark larger, are produced on the outer bark at brown-colored upper surface with concen- the root collar, under the bark of dead tric furrows and a smooth, cream-colored trees, and in the duff layer (fig. 1). under surface that has tiny pores and a Similar conks are found, but less frequent- narrow sterile (non-pored) margin. Conks ly, on true firs. On most species of are perennial and may have more than one conifers, early stages of fruiting bodies tube layer. appear as small buff-colored pustules scat- 3 #172 Annosus no spreads 4/20/00 9:52 AM Page 4

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 primary mechanism for root to root spread, growing along the surface of roots and moving onto the roots of adjacent trees across contacts and grafts. Some other root disease fungi form similar Fig. 3. Mature H. annosum conk in the interior of a pon- mycelia, and its occurrence derosa pine stump 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 Fig. 4. Ectotrophic mycelia on the exterior of an infected initially laminated, meaning the root. 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 commonly in pine, advanced decay will be wet, spongy, and stringy with large white streaks and Fig. 5. Characteristic red stain in the interior of a live scattered small black flecks (fig. H. annosum-infected grand fir root. 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

Fig. 6. Typical laminated advanced decay caused by H. annosum. 4 #172 Annosus no spreads 4/20/00 9:52 AM Page 5

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 Fig. 7. White streaks and black flecks throughout wet (Olson) Stalpers (=Oedocephalum spongy advanced decay most often found on H. annosum-infected grand fir, Douglas-fir or hemlock. 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 tissues by secreting enzymes that break down the cellulose and lignin Fig. 8. Spiniger meineckellus conidiophores characteris- of the wood cells to simple carbo- tic of the asexual form of H. annosum. These are produced on incubated infected material and provide posi- hydrates that the fungus uses for tive diagnosis and identification of infection. 50X mag- food. While decay is often in nification. “dead” heartwood, in some species lateral branch growth. In recent root exca- (notably pines), living cells of the cambi- vations of annosus-infected live ponderosa um and phloem are attacked and killed. pine in the southern Blue Mountains, at In true firs, the inner sapwood is com- least 90 percent of the root systems were monly attacked and the fungus may grad- killed by the pathogen before crown symp- ually invade and kill the outer sapwood. toms were noticeable. Crown symptoms Trees so attacked can be girdled and are also produced by other root diseases, killed or rendered susceptible to bark bee- such as black stain root disease, caused by tles or to toppling because of extensive Leptographium wageneri var. ponderosum root decay. (Harrington & Cobb). Two kinds of spread are impor- Because conks are not always found, tant in the life cycle of H. annosum: local, decay is highly variable, and crown symp- underground tree-to-tree spread within a toms may be caused by other agents, posi- center and long distance, aerial spread that tive identification of H. annosum infection establishes new centers. Most local by finding definite signs and symptoms is spread involves hyphal growth within and not always assured. Frequently, other along the surface of roots. When there is more readily identifiable fungal pathogens contact between an infected root and a are found and mistakenly identified as healthy root, H. annosum hyphae can being the sole or primary cause of tree grow across the contact to the healthy root decline or mortality. Because of this, mask- and begin growing on the surface and ing of annosus symptoms by those of other through the phloem and xylem. By this means, the fungus spreads from tree to 5 #172 Annosus no spreads 4/20/00 9:52 AM Page 6

tree, creating an enlarging disease center during prolonged drought. Stump colo- in the stand. nization is unlikely when stump tempera- tures are high and relative humidity is Rates of center enlargement depend on low. Stumps are susceptible to infection stand and site conditions and generally are for 2 to 4 weeks following cutting. estimated to be between 1.6 and 5 feet Colonized stumps less then 6 inches in (0.5-1.5 m) per year. Some centers even- diameter may heat sufficiently during hot tually cease enlarging, but others continue summer days to kill H. annosum myceli- to spread for years. All the factors affect- um in the wood. ing rate of spread are not fully understood. Numerous field observations indicate that Once established in roots, the fungus the disease in seedling and sapling size may persist for several decades in resinous pine trees around large stumps will spread tree species. In non-resinous species such to the limit of the rooting zone for the as firs and hemlocks, persistence may not stump and then stop. In similar stands of be as long, but good data are wanting. As poles or larger size trees, the root disease long as viable hyphae remain in old roots will continue to spread, moving beyond they can infect roots of susceptible trees the rooting zone of the original stump that that become established in old centers, served as the source of the infection. thus regenerated trees may be damaged or die prematurely. Long distance spread occurs when airborne sporidia produced from H. annosum Damage conks disperse and infect freshly-exposed stump surfaces or woody tissues at True firs wounds. Wounds can be colonized and result in decay anywhere on the roots, True firs infected by H. annosum suffer butt, or upper bole. While infections direct mortality, butt rot (and associated resulting from wound colonization usually reduction in merchantable volume), pre- result in decay of the scarred tree, they disposition to bark beetles, and wind- rarely cause root disease since the decay is throw. Impacts are observed in both usually compartmentalized within the bole enlarging centers (fig. 9) and as isolated and the infection does not extend to the single diseased trees (fig. 10). Losses are exterior of roots where it can spread greatest in stands of pure fir or where fir between trees. basal area exceeds 26 square ft./acre (20 square m/ hectare), where total stand basal Sporidia on tree wounds or freshly cut area exceeds 100 square ft./acre (75 stump surfaces germinate, produce hyphae square m/hectare), where stand age that colonize exposed wood, and initiate exceeds 120 years, and in stands that have new infections. Spores also can percolate been partially cut. Surveys in the down through soil and infect wounded Rockies, the Northwest, and the roots. The fungus has been isolated from Southwest indicate that H. annosum is insects that feed on lower stems and roots, widespread and prevalent in true firs. but insect transmission of the pathogen has Except during droughts, activity of fir not been verified. Another spore type, the engraver beetles (Scolytus ventralis asexual conidia, is also produced, but its LeConte) is closely associated with occur- role in the life cycle is uncertain. rence of root disease in firs. Sporulation, spore germination, and Pines colonization of wounds or stumps are affected by temperature and humidity. Annosus root disease has been serious Spores are produced throughout the year, on pines in some localities and under cer- except in extreme cold, very high heat, or tain site and stand conditions. Generally,

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stands on poor, dry sites suffer the greatest than mortality in such situations. In some impacts (fig. 11). There is some indica- cases, planted pine have had high rates of tion from root excavations and stump infection. High levels of damage have investigations that infection rates are actu- occurred where off-site planting stock had ally rather high throughout the pine type 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 Fig. 9. A small annosus root disease center with several toppled grand fir. and the lower butt, though rot also may be substantial in the stems of older trees. Decay is usually associated 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 Fig. 10. A recently toppled H. annosum infected grand seldom have appreciable decay fir with extensively rotted roots showing the characteris- even if there is a high incidence of tic laminated decay. wounds associated with a history of partial cutting. While some infection occurs from stump colonization, 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.

Fig. 11. An annosus root disease center in Disturbances associated with young ponderosa pine. high use areas such as campgrounds and other recreation areas in hemlock types but mortality is manifested mainly on the will predispose trees to large amounts of poorer sites. There are indications that H. H. annosum infection. Hazard tree poten- annosum readily infects pines on better tial will likely be a major concern, espe- sites but causes mainly growth loss rather cially in older trees.

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Prevention/Control-Silvicultural can be further minimized by requiring logging techniques that minimize damage to True fir residuals during intermediate entries. Injured trees should be removed during True firs seem to be especially suscepti- entries since they are most susceptible to ble to annosus root disease as well as sev- decay. Thinning of overstocked stands eral other common root diseases and stem should not be avoided since increases in decays. In mixed-conifer stands with a growth and yield of residuals resulting substantial true fir component, partial cut- from stocking control are usually many ting should be avoided or minimized. times greater than the increased amount of When intermediate entries are done and fir decay. Managers should strive for a mix- will continue to be managed on the site, ture of other species such as Douglas-fir care needs to be taken to minimize both and western redcedar in stands where wounding of residuals and site distur- hemlocks are affected by annosus root dis- bance. ease. Reducing rotation length to less than 120 years will usually limit losses where other root diseases and stem decays are Prevention/Control-Chemical not a concern. Restricting cutting to sum- Stump infection by H. annosum can be mer months may reduce potential of stump largely prevented by treating freshly cut and wound colonization by H. annosum in stump surfaces with a light coating of some warm, dry localities. It has been granular Sodium Tetraborate Decahydrate suggested that thinning overstocked true or Disodium Octaborate Tetrahydrate. fir stands having annosus root disease will Currently, the only borate products regis- reduce disease impacts by increasing vigor tered for annosus control are Sporax® and of residuals. The success of this strategy Tim-Bor®. Properly treated stumps are has not been well supported by research. protected at an efficacy level of at least 90 percent from colonization by airborne Mixed Conifer spores of H. annosum. Currently, the In many mixed-conifer stands that have Pacific Northwest and Southwest Regions been partially cut, annosus root disease of the USDA Forest Service have provi- may have already developed to levels con- sions that can be specified in timber sale sidered excessive. Because of past cutting contracts requiring purchasers to treat practices and the absence of fire, many stumps. stands previously dominated by pine have Stump treatment with borate is current- become dominated by less fire resistant ly recommended only for those timber species, especially true firs. Where such a production sites with known annosus root trend has occurred and root disease affects disease potential where cultural control is are impacting management goals, it is rec- not viable. Such situations include treat- ommended to reverse the pine-to-fir trend. ment on dry pine sites, mixed conifer sites Regeneration-type cultural systems and where true firs will be managed in the use of prescribed fire can both be effective future, and all true fir sites. The recom- in discriminating against the shade-tolerant mended minimum stump treatment size is true firs and restoring the stand to a state 12 inches diameter for pine and true fir more similar to its historic condition. felled using chainsaws. Where mechani- Western hemlock cal shearers are used, the minimum diameter should be reduced to 8 inches. High Western hemlock stands will not devel- elevation true fir stumps should be treated op significant levels of decay unless man- down to 8 inches regardless of type of aged to ages beyond 120 years. Impacts felling.

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Stump size recommendations have var- Goheen, D.J.; Filip, G.M.; Schmitt ied in the past, especially between differ- C.L.; Gregg, T.F. 1980. Losses from ent USDA Forest Service Regions and decay in 40- 120 year old Oregon and states. However, differences in stump Washington western hemlock stands. sizes for effective treatments are not Portland, OR: USDA Forest Service, believed to be substantial between similar Forest Pest Management; Pacific stand types in different areas. Northwest Region. 19 p. Borate stump treatment is not effective Otrosina, W.J., and R.F. Scharpf (tech- on stumps of trees that are already infect- nical coordinators). 1989. Proceedings of ed. In stands with numerous already- the Symposium on Research and infected stumps, silvicultural treatments Management of Annosus Root Disease should be employed to deal with the dis- (Heterobasidion annosum) in Western ease. Where possible, stands should be North America. April 18-21, 1989; managed by conversion to full stocking of Monterey, CA: USDA Forest Service, site-adapted, less susceptible species. General Technical Report PSW-116. 117 p. Stump treatment should be standard Russel, K.W.; Thompson, J.H.; Stewart, procedure when cutting conifers in recre- J.L.; Driver, C.H. 1973. Evaluation of ation and other high-use areas. In chemicals to control infection of stumps California, treatment of all conifer stumps by Fomes annosus in precommercially in recreation areas is required. It is strong- thinned western hemlock stands. Wash. ly recommended that stumps of highly Dept. of Nat. Res. Rpt. No. 33, 17 p. susceptible species be treated in Oregon and Washington. Treatment is also recom- Schmitt, C.L.; Goheen, D.J.; Goheen, mended for pine and true fir seed orchards, E.M.; Frankel, S.J. 1984. Effects of man- progeny test plantations, and other stands agement activity and dominant species of high value trees. type on pest-caused mortality losses in true fir on the Fremont and Ochoco National Forests. Portland, OR: USDA Assistance Forest Service, Forest Pest Management, Pacific Northwest Region, 34 p. If you need assistance in recognizing and controlling annosus root disease, contact 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 natural 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.

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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.

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