Annosus Root Disease by Susan Hagle US Forest Service Heterobasidion Sp

February 2007 Forest Health Protection and State Forestry Organizations

11.2 Mangement Guide for WEB July 2010 Annosus Root Disease By Susan Hagle US Forest Service Heterobasidion sp. (fir-annosum)

Topics Hosts: In northern Rocky Mountain forests,  True firs Introduction 1 mortality is common in Douglas-fir, grand fir  Douglas-fir and subalpine fir. Butt rot commonly Taxonomy 2  Engelmann develops with infection in spruce, true firs, Incidence of fir-type 2 spruce western redcedar and western hemlock.  western Species 3 redcedar In the central Rockies, butt rot is common in susceptibility  western true firs and spruce but mortality is rare . hemlock Life History 3 Spore production 5 Ecology: infection 6 Introduction Ecology: stumps 7 Ecology: secondary 8 Annosus root disease is the northern and central Rocky spread most common and damaging Mountains, Douglas-fir, grand fir, fungus disease of conifer forests and subalpine are commonly killed Biological Control 9 in the northern hemisphere. In by the fir-disease type. Other tree Management 10 northern Idaho and western species, particularly spruces, Considerations for 11 Montana, Annosus root disease is western redcedar and western Cedar economically important in true hemlock develop extensive butt rot firs and Douglas-fir. Further south and occasionally die from Other Reading 12 in Idaho, Wyoming, Utah, and infections of fir-annosus. Field Guide Nevada, it is frequently found Ponderosa pine is the only decaying roots and butts of significant host for pine-annosus in Management Guide Index mature trees, and sometimes this area. killing small trees, but the overall Trees of all ages can die from impact is thought be minor. this disease and volume losses Annosus root disease is from butt rot are substantial in Key Points caused by several species which, some species. Establishment of  One of two until recently, have been grouped new infections through root or important species under the names Fomes annosus basal stem wounds appears to be of Heterobasidion in North America or Heterobasidion annosum. They the most common means of spread are differentiated most readily of fir-annosus.  Serious disease of based host preference. In the true firs, Douglas- fir and cedar

 Spore-initiated OVERVIEW OF infections directly FIR-ANNOSUS ROOT DISEASE MANAGEMENT or through wounds 1. Favor resistant species. Especially pines and western larch. on roots 2. Thin early and avoid partial harvests. Precommercially thin.  Usually found with Armillaria or 3. Avoid basal stem and root damage. Use care when logging. Phellinus weirii 4. Use caution when thinning western redcedar. Cedar decline may become a problem if cedar residuals are to be managed.

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About Types of The basidiomycete fungus found primarily on Picea abies Annosus Heterobasidion annosum (Fr.) (Norway spruce). Heterobasidion Bref. has been known for many abietinum Niemela & Korhonen, Similar but Genetically- years to consist of at least two is the new name suggested for Distinct Types of distinct types, based on host the pathogen of European true Annosus preferences. Molecular and genetic firs (Abies). studies of European isolates have The fir pathogen of this Heterobasidion annosum demonstrated that the former H. complex in western North America in western North America consists of two inter- annosum consists of at least three has yet to be named, and is sterile (non-interbreeding) distinct species. The pine pathogen currently referred to as the “North groups. These two types, retains the name H. annosum. The American S group” (Korhonen and 'fir' and 'pine', have very species formerly referred to as “s” others 1998). For this publication, different host specificities. type in Europe was recently named it will be referred to as ‘fir The hosts for the fir type Heterobasidion parviporum Niemela annosus’. include true firs, Douglas- & Korhonen. This species is fir, Engelmann spruce, western red cedar, and western hemlock. (See Incidence in northern Rocky Mountains Table 1 for details.) Grand fir and Douglas-fir disease-afflicted trees are probably

Ponderosa pine is the In northern Idaho and western significantly increased by bark main host for the Montana, fir-annosus is broadly beetle attacks. pine type. distributed and very common in forest types that include grand fir Subalpine fir and Douglas-fir. Armillaria ostoyae Fir-annosus is implicated in a root disease generally co-occurs widespread decline of subalpine fir with fir-annosus, making it in the northern Rocky Mountains. impossible to distinguish the Mature trees are especially individual impacts of the two damaged, with rapid death diseases. following long periods of growth Central Rocky Stands without prior harvests as decline. Western balsam bark Mountains well as harvested stands with beetle (Dryocoetes confusus), fir

1. Annosus root and sufficient host composition, have engraver beetles, and Armillaria butt decay are abundant symptoms and signs of ostoyae also are involved in the common in older annosus root disease. First-entry decline. trees, with little grand fir stumps, in particular, apparent mortality. produce abundant annosus conks, Other tree species 2. Conks are common in decayed stumps indicating pre-existing root Extensive root decay and very and dead wood. infections in a high proportion of gradual death of western redcedar 3. Small trees are trees. Northern Idaho, from St. is common on drier and partially- occasionally killed. Maries to the Salmon River, harvested cedar sites (Hagle, 4. Good data are appears to have an especially heavy unpublished data). Fir-annosus, lacking on the incidence of fir-annosus. Most the Armillaria ostoyae, and Phellinus extent or impact of annosus-related Douglas-fir weirii appear to be about equally the disease. mortality is reported from this responsible for the damage. Butt geographic area as well. rot in western redcedar, Bark beetles, especially fir Engelmann spruce and western engraver in grand fir, frequently hemlock are also very common, attack trees with fir-annosus root particularly in mature trees. disease. Mortality rates of root 11.2 Back to menu Annosus Root Disease Page 3

Table 1. Conifer species susceptibility to fir-annosum root disease in the northern and central Rocky Mountains.

Least Susceptible Highly Location Susceptible but tolerant Susceptible

Spruces, hemlocks, True firs, Douglas-fir; Northern Rockies Larch, western redcedar, butt rot is common in (Montana and Idaho north ponderosa, western white pine; butt grand fir and mortality is of the Salmon River) lodgepole, and rot and extensive root common in trees of all

whitebark pines decay may develop but sizes.

mortality rates are low.

True firs, Engelmann Unknown Central Rockies spruce; Butt rot and Extent and severity of (southern Idaho, Utah, Pines root decay, some small annosum remains Nevada, western Wyoming) pockets of mortality. unknown in many areas.

Life History Basidiospore-initiated infections of the disease from tree to tree via Trees can become infected in root contacts compared to other Genet numerous ways but it appears the important root diseases such as most common occurrence is spore Armillaria root disease and A genet is an -initiated infections in live trees laminated root rot. Most individual derived (Figure 1). Airborne basidiospores individuals, or genets, are confined from compatible land on, or are rain-washed to, a to a single tree. Occasionally spore pairing; a freshly wounded root or lower groups of several trees are infected diploid mycelium. stem. Here the spores germinate by the same genet but this appears and hyphae penetrate the wood to to be uncommon. establish either latent or active Despite minimal tree-to-tree infections. Latent infections may spread, very high rates of infection Spore-initiated remain viable for decades before are typical of true fir, western infections through resuming growth (Garbellotto and hemlock and western redcedar tree roots or basal others 1999) while active stands in the interior West. The stem wounds may infections begin expanding abundance of spores capable of account for most of immediately. The infection taking advantage of wounds and this disease. expands preferentially toward the high frequency of root and stem root collar. The pathogen grows wounding in these species nearly unhindered in root and butt apparently provide ample heartwood of true firs. In true firs opportunity for successful Mortality due to and western redcedar, particularly, establishment of new infections. Armillaria root annosus often produces large disease often cavities in roots and lower stems Abundant spore production in obscures the of trees showing little or no dead trees and stumps effects of fir- outward symptoms of disease. When infected trees die, the annosus when the two occur together fungus may continue to live for in stands. Minimal secondary spread many decades in the moist, There is relatively little spread underground portions of the tree.

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Figure 1. Life History of fir-annosus

Basidiospores are produced by basidia in the pores on the underside of conks

Spores carried by wind and rain to infect through dead, broken or wounded roots or through basal stem wounds.

Conks develop in decayed stumps and roots.

Roots are decayed and the Conidia, the tree is eventually killed. asexual spore Mycelium can spread stage, may be produced on across root contacts to infect decayed wood. other trees. Their role in the disease cycle is The fungus may live for uncertain. many decades in dead roots.

Although mycelia in stumps and Asexual spores dead trees infrequently spread to Fir-annosus conidiospores are nearby living trees, they produce commonly seen in culture and on conks that are important sources of incubated specimens of infected Sporophore spores that spread the disease. wood but are not often found in production on roots Sporophore production nature. They do not appear to and in hollow continues for many years after the produce a mycelium that is stumps continues tree has died and airborne vigorous enough to infect live for many years basidiospores can nearly always be tissue nor to compete with other after the host has found in abundance in coniferous fungi for dead wood substrates. died. forests. These spores are able to Garbelloto and others (1999) infect freshly cut stump surfaces suggested that they may play a as well as basal and root wounds sperm-like role in producing the in live trees. heterokaryotic mycelia typically found in stumps. For now, their function remains a mystery. 11.2 Back to menu Annosus Root Disease Page 5

Spore production by fir-annosum Figure 3. Sexual spores of annosus Annosus sexual sporophores, the basidia, effectively launching commonly called “conks”, are them into the air. In conifer Basidium often found inside decayed, forests, basidiospores of annosus hollowed stumps (Figure 2). Less may be found in the air whenever often, they are found on the the temperature is above freezing outside of roots of dead trees, just and the humidity is not too low. below the duff. Small, Basidiospores are washed into soil incompletely formed, sporophores and along roots by rain and may called "button conks" occasionally remain viable for a year. Annosus appear on roots of small trees is incapable of living freely in soil killed by annosus root disease. or duff so the spores must Sterigmata Annosus conks usually are germinate on a suitable substrate. perennial, sometimes annual. Clearly, few spores survive. Basidiospores They may be effused-reflexed The basidiospores are typically (shelf-like) or resupinate (crust dikaryotic, that is, they bear two like). The older layers are tough nuclei, and these nuclei are and woody but the newest pore haploid. Upon germination, layer is softer and white to cream- basidiospores produce a colored. The pore layer homokaryotic mycelium which (hymenium) wraps over the outer must mate before producing the edge of an effused-reflex conk sexual sporophores. Mating is a producing a “sterile margin” of simple matter among fungi. cream-colored tissue. This Compatible mycelia that meet, can contrasts with the dark brown or fuse and exchange nuclei. There is gray upper surface of the conk another reason for mating of two (Figure 4) making them easy to homokaryotic mycelia; spot in dark stump hollows. The heterokaryotic mycelia are more pores of the hymenium are small, vigorous than homokaryons typically 0.3-0.6 mm diameter. (Korkonen and Piri 1994), making Figure 4. Effused-reflexed them more effective pathogens. annosus conks growing inside Annosus also produces an a stump. [Photo by S. Hagle] asexual spore stage in the form of Figure 5. Asexual spores of conidia. They are borne on top of annosus; Spininger club-shaped conidiophores (Figure meinekellus 5). Both homokaryotic and heterokaryotic mycelia produce Conidia conidia so these spores can be either. The conidia-producing stage bears it’s own name, Figure 2 Annosum sporophores (conks) Spiniger meineckellus (A.J. Olson) often are produced in abundance in Stalpers. decayed stumps. This grand fir stump This spore stage is readily had 14 conks lining the perimeter of the hollow, including those in Figure 4 at produced in culture and on right. [Photo by S. Hagle] incubated specimens of infected wood. However, it is not generally They are mostly round or oval but observed outside of the laboratory. can be elongate near the margins. The role of these spores in the Basidia line the interior of the disease cycle is not known. They pores producing basidiospores on do not appear to be capable of Conidiophores short sterigmata (Figure 3). The producing infections in living spores are forcibly ejected from hosts.

Page 6 Back to menu Mangement Guide for 11.2 Ecology of fir-annosus root rot Annosus root disease is the insect vectors (Hunt and Cobb most common and damaging 1982) High rates of fir- fungus disease of conifer forests annosum infection in the northern hemisphere. It has Primary spread are typical of mature been studied extensively in Fir-annosus, at least in western true fir, western hemlock, and Europe, especially Sweden, North America, appears to rely western redcedar Finland, Great Britain, and more on spore-initiated infection stands in the interior France, as well as in North directly in live hosts, than on West. America. Only recently, stump-to-tree or root-to-root technology has provided the spread (Otrosina and Cobb 1989, means to separate the species that Garbelloto and others 1993). have been known under the name Several studies have reported fir Heterobasidion annosum. annosus genets to be numerous Therefore, most of the literature and of limited size Lockman 1993, refers to the species complex as H. Garbelloto and others 1997, 1999. Fir-annosus annosum. The following summary Garbelloto and others (1999) infection applies to the ecology of fir studied genet distribution in white in the northern annosus. fir stands in California. They Rockies: found that genets of fir-annosus Modes of spread tended to be small, often infecting  High rates of Annosus root disease can a single tree or even a single root. infection are typical of mature grand fir, spread in several ways. “Primary Multiple homokaryotic infections subalpine fir, and spread” is due to airborne spores are commonly seen in live trees, western redcedar. produced by a fruiting body or indicating there are abundant “conk” (Hodges 1969, Hsiang et opportunities for basidiospore  Despite high al. 1989). When spores land on a infections to establish. infection rates, mortality rates newly cut stump or fresh basal Wounds on the basal stem and usually are low and root wounds they may on roots appear to be likely entry except where germinate and colonize the wood, points for basidiospore infections, Armillaria ostoyae is present as well. if conditions are favorable. but there is considerable “Secondary spread” results from uncertainty regarding the modes  Butt rot is very growth of the mycelium along of establishment of fir- annosus in common in grand fir host roots. From a diseased tree live trees and other substrates. and western annosus can spread to a Small root wounds from insect redcedar. neighboring tree by ectomycelium and rodent feeding, and superficial  Most infections in growing across root contacts, or wounds resulting from surface live trees probably internally by endomycelium fires and rock abrasion may originate from expanding through root grafts. provide entry courts. Garbelloto basidiospores but the mechanism of Fine roots can be infected by and others (1999) postulated that a infection is poorly mycelium from woody inoculum period of latent infection may understood. or by germinating spores. Dead occur based on isolations of roots are less likely to be avenues pathogen from asymptomatic  Root-to-root spread between trees is of infection because annosus is a sapwood and roots. Wounding or minimal. poor competitor with saprophytic a period of drought stress may fungi that inhabit dead roots trigger growth of the fungus from (Stenlid and Redfern 1998). latent infections. Annosus is not known to have 11.2 Back to menu Annosus Root Disease Page 7

Origins of stump infections Lockman (1993) found only Filip and others (1992) found 19% H. annosum infection in that infection of fresh stump stumps of clearcut-harvested Role of stumps: surfaces probably plays an stands in northern Idaho. The insignificant role in initiating stumps were mostly Douglas-fir  Most fir-annosus in infections in stands in eastern and grand fir that had been stumps was present Oregon. High rates (89%) of harvested several decades earlier. in the roots of the stump infection in true fir stumps Subsequent, naturally regenerated, tree prior to cutting. were measured following clearcut 10-30 year-old Douglas-fir and  Neither harvest harvesting but most were thought grand fir trees had a 1.7% rate of season nor stump to have originated from mycelia infection. This was lower than the size appear to already present in the trees before 2.6% infection in paired stands on influence frequency of stump infection harvest. This observation is never-harvested sites. Douglas-fir consistent with that of Garbelloto and grand fir were about equally  This fungus rarely and others (1999) who also infected. Like Filip and others transfers from concluded that most trees already (2000) Lockman commonly found infected stumps to kill young trees. had root infections before tree both fir-annosus and Armillaria harvest activity occurred. ostoyae in symptomatic roots.  Stumps and dead Additionally, neither harvest Similarly, Slaughter and trees are sites for season nor stump size appear to others (1991), found no significant mycelium mating and sporophore influence frequency of stump mortality in trees surrounding production. infection. (Filip and others 1992). infected fir stumps in California Lockman (1993), studying fir- up to 6 years after harvest. This annosus in northern Idaho, found lack of spread of annosus from a possible increase in diversity of stumps may be partly due to loss annousm from clearcut compared of viable mycelia in stumps within to uncut stands, using vegetative a short time. Morrison and compatibility testing. Basidiospore Johnson (1978) reported a steep infection of stumps could account decline in stump infection rates of for such an increase. She also coastal Douglas-fir and western H. annosum found that at least 70% of the hemlock. Initially 82% of is a poor genets were limited to a single tree Douglas-fir stumps and 62% of competitor with or stump, leading her to conclude western hemlock stumps were saprophytic that most infections are spore- infected, but within five years fungi that initiated and had not spread to those rates dropped to 5% and inhabit dead other trees or stumps. 7.5%, respectively. wood. Small genets in live trees have Mycelium spread from stumps is consistently been found to be uncommon unrelated to stump infections Despite high rates of infection (Filip and others 1992, Lockman in fir stumps (89%), Filip and 1993, Sullivan and others 2001, others (2000) reported finding Garbelloto and others 1999). In very low rates of infection of trees the latter study, infected trees regenerated near stumps. Less than generally were not near stumps 0.5% of young fir trees growing and isolates from stumps were near stumps died of annosus heterokaryotic, while infections in infection in the ensuing 15-19 live trees were homokaryotic. It is, years. If primary spread had therefore, unlikely that the live- occurred, it had caused little tree infections originated from mortality. stumps.

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The fact that live-tree infections Armillaria ostoyae genets. The were homokaryotic probably largest published H. annosum Airborne basidiospores indicates that they were genet was about 50 m. (Korhonen are abundant most basidiospore-originated. Lockman and Stenlid 1998) Assuming an times of the year, and (1993) reported finding the same average radial growth of the individual spores may genet in a tree and nearby stump fungus to be 20cm per year, the survive a year or more in bark crevices. only once in 53 isolates. age would be not much more than 100 years. These factors allow Mycelium mating and sporulation annosus basidiospores in stumps and dead trees Tree-to-tree transmission to take advantage of most of the wounds The significance of stumps and Secondary spread between live that occur throughout dead trees appears to be that they trees also appears to be minimal. the life of a tree. provide a substrate for mating of Lockman (1993) found genets to homokaryotic mycelia. The be mostly confined to single trees. homokaryons originate either from At least 70% of genets in stands basidiospore infection of the live included in her northern Idaho tree (before it was cut or otherwise study were limited to a single tree killed) or spore infection of stump or stump. She concluded that most surfaces. The resulting infections are spore-initiated. heterokayons produce sporophores However, in at least one case, the (conks) in the stumps or dead genet had clearly spread to several trees. This process plays a adjacent trees producing a significant role in increasing mortality cluster in a stand Fir-Annosus spore-loading on a site. In order otherwise apparently unaffected Rate of Spread for the fungus to take advantage of by the disease. Four mature grand

Longitudinally in roots: wounds as they occur in live trees, fir and Douglas-fir trees were an abundance of spores must be symptomatic or dead and a single Average — present continuously. Therefore, genet of H. annosum was isolated 23-58cm even without direct spread of from them. These trees were (9-23 in.) per year mycelium, stumps and dead trees growing close together and thus probably play a important role in tree-to-tree transmission was True fir in California increase of the disease in stands. suspected. In both cases the trees (Garbelloto and others Basidiospores are wind bearing isolates of the same genet 1997) transported and capable of were less than 7 m (23 ft) apart. establishing mycelium in live and Garbelloto and others (1999) dead host tissues. Stump surfaces also found that nearly all genets are only infected when they are (86%) occupied only one tree in fresh (Morrison and Redfern 1994, white fir stands in California. Morrison and others 1986), before Multiple-tree genets colonized up competing saprophytic fungi have to 11 trees, and extended up to 10 become established. m diameter. Despite the low Heterobasidion annosum is a poor frequency of secondary spread, Site Factor competitor. the few genets that had spread to multiple trees accounted for 33% Acidic soils inhibit Secondary spread of the infected basal area. All ectotrophic mycelium There is no evidence that H. inter-tree spread was via root development— growth is slower without annosum can achieve the contacts or grafts by endotrophic ectotrophic growth tremendous sizes and ages that mycelium. (Ectotrophic mycelium result from secondary spread in was not observed.) 11.2 Back to menu Annosus Root Disease Page 9

Although wounding appears These diseases occur on the same necessary for infection by spores, sites with fir-annosus and, Clustered mortality is penetration of intact bark by commonly, in the same tree. The characteristic of fir- annosus infected mycelium is common in the case relative ease of diagnosis of stands even though of spread from root contacts. Armillaria root disease also studies indicate that probably results in under- most trees are Mortality is clustered in stands diagnosis of annosus root disease. independently infected by basidiospores rather Garbelloto and others (1999) Armillaria ostoyae root than by mycelium noted that, although the trees were disease, in particular, could be the spreading from not infected by the same genet, cause of clustered mortality adjacent trees or mortality tended to be clustered in without regard to annosus genet stumps. stands. Clusters of mortality distribution. Additionally, fir typically had several genotypes of engraver and the western balsam fir-annosus. Similar clustering of bark beetle are known to frequent mortality is often observed in the trees with annosus root disease northern and central Rockies. (Hertert and others 1975, Lane Several factors may be involved in 1976, Ferrell and Parmeter 1989). producing this mortality pattern. These beetles commonly cause Study of fir-annosus is often clustered mortality as bark beetle confounded by the close- pheromones aggregate attacking association of Armillaria root beetles. disease and laminated root rot. Biological Control Many naturally-occurring Another fungus that is saprophytic fungi invade conifer occasionally seen fruiting in the Figure 6. Saprophytic fungi such as Antrodia stumps shortly after tree harvest northern Rockies, Phlebiopsis heteromorpha (shown on a or thinning. These organisms have gigantea (Fr.) Jül, has been Douglas-fir stump above and below) quickly establish on the potential to limit the developed as a biological control stumps and dead trees and development of root disease fungi. for European species of effectively exclude root Among the most common fungi Heterobasidion. Spores of this pathogens from the resource. They probably play an seen fruiting on stumps in the decay fungus are commercially important role in limiting the northern rockies are Fomitopsis available as Rotstop ® for buildup of root diseases on harvested sites. (Photos by pinicola (Swartz:Fr.)Karst., inoculation of fresh stump S. Hagle) Trichaptum abietinum (Dicks.:Fr.) surfaces (Nicolotti and Gonthier Ryv., and Gloeophyllum 2005). The current state of our sepiarium (Fr.) Karst. and knowledge of fir-annosus suggests Antrodia heteromorpha (Fr.) that this or other direct methods to Donk. In addition, several are prevent stump infections are not routinely isolated from dead roots warranted because 1) most stump of trees, in particular infections arise from pre-existing Perenniporia subacida (Pk.) root lesions rather than stump Donk, F. pinicola, Resinicium surfaces and 2) fungus does not bicolor (Alb.& Schw. ex Fr.) appear to spread aggressively from Parm. and T. abietinum. These stumps. However, the spore- fungi are probably natural producing role of stump-inhabiting controls for this and other root mycelia could be important in diseases by competing for woody maintaining the disease. substrates.

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Management of fir-type annosus

MANAGING Silvicultural Management possibly also by reducing the FIR-ANNOSUS Altering species composition impacts of drought. Care should to increase the proportion of root be taken to avoid over-thinning Resistant species disease resistant species, avoiding western redcedar which also Conversion to disease tree wounding during thinning, seems to stress the trees and resistant species is and reducing tree density at an possibly cause increased infection usually the most practical early age to minimize drought by annosus and expansion of method to control effects are recommended measures existing infections. damage. to manage fir-annosus impacts.

Thin early Also an important consideration Avoid partial harvests that leave Density may promote for management is the fact that susceptible residuals mycelial spread tree-to- other root pathogens and bark This is recommended for all of tree and may increase beetles usually co-occur with fir the major fir root diseases. effects of drought stress annosus. Although this method may not including more rapid increase mortality rates, it is extension of annosus root Alter stand composition— unlikely to decrease them and lesions and attack by bark beetles. manage for resistant species often renders the residual stand Pines and western larch are not less manageable because the Avoid partial harvests significantly damaged by fir continuing mortality in the Partial commercial annosus. They provide the most residual susceptible trees leaves harvests that leave a practical means to minimize root little commercial value to finance large composition of disease impacts. True firs and site preparation and artificial susceptible species may Douglas-fir are the species most regeneration. Natural regeneration produce the undesirable outcome of losing most of likely to be killed by fir-annosus, is generally heavy to susceptible the remaining trees while growth loss and slow species and therefore unlikely to within a few years. decline is typical of annosus improve the overall condition. infected western redcedar. Avoid wounding Regeneration harvest, planting, Avoid wounding trees Wounds may establish and stand-tending to maintain Wounds may also be new infections and pines and larch are efficient means significant in fir-annosus stimulate growth of existing lesions. of managing fir-annosus and other development in susceptible stands. fir root diseases. In addition to mechanical wounds, Use particular care it is likely that infection also with cedar Thin early occurs directly though root bark or Western redcedar often Density may affect tree-to-tree through minor wounds caused by goes into a long-term spread of fir-annosus root disease, insect and rodent feeding. In any decline after thinning, perhaps more than the other root case, prevention of wounding is due to rot diseases. pathogens. Early thinning may always a good practice also help alleviate some of the management practice. effects of drought. If, in fact, latent infections do establish in fir, and if About those stumps... these infections are stimulated by Harvest of grand fir stands, in factors such as drought, preventing particular, often reveals high rates over-crowding may forestall the of pre-existing butt rot from lethal effects of annosus. Thinning annosus. Even at the time of the is also thought to reduce the first harvest entry the rates of butt impacts of fir engraver beetles, rot often are very high, indicating 11.2 Back to menu Annosus Root Disease Page 11 that a history of harvest is not increase. Evidence appears strong necessary to incite high infection that stump-infesting mycelia do rates. However, studies in eastern not commonly expand to infect Oregon indicated that incidence of live trees. At this time, it appears annosus root disease in true firs efforts to directly control infection increased with each stand entry. in fir stumps are unlikely to Wounding associated with logging produce much improvement. may account for most of this Special considerations for cedar

Western redcedar can be years after thinning (Koenigs considerably damaged by fir 1969). annosus although it is Recent excavations on the considered a moderately Clearwater National Forest in resistant species. In fact, on north Idaho revealed that at least some sites cedar has a high rate 80% of the lateral roots of of root decay and butt rot caused western redcedar (trees at least 5 by fir-annosus, especially in inches dbh) were infected by fir residual cedar after a partial annosus, Armillaria ostoyae or harvest. Several other root Phellinus weirii whether stands pathogens are involved and had been disturbed by harvest or although mortality rates are low, not. However, extent of root and Figure 7. Crown thinning, growth decline and loss of basal stem girdle was chlorosis and poor growth crown vigor is often dramatic significantly greater on sites with are typical symptoms of cedar (Hagle, unpublished data). evidence of harvest activity decline. Koenigs (1969) reported several years prior (average 63% severe root infection of western compared to 21%). Also, the redcedar by 20 years after cause of root decay and basal thinning in Priest River stem girdle was more often Experimental Forest in northern Armillaria ostoyae or fir-annosus Idaho. Armillaria (probably on harvested sites, and more ostoyae), Corticium galactinum, often Phellinus weirii on 80 Phellinus weirii and H. annosum unharvested sites. 70

(probably fir-annosus) were The amount of root girdle 60 found in decayed roots. Roughly near the root collar correlates 50 90% of the basal area had been with decline symptoms (Figure removed from 80-yr old stands 7) in the crowns of mature cedar. 40 leaving only western redcedar. Although mortality rates are low, 30 The released cedar were young, decline rates indicate substantial 20 understory trees; 20 years after cumulative effect of these 10 thinning they averaged 4.4 to infections. girdle percent disease Root 0 5.5. inches dbh. Both thinned Although research on this 0 102030405060 and unthinned stands had high continues, it is clear that annosus Cedar decline; percent rates of root infection (94% and and other root diseases cause crown loss 67%, respectively) but the rate significant damage in cedar of basal cankering was much stands and that severe thinning Figure 8. Relationship between root collar girdling higher in thinned stands (75% that leaves residual western by basal cankers caused by compared to 27%). These cedar redcedar promotes development root disease and visible crown also exhibited chlorosis, basal of long-term, root-disease loss in western redcedar at resinosus and growth decline 20 caused, decline. least 5 inches dbh.

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