Red heart rot

Written by B.E. Callan Revision 2024

• French disease name: Carie rouge du sapin
• Pathogen name: Stereum sanguinolentum (Albertini & Schwein) Fr.
• Kingdom: Fungi
• Phylum: Basidiomycota
• Class: Agaricomycetes
• Order: Russulales
• Family: Stereaceae
• Partial list of synonyms:
  • Stereum balsameum Peck

General information and importance

Stereum Sanguinolentum causes heart rot through wounds in conifers. It is particularly damaging to balsam fir (Abies balsamea). Wood with advanced decay has a distinctive red discolouration, hence the common name “red heart rot”.  When fresh, the fruiting bodies of S. sanguinolentum have a distinctive “bleeding” reaction when damaged, turning red and if sufficiently moist, exuding red liquid. Decays such as red heart rot are also important in the natural recycling of fallen wood and slash in conifer forests.

Distribution and hosts

Red heart rot is present in every forested province and territory in Canada. It is widespread in North America and found worldwide in conifer forests. In North America, the main hosts are all conifers, with the thin-barked species being most susceptible, especially true firs (Abies), spruce (Picea), and to a lesser extent pine (Pinus). Balsam fir is the most susceptible, followed by red spruce (P. rubens) in eastern Canada. In British Columbia, it causes significant damage on grand fir (Abies grandis) and amabilis fir (A. amabilis). Other conifers in Canada that are also affected include lodgepole, ponderosa, eastern white, and western white pines (respectively, Pinus contorta, P. ponderosa, P. strobus, P. monticola); white, Englemann, and Sitka spruces (respectively, Picea glauca, P. engelmanii, P. sitchensis); western redcedar (Thuja plicata); western and mountain hemlock (respectively, Tsuga heterophylla, T. mertensiana); Douglas-fir (Pseudotsuga menziesii); western larch (Larix occidentalis) and tamarack (L. laricina); and subalpine fir (A. lasiocarpa). Secondary hosts are less likely to develop extensive heart rot, and on these hosts, the fungus is associated with the decay of dead fallen trees and slash.

Non-conifers such as American beech (Fagus grandifolia), alder (Alnus), and serviceberry (Amelanchier) species have been reported as hosts in Canada. On hardwood hosts, fruiting bodies of other species—such as Chondrostereum purpureum, which has a similar appearance to S. sanguinolentum—are more likely to occur. On oaks (Quercus), the closely related S. gausapatum is common and limited to this host genus.

Host parts affected

Primarily sapwood of dead, fallen conifer trees. Occurs also on exposed dead sapwood at wound sites of living trees.

Symptoms and signs

Fruiting bodies develop on wounds on live trees, dead branches, stumps, and the underside of fallen conifer logs and slash in recently logged conifer forests, and rarely on hardwood logs. Fruiting is less common on live hosts. Fruiting bodies form a thin crust on the bark or exposed wood surface and remain flat on fallen logs and woody debris. On vertical surfaces, one edge of the fruiting body will often lift off and recurve to form a leathery, narrow, shelf-like cap, the upper surface of which is velvety and covered with fine hairs. When present, the caps are grey to pale olive brown, with fine concentric zones. The undersurface is wrinkled, grey to light brown, and does not produce pores or gills. When the fruiting bodies are fresh, they turn blood red when bruised, which is why they are commonly called “bleeding fungus”, or “bleeding conifer parchment”.

The fruiting body is made up of thin-walled yellowish to hyaline septate hyphae, and thick-walled non-septate hyphae. The basidiospores develop on the undersurface of the fruiting body, and are hyaline, cylindrical, smooth-walled, and amyloid (dark blue reaction viewed microscopically after Melzer’s iodine reagent is added). Basidiospores are either borne four to a basidium, on which they average 7 to 10 micrometres × 3.0 to 4.5 micrometres or borne two to a basidium, in which case they are larger, measuring 8 to 14 micrometres × 3 to 5 micrometres.

Stereum gausapatum (Fr.) Fr. is very similar in appearance and “bleeds”, but it has a host range limited to oaks. Chondrostereum purpureum (Pers.) Pouzar forms similar fruiting bodies on slash and wounds, but is more common on angiosperms, does not bleed, and its basidiospores are not amyloid.

The first sign of wood colonization, which occurs while the wood is still firm, is a pale yellow, then reddish-brown stain in the heartwood, which may have a water-soaked appearance. Conifer wood with advanced decay is light brown to reddish brown, soft and easily broken apart, eventually becoming stringy and fibrous. Thin white felts of mycelium may appear in shrinkage cracks of wood with advanced decay. The fungus breaks down both cellulose and lignin in the wood and is thus classified as a white rot, but the advanced stages of the decay are discoloured due to fungal pigments and decay byproducts.

Disease cycle

Spore dispersal occurs during rainy weather from early spring until late fall, ending with the onset of freezing temperatures. Basidiospores are wind-dispersed from fruiting bodies. If they land on suitable host materials such as damaged trunks and branches of trees, they germinate and colonize the exposed wood when temperatures range from 7 to 24°C. The fungus is primarily a pioneering organism and is most successful if the host surface is not already colonized by other organisms. Optimum infection occurs during prolonged (several days) periods of cool wet weather. Wounds such as those caused by logging operations, pruning scars, fire, and storm damage provide infection courts. Annual growth of the decay column varies depending on tree host and location. For the most susceptible conifers in British Columbia (true firs and spruces), the decay column progresses 12 to 13 centimetres per year. Decay columns in Norway spruce (P. abies) planted in Europe may progress as quickly as 40 centimetres per year.

Damage

Extensive heart rot reduces wood value due to stain and wood loss in mature and overmature pine, spruce, and true firs. In mature trees, broken tops and branches caused by wind and snow damage provide natural wounds where infections can be initiated in the upper canopy and trunk. Certain forestry practices that cause large wounds, such as logging scars, are most likely to result in the establishment of infections on the lower trunk and butt.

One heart rot decay study reported that cull due to trunk rot caused by S. sanguinolentum in overmature Englemann spruce averaged 80 board feet (0.189 cubic metres), and the average length of the rot column was 6.4 metres. In the same study, S. sanguinolentum was cultured from 37% of heart-rotted trunks of subalpine fir, with the average cull being 6.9 board feet (0.016 cubic metres).

Infections in young conifers can result in tree mortality. Large wounds are most likely to become infected, but even small pruning wounds that are 1 to 3 centimetres in diameter can result in severe disease. One study indicated that pruning wounds greater than 5 centimetres in diameter on eastern white pine are more prone to infection than those of smaller diameter. Infection via basal wounds has been linked to “mottled bark disease” of conifer saplings stressed by drought. The infected trees showed symptoms of resinosis at the root collar, with eventual death.

Prevention and management

Thin-barked species such as western hemlock, true firs, and spruces are more easily damaged during harvesting operations than thick-barked species such as Douglas-fir. In newly opened stands, the stems of thin-barked species are prone to sunscald and the resulting lesions provide infection courts. Thinning operations need to be conducted carefully to minimize damage to residual crop trees.

Thick-barked species such as Douglas-fir or western redcedar, which is very resistant to decay, are less susceptible to damage and subsequent infection during partial cutting and thinning operations. Wounds that occur in winter are more susceptible to becoming infected, likely due to less competition from other pioneer wound colonizers that have higher optimal growth temperatures.

Pest management strategies for a particular pest vary depending on several factors. These include:

• the population level of the pest (i.e., how numerous the pest is on the affected host[s]);
• the expected damage or other negative consequences of the pest’s activity and population level (either to the host, property, or the environment);
• an understanding of the pest’s life cycle, its various life stages, and the various natural or abiotic agents that affect population levels;
• how many individual host specimens are affected (an individual tree, small groups of trees, plantations, forests);
• the value of the host(s) versus the costs of pest management approaches; and
• consideration of the various silvicultural, mechanical, chemical, biological, and natural control approaches available and their various advantages and disadvantages.

Decisions about pest management strategies require information about each of these factors for informed decision-making. These various factors should then be weighed carefully in terms of costs and benefits before action is taken against any particular pest.

Selected references

Allen, E.A.; Morrison, D.J.; Wallis, G.W. 1996. Common tree diseases of British Columbia. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre. Victoria, British Columbia. 178 p.

Davidson, A.G.; Etheridge, D.E. 1963. Infection of balsam fir, Abies balsamea (L.) Mill., by Stereum sanguinolentum (Alb. and Schw. ex Fr.) Fr. Canadian Journal of Botany 41(6): 759–765. https://doi.org/10.1139/b63-063

Etheridge, D.E. 1969. Factors affecting infection of balsam fir (Abies balsamea) by Stereum sanguinolentum in Quebec. Canadian Journal of Botany 47(3): 457–479. https://doi.org/10.1139/b69-062

Etheridge, D.E. 1972. True heartrots of British Columbia. Canadian Forest Service, Pacific Forest Research Centre. Victoria, British Columbia. Forest Pest Leaflet No. 55. 14 p.

Filip, G.M.; Aho, P.E.; Wiitala, M.R. 1984. Strategies for reduction of decay in the Interior Douglas-fir and grand fir types. Pages 73–80 in D.M. Baumgartner and R. Mitchell (editors). Silvicultural management strategies for pests of the Interior Douglas-fir and grand fir types. Cooperative Extension, Washington State University. Pullman, Washington.

Ginns, J.H.; Lefebvre, M.N.L. 1993. Lignicolous corticioid fungi (Basidiomycota) of North America: systematics, distribution, and ecology. The Mycological Society of America Mycologia Memoir No. 19. American Phytopathological Society Press. 247 p.

Hinds, T.E. 1977. Heart rots of Engelmann spruce and subalpine fir in the central Rocky Mountains. United States Department of Agriculture, Forest Service. Forest Insect & Disease Leaflet 150. 8 p.

Hunt, R.S.; Etheridge, D.E. 1995. True heart-rots of the Pacific region. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre. Victoria, British Columbia. Forest Pest Leaflet 55, Co-published by the British Columbia Ministry of Forests.

Vasiliauskas, R.; Lygis, V.; Larsson, K.-H.; Stenlid, J. 2005. Airborne fungal colonisation of coarse woody debris in north temperate Picea abies forest: impact of season and local spatial scale. Mycological Research 109(4): 487–496. https://doi.org/10.1017/S0953756204002084

Zeglan, S. 1997. Tree wounding and partial-cut harvesting: a literature review for British Columbia. British Columbia Ministry of Forests, Forest Health, Vancouver Forest Region. Pest Management Report 14. 40 p.

Cite this fact sheet

Photos

Red heart rot visible in a cross section of balsam fir trunk.

Fruiting bodies of Stereum sanguinolentum.

CFS

Fruiting bodies of Stereum sanguinolentum.

R.B. Dickens

Fruiting bodies of Stereum sanguinolentum on balsam fir.