Brown cubical butt and pocket rot of cedar

Written by B.E. Callan Revision 2024

• French disease name: Carie brune cubique du pied et alvéolaire du thuya
• Other disease names: Pocket rot of cedar
• Pathogen name: Oligoporus sericeomollis (Romell) Bondartseva
• Kingdom: Fungi
• Phylum: Basidiomycota
• Class: Agaricomycetes
• Order: Polyporales
• Family: Dacryobolaceae

General information and importance

Oligoporus sericeomollis causes a brown cubical heart rot of conifers. The rot forms large decay columns in the butt of cedars and isolated pockets in the trunk. It is one of two species of fungi responsible for most of the decay of standing live western redcedar (Thuja plicata), following closely in second place to laminated root rot caused by Coniferiporia (formerly Phellinus) weirii. Cedar (Thuja) and cypress/yellow-cedar (Chamaecyparis) species are the only conifers that are infected and decayed while living, but the fungus is also saprophytic on many dead conifer species.

Distribution and hosts

Oligoporus sericeomollis has been reported in British Columbia, Alberta, Ontario, Quebec, and the Northwest Territories. It is endemic to North America. In western Canada, its distribution roughly follows that of its main hosts, western redcedar and yellow-cedar (Chamaecyparis nootkatensis). It has also been reported from Europe and Asia.

Mature or overmature western redcedar and yellow-cedar are the only living hosts. Oligoporus sericeomollis also decays dead trunks and slash of many conifers and occasionally is found on hardwoods in Canada. Elsewhere in North America, it has been associated with a heart rot in black cherry (Prunus serotina).

Other hosts (on dead trees only) in Canada are as follows: balsam fir (Abies balsamea), subalpine fir (A. lasiocarpa), white birch (Betula papyrifera), western larch (Larix occidentalis), Engelmann spruce (Picea engelmannii), white spruce (P. glauca), black spruce (P. mariana), red spruce (P. rubens), Sitka spruce (P. sitchensis), jack pine (Pinus banksiana), shore pine (P. contorta var. contorta), lodgepole pine (P. contorta var. latifolia), and Douglas-fir (Pseudotsuga menziesii).  

Host parts affected

The butt and trunk of conifers are affected. The fungus also grows saprophytically on woody conifer debris.

Symptoms and signs

Fruiting bodies are produced on dead logs and slash. They are not found on live trees. Fruiting bodies are annual, effuse (entirely attached to the substrate with no cap or stalk), white and poroid, with margins that are fimbriate (fringed with coarse hair-like projections). Mature fruiting bodies grow up to 15 centimetres in diameter and form a layer of tubes up to 4 millimetres deep. The pore surface is white to tan, with 4 to 6 round to angular pores per millimetre.

The hyphae in the fruiting body are from 2 to 4 millimetres in diameter with walls varying from thick to thin. The hymenium lining the tubes comprises basidia and cystidia, although cystidia are scarce in some specimens. Cystidia are ventricose (swollen in the middle and tapering at the apex), thick-walled, and occasionally encrusted at the tip with crystals, measuring 14 to 26 micrometres × 6 to 10 micrometres. Basidia are club-shaped, measuring 18 to 20 micrometres × 6 to 10 micrometres and bearing four hyaline (colourless) thin-walled basidiospores, which are oblong to narrowly ellipsoid, measuring 4 to 5 micrometres × 2.0 to 2.5 micrometres.

Oligoporus is close in appearance to Postia and has previously been treated as a synonym of this genus. However, recent studies indicate that O. sericeomollis, and a closely related European/Asian species O. rennyi (Berk. & Broome) Donk, form a separate lineage that is genetically distant from other Postia species. Morphologically, there are few consistent distinctions between the two genera, but the two Oligoporus species have thin basidiospore walls whereas Postia basidiospore walls are thick.

There are no external indicators of decay on live trees. Early (incipient) decay in wood is straw-coloured to pale yellowish-brown. Wood with advanced decay is light brown, brittle, and cracked into cubes, with thin white mycelia sometimes growing in the cracks. Decay in the butt of the tree forms a roughly cylindrical column but further up in the trunk the rot may form series of isolated pockets, eventually merging in crescents or concentric rings.

The appearance of advanced brown cubical butt rot is like that caused by Phaeolus schweinitzii, a polypore fungus that rarely infects western redcedar. However, P. schweinitzii always forms intact decay columns, tends to establish higher in the trunk, and produces fruiting bodies that are large and dark brown.

Disease cycle

Little is known about the infection biology of O. sericeomollis. It is uncertain whether wounding is a requirement for infection, although this is a common mode of infection for many decay fungi. The primary source of inoculum is thought to be the basidiospores, which are released from the pores of the fruiting bodies and carried by wind. Once established in a living cedar tree, the fungus colonizes the heartwood, and during a period of many years, forms a decay column. After the tree dies, fruiting bodies are formed on the dead wood.

Damage

There is little structural loss in cedar wood until the decay is advanced. Estimation of decay levels and wood quality in logs (scaling) is difficult because the decay is scattered in pockets in parts of the tree.

Prevention and management

Because wounds provide entry courts for many decay fungi, prevention of wounding in young stands can reduce levels of decay in the trees once they are mature. This is especially important for thin-barked trees such as cedar. Harvesting younger trees also decreases the odds of having large decay columns.

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.

Buckland, D.C. 1946. Investigations of decay in western red cedar in British Columbia. Canadian Journal of Research 24c(5): 158–181. https://doi.org/10.1139/cjr46c-018

Gilbertson, R.L.; Ryvarden, L. 1987. North American Polypores Vol. 2: Megasporoporia – Wrightoporia. Fungiflora, Oslo, Norway. 437–885 pp.

Ginns, J. 2017. Polypores of British Columbia. Province of British Columbia. Victoria, British Columbia. Technical Report 104. https://www.for.gov.bc.ca/hfd/pubs/Docs/Tr/TR104.pdf [Accessed August 2024]

Hagle, S. 2006. Management guide for cedar brown pocket rot. Publication 13.4 United States Department of Agriculture, Forest Service, Forest Health Protection and State Forestry Organizations. 3 p.

Scharpf, R.F. 1993. Diseases of Pacific coast conifers. United States Department of Agriculture, Forest Service. Washington, D.C. Agriculture Handbook 521 (revised). 199 p. https://archive.org/details/diseasesofpacifi521scha/page/n1/mode/2up [Accessed August 2024]

Shen, L.L.; Wang, M.; Zhou, J.L; Xing, J.H.; Cui, B.K.; Dai, Y.C. 2019. Taxonomy and phylogeny of Postia. Multi-gene phylogeny and taxonomy of the brown-rot fungi: Postia (Polyporales, Basidiomycota) and related genera. Persoonia 42: 101–126. https://doi.org/10.3767/persoonia.2019.42.05

Sturrock, R.N.; Braybrooks, A.V.; Reece, P.F. 2017. Decay of living western redcedar: A literature review. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre. Victoria, British Columbia. Information Report FI-X-014. 41 p.

Sturrock, R.N.; Pellow, K.W.; Hennon, P.E. 2010. Phellinus weirii and other fungi causing decay in western redcedar and yellow-cedar. Pages 47–52 in C.A. Harrington, editor.  Proceedings of a tale of two cedars—international symposium on western redcedar and yellow-cedar. 24–28 May 2010. University of Victoria, Victoria, British Columbia. United States Department of Agriculture, Forest Service, Pacific Northwest Research Station. Portland, Oregon. General Technical Report PNW-GTR-828. https://www.fs.usda.gov/pnw/pubs/pnw_gtr828.pdf [Accessed August 2024]

Zeglen, S. 1997. Tree wounding and partial-cut harvesting: A literature review for British Columbia. British Columbia Ministry of Forests, Forest Health, Vancouver Forest Region. Vancouver, British Columbia. Pest Management Report No. 14. 40 p. https://www2.gov.bc.ca/assets/gov/farming-natural-resources-and-industry/forestry/stand-tending/treewounding.pdf [Accessed August 2024]

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Photos

Resupinate sporophore of the fungus Oligoporus sericeomollis on western redcedar.

Dave Buckland

Brown cubical butt and pocket rot caused by Oligoporus sericeomollis in western redcedar.

Brown cubical butt and pocket rot caused by Oligoporus sericeomollis in western redcedar.

Brown cubical butt and pocket rot caused by Oligoporus sericeomollis in western redcedar.

Brown cubical butt and pocket rot caused by Oligoporus sericeomollis in western redcedar lumber.