Fungus spotlight: Phaeolus schweinitzii

Common hosts: Conifers such as Larix spp., Picea spp., Pinus spp., and Pseudotsuga menziesii (Dewey et al., 1984; Levy, 1982; Lonsdale, 1999; Schwarze, 2008; Watson & Green, 2011) are frequent hosts, though it may also infect broadleaved species such as Prunus spp. and Quercus spp. (Schmidt, 2006).

A slightly-less-than-fresh set of sporophores upon the stem wound of a pine (Pinus sp.)

Colonisation strategy: Heart rot strategist. If damage is present on the stem, entry can be achieved via the wounds (Lonsdale, 1999; Watson & Green, 2011). Alternatively, entry can be through the root system (Schwarze et al., 2000; Watson, 2006), where it usually follows Armillaria spp. (Starr, 2013; Watson & Green, 2011). Very commonly found in coniferous forest located on formerly hardwood forest soils (Schmidt, 2006).

Rot type: Cubical brown rot (Lonsdale, 1999; Schwarze et al., 2000; Watson & Green, 2011) with discernible mycelial sheets (Rayner & Boddy, 1988).

A look at the underside of the sporophores shown above.

Significance: A loss of tensile strength triggers brittle fracture. As decay progresses, fracturing under wind loading becomes an increasing possibility at the base of the stem or in the root plate (Blakeslee & Oak, 1980; Lonsdale, 1999; Watson & Green, 2011). Decayed zones are viewed like a cavity, given how P. schweinitzii decay brings about the same properties as a hollow would (Lonsdale, 1999). A driver of standing timber damage in coniferous forests (Levy, 1982).

A very degraded bunch of sporophores at the base of a storm-damaged douglas fir.

Location of decay: Decay usually occurs around the base of the stem and within the root system (Dewey et al., 1984; Schwarze et al., 2000; Watson & Green, 2011), though decay columns can reach as high as 6-8m (Lonsdale, 1999).

Methods for prevention: Limit heartwood exposure where possible when pruning. If decay has established significantly, it may be worth felling depending on location. However, as its presence is rare on amenity trees (Lonsdale, 1999), such a responsive step is likely to be rare. The avoidance of planting susceptible species (Larix spp., Picea spp., Pinus spp., and Pseudotsuga menziesii) to the fungus is recommended in sites where risk of infection is likely (Dewey et al., 1984; Starr, 2013), if this is practicable.

A cross-section of a ‘spent’ bracket, showing the tube layer.

Sources:

Blakeslee, G. & Oak, S. (1980) Residual naval stores stumps as reservoirs of inoculum for infection of slash pines by Phaeolus schweinitzii. Plant Disease. 64 (2). p167.

Dewey, F., Barrett, D., Vose, I., & Lamb, C. (1984) Immunofluorescence microscopy for the detection and identification of propagules of Phaeolus schweinitzii in infested soil. Phytopathology. 74 (3). p291-296.

Levy, J. (1982) The place of basidiomycetes in the decay of wood in contact with the ground. In Frankland, J, Hedger, J, & Swift, M. (eds.) Decomposer basidiomycetes: their biology and ecology. UK: Cambridge University Press.

Lonsdale, D. (1999) Principles of Tree Hazard Assessment and Management (Research for Amenity Trees 7). London: HMSO.

Rayner, A. & Boddy, L. (1988) Fungal Decomposition of Wood: It’s Ecology and Biology. UK: John Wiley & Sons.

Schmidt, O. (2006) Wood and Tree Fungi: Biology, Damage, Protection, and Use. Germany: Springer.

Schwarze, F. (2008) Diagnosis and Prognosis of the Development of Wood Decay in Urban Trees. Australia: ENSPEC.

Schwarze, F., Engels, J., & Mattheck, C. (2000) Fungal Strategies of Wood Decay in Trees. UK: Springer.

Starr, C. (2013) Woodland Management: A Practical Guide. 2nd ed. India: The Crowood Press.

Watson, B. (2006) Trees – Their Use, Management, Cultivation, and Biology. India: The Crowood Press.

Watson, G. & Green, T (2011) Fungi on Trees: An Arborist’s Field Guide. UK: The Arboricultural Association.