Typically identified on rosaceous species – particularly Prunus cerasifera, Prunus domestica, and Prunus spinosa (Lonsdale, 1999; Rayner & Boddy, 1988; Watson & Green, 2011), but it can also can occur on Corylus spp. (Mattheck et al., 2015). This fungus is particularly common in neglected and old orchards (Cartwright & Findlay, 1958; Watson & Green, 2011), or on Prunus spp. that have been aggressively pruned.
The entry of spores is typically via large pruning wounds or limb fractures that have resulted in exposed heartwood (Cartwright & Findlay, 1958; Lonsdale, 1999; Stokland et al., 2012). In this sense, decay is normally found along the main stem and principal branches (Lonsdale, 1999; Watson & Green, 2011), and particularly around the wounded sites (Cartwright & Findlay, 1958).
As colonisation occurs, the extent of decay can be observed via a demarcation line, purple-brown in colour, that is laid down by the sapwood is response to decay. This line gradually extends outwards, as the decay propagates radially (Cartwright & Findlay, 1958; Lonsdale, 1999). Evidence suggests that during the initial stages of decay a soft rot can be observed (Lonsdale, 1999), though once decay progresses a crumbly and simultaneous white rot manifests (Cartwright & Findlay, 1958; Lonsdale, 1999; Mattheck et al., 2015; Watson & Green, 2011).
Because decay advances through the heartwood and eventually into the sapwood, extensive cross sections of wood may become brittle in time (Mattheck et al., 2015) and subsequently fracture (Lonsdale, 1999; Watson & Green, 2011). Wood, because of the modes of decay that can be observed, only becomes soft at very late stages of decay (Mattheck et al., 2015). In old orchards, the presence of Phellinus pomaceus can be particularly significant as it is potentially difficult to detect decay, once a specimen is infected (Cartwright & Findlay, 1958).
In this sense, in order to reduce the onset of decay, the pruning wounds of susceptible species should be as small as possible (Cartwright & Findlay, 1958). Where a branch has failed in wind loading conditions, it should be cut cleanly as not to expose an unecessary amount of heartwood surface (Cartwright & Findlay, 1958). In instances of anticpated advanced decay, wood properties should be determined (Mattheck et al., 2015), if there is a target zone within falling distance of the tree.
References
Cartwright, K. & Findlay, W. (1958) Decay of Timber and its Prevention. 2nd ed. London: HMSO.
Lonsdale, D. (1999) Principles of Tree Hazard Assessment and Management (Research for Amenity Trees 7). London: HMSO.
Mattheck C., Bethge, K., & Weber, K. (2015) The Body Language of Trees: Encyclopedia of Visual Tree Assessment. Germany: Karlsruhe Institute of Technology.
Rayner, A. & Boddy, L. (1988) Fungal Decomposition of Wood: It’s Ecology and Biology. UK: John Wiley & Sons.
Stokland, J., Siitonen, J., & Jonsson, B. (eds.) (2012) Biodiversity in Dead Wood. USA: Cambridge University Press.
Watson, G. & Green, T (2011) Fungi on Trees: An Arborist’s Field Guide. UK: The Arboricultural Association.
Arboriculture 
This is becoming a very useful resource.
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