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Fungi

Occurrence
A basidiomycetes that is common and widely distributed in Europe; in this country
frequently attacking Ash (Fraxinus excelsior). It is also commonly found on apple,
walnut and London plane. A.D.C. Le Sueur writing in 1934 described the fungi as
chiefly attacking ash and plane, being of a reddish colour and hairy. Schwarze in 2000
described it as attacking also the pagoda tree and more rarely elm, sycamore and lime.
Fruiting Body

Inonotus hispidus
Inonotus hispidus fruiting body relatively fresh
The fruiting body (Sporophore) appearing annually usually in July to September is
shaped either like a hoof or a short, thick, broad bracket 10-30 cms across with a
shaggy upper surface and a thick spongy fibrous flesh. The brackets have a slightly
wavy to lumpy upper side that is initially covered in a felt. At first it is a rusty reddish
yellow, when mature an iron rust colour, and when finally old and dead it becomes
practically black. The fruiting bodies which develop on the tree while it is alive
usually appear at the point of infection.
Old fruiting body in winterColonisation Strategy
Infection occurs at a branch stub or pruning wound, the fungi moving from exposed
sapwood into the centre of the tree where the rot spreads up and down the heartwood.
The infection is often accompanied by bark necrosis and large ribs of wound wood
may form along the walls of the bark necrosis on many species e.g. London plane.
Rot Type
In the first stages of attack there are always whitish or yellowish “flames” of
discolouration that appear in the wood which are limited by a brown zone. It was
shown as early as 1931 by W.G. Campbell in his book The Chemistry of White Rots
that the rot is a white-rot type in which both lignin and cellulose are attacked.
Mechanical tests by K. Cartwright et al. (1936) on small examples of wood exposed
to infection proved that the toughness of the wood is quickly affected, being reduced
by 27% after two weeks exposure. The bending strength of the infected test pieces
decreased at a much slower rate than the toughness, only a 14.3% reduction after
twelve weeks exposure.
D. Lonsdale in 1999 initially describes the rot type as a simultaneous white-rot
destroying both lignin and cellulose at roughly equal rates resulting in a fairly brittle
fracture – this description may be particularly linked to ash. He acknowledges that the
type of decay may vary depending on the host being invaded and may in some species
cause a soft-rot pattern.
Lonsdale and F. Schwarze have identified that in London plane the xylem rays are
largely preserved (due to heavy lignifications) whereas, in ash the xylem rays are
obviously degraded. This indicates that there is a clear difference with I. hispidus in
terms of wood degradation and the host specific response. Also Schwarze has
demonstrated that the fungi can cause soft rot in London plane, an unusual rot as it is
normally exclusively the Ascomycetes and Fungi Imperfecti that cause soft rots.
Arboricultural Significance
The fungus is probably the most important cause of decay in standing ash trees and
causes much damage, especially to hedgerow and isolated trees that have lost
branches. My experience in Leicestershire (an ‘ash’ county) is that, considerable
numbers of ash trees located on the boundaries of agricultural holdings are infected
and this is probably due to the removal of branches (not always to arboricultural
standards) by farmers to allow access with agricultural machinery.
Since the ash is used largely for purposes where high strength and great toughness are
required, such as in sports goods, any reduction strength is serious. Any timber
showing even the slightest signs of decay should be rejected for use.
Due to the clear difference between how the wood of ash is degraded to that of
London plane, I. hispidus must be classed as much more dangerous when found on
ash than on London plane. Failure of limbs and trunks of ash and walnut is likely tooccur, in London plane the extent and strength of the remaining sound wood may
need to be assessed.
There are no appropriate control measures for the fungal decay organism therefore,
prevention of the infection by resisting the need to prune trees is required and where
this happens that the cuts are made in accordance with current best practices.
Dave Dowson Tree Life AC Ltd
Bibliography
Le Sueur, A.D.C., The Care and Repair of Ornamental Trees. London Country Life
Limited. 1934.
Cartwright, K. ST. G., and Findlay, W. P. K. Decay of Timber and its Prevention.
London: His Majesty’s Stationary Office 1946.
Lonsdale, D. Principles of Tree Hazard Assessment and Management. Forestry
Commission. London: The Stationary Office 1999.
Mattheck, C., and Weber, K. Manual of Wood Decays in Trees. Arboricultural
Association 2003.
Schwarze, F. W. M. R., Engels, J., and Mattheck, C. Fungal Strategies of Wood

Decay in Trees. Springer 2000.