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Principal Wood-Rotting Fungi on Standing Trees:
Root and/or butt-rotters: Ganoderma adspersum/aplannatum

Most of the fungi that can be included in this particular section are of the bracket and gill variety. They all instigate wood decay to a greater or lesser extent with or without bark killing.

Symptoms and Diagnosis

  • The crown of the tree is thin (i.e. less dense than to be expected for the species). The leaves are generally small and pale; a scattering of dead twigs and branches may be present; or
  • The tree has flushed much later and more feebly then usual, or in autumn has shed its leaves much earlier than usual; or
  • The tree is dead, almost dead or has suffered progressive die back throughout the established canopy or has fallen over; or
  • Fruit bodies of a known root and butt-rotting species are growing from the base of the trunk, from buttress roots or from the ground over the roots.


Parts of the stem base below (and perhaps also above) ground level and/or some major roots are found to be dead and either decayed or the bark permeated by or overlying mycelium.

Additional Indicators

The growth rate of the tree (shoot extension, annual ring widths) has markedly fallen off over the past few years; adjacent trees also show or have shown such symptoms.


Similar crown symptoms result from the death or malfunction of roots from whatever cause e.g. Phytophthora root disease, poisoning, flooding, soil compaction, abiotic interference (machinery, man, animals etc). Some harmless fungi produce fruit bodies resembling those of damaging species.


This type of disease is common and widespread, though some of the causal fungi are not.



Among the most damaging of diseases, particularly in older trees: crown deterioration spoils the tree’s appearance and screening capabilities; decay may render the tree unsafe; ultimately the tree may blow over or die.

Host Trees

It is doubtful if any species is immune from attack by every one of our many root and butt rotting fungi but some are particularly prone to such disease, Fagus sylvatica (Beech) among them.

Infection & Development

Of the many root and butt rotting fungi in this country, the infection biologies of only the Armillaria species (Honey fungus), Phaeolus schweinitzii and Hetero-basidion annosum are fully understood.
It is probable that most of the remainder infect tree roots by means of air-borne spores washed into the soils. The spores are produced in fruit bodies, which arise either directly from the stem base or from exposed roots (e.g. the deadly Ustulina deusta), or grow out of the ground over infected roots, attached to them by mycelial strands. It is also likely that some species can spread to neighbouring trees by growing out of an infected root into a contiguous root of the healthy susceptible tree.
After infecting the root, the fungus grows through it, both killing and later decaying it. Depending on the species, this killing may extend above ground into the basal stem bark, but often the fungus above ground is confined to the heartwood. Some species affect few roots but cause extensive decay in the butt, and some extend far up the main stem to cause fatal, structural rot. The rate of spread and therefore of root death and decay will depend on the species of fungus and host (tree), the tree’s vigour and environmental conditions. The tree may survive for many years without obvious distress but eventually crown symptoms will begin to appear. This occurs when root killing has finally outpaced regeneration and the reduced root system can no longer supply the demands of the fully foliated crown. This point may be reached gradually or suddenly, for example in a period of drought, and the progression of symptoms may be correspondingly slow or fast.
Sometimes, as a result of the root killing and decay combined with such factors as wind, tree crown weight and soil type, the root anchorage fails, and the tree falls over; or the decay in the butt may be so extensive that the stem snaps.
After the death or fall of the tree, the fungus is likely to persist saprophytically (existing by extracting moisture out of the air without obvious ground anchorage e.g. orchids) in the stump for years, dying only when all the nutrients are exhausted and the wood thus destroyed.
Some of the root and butt rotting fungi also infect above ground wounds to cause branch and top rots. Occasionally such infections spread downwards into the stump and roots.


Where tree safety is the prime consideration: Tree hazard assessment, the detection of decay and available control measures are to be implemented by arboricultural professionals/consultants.
Legal Liability: ‘In law, where a tree shows direct external evidence of decay, its owner is normally liable for any damage it causes if it breaks or falls. The situation regarding indirect evidence of decay is less certain…The courts have accepted the principle that people with responsibility for trees, whether owners, tenants or agents, should inspect their trees at regular intervals. Where, on such an inspection, symptoms of ill health or unusual growth are observed, expert advice should be sought. Failure to obtain or act upon such advice could lead to allegations of negligence.’ (Young, revised Lonsdale, 1984, p.3.).
Inspections should be made annually, preferably on clear days in September or early October when ephemeral sporophores are usually well developed, and when the crown symptoms of extensive root decay are likely to be so far advanced that they contrast sharply with the dense green foliage of healthy crowns. Binoculars are essential for the adequate inspection of the upper part of large trees…The following points MUST be taken into consideration in order to fully assess al potential risks and subsequent action/control:

  • Is the tree dangerous? Failure risk assessments taking into account structural anomalies; tight forks, included bark, species and typical behaviour. In this way it is essential to have a sound working species-specific knowledge. To what degree the integrity of a decayed tree is compromised depends on the extent of decay, its severity, its location within the tree, the amount of sound wood that remains to support the tree, and the configuration of the tree in relation to the decayed part.
  • Consequential damage assessment: Having judged the tree’s chances of failure it is necessary to judge the degree of damage should it fall. This depends on the size and dimension, what it might hit and in particular whether it might injure people.
  • Danger Assessment: Taking both the failure risk and damage assessment into consideration the degree of danger posed by the tree (its hazard rating) can be judged
  • Hazard Reduction: The outcome of an infection depends not only on the activity of the fungus but also on the behaviour of the tree; in response to wounding and infection the tree musters physical and chemical defences which limit the extent of fungal decay. Thus, decay which, has entered through aerial wounds is usually confined to the wood present at the time of wounding. The spread of decay will slow down or cease once the wound has occluded. Furthermore, the tree is laying down new wood each year which, if the decay process has ceased, slowly begins to compensate for the strength lost to decay, or if continuous, may counterbalance the ill effects.
  • Remedial Measures: Dangerous trees can be felled; dangerous branches can be removed, though new wounds created in so doing are themselves liable to decay in time.
  • Where a decayed tree is judged to require remedial action short of felling, cable-bracing, propping, crown thinning or reduction may be sufficient to lessen the risk of failure appreciably, at least temporarily.
  • As an alternative or in addition to pruning or removing trees, consideration should be given to relocating structures or facilities at risk of damage, and to discourage the public from frequenting the vicinity of potentially dangerous trees.
  • N.B. An attempt to arrest decay by excavating the rotten and infected wood may injure the defensive barriers around the infection and lead to even more extensive decay.

Preventing Decay:

  • Roots killed by other diseases or environmental conditions (waterlogging, compaction) and wounds to the underground parts (e.g. from trenching, foundations) are liable to infection from wood-rotting fungi, so such injuries should be avoided. However, some root-infecting, wood-rotting fungi spread vegetatively from neighbouring infected trees or stumps and can then penetrate live, uninjured roots. These can only be guarded against when they are known to be present and only then in certain circumstances.
  • Many decay fungi enter the tree when airborne spores germinate on stem or branch wood exposed by injuries to the bark. These should therefore be avoided as much as possible. Injuries, which, expose the end grain (e.g. pruning cuts), are particularly vulnerable.
  • If pruning is unavoidable, it must not involve injury to the ‘branch bark ridge’ or the ‘branch collar’, if present. Broken and dead branches must be cut back with similar care to the nearest live branch junction or main stem.
  • Formative pruning when the tree is young and branches are small can avoid the later need for larger limb removal.
  • No available wound treatment is capable of protecting wounds against decay for more than a year or so.
  • On present evidence, the increase in early callus growth brought about by certain wound paints is too short-lived to warrant their general use.
  • Theory and recent, limited short-term investigations indicate that wounds made in summer are less favourable for the development of early wound colonising, wood-rotting fungi than those made at other seasons, but whether season of wounding has a significant influence on decay development in the long term remains uncertain.

Fungal Identification

Ganoderma adspersum


Top dark brown to blackish; white rim underside when growing. Pore surface whitish.


Hard outside, tough inside.


Dark brown, fibrous; silky sheen when torn apart.


Often several clear layers of tubes once cut and cross-sectioned.

Other Distinctive Features

Upper surface and vegetation beneath the brackets sometimes covered in cocoa-brown spores, like dust.

Dead State

Persistent, without white rim.

Decay Characteristics

White, mottled, dry, firm, becoming soft and spongy.

Long Term Damage Effects

  1. Root and/or butt rotter.
  2. May render tree unsafe.
  3. May cause stem or branch snap.
  4. Top rotter.

Rots of Stems and Branches (Top Rots):

Symptoms and diagnosis:

  • There are clear areas of exposed wood visible (no longer covered with bark) on either the main stem or limbs, or both and these are physically decayed, or a cavity has formed at such a wound.
  • There may be fruit bodies of known root butt and/or top rotting fungi present, formed on bark or exposed wood on limbs of the host tree infected.
  • A stem or branch may fail and snap. There are areas of the upper crown suddenly sparsely foliated, or devoid of any foliate where the remaining canopy appears unaffected.
  • Confirmation: When tested with a knife or similar instrument the decayed timber is usually palpably softer or easily picked out, broken or cut than other sound wood.
  • Caution: Even perfectly sound limbs and stems will break if the wind is strong enough. In calm weather apparently sound limbs may fall ~ a phenomenon known as ‘summer branch drop’.


Top rots are common and widespread, particularly where large branches have been cut off or have broken out.


Ultimately may render the tree or limb unsafe.

Host Trees

It is doubtful whether any species is immune from attack by every one of our many top-rotting fungi but some are particularly prone to such disease.

Infection & Development

Airborne spores are released by fruit bodies borne on decayed parts of standing or fallen trees or on infected timber left out in the open. For infection, most fungal species probably need wood unprotected by living bark and even then infection is more likely if the end grain is exposed, as in pruning wounds, or where the wood is not only exposed, but also torn.
The fungus slowly spreads through the wood, converting the tissues to its own substance and to energy for growth. The manifestation of this process is the decay of the wood. Once the fungus has exhausted all of the materials it is capable of utilising it dies out in that portion of timber/wood. The decayed wood may be further broken down by micro-organisms, arthropods and birds so that eventually cavities may be formed. The ultimate extent of the decay is restricted by various anatomical, chemical and physiological characteristics of the specific wood and varies from species to species.


Therapy: None available. The excavation of a decayed area will not arrest the development of established fungi and may exacerbate the deterioration further.

Chicken of the Woods

Chicken of the Woods

‘Chicken of the Woods’: (Laetiporus sulphureus)

This is a porous bracket fungus, found most commonly within the woodland environment, though other areas may also be susceptible to the infection when established.

  • Typically the fruit body appears a sulphur yellow ranging to warm orange in hue, sometimes the outer surface exudes yellow liquid droplets from the inner core. The texture is firm but soft, the flesh exudes a yellowish juice when squeezed and pressure applied however, when dried out the fungus becomes a powdery white and tastes pleasant. Laetiporus also has tubes within the flesh mass as opposed to gills, which can be clearly seen when the fruiting body is sectioned for diagnosis.
  • Perhaps the other most distinctive feature for the diagnostic process is the physical appearance of the fungus itself. It grows in thin, tiered very pretty brackets and can be seen from spring to autumn in the woodland habitat that is its ideal preferred environment.
  • In its dead state the fungus deteriorates relatively slowly, becoming whitish and chalky looking. It is light in weight, dry and very crumbly and is readily edible with no ill effects whatsoever. Its decay characteristics becoming brown dry, crumbly and cubical,   sometimes with chamois leather-like mycelium in cracks.

Laetiporus is a root and/or butt rotter also extending towards top-rotting additionally. It may render the tree unsafe and may cause stem and/or branch failure relative to its growth location within the inner structure of the canopy it infests.

Ustulina deusta:

ustulina deusta

ustulina deusta

The principle killer of all Fagaceae species/family, and the majority of native trees within the UK. Once infected the tree falls into rapid decline, the main tap root and lateral systems attacked, undermined and the structural integrity quickly compromised. This virulent aggressive fungus is a root and/or butt rotter, may cause total stem/branch failure, a top rotter and is highly likely to render the host unsafe.
Fruit bodies are a black lumpy mass at the base or infected area, reminiscent of lumpy tarmac or charcoal, the texture hard, brittle and crumbling. The flesh is black and fruit bodies exhibit no tubes or gills. Other distinctive features include thin circular grey patches with a white margin growing close to the black fruit bodies (the asexual state of the fungus. Decay characteristics of infected timbers include a pale yellowish or greyish hue with fine black lines running throughout.

Boot Lace Fungus

Boot Lace Fungus

Ustulina may take hold and ravage the vascular system of the host tree following very dry or exceptionally hot years. These conditions allow fungi lying widespread but normally dormant in the sapwood (endophytes) to develop rapidly invading and rotting the sapwood killing the bark.