Some organisms look like fungi, but clearly are not true fungi.
These pseudofungi are the fungoids.
Fungoids such as the Oomycota water-moulds and various slime moulds sometimes are of concern in garden settings.
Phytophthora and damping-off are serious diseases caused by oomycete fungoids.
Note: In different English dialects the words ‘toadstool’ and ‘mushroom’ are used differently.
Anglo-Canadians usually reserve the word ‘mushroom’ for edible fungi, and they use ‘toadstool’ in a less clearly defined manner.
In the U.K. mushrooms are those toadstools which are edible.
In the U.S.A., ‘toadstool’ means a poisonous mushroom!
Wood Rot Fungi
Toadstools are often visible under trees.
Some toadstools are mycorrhizae fungi, which are in fact beneficial, as they live symbiotically with tree roots.
The Amanita toadstools are important mycorrhizae fungi of birch, pine and fir.
Boletus toadstools often form mycorrhizae in deciduous forests.
Very few soil toadstools are harmful to trees in any way.
Most micro-fungi are saprobes which are beneficial as decay agents.
A number of micro-fungi do cause some problems for plants.
Micro-fungal parasites cause needle cast and a host of other plant diseases.
A few toadstools and bracket fungi (fomes) also grow upon plant tissues as parasites.
A fungus does not engulf food as an animal does.
Rather, it is as if a fungus wears its stomach on its outside.
Each feeding hypha releases digestive enzymes from its surface.
These enzymes digest food in the surrounding milieu, and then the nutrients are absorbed back into the hypha.
A wood rot fungus tends to gain access to wood by insinuating its hyphae into the conductive cells of the plant.
Once inside a tracheid, or a vessel, a hypha releases enzymes which breaks down the cell's wall.
In this manner they devour wood from the inside out.
Most of these wood rot fungi have both asexual and sexual sporocarps.
The asexual anamorphs can differ greatly from sexual sporocarps in form and colour.
The chlamydospore and conidiospore bodies are often small and hidden inside the wood or in hollows.
The asci or basidia bearing bodies are larger and more exposed.
If the 'fruiting bodies' of wood-rotting fungi appear on trees, this means two possible things:
(1) fungi are digesting dead tissue in the tree, or
(2) fungi are killing and then digesting living tissues in the tree.
The dead tissue is usually heartwood, and the living tissue is usually sapwood.
The vast majority of wood-feeding fungi live off dead wood.
These can still be a problem, if they make the tree structurally less sound.
Hollow trees are often hollow because fungi have digested away the dead heartwood in the core.
Such hollow trees are prone to breaking in windstorms, ice storms and other stresses.
In temperate climates very few wood-rotting fungi are significant threats to tree health:
(1) honey fungi (Armillaria spp.),
(2) white pocket rot (Heterobasidion annosum), and
(3) artist's fungus (Ganoderma spp.).
Honey Mushroom / Honey Fungus
Honey fungus is one of the major wood-rotting fungi.
They are also known as ‘stumpers’, tête de méduse, or Hallimasch.
Armillaria mellea is one of the main pathogenic species of mushrooms.
It is thought to be the same species as occurs in the Old World.
There are other Armillaria species in the Americas.
For example, the A. bulbosa is a species which seems to mostly afflict trees that are already stressed.
Most honey-mushrooms look very similar.
This includes the many species which live in the southern hemisphere.
Not all members of the genus actually kill living wood.
Some only feed off dead tissue, ie they are saprobes.
The toadstools are pale and tan coloured.
They appear as clusters of gilled toadstools near the base of a tree, usually where some dead wood is exposed.
As with all toadstools these are merely the 'fruiting bodies', the vast majority of the fungal tissue being hidden, in this case inside the tree's wood.
Honey fungi toadstools are usually visible in the autumn.
Inside the wood they cause damage throughout the year.
Cream-white mycelial fibres grow outward from the dead wood into living, but now dying, wood in the lower trunk and roots.
When actively growing, this mycelium can be bioluminescent.
Hence, sometimes one can see the mycelial fibres of the fungus glowing on a dark night.
The honey mushrooms are very versatile parasites.
Honey mushrooms also are saprobes, they digest deadwood and can stretch their mycelium through soil to infect neighbouring trees.
These rhizomorph runners are dark, and thick like shoe-strings.
These runners contrast sharply with the pale mouldy mycelial fans that spread out under dead bark.
In total the mycelial mat of a honey mushroom can be very large.
In fact, if an ‘individual’ is defined in genetic terms, a honey mushroom can be one of the larger organisms on Earth.
Mycelium from one ‘genetic individual’ can weigh many tonnes.
Although, in reality the links within a mycelium mass tend to break apart as a fungus grows.
Honey mushrooms often grow in association with the hunter's heart mushroom.
There are still questions about which organism parasitises which.
But it is almost certainly the honey mushroom which, in this case, is the victim.
Most mushrooms in the Armillaria genus are edible, if they are cooked.
However, if they are eaten raw, mild symptoms of poisoning may occur.
Mediterrenian and Slavic Europeans, as a whole, have a stronger tradition of eating the mushroom than do the British.
But this stereotype is slowly changing.
White Pocket Rot
White pocket rot, the conifer fome, maladie du rond, or Wurzelschwamm (Heterobasidion annosum), is peculiar in that the bracket fungi grows on fresh tree stumps, and on standing trees.
The fruiting bodies are bracket fungi, they are often reddish with a white margin.
The inner edge of the bracket can become very dark with age, but newer margin fades into a pale colour.
The spore bearing surface on the underside of the bracket is white.
The pores on this surface are oblong, and typically less than one millimetre wide.
The bracket is very 'woody' in texture and can be up to 35 cm wide.
Usually these fungi are visible near the soil level.
Sometimes the brackets are hidden in hollow stems.
Generally speaking, once the fruiting body is visible, this indicates that the fungi has become firmly established.
In which case, significant wood rot has already occurred.
The fungal disease is mostly a problem in conifer monocultures.
Mycologists still debate the seriousness of this pathogen on broadleaf species.
Broadleaf trees with pocket rot can sometimes live for many years.
Its seriousness for conifers is quite evident.
Spores from the fungus most easily infect freshly exposed stumps.
The mycelia enter the roots of these stumps,
then they multiply feeding on the root xylem.
From the stumps they spread-out to living pine roots.
In this manner the fungi-infected stumps in a clearcut can infect nearby pine stands.
In the 1960s Dr John Rishbeth, at the Cambridge Botany School, developed a novel method of controlling pocket rot.
Fresh stumps can be inoculated with the spores of Phlebiopsis gigantea, a type of crust fungus.
This competitor fungus pushes out most of the pocket rot mycelia which may attempt to grow in the stump wood.
The technique can be used on clearcuts in regions prone to pocket rot infestations.
Ganoderma / Artist's Fungus
Several species of Ganoderma can cause root and butt rot on broadleaf trees.
G. lucidum and G. applanatum are the main culprits.
The fruiting bodies are medium sized tan-brown brackets which grow in clusters on the base of a broadleaf tree.
Extensive rot can cause a tree to break and fall, during a wind storm.
This butt-rot mostly occurs on landscape trees which have had their bark damaged.
Lawnmower and line-trimmer scars are usually the instigating stress.
Ganoderma seldom occurs on trees that have not been damaged.
It is very seldom contagious from an infected tree to a healthy tree.
In the wild ganoderma grows mostly on old trees which have structural disorders.
Ganoderma is also known as “artist’s fungus” or polypore des artistes.
This is because the pale spore bearing layer on the underside of the bracket can be used as a surface to engrave images upon.
Drawing pictures on bracket fungi was once a common rural folk craft.
The craft is now somewhat passé.
Assorted Bracket Fungi
Many species of bracket fungi are wood rot agents.
However, most do not actually kill living tissue.
The birch polypore (Piptopous betulinus) has a pale and smooth upper surface.
The tinder fungus (Fomes fomentarius) is grey with a down-curved ‘hoof-shape’.
Brackets in the Fomitopsis genus often have strongly coloured bands of red and brown.
The Phellinus genus tends to form hard grey conks with tiny pores.
There are also several members of the Ganoderma genus which do not kill living wood.
All of these genera cause wound and heartwood rot.
But most of these brackets do weaken stem wood, and thereby can contribute to tree failure.
Jack-O-Lantern
Jack-o-lantern mushrooms (Omphalotus olearius, formerly O. illudens) is a yellow to vivid orange toadstool that sometimes is found near root crowns.
Often it grows on oaks, although other trees can be afflicted.
Most often the fruiting bodies are visible in the late summer or autumn.
The young fruiting-body looks like a red mushroom.
The mature toadstool has a trumpet-shape, somewhat like a chanterelle.
The toadstool is peculiar in that it can have a faint bioluminescence.
Masses of these fungi can sometimes be seen glowing on very dark nights.
In French the toadstool is known as clitocybe lumineux, because it can be luminous.
The fungus is a pathogen, but it seems to be most common on trees which are already stressed.
Furthermore, once the fruiting bodies are visible the infection is probably beyond repair.
Jack-o-lantern is not an edible mushroom.
It is quite poisonous to humans, if eaten.
They are not poisonous to mere touch, very few toadstools are that dangerous.
Sulphur-Shelf Bracket
Sulphur-shelf fungus, chicken mushroom, or polypore soufré (Laetiporus sulphureus) is a yellow to orange bracket fungus that is sometimes found on the sides of oak trees.
Tight packs of yellowish brackets may be found growing near cracks or creases on an oak trunk.
The soft bracket fungus is not directly pathogenic.
It is another example of a wood rot fungus which feeds on deadwood.
The fungal brackets grow where the deadwood is close to the surface.
Like the other decay fungi its can increase the rate of heartwood hollowing.
Sulphur-shelf brackets are edible, if they are cooked.
However, some people experience digestive upset after they eat cooked sulphur-self fungi.
It is probably best to consider the fungus to be mildly poisonous.
Stereum Disc Fungi
Wood rot can be caused by basidiomycetes in the genus Stereum.
They are called “false turkey-tail” brackets, in French they are the stérées.
Many of these ‘rots’ are relatively benign.
They devour mostly localised deadwood, or they occur on fallen deadwood.
Some can weaken the outer layers of living trees.
Their pale white to tan sporocarps tend to appear on the bark.
These vary from flat discs, to crusts, small brackets, or as discs with bracket-like ‘lips’.
The spore bearing surface is very fine textured.
Red rot (Stereum sanquinolentum) tends to occur on conifer wounds.
The rot is fairly isolated, and does not spread to living wood.
Oak pipe rot (S. gausapatum) occurs on oak tree wounds, but its mycelial spread is usually less extensive than the sulphur-shelf rot.
Relatively benign species of Stereum occur on magnolia bark.
False turkey-tail (S. ostrea) is peculiar in that it is a tiny bracket fungus when it is on a vertical surface, but it is crust-like on the underside of deadwood.
Chestnut Tongue Brackets
The chestnut tongue, beefsteak fungus or fistuline hépatique (Fistulina hepatica) is a good example of a mild parasite (endophyte) that becomes a saprobe as its host ages.
This fungus can live for decades in oak or chestnut xylem without causing any great damage.
The mycelium causes very little weakening of the wood. The fungus even produces asexual conidiospores and chlamydospores inside the xylem vessels.
In this Confistulina phase it is very much like an endophytic imperfect fungus. When the tree host weakens with age, the chestnut tongue fungus blooms forth as a rotting agent or saprobe.
First the tree’s heartwood is slowly consumed by a type of brown rot, which later becomes a true soft rot.
Then the beef-red brackets form to produce the sexual basidiospores (Schwarze et al 2004).
Inonotus Heart Rots
‘Heart rots’ (Inonotus spp. ) are fungi that form plump yellow to orange-brown brackets.
Very young brackets can look like velvety balls.
Sometimes the ‘balls’ have little droplets exuding from them.
The inonoti are agents of ‘white rot’.
They digest lignin before they digest the cellulose.
The I. dryadeus causes root rot, mostly on oaks.
It can easily lead to root failure on an otherwise sound looking tree.
The I. hispidus is a particularly troublesome species.
It causes white rot not only of a variety of broadleaf trees, including oaks, apples and plane trees.
This inonotus can kill living cambium.
Usually the fungus gains access to xylem via wounds in the bark.
There the hyphae spread into the heartwood and into the surrounding cambium.
The fungus can cause a canker-like wound, which heals slowly.
The rotten heartwood can instigate a tree fall.
Scaly Pholiota
Scaly pholiota or pholiote (Pholiota squarrosa) is a toadstools which fruits in wood-wounds on both broadleaf and coniferous trees.
The toadstools usually occur in tight little clusters.
The cap is hemispherical, with brown ‘scales’, and it can expand up to fifteen centimetres wide.
The stipe is also scaly and lacks a distinct annular ring.
The toadstools are commonest in the autumn, and usually fruit lower in the tree's trunk, or on the root crown.
Many other pholiota species exist.
Most of these species rot only dead wood.
The pholiotas in general are edible, but they are not esteemed.
The scaly pholiota occurs in both the Americas and in Europe.
Research suggests that the scaly pholiota is a rather weak pathogen.
It is usually some other non-pholiota fungus which is the main cause of the white rot.
Fairly often the other species is a honey mushroom.
Therefore, the toadstool is more of a symptom than a cause of tree decline.
Dryad’s Saddle
Scaly polypore, dryad’s saddle or polypore écailleux (Polyporus squamosus) is a white rot agent.
It is common in injured hardwoods, such as old Manitoba maples.
The polypore is more of a saprobe than a parasite.
Dryad’s saddle mostly rots dead wood, and commonly affects improper pruning scars or other wounds in the trunk.
It is one of those fungi that can weaken support-wood enough to cause tree failure.
This polypore forms a large soft off-centre toadstool, or quasi-bracket, which can grow to several decimetres wide.
The pore surface has closely packed small pore, and is pale to slightly yellowish.
The upper surface eventually forms scale-like scabers.
When it grows on a horizontal surface it forms a toadstool-like body similar to the winter polypore.
On a vertical surface the stipe connects off-centre, with a thin wisp of a ridge of a pileus (cap) on one side.
Dryads’ polypore can look something like a saddle.
(Dryads are mythical wood-fairies.)
The conk/toadstool is rather pleasant tasting.
Young specimens are juicy and quite comestible.
It is one of the first fungi to attract the attention of children and other novice naturalists.
It is especially fun to watch the toadstool expand over the course of a few days.
The fruiting-bodies sprout during the spring and autumn in Ontario.
European foresters seem to have more complaints about the fungus than do North Americans.
Possibly this is another example of a subspecies difference between the American and Eurasian mycoflora.
Perhaps the dryads’ saddle is a similar case in point.
But for now it is considered to be a single species that occurs from India, to Europe, to the Americas and even Australia.
(It may have been introduced in some cases.)
In the Americas the fungal conks are considered a sign of wood-rot, and not a disease per se.
Although, the distinction is academic as the appearance of these conks are a sign of a decay problem.
Burnt Crust Fungus
Burnt crust fungus, ustuline brûlée, or Brandkrustenpilz (Kretzschmaria deusta), is a very important wood rotting agent.
Formerly its binomial name was Ustulina deusta, and it is commonly called just ustulina.
This fungus is an ascomycete with small fruiting bodies.
It has an ability to penetrate its hyphae into a plant's cell walls.
There the fungus digests mostly the cellulose, leaving much of the lignin layer behind.
The rot is considered a type of soft rot.
Ustulina's rot can seriously weaken a tree's heartwood.
Many tree falls are instigated by this soft rot fungus.
Ustulina's conidial bodies are pale, but its asci are borne on dark crust-like sporocarps.
It also produces dark pseudosclerotial bodies inside the wood.
Its active mycelium is sometimes visible as an irregular dark layer between the rotten and sound wood.
Often on exposed deadwood the dark crust and the fungal patina looks very much like burnt wood.
White, Brown & Soft Rots
If a fungus digests mostly the brown lignin, and not the pale cellulose, it is a white rot.
Cellulose is located mostly on the inner layers of the tracheid and vessel cell walls.
Cellulose tends to give wood its tensile strength.
If a fungus digests mostly cellulose, leaving behind the lignin, it is a brown rot.
Lignin is concentrated largely in the outer layers of tracheid or vessel cell walls.
Lignin tends to lend compressive strength to wood.
If a fungus digests both cellulose and lignin it can produce a soft rot.
Soft rot tends to weaken both the tensile and compresive strength of the wood.
White Rot:
White rot can occur in conifer wood, but it is most common in broadleaf xylem.
The plump orange brackets of the Inonotus species are often a sign of white rot.
Ganoderma fungi are also white rot agents.
The white pocket rot (Heterobasidion annosum) gets its English name from the colour of its rot.
Brown Rot:
Brown rots are almost entirely due to basidiomycetes.
The majority of brown rots occur in conifers.
Some Stereum fungi can cause brown rots.
The Fomitopsis brackets is brown rot which occurs in conifer wood.
The chestnut tongue bracket (Fistulina hepatica) can cause a kind of brown rot in broadleaf trees such as oak and chestnut.
Although, the rot caused by chestnut tongue is a mixed form of rot.
Soft Rot:
Soft rots are caused by fungi that digest both cellulose and lignin.
Often these fungi have very branched hyphae which enzymatically bore into the plant's cell walls.
Kretzschmaria deusta is one very important type of soft rot fungus.
The soft tan brackets of Meripilus giganteus can cause soft rot.
The Inonotus, Chaetomium and Rigidoporus fungi can also cause soft rot in some of their hosts.
Both white, brown and soft rots can weaken a tree's heartwood.
Usually, white rot is more flexible, because the cellulose fibres remain fused together.
Brown rot is often very brittle.
Hence, when lignin is left behind, the woodrot is often dark and broken into cubical sections.
White rot tends to be stringy, and less brittle.
All types of heartwood rot can weaken a tree such that it breaks during a windstorm.
Soft rot is often the most dangerous of the rots.
Ustulina soft rot tends to weaken the base of the tree's trunk.
When an entire tree falls, soft rot is often to blame.
Control
Fungicides are not very effective in killing well established wood-rotting fungi.
For both honey fungus and pocket rot it is recommended that seriously infected trees be removed.
After removal it is advised that the stump be removed.
The more thorough the stump removal the better.
Removal is most important for pocket rot infestations.
White pocket rot can live on stumps that still have some living root tissue in them.
The spores from these stumps can infect standing trees.
Most fungi should be given the 'wait-and-see' approach.
For jack-o-lanterns one should monitor the situation.
Most fungi, such as the sulphur-shelf, should not be considered a great concern.
One should always assume that very old trees have some hollowing.
Visible fruiting bodies are just one of the signs of heart rot.
Sudden Oak Death
Sudden oak death (Phytophthora ramorum) is a particularly troublesome form of phytophthora.
Certain strains of this oomycete fungoid have begun to seriously afflict coast live oaks in California.
This epidemic may have begun when a strain of phytophthora from Europe, or Asia, was accidentally introduced to the Americas in the 1990s.
The symptoms of 'sudden oak death' are like those of other phytophthora diseases.
However, in coast live oak (Quercus agrifolia) the disease tends to be fatal.
In addition, cankers can appear on the lower boles of infected trees.
Lesions of dead cambium under the bark can issue a dark exude though cracks in the bark.
As is also too typical of phytophthora species, the fungoid can live in more than one host species.
Rhododendrons, laurels, and tanoaks (Lithocarpus spp.) can also host the fungoid.
Tanoak and a number of oak species are very sensitive to the fungoid.
It now seems probable that the P. ramorum fungoid came from Europe on imported rhododendrons.
Furthermore, contrary to early reports, redwood trees are not very sensitive to the fungoid.
However, laboratory studies indicate that the fungoid could seriously harm many eastern oak species.
Luckily, it has not yet established itself in the east.
Control
Sudden oak death is most prevalent where rhododendrons have been planted in the vicinity.
Rhododendrons can act as carriers, and are themselves only mildly affected by the fungus.
The nursery trade of rhododendrons has been in part responsible for the spread of this disease.
It is possible that eastern oaks could become endangered by this epidemic.
Diligence is required to ensure that this phytophthora strain spreads no further than it has already.
Recently a treatment for sudden oak (SOD) death has been found.
This control is a pre-emptive treatment for SOD infection.
It is not a very good post-infection ‘cure’ per se.
So far it has been tested and proven efficacious for treating oaks and tanoaks.
Applications of phosphites (PO33-) or salts of phosphonic acid can incur a degree of resistance to SOD and some other oomycetes.
Injections of the solution into the active xylem (sapwood) are fairly effective.
Spraying the bark with the phosphite solution is somewhat less effective - but cheaper.
With spray applications, a surfactant is required to keep the solution in place until it is adsorbed into the tree’s tissues.
The application should be during the active growing season, and the concentration and dose must be very carefully controlled (Garbelotto et al 2007).
References
Freinkel, Susan. 2002. If all the trees fall in the forest ... Discover. 23 (12) 67-73.
Hagen, Bruce W. 2001.
Sudden Oak Death Part 1: symptoms, biology and potential impact.
Arborist News. 10(6):29-31.
Heinrich, Bernd. 1997. The Trees in My Forest. Cliff Street Books. New York.
Holiday, Paul. 1989.
A Dictionary of Plant Pathology. Cambridge University Press.
New York. 140-141, 233-240.
Garbelotto, M., Schmidt, D.J. and Harnik, T.Y. 2007.
Phosphite Injections and Bark Application of Phosphite + PentrabarkTM Control Sudden Oak Death in Coast Live Oak.
Arboriculture & Urban Forestry.
33(5): 309-317.
Schwarze, F.W.M.R., Engels, J. and Mattheck, C. 2004.
Fungal Strategies of Wood Decay in Trees.
Springer. Berlin.
Thorn, R. Greg. 1991.
Mushrooms of Algonquin Provincial Park.
The Friends of Algonquin Park. Whitney Ontario.
Tudge, Colin. 2000.
The Variety of Life.
Oxford University Press. Oxford.
127-157.
