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Honey Fungus

Honey Fungus is a name used to describe various fungi which decay trees by affecting the root system and then subsequently spreading decaying parts of the tree above the ground.


Usually it is initiated by a tree wound or a tree weakened by unsuitable environmental factors.


Rhizomorphs spread under the ground from the affected tree further infecting other healthy trees and shrubs that they reach.

These rhizomorphs remain invisible underground and spread up the tree under the bark.


The ability to reproduce itself this way means honey fungus doesn't necessarily depend on finding damaged wood to infect as other fungi do.


A root examination can assist in early diagnosis.






Parts of the upper tree may die as damage to the root system prohibits enough nutrients reaching these parts.


A yellow coloured Fungi may appear at the base of the tree trunk and the bark may bleed and crack in this area.


If the bark comes away from the tree, rhizomorphs with a bootlace appearence may be seen.


The tree may not flower as expected. Either not flowering at all, or overly heavy flowering.


Leaves may be weak in colour and small in size.


A white fungus may develop at the base of the tree under the bark leading to the bark falling away.


The leaves may appear to be going dormant too early.






Unfortunately there is little one can do in the way of controlling honey fungus and ultimately the tree and its roots will need to be removed taking care not to scatter debris away from the root site in order not to infect other plants.


Because honey fungus is so infectous it is important to burn all arisings from the tree and root system rather than to compost.


It is recommended to dig at least 2 foot down, remove all arisings from the hole and line the hole with a heavy duty plastic before refilling and replanting.










Prevention and Control

Visible Signs

Meripilus giganteus - Giant polypore

Unlike Honey fungus, Meripilus regenerates itself via wind blown spores rather than rhizomorphs.


Spores from the fungus are blown into a crack or crevice caused by a wound in the tree then settle and become established on the dead or dying wood.


Celluose and lignin which are integral to the trees strength and structure are then digested by enzymes secreted by the giant polypore thus weakening the tree as it starts to eat away at the healthy tissues.


The trunk base or roots are the areas which are attacked by this fungus and drought  and flooding as well as wounds can create a suitable environment for this fungus to inhabit.


As the fungus only fruits from the late Summer though to Autumn and not necessarily in its first few seasons there is a danger that the disease is not noticed for some time whilst the damage to the roots continues.


On the other hand it is worth noting that the fungus can sometimes appear very early into the infection, despite not having yet caused much root damage at that point.


The spread of decay into the trees root system may lead to such a weakening of the trees structural integrity that it may be more liable to topple.


It has been suggested that Meripilus may be benificial to very old trees in so much as while prolonged infection can cause the rot of the inner base of the trunk, this may actually allow the outer new growth of the trunk more elasticity enabling it to withstand high winds and lessen the likelyhood of toppling over.

However considering the fungus also causes the roots to rot, the tree would  start to have drastic dieback in the upper canopy which may prove hazardous if the tree is situated in a residential area if branches were to drop or extensive root damage which could cause the tree to collapse from the base.






Visible Signs


The fruit appear in late Summer to Autumn and can be a yellow to grey colour becoming darker with age. The new fruit are fleshier and bulbous becoming thinner and rosette like as they age, taking on a cabbage like form.


If bruised the fungus will stain black.


Meripilus fruit will usually be seen growing at the base of the tree.


The fungus may also appear in ground areas several metres from the tree as it grows up from roots that are close to the ground surface.


The fungus can grow in clusters up to a metre square.


Thinning or dieback of the crown of the tree may be noticed before the fungus fruits are apparent.



Prevention and Control


If any crown thinning or dieback is noticed it would be advisable to have the trees roots checked. If infected, the roots become spongy.

It is important to check roots that are as deep as 20 inches below ground as it is not necesarily the roots that are higher up that show infection.


Measures can be taken to improve the environmental conditions for the tree. Irrigation can help water logging as can mulching. Additional nutrition may be given to mature trees to help assist tree vigour.


Unfortunately there is no way to prevent Meripilus, but by avoiding detrimental environmental factors and creating ideal soil conditions the tree will have a greater chance of resisting any attack.


It is advisable to fell trees suffering from Meripilus that stand in a residential or public area due to the risk of damage to property or people from falling dead upper branches or the tree collapsing.  






Horse Chestnut Leaf Blotch  (Guignarda aesculi)

The fungis Giugnarda aesculi is seen in horse chestnuts from around June. It is often seen on trees that have already been attacked by the Horse Chestnut leaf miner and therefore it can be difficult to identify between the 2 problems as the visable signs are very similar. 


Visible Signs


Blothes of a reddish brown colour develop on the foliage. Often a yellowing ring around the blotches is seen.


Although being very similar in appearance to the damage caused by the Leaf Miner, there are a couple of ways to tell the damages apart.


The leaf miner grub when residing within the leaf eats away at the inside of the leaf so on holding the leaf to the light it is almost transparant and a paler greyish green colour. wheras the leaf bloch is dark red or brown in colour







Shaggy Polypore

(Inonotus hispidus)

This type of polypore is a fairly common fungus which generally attacks apple trees, ash, walnuts, poplar, oak, beech and plane trees, however other broad leaved trees may be attacked by it. The fungus is visible from late June until into the winter.


Some trees are better adept at resisting damage fron Shaggy polypore than others. Ash trees are probably the most suceptible to attack and have the least resistance towards an attack. However, many tree species can form a natural barrier to inhibit the spread of the fungus.


The fungus will enter through an old wound on the tree, for instance a broken off branch and by attacking the cellouse and lignin of the tree will eventually cause decomposition of the heartwood.


The picture on the right are of a tree which had a lighning strike and consequently became succeptible to the fungus.



Visible signs


Small globular fungi which are yellowish / buff orange in colour will appear on the bark around June.


As they mature over the Summer they flatten out and become paler around the edges. Where spores have been dropped onto the lower stem, new fungi may appear. Underneath the fungi, the tubes will appear cream and darken with age into a buff colour.


During late Autumn the fungi will become harder on the top and darker in colour until all the fungus eventually turns black. The top of the fungi can resemble a hoof like shape.







New growth of Inonotus hispidus

The same fungus develoving on the same tree as the pictures above 2 months later into the Autumn


These pictures show this tough fungus through the Autumn months as it gradually hardens after dropping its spores and turns darker in colour. It is still firmly holding onto the tree in January, despite enduring several frosts.

inonotus hispidus inonotus hispidus inonotus hispidus October inonotus hispidus October inonotus hispidus inonotus hispidus January inonotus hispidus November Click to enlarge photos Honey fungus 8 Honey fungus 7 Honey fungus 5 Honey fungus 1 Honey fungus 6