Benbow Brothers Timber Ltd

Fungal Tree Infections

British Fungi Expertise

a fungal bulb extends from a tree trunk.
Is this good or bad? Find out here

You might assume that every fungus you see on a tree is a sign that that tree is rotting and diseased. That isn’t always true, whilst it is true that Tree Fungi can be harmful (pathogenic), they can also non-harming (Saprotrophic) and even helpful (Symbiotic). This page has details on the different Fungi that you might encounter on your trees. We hope that it will help you to identify the harmful growths on your trees and call us while we can still hopefully do something to save the tree.


Symbiotic Fungi

The most common symbiotic relationship between trees and fungi is an infection of the soil around the roots known as Mycorrhizae. This mutually beneficial infection has the fungi eating the sugars produced by the tree during photosynthesis, in return the fungus enhances the trees ability to uptake water and soil nutrients like nitrates and minerals. This form of symbiosis seems to have first evolved about four-hundred million years ago during the Emsian period of the Devonian Age, which is around the time that trees really started to spread across the world.

Ectomycorrhiza fruiting body, a brown conic mushroom that grows near tree roots.
Ectomycorrhiza fruiting body

Ectomycorrhizae: Mainly infesting oaks, birches, willows, pines, and the non-native dipterocarps and eucalypts these infections form between the roots of these trees and consist of the Basidiomycota, Ascomycota, and Zygomycota families of fungi. They are characterized as having fruiting bodies (mushrooms and toadstools) that appear above ground usually near the tree.

Arbuscular mycorrhizae: The most common form of plant symbiosis on the planet according to many researchers. Approximately seventy to eighty percent of all vascular plants are infected. These infections are characterized by the lack of fruiting bodies.


Saprotrophic Fungi

These fungi feed exclusively on dead organic matter, as such they don’t generally damage a living tree, but the presence of these fungi on a tree can be an indicator of ill health, especially when found on a leafless area, or limb. Areas of  dead wood tend to become infected with these fungi causing rot, and can lead to structural collapse.

Brown-Rot:

Characterized by the dead wood breaking into red-brown coloured, crumbly, cubical chunks. Sometimes known as Dry rot, Brown Rot is always a serious problem to the structure of a tree, and spreads rapidly it can become pathogenic as noted below.

White-Rot:

Characterized by the dead wood paling to white and softening into a fibrous material. White-rot is usually less troublesome than Brown-rot but can still lead to structural collapse. A few dead-wood fungi that cause white rot can turn pathogenic as noted below.

Soft-Rot:
Daldinia concentrica or King Alfred's cake a burnt looking fungus responsible for soft rot.
Daldinia concentrica one of the causes of soft rot.

Characterized by a slow weakening of the wood, usually involving long, thin open spaces forming within the wood, or splintering similar to Brown-rot.

Soft rot fungi require nitrogen from the tree to help them consume the cellulose of the wood, effectively starving the tree of this essential element.

There are bacterial soft-rot strains that can have similar effects to fungal rots and it can be tricky for an untrained eye to spot the difference in the absence of obvious fruiting bodies.


Pathogenic Fungi

These fungi are similar to viral or bacterial infections. They are diseases and will weaken and kill the tree they infect. Many have symptoms very similar to attacks of Saprotrophic Fungi, such as rotting, but they affect living wood rather than dead. There are a lot of fungal diseases that we encounter repeatedly, here are some examples. Please click the images to find out more about the fungi.


White-rot Fungi

Dark ribbons (Rhizomorphs) of fungus grow in a tree trunk
Rhizomorphs
Leaf like blades of fungus near the base of a tree
Armillaria or honey fungus

White-rot fungal infections attack the hard lignin of the wood, leaving the cellulose of the cells as a skeletal white, often powdery, substance.

Ganoderma Adspersum or Artist's Fungus, a dark, bracket-like fungus with a white edge, pictured here on a tree trunk.
Ganoderma Adspersum or Artist’s Fungus
The brown Artist's bracket fungus is pictured here feathering a trunk
Artist’s Bracket is usually a bad sign

Science has discovered that through enzymes containing powerful oxidants the white rot fungi chemically burn their way through the tough lignin that gives wood its physical strength.

An ear shaped and slightly furry looking fungus
Hairy Ear on a tree? Well sort of… Click for more details
A brown bracket fungus drooping from a tree trunk to show the dark hair like patterns.
Less ear shaped, but more obviously hairy
A rough fungus arranged around the roots of a large tree
A danger sign for a tree

Brown Rot

A silver birch with ears of fungus growing from the trunk
Birch Bracket
A bright sulphurous-yellow-coloured fungus commonly called Chicken fungus
Laetiporus sulphureus

These fungi attack the cells (in the form of the cellulose and hemicellulose) of the tree, but leave the brown lignin structure untouched.

This causes the wood to become fractured into cube, or brick-like, pieces that have little structural strength.

A saddle shaped yellow fungus
A saddle for a dryad? Click to find out more

Soft-rot

A brown, blister like fungus growing underneath a branch.
Bracket fungus
A black fungus with white fruiting bodies, commonly called Brittle CInder
One of the Deusta fungi

Soft-rot fungi require damp, moist even semi-aquatic conditions in order to grow and spread. These fungi are the most common of the decomposers of dead wood, you will often see them growing on untreated fence posts and poles in the countryside.


Dutch Elm Disease

A sapling with bright yellow leaves as well as healthy green
Leaf scorching doesn’t get more obvious than this.
An Elm with browned leaves amongst green,
The characteristic leaf scorch of Dutch Elm

DED is a killer, it attacks almost all Elm varieties, but does have varieties of its own. Recent work in tree breeding is making some progress in crossbreeding several strains of Elm to produce a more resilient variety that can resist this terrible fungal infection.

Dutch Elm Disease is famously spread by beetles, but it also spreads through interconnected root systems and can be spread by spores on saws used to treat and fell Elms that have been infected. We disinfect all saws after use on Elm so there is no danger of spreading spores into a healthy tree.

Three trees that look blighted by Dutch Elm Disease
The signs of Dutch Elm Disease are often visible from a distance.

Dutch Elm disease looks like burning or tree de-hydration. This is due to the tree blocking it’s own vascular system in an “allergic-reaction” immune response to the fungus.


It can be hard to distinguish a Saprotrophic fungal infection from a Pathogenic one (especially as they are often only a matter of intensity of infection). If you have any questions or concerns about a fungus on your property, please contact us via email, telephone, fax or post. Our expert arborists will be happy to examine the tree and assess risks from fungal growths to it and your property.