Mushrooms: Tree Rot Or Not?

Mushrooms growing on trees can be a sign of a serious fungal infection, which can cause rot and decay, and in some cases, lead to the death of the tree. While not all mushrooms are harmful, many can cause significant damage by attacking the roots and causing decay at the heart of the trunk. These fungi enter the tree through wounds caused by factors such as improper pruning, lightning strikes, or construction damage. Once the fungal infection takes hold, mushrooms start to grow, and the spores spread to other trees. Some common types of rot caused by fungi include white rot, brown rot, soft rot, and varnish rot. Honey fungus, for example, is a particularly destructive type of fungus that spreads underground and can be challenging to treat. In such cases, removing and destroying infected plants may be the only option to prevent the spread of the infection.

Mushrooms and rot-inducing pathogens

Mushrooms on trees are often a sign of rot-inducing pathogens. While not all mushrooms are harmful to trees, many are, causing heart decay and making healthy trees rot at their core. These fungi enter the tree at wound areas, which can be caused by improper pruning, lightning strikes, windstorms, fire, construction, or other means of damage. The fungi reproduce through fruiting bodies, or conks, that develop in old wounds, cracks in the bark, or old branch stubs. These fruiting bodies produce spores that spread to other trees via animals, insects, water, or wind.

There are several kinds of rot caused by fungi, including white rot, brown rot, soft rot, and varnish rot. White rot is much more widespread in nature, and several fungal species are capable of degrading all wood components, including lignin. Brown rot is caused by fungi that feed on cellulose and hemicellulose, leaving the brownish-coloured lignin behind. Soft rots grow more slowly than white or brown rots and attack the cellulose, hemicellulose, and lignin in the areas in close proximity to their growth. Varnish rot, as the name suggests, leaves a varnish-like coating on the top of the conks, which can grow up to 14 inches wide.

Some of the most common types of harmful mushrooms include sulfur mushrooms, beefsteak fungus, red-banded polypore, and honey mushrooms. Sulfur mushrooms are one of the most serious causes of decay in oaks and are one of the few fungi that attack yew trees. The reddish-brown, thick beefsteak fungus causes severe brown rot in older oak, chestnut, and other hardwoods. Red-banded polypore usually targets coniferous trees. Honey mushrooms, also called honey fungus, are particularly dangerous as they grow near the tree's roots and can cause Armillaria root rot. They are yellowish-brown and grow in clusters around the base of the tree or its roots.

While most mushrooms that grow on trees are harmful, some can form symbiotic relationships with the trees they grow under. The oyster mushroom, for example, is edible and grows on a variety of trees. Other benign mushrooms found on trees include Turkey Tail, Artist Conk, and Reishi. If you notice mushrooms growing on your tree, it is best to have an arborist identify the mushroom and determine if it is harmful.

Identifying harmful fungi

Mushrooms growing on trees can be a sign of harmful fungi infecting the tree. While not all mushrooms are harmful to trees, many are. They cause heart decay, which causes healthy trees to begin to rot at the heart of the trunk. These fungi enter the tree at wound areas, which are caused by improper pruning, lightning strikes, windstorms, fire, construction, or other means of tree damage.

To determine if the mushrooms growing on your tree are benign or harmful, you need to identify them correctly. Some common benign mushrooms found on trees include Turkey Tail, Artist Conk, and Reishi. Mushrooms come in different colours, shapes, and sizes. Some are small and subtle, while others are large and showy. Some mushrooms are flat, while others resemble a dome or a cone.

• Colour: Fungi can be identified by their particular colour. For example, sulfur mushrooms are orange-yellow on the top and red-orange on the bottom when they are young. As they age, they turn white. Similarly, needle blight manifests as reddish-brown spots on normally green needles. It eventually causes the needles to turn completely brown.
• Shape: The shape of the mushrooms can also help identify them. For example, chicken of the woods appears as yellow to bright orange fan-shaped mushrooms growing in overlapping tiers.
• Texture: The texture of the mushrooms can also provide clues to their identification. For example, conks have a varnish-like coating on top.
• Location: The location of the mushrooms on the tree can also be indicative of certain fungi. For example, mushrooms growing at the base of a tree may indicate honey fungus, which is a particularly dangerous mushroom that grows near a tree's roots.
• Tree species: Knowing the species of the tree can also help identify the type of fungus, as certain fungi infect specific types of trees. For example, oak wilt is very harmful to oaks, especially red oaks.
• Symptoms: Visible infection, leaf blight, wilting, browning out of season, leaf drop, and stunted growth can all be signs of fungal infection.

If you are unable to identify the mushrooms or fungi yourself, it is recommended to contact a certified arborist who can help identify and treat the issue.

The role of arborists

Mushrooms on trees are a sign of rot-inducing pathogens. While not all mushrooms are harmful, many are, causing heart decay and making healthy trees rot from the inside. These fungi enter the tree at wound areas and reproduce through fruiting bodies, or conks, that develop in old wounds, cracks in the bark, or old branch stubs. The mushrooms produce spores that spread the fungi to other trees.

Arborists play a crucial role in identifying and managing tree fungi. They can determine whether mushrooms on a tree are harmful and recommend appropriate treatments. When mushrooms are spotted on a tree, it is best to consult an arborist as soon as possible. The arborist will evaluate and identify the type of fungi and recommend a course of action. This may involve cutting off the infected branch to save the tree, or in more severe cases, removing and destroying the infected tree to prevent the spread of the fungus.

Fungi can be grouped into three categories based on their interaction with trees: beneficial, neutral, and harmful. Beneficial fungi, such as mycorrhizal fungi, work with tree roots to help trees absorb more food, water, and nutrients from the soil, promoting their growth. Neutral fungi, or saprophytes, feed on dead organic matter and do not harm the tree. They will eventually stop growing and disappear once the organic matter is exhausted. Common benign mushrooms found on trees include Turkey Tail, Artist Conk, and Reishi.

On the other hand, harmful fungi, such as Armillaria and honey fungus, can cause significant damage to trees. Armillaria infects the roots of trees, leading to root rot, while honey fungus spreads underground and can infect nearby plants. These parasitic fungi weaken the host tree, making it more susceptible to other issues like drought or infestations. To manage parasitic fungi, arborists may recommend keeping the tree healthy through proper watering, mulching, and pruning practices.

In summary, arborists play a vital role in identifying and managing tree fungi. They can determine the type of fungi, assess the level of damage, and recommend appropriate treatments to prevent further spread and maintain the health of the tree and surrounding ecosystem.

Honey fungus

Initial symptoms of honey fungus infection include dieback or a shortage of leaves in the spring. Rhizomorphs appear under the bark and around the tree, and mushrooms grow in clusters from the infected plant in autumn and die back after the first frost. The mushrooms are typically honey-coloured, but the fungus is variable in appearance and sometimes has a few dark, hairy scales near the centre. They have a smooth cap, 3 to 15 cm in diameter, convex at first but becoming flattened with age, often with a central raised umbo, later becoming dish-shaped. The gills are white at first, sometimes becoming pinkish-yellow or discoloured with age, and the flesh has a sweetish odour and flavour with a tinge of bitterness.

To check whether a plant is infected with honey fungus, peel away the bark at the base and look for a white or creamy white, paper-thin layer of fungal tissue (mycelium). The upper parts of the plant may die, sometimes suddenly during periods of hot, dry weather, indicating a failure of the root system. There are no chemicals available for the control of honey fungus. If an infection is confirmed, the only effective remedy is to excavate and destroy all the infected root and stump material. Infected trees should be removed and destroyed by burning or landfill to prevent the fungus from spreading to other plants.

Different types of rot

Mushrooms on trees are usually a sign of rot caused by a pathogen. While not all mushrooms are harmful, many are, causing heart decay and making healthy trees rot from their core. These fungi enter the tree through wounds caused by improper pruning, lightning strikes, windstorms, fire, construction, or other means of damage. The fungi reproduce through 'conks' or 'bracts'—fruiting bodies that develop in old wounds or cracks in the bark. These fruiting bodies produce spores that spread to other trees through animals, insects, water, or wind.

There are several types of rot caused by fungi, including white rot, brown rot, soft rot, and varnish rot. White rot is more commonly found in broadleaf trees but can also infect conifers. The wood becomes fibrous, wet, spongy, and white or yellow due to oxidation and loss of lignin. Brown rot is caused by the fungi basidiomycotina and primarily affects conifers. The wood becomes brittle and dark brown due to the loss of cellulose and the oxidation of lignin. As the wood dries, it shrinks and breaks into cubes. Brown rot is considered more serious than white rot as the tree loses flexibility and becomes more vulnerable to wind.

Soft rot can be caused by both fungi and bacteria and affects only broadleaf trees. Soft rot breaks down lignin, hemicellulose, and cellulose but only in localized areas that spread slowly, making it less serious than white and brown rot. Root rot is caused by decay moving up through the tree from the roots and can also be contracted by waterborne or airborne spores. It causes dieback in the roots, taking away their ability to absorb nutrients, which eventually leads to crown dieback and tree death. Butt rot is similar, caused by decay moving up the trunk from the roots or injuries to the trunk. Sap rot is often found on dead wood or as a secondary fungal invasion after an area of the tree has been killed by other factors. It progresses quickly but is usually not associated with structural failures.

Frequently asked questions