Mushrooms are fascinating organisms and they are essential to the ecosystem, but if you find one growing on a living tree, you probably have a challenge on your hands. Mushrooms are late-warning signs that a tree is unwell. This means that by the time you see a mushroom on the bark of your tree, the fungus has already built a network inside and is in the process of consuming the tree from within.
In order to save the tree, or at least the other trees in the area, it’s important to call a professional arborist as soon as possible so that they can address and contain the situation.
What Are Mushrooms?
A mushroom is actually the fruiting body of a fungus. Fungi is a “kingdom” of its own (neither plant nor animal) that also includes yeasts and moulds. Some fungi spread a network of threads through the ground or other organic matter called mycelium. This network eventually sprouts fruit (the mushrooms we see on the surface).
Fungi were some of the first organisms to colonize land and they are responsible for creating the soil that lays the foundation for plants and animals to spread on earth. They are still essential to the growth of forests, sharing nutrients between trees and helping to break down dead wood and release nutrients back into the soil.
If a tree has already been weakened, a fungus can move in and feed off the tree’s nutrients while the tree is still alive.
What Causes Mushrooms to Attack Trees?
Various stressors can cause fungal attacks on trees:
Soil Conditions – Sub-optimal soil conditions (such as drought, compacted soil or overly-wet soil) can cause root damage. When this happens, fungi such as Armillaria that usually live in soil or on the surface of the root will invade.
Physical Damage – Wounds to a tree (such as cuts or scrapes) expose the interior tissue to attack from fungi. These wounds can be from ice damage, broken limbs, cuts from landscaping equipment, or straps left on the base of a tree after it has been planted. Even pruning can leave trees vulnerable to attack. This is why, for example, fruit trees should be pruned in summer when silver leaf fungus is least likely to spore.
Types of Mushrooms That Grow on Living Trees
There are different types of mushrooms we might find on a tree; each means a different prognosis for its host.
Dryad’s Saddle is a type of bracket polypore mushroom.
Dryad’s Saddle Polyporus squamosus
Characteristics:
- fan-shaped with a central stalk
- whitish-yellow with brown scales
- pores instead of gills
Fruiting Season:
- spring to fall
Disease caused:
- white rot of a tree’s heartwood
Trees affected:
- hardwood
Dryad’s Saddle is a type of bracket polypore mushroom.
Turkey Tail Trametes versicolor
Characteristics:
- thin cap
- bracket mushroom
- velvety surface with concentric bands ranging in colour from brown, red, yellow, gray and blue.
- polyporus – with whitish yellow pores.
Fruiting Season:
- Spring to fall
Disease Caused:
- white rot
Trees Affected:
- hardwood
The fungus leaves intricate lines in the affected wood which can produce beautiful patterns in bowls, vases and other objects that are crafted from this “spalted” wood.
Sulfur Shelf or “Chicken of the Woods” Laetiporus sulphureus
Characteristics:
- grows in multiple clusters of yellowish-orange shelves
- young fruit is fleshy and soft and hardens as it matures.
Fruiting Season:
- summer to fall
Disease Caused:
- brown cubical rot
Trees Affected:
- hardwood
- conifer trees
- very common on red oaks
Honey Mushroom Armillaria ostoyae
Characteristics:
- golden yellow cap
- distinct ring on stem
Fruiting Season:
- late summer to fall
Disease Caused:
- armillaria root rot – a destructive and widespread disease in Ontario.
Trees Affected:
- deciduous and evergreen species including balsam fir, spruce, pine, maple poplar and oak
All Armillaria species are luminescent, glowing in decayed root and stem tissue. Armillaria networks can be extensive. Some have been discovered as large as 4 square kilometers.
Artist’s Conk Ganoderma applanatum
Characteristics:
- bracket or shelf mushroom
- upper surface is hard with gray-brown patterns of bands;
- lower surface is white and turns brown when scratched
Fruiting Season:
- perennial
Disease Caused:
- white stem and butt rot
Trees Affected:
- hardwoods (the most common perennial wood decay fungus of dying hardwood trees; a single conk can produce 1.25 billion spores each hour for 5-6 months each year)
This fungus causes silver leaf disease in many fruit trees.
Silver Leaf Fungus Chondrostereum purpureum
Characteristics:
- starts as a white crust and develops into wavy clusters of leathery bracket mushrooms, each about 3cm wide
- pale to bright purple patches or rings with a white edge
- mushrooms dry after a few weeks turning brittle and brown
Fruiting Season:
- perennial
Disease Caused:
- silver leaf disease – progressive and often fatal to the tree.
- this disease also presents as silvering on the leaves of affected branches
Trees Affected:
- all plants in the Rosaceae family, including most edible fruit trees (such as apple, pear, cherry, peach, plum and almond trees)
- many other broad-leafed trees can also be affected (e.g. poplar, oak, maple)
How a Mushroom Damages a Tree
Once a mushroom has invaded its tree host, it spreads through the interior of the tree and releases enzymes which break down the tree’s tissue and turn it into a food source for fungus. This fungal network will eventually cycle back to the surface of the tree and fruit mushrooms which will spore and spread the fungus to other trees in the area.
Once a tree has been depleted from the inside by a fungus, it is at risk of limbs breaking or the entire tree toppling from high winds — endangering people and surrounding property. A tree can be extensively hollowed even before mushrooms have become visible on the tree, so it’s important to act quickly if you suspect fungal infection.
What To Do
If you find a mushroom on your tree – leave it there. Removing it won’t affect the fungus and might spread spores to neighbouring trees. Call an arborist as soon as possible to assess the tree. Hopefully, only a portion of the trunk has been affected and a professional can remove the infected sections in time to save the tree. Otherwise, they will be able to safely remove the tree and contain the fungus, testing the soil and assessing other trees to ensure they remain healthy.
At Dave Lund Tree Service & Forestry Co. Ltd., we specialize in treating trees damaged by insect or fungal disease. We have arborists available in Bradford, Newmarket, Aurora, and Richmond Hill. If you a mushroom on your tree or any signs of fungal infection, don’t hesitate to call us at 1-800-363-0511.
