Mushroom Root Rot

Mushroom Root Rot

Mushroom root rot is a disease that affects a wide range of trees, including hickories and oaks, as well as other conifers and hardwoods. It is caused by the Armillaria species of fungus. It is also called shoestring root rot, and it attacks the plant by preventing it from properly absorbing water.

This fungus infects the roots of trees and shrubs, and they will weaken, decay, and eventually die.

In this article, we will discuss the signs and symptoms of mushroom root rot and what you need to do if your tree is affected.

How do I identify mushroom root rot?

You should suspect mushroom root rot if your tree has been growing poorly for some time. The leaves will have started becoming smaller and turning yellow. If you have an evergreen tree, the needles will have turned brown. Trees with mushroom rot also have dead or dying branches in their upper canopy.

One of the most telling signs of mushroom root rot is the presence of honey-colored mushrooms growing at the base of the tree in the autumn. If you peel off the bark near the base of the tree, you will probably see a white layer of fungal growth.

Fungal strands that look like black shoestrings will grow in a net-like pattern on the tree and on the soil around the base of the tree.

For evergreen trees, the base of the tree may be encrusted in resin just below the surface of the soil.

The wood of the infected tree may become soft and white. This indicates decay, which may spread upwards from the base to around five feet into the trunk of the tree.

Trees that are severely affected become very weak and will easily be broken by strong winds and storms.

Where does mushroom root rot disease come from?

This disease results from an infection by the Armillaria species of fungus. This fungus can survive for years in wood debris, such as old stumps and roots. The fungus produces rhizomorphs, which are cord-like strands that grow from the decaying roots and stumps and into the soil. When a new tree is planted near where an infected tree once stood, the rhizomorphs will penetrate its healthy roots. These rhizomorphs can grow up to 10 feet long, so they can easily infect neighboring trees and shrubs.

Once the rhizomorphs have penetrated the healthy tree, the fungus will colonize the roots and the base of the trunk and slowly cause the wood to decay. If the newly infected tree is healthy and vigorous, it can usually slow the spread of the fungus, but if its health is already compromised, the disease will ravage it quickly.

A tree with mushroom root rot will die if the infection girdles the base of the trunk. The tree will fall over due to the weakened roots and its trunk will break.

Mushroom root rot management

It should be noted that neither wide spacing, fertilization, stump-top chemical treatment or fire are effective treatments for mushroom root rot. so do not try to incorporate any of these methods when attempting to treat your tree.

You can reduce the chances of mushroom root rot by increasing the tree’s vigor. If the tree is stressed, it will be more susceptible to the disease. Protect your tree from pests and use good planting practices.

You can also choose to plant resistant species to avoid mushroom root rot. If you continue planting resistant species in soil that is harboring the fungus, the pathogen will simply die out. Once you are sure that the pathogen has died, you can go back to planting susceptible species of trees on the same land without worrying about infection.

You can do inoculum reduction by mechanically removing the stump of the infected tree using an excavator. You might not be able to clear all of the smaller roots from the soil, but the pathogen will not be able to survive for very long if all it has to survive on are the small roots. Unfortunately, renting an excavator is quite pricey, so this option is not for everyone.

You can also try fumigation, but be warned that this method is still experimental and does not guarantee the best results. This is done by drilling a hole into the tree’s infected stump and placing chemicals inside the hole. The chemicals will weaken the fungus enough that other fungi can kill it, or it could simply die from the chemicals themselves.


Mushroom root rot is a disease that affects a large variety of trees and shrubs. It can spread from tree to tree through rhizomorphs that grow out from infected stumps and roots and penetrate the healthy roots of neighboring trees.

This disease can be fatal to trees that are already weak, so keeping your trees healthy and vigorous will help them fight off the infection for longer.

You can try to manage the disease by uprooting the stump of the infected tree to stop the spread to other trees, or you can fumigate the stump. 

Image: / kostik2photo