Armillaria root rot

Root Diseases Caused By Basidiomycota

Armillaria Root Rot

Armillaria in saplings

Root system of young pine with root rot. Resin oozes out of the attacked trees and soil adheres to the resin.

Armillaria root rot

Bark removed from saplings with root rot showing white mycelial fans.

Armillaria root rot

Closer view of the white mycelial fan under the bark of an infected pine.

Armillaria in living tree

A section through the base of a living tree infected with Armillaria showing tree defense reactions (dark areas with resin). 

Armillaria decay

Armillaria can be an agressive pathogen of trees and it cuases a white rot. After killing a tree, the fungus decays the wood. In this oak cross section, the fungus can be seen decaying the sapwood and heartwood. This tree was in a Gibbon enclosure at the Minnesota Zoo. The tree failed and almost killed the swinging gibbon. 


Subterranean rhizomorphs produced by Armillaria. These round rhizomorphs grow underground from one tree to another.


Subcortical rhizomorphs produced by Armillaria. These flat looking rhizomorphs grow under the bark of dead trees.


Fruiting bodies of Armillaria ostoyae are often found in clumps and are produced for only a short time in the fall.


Another clump of Armillaria fruiting bodies.

Armillaria mushrooms

A common name for Armillaria is the "Honey Mushroom". Some people collect and eat these, however, the person that canned these mushrooms ended up at the emergency room. This fungus does have some toxic compounds that make some people sick. It is recommended to cook this mushroom very well to make sure the toxins are destroyed.



Culture of Armillaria showing rhizomorphs growing in the culture media.


The white mycelial fans of Armillaria glow in the dark. Cultures growing in the laboratory also show this bioluminescence if you view them in a very dark room and allow your eyes to adjust to the dark. Here are some petri dishes with Armillaria glowing. In the back ground is a bag of wood sawdust inoculated with Armillaria which is also glowing.


For people not familiar with Armillaria bioluminescence, the glowing of wood in the forest at night can be a frightening experience causing people to associate it with ghosts or something supernatural.