Armillaria Root Rot (Shoestring Rot)

Fraser fir killed by Armillaria

This disease is caused by several species of the fungus Armillaria.  It is also known as shoestring rot due to the dark wiry strands it produces.  These fungal “shoe strings” can spread the disease.  It most frequently attacks trees weakened by environmental stress or other factors.

Unfortunately the shoestrings are often confused with roots. One of the easiest ways to recognize the disease is the white layer of mycelium that can be found under the outer surface of the roots or just below the bark at the base of the tree.

This fungal disease will sometimes produce small groups tan colored mushrooms near the base of affected trees.  Although not present every year the mushrooms most often appear in the early fall following rainy weather.


White mycelial fan on trunk

Fungal “shoestrings” on rotting stump next to infected tree

Disease Management:

·      Keep tree vigor as high as possible to avoid tree stress

o   Avoid planting trees in droughty or poor planting sites. 

o   Water trees, if possible, during extended periods of drought.

·      If found remove and destroy stumps and roots of affected trees.

·      Plant new trees as far as practical away from where an affected tree was removed.

·      Avoid planting new trees in a recently cleared woodlot that had a problem with Armillaria.

One thought on “Armillaria Root Rot (Shoestring Rot)

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