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Extension > Garden > Yard and Garden > Tomentosus root rot

Tomentosus root rot

Michelle Grabowski - University of Minnesota Extension Educator
Cynthia Ash Kanner - former University of Minnesota Extension Specialist

Back to Diseases of spruce trees in Minnesota


Photo by USDA FS


Photo by USDA FS


Photo by USDA FS

Armillaria root rot

Photo by J.Baker

This disease is caused by the fungus Inonotus tomentosus.

Black, white and Colorado blue spruce trees (Picea mariana, P. glauca, and P. pungens) are commonly infected with tomentosus root rot. Larch (Larix laricina) and Norway spruce (P. abies) can also become infected.



Spores from the fungus that causes tomentosus root rot can infect wounds in roots or in the wide base of the tree, known as the root flair. In addition the fungus will spread from infected roots or tree stumps to healthy roots that grow close by, often resulting in a cluster of infected trees. Once inside the tree, I. tomentosus causes discoloration and decay of the heartwood and sapwood of both the tree roots and the tree trunk. Infected roots eventually die. The above ground parts of the tree are not able to receive the needed water and nutrients. Growth slows and the canopy looks thin and yellow. With time the tree dies. Often, however, infected but living trees fall over or break in a storm due to trunk and roots weakened by decay. The fungus can survive in the root system and stump of an infected tree for over 30 years, and will infect new trees planted nearby.


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