Extension > Garden > Yard and Garden > Trees and Shrubs > Diseases of spruce trees in Minnesota > Tomentosus root rot
Tomentosus root rot
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Photo by USDA FS Bugwood.org
Photo by USDA FS Bugwood.org
Photo by USDA FS Bugwood.org
Photo by J.Baker Bugwood.org
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.
Identification
- Heartwood of infected roots and trunks is initially reddish brown.
- As infection continues white pocket rot develops. Decayed wood has elongated pockets or pits, and may appear honeycomb-like in cross section.
- Infected trees have reduced growth and thin canopies, produce large amounts of cones and eventually die.
- Infected trees frequently break or lodge during storms.
- Mushrooms that are velvety brown above and porous and buff colored below appear around the base of the tree in late summer.
Biology
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.
Management
- Mulch the soil around the base of all spruce trees to prevent injury from lawn mowing or other garden equipment.
- Have infected trees assessed by a certified arborist to determine its structural stability.
- Remove unstable trees to prevent damage that might occur if the tree were to fall.
- Remove the stump and as many roots as possible of infected trees.
- Do not plant spruce or other susceptible conifers at a site where trees have been infected with tomentosus root rot. Most deciduous trees are immune to the disease and can be safely planted.
