Tomentosus root rot

Tomentosus root rot is a significant forest disease caused by the fungus Inonotus tomentosus. This pathogen is a wood-decay basidiomycete that specifically targets the root systems and the lower trunks (butt) of coniferous trees. It is responsible for significant mortality and growth reduction in forests, leading to windthrow and structural instability of infected stands.

The disease affects a wide range of conifers, with spruce and fir species being particularly susceptible. Of major concern is its impact on Douglas Fir, where the fungus causes severe decay of the roots and the butt log. The loss of root integrity often leads to tree collapse long before the wood is fully consumed by the fungus, posing risks in both commercial forests and recreation areas.

Symptoms of the infection include a general decline in tree vigor, characterized by stunted shoot growth and thinning of the foliage. In advanced stages, the crowns of affected trees become chlorotic and sparse. Close examination of the tree base may reveal small, leathery, stalked or sessile mushrooms (sporocarps). Inside the wood, the pathogen causes a characteristic white-pitted rot that leaves the timber brittle and prone to breakage.

The fungus spreads primarily through root-to-root contact, allowing the pathogen to move slowly through a stand from an infected tree to healthy neighbors. Spores (basidiospores) produced by the fruiting bodies can also colonize fresh wounds on roots or the base of trees. Conditions such as cold, moist sites and densely stocked stands favor the long-term survival and spread of the pathogen.

Management of Tomentosus root rot focuses on minimizing the impact through silvicultural adjustments:

• Removal of infected trees along with their stump and major roots.
• Avoiding wounding of root systems during thinning or harvesting operations.
• Planting non-host species in areas with a history of high infection rates.
• Maintaining lower stand densities to reduce the probability of root contact.
• Implementing regular forest health inspections to identify and isolate infection centers.