The tree-stump-treating season against the spread of the fungus heterobasidion annosum, commonly known as annosum root rot, is in full swing in Finnish forests. The treatment is started when temperatures rise above zero and no longer fall below zero during the night. This year the process was started in early May and will continue until the end of November.
Heterobasidion annosum is the main cause of rotting during the tree growth period in Southern and Central Finland, causing butt rot in both spruce and pine. The fungus causes rotting in the most valuable part of a tree trunk, i.e. the part that produces the best sawn timber. This type of root rot spreads most often trough the surface of the stump, but the tree can also be infected through a damaged root collar. The rotting can spread to healthy trees via contact with infected root systems.
During summer harvesting, the spread of annosum root rot is prevented by treating the stumps with a urea solution or with a preparation made from the fungus phlebiopsis gigantea. The stump treatment is carried out in mineral-soil coniferous forests, as the fresh stumps of pine and spruce are susceptible to the spores of heterobasidion annosum. The treatment is administered automatically in connection with harvesting via a device installed on the harvester. As a tree is cut, the device sprays the stump with the special treatment, which has been mixed with a dye. This makes it easy to monitor the successful treatment of the stumps.