Oct 20, 2008. /Lesprom.com/. One fifth of mature spruce stands have been hit by root rot. This illness costs Swedish forestry 500 million SEK (Euro 51 million) per year. Root rot is an illness caused by fungi and bacteria. It mainly hits spruce, but also to some extent pine. The fungi Heterobasidion annosum and Armillaria mellea are the main species, which attack the trees. Contaminated stems are broken down from the inside and are useless as both timber and pulpwood. Thinning is one of the major reasons for root rot. Thinning creates more stumps than before, which constitute favourable environments for fungus growth when winters are getting warmer. Root rot is considered able to survive final felling and to infect future forest stands. The main reason for the increase of root rot is the rising amount of forest stands which are harvested during the summer time instead of winter. Mr Jonas Rönnberg, researcher at the Swedish University of Agricultural Sciences says that we have ourselves to blame for the problem. Root rot hits forests all over Sweden, but Southern Sweden and the coastal regions are most severely hit.