Incidence of Heterobasidion spp.in Scots pine on "low risk" sites in Southern Sweden

Sammanfattning: Heterobasidion spp. fungi cause pathogenic infections in woody plants throughout the northern hemisphere, causing the most damage in the Boreal forest zone. In Sweden Scots pine, being the second most economically important tree species, suffers a considerable amount of damage as Heterobasidion spp. fungal infections hinder the annual increment of a tree. This causes significant financial losses. The aim of this research is to determine Heterobasidion spp. incidence in Scots pine stands growing on sites, considered unlikely to be infected in Southern Sweden. In this study Scots pine trees, growing on “low risk” sites in Southern Sweden were sampled. 15 trees were sampled - 5 samples discs per tree were taken from the root systems of each. In total 75 trees were sampled. Sample discs were taken at 20-75 cm from root collar. Each tree was measured for volume calculations and visually evaluated for defoliation. Afterwards, samples were incubated at room temperature and checked for conidiophore presence using a stereo microscope. The results revealed that Heterobasidion spp. infection was present in Scots pine trees on two out of five sampled stands. There was no correlation found between the sampled root diameter and the infection presence. Defoliation proved not to be a viable method for diagnosing the Heterobasidion spp. infection on living Scots pine trees. Current forest management practices in Sweden are not adapted for Heterobasidion spp. infection control, causing significant financial losses for the forest owners. This could be prevented by thinning the stands in winter as well as treating the stumps after each thinning.