Comparison of Phlebiopsis and urea and their effect when treating young spruces against Heterobasidion spp

Abstract: Control of the economically important forest pathogen Heterobasidion spp. can be done by control with chemical and biological agents such as urea and Phlebiopsis. Today in Europe this action is mainly done during the mid stages of the rotation, thinning foremost and to a small extent in final felling. Studies have shown that the fungus is spreading not only in the late stage but also during the early pre commercial thinning stage, preventive actions should be taken also at this stage. In this thesis focus has been on investigating the differences in effectiveness of Phlebiopsis and urea. The aim was to compare the agents when used on small Norway spruce stumps in Sweden. The study was conducted at 18 sites distributed in southern and the central parts of Sweden. 1080 stumps were created and treated with Phlebiopsis and urea, 1/3 was left untreated as control. Results from the study show that stumps treated with urea wasn’t infected by Heterobasidion sp. Control stumps and Phlebiopsis treated stumps were infected by the fungus at the rate of 20,9 % and 8,1%. The effect of using Phlebiopsis decreases the infection frequency but doesn’t rule it out. This thesis also further consolidates the fact that small stumps of Norway spruce need protection against infection of Heterobasidion spp, where the treatment agent urea could be seen as more effective. Even though urea was more effective in this thesis, Phlebiopsis is an agent that also decreases the infection rate and it is significantly better to treat stumps after pre commercial thinning than to leave the stumps untreated. Urea is an agent that, with tax legislation today, is expensive to use and of this reason Phlebiopsis might still be the economically best agent to use.