Drenkhan, T., Hanso, S. and Hanso, M. 2008. Effect of the Stump Treatment with Phlebiopsis gigantea against Heterobasidion Root Rot in Estonia. Baltic Forestry, 14 (1): 16-25

Efficiency of the biological control agent Rotstop® against spore infection by the pathogenic basidiomycetes of the genus Heterobasidion was investigated in Estonia during two years. First, in vitro laboratory experiments were carried out for comparison of the efficiency of the basic strain of Phlebiopsis gigantea in Rotstop® with an Estonian strain of the same species against several Estonian strains of Heterobasidion spp. Preliminary laboratory tests on artificially infected wood pieces of Picea abies and Pinus sylvestris were conducted, as well, for the learning of visible characteristic features of rot caused by Phlebiopsis gigantea, and the diagnostic features of Heterobasidion spp. on wood surfaces. Following experiments in forests in four Norway spruce and two Scots pine before unthinned stands, in south-eastern and north-eastern Estonia, respectively, comprised in each site as a mean 83 stumps, which were treated with the suspension of Rotstop®, and 21 stumps, which were left untreated as the control. Rotstop® had especially effectively controlled airborne infection of Heterobasidion annosum s. str. in P. sylvestris stands (average areas occupied by the fungi on treated stumps: P. gigantea, 113.3 cm² and H. annosum s. str. 0.6 cm², respectively). Noticeable natural infection by the indigenous Phlebiopsis gigantea occurred in the control stumps as well, but it was too limited to really keep the pathogen away from fresh cuttings. In spruce the preparation Rotstop® was effective (average areas 75.2 cm² and 4.3 cm², respectively), but less than in pine, possibly because of the extremely high infection level of Heterobasidion parviporum in our experimental spruce stands (up to 85 % of the number of untreated stumps).

Key words: Biological control, Rotstop® Phlebiopsis gigantea, Heterobasidion spp., Scots pine, Norway spruce.