Stump treatment against Heterobasidion root rot in practical forestry : how well does it work?

Sammanfattning: The effect of Phlebiopsis gigantea on root and butt rot causing fungus Heterobasidion spp. was investigated in fifteen stands of Norway spruce (Picea abies) in southern Sweden. The stumps were mechanically treated immediately after felling and only stumps with no sign of decay were sampled for the study. A pictorial sampling of 396 stumps was conducted one to six hours after felling to analyze the treatment coverage. Six to seven weeks later, discs of the photographed stumps were cut and analyzed for the presence of Heterobasidion. The effect of P. gigantea on Heterobasidion was calculated using four measurements: treatment coverage of Rotstop®S Gel, relative infected area, number of Heterobasidion colonies per disc and infection frequency (proportion of infected stumps). Overall, treatment with Rotstop®S Gel did not protect against spore infection. Larger stumps were more susceptible and suffered from more severe infections, regarding size and number of Heterobasidion colonies. However, the relative infected area decreased with an increasing coverage of P. gigantea, highlighting the importance of having a 100% treatment coverage on all stumps. By contrast, treatment coverage failed to reach minimum coverage (85-95%), commonly required by stakeholders, on a large proportion of the stumps, pointing to the need of improving the technology calibration. Further studies on stump treatment against root and butt rot in practice are necessary, as the results from this study are inferior to earlier studies with controlled measurements.