Comparative efficacy of new and traditional stump treatments against Heterobasidion spp. in Norway spruce, silver fir and pine stands.

The destructive Heterobasidion annosum species complex includes in Europe four species, one of which, i.e. H. irregulare, introduced from North America. The three native Heterobasidion species attack preferentially Norway spruce (Picea abies), silver fir (Abies alba) and pines (Pinus spp.), while H. irregulare is associated with Italian stone pine (Pinus pinea). The efficacy of stump treatments with Proradix ® (based on Pseudomonas protegens strain DSMZ 13,134), the cell-free filtrate (CFF) of Pseudomonas protegens (strain DSMZ 13,134), Rotstop ® (based on Phlebiopsis gigantea), a native strain of Phlebiopsis gigantea and urea was investigated in Abies alba, Picea abies, Pinus pinea and Pinus sylvestris stands against airborne infections by all Heterobasidion species present in Europe. All tested treatments reduced significantly infection rates compared to controls on stumps of all tree species. The performances of treatments varied depending on the tree species. While urea was the most effective treatment regardless of the tree species, the CFF of Pseudomonas protegens resulted very promising. Authors are grateful to the staff of the Parco della Gallinara (Rome, Italy) and the Corpo Forestale/Corps Forestier of Regione Autonoma Valle d’Aosta/Région Autonome Vallée d’Aoste for helping with treatments and field samplings. A special thanks to Jean-Claude Haudemand, Giancarlo Zorzetto and Alessandro Porru.