Incidence of butt rot in a tree species experiment in northern Denmark

The susceptibility to infections by Heterobasidion annosum (Fr.) Bref. was examined in a 28-year-old tree species experiment in northern Jutland, Denmark. Silver fir (Abies alba Mill.), Caucasian fir (Abies nordmanniana (Stev.) Spach), grand fir (Abies grandis (Dougl) Lindl.), noble fir (Abies procera Rehd.), Japanese larch (Larix kaempferi (Lamb.) Carr.), Norway spruce (Picea abies (L.) Karst.), Sitka spruce (Picea sitchensis (Bong.) Carr.), and Douglas fir (Pseudotsuga menziesii (Mirb.) France) were planted after shelterwood falling of a mountain pine (Pinus uncinata Mill. ex Mirb.) stand that had been infected by H. annosum. Douglas Br and noble fir showed the greatest mortality due to H. annosum during the first 5 years after planting. At first thinning the highest incidences of butt rot were recorded in noble fir, Japanese larch and Sitka spruce, with 44%, 43% and 36% of the thinned trees infected, respectively. Silver fir and Caucasian fir were almost free from infections. Maximum extension of H. annosum rot columns were in Japanese larch (18 dm). Heterobasidion annosum was found to be the most important decay causing fungus. Mating tests assigned all isolated strains of H. annosum to the P-intersterility group.