No abstract

An alternative precommercial thinning technique results in trees being cut higher up the stem compared to the normal method using a brush saw. The aims of this study were to investigate if primary infection of Heterobasidion spp. on precommercial thinning stumps of Norway spruce and birch is influenced by stump height and to test the control efficacy of stump treatment with Phlebiopsis gigantea on precommercial thinning stumps of Norway spruce. Small Norway spruce and birch trees were felled on five sites in southern Sweden and their stumps subjected to natural spore infection. For each species, two treatments of stump height were created: 15 and 100 cm. Half of the Norway spruce stumps were treated with P. gigantea. After two months, 896 stumps were sampled and infection by Heterobasidion spp. was quantified. The height of stumps did not significantly influence infection frequency or size of infection on either tree species. Untreated Norway spruce stumps had an infection frequency of 55% while 31% of the treated stumps were infected. The control efficacy of stump treatment in terms of reduced relative infected area was 61-65%. The area occupied by Heterobasidion spp. on birch stumps was generally small, on average 0.4 cm 2 per infected stump, although 15% of the stumps were infected. The risk of primary infection in Norway spruce dominated stands should be considered when precommercial thinning is conducted but the control efficacy and economy of stump treatment warrants further investigation before practical recommendations can be made.

The development of Heterobasidion infection following one precommercial thinning (PCT) in a Norway spruce stand was simulated in the root disease model RotStand, adjusted with a specific growth model for young trees. The effects of stand age at PCT, spore infection probability on PCT stumps, intensity of PCT and efficacy of control measures on disease development were simulated for different management alternatives and the percentage of decayed stems at final felling was compared. Economic outcomes during a rotation were calculated in the decision support system, Heureka. Stand age and the probability of spore infection at PCT did not significantly influence decay frequency at final felling. The percentage of decayed stems at final felling increased with increasing PCT intensity. PCT at stand age of 20 years with stump treatment reduced disease impact, and summer PCT with stump treatment resulted in higher economic outcome compared to PCT without stump treatment during summer or winter. Infection of PCT stumps can negatively impact timber production. If economic gain from stump treatment during PCT is sought, new cost efficient application techniques should be developed. Because results and conclusions are based on simulated disease development and treatment, more field research is needed to validate some findings.

Two species of the tree pathogenic fungus Heterobasidion spp. exist in Sweden, Heterobasidion annosum s.s. and Heterobasidion parviporum. Both species are known to infect Norway spruce (Picea abies). The aim of the study was to examine the interspecific competition between H. annosum s.s. and H. parviporum as well as their colonization rate in fresh Norway spruce wood. Equal amount of conidiospores from each species was sprayed together on 30 fresh, previously uninfected, Norway spruce billets. After incubation in a greenhouse, the proportion of Heterobasidion spp. colonies belonging to each species was recorded. Of the 196 colonies isolated from the upper part of billets, 195 were H. parviporum. All isolated colonies further down in the billets were H. parviporum. To study the colonization rate, H. annosum s.s. and H. parviporum were sprayed alone on 30 spruce billets each, incubated and growth recorded both vertically and horizontally. H. parviporum grew further down in the billets (p = 0.008) and covered a larger area (p < 0.001) than H. annosum s.s. While H. annosum s.s. and H. parviporum both infected fresh Norway spruce wood H. parviporum outgrew and outcompeted H. annosum s.s during the early colonization stage.