The effect of Phlebiopsis gigantea and urea stump treatment against spore infection of Heterobasidion spp. on hybrid larch (Larix × eurolepis) in southern Sweden

Abstract

SummaryThe efficacy of stump treatment with 40% urea solution and spore suspension of Phlebiopsis gigantea against primary infection by Heterobasidion spp. on hybrid larch (Larix × eurolepis) was tested in two field studies in southern Sweden. In the first study, stumps treated with urea or P. gigantea were sampled by cutting a cross‐section disc after 3 months following exposure to natural conditions, and in the second study, stumps treated with only P. gigantea were sampled after 2 months. Spore traps made from hybrid larch, Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) were used to estimate the abundance of ambient spores of Heterobasidion spp. in the second study. Urea significantly reduced infection frequency of Heterobasidion spp. compared to the control. Phlebiopsis gigantea was less effective at reducing infection frequency in the first study than in the second study. Infections were caused by both H. parviporum and H. annosum sensu stricto. The amount of H. annosum infection in proportion to Heterobasidion spp. was significantly lower on the stumps treated with P. gigantea compared to the control; however, the proportion of H. parviporum on the treated stumps was not higher than the control in the first study. Spore traps made of Scots pine had a significantly higher frequency of infection than Norway spruce and hybrid larch. Only the spore traps made of hybrid larch showed significant correlation with the control stumps in terms of relative infected area. Conclusively, it seems prudent to protect hybrid larch stumps from primary infection by Heterobasidion spp., and both urea and P. gigantea can be recommended as stump treatment agents on hybrid larch, even if urea seemed to present more stable results.