Abstract:
Pole-sized, live western larch Larix occidentalis Nutt.) were inoculated with Ophiostoma pseudotsugae(Rumb.) von Arx or Leptographium abietinum (Peck) Wingf., two blue stain fungi associated with the Douglas-fir beetle (Dendroctonous pseudotsugae Hopkins), to assess their pathogenicity. Inoculation with O. pseudotsugae resulted in a significantly greater percentage of necrotic phloem compared to inoculations with L. abietinum. The percentage of occluded sapwood was significantly greater after L. abietinum inoculations compared to O. pseudotsugae inoculations. Percentages of necrotic phloem and occluded sapwood were positively correlated with inoculation density. In the inoculation band, all trees had greater than 60% functional sapwood four months after inoculation. The results suggest that western larch can successfully limit colonization by Q. pseudotsugae and L. abietinum. The inability of the fungi to thrive in live western larch may be a factor in the consistent failure of Douglas-fir beetle brood to survive in live western larch.
