Spread of Armillariaostoyae in juvenile lodgepole pine stands in west central Alberta

Juvenile lodgepole pine (Pinuscontorta Dougl. var. latifolia Engelm.) were excavated at three sites near Hinton, Alberta. In all cases in which Armillariaostoyae (Romagn.) Herink had become established in the root collar or taproot, it was also able to colonize lateral roots. In cases in which only lateral roots were infected, subsequent colonization generally was primarily distal to the point of infection. Rhizomorphs were associated with 89% of 21 infected roots, whereas only 19% of 70 roots with no associated rhizomorphs were infected. Stumps, roots, and debris from the previous generation of trees were the inoculum sources for 78% of 36 infected juvenile trees, and infected regeneration served as the inoculum source for the remaining trees. Rhizomorphs occasionally were attached to the roots or rhizomes of plants other than pine, especially fireweed (Epilobiumangustifolium L.). There was no spatial relationship between stumps and symptomatic trees. Nearest neighbor analysis indicated that the likelihood of an individual tree developing symptoms was dependent on whether trees within 0.15 m were dead or dying but independent of the apparent health of trees at greater distances.