Visible versus actual incidence of Armillaria root disease in juvenile coniferous stands in the southern interior of British Columbia

The relationship between aboveground symptoms and belowground incidence of Armillaria ostoyae (Romagn.) Herink on conifers in 13- to 24-year-old stand s was investigated at five sites in each of the dry, moist, and wet climati c regions in the Nelson forest region, British Columbia. All trees > 1.3 m in height in 0.01-ha circular plots centred on a tree killed fewer than two or more than five years previously or located where there were no symptoma tic trees were removed from the soil by an excavator. The location and host response at each A. ostoyae lesion on root systems were recorded. Signific ant differences in belowground incidence were seen among climatic regions a nd plot types, with distance from the centre of plots, and between planted and naturally regenerated trees. Belowground incidence was related to the p ercentage of putatively colonized stumps within and adjacent to plots. Ther e were significant differences among climatic regions in the intensity of i nfection, host reaction to infection, and percentage of diseased trees show ing aboveground symptoms. These results have implications for interpreting results of surveys for Armillaria root disease in juvenile stands and for t ending of such stands.