Symptom development and mortality rates caused by Armillaria ostoyae in juvenile mixed conifer stands in British Columbia's southern interior region

Plots were established in 20 juvenile mixed conifer stands in the Interior Cedar Hemlock biogeoclimatic zone of British Columbia's southern interior region in western Canada to assess mortality and host response to infection in the form of basal lesions caused by Armillaria ostoyae. Western redcedar showed significantly lower mortality and a higher proportion of callused lesions at the root collar than Douglas-fir and western hemlock. Mortality decreased with increasing tree diameter for all species; however, the rate of decrease was markedly greater for western redcedar than Douglas-fir or western hemlock. Results from logistic regression analysis showed that the probability of Douglas-fir being killed is 14.6 times greater than western redcedar in these juvenile stands. Because western redcedar displayed significant resistance to A. ostoyae at both the root and stand level, this species represents an excellent choice as a significant stand component with more susceptible conifers. Should susceptible conifers succumb to Armillaria root disease, western redcedar will likely fill in the stand.