Black stain root disease progression in coastal Douglas-fir in British Columbia

Abstract

Periodic monitoring of black stain root disease (Leptographium wageneri var. pseudotsugae) in coastal Douglas-fir (Pseudotsuga menziesii) on Vancouver Island and mainland British Columbia, Canada, provided intensification and mortality rates for this disease. Fifteen plots with Douglas-firs of varying ages and sizes and growing on sites with different conditions were established in 1989 and assessed in 1994 and 2000. Overall mortality from black stain root disease increased from 11.4% in 1989 to 19.0% in 2000, or 0.7% per year. A further 6.5% of trees succumbed to other root diseases and 9.4% to unknown causes but most likely black stain root disease. When trees were placed in three diameter classes, there were no significant differences in disease incidence among size classes or over time. Based on plot-level data, the incidence of disease increased with an increase in elevation (P < 0.09) and with an increase in slope (P < 0.08). Mean tree age and aspect were not significantly related to disease incidence. Crown condition rating of trees within the black stain root disease centers was a good predictor of future mortality and further disease progression. Trees with crown condition classes of slightly yellow foliage, moderately yellow foliage, totally yellow foliage, and >50% defoliated in 1989 died at a higher rate as crown condition deteriorated with 26%, 45%, 64%, and 77% tree mortality, respectively, by 2000.