Cylindrocladium root rot in Ontario bare-root nurseries: estimate of spruce seedling losses

Estimates of cylindrocladium root rot losses in three black and three white spruce compartments at five Ontario bare-root nurseries were determined through visual field assessment and seedling isolation. The causal fungus, Cylindrocladiumfloridanum Sob. & C.P. Seym., was isolated from 10–77% of the symptomatic and 0–28% of the apparently healthy seedlings in each compartment. In five compartments, estimates of mean incidence based on seedling isolations and visual assessment, were higher than those based on visual assessment alone. The percentage of living spruce (apparently healthy or symptomatic) estimated to be infected in each compartment was 0.1–32.7%. No fungus isolations were attempted from dead seedlings. Mortality in the plots in the six compartments was 0.02–17.7%. The correlation between the level of Cylindrocladium incidence and the inoculum density was significant (p < 0.01) in two compartments. The use of inoculum density to predict disease incidence warrants further investigation.