Abstract
The root-rot of sugar beets caused by Pellicularia filamentosa (Pat.) Rogers (Rhizoctonia solani) is prevalent in some regions of Hokkaido. The occurrence of the disease and the amount of the pathogens in soil were observed during the growing season of the host plants in the farm where has been observed the severe annual occurrence of the dry-rot canker or crown-rot of sugar beets. The damping-off of seedlings caused by the same pathogen was severe in May and the root-rot or crown-rot in matured plants appeared after the last decade of July, but few rotting symptom of the roots could be observed during the intermediate seasons between these severe outbreaks of the root disease. The increasing tendency of the density of pathogens in soil was almost parallel to the prevalence of the disease.
