An assessment of the fumigant metam sodium and a Brassica juncea-derived biofumigant as management tools for clubroot (Plasmodiophora brassicae) of canola (Brassica napus)

Abstract

Clubroot of crucifers, caused by the soilborne parasite Plasmodiophora brassicae, is spreading across canola (Brassica napus) fields in Alberta, Canada. Dissemination of the parasite is associated with the movement of infested soil on farm and other machinery, with the disease generally occurring first as localized patches near field entrances. The soil fumigant Vapam (metam sodium) was evaluated as a tool to manage foci of P. brassicae infestation. Replicated experiments at two field sites in central Alberta showed reductions in clubroot severity ranging from 9-51% following treatment with varying rates of Vapam. Some residual effects also were detected, as decreases in disease severity of up to 28% were observed in the year following Vapam treatment. In a second set of experiments, a commercial seed meal (B. juncea)-based biofumigant, MustGrow, was assessed for efficacy against clubroot under greenhouse conditions. No significant declines in clubroot severity were detected, and the concentration of P. brassicae resting spores in the soil, as measured by quantitative PCR analysis, did not decrease after treatment with the biofumigant. However, plant mortality was high, likely due to the presence of root rot pathogens in the soil, and the results of the biofumigant study should be interpreted with caution. While Vapam shows some potential as a clubroot management tool, additional research is needed to fully evaluate the efficacy of the biofumigant. An integrated approach will be required for the sustainable management of clubroot of canola.