Soil fumigation with Vapam (metam sodium) to control clubroot (Plasmodiophora brassicae) of canola (Brassica napus)

Abstract Clubroot, a damaging disease of canola (Brassica napus L.) caused by the soilborne parasite Plasmodiophora brassicae Woronin, is spreading across Alberta and other provinces of western Canada. The movement of infested soil on field machinery is the main mechanism of dispersal, with clubroot generally occurring first as localized patches near field entrances. In this study, the soil fumigant Vapam (metam sodium) was evaluated as a management option for foci of P. brassicae infestation. Replicated experiments at two field sites in central Alberta showed reductions in clubroot severity ranging from 9% to 51% following treatment with varying rates of Vapam. Decreases in clubroot severity of up to 28% were observed in the year following Vapam treatment, indicating some potential residual effects and (or) a reduction in the amount of inoculum returned to the soil in the previous year. While Vapam shows some promise as a clubroot management tool, an integrated approach will be required for the sustainable management of this disease on canola.