The efficacy of an experimental biofumigant on Plasmodiophora brassicae

Clubroot, Plasmodiophora brassicae, is a soilborne pathogen that causes clubs to form on the roots of brassica crops. Management is difficult due to the longevity of resting spores, the overwintering structure, in the soil. The efficacy of an experimental biofumigant was tested in both field and controlled environment studies. The field trial was conducted on high organic matter (muck) soil comparing 150 L/ha of biofumigant applied with a watering can to a control. In repeated controlled environment studies, 150 L/ha was applied to mineral and muck soils, in sealed plastic bags before transferring soil into pots. Soil samples were taken pre-and post-treatment application to determine the effect on resting spore number. All trials were seeded with clubroot susceptible canola and assessed for clubroot development six or seven weeks after seeding using a 0-3 scale to calculate disease severity index. In the field trial, there was no effect on clubroot severity. There was a decrease in resting spore concentrations, however it was not significant enough to decrease disease development. In the first repetition of the controlled environment study there was low severity and incidence in both soil types. The biofumigant caused a decrease in severity, however there was no interaction with soil type. In the repetition there was no clubroot development in mineral soil but high disease severity in muck soil. There was no effect of the biofumigant on disease severity. The experimental biofumigant may be more efficacious when there is lower disease pressure, however, more research is required.