Field evaluation of meadowfoam (Limnanthes alba) seedmeal as a soil amendment to control clubroot caused by Plasmodiophora brassicae was conducted using cauliflower seedlings and seeded mustard grown in naturally infested soils. Ionic surfactant drench was applied as a comparative treatment. Meadowfoam seedmeal (MSM) incorporation at a rate of 15,000 kg·ha-1 resulted in greatest control of clubroot incidence and severity. This treatment also resulted in significantly greater fresh weight yield of cauliflower compared to controls and surfactant drench application. Some phytotoxicity symptoms were observed at high rate (30,000 kg·ha-1) of MSM treatment. MSM glucosinolate products may have an important role in regulating plant-pathogen interactions.