Interaction of solarization, fumigation, and totally impermeable film for the management of clubroot (Plasmodiophora brassicae) on brassica crops
The organism that causes clubroot of brassica crops, Plasmodiophora brassicae Woronin, persists as long-lived resting spores in soil. Methods to reduce or eradicate the resting spores are needed. Controlled environment and field studies, both with high organic matter soil, were undertaken to evaluate the efficacy of fumigation with metam sodium, (rates 10, 75, 150 and 300 kg a.i. ha‑1). Chloropicrin (rates 128, 164, 224, 280, 336 kg a.i. ha‑1) was also evaluated in the field. Soil solarization alone and in combination with fumigants was evaluated in field trials covered with totally impermeable film (TIF) and polyethylene tarps. Efficacy was determined by bioassays with susceptible host Shanghai pak choi (Brassica rapa L. ssp. chinensis) and quantification of resting spores using qPCR. Soil dilutions were treated with propidium monoazide (PMA) prior to qPCR to inhibit the amplification of DNA from dead resting spores and thus quantify only viable resting spores. Controlled environment studies showed that all rates of metam sodium-reduced clubroot severity. Shoot weight was higher in plants grown in the fumigated soil than the untreated check. In the field in 2015, chloropicrin, and metam sodium at rates over 75 kg a.i. ha‑1, reduced clubroot incidence and severity. Covering soil with TIF following fumigation improved the efficacy of the fumigants. Covering soil with TIF alone (soil solarization) for two weeks in June 2017 reduced clubroot severity from 82% in the untreated check to 35%. Adding fumigant did not further reduce clubroot severity. Treatment with PMA demonstrated that the number of viable resting spores was lower in all of the treatments compared to the untreated, uncovered check. Soil solarization using TIF alone looks promising for management of clubroot. Further research on time and temperature combinations under Canadian conditions is warranted.
McDonald, M.R., Gossen, B.D., Robson, J. and Al-Daoud, F. (2020). Interaction of solarization, fumigation, and totally impermeable film for the management of clubroot (Plasmodiophora brassicae) on brassica crops. Acta Hortic. 1270, 153-160
soil-borne plant disease, chloropicrin, metam sodium, soil solarization, pathogen detection, spore viability