Opportunities for use of fumigation / solarisation to manage clubroot in Canada.
Robson, J., Gossen, B.D., and McDonald, M.R. 2016. Opportunities for use of fumigation / solarisation to manage clubroot in Canada. Can. J. Plant Pathol. 38: 122.
Clubroot (Plasmodiophora brassicae Woronin) is an important disease of Brassica crops worldwide. Lab and field trials were conducted in 2014 to assess the efficacy of the fumigants metam-sodium and chloropicrin against resting spores of P. brassicae in soil and the potential for interaction with solarization. Efficacy was assessed using a plant bioassay of clubroot severity on Shanghai pak choi and a vital stain (Evan's blue) to assess resting spore viability. In a controlled environment study, two formulations of metam-sodium (Busan 1236 and Vapam HL) both virtually eliminated symptoms while the control showed substantial infection (70 DSI). In a field trial on a soil with a high organic content, chloropicrin at 128 kg a.i. ha-1 substantially reduced severity relative to the control (46 vs. 89 DSI) but metam-sodium at 150 and 300 kg a.i. ha-1 was not effective. Within this trial, plots with chloropicrin were covered with an impermeable plastic film, but metam-sodium treatments were not. In a field trial on mineral soil where disease pressure was low, each rate of metam-sodium and chloropicrin assessed eliminated symptoms. In a trial with mineral soil in bins, a 6-wk-long solarization pre-planting treatment increased severity relative to the control. This result was unexpected, and may be an artifact unrelated to treatments. Spore viability was not closely associated with treatment efficacy. The high effectiveness of metam-sodium under controlled conditions relative to the field indicated that effective sealing of the soil may greatly improve the effectiveness of fumigant treatments.
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