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Metam-sodium and chloropicrin soil treatments reduce resting spore populations of Plasmodiophora brassicae, 2014.

Robson, J., Gossen, B.D., and McDonald, M.R. 2016. Metam-sodium and chloropicrin soil treatments reduce resting spore populations of Plasmodiophora brassicae, 2014. Can. J. Plant Pathol. 38: 130–131.

Abstract

Clubroot (Plasmodiophora brassicae Woronin) is an important disease of canola (Brassica napus L.) and other Brassica crops. The efficacy of metam-sodium (trade name Vapam HL or Busan 1236) and chloropicrin (Pic Plus) fumigants against P. brassicae was assessed in growth room and field studies. Efficacy was assessed in a bioassay of severity (disease severity index, DSI) on Shanghai pak choi (B. rapa L. subsp. chinensis var. communis) under controlled conditions. In a growth room study, severity was low (< 2 DSI) on infested muck soil treated by drenching with Vapam (146, 292, 585 L a.i. ha-1) or Busan (145, 290, 581 L a.i. ha-1) in air-tight plastic bags, but high (70 DSI) in the nontreated control. In soil from treatments on a muck soil (~70% organic matter) site, a low rate of chloropicrin (89 L) covered with an impermeable plastic film reduced subsequent clubroot severity compared to the check (45 vs. 89 DSI), but moderate to high rates of Vapam (292, 585 L) that was packed but not tarped were much less effective (78 DSI). In soil from treatments on mineral soil, severity in the control was low (3 DSI) and no symptoms developed from treatment that received metam-sodium (Vapam and Busan) or chloropicrin. There was no difference between Vapam and Busan at any application rate in any study. Chloropicrin was more effective than metam-sodium in the field, but sealing the soil surface (as used with chloropicrin) may improve the efficacy of metam-sodium.

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