Of 14 fungicides with different modes of action, cyproconazole and tolclofos‐methyl were generally inhibitory both in vitro and in vivo against all tested isolates of five Rhizoctonia species belonging to the teleomorphs Thanatephorus cucumeris, Waitea circinata or Ceratobasidium cereale. Triadimenol and carboxin provided considerable variation in activity against different species and isolates, whereas prochloraz was ineffective against all isolates. Imazalil and fenarimol showed moderate control, whereas flusilazole, propiconazole, fenpropimorph and benomyl showed strong activity against R. zeae and R. oryzae, but were much less effective against R. sasakii, R. cerealis and R. solani. Benodanil and iprodione controlled all isolates of R. cerealis and R. solani, but were not very effective against R. zeae and R. oryzae. Pencycuron showed strong activity against R. sasakii and most R. solani isolates, moderate activity against R. zeae, and was ineffective against R. oryzae and R. cerealis.

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Tolclofos-methyl, iprodione and cyproconazole, among the eleven fungicides tested in vitro, gave consistently strong inhibition against all ten anastomosis groups (AGs) of Rhizoctonia solani. Carboxin, furmecyclox, thiabendazole, fenpropimorph and vinclozolin also inhibited all AGs but with wide variations in toxicity levels (EC90 values). Pencycuron showed strong activity against four AGs but was ineffective against the other six AGs. Generally, R. solani AGs were insensitive to fenarimol and imazalil. Tolclofos-methyl strongly inhibited 23 AG2-1 and 20 AG4 rapeseed/canola R. solani isolates from different locations in Saskatchewan, Alberta and Manitoba. The same isolates were also sensitive to iprodione, cyproconazole and carboxin. All AG4 canola isolates were insensitive to pencycuron (EC90 > 500 mg/1) while AG2-1 isolates showed highly variable levels of sensitivity with EC90s ranging from 0.5 to 220 mg/1. Tolclofos-methyl, applied to Brassica napus (canola) cv. Westar seed at 1 g a.i./kg, provided 75-100 % control of seedling damping-off in pots infested with AG2-1 or AG4 isolates. In parallel experiments, pencycuron (1 g a.i./kg seed) failed to control damping-off by AG4 canola isolates and gave variable disease control against AG2-1 isolates.

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Eight fungicides (benodanil, carboxin, cyproconazole, fenpropimorph, furmecyclox, iprodione, pencycuron and tolclofos-methyl) were evaluated, under growth chamber conditions, as seed treatments against pre-emergence dampingoff and post-emergence seedling root rot in six Brassica species. Five cultivars of B. rapa, four cultivars of B. juncea, four cultivars of B. napus and one cultivar/ strain from each of B. carinata, B. nigra and B. oleracea were grown in soilless mix infested with an isolate of Rhizoctonia solani AG-2-1, B. nigra and B. juncea were considerably less susceptible to R. solani than the four other species. Cyproconazole at 0.05-0.1 g a.i./kg seed and the other fungicides at 2-4 g a.i./ kg seed provided almost complete control of pre-emergence damping-off in most Brassica species and their cultivars. Their efficacy varied against the postemergence seedling root rot. Furmecyclox, iprodione, tolclofos-methyl and pencycuron consistently gave good control of seedling root rot in all Brassica species and their cultivars. Benodanil and fenpropimorph provided moderate control, and carboxin and cyproconazole gave poor control against root rot. Efficacy of carboxin, cyproconazole, benodanil and fenopropimorph against seedling root rot varied significantly ( P G 0.05) among cultivars within a Brassica species.