EFFICACY OF FUNGICIDAL SEED TREATMENTS AGAINST PREEMERGENCE DAMPING-OFF AND POSTEMERGENCE SEEDLING ROOT-ROT OF GROWTH CHAMBER GROWN CANOLA CAUSED BY RHIZOCTONIA-SOLANI AG-2-1 AND AG-4

Twenty-one fungicides were tested in vitro against the mycelial growth of an AG-2-1 and an AG-4 isolate of Rhizoctonia solani. Sixteen of these fungicides were evaluated as seed treatments against pre-emergence damping-off and eight against post-emergence seedling root rot of canola cv. Westar (Brassica napus) and cv. Tobin (B. campestris). Seed was planted in soilless mix infested with an isolate of AG-2-1 or AG-4, or their mixture. Benodanil, benomyl, carbathiin (carboxin), cyproconazole, flutolanil, furmecyclox, iprodione, thiabendazole, and tolclofos-methyl showed strong in vitro activity against both isolates. Fenpropimorph, flusilazole, propiconazole, triadimenol, and vinclozolin had moderate activity and tebuconazole, triadimefon, and chlorothalonil poor activity; while fenarimol, imazalil, and nuarimol were ineffective against both isolates. Pencycuron gave very strong inhibition of the AG-2-1 isolate but was ineffective against the AG-4 isolate. Fenpropimorph, furmecyclox, iprodione, and tolclofos-methyl, applied to Westar and Tobin seed at 1 g a.i./kg, provided about 90% control of pre-emergence damping-off in pots infested with either isolate AG-2-1, AG-4, or both. Furmecyclox and iprodione at 2-4 g a.i/kg were the most effective fungicides against post-emergence seedling root rot caused by the AG-2-1 isolate. Cyproconazole provided 90% control against damping-off ((AG-2-1) at the lowest rates of 0.03 and 0.12 g a.i./kg seed of Westar and Tobin, respectively, but gave poor control of seedling root rot. Generally a higher quantity of fungicide was required in cv. Tobin than in cv. Westar for an equivalent level of disease control. This was related to the larger number of seeds per g in Tobin (418) than in Westar (277).