Hwang, S. F., Cao, T., Xiao, Q., Ahmed, H. U., Manolii, V. P., Turnbull, G. D., Gossen, B. D., Peng, G. and Strelkov, S. E. 2012. Effects of fungicide, seeding date and seedling age on clubroot severity, seedling emergence and yield of canola. Can. J. Plant Sci. 92: 1175–1186. The infestation of seeds by Plasmodiophora brassicae can result in the transmission of clubroot disease in canola. Five fungicides, including Dynasty 100 FS (azoxystrobin), Helix Xtra (thiamethoxam+difenoconazole+metataxyl+fludioxonil), NebijinTM 5SC (flusulfamide), Prosper FX (clothianidin+carbathiin+trifloxystrobin+metalaxyl), and Vitavax RS (carbathiin+thiram), were evaluated under greenhouse conditions using artificially infested canola seeds for their efficacy in eliminating seed-borne inoculum. All of the fungicides significantly reduced clubroot relative to the non-treated control, but NebijinTM 5SC and Dynasty 100 FS were the most effective. However, in field trials with Cruiser 5 FS (thiamethoxam), Helix Xtra, Dynasty, Prosper and Sedaxane (pyrazole anilide) applied alone or as a mixture, none of the treatments reduced clubroot severity or improved seedling emergence or yield compared with the insecticidal control (Cruiser 5 FS) in the susceptible cultivar. Clubroot severity was lower in early-seeded canola compared with the late-seeded crops in 2 site-years. The younger seedlings had greater disease severity and reduced plant height and yield than did older seedlings in both resistant and susceptible canola cultivars. We conclude that a combination of approaches including seed treatments and manipulation of seeding dates in conjunction with deployment of resistant cultivars is necessary for the sustainable management of clubroot in canola.