Soil treatments and amendments for amelioration of clubroot of canola

Hwang, S. F., Strelkov, S. E., Gossen, B. D., Turnbull, G. D., Ahmed, H. U. and Manolii, V. P. 2011. Soil treatments and amendments for amelioration of clubroot of canola. Can. J. Plant Sci. 91: 999-1010. Clubroot, caused by Plasmodiophora brassicae, has become a long-term challenge to canola production in central Alberta, Canada. Trials were established in P. brassicae infested commercial fields near Leduc, Edmonton, and St. Albert, AB, to examine the effects of fungicidal soil treatments and soil amendments on crop damage caused by clubroot. Treatment of the soil with Terraclor (quintozene) reduced clubroot severity and increased plant growth (canopy coverage and plant height) and seed yield in severely infested soils. Raman (cyazofamid) at 7.5 L ha(-1) increased canopy coverage and height in 2 of 4 site years, and yield in 1 of 4 site years. Among the soil amendment treatments, wood ash at 7.5 t ha(-1) or ground limestone (calcium carbonate) at 5.0 or 7.5 t ha(-1) increased plant height and yield in severely infested soils at Leduc. Limestone at 7.5 t ha(-1) reduced clubroot severity at both sites and at 5.0 t ha(-1) reduced clubroot at St. Albert. Wood ash at 7.5 t ha(-1) reduced clubroot severity at Leduc in both years and all rates of wood ash reduced clubroot severity at St. Albert in 2008. Canopy coverage was increased by limestone at 7.5 t ha(-1) in both years at Leduc and by wood ash at 7.5 t ha in one of the site-years at Leduc. In 2009 and 2010, in-row treatments with Terraclor (quintozene), calcium carbonate, wood ash or quintozene + calcium carbonate or wood ash reduced clubroot severity at the Edmonton site, but yield was unaffected. We conclude that quintozene and/or high levels of limestone or wood ash can reduce the impact of P. brassicae on canola. However, in-row assessment at application rates that might be economically feasible showed little potential to increase yield in infested commercial fields.