Soil treatments and amendments for amelioration of clubroot of canola

Transcription

1 Soil treatments and amendments for amelioration of clubroot of canola S. F. Hwang 1, S. E Strelkov 2, B. D. Gossen 3, G. D. Turnbull 1, H. U. Ahmed 1, and V. P. Manolii 2 1 Alberta Agriculture and Rural Development (AARD), Crop Diversification Centre North, Edmonton, Alberta, Canada T5Y 6H3 ( sheau-fang.hwang@gov.ab.ca); 2 Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5; and 3 Agriculture and Agri-Food Canada, Saskatoon Research Centre, Saskatoon, Saskatchewan, Canada S7N 0X2. Received 9 February 2011, accepted 5 July Hwang, S. F., Strelkov, S. E., Gossen, B. D., Turnbull, G. D., Ahmed, H. U. and Manolii, V. P Soil treatments and amendments for amelioration of clubroot of canola. Can. J. Sci. 91: 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. Ranman (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 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 1 in one of the site-years at Leduc. In 2009 and 2010, in-row treatments with Terraclor (quintozene), calcium carbonate, wood ash or quintozenecalcium 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. Key words: Plasmodiophora brassicae, Brassica napus, terrachlor, calcium carbonate, wood ash, ph Hwang, S. F., Strelkov, S. E., Gossen, B. D., Turnbull, G. D., Ahmed, H. U. et Manolii, V. P Traitements et amendements du sol dans le cadre de la lutte contre la hernie du canola. Can. J. Sci. 91: La hernie du chou cause e par Plasmodiophora brassicae pose depuis longtemps un proble` me aux producteurs de canola du centre de l Alberta, au Canada. Les auteurs ont entrepris des essais dans des champs commerciaux infeste s par P. brassicae, pre` s de Leduc, Edmonton et St. Albert, dans la meˆme province, afin de ve rifier l incidence de l application de fongicides sur le sol et de divers amendements sur les dommages résultant de cette maladie. Traiter le sol avec du Terraclor (quintoze` ne) réduit la gravite de la hernie du chou et ame liore la croissance des plantes (couverture du feuillage et hauteur des plants), ainsi que le rendement grainier dans les sols fortement infeste s. L application de Ranman (cyazofamide) a` raison de 7,5 L par hectare a augmente la couverture du feuillage et la hauteur des plants deux anne es-sites sur quatre ainsi que le rendement une annéesite sur quatre. Parmi les amendements, l application de 7,5 tonnes de cendre de bois par hectare ou de 5,0 ou 7,5 tonnes de calcaire en poudre (carbonate de calcium) par hectare a accru la hauteur des plants et le rendement dans les sols fortement infeste s de Leduc. L application de 7,5 tonnes de calcaire par hectare a atte nué la gravité de la hernie du chou aux deux endroits, tandis que l application de 5,0 tonnes par hectare l a atte nue ea` St. Albert. Appliquer 7,5 tonnes de cendre de bois par hectare a diminue la gravite de la maladie à Leduc les deux années alors que la cendre de bois l a atte nuée à St. Albert, en 2008, peu importe le taux d application. Le calcaire a rehausse la couverture du feuillage lorsqu on l a appliqué au taux de 7,5 tonnes par hectare a` Leduc, les deux années de l expe rience, tandis que l application de 7,5 tonnes de cendre de bois par hectare en a fait autant, une des années-sites, a` Leduc. En 2009 et 2010, l application dans les rangs de Terraclor (quintoze` ne), de carbonate de calcium, de cendre de bois ou de quintozène et de carbonate de calcium ou de cendre de bois a diminue la gravité de la hernie au site d Edmonton, sans que le rendement en soit affecte. Les auteurs en concluent que l application de quintozène ou d une grande quantite de calcaire ou de cendre de bois, ou les deux, peut atte nuer l incidence de P. brassicae sur le canola. Toutefois, l e valuation d un taux d application dans les rangs e conomiquement re alisable pre sente peu de potentiel pour ce qui est d accroıˆtre le rendement dans les champ commerciaux infeste s. Mots clés: Plasmodiophora brassicae, Brassica napus, Terraclor, carbonate de calcium, cendre de bois, ph Can. J. Sci. (2011) 91: doi: /cjps

2 1000 CANADIAN JOURNAL OF PLANT SCIENCE Plasmodiophora brassicae Woronin is a persistent soilborne biotrophic pathogen that causes clubroot disease (Fig. 1) of canola (Brassica napus L.) and other cruciferous species worldwide (Dixon 2009). When inoculum density is high, clubroot can cause yield losses in canola of 3050% or more (Wallenhammar 1999; Strelkov et al. 2006). Since the first reports of clubroot on canola in Alberta (Tewari et al. 2004, 2005), the disease has spread from 12 fields in 2003 to over 560 in The rapid increase in the number of P. brassicaeinfested fields and the enormous potential for crop loss has raised concerns about clubroot across the Canadian prairie region (Strelkov et al. 2010). Several options have been put forward for the management of clubroot in infested fields (Shimotori et al. 1996; Donald et al. 2001; Mitani et al. 2003), including the deployment of resistant cultivars (Diederichsen et al. 2009), manipulating the seeding date (Gossen et al. 2009), liming the soil to increase soil ph (Murakami et al. 2002), and crop rotation with non-hosts and bait crops to reduce the concentration of pathogen resting spores (Kroll et al. 1984; Ikegami 1985; Murakami et al. 2001). Many of these management options are not practical or cost effective in a canola cropping system (Campbell et al. 1985; Myers and Campbell 1985; Strelkov et al. 2006), especially when the levels of resting spores in the soil are high. Crop rotation is complicated by the fact that the pathogen can survive as resting spores in the soil for long periods (Wallenhammar 1996), and many common weed species on the Canadian prairies act as hosts for the pathogen. The efficacy of a range of older fungicides including benomyl and trichlamide on clubroot has been evaluated, but the benefits have rarely been sufficient to justify their commercial use (Naiki and Dixon 1987; Suzuki et al. 1995; Hildebrand and McRae 1998). Terraclor (quintozene) interferes with mitotic division and suppresses fungal sporulation. Based on a long history of control of clubroot in cole crops (Finlayson and Campell 1971), it was registered for control of this disease in cole crop transplants in Canada. As an alternative to pesticide use, this study focused on a proprietary rhamnolipid surfactant formulation, Zonix, with a proven ability to disrupt oomycete and zygomycete reproduction (Nielsen et al. 2006) by interrupting the ability of zoosporangia to produce secondary plasmodia. A previous study by Hildebrand and McRae (1998) showed some reduction in clubroot severity with the incorporation of non-ionic surfactants; however, phytotoxicity has been noted. Two new fungicides, Allegro (fluazinam) and Ranman (cyazofamid), have shown promise for the management of clubroot in vegetable production (Mitani et al. 2003; Adhikari 2010), but have not been assessed for canola. In addition, calcium cyanamide (nitrogen/calcium oxide) has been used to manage clubroot for nearly 60 yr (Karling 1968). It has also been used as a slow-release nitrogen fertilizer and herbicide (Cornforth 1971; Rieder 1981). Its effect may arise from its high lime content, which raises the soil ph and so makes the soil environment less favorable to infection and development of P. brassicae. Although the application of calcium cyanamide and lime (Klasse 1996; Dixon and Page 1998; Donald et al. 2006) may represent effective management options, their efficacy has not been examined in a canola cropping system under the extensive production management system that is utilized on the Canadian prairies. The objective of this study was to assess the effect(s) of amending clubroot-infested soil with fungicides or with ph-altering soil amendments on plant survival, clubroot severity and seed yield of canola. MATERIALS AND METHODS Soil Amendments Trials were established in 2007 and 2008 at two clubroot-infested commercial field sites (black chernozemic Fig. 1. Clubroot galls on canola roots.

3 HWANG ET AL. * AMELIORATION OF CLUBROOT OF CANOLA 1001 Table 1a. Effects of soil amendment treatments on plant height, canopy coverage, plant mortality, and seed yield in canola grown in Plasmodiophora brassicae-infested soil near Leduc, AB, in 2007 and 2008 Soil amendment and year Rate (t ha 1 ) Emergence (plants m 2 ) height (cm) Canopy coverage (%) mortality (%) Yield (t ha 1 ) 2007 Limestone a 43bcd 13bc 19a 0.03b a 49abc 20ab 15a 0.07a a 51ab 23a 14a 0.08a Wood ash a 45abcd 15abc 13a 0.04b a 45abcd 13bc 20a 0.03b a 52a 23a 14a 0.08a Calcium cyanamide a 43bcd 11c 21a 0.02b a 41cd 9c 18a 0.03b Untreated control 42a 40d 13bc 21a 0.02b 2008 Limestone a 75bc 66bcd 2.7a 0.37b a 83a 79abc 2.4ab 0.87a a 83a 88a 2.1b 1.07a Wood ash a 73cd 65cd 2.7a 0.37b a 81ab 74abcd 2.7a 0.50b a 84a 81ab 2.3ab 0.94a Calcium cyanamide a 66de 59d 2.7a 0.36b a 66e 64cd 2.8a 0.32b Untreated control 72a 71cde 71bcd 2.6a 0.48b ae Means followed by the same letter do not differ significantly based on Duncan s Multiple Range Test at P soil) in Alberta to assess the effect of three types of soil amendments on clubroot severity and yield loss. Each study was arranged in a randomized complete block design with four replications. Each plot consisted of four, 6-m-long rows with a 30-cm inter-row spacing. There was a 60-cm spacing between plots and a 2-m buffer between replications. The experiment was established using the canola cv RR at two sites, one near St. Albert, AB (silty clay; ph 5.6; organic matter 11.8%), on 2007 May 27 and 2008 May 28, and the other near Leduc, AB (soil texture loam; ph 5.8; organic matter 9.9%), on 2007 May 30 and 2008 May 29. Nine treatments were assessed: limestone (extra fine grind, source of calcium carbonate, Graymont Western Table 1b. Effects of soil amendment treatments on plant height, canopy coverage, plant mortality and seed yield in canola grown in Plasmodiophora brassicae-infested soil near St. Albert, AB, in 2007 and 2008 Soil amendment and year Rate (t ha 1 ) Emergence (plants m 2 ) height (cm) Canopy coverage (%) mortality (%) Yield (t ha 1 ) 2007 Limestone a 104a 80a 0a 0.43bcd a 106a 88a 0a 0.59abc a 105a 93a 0a 0.87a Wood ash a 101a 80a 0a 0.39bcd a 102a 80a 0a 0.30cd a 110a 93a 0a 0.64ab Calcium cyanamide a 97a 80a 0a 0.29cd a 101a 85a 0a 0.37bcd Untreated control 69a 95a 75a 0a 0.24d 2008 Limestone ab 73a 95a 0a 1.06a ab 70a 92a 0a 0.93a a 67a 92a 0a 0.89a Wood ash b 71a 90a 0a 1.06a ab 71a 95a 0a 0.99a a 75a 91a 0a 0.99a Calcium cyanamide b 75a 91a 0a 1.05a ab 77a 97a 0a 1.05a Untreated control 79ab 67a 96a 0a 1.06a ad Means followed by the same letters do not differ significantly based on Duncan s Multiple Range Test at P50.05.

4 1002 CANADIAN JOURNAL OF PLANT SCIENCE Canada Inc., Calgary, AB) and wood ash (source of Ca, P, K) applied at rates of 2.5, 5.0 and 7.5 t ha 1, calcium cyanamide (source of Ca and N, Evonik Industries AG, Essen, Germany), applied at rates of 0.5 and 1.0 t ha 1 and a nontreated control. The amendments were spread on the soil surface of each plot and incorporated into the soil to a depth of 8 cm using a rototiller, 1 wk prior to seeding. The canola was seeded at a rate of 6.4 kg ha 1. Seedling emergence was counted over the entire 6-m 2 area of each plot; plant height was measured on 10 plants per plot, canopy coverage was rated based on a visual estimate of the percentage of ground coverage and plant mortality was rated based on a visual estimate of the percentage of dead plants. Canopy coverage and plant mortality were recorded at both sites on 2007 July 30 (GS approx. 75) and 2008 Aug. 20 (GS approx. 85). Clubroot symptom severity was assessed for 10 plants in each plot on 2007 Jul. 24 and 2008 Jul. 23 on a 03 scale (Kuginuki et al. 1999), where 0no galling, 1a few small galls, 2 moderate galling, and 3 severe galling. The plots were harvested on 2007 Oct. 03 and 2008 Sep. 25 at St. Albert, and on 2007 Oct. 04 and 2008 Sep. 30 at Leduc. The seed was cleaned, dried, and weighed, and yield was recorded for each treatment. Fungicidal Soil Treatments An experiment was established at the same sites as the soil amendment trials in 2007 and 2008 to assess the effect of fungicidal soil treatments. The plots were arranged as described previously using the canola cv RR. Ten treatments were assessed: fluazinam applied at 1750 and 2000 g ha 1 (Allegro 500 F, ISK Biosciences, Concord, OH), cyazofamid applied at 800 and 3000 g ha 1 (Ranman 400 SC, ISK Biosciences), a proprietary rhamnolipid biosurfactant applied at 1000 L ha 1 (Zonix 8.5%, Jeneil Biosurfactant Company, Saukville, WI), quintozene applied at 33.8 and 67.5 kg ha 1 (Terraclor 75 WP, Chemtura, Middlebury, CT), calcium cyanamide (Evonik) applied at 0.5 and 1.0 T ha 1, and a nontreated control. Terraclor was applied as a drench (in 6900 L ha 1 of water), Allegro and Ranman were applied in 1000 L ha 1 water, and Zonix was applied as an undiluted liquid spray. The treatments were incorporated to a depth of 8 cm using a rototiller. The trials were seeded, assessed (seedling emergence, plant height, canopy coverage, clubroot severity, seed yield) and harvested on the same dates and in the same way as in the soil amendments experiment. In-row Soil Treatments In an experiment to assess the effect of in-row soil application of quintozene, limestone, and wood ash, one trial was established in a clubroot-infested commercial field near Edmonton (black chernozemic clay soil; ph 5.0; organic matter 10.0%) on 2009 Jun. 01, and two trials were conducted in 2010, one at the same site seeded on May 26 and the other, a clubroot-infested site near Leduc, seeded on Jun. 02 using the canola cv RR at 6.4 kg ha 1 as above. Five treatments were incorporated with the seed at the time of seeding: Terraclor (quintozene, Chemtura), applied at 6.7 kg ha 1 alone or in combination with limestone or wood ash at 67 kg ha 1, and wood ash or limestone applied alone at 67 kg ha 1 and compared with a nontreated control. The rates were lower than those used in the previous study based on the anticipated concentrations of the active compounds being in close proximity to the roots, at least in the early crop development phases. Clubroot severity was assessed as described previously on Aug. 25 at Edmonton in 2009, Jul. 28 at Edmonton in 2010, and 2010 Jul. 27 at Leduc. The plants were hand-harvested on 2009 Oct. 06, 2010 Sep. 17 at Edmonton, and 2010 Sep. 30 at Leduc, and the seed was cleaned, dried, and weighed. Fungicidal Seed Treatments Field trials were conducted at the same commercial field site as the in-row soil treatment experiment near Edmonton in 2009 and 2010 to evaluate the effect of fungicide seed treatments in the control of clubroot. Seed of the canola cv. 43H57RR was treated with SYN 524 (proprietary content and formulation, Syngenta, Guelph, ON) at 5 g a.i. ha 1, Dynasty FL (azoxystrobin, 75 g L 1 metalaxyl-m, 37.5 g L 1 fludioxonil, 12.5 g L 1, Syngenta) at 20 g a.i. ha 1,or Helix XTRA FS (difenconazole, 1.25%fludioxonil, 0.13%metalaxyl-M, 0.39%thiamethoxam, 20.7%, Syngenta) at 430 g a.i. ha 1, alone or in combination with SYN 524, Dynasty FL or SYN 524Dynasty FL. Untreated seed was planted as the control. The trials were seeded on 2009 Jun. 01 and on 2010 May 27. Each trial was arranged as described previously. Seeds were planted 1.5 cm deep at 1.0 g of seed per row (6.4 kg ha 1 ). Seedling emergence was counted on 2009 Jul. 07 and 2010 Jun. 17. Clubroot assessments were conducted on 2009 Aug. 25 and twice in 2010, on Jul. 28 and Aug. 14. s were harvested at maturity on 2009 Oct. 06 and 2010 Sep. 17, as previously described. Data Analysis Initially, a mixed model analysis of variance was carried out on each experiment using the PROC MIXED option in SAS (SAS Institute, Inc. 2005). There were significant effects of site and site year interactions for both the fungicide and soil amendment trials, so the data from these experiments were analyzed separately by site-year using PROC GLM. Means separation was conducted using Duncan s New Multiple Range Test. Differences were significant at P unless otherwise noted. Clubroot symptom severity in all of the experiments was rated on a 03 scale, so a non-parametric marginal effects analysis was performed to determine the treatment effects using a SAS macro (available for download at: Projekte/LD/Makros_LD.hmtl or

5 HWANG ET AL. * AMELIORATION OF CLUBROOT OF CANOLA 1003 Table 1c. Mean, mean rank, and estimated relative effects (pi) of soil amendment treatments on clubroot severity of canola under field conditions Confidence interval (95%) for the estimated relative treatment effect Site/year and treatment Rate (L ha 1 ) Median disease rating Median rank (Ri) Estimated relative effect (pi) Lower Upper Leduc 2007 Limestone (0.026) (0.032) (0.041) Wood ash (0.033) (0.031) (0.037) Calcium cyanamide (0.033) (0.031) Untreated control (0.026) Leduc 2008 Limestone (0.036) (0.042) (0.044) Wood ash (0.036) (0.035) (0.042) Calcium cyanamide (0.035) (0.032) Untreated control (0.037) St. Albert 2007 Limestone (0.036) (0.039) (0.040) Wood ash (0.029) (0.030) (0.032) Calcium cyanamide (0.021) (0.029) Untreated control (0.032) St. Albert 2008 Limestone (0.039) (0.043) (0.040) Wood ash (0.042) (0.041) (0.045) Calcium cyanamide (0.045) (0.042) Untreated control (0.044) z Standard errors (SE) are given in parentheses after the pi estimates were determined by SE(Ri)/N, in which SE(Ri) is the standard error of the mean rank for the ith treatment as determined in the Mixed procedure of SAS with the lsmeans option (SAS institute, Inc., Cary, NC). Treatments with pi values outside the confidence interval for a treatment are significantly different from that treatment (P50.05). uni-goettingen.de/de/sof/ld/makros.html). The datasets consisted of the following variables: treatment, replication, severity rating, and subject (a unique identifier that is needed for calculating confidence intervals) (Shah and Madden 2004). Within each dataset, severity was ranked within each replicate, and analysis of variance of the ranks was conducted using the Proc Mixed option. The treatment effects on disease severity were represented by the estimated relative effects. Median and mean rank values for each treatment were calculated and treatments with pi values outside the confidence interval for a treatment were deemed significantly different from that treatment. RESULTS Weather Conditions Temperatures for May were near average in 2007 and 2008 and about 28C below average in 2009 and 2010 (Environment Canada, gc.ca). Precipitation in May was above average in 2007 and 2010, near average in 2008 and far below average in Temperatures for June were near average in every year except 2009, when they were 1.58C below average. Precipitation in June was near average in 2007 and 2010, below average in 2008 and far below average in Temperatures for July were 2.58C above average in 2007, but otherwise near average. Precipitation in July

6 1004 CANADIAN JOURNAL OF PLANT SCIENCE Table 2a. Effects of fungicidal soil treatments on plant height, canopy coverage, plant mortality and seed yield in canola grown in Plasmodiophora brassicae-infested soil near Leduc, AB, in 2007 and 2008 Soil treatment Rate (ha 1 ) Emergence (plants m 2 ) height (cm) Canopy coverage (%) mortality (%) Yield (t ha 1 ) 2007 Terraclor 45 kg 82ab 60b 31b 11cd 0.15b 90 kg 93a 81a 50a 7d 0.39a Ranman 2.0 L 82ab 43c 11c 29ab 0.02c 7.5 L 72b 45c 14c 23abc 0.04c Allegro 3.5 L 69b 45c 15c 16bcd 0.04c 5.0 L 73b 48c 15c 20abc 0.05c Calcium cyanamide 0.5 t 78ab 46c 15c 30a 0.04c 1.0 t 80ab 46c 14c 29ab 0.04c Zonix 1000 L 78ab 44c 11c 28ab 0.02c Untreated control 74b 40c 14c 30a 0.02c 2008 Terraclor 45 kg 140a 78a 74b 2.0c 0.76b 90 kg 160a 80a 86a 2.1bc 1.34a Ranman 2.0 L 159a 66bc 61cde 2.7ab 0.35cde 7.5 L 160a 71ab 70bc 2.7ab 0.55bc Allegro 3.5 L 151a 66bc 66bcd 2.8a 0.50cd 5.0 L 158a 64bc 73bc 2.5abc 0.41cde Calcium cyanamide 0.5 t 133a 51d 50e 2.6abc 0.25de 1.0 t 158a 58cd 55de 2.9a 0.21e Zonix 1000 L 137a 61bcd 65bcd 2.6abc 0.39cde Untreated control 146a 60bcd 51e 2.8a 0.22e ae Means followed by the same letter do not differ significantly based on Duncan s Multiple Range Test at P was below average in 2007, 2008 and 2009 and above average in Temperatures for August were 1.98C below average in 2007, but otherwise near average. Precipitation for August was below average for all four years. Soil Amendments The effect of year was significant in the analysis of variance for all of the response variables at both locations. In addition, there were year treatment interactions for canopy coverage and seed yield at Table 2b. Effect of fungicidal soil treatments on seedling emergence, plant height, canopy coverage, plant mortality, and seed yield of canola grown in Plasmodiophora brassicae infested soil near St. Albert, AB, in 2007 and 2008 Soil treatment and year Rate (ha 1 ) Emergence (plants m 2 ) height (cm) Canopy coverage (%) mortality (%) Yield (t ha 1 ) 2007 Terraclor 45 kg 159ab 104ab 90a 0a 0.53ab 90 kg 156ab 108a 85ab 0a 0.63a Ranman 2.0 L 164ab 92bc 63c 0a 0.17bc 7.5 L 165ab 105ab 88a 0a 0.32abc Allegro 3.5 L 150b 98abc 68bc 0a 0.29abc 5.0 L 169a 95abc 75abc 0a 0.21bc Calcium cyanamide 0.5 t 163ab 97abc 80abc 0a 0.22bc 1.0 t 166ab 97abc 73abc 0a 0.16bc Zonix 1000 L 157ab 88c 73abc 0a 0.13c Untreated control 154ab 88c 65c 0a 0.11c 2008 Terraclor 45 kg 105a 70a 88a 1.1c 0.68a 90 kg 100a 71a 89a 1.1c 0.77a Ranman 2.0 L 98a 68a 84a 1.5abc 0.65a 7.5 L 106a 65a 78a 1.2bc 0.47a Allegro 3.5 L 116a 66a 78a 1.4abc 0.55a 5.0 L 106a 65a 79a 1.3bc 0.61a Calcium cyanamide 0.5 t 114a 69a 81a 1.7ab 0.64a 1.0 t 106a 68a 86a 1.6abc 0.62a Zonix 1000 L 103a 68a 83a 1.8a 0.73a Untreated control 95a 67a 83a 1.7ab 0.67a ac Means followed by the same letter do not differ significantly based on Duncan s Multiple Range Test at P50.05.

7 HWANG ET AL. * AMELIORATION OF CLUBROOT OF CANOLA 1005 Table 2c. Median, rank, and estimated relative effects (pi) of fungicidal soil treatments on clubroot severity of canola at two sites in Alberta in 2007 and 2008 Confidence interval (95%) for the estimated relative treatment effect Site-year and treatment Rate (per ha) Median disease rating Median rank (Ri) Estimated relative effect (pi) Lower Upper Leduc 2007 Terraclor 45 kg (0.036) kg (0.038) Ranman 2.0 L (0.018) L (0.031) Allegro 3.5 L (0.017) L (0.023) Zonix 1000 L (0.018) Calcium cyanamide 500 kg (0.017) kg (0.024) Untreated control (0.017) Leduc 2008 Terraclor 45 kg (0.044) kg (0.039) Ranman 2.0 L (0.032) L (0.034) Allegro 3.5 L (0.022) L (0.040) Zonix 1000 L (0.039) Calcium cyanamide 500 kg (0.038) kg (0.026) Nontreated control (0.030) St. Albert 2007 Terraclor 45 kg (0.041) kg (0.040) Ranman 2.0 L (0.023) L (0.038) Allegro 3.5 L (0.037) L (0.027) Zonix 1000 L (0.032) Calcium cyanamide 500 kg (0.011) kg (0.022) Untreated control (0.017) St. Albert 2008 Terraclor 45 kg (0.039) kg (0.044) Ranman 2.0 L (0.038) L (0.036) Allegro 3.5 L (0.042) L (0.045) Zonix 1000 L (0.040) Calcium cyanamide 500 kg (0.040) kg (0.038) Untreated control (0.040) z Standard errors (SE) are presented in parentheses after the pi estimates were calculated as SE(Ri)/N, where SE(Ri) is the standard error of the mean rank for the ith treatment. Treatments with pi values outside the confidence interval for a treatment are significantly different from that treatment (P50.05). Leduc, and for canopy coverage, clubroot severity and seed yield at St. Albert. As a result, each site-year was analyzed separately. None of the soil amendment treatments increased seedling emergence in any of the site-years (Table 1a and 1b). Application of high rates of limestone or wood ash increased plant height in 2007 and 2008 at Leduc, but had no effect at St. Albert. The moderate rate of wood ash also increased plant height at Leduc in The moderate rate of limestone also increased plant height in both years at Leduc. Application of high rates of limestone or wood ash increased canopy coverage in 2007 at Leduc, and the high rate of limestone increased canopy coverage in 2008 at Leduc, but neither treatment had an effect at St. Albert. There was no seedling mortality at St. Albert in either of the years and no difference among treatments at Leduc in In 2008 at Leduc, mortality was lower for the high rate of

8 1006 CANADIAN JOURNAL OF PLANT SCIENCE Table 3. Mean, mean rank, and estimated relative effects (pi) of in-row chemical treatments on clubroot severity on canola under field conditions in Plasmodiophora brassicae infested soil Confidence interval (95%) for the estimated relative treatment effect Site/year and treatment Rate (per ha) Median disease rating Median rank (Ri) Estimated relative effect (pi) Lower Upper Edmonton 2009 Limestone 67 L (0.030) Wood ash 67 L (0.024) Terraclor 6.7 kg (0.029) TerraclorLimestone 6.7 kg67 L (0.030) Terraclorwood ash 6.7 kg67 L (0.031) Untreated control (0.026) Edmonton 2010 Limestone 67 L (0.038) Wood ash 67 L (0.039) Terraclor 6.7 kg (0.40) TerraclorLimestone 6.7 kg67 L (0.045) Terraclorwood ash 6.7 kg67 L (0.036) Untreated control (0.010) Leduc 2010 Limestone 67 L (0.040) Wood ash 67 L (0.037) Terraclor 6.7 kg (0.039) TerraclorLimestone 67 kg67 L (0.041) Terraclorwood ash 6.7 kg67 L (0.042) Untreated control (0.047) z Standard errors (SE) are given in parentheses after the pi estimates were determined by SE(Ri)/N in which SE(Ri) is the standard error of the mean rank for the ith treatment as determined in the Mixed procedure of SAS with the lsmeans option (SAS institute, Inc., Cary, NC). Treatments with pi values outside the confidence interval for a treatment are significantly different from that treatment (P50.05). limestone compared with the nontreated control. Clubroot symptoms were severe at the Leduc site in both 2007 and 2008 and at St. Albert in 2007, but severity was low at St. Albert in 2008 (Table 1c). Limestone at 5.0 and 7.5 t ha 1 reduced clubroot severity at St. Albert in 2007 and limestone at 7.5 t ha 1 reduced clubroot severity at St. Albert in All rates of wood ash reduced clubroot severity at St. Albert in Both limestone and wood ash reduced clubroot severity at Leduc in both 2007 and 2008 when applied at 7.5 t ha 1 (Table 1c). The highest rates of limestone and wood ash and the moderate rate of limestone also improved seed yield at Leduc in 2007 and 2008 and at St. Albert in 2007 (Table 1a and Table 1b). Calcium cyanamide had no effect on any of the response variables (Table 1a, b and c). Fig. 2. Effect of in-row soil amendment on seed yield of canola grown in heavily infested commercial fields near Edmonton in 2009 and 2010, and at Leduc in Within each site-year, treatments do not differ at P The application rates were: Terraclor at 6.7 kg ha 1, and calcium carbonate and wood ash at 67 L ha 1.

9 HWANG ET AL. * AMELIORATION OF CLUBROOT OF CANOLA 1007 Table 4. Mean, mean rank, and estimated relative effects (pi) of fungicidal seed treatments on clubroot severity on canola under field conditions in Plasmodiophora brassicae infested soil Confidence interval (95%) for the estimated relative treatment effect Site/year Treatment Rate (g a.i. ha 1 ) Median disease rating Median rank (Ri) Estimated relative effect (pi) Lower Upper Edmonton Untreated control (0.028) Helix XTRA (0.027) SYN (0.027) Helix XTRASYN (0.026) Dynasty (0.024) Helix XTRADynasty (0.023) Helix XTRASYN (0.025) Dynasty 2010 Untreated control (0.034) Helix XTRA (0.027) SYN (0.030) Helix XTRASYN (0.031) Dynasty (0.032) Helix XTRADynasty (0.030) Helix XTRASYN 524Dynasty (0.023) z Standard errors (SE) are given in parentheses after the pi estimates were determined by SE(Ri)/N in which SE(Ri) is the standard error of the mean rank for the ith treatment as determined in the Mixed procedure of SAS with the lsmeans option (SAS institute, Inc., Cary, NC). Treatments with pi values outside the confidence interval for a treatment are significantly different from that treatment (P50.05). Fungicidal Soil Treatments There was a significant effect of year at both sites, as well as year treatment interactions for plant height, canopy coverage and seed yield at Leduc and for canopy coverage at St. Albert. As a result, each site-year was analyzed separately. Application of either rate of Terraclor (quintozene) increased plant height, canopy coverage and seed yield, and reduced plant mortality at Leduc in both years (Table 2a). At St. Albert, Terraclor increased plant height, canopy coverage and seed yield in 2007 and reduced plant mortality in 2008 (Table 2b). Terraclor also reduced clubroot severity in each of the site-years (Table 2c). Application of Ranman (cyazofamid) did not affect emergence or plant mortality in any of the site-years (Table 2a and 2b). Application of the high rate of Ranman resulted in greater plant height relative to the control at St. Albert in 2007, greater canopy coverage at St. Albert in 2007 and Leduc in 2008, and greater yield at Leduc in The high rate of Ranman reduced clubroot severity at Leduc and St. Albert in 2007; both rates of Ranman reduced clubroot severity at St. Albert in 2008 (Table 2c). Allegro did not affect seedling emergence or plant height in any of the site years (Table 2a and Table 2b). The low rate of Allegro reduced plant mortality at Leduc in 2007, and both the low and high rates of Allegro improved canopy coverage at Leduc in The high rate of Allegro reduced clubroot severity at Leduc in 2008, while both rates of Allegro reduced clubroot severity at St. Albert in both years (Table 2c). Also, the low rate of Allegro improved yield at Leduc in Calcium cyanamide and the biosurfactant (Zonix) had no effect on emergence, plant height, canopy coverage or yield in any siteyear (Table 2aa and Table 2b), although the application of Zonix and the low rate of calcium cyanamide resulted in lower clubroot severity at Leduc in 2008 (Table 2c). As in the soil amendment trial, clubroot severity was high in both years at Leduc and at St. Albert in 2007, but was low to moderate at St. Albert in 2008 (Table 2c). In-row Soil Treatments Extremely dry conditions delayed germination until early July As a result, maturity was delayed and yields were extremely low. Wet weather in July and August resulted in rapid development of clubroot. Clubroot severity at the Edmonton site was moderate in 2009 and high in 2010, but severity was low at Leduc in All of the treatments reduced clubroot severity compared with the nontreated control at Edmonton in 2009 and 2010, but none of the treatments affected clubroot severity at Leduc in 2010 (Table 3). At Edmonton in 2009 the wood ash treatment had a significantly lower clubroot rating than all other treatments. Treatment had no statistical impact on yield in any of the site-years, but yield at Edmonton in 2009 was too low for assessments to be reliable (Fig. 2). Fungicidal Seed Treatments Clubroot severity was moderate to high in both 2009 and 2010 (Table 4). There were no treatments that showed a lower clubroot severity compared with the untreated control; all of the treatments showed a greater clubroot severity compared with the untreated control in at least 1 of the 2 site-years. Seed treatment had no

10 1008 CANADIAN JOURNAL OF PLANT SCIENCE Fig. 3. (a) Effect of fungicide seed treatments on canola seedling emergence in a Plasmodiophora brassicae-infested field at Edmonton in Bars capped with the same letter do not differ at P50.05 as determined by Duncan s New Multiple Range Test. Application rates were: Helix XTRA at 430 g a.i. ha 1, SYN524 at 5 g a.i. ha 1, and Dynasty 20 g a.i. ha 1. (b) Effect of fungicidal seed treatments on yield of canola grown in a heavily infested commercial field at Edmonton in 2009 and Bars for the same year capped by the same letter do not differ at P50.05 as determined by Duncan s New Multiple Range Test. The application rates were: Helix XTRA at 430 g a.i. ha 1, SYN524 at 5 g a.i. ha 1, and Dynasty at 20 g a.i. ha 1. impact on seedling emergence in 2009 (data not shown), but Helix XTRA, SYN 524, and Helix XTRASYN 524Dynasty increased seedling emergence in 2010 (Fig. 3a). Helix XTRA and Dynasty increased seed yield in 2009, but yields were so low that these estimates are not considered to be reliable (Fig. 3b). In 2010, all of the fungicides increased yield relative to the control, but there were no differences in yield among the fungicides. DISCUSSION Clubroot development is regulated by the dynamic interaction of host, pathogen, and environment (Crute 1986; Williamson 1987). In each trial, location and year had a substantial impact on plant growth and clubroot severity. In 2007, clubroot severity was exceptionally high at Leduc, probably due to good soil moisture early in the growing season, combined with hot conditions in July. As a result, yield was much lower than in subsequent years. Field observations have shown that clubroot typically develops in soils with a ph lower than 7.1 (Myers and Campbell 1985). Soil amendment with limestone, wood ash, or calcium cyanamide is intended to raise the ph of the soil and so create conditions that are less favourable for the disease. A ph of 7.2 or higher is considered optimal for clubroot management. In the current study, high rates of limestone and wood ash increased plant height and canopy coverage of the crop, and occasionally reduced clubroot severity and increased seed yield of canola. Although the impact of soil amendments was greatest in severely infested soils, it was not consistent over site and year, even at very high rates of application. This study demonstrates that while soil amendments may have the potential to reduce the impact of clubroot in agricultural land, the amounts required would be

11 HWANG ET AL. * AMELIORATION OF CLUBROOT OF CANOLA 1009 prohibitively large and expensive, incorporating them would be excessively time-consuming and the effects on yield would be too small to justify large-scale application. Although all of the in-row treatments reduced clubroot severity at Edmonton in 2009 and 2010, none of them affected yield relative to the individual amendment treatments, and none of them affected clubroot severity at the less heavily infected site at Leduc. In the study of soil treatment with fungicides, the fungicides generally had a minimal impact on the crop or on clubroot symptoms. The exception was Terraclor (quintozene), which has been used on cole crop transplants on a commercial basis for many years. This product consistently improved plant growth and reduced clubroot severity in the 2007 and 2008 studies. Application of Terraclor increased yield at both sites in 2007 and at Leduc in It is important to note that the yields achieved in these trials were very low, and even the best treatment (the high rate of Terraclor) brought yield close to a commercially acceptable level in only 1 of 4 site-years. A combination of Terraclor and limestone or wood ash as in-row treatments reduced clubroot severity in years and locations with high clubroot severity (i.e., Edmonton in 2009 and 2010) in non-treated plots, but not where it was low (i.e., Leduc in 2010). Ranman and Allegro reduced clubroot severity, but not consistently, and their effects were more apparent at St. Albert, where inoculum levels were lower than at Leduc (Ahmed et al. 2011). Ranman improved canopy coverage in 2 of 4 station years and plant height in one; Allegro improved canopy coverage and reduced seedling mortality in 1 of 4 site-years. These two products showed promise under cole vegetable production systems in Japan (Mitani et al. 2003; Adhikari 2010), but in the present study their effects were mostly limited to the site with lower inoculum levels. The surfactant (Zonix) had little or no effect in any site-year. Similarly, the application of calcium cyanamide, even at high rates, had no effect on clubroot severity or other agronomic variables in these trials. Researchers in Europe and eastern Canada have reported that this product is effective against clubroot (Williamson and Patricia 1989; Cornforth 1971; Donald et al. 2004; Tremblay et al. 2005), but more arid soil conditions probably limit its efficacy in Alberta. Calcium cyanamide inhibits resting spore germination, and its efficacy increases with the length of the interval between incorporation into the soil and planting of the crop (Naiki and Dixon 1987). In the current study, the interval between application and planting may have been too short for the product to exhibit its full efficacy. In contrast, while Terraclor has little impact on resting spore germination and primary infection (Naiki and Dixon 1987), it substantially reduced clubroot severity and symptom expression in the current study. However, since the study began, severe restrictions have been placed on its use by Health Canada (2009), so that it is unlikely that this product will ever be a viable option for clubroot control in largescale agricultural production. Seed treatment with the fungicides Helix XTRA, SYN 524 and Helix XTRADynastySYN 524 increased seedling emergence in clubroot-infested soils in This increase in seedling emergence may have been associated with a suppression of other soil-borne pathogens, such as Fusarium spp. and Pythium spp. and Rhizoctonia solani Ku hn., since none of these treatments reduced final clubroot severity. All of the treatments improved yield slightly, but this may have resulted from the reduction in root disease caused by other soil pathogens. We conclude that Terraclor (quintozene) and/or high levels of limestone or wood ash can reduce the impact of P. brassicae on canola. However, our assessment using in-row application rates that might be economically feasible showed that they had little potential to increase yield in infested commercial fields. Further investigation is needed to determine other practical means of reducing the inoculum levels or virulence of P. brassicae in clubroot-infested fields. ACKNOWLEDGEMENTS Financial support from the Agriculture & Food Council Advancing Canadian Agriculture and Agri-Food (ACAAF) Program, the Alberta Crop Industry Development Fund (ACIDF), the Alberta Canola Producers Commission, the Clubroot Risk Mitigation Initiative through Agriculture and Agri-Food Canada and the Canola Council of Canada, and the Saskatchewan Canola Development Commission is gratefully acknowledged. The authors also wish to thank D. Rennie, J. Tieulie, Y. Yang and D. Cui for technical support. Adhikari, K. K. C Effect of temperature, biofungicides and fungicides on clubroot of selected brassica crops. M.Sc. thesis. University of Guelph, Guelph, ON. 207 pp. Ahmed, H. U., Hwang, S. F., Strelkov, S. E., Gossen, B. D., Peng, G., Howard, R. J. and Turnbull, G. D Assessment of bait crops to reduce inoculum of clubroot (Plasmodiophora brassiceae) of canola, Can. J. Sci. 91: Campbell, R. N., Greathead, A. S., Myers, D. F. and De Boer, G. 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