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Evaluation of fungicide seed treatments for their efficacy in controlling blackleg of canola

Luis del Rio Mendoza: North Dakota State Univ

<div>Blackleg, caused by <em>Leptosphaeria maculan</em>s<em>,</em> causes greatest yield losses when canola plants are infected before reaching the six-leaf growth stage. The objective of this study was to evaluate the efficacy of newly-registered seed treatments to control blackleg. Five treatments were applied to seeds of susceptible cultivar Westar and evaluated in greenhouse at NDSU greenhouse facility, Fargo, ND and in field trials at Langdon and Prosper, ND in 2017 using a RCB design with four replications. In greenhouse, plants were inoculated once with pycnidiospores suspensions at cotyledon stage and three times before plants reached the four-leaf stage in field trials. Field plots also were supplemented with blackleg-infested canola residues. Disease severities were assessed 12 days after inoculation and at harvest time in greenhouse trials. Yield and disease severities were assessed at harvest in field trials. All treatments reduced disease severity compared to the non-protected control at seedling stage in greenhouse, but only Obvius (fluxapyroxad + pyraclostrobin + metalaxyl) and Helix (metalaxyl + fludioxonil + sedaxane + difenoconazole + thiamethoxam) showed significant (<em>P</em> < 0.05) reductions in severity at harvest. In field trials, Maxim (fludioxonil) reduced disease severity at Prosper (<em>P </em>< 0.05) but not at Langdon (<em>P </em>< 0.05). None of the treatments improved yields significantly (<em>P </em>< 0.05) compared to non-treated control. This study will be repeated in 2018.</div>