| Summary: | Blackleg, caused by Leptosphaeria maculans, inflicts greatest canola yield losses when plants are infected before reaching the six-leaf growth stage. Studies were conducted to model pseudothecia maturation and ascospore dispersal to help growers make timely foliar fungicide applications. Pseudothecia maturation occurred mostly during the second half of June or in July in 2017 and 2018 in North Dakota and ascospores concentrations peaked during mid to late June in both years. A logistic regression model developed using temperature and relative humidity predicted the maturation of pseudothecia and ascospore dispersal with approximately 74% and 70% accuracy respectively. In addition, trials to evaluate the efficacy of five seed treatment fungicides were conducted under greenhouse and field conditions. All treatments reduced (P = 0.05) disease severity on seedlings in greenhouse trials, but not in field trials. Seed treatments, while a valuable tool, should not be used as the only means to manage blackleg.
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