Effects of time and rate of application of triazole fungicides on incidence and severity of blackleg and growth and yield of canola

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Abstract
The ability of three triazole fungicides to reduce blackleg and to increase the yield of spring canola (Brassica napus) was tested at four locations in Ontario in 1990 and 1991 in fields containing stubble infested with Leptosphaeria maculons. In test 1, triadimefon (3.46 kg ha−1), diconazole (1.41 kg ha−1) and uniconazole (2.12 kg ha−1) were sprayed on foliage at the late rosette stage, or when flowers were opening on the main raceme, or at both growth stages at half rate (split). Split applications were most effective and reduced disease incidence and severity by 9.2 and 22.6%. Yields were not increased. In test 2, the fungicides were applied at the late rosette stage at four rates. The highest rates of triadimefon (9.24 kg ha−1), diconazole (3.76 kg ha−1) and uniconazole (5.64 kg ha−1) reduced disease incidence by 12.8, 10.6 and 6.4%, reduced disease severity by 25.7, 31.8 and 24.2%, and increased yield by 17, 33 and 30%, respectively. In both tests, most treatments increased seed weight, delayed crop flowering and maturity, reduced lodging and height, and increased vigor. Triazole fungicides applied as foliar sprays can reduce blackleg and improve yield of canola. Key words:Brassica napus, canola, triadimefon, diconazole, uniconazole, blackleg

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