Abstract

Blackleg [Leptosphaeria maculans (Desm.) Ces. & de Not.] is the most widespread disease of canola (Brassica napus L.) on the Canadian prairies. It has a noticeably increased incidence in recent years possibly due to shifts in the pathogen population and erosion in cultivar resistance. This study was conducted to assess foliar-applied fungicides for mitigating the risk of blackleg. Field trials were conducted at five locations in the Black or Dark-Brown Soil Zones for four years using the susceptible canola ‘Westar’. The fungicides pyraclostrobin (Headline^®), azoxystrobin (Quadris^®), propiconazole (Tilt^®), and azoxystrobin + propiconazole (Quilt^®) were applied at the 2–4 leaf stage against early infection. For comparisons, pyraclostrobin was also applied at bolting of ‘Westar’ and at the 2–4 leaf stage of two resistant cultivars (‘43E01’, ‘45H29’). These early treatments, except propiconazole, significantly reduced the mean disease incidence (MDI) and disease severity index (DSI) on ‘Westar’, relative to untreated control, reducing the impact of disease on yield by 16.5–26.9%. Late application of pyraclostrobin at bolting was ineffective. Two-application treatments, with pyraclostrobin at the 2–4 leaf stage and propiconazole at the bolting stage, or vice versa, provided no further efficacy or yield benefit relative to the early application of pyraclostrobin alone. None of the treatments showed substantial disease reduction or yield benefit in two low-disease station years (MDI <30%). On the resistant cultivars, pyraclostrobin reduced MDI and DSI, but showed no yield benefit. As resistant canola cultivars are used commonly on the prairies, a routine application of foliar fungicide is not recommended.

摘要

黑腿病 [ Leptosphaeria maculans (Desm.) Ces. & de Not.] 是加拿大草原上最普遍的油菜 ( Brassica napus L.)病害。近年来，它的发病率显着增加，可能是由于病原体种群的变化和品种抗性的侵蚀。进行这项研究是为了评估叶面喷洒杀菌剂对降低黑腿病风险的作用。使用易感油菜“Westar”在黑色或深棕色土壤区的五个地点进行了为期四年的田间试验。杀菌剂唑菌胺酯 (Headline ^® )、嘧菌酯 (Quadris ^® )、丙环唑 (Tilt ^® ) 和嘧菌酯 + 丙环唑 (Quilt ^®) 在 2-4 叶期应用以防止早期感染。为了进行比较，唑菌胺酯也用于“Westar”的抽薹和两个抗性品种（“43E01”、“45H29”）的 2-4 叶期。除丙环唑外，这些早期处理与未处理的对照相比，显着降低了“Westar”的平均病害发生率 (MDI) 和病害严重程度指数 (DSI)，将病害对产量的影响降低了 16.5-26.9%。在抽薹期后期施用唑菌胺酯无效。与早期单独使用唑菌胺酯相比，在 2-4 叶期使用唑菌胺酯和在抽薹期使用丙环唑（反之亦然）的两次施用处理没有提供进一步的功效或产量收益。在两个低疾病站年（MDI <30%）中，没有一种处理显示出显着的疾病减少或产量收益。在抗性品种上，唑菌胺酯降低了 MDI 和 DSI，但没有显示出产量收益。由于抗性油菜品种在草原上普遍使用，因此不建议常规使用叶面杀菌剂。