Things to consider:
- Crop rotation – the tighter the rotation the higher the risk of blackleg
- Historic levels of blackleg in that field – have you experienced yield loss from blackleg?
- Weather forecast – infection requires free moisture (light-moderate rainfall, not soil saturation)
- Presence of inoculum –can you see leaf lesions on first true leaves? or pseudothecia present on canola stubble?
- Yield potential – what is your target yield, return on investment expected?
If you have made the decision to spray, what else do you need to know?
- Application timing – apply at the 2 to 4 leaf stage, later applications are not as effective at reducing disease.
- Fungicide type – strobilurin fungicides (Group 11) are more effective at reducing disease than triazoles (Group 3). For more information on what products are registered for blackleg management, see the MB Guide to Field Crop Protection http://www.gov.mb.ca/agriculture/crops/guides-and-publications/pubs/crop-protection-guide-disease.pdf.
- Yield increase….not guaranteed – while strobilurin fungicides applied at the 2 to 4 leaf stage did significantly reduce the severity of the disease, yield bumps were only observed when a susceptible cultivar was grown.
Reference: Liu, C. 2014. Evaluation of fungicides for management of blackleg disease on canola and QoI-fungicide resistance in Leptosphaeria maculans in Western Canada. Master of Science Thesis. University of Manitoba. 172 pp.