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.
Have a follow-up question?
There are a number of great resources and articles by experts in other areas of Canada and the United States. Here are two articles by Andrew Friskop, Extension Plant Pathologist with North Dakota State University, on the factors producers should consider when evaluating an early-season fungicide application in wheat (i.e. herbicide timing or T1).
The first article appeared in the NDSU Crop & Pest Report – May 19, 2016 edition. The complete article is available here: Early-season fungicide application in wheat.
An updated article was recently posted in the NDSU Crop & Pest Report – May 18, 2017 edition: Early-Season Fungicide Application for Wheat (5/18/17)
There are several factors that will influence the value of an early-season fungicide and Andrew Friskop reviews some of those, including crop rotation, tillage, weather, variety selection, scouting & fungicide selection. The 2016 article reads “What to expect from an early-season fungicide application? – Studies conducted by NDSU over the last 20 years have shown that a 2 to 6 bushel response occurs when an early-season fungicide was used in a wheat-on-wheat production system with minimum tillage when favorable weather was present. The incorporation of other management tools such as crop rotation and tillage will reduce the risk of tan spot development and reduce the expectant yield response. Also, remember an early-season fungicide will protect the leaves available at the time of application, but as the wheat crop matures, newly developed leaves will be left vulnerable to leaf spot and rust pathogens.”
One factor not discussed in the articles was disease resistance management – it must be another consideration. When a fungicide is used multiple times, the risk that pathogens can develop resistance to the fungicide can increase. Where fungicide application is required, producers should rotate between fungicide groups.
Have a follow-up question?