Blackleg in canola can cause yield and quality losses, impact profitability and may create a market risk.
To help manage the disease and maintain the effectiveness of varieties’ genetic resistance, growers are encouraged to employ an integrated blackleg management strategy, including pre-harvest scouting for the disease, rotating crops, and growing and rotating resistant varieties.
INTEGRATED BLACKLEG MANAGEMENT STRATEGY
The following practices should make up a grower’s integrated blackleg management strategy:
- The blackleg pathogen overwinters on infected residue. Maintain a break between canola crops to allow time for crop residue to decompose – a minimum break of 2 years is recommended.
- Scout canola fields regularly for blackleg symptoms and incidence to help determine the effectiveness of your blackleg management plan. See below for scouting tips.
- Plant only canola varieties rated R (resistant) or MR (moderately resistant) to blackleg. Rotate varieties to bring a mix of blackleg resistance genes and sources to the field over time. Use a blackleg race identification test to determine predominant races in the field and help match appropriate major gene resistance.
- Consider fungicide options: a fungicide seed treatment is available for many canola varieties to protect plants when they are most susceptible; an early season foliar fungicide application can help to prevent yield losses in higher risk situations.
- During non-canola years, control volunteer canola and other Brassica weeds (e.g. stinkweed, shepherd’s purse, wild mustard and flixweed) to prevent build up of the blackleg pathogen in the field.
Although symptoms of blackleg appear throughout the season, the optimal time to scout for the disease is just before swathing or around 60% seed colour change.
To scout for blackleg, pull up at least 50 plants in a W-pattern through the field and clip at the base of the stem/top of the root to look for blackened tissue. Any black discoloration seen in the cross section can be compared to the disease severity scale (below). The scale rates plants from 0 (no discoloration) to 5 (completely discoloured), and with each step on the rating scale there is a reduction in yield.
Use the Canola Council of Canada’s Blackleg Yield Loss Calculator to determine losses and watch the video below for more tips on blackleg scouting.
Visit blackleg.ca to learn more about blackleg management.
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