Assess blackleg risk to canola yields before spraying crops

Author: | Date: 26 Jun 2012

Blackleg in canola. Photo courtesy Ray Cowley (NSW DPI)

Assess blackleg risk to canola yields before spraying crops

Canola growers in the southern cropping region must determine the potential for significant yield losses caused by blackleg infection before investing in and applying post-emergent treatments.

A foliar fungicide has for the first time been registered in Australia for the control of blackleg in canola, but industry authorities advise that careful consideration should be exercised before using the new treatment.

Blackleg experts, with support from the Grains Research and Development Corporation (GRDC), say the foliar fungicide Prosaro® 420 SC (prothioconazole and tebuconazole) is a welcome additional control tool in the industry’s battle against blackleg.

To ensure the industry’s long-term access to the product (which can be used in crops up to the 4-6 leaf stage in accordance with label instructions), authorities recommend judicious use of the foliar fungicide.

National Brassica Pathology Working Group spokesperson and blackleg authority, Steve Marcroft, of Marcroft Grains Pathology, says as well as being a return on investment consideration, unnecessary applications could eventually lead to potential resistance issues.

Steve Marcroft“Growers need to be confident that they will incur significant yield losses before investing in this form of control,” Dr Marcroft said. “If they are growing a cultivar with low blackleg resistance in a high risk situation, applying a foliar fungicide is an additional control option worth considering.”

Dr Marcroft said it can be difficult for growers to determine from a visual assessment as to whether a significant impact on production was likely to result from blackleg. To assist growers in their assessments and management strategies, the GRDC has just released a new Blackleg Management Guide Fact Sheet.

The fact sheet, available via, sets out all the steps needed to determine whether growers are in a high-risk situation and what practices they can implement or change to reduce or prevent yield loss from blackleg.

Key points contained in the fact sheet include:

• Monitor crops to determine yield losses in the current crop
• Choose a cultivar with adequate blackleg resistance for your region
• Never sow a canola crop into last year’s canola stubble
• Relying only on fungicides to control blackleg poses a high risk of fungicide resistance
• If monitoring has identified yield loss and the same cultivar has been grown for three years or more, choose a cultivar from a different resistance group.

“It is important for growers to monitor crops each season so they know the extent of blackleg infection and can make more informed management decisions,” Dr Marcroft said.

“Each year paddocks need to be inspected and plants cut open to assess the levels of blackleg infection. The GRDC management guide provides clear advice on how to do this.”

The risk of blackleg infection in crops and potential for yield losses this year is severe due to the increased area sown to canola in 2011 and another large planting this year due to favourable oilseed prices.

Blackleg is the most severe disease of canola in Australia. Because it survives on canola stubble, last year’s expansive crop has heightened the risk this season.

Dr Marcroft said sowing canola on canola could result in the fungal pathogen overcoming cultivar resistance genes, resulting in many cultivars being destroyed and risking the long-term viability of the canola industry.

“Blackleg is managed by breeding disease resistance into canola cultivars and by crop management practices,” Dr Marcroft said. “However, the blackleg fungus is adept at overcoming cultivar resistance, leaving many crops vulnerable to significant yield loss.”

In addition to being available for viewing and downloading via the GRDC’s website, the Blackleg Management Guide Fact Sheet will be included in the July-August edition GRDC’s Ground Cover magazine and free copies can also be ordered via GRDC’s Ground Cover Direct, free phone 1800 11 00 44 or email


Caption: Canola stalks (right) infected with blackleg. Photo Ray Cowley, NSW DPI.
Caption: National Brassica Pathology Working Group spokesperson and blackleg authority Steve Marcroft.

GRDC Project Codes: DAN0115, UM0034, UM0042, MGP0002

Media releases and other media products can be found at

For further information: Dr Steve Marcroft, Marcroft Grains Pathology
0409 978 941

Contact: Sharon Watt, Porter Novelli
0409 675100

GRDC Project Code DAN0115, UM0034, UM0042, MGP0002