- Canola-on-canola plantings bring high risk of disease.
- Record plantings this season increase likelihood of future industry losses.
- In the longer term, the practice could reduce the life of canola cultivars and the fungicides developed to protect them.
A leading Australian pathologist is warning grain growers that record rates of back-to-back canola plantings this season could significantly increase the risk of difficult to control diseases such as blackleg, Sclerotinia and Alternaria and threaten crops across whole regions.
New data from Digital Agriculture Services shows that approximately 92,000 hectares of canola were sown back-to-back across Australia in 2026, representing 2.1% of total canola plantings. This area is about 6.9 times the average number of hectares planted back-to-back during 2019–2021, while the share of the 2026 national canola crop is around four times higher than in 2019–2021.
University of Melbourne researcher Dr Angela Van de Wouw warned planting canola-on-canola comes with significant risk of yield loss and could shorten the effective life of canola cultivars and the fungicides developed to protect them.
Researcher Dr Angela Van de Wouw says planting canola-on-canola multiplies the risk of industry-wide disease outbreaks, fungicide resistance and accelerated the breakdown of cultivar resistance. Photo: © Melissa Marino | GRDC
“Growers who plant canola into last season’s canola stubble significantly increase the risk and rates of blackleg, Alternaria and Sclerotinia infection,” Dr Van de Wouw said.
Blackleg and Alternaria spores survive on canola stubble while Sclerotinia fruiting bodies persist in the soil. A second consecutive canola crop maximises carry-over disease pressure at the start of the season, leading to higher rates of infection and a greater risk of losses.
“You might be able to manage blackleg with fungicides, but the additional exposures will encourage fungicide resistance that leaves the chemistry less effective in subsequent years,” Dr Van de Wouw said.
“Blackleg is continually evolving to overcome cultivar resistance and fungicides. Canola breeders are constantly working to keep ahead of it. Meanwhile, Sclerotinia and Alternaria are even more difficult to control.
“Both blackleg and Alternaria can infect canola pods, causing yield losses and harvest downgrades.”
A disease expert says record rates of canola-on-canola planting in 2026 could result in uncontrollable diseases emerging. Canola rotations should always be separated by time and distance as the basis for disease management. Photo: © AM Photography | GRDC.
The latest DAS report shows canola-on-canola planting is common across many local government areas (LGA).
In Western Australia, which accounts for 78% of the nation’s total canola-on-canola planting this season, three south coast shires make up more than half that total – Esperance with 8.5% of the canola program, Jerramungup with 6.1% and Ravensthorpe with 9.6%.
Across New South Wales, provisional analysis shows canola-on-canola plantings increased. High rates of back-to-back canola were observed in Walgett and Bogan, at 5.4% and 5.0% of those LGAs’ total canola programs respectively.
In Victoria, back-to-back canola is concentrated in the Ararat and Pyrenees LGAs, which account for 37% of the state’s total canola-on-canola area.
South Australia’s share of back-to-back canola fell from 0.7% to 0.6% this season, even as its canola program grew 53%. However, the exception is the lower Eyre Peninsula, where growers increased their canola-on-canola plantings equating to 50% of the state’s back-to-back canola area.
Dr Van de Wouw said the DAS report indicated some canola growers were taking a significant risk for potential short-term benefit.
“Maintaining canola yields requires a long-term approach that includes planting non-canola rotations, so that soil and stubble borne diseases will break down rather than reinfect a second crop in the same paddock,” Dr Van de Wouw said.
“Failure to provide this break can allow high rates of disease to build up. If this disease pressure gets too high, normal fungicide use may not provide adequate control and applying more fungicide may only support the emergence of resistant pathogen strains.
“The canola sector needs growers to follow best practices for managing disease. Planting canola-on-canola increases everybody’s risk exponentially.”
For more information about disease management in canola go to the GRDC website.
About Us: GRDC is one of 15 Rural Research and Development Corporations (RDCs) responsible for planning, investing in and overseeing research, development and extension (RD&E) for 27 leviable grain crops. Our purpose is to invest in RD&E to create enduring profitability for Australian grain growers.
For interviews
Dr Angela Van de Wouw, University of Melbourne
apvdw2@unimelb.edu.au
0439 900 919
Contact
Danielle Gault, GRDC Communications Manager – West
danielle.gault@grdc.com.au
0448 766 881
GRDC Code: ACO2601-005RTX