Blackleg management on the Eyre Peninsula: 2025 observations and implications

March 25, 2026
| Posted in

By Andrew Ware, EPAG Research

Blackleg remains a significant disease in canola on the Eyre Peninsula and its management requires vigilance and careful planning. Recent monitoring highlights some important shifts in how resistance and fungicides are functioning.

This article summarises key findings from 2025 and outlines practical implications for 2026.

 

Major gene resistance: reduced reliability

Major gene resistance: A single gene that gives strong, specific protection against blackleg, but can stop working if the disease adapts. When effective, major gene resistance acts like a shield and stops the blackleg fungus entering the plant (you will not see any plant symptoms).

Monitoring in 2025 confirms that several major gene resistance groups (A, B and C) are now ineffective across Australian growing regions, with Group D and Group F also declining.

Group H remains the most reliable source of major gene resistance currently available, particularly when combined with other genes (the blackleg management guide has the major gene resistance of all commonly grown varieties).

Implications for EP

  • Many crops are now not receiving strong protection from major genes alone
  • Where the same resistance group has been used repeatedly, disease levels are increasing
  • Crops are increasingly dependent on quantitative resistance (blackleg rating)

Practical considerations

  • Rotate resistance groups, not just varieties
  • Where possible, select varieties with stacked resistance
  • Monitor crops for:
    • Leaf lesions early
    • Crown canker at windrowing

 

Quantitative resistance: still effective, but under pressure

Quantitative resistance: A combination of genes that provides background, partial resistance across all growth stages and tends to be more stable over time, though it can gradually decline with repeated use. Quantitative resistance won’t stop the disease entering the plant but will slow the development of the disease and reduce damage, however symptoms will be present. The blackleg rating each variety holds in the blackleg management guide is a good indicator of the level of quantitative resistance.

Quantitative resistance (QR) remains effective across the EyrePeninsula, but there is clear evidence of gradual erosion in widely grown cultivars.

This is not a sudden breakdown. Instead:

  • Resistance declines over time
  • Disease levels increase gradually
  • Variety performance becomes more variable between paddocks

Importantly, varieties with similar blackleg ratings do not behave the same.

Implications for EP:

  • Repeated use of the same cultivar increases risk of local adaptation of the pathogen
  • Some paddocks will show higher disease despite similar ratings

Practical considerations:

  • Avoid growing the same cultivar in the same area for more than 2–3 years
  • If disease is increasing, treat the rating as lower than advertised
  • Switching to a different cultivar with the same rating can reduce disease

 

Upper canopy infection and fungicides: effective but inconsistent returns

In 2025, upper canopy infection (UCI) levels were generally low in South Australian paddocks.

Fungicide application at 30% bloom:

  • Reduced infection levels consistently
  • Produced variable yield responses

Across sites:

  • Most responses were in the range of 5–10% yield increase
  • Some paddocks showed larger responses
  • Others showed no response or a slight reduction

Drivers of response:

  • Variety resistance (QR) was the strongest driver
  • Seasonal conditions and flowering timing also play a role
  • Early disease symptoms (leaf lesions) were not a reliable predictor

Implications for EP

Fungicides are effective at reducing disease, but:

  • Do not consistently provide an economic return
  • Are best considered a risk management tool

 

Fungicide resistance: an emerging issue on EP

Recent GRDC-supported research has identified fungicide resistance in blackleg populations on the Eyre Peninsula, including:

  • Reduced sensitivity to Group 3 (DMI) fungicides across Australia
  • Detection of Group 7 (SDHI) resistance on EP for the first time

In some EP paddocks:

  • SDHI resistance developed rapidly between 2022 and 2024
  • Resistance has continued to be detected in 2025 samples

At this stage:

  • No widespread field failure has been confirmed
  • However, the presence of resistance indicates increasing selection pressure

 

What is driving fungicide resistance?

Key drivers include:

  • Repeated use of the same fungicide group
  • Applying fungicides where yield benefit is uncertain
  • Early-season applications (e.g. 4–6 leaf stage) increasing selection pressure

Fungicide resistance can spread rapidly via spores, meaning:

  • It is not just a paddock issue
  • It can become a regional issue over time

 

Conclusion

Blackleg management on EP remains effective where an integrated approach is used:

  • Variety selection
  • Rotation
  • Targeted fungicide use

The current challenge is maintaining the effectiveness of these tools over time.

Further reading: Blackleg management guide

 

Acknowledgement

This information has been generated through the GRDC funded projects: Effective Control of Blackleg of Canola MGP2307-001RTX and Blackleg Management Guide MGP2404-004SAX.

 

 

 

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