Paddock Practices: Fungicide decisions for high blackleg risk in canola

Consistent early rainfall has increased blackleg risk for canola. Protect yields through early disease identification and appropriate management tactics.

Key points

• High levels of blackleg infection are already being reported in many regions.
• If growing a canola cultivar rated Moderately Resistant (MR) or below for blackleg, consider the application of a foliar fungicide application to help control crown canker of blackleg while crops are at the 4-8 leaf growth stage.
• If growing a canola cultivar rated Moderately Resistant (MR) or below for blackleg upper canopy infection (UCI) and flowering will commence in July or early August, consider a fungicide application at 30% bloom.
• Consult the BlacklegCM and BlacklegCM UCI apps, or the 2026 Blackleg Management Guide, to determine blackleg risk.
• Consider fungicide resistance management strategies, such as rotating active groups, as part of any fungicide decision.

With the perfect start to the growing season for many regions, conditions are not only optimal for canola, but also for blackleg disease.

High rates of blackleg infection are already being reported from many regions where significant rainfall has occurred, including western Victoria and the Eyre Peninsula. Early and consistent rainfall has led to early maturation of blackleg spores on canola stubble.

Once spores mature, they are released from the infected stubble with each rainfall event.

These early infections allow increased time for the fungus to grow into the crown and cause cankers.

Know which form of blackleg to target

To cause yield loss, blackleg spores must be released from canola stubble, land on a living plant, infect the plant and grow within the vascular tissue, thereby causing necrosis that blocks nutrient flow within the plant.

If spores land on seedlings and early true leaves (up to the 4 to 6 leaf stage) then the result will be crown cankers at the end of the growing season.

Alternatively, if spores land on the flowers and upper branches, the result will be upper canopy infection.

Therefore, when making spray decisions for controlling blackleg, growers and advisers must first know which form of the disease they are trying to control – crown canker or upper canopy infection.

Act early to manage your blackleg risk

Angela Van de Wouw, a blackleg pathologist with Marcroft Grains Pathology and part of the GRDC Disease Management Extension Network (DMEN) team, recommends scouting each canola paddock to look for lesions as the best indication of whether blackleg is a potential problem.

“Consult the Blackleg Management Guide or BlacklegCM app to determine your risk and the potential economic benefit of a foliar fungicide application,” she says.

A foliar fungicide may be necessary if growing a cultivar rated Moderately Resistant (MR) or below for blackleg, if the same cultivar has been grown for 3 or more years (regardless of resistance rating), and in a high intensity canola growing region.

For crops that are currently at the 4 to 6 leaf stage with significant leaf lesions, growers/advisers should be considering a foliar application for crown canker control.

For crops that have passed the 6-leaf stage and are likely to commence flowering between now and late July or early August, a fungicide spray at 30% bloom may be necessary to control upper canopy infection in cultivars rated MR-UCI or below.

Consulting the Blackleg Management Guide or BlacklegCM-UCI app will help growers determine their risk and the potential benefit of a foliar fungicide application. 

Plan to protect yields and fungicide options

Useful resources

• GRDC Blackleg Management Guide with links to blackleg apps (Mar 2026)
• GRDC Video: Tools for tackling blackleg of canola (Oct 2024)
• GRDC Update Paper: How to manage canola disease in a time of ever increasing production and fungicide resistance? (Feb 2026)
• GRDC Update Paper: Understanding fungicide resistance in the blackleg pathogen of canola and how to reduce your risk (Feb 2026)
• GRDC Publication: Fungicide resistance management in Australian grain crops (Feb 2026)

Contacts

Angela van de Wouw
Marcroft Grains Pathology
e angela@grainspathology.com.au
m 0439 900 919