PestFacts WA

Blackleg - spores are present and forecasts have begun for 2021

  • Albany region

A spore trap
A spore trap and trap plants. Photo courtesy of: Kithsiri Jayasena (DPIRD).

Plant pathologist Kithsiri Jayasena (DPIRD) has reported finding blackleg spores in spore traps in the Albany region.

Kithsiri also reports that very early sown canola crops in the South Stirlings area are already coming into the flowering stage. As these crops will be flowering during a period when blackleg spores are being released, they are at increased risk of developing blackleg upper canopy infections (UCI).

With the increase in canola prices, many WA growers are taking the opportunity to sow canola now, which is quite late in the canola sowing window for some areas of WA. There are concerns that untreated canola seed, such as ATR Bonito (rated moderately susceptible or MS as a bare seed), is being sown. Late sowing of canola with untreated seed is a concern because it puts crops at risk of emerging and being at their most susceptible growth stage (4-6 leaf) during the high risk blackleg spore release period. The use of flutriafol,  as either a liquid in-furrow or treated fertiliser, at seeding will help reduce blackleg infections but, ideally, seed should be treated with a seed dressing prior to sowing. If untreated seed is sown, growers will need to make decisions regarding applying foliar fungicides during this early vegetative stage to control blackleg stem canker infection.

What is blackleg?

Blackleg in canola
Blackleg on a canola leaf. Photo courtesy of: DPIRD.

Blackleg, caused by the fungus Leptosphaeria maculans, is one of the most serious diseases of canola in Western Australia. Blackleg can cause significant damage by infecting the cotyledons, or first leaves, early in the season, leading ultimately to crown lesions or cankers later in the season.

Blackleg is spread primarily by wind, with the heaviest spore fall out normally occurring within 500 metres of any canola residue. Each year, canola residue continues to produce blackleg spores at a diminishing rate until the stubble has completely broken down.

The overall risk of blackleg infection on a property will be determined by factors such as choice of variety resistance group (and frequency of variety use), paddock rotation, fungicide usage, distance from previous year’s canola residues, and stubble reduction.

To minimise the risk of blackleg infection, growers should consider:

  • Sowing into paddocks that are out of canola rotation for more than three years.
  • Avoiding sowing within 500m of last year’s canola residues.
  • Applying seed dressing and fertiliser applied fungicide. Reduced sensitivity to Jockey® and flutriafol has been reported in some WA blackleg populations. Please report any unexpected failures to your agronomist or DPIRD.
  • Applying a foliar seedling fungicide in case of high disease pressure. You can assess your risk level by referring to GRDC’s Blackleg Management Guide 2021 Autumn Fact Sheet, and DPIRD’s BlacklegCM  decision support tool.

For more information, refer to DPIRD’s Diagnosing blackleg in canola page.

Managing blackleg infection

For both blackleg stem canker and blackleg UCI, growers need to consider their varietal resistance levels before they spray as it may not be economical to spray varieties with high resistance levels (look at the bare seed rating as an indication of UCI susceptibility).

Fungicides applied during the bloom stage (before 50% bloom) may reduce UCI, and there are now some products, like Aviator Xpro®, registered for use. These products should be applied at similar times to the fungicides used for Sclerotinia control. These fungicide applications for UCI are likely to be more economical in higher yielding crops.

For more information regarding canola variety resistance ratings and blackleg management, refer to GRDC’s Blackleg Management Guide 2021 Autumn Fact Sheet, and DPIRD’s Registered foliar fungicides for canola in WA page.

Deciding on your best course of action

DPIRD’s BlacklegCM is a useful decision support tool for assessing the value of spraying to manage blackleg stem canker during the 4-6 leaf stage. Growers can manually enter the blackleg risk levels (low, moderate and high) that relate to your sowing date and location into the tool. These risks can be found online at DPIRD’s blackleg spore maturity forecasts for Western Australia. BlacklegCM cannot be used to determine the value of flowering sprays for management of upper canopy infection. For more information on this decision support tool, refer to DPIRD's BlacklegCM page. This tool can be used on both Apple and Android tablet devices and can be downloaded for free from the App stores. 

Canola blackleg risk forecasts

DPIRD's blackleg spore maturity forecasts for Western Australia for the 2021 growing season have begun, and forecasts are available online. The latest forecast is current to 19 May 2021.

The forecasts show the expected risk during the 4-6 leaf stage, relative to the date of sowing. For crops sown in late April and early May, the risk of blackleg spore showers coinciding with the seedling susceptible stage are already at high or moderate risk.

For more information, refer to DPIRD’s Canola blackleg spore maturity forecast for Western Australia page to check the blackleg model forecast for your district.

For more information about blackleg in canola, contact Andrea Hills, Senior Research Scientist, Esperance on +61 (0)8 9083 1144 or Ravjit Khangura, Senior Research Scientist, South Perth on +61 (0)8 9368 3374. 

For more information about the blackleg risk forecast, or the BlacklegCM decision support tool, contact Jean Galloway, Senior Research Scientist, Northam on +61 (0)8 9690  2172 or Art Diggle, Principal Research Scientist, Nash Street on +61 (0)8 9368 3563.



Article authors: Jean Galloway (DPIRD Northam) and Cindy Webster (DPIRD Narrogin).

Article input: Andrea Hills (DPIRD Esperance).