AN updated management guide for blackleg disease in canola crops has been released by the Grains Research and Development Corporation (GRDC).
The Blackleg Management Guide autumn 2020 edition features the latest blackleg ratings for canola cultivars and suggests that sowing canola crops early and in warm conditions may help canola crops to escape potentially severe blackleg disease during the growing season.
Marcroft Grains Pathology principal Steve Marcroft said crops sown before April 30 into warm conditions that allowed them to quickly progress through the seedling growth stage were at the lowest risk of developing blackleg.
"Crops sown from May onwards are likely to face more disease pressure from blackleg, with crops sown from June onwards at the highest risk," Dr Marcroft said.
"Blackleg ratings can change from year to year if the fungus overcomes cultivar resistance.
"Results from the latest blackleg screenings of canola cultivars have been factored into the updated ratings for 2020."
Leptosphaeria maculans, the causal agent of blackleg disease, is a sexually reproducing pathogen that may overcome cultivar resistance genes.
Fungal spores are released from canola stubble and spread extensively via wind and rain splash.
Dr Marcroft, who is also the co-ordinator of the GRDC's National Canola Pathology Program investment, said blackleg could cause severe yield loss, but can be successfully managed.
"The GRDC Blackleg Management Guide can be used by growers to determine whether they are in a high-risk situation and the best management practices to reduce or prevent yield loss from blackleg," he said.
"The guide also emphasises that fungicides will only provide an economic return if a crop is at high risk of yield loss.
"Fungicides complement other management practices and growers should never rely solely on fungicides to control disease as this poses a high risk for development of resistance."
The BlacklegCM management app, which is a GRDC investment, has also been updated with the latest disease ratings.
The app provides growers with a tool that can forecast the likelihood and severity of the disease, associated yield loss and economic returns on a paddock-by-paddock basis.
Dr Marcroft said the app provided growers and advisers with "an interactive interface" to explore and compare the economic outcomes of different management strategies for blackleg.
"BlacklegCM assists growers to manage blackleg by integrating the information provided in the Blackleg Management Guide and producing a predicted economic outcome," he said.
"It can be modified to account for some of the major factors that relate to risk of yield loss due to blackleg in a particular paddock.
"It allows the user to compare the likely relative profitability of different disease management strategies, including paddock selection, cultivar choice, seed dressing, banded fungicide and sprayed fungicide."
The app, available for use on iPads and tablets via the App Store and Google Play, is an extension of the Blackleg Management Guide which is updated twice a year to reflect any changes in the resistance status of individual cultivars.
The Blackleg Management Guide autumn 2020 edition is available at https://grdc.com.au/GRDC-FS-BlacklegManagementGuide
