WHEN canola crops are sown early in warm conditions they may escape potentially severe blackleg disease during the growing season.
Marcroft Grains Pathology principal Steve Marcroft, who is co-ordinator of the Grains Research and Development Corporation’s (GRDC) National Canola Pathology Program investment, says crops sown before April 30 into warm conditions that allowed them to quickly progress through the seedling growth stage are 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,” he said.
Dr Marcroft said results from the latest blackleg screenings of canola cultivars had been factored into the updated ratings for 2020.
Blackleg ratings can change from year-to-year if the fungus overcomes cultivar resistance.
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.
The impact is more severe in areas of intensive canola production.
“Blackleg can cause severe yield loss, but can be successfully managed,” Dr Marcroft said.
“Growers are advised to closely follow the recommended strategies for reducing the risk of disease which are contained in the GRDC Blackleg Management Guide.”
Dr Marcroft said fungicides could also complement other management practices.
“Growers should never rely solely on fungicides to control disease as this poses a high risk for development of resistance,” he said
Dr Marcroft said the severity of blackleg disease in 2020 would be dependent on seasonal conditions.
The GRDC-supported National Variety Trials (NVT) Online website, www.nvtonline.com.au, provides the latest information from blackleg monitoring sites across Australia.
Representative cultivars from all blackleg resistance groups are sown in trial sites in every canola-producing region and monitored for blackleg severity. This data provides regional information on the effectiveness of each blackleg resistance group.
The BlacklegCM blackleg management app has also been updated with the latest disease ratings.
The ‘GRDC Blackleg Management Guide autumn 2020’ edition features the latest blackleg ratings for canola cultivars. https://grdc.com.au/GRDC-FS-BlacklegManagementGuide
Comprehensive information on management of canola diseases can be found in the GRDC’s ‘Diseases of Canola and Their Management: The Back Pocket Guide’, available https://grdc.com.au/GRDC-BPG-CanolaDiseases.
Videos featuring Dr Marcroft diagnosing and explaining how to control blackleg upper canopy infection can be found at https://bit.ly/2VHwBNZ and https://bit.ly/2Kk3xqs respectively, while a podcast on upper canopy infection can be downloaded via https://bit.ly/2KikMsb.