Canola growers urged to check revised blackleg ratings
Author: Sharon Watt | Date: 11 Apr 2017
Grain growers in the southern cropping region are being urged to check the latest blackleg disease ratings for canola cultivars ahead of sowing in 2017.
The ratings, contained in the Grains Research and Development Corporation (GRDC) Blackleg Management Guide, have been revised following the confirmation of reduced resistance in some Group A canola cultivars.
With increased demand for canola seed leading to a shortage of some commercial seed supplies, it is imperative that growers planning to instead use seed retained from last year’s crops know if their retained seed is from a cultivar now classified as having increased susceptibility to blackleg.
Marcroft Grains Pathology principal Dr Steve Marcroft says results from the latest blackleg screenings of canola cultivars, undertaken as part of the GRDC-funded National Canola Pathology Project, have been factored into the updated disease ratings for 2017.
“Those screenings have confirmed that the resistance status of some Group A cultivars has changed and growers must be aware of these new ratings before they sow this year’s canola crops,” Dr Marcroft says.
“If open pollinated (OP) cultivars were grown in 2016 and growers plan to sow seed retained from these crops this year, it is vital they check the 2017 blackleg ratings.
“For example, ATR Bonito and ATR Wahoo previously each had a moderately resistant (MR) rating, but that has fallen to moderately susceptible (MS).
“An MS cultivar may not be suitable for medium to higher rainfall zones if not protected.
“When sowing retained MS cultivars in higher rainfall zones, growers should protect seed with Jockey® and Impact In-Furrow® fungicides and budget for a foliar fungicide to apply if required.”
The southern grains industry is anticipating a significant increase in plantings of canola in 2017 as prices for the oilseed continue to be more favourable than those for cereal grain.
This likely expansion in plantings will add another complexity to proactive management of blackleg this year, as a key strategy for minimising disease risk is sowing into paddocks at least 500 metres away from the previous year’s canola stubble.
“Crop rotations will be tight this year,” Dr Marcroft says. “Therefore adequate separation of new crops from last year’s stubble will be problematic.”
Blackleg is a sexually reproducing disease. Fungal spores are released from canola stubble and spread extensively via wind and rain splash. The disease is more severe in areas of intensive canola production.
Blackleg has caused up to 90 per cent yield loss in trials and is cited as the number one threat to the canola industry.
Blackleg has historically been noticed in the form of crown cankers, however upper canopy infections, where the disease infects branches, flowers and pods, are also proving to be an issue for some growers.
Dr Marcroft says the wet winter and spring experienced in many parts of the southern cropping region in 2016 made for ideal blackleg conditions, with prolonged leaf wetness coinciding with ascospore release.
“The increased area of canola production, possible tolerance of the blackleg pathogen to Jockey® Stayer® (fluquinconazole) fungicide and increased sowing of Group A cultivars over the past five years are also possible reasons for the rise of the disease.
“Blackleg was even observed in areas typically regarded as low-risk, such as the Mallee, in 2016.”
Dr Marcroft warns that the risk of blackleg in 2017 will be increased due to the increased forecast canola plantings, but the actual disease severity will also be dependent on seasonal conditions.
Growers are therefore advised to closely follow the recommended strategies for reducing the risk of blackleg disease which are contained in the GRDC Blackleg Management Guide.
To further assist growers in determining the level of risk in their area, the GRDC-supported National Variety Trials (NVT) Online website, https://www.nvtonline.com.au, provides the latest information from blackleg monitoring sites across Australia.
Steve Marcroft, Marcroft Grains Pathology
03 5381 2292 / 0409 978941
Sharon Watt, Porter Novelli