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Early sown canola may avoid blackleg

CANOLA crops sown early in warm conditions over recent weeks may escape potentially severe blackleg disease during the growing season.

Many crops are being sown earlier than usual this year following decent summer and early autumn rains.

Marcroft Grains Pathology principal Steve Marcroft, who is coordinator of the Grains Research and Development Corporation’s National Canola Pathology Program investment, said 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.”

This advice is contained in the GRDC Blackleg Management Guide autumn 2020 edition which also features the latest blackleg ratings for canola cultivars.

Dr Marcroft said results from the latest blackleg screenings of canola cultivars have 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.”

The 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.

The guide also emphasises that fungicides will only provide an economic return if a crop is at high risk of yield loss.

“Growers should never rely solely on fungicides to control disease as this poses a high risk for development of resistance.”

The BlacklegCM blackleg management app has also been updated with the latest disease ratings.

The app, a GRDC investment, 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 tool provides growers and advisers with ‘an interactive interface’ to explore and compare the economic outcomes of different management strategies for blackleg, which can cause up to 90 per cent yield loss where a cultivar’s blackleg resistance has been overcome.

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.

“BlacklegCM assists growers to manage blackleg by integrating the information provided in the Blackleg Management Guide and producing a predicted economic outcome,” Dr Marcroft 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.”

BlacklegCM factors in costs, yield benefits and grain prices to give the best case, worst case and most likely estimates of economic return.

It also accounts for the major factors that influence blackleg severity and can be used during the growing season to assist with foliar fungicide application decisions.

Dr Marcroft said the severity of blackleg disease in 2020 will be dependent on seasonal conditions.

To further assist growers in determining the level of risk in their area, the GRDC-supported National Variety Trials Online website 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. 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.