A forecast for blackleg showers in some of Australia’s highest yielding canola growing regions is prompting renewed calls for caution concerning this devastating disease. 

Blackleg is caused by the fungus Leptosphaeria maculans which survives on crop residue over summer, releasing spores in humid conditions during early crop emergence – these spores are able to travel long distances to land on seedlings. 

Early infection can lead to stem cankers and yield losses of up to 50 per cent, while upper canopy blackleg is becoming more prevalent with early sowing of canola crops. 

Early sowing is also placing an increased emphasis on fungicide use.

Frankland River Rural’s Tim Trezise said managing rotations was challenging in his patch, given the performance and bankable returns canola had delivered to growers in recent seasons.  

“People are starting to put their canola in mainly early April, but even late March.

“With this change, we're actually seeing a little bit more blackleg, particularly upper canopy blackleg, but a little less sclerotina because flowering is happening in the colder, wetter months, but it’s still there,” Mr Trezise said.  

“Blackleg is the main one we’re spraying for and some sclerotinia - we saw a bit more of that last year.”  

The Western Australian Department of Agriculture issued an alert for blackleg spore showers, tending to high risk during May, for southern parts of the state in an area stretching from Mount Barker to Esperance. 

AGRIC provides an app to guide growers on the optimum time for crop establishment, helping to avoid anticipated spore showers during the vulnerable 5-6 leaf stage.  

Syngenta Technical Services lead Pete Wilson said blackleg was a serious issue across many temperate canola growing regions, in WA and beyond. 

“Unfortunately, blackleg has become a serious concern for canola growers across large parts of Australia in recent years,” Mr Wilson said. 

“Crop rotations are an important tool and should be part of a management program. But as we know, the spores of the fruiting bodies can be carried many kilometres and it’s almost impossible to know where they will land.” 

Strategies to minimise the impacts of blackleg include rotation, time of crop establishment, selection of resistant gene types, seed applied fungicides and foliar fungicide applications. 

Some of the most effective fungicides for blackleg management have been SDHIs.

To make sure your fungicide program is helping to maximise the life of these valuable tools visit croplife.org.au.