Blackleg caution for State’s bumper canola crop

The Department of Primary Industries (DPI) is urging farmers to assess the risk of blackleg in canola and consider available management options following recent rain across central and southern NSW.

DPI Technical Specialist Pulses; Oilseeds, Don McCaffery, said blackleg is the most serious disease of canola in Australia and can lead to yield losses of up 90 per cent in worst case scenarios.

"On top of the recent wet weather, large areas have been sown to varieties that have a moderately susceptible resistance rating to blackleg and in many cases sown in adjoining paddocks or within 500 metres of last season’s canola stubble,"
Mr McCaffery said.

"These factors have combined to increase the risk for the development of blackleg in these situations.

"While blackleg is a key challenge for this year’s bumper canola crop there are a number of steps growers can take to reduce the severity of the disease and the risk of yield loss.

"Growers and advisers should consult the new GRDC Blackleg Management Guide (www.grdc.com.au) and review relevant management options for their own farm."

DPI Plant Pathologist based at Wagga Wagga, Kurt Lindbeck, said the recent registration of the foliar fungicide Prosaro is an additional tool in the management of blackleg.

"The fungicide is not a silver bullet and should be used to complement existing management tools such as crop rotation and seed and fertiliser fungicide treatment, specifically under conditions of high blackleg pressure," Mr Lindbeck said.

"The efficacy of foliar fungicides like Prosaro is best achieved when used as a protectant and applied at the correct growth stage.

"The Prosaro label specifies two treatments – the first at the 4 to 6 leaf stage and, if needed, a follow up treatment at the green bud stage.

"The green bud stage is when flower buds become visible when viewed from above and occurs after the start of stem elongation, about 2-4 weeks before the start of flowering.

"Applying a foliar fungicide after the green bud stage or at early flowering is a breach of the label directions and therefore a breach of the Pesticides Act in NSW."

Mr Lindbeck said blackleg incidence within a crop does not automatically translate to a direct yield loss.

"The level of blackleg stem infection that forms with a canola crop depends on the resistance genes within the variety and the interaction with the blackleg pathogen population," he said.

"Other crop types can carry some disease through to maturity without causing economic yield loss. This means that any extra yield benefit would not have covered the cost of the fungicide and its application.

"If growers are uncertain about the cost-benefit of Prosaro, then applying boom width strips is probably the simplest way of testing the product at the farm scale," Mr Lindbeck said.

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