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Control Blackleg Early to Minimise Canola Yield Losses

20 June 2012
GRDC

AUSTRLIA - Growers are encouraged to inspect young canola crops now for signs of blackleg disease, and apply a registered foliar fungicide if necessary.

Department of Agriculture and Food (DAFWA) plant pathologist Ravjit Khangura, who conducts Grains Research and Development Corporation (GRDC) supported research in WA, said it was important to control blackleg early in the season to minimise yield losses.

“Blackleg can attack the crop at any stage, but early seedling infections – especially up to the four or five-leaf stage - are the most damaging in terms of the development of severe stem cankers and yield loss,” she said.

Blackleg lesions on a canola leaf.

“It is a high risk year for blackleg due to the high number of wind-borne spores likely to be produced from the big area of canola stubble left from last year’s crop, and the large area of land planted to canola this season.”

Dr Khangura said growers should inspect crops for blackleg lesions caused by blackleg ‘spore showers’ – the release of spores from canola residue on paddocks, stimulated by rain in late autumn and throughout winter.

“If you are seeing a lot of lesions on canola, you should consider applying, in accordance with label instructions, the foliar fungicide Prosaro® (prothioconazole and tebuconazole) which has now been registered for use on blackleg in canola,” she said.

Dr Khangura said canola crops at highest risk of blackleg infection were varieties rated as moderate to susceptible for blackleg; those sown close to 2011 canola stubble or in close rotations; and those which had not been treated with a fungicide seed dressing or fungicide-amended fertiliser.

“Growers who have used only a fungicide seed dressing only are more likely to have blackleg infection in crops than those who have used a fungicide-amended fertiliser,” she said.

Dr Khangura said growers should also look at the ‘Canola Blackleg Risk Forecast for WA’ at www.agric.wa.gov.au/cropdisease to determine their blackleg risk.

“This forecast provides information about the risk of blackleg disease in different districts, with the predictions based on results from the GRDC-supported DAFWA ‘Blackleg sporacle’ model, and researcher knowledge and experience of blackleg,” she said.

“The blackleg risk in districts where spores have not yet matured can change as the season progresses.”

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