Blackleg could be a major threat to the 2004 canola crop, with a survey by the Department of Agriculture indicating a significant risk of encountering the disease this year.

However, the disease risk could be minimised through careful crop management to maintain profitability.

Department pathologist Ravjit Khangura presented details of the survey at the Agribusiness Crop Updates in Perth.  The Updates were supported by the Department of Agriculture and the Grains Research and Development Corporation.

Dr Khangura said the survey found a significant level of disease in varieties with resistance derived from Brassica sylvestris.

"Resistance in varieties derived from Brassica sylvestris are controlled by a single major gene, however, these canola crops can break down when challenged by a compatible strain of pathogen," Dr Khangura said.

"Our survey found that both the incidence and severity of blackleg in varieties with sylvestris resistance almost doubled last year.

"This was predicted after the strains that have the ability to attack them were found in WA and the Eastern States."

In the Eastern States, breakdown of this resistance has already cost local canola growers $20 million. 

Dr Khangura said a total of 64 canola samples from the Geraldton to Esperance grainbelt were evaluated by the survey, most of which were the variety Surpass 501TT, with 11 per cent of the Pinnacle variety.

An average of 64 per cent of plants were affected by blackleg, up six per cent on the previous year, and the severity was 34 per cent, down five per cent compared to the previous season.

The research was supported by funding from the Grains Research and Development Corporation.

Dr Khangura said growers in areas where blackleg incidence was more than 50 per cent on varieties with sylvestris resistance could be most at risk of blackleg this year, but the impact could be minimised through careful crop management.

"Growers should destroy residue from last year's sylvestris resistance varieties and sow this year's canola crop as far away as possible from the residues of these varieties," she said. 

"Experienced growers use the technique of raking canola stems into windrows and burning the rows to reduce the carryover of disease from last year’s canola stubbles.

"They should also include fungicide protection in their program and consider using varieties with non-sylvestris resistance to blackleg." 

For fungicide protection in high-risk situations, grower should consider using Impact^® in Furrow which is applied to the fertiliser.  Growers should contact their seed merchant or agronomist for the best advise on what seed dressing fungicide could also be applied to aid protection against blackleg this season.

More information is available in the Department's Blackleg Management Package, Bulletin No 4571 and Farmnote No. 12/2004, ‘WA Blackleg resistance ratings on canola varieties for 2004’ on identifying varieties with B. sylvestris resistance.

The information is available from the Department' s local district offices or online at www.agric.wa.gov.au by using the Bulletin or Farmnote number in the search engine.