Pre-sowing strategies to prevent disease

Pre-sowing strategies to prevent disease

Cropping News
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Canola growers are being encouraged to consider pre-sowing management strategies to prevent crop losses from diseases, like blackleg, this season.

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CANOLA growers are being encouraged to consider pre-sowing management strategies to prevent crop losses from diseases, like blackleg, this season.

The risk of blackleg infection in crops and the potential for yield losses this year is high due to the significant area sown to canola in recent years.

Blackleg is Western Australia's most common and economically serious canola disease, causing yield losses of up to 30 per cent when not controlled, and up to 50pc in worst case scenarios.

The fungal disease survives on canola stubble and early seedling infections (particularly at four-to-five leaf stage) are the most damaging.

Department of Primary Industries and Regional Development (DPIRD) plant pathologist Ravjit Khangura is encouraging growers to put in place management strategies before the 2019 crop is sown.

Dr Khangura, who features in a new Grains Research and Development Corporation (GRDC) video about detecting and managing blackleg, said selecting a resistant cultivar, separating this year's canola crop from last season's stubble and using a fungicide seed dressing or in-furrow treatments were effective strategies for blackleg management.

She said while fungicide seed dressings and in-furrow products could protect canola seedlings, it was important growers took an integrated approach to management.

"The good news is this fungal disease is easily identified and can be managed with an integrated approach that utilises variety resistance, cultural control and the strategic use of fungicides," Dr Khangura said.

"Growers should only use fungicides if there is a high probability of yield loss - such as if they are sowing canola in tight rotations, or next to last year's canola stubble and/or sowing a variety with low blackleg resistance for their region."

The GRDC Blackleg Management Guide reflects the latest blackleg ratings and blackleg resistance groups of canola varieties.

The BlacklegCM app can also assist growers and consultants to determine the best and most profitable management strategy to reduce blackleg disease and increase profits.

"Leptosphaeria maculans, which causes blackleg disease, is a sexually reproducing pathogen that may overcome cultivar resistance genes, and blackleg ratings can change from year to year," Dr Khangura said.

"Therefore, it is important that growers refer to the latest ratings."

Dr Khangura said growers should also be conscious of fungicide resistance when planning management strategies.

"In 2015, a nation-wide survey conducted by the National Canola Pathology team found that 15pc of 200 canola stubble samples collected had tolerance to the fungicide fluquinconazole," she said.

Preliminary results have been released from more recent fungicide tolerance trials, being run by Angela Van de Wouw, of the University of Melbourne, with investment from the Australian Research Council, Syngenta, Bayer and Adama.

The results showed 22pc and 28pc of populations tested nationally were highly resistant to the fluquinconazole and flutriafol fungicides respectively, compared to 7pc of populations screened against the tebuconazole-priothioconazole mixture.

Dr Van de Wouw stressed it was not yet known how these results translated to on-farm performance of these fungicides.

The screening will continue in 2019 and 2020, and growers are encouraged to submit samples for testing.

To be involved in the free fungicide resistance screen, please email Dr Van de Wouw (angela@grainspathology.com.au).

Growers can manage blackleg by adhering to the following recommendations:

Never sow your canola crop into last year's canola stubble. Maintain a 500 metre separation from the previous year's stubble.

Choose a cultivar with adequate blackleg resistance for your region.

Regularly check DPIRD's canola blackleg forecast webpage for the current risk of blackleg spore showers in your canola.

Use fungicides when warranted, depending on expected disease severity, blackleg rating and seasonal conditions. Consult BlacklegCM app for spray decision advice.

Relying only on fungicides to control blackleg poses a high risk of fungicide resistance.

At the end of the season, monitor crops for blackleg severity. Change your cultivar to a different resistance group in the following season if you notice high levels of disease, indicating your current cultivar has reduced resistance to blackleg.

Monitoring crops will also help determine if current management techniques are adequate or if more rigorous management is required.

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