Western Australia
May 26, 2016

Western Australian trials are fine-tuning management practices to enable canola growers to best manage costly diseases such as blackleg and sclerotinia.

On the back of good autumn rains across much of the State’s grainbelt this year, Department of Agriculture and Food (DAFWA) researcher Ravjit Khangura recommends close monitoring of canola crops so that risk factors are noted as the season unfolds.


DAFWA researcher Ravjit Khangura says summer and early autumn rainfall has accelerated the maturation of blackleg spores on stubble. Photo by DAFWA.

Dr Khangura leads WA canola disease research as part of the Grains Research and Development Corporation (GRDC) National Canola Pathology Program.

“Blackleg remains the most costly canola disease in WA but the complexity of the sclerotinia stem rot pathogen and lack of genetic resistance also pose significant agronomic challenges, especially in tight rotations and in medium-high rainfall areas,” she said.

Dr Khangura said the most economical fungicide treatment for blackleg control was in-furrow at seeding, but that this might not totally prevent yield losses if conditions were ripe for disease development in winter and spring.

“Field trials in 2015 have indicated positive responses from fungicide use are more pronounced in moderately susceptible (MS) to moderately resistant (MR) canola varieties,” she said.

Dr Khangura said relying on fungicides alone posed a high risk of fungicide resistance. Blackleg could also be minimised by choosing varieties with adequate resistance; rotating varieties with different resistance genes; sowing at least 500 metres away from the previous year’s canola crop; and never sowing canola into canola stubble.

“Best results from foliar fungicides for blackleg are guided by information generated by the Blackleg Sporacle model (www.agric.wa.gov.au/crop-disease-forecast-2016) which predicts spore release for this disease and associated risks based on time of seeding and current seasonal conditions.”

“This year, summer and early autumn rainfall events have accelerated the maturation of blackleg spores on stubble.

“The spores have matured about a month earlier than usual in most of WA’s southern, south-coastal and central cropping regions.

“Growers are urged to regularly check the blackleg spore release forecast to determine the blackleg risk for their canola and to apply appropriate management strategies to minimise losses from blackleg this season.”

Dr Khangura said stem rot caused by sclerotinia severely damaged canola crops across high and medium rainfall zones of WA in 2013 and 2014, but disease levels were generally low to moderate last year.

“Yield losses from sclerotinia can be as high as 30 to 40 per cent – or up to 0.5-1 tonnes per hectare - in heavily infested crops in high rainfall years. Control with fungicides costs about $30-$50/ha per application,” she said.

Dr Khangura said the main control tactic was to reduce the frequency of host species, such as canola and lupins, and it was recommended growers avoid planting canola on paddocks with high sclerotinia levels during the past three years.

“Previous research in WA’s northern cropping region has shown that applying a single fungicide spray is often effective in reducing canola yield losses from sclerotinia when the crop is at the 15 to 30 per cent flowering stage (coinciding with the onset of spore release) and conditions are conducive to disease,” she said.

“But if the sclerotinia pathogen begins releasing spores late in the season, which occurred in WA’s northern region in 2013, fungicide application has been shown to be effective at the 50 per cent flowering stage.”

Dr Khangura said similar results were obtained from timing of fungicide application trials in WA’s southern region in 2015, which indicated that a single fungicide spray application targeted at the 25 to 50 per cent bloom stage was highly cost effective in reducing disease levels and improving yield.

Links to information about managing canola diseases in WA are available at www.grdc.com.au/GrowNotes and www.grdc.com.au/CanolaDiseaseManagementWesternRegion

Website: http://www.grdc.com.au

Published: May 26, 2016