NSW Department of Primary Industries (DPI) plant pathologist Kurt Lindbeck, who is part of a team studying the fungal disease blackleg with Grains Research and Development Corporation (GRDC) support, said increasing pressure from blackleg was unsurprising in southern New South Wales, where intensive canola plantings have been eroding blackleg resistance across all canola varieties.

Recent blackleg monitoring trials showed blackleg severity in southern NSW last year was significantly higher when compared to other canola producing regions in Victoria and South Australia.

“We have 10 sites co-located with NVT (National Variety Trials) canola sites throughout NSW, where we monitor what the local blackleg pathogen population is doing,” he said.

“We deliberately sow each of the representative canola varieties of each of the canola resistance groups at each of those sites, deliberately without any fungicide protection at all, and the idea is to expose those resistance genes within those varieties to the local blackleg pathogen population.

“We are observing increases in the level of blackleg at those monitoring sites located in districts with a high intensity of canola production, which is not surprising and reflects the ability of the blackleg pathogen to adapt and eventually overcome resistance within canola cultivars.

“The elevated levels of blackleg we saw in the Group D variety for the first time at our monitoring sites is a warning that growers should now consider increasing levels of protection when sowing cultivars from this resistance group.

“In previous years this resistance group has been virtually immune, but given that Group D varieties have been on the market now for around 7 years, we are now starting to see warning signs that this resistance is being overcome by the pathogen population.”

The blackleg fungus which causes the disease can manifest in canola and can develop into a diverse range of populations, which means the disease can respond effectively to different measures taken by growers, including the introduction of differing resistance types.

The rate of blackleg infection can increase significantly when the same resistance group is planted repeatedly, and the previous year’s stubble can significantly increase disease pressure on the following crop.

Dr Lindbeck said the trend of intensive canola plantings would place greater pressure on variety resistance and fungicide use in the long-term.

“A wheat and canola rotation is quite profitable for growers, and if they are choosing to follow that cropping cycle, they have to become smarter about it and use the appropriate tools that are available.

“This makes optimising blackleg management even more important and for growers to have a disease management plan in place based on the varieties being grown and cropping rotation. This includes utilising all the available management tools such as variety resistance, paddock location, crop rotation and fungicide use.

“Genetic resistance is very important when managing blackleg, and so choosing varieties with an appropriate level of resistance is a good start.

“Using the appropriate level of fungicides is also very good, whether it be a Jockey® seed treatment or fungicide amended fertiliser for example, or a foliar fungicide like Prosaro®, or combinations of all three under conditions of high disease pressure.

“It’s about matching up the right level of fungicide protection to the particular variety and your particular district as well.”