Full toolbox approach to beat blackleg

Aug. 13, 2023 | 5 Min read
Ongoing research into canola blackleg fungicide resistance is continuing to reinforce that growers should deploy a full combination of management tools against the disease, including avoiding fungicide applications where it is not necessary.

Ongoing research into canola blackleg fungicide resistance is continuing to reinforce that growers should deploy a full combination of management tools against the disease, including avoiding fungicide applications where it is not necessary.

Blackleg disease causes an average 10 per cent yield loss in canola crops and has reduced yields by up to 90 per cent in some regions of the country.

The University of Melbourne and Marcroft Grains Pathology at Horsham in Victoria have conducted blackleg fungicide resistance surveys annually in recent times and its 2022 survey was particularly extensive.

It monitored fungicide resistance levels from where resistance already had evolved, also to determine if resistance was evolving to newer fungicide classes including SDHI and QoI.

Data extracted from the 2022 blackleg fungicide resistance survey conducted by Marcroft Grains Pathology
continued to show nil levels of resistance to Aviator Xpro fungicide. Notes: 122 stubble
samples collected in 2022 and 103 screened (19 samples had insufficient disease for screening). 

About 50 stubble samples from high blackleg risk regions on the Eyre Peninsula in South Australia, in Central New South Wales and in Western Australia were used to inoculate fungicide-treated seedlings of Stingray canola.

Up to four applications of different fungicides are often applied annually in these regions and this allowed more than 120 blackleg populations to be screened against the fungicides, which were applied at recommended label rates.

Angela Van de Wouw from the University of Melbourne said the survey screened millions of spores, which allows detection of very low levels of resistance if present.

Punnets of the Stingray seedlings were placed into plastic tubs and had the stubble suspended over them and wet-up to promote spore release. They were inoculated for two days before returning to the glasshouse.

Disease presence and severity was scored for each plant and in vitro assays of infected plant material were conducted to confirm resistance.

The latest blackleg resistance survey again confirmed significant resistance to DMI fungicides, while no resistance was detected to SDHI fungicides.

There was some potential resistance to QoI (strobilurin) fungicides, which also has been identified previously, although it is suspected the resistance could be to the DMI chemistry in these fungicide mixtures rather than the QoI chemistry and this will continue to be investigated.

These results have been highlighted with several fungicides in recent surveys, including Jockey Stayer, Prosaro, Veritas Opti and Aviator Xpro.

Of the samples with moderate to high levels of fungicide resistance over recent years, Jockey Stayer treatments have accounted for 40 per cent and up to more than 50 per cent, Prosaro from around 20 per cent to more than 30 per cent, and it has been a similar story with Veritas Opti, while Aviator Xpro fungicide has recorded nil levels of resistance.

Aviator Xpro, from Bayer, contains two strong active ingredients from different modes of action, including bixafen, a novel member of the SDHI fungicides, and prothioconazole, which is a third generation DMI.

CropLife Australia supports the use of different fungicide modes of action for blackleg management as either mixtures, co-formulations or rotations and, hence, these two modes of action can help reduce the risk of resistance developing.

Bayer’s own registration trials show that in addition to controlling blackleg in canola, including in the upper crop canopy, Aviator Xpro also controls sclerotinia and provides suppression of alternaria black spot and powdery mildew.

Its rapid rainfastness when compared with alternatives is another key attribute, helping growers to effectively manage disease during challenging seasonal conditions.

Ms Van de Wouw said said Aviator Xpro had shown a strong performance in recent resistance surveys.

She said the survey results echoed the strong industry messages around rotation of fungicide products and utilising multiple modes of action, however it also reinforced to growers that they should use all available tools to assist their applications and resistance management strategies, including the blackleg management app, BlacklegCM.

“Whether your canola crop is next to a canola stubble or a certain distance away from stubbles, the particular genetic resistance of your variety against blackleg, the region you are in and good monitoring during the growing season – these are all factors that contribute to whether you actually use a fungicide or not,” Ms Van de Wouw said.

“Canola has become our second most valuable crop and, as a result, I understand that people may have just been putting fungicides on, but potentially they haven’t needed to.

“We need to look at more strategic use of fungicides in combination with all the other tools,” she said.

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