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 90pc in some regions of the country.
The University of Melbourne and Marcroft Grains Pathology Pty Ltd, both in Victoria, have conducted blackleg fungicide resistance surveys annually 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 succinate dehydrogenase inhibitor (SDHI) and strobilurin (QoI).
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.
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 demethylation inhibitors (DMI) fungicides, while no resistance was detected to SDHI fungicides.
There was some potential resistance to QoI 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 40pc and up to more than 50pc, Prosaro from about 20pc to more than 30pc, 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.
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.
Angela Van de Wouw, University of Melbourne, said Aviator Xpro had shown a strong performance in recent resistance surveys.
Ms Van de Wouw 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."
Jasmine Peart
Jasmine is a earnest listener and a passionate advocate for justice. She feels privileged to be trusted by farmers across Western Australia to tell their truth.
Jasmine is a earnest listener and a passionate advocate for justice. She feels privileged to be trusted by farmers across Western Australia to tell their truth.
