![\"\"](\"https:\/\/www.europesays.com\/ie\/wp-content\/uploads\/2025\/08\/MGP-19-scaled.jpg\")
<\/p>\n<\/p>\n
Dr Steve Marcroft inspects canola growing in a trial site. Photo: Marcroft Grains Pathology<\/p>\n
CROP pathologists and fungal disease experts are concerned about the increasing use of precautionary fungicide applications in Australian canola.<\/p>\n
Repeated applications of a single fungicide as \u201ccheap insurance\u201d against disease could have serious long-term consequences.<\/p>\n
Australian Fungicide Resistance Extension Network (AFREN) project lead Fran Lopez-Ruiz<\/strong>, said fungicide resistance posed an ongoing threat to canola production, with frequent and repeated application of the same fungicide group being one of the main drivers.<\/p>\n AFREN is an initiative of the Grains Research and Development Corporation.<\/p>\n \u201cRepeated use of fungicides from the same chemical group, especially when there\u2019s no clear evidence of yield benefit, can drive the development of fungicide resistance within disease populations,\u201d Dr Lopez-Ruiz said.<\/p>\n Fungicide resistance means a fungicide is no longer effective for disease control and denies growers the option to use the affected fungicide group.<\/p>\n This loss increases reliance on other registered fungicide groups, increasing the risk of multiple fungicide resistance scenarios.<\/p>\n Spores released by fungicide-resistant fungi can spread over large areas in a short time.<\/p>\n This means overuse of fungicides and poor disease management practices on a single farm can quickly become a regional problem.<\/p>\n \u201cWe are seeing this with net form net blotch (NFNB) of barley in parts of South Australia, Western Australia and Victoria.\u201d<\/p>\n \u201cNFNB pathogen populations with triple fungicide resistance to all three registered fungicide groups have limited growers\u2019 options for protecting their barley yields.<\/p>\n \u201cThis is why AFREN recommends a targeted approach to fungicide application \u2013 only apply fungicide when necessary and when there is a clear economic benefit from doing so.<\/p>\n \u201cEven then, different fungicide groups should always be used in rotation so any pathogens with fungicide resistance or reduced sensitivity will be controlled by one of the treatments.\u201d<\/p>\n The comparison between NFNB of barley and blackleg of canola should not be taken lightly, according to Steve Marcroft<\/strong> of Marcroft Grains Pathology, based in Horsham, Vic.<\/p>\n Blackleg with reduced sensitivity to Group 3 fungicides prothioconazole, fluquinconazole, flutriafol and tebuconazole is present in NSW, SA, Vic and WA.<\/p>\n There is a high likelihood of resistance developing with the potential for field failure in pathogen-conducive environments.<\/p>\n Mutations for reduced sensitivity to Group 7 SDHI fungicides and Group 12 fungicide fludioxonil, the only other fungicide groups registered for blackleg control, have also been detected in SA.<\/p>\n There is a potential for reduced sensitivity to these two groups under high disease and fungicide selection pressure.<\/p>\n Dr Marcroft said he has received several inquiries about using double rates or off-label timings to help control blackleg or mitigate efficacy issues due to fungicide resistance.<\/p>\n \u201cBoth practices are illegal, as label rates and requirements must be followed, and they will also contribute to increased levels of fungicide resistance,\u201d Dr Marcroft said.<\/p>\n \u201cFungicides must only be applied in accordance with label recommendations and only used when disease pressure is high and there is a clear risk of yield loss.\u201d<\/p>\n Preliminary results from GRDC-supported research by Marcroft Grains Pathology, using blackleg of canola as a model, suggests that foliar applications during the four to eight-leaf stage are the main driver of fungicide resistance.<\/p>\n Canola plants can typically tolerate crown canker infection of up to 20 per cent before any yield loss occurs. Photo: Marcroft Grains Pathology<\/p>\n Growers should avoid spraying fungicide during this growth stage if possible.<\/p>\n \u201cIt\u2019s important to remember that canola plants can tolerate a significant amount of disease before any yield loss occur,\u00a0 typically up to 20 percent crown canker infection,\u201d Dr Marcroft said.<\/p>\n \u201cWhile skipping early foliar applications will lead to a small amount of crown canker, this is unlikely to result in yield losses but will have a massive impact on minimising the risk of fungicide resistance evolving.\u201d<\/p>\n Low levels of Upper Canopy Infection (UCI) are also unlikely to impact yield. Furthermore, applying fungicide after 50 per cent bloom can breach maximum residue limit (MRL) restrictions.<\/p>\n \u201cIf fungicides are used to excess when disease pressure is low or there is no threat to yields, they may no longer be effective when we genuinely need them,\u201d Dr Marcroft said.<\/p>\n \u201cWhat may seem like cheap insurance now could actually be a longer-term risk to canola production. Weighing the pros and cons of a fungicide spray with your agronomist is a much better investment.\u201d<\/p>\n Growers should also follow the AFREN Fungicide Resistance 5 principles for integrated disease management.<\/p>\n This includes planting canola at least 500m from the previous season\u2019s stubble, using time of sowing to manage disease risk, and using more resistant varieties and rotating them.<\/p>\n![\"\"](\"https:\/\/www.europesays.com\/ie\/wp-content\/uploads\/2025\/08\/Canola_crown_canker-e1755735867111-342x400.jpg\")
<\/p>\n