In Australia's canola growing regions, a seemingly cautious farm management practice—"insurance" spraying of fungicides—is now being viewed by agricultural pathologists as a long-term risk that could shake the foundations of the entire industry. Experts are issuing an urgent call for growers to re-evaluate their disease management strategies to avoid repeating the fate already seen in parts of the barley industry.

The core issue lies in routine, preventative spraying, especially in the absence of significant disease pressure or clear economic benefit, which creates an invisible "breeding ground" for the evolution of fungal diseases. Associate Professor Fran Lopez-Ruiz, leader of the Australian Fungicide Resistance Extension Network (AFREN), a Grains Research and Development Corporation (GRDC) investment, points out that when farmers repeatedly rely on fungicides from the same chemical group, they are effectively selecting for and cultivating pathogen strains that are insensitive to that agent.

Once this resistance is established, it means that once-effective chemicals are rendered into "placebos," unable to control the disease. Worse, this forces growers to turn to the few other registered options, thereby intensifying the selection pressure on the remaining "weapons" and potentially leading to a "no-cure" situation where pathogens are resistant to multiple fungicides. As spores from resistant fungi can spread over vast areas in a short time, improper fungicide use on a single farm can quickly escalate into a regional disaster.

Associate Professor Lopez-Ruiz uses the case of net form net blotch in barley in parts of South Australia, Western Australia, and Victoria as a warning. In these areas, the pathogen has already developed resistance to all three registered fungicide groups, severely limiting farmers' options to protect their yields. This real-world lesson is precisely why experts fear the canola industry could be heading down the same path.

Dr. Steve Marcroft of the Marcroft Grains Pathology institute stresses that the problem of blackleg in canola is equally concerning. Currently, in New South Wales, South Australia, Victoria, and Western Australia, blackleg strains with reduced sensitivity to Group 3 fungicides (such as prothioconazole and tebuconazole) are already widespread. Meanwhile, in South Australia, scientists have also detected genetic mutations for resistance to the other two key fungicides—from Group 7 and Group 12. This indicates that under conditions of high disease and frequent fungicide use, canola growers could rapidly lose all effective chemical defenses.

Research shows that a key driver of resistance is foliar spraying conducted when canola plants are in the four-to-eight-leaf stage. Dr. Marcroft advises growers to avoid spraying at this stage whenever possible. He explains that canola plants themselves have considerable tolerance, typically not suffering any actual yield loss until the crown canker infection rate reaches 20%. Therefore, forgoing early preventative sprays, while it may lead to a small number of lesions on the plants, will not affect the final harvest but will significantly delay the development of resistance.

Furthermore, experts refuted erroneous practices common among some growers, such as arbitrarily doubling the dose or applying at off-label times. Dr. Marcroft clearly states that these actions are not only illegal but also further exacerbate the resistance problem. The correct approach is to apply fungicides precisely according to label instructions and only when disease pressure is genuinely high and there is a clear risk of yield loss.

Therefore, the future of canola disease management requires a shift from a singular reliance on chemical spraying to a more intelligent and comprehensive integrated strategy. To this end, AFREN has proposed the "Five Principles of Resistance Management," advocating a multi-pronged approach:

Rotation and Isolation: Ensure new canola fields are at least 500 meters away from the previous season's crop stubble.

Sowing Time: Utilize different sowing times to avoid periods of high disease prevalence.

Variety Selection: Plant more disease-resistant canola varieties and rotate them regularly.

Precision Application: Strictly adhere to the principle of "apply only when necessary" and rotate between fungicide groups with different modes of action.

Professional Consultation: Work with an agronomist to assess risks and weigh the pros and cons of application, making data-driven decisions.

In conclusion, the seemingly convenient "cheap insurance" of today is likely mortgaging the future of Australia's canola industry. To protect these precious chemical tools so they remain effective when genuinely needed, the entire industry must act immediately, shifting from blind reliance to scientific, precise, and integrated disease management.