Agronomy •  2021-05-07

‘Talking Resistance’ - Managing and preventing fungicide-resistance

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Fungicide resistance is becoming a growing problem in Canadian agriculture, impacting the yield and quality of several crops across the country. 

While most farmers know the lay of the land when it comes to managing herbicide resistant weeds, there is much less awareness around fungicide resistance in Canada.

Disease resistance is often harder to notice than weed resistance, issues vary between crops and growing regions, and the economic damage is not yet as severe. But, over the past decade, growers have ramped up the use of fungicides to alleviate mounting disease pressure - which has subsequently led to an increased risk of selection pressure for resistance.

Travis Schoonbaert, category leader at Corteva Agriscience Canada, believes this is problematic as we have a limited number of fungicide Groups available to us as an industry. To protect crop yield and quality today and in the future, and to ensure the tools we have now stay effective for as long as possible, Travis stresses the importance of maintaining a diverse resistance management strategy where fungicide use is but just one tool in a farmer’s belt.

For resistance best management practices, he points to - a trusted go-to resource developed by CropLife Canada, with unbiased, industry-leading research and advice for Canadian farmers. The development was overseen by the Resistance Management Committee representing all manufacturers, with the information reviewed and commented on by recognized industry experts.

Disease Resistance: Q&A with Travis Schoonbaert 

Travis Schoonbaert

How big of a problem is fungicide resistance in Canada?

While fungicide resistance is not nearly as big an issue as herbicide resistance in terms of economic impact, fungicide use has increased a great deal over the past decade. And since we have a limited number of fungicide Groups available to us as an industry, we really need to be proactive about managing those tools carefully so they’re available for the long term. The ultimate goal is to build sustainable cropping systems.

How can Canadian farmers better manage disease resistance?

The first step is to understand the three key factors that contribute to the risk of resistance. Often represented in a ‘resistance risk triangle’, they are 1. Disease risk; 2. Fungicide risk, and 3. Agronomic factors. Disease risk is often dictated by weather conditions and the presence of the pathogen. To lower your disease risk, you must manage the other two elements of the risk triangle. This entails using agronomic practices that promote healthy plants and selecting fungicides strategically to reduce disease and resistance risk.

How can farmers start with a resistance management strategy?

Resistance management starts with making sure you're using all the tools in your toolkit - your first tool is planting seeds that have genetic resistance to disease and then layering other management techniques on top of that. Crop rotation is the second tool, and we have good rotations in place in both eastern and western Canada. The third tool is maintaining smart cultural practices that make a field less attractive to disease. And that fourth and final tool you should consider is fungicides - that way you’re checking all the boxes before deciding if you need to spray one.

What factors should farmers consider before spraying a fungicide?

When considering whether to use a fungicide, you need to look at your crops on a field-by-field basis to assess risk. Some may have a history of disease while others might be relatively low risk. So, it’s about being a good manager and making sure you're going to get a return on investment on a fungicide. Weather is another important factor. There’s an old saying, “where there’s gold there’s mould” because most fungal diseases thrive in the same rainy, wet conditions that produce lush, high-yielding crops. Therefore, you need to constantly scout for disease - especially with a soybean or canola crop as you can’t chase white mould/sclerotinia from behind. Once the disease is in your field, it's often too late.

Fungicide Resistance Best Management Practices (BMPs)

1. Use agronomic practices that promote healthy plants

  • Use resistant varieties or cultivars for problematic diseases in your area.

  • Know what environmental conditions contribute to disease development and be aware of disease issues in previous years.

  • Rotate field crops to reduce pathogen populations.

  • Reduce crop stress by: optimizing planting date, planting at the proper seed depth, using high-quality seed, controlling other pests, and minimizing herbicide injury.

  • Use quality seed treatments when possible for early disease protection.

2. Evaluate the need for disease control

  • Assess your level of disease risk in your crop for that year based on agronomic factors (for example crop type and stage), disease issues in previous years, and environmental conditions in the current year.

  • Understand the target disease risk, pathogens have different levels of risk with regards to resistance development.

  • Scout fields to identify problems and assess early and often. Correctly determine the level of disease risk before deciding whether fungicides are needed.

  • If you have a high disease risk based on agronomic and environmental factors, very early fungicide applications can be beneficial to prevent populations from getting out of control.

3. Select fungicides strategically

  • Use fungicides that are labelled for the diseases that pose a threat to your crop yield.

  • Rotate fungicide Groups both during a growing season and between growing seasons, either through tank mixes or alternating sprays with fungicides that have different modes of action but work on the same target disease.

  • Mix fungicides. Combinations of two or more fungicides with different modes of action against the targeted pathogen, applied as a mixture at the recommended rates according to label directions, can delay the onset of resistance.

4. Maximize fungicide efficacy

  • Consult the product label for the most effective time to spray.

  • Be mindful of proper spray techniques and adequate water volumes when applying fungicides, whether the disease is foliar, seed, or tuber.

For more best practices to manage fungicide resistance, visit:


How can farmers maximize fungicide efficacy? 

Spraying field crops with fungicides is a relatively new development in the past 10 to 15 years. For the uninitiated, I like to stress the importance of using a fungicide Group at its labelled effective rates - as not doing so can lead to reduced control and increased selection pressure. Coverage is also critical when applying a fungicide. Unlike herbicides, most fungicides move upwards in the plant, so you really need the product to penetrate deep into the crop canopy and treat those lower parts of the plant. This necessitates using adequate water volumes and ensuring you’re using the right nozzles and sprayer set up to get the proper coverage. Finally, much like with herbicides, it’s important to rotate fungicide Groups and utilize multiple effective modes of action to help offset the risk of resistance developing. 

Does the industry need to do a better job of educating farmers on fungicide Group rotations? 

Definitely - often you’ll see companies promote multi-modes of action, even though the product’s actives work on different diseases and may not provide overlapping control on key target diseases. That’s why the site is such a valuable resource as it provides practical, unbiased advice. At Corteva, we're also trying to eliminate confusion and raise the level of knowledge in all our communications, so farmers can be confident in their fungicide decisions and set themselves up for success both today and in the future. 

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