Farmers have trusted fungicides to protect their crops against disease and maintain the health and quality of their crops for many years. However, over time, repeated use of the same fungicide will only make efforts to prevent certain fungal infections seem futile, but smart management practices can help mitigate the effects of fungicide resistance.
Managing Fungicide Resistance
Fungicides have been used for many years to prevent disease and safeguard crop yield and quality, however, fungicide resistance has appeared in areas throughout the prairies, threatening the farmer’s ability to prevent disease in their crops. Predicting where and when resistance will occur is difficult, but fortunately, there are a wide variety of techniques farmers can use as part of an integrated management strategy to protect their crops.
Management of fungicide resistance is critically important to extend the likelihood that a fungicide is effective. Certain fungicides have been identified as having a higher risk of developing resistance. Single-site fungicides attack one metabolic path within a pathogen and thus, it’s easier for the pathogen to evolve and become resistant. Multi-site fungicides will delay resistance, as the pathogen must build resistance to each of the active ingredients within the multi-site fungicide.
“Poor disease control with fungicides can result from the insufficient application of the fungicide, low effectiveness of the fungicide on the plant pathogen, improper application method or timing, and more commonly, extreme weather conditions such as excessive rainfall,” said Danean Richardson, Crop Protection Manager at Central Plains Co-op in Rosetown, Saskatchewan. “With an integrated approach, farmers can manage disease more effectively.” Different methods to be used in the integrated approach include crop rotation, disease forecasting, sanitation and field monitoring with Co-op AgZone.
When choosing a fungicide, it’s important to consider the mode of action, or how the fungicide interacts with the cells. Different groups of fungicides affect the different areas of the cell. The most effective use of fungicide application is preventative, or before the disease attacks or almost immediately after lesions appear — when the pathogen population is small.
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Fungicidal Use Pattern
Poor performance or fungicide failure does not equal fungal resistance. In fact, field resistance refers to changes that occur with the specific fungal species under natural conditions in the field. The first indication of the possibility of resistance may be found through routine monitoring or is seen in the fungicide, providing poor performance on the disease. A preventative spray program is less risky than a rescue program, with less fungal pathogens present to reduce the selection pressure. Finally, an increase in selection pressure results from an excessive number of applications where the disease was already established before spraying the first application.
Some biotypes are naturally resistant, while others become resistant by spraying the same single site fungicide over multiple years. It is important to use alternating of modes of actions. Spraying fungicides that have a mixture of active ingredients will also lower the risk of fungicide resistance.
Resistance Management Strategies and The Seven-Step Program
The following resistance management strategies are part of the seven-step program that is recommended. When possible, use several strategies together.
- Avoid repetitive use or overuse of a single fungicide
- Do not rely exclusively on a single fungicide product (it’s okay to alternate with a partner brand)
- Restrict the number of treatments applied per season with the same product/mode of action
- Avoid over-spraying
- Apply the recommended treatment rate from the manufacturer
- Use multiple modes of action and integrate several disease management strategies
- Use the principles outlined for integrated disease management
With proper record keeping, stewardship and planning with your local Co-op Grow Team member, you can maintain the effectiveness of fungicide efficacy.