Resisting the Next Resistance
Incidents of fungicide resistance, particularly with frogeye leaf spot, have emerged in recent years, most noticeably with soybean production in the Southern states. Fungicide resistance cases continue to move northward along a path similar to that of herbicide resistance. While fungicide resistance has not been diagnosed in U.S. corn production, it is not a question of if it could happen, but more likely when it will happen.
“Natural mutations are responsible for fungicide-resistant isolates. The fungicides applied do not cause these mutations. These mutations occur naturally,” says Carl Bradley, Ph.D., plant pathologist for the University of Illinois.
University researchers and fungicide providers have identified five fungicide best management practices to ensure long-term fungicide effectiveness in corn, soybeans and wheat:
- Choose a resistant hybrid/variety. Bradley says selecting a resistant hybrid/variety is the most important decision you can make in managing disease. Seed companies often provide disease ratings for their seed products. Factor in field history when selecting a disease-resistant seed.
- Scout fields regularly. Monitor fields consistently, documenting the presence and severity of diseases. Keep records over several years, as diseases can reappear after an absence of some seasons when the conditions are favorable for development.
- Implement crop rotation. As you know,the risk of disease increases in non-rotated fields. Using a crop rotation appropriate for your region can reduce this risk. In continuous crop situations, alternate disease-resistant hybrids/varieties and monitor fields closely.
- Mix and rotate fungicide classes. Applying fungicides with a single active ingredient can create a high risk for resistance. Use fungicides or tankmixes with multiple modes of action. A fungicide such as Stratego YLD has two modes of action (see pictured label). The Fungicide Resistance Action Committee (FRAC) provides a fungicide modes of action list.
- Follow label recommendations. Timing, plant size and target disease may dictate the use rate and spray interval. Check the label for size-appropriate rates. Using lower-than-labeled fungicide rates could enable resistance to emerge sooner. Fungicide labels include FRAC modes of action and the number of fungicide applications permitted per season.
Information Platform for Extension
Additional fungicide management practices include:
- Maintain proper soil fertility
- Use Integrated Pest Management practices
- Improve surface and subsurface drainage
“Growers should apply fungicides preventively or early in the disease cycle and also when a disease threat is looming,” says Thorsten Schwindt, product manager for Bayer Crop Science.
“By implementing multiple best management practices, growers can preserve the long-term effectiveness and viability of fungicides.”
The Plant Management Network and Integrated Pest Management – Pest Information Platform for Extension and Education also have additional fungicide resistance management information.