What is the role of FRAC classification in disease management?

• A. It measures the effectiveness of fungicides in field trials.
• B. It ranks fungicides by price.
• C. It groups fungicides by mode of action; rotating FRAC groups helps prevent resistance development.
• D. It indicates optimal spray volumes.

Answer: (C)

FRAC classification organizes fungicides by how they affect the pathogen—their mode of action. This grouping is the basis for resistance management, because rotating among different FRAC groups changes the target site that the fungus encounters from one application to the next. When you alternate products with different modes of action, you reduce the consistent selective pressure that would otherwise favor fungi that are already or becoming resistant to a single action.

A practical takeaway is that if a population of fungi becomes resistant to one mode of action, products from a different FRAC group can still be effective. However, resistance within a FRAC group can cross-protect other products in the same group, so simply switching to another product in the same group won’t break the problem. That’s why rotating across distinct FRAC groups and avoiding repeated use of the same group in sequence is a cornerstone of sustainable disease control.

FRAC is not about how effective a product is in field trials, nor about price, nor about spray volumes. It’s a tool to guide the design of spray programs so they use diverse modes of action over time. Growers use FRAC codes on product labels to plan rotations and to minimize the risk of resistance development while maintaining overall disease control.