Which statement about fungicide modes of action is true?

Which statement about fungicide modes of action is true?

• A. They are all systemic inhibitors.
• B. Fungicides are equally effective regardless of mode of action.
• C. They can be fungitoxic or fungistatic; some are systemic inhibitors while others are contact protectants; rotation is advised to avoid resistance.
• D. Fungicides never require rotation if the disease is dollar spot.

Answer: (C)

Fungicide modes of action vary, and that diversity is key to effective, long-term control. Some products are systemic, moving within the plant to protect new tissues, while others are contact protectants that stay on the surface and must contact the pathogen to work. Fungicides can also be fungitoxic (kill the fungus) or fungistatic (inhibit its growth). Because pathogens can adapt to a single mode of action, rotating products with different modes helps delay or prevent resistance while preserving overall effectiveness. This is why dollar spot programs often emphasize rotation rather than relying on one product alone.

Fungicide modes of action vary, and that diversity is key to effective, long-term control. Some products are systemic, moving within the plant to protect new tissues, while others are contact protectants that stay on the surface and must contact the pathogen to work. Fungicides can also be fungitoxic (kill the fungus) or fungistatic (inhibit its growth). Because pathogens can adapt to a single mode of action, rotating products with different modes helps delay or prevent resistance while preserving overall effectiveness. This is why dollar spot programs often emphasize rotation rather than relying on one product alone.