Mixing modes of action has what effect on resistance risk?

• A. Reduces resistance risk
• B. Increases resistance risk
• C. Has no effect
• D. Guaranteed pest elimination

Answer: (A)

Mixing modes of action reduces resistance risk because it makes survival harder for pests that have begun to tolerate one particular action. When two different modes are used together, a pest would need resistance to both modes to survive the treatment. Since resistance to both distinct modes is much less common than resistance to just one, far fewer individuals survive and reproduce, slowing the spread of resistance through the population. This approach helps keep pesticides effective longer and is a key part of resistance management, alongside proper timing, correct rates, and regular monitoring. If the two ingredients don’t work well together or one is ineffective, the benefit is lost, so it's important that both are effective and compatible.