______________ occurs when the pest control effectiveness of one or both mixed pesticides is reduced.

• A. Synergism
• B. Antagonism
• C. Synchronism
• D. Inhibition

Answer: (B)

Antagonism is when mixing two pesticides leads to a lower pest-control effect than either would have alone. This happens when the chemicals interfere with each other’s activity—one might block the other’s uptake, they could react to form a less active compound, or one pesticide could trigger pest defenses that reduce the effectiveness of the other. The essential point is that the combined effect is reduced, not enhanced.

Synergism would make the mix more effective than expected, which is the opposite. Synchronism isn’t a standard term for pesticide interactions in this context, and while inhibition can describe a mechanism, the established term for reduced effectiveness due to mixing is antagonism.