What term describes a situation where the pest control activity of at least one component in a tank mix is reduced when two or more products are combined?

• A. Synergism
• B. Physical incompatibility
• C. Additive effect
• D. Antagonism

Answer: (D)

Antagonism occurs when mixing two or more pesticides reduces the effectiveness of at least one of them. This happens when the chemicals interfere with each other’s action—whether by chemical reactions, changes in absorption, or altered stability—so one product doesn’t work as well as it would alone.

Understanding the other terms helps place this in context: synergism is when the combination works better than expected, additive means the combined effect is simply the sum of each product’s effect, and physical incompatibility refers to issues like precipitation or separation that disrupt the mix's physical form rather than directly reducing one product’s activity through interaction.