When two or more pesticides mixed together form a putty or paste, separate into layers, or look like cottage cheese, this is an example of:

• A. Chemical incompatibility
• B. Biological incompatibility
• C. Physical incompatibility
• D. Operational incompatibility

Answer: (C)

The signs described—forming a putty or paste, separating into layers, or looking like cottage cheese—show physical incompatibility. This happens when the components don’t stay evenly dispersed because of differences in solubility, density, or emulsifying properties, so the mixture is physically unstable even though no chemical reaction occurs. If it were chemical incompatibility, you’d expect evidence of a chemical reaction such as heat, gas evolution, color change, or a new solid forming. Biological incompatibility would involve effects on living organisms or degradation, not the texture of the mixture, and operational incompatibility relates to equipment or handling, not the actual blend’s stability. A practical check is a jar test to see if the mixture remains uniform before making a full tank mix.