Before mixing two pesticides, what test should you perform to check compatibility?

• A. A jar test (compatibility test) to observe for separation or precipitation.
• B. A pH test of the mixture.
• C. A quick smell test.
• D. A field trial on crops.

Answer: (A)

Before mixing two pesticides, the important thing to know is whether they will stay mixed in the spray solution rather than separate or form precipitates. The best way to predict this is a jar test. You mix small, measured amounts of the two products with water in a clear jar, shake it as you would during spraying, and then watch immediately and for a short time. If the mixture stays uniform without layers forming or a solid settling out, it’s a good sign the combination will stay compatible in the tank. If you observe separation, cloudiness that doesn’t clear, or a visible precipitate, that signals incompatibility and you should not use that combination as-is. This test directly reproduces the conditions of the spray tank and tells you whether the products will interact physically.

A pH check can provide additional context about stability, but it doesn’t tell you whether the products will physically mix and remain uniform. A quick smell test doesn’t reveal compatibility, and a field trial is not appropriate for a preliminary compatibility check because it risks crop harm and poor spray performance.