Compatibility Test For Pesticide Mixtures

WARNING: Always wear personal protective equipment (PPE) when pouring or mixing pesticides.

Perform this test in a safe area away from food and sources of ignition.

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Compatibility Test For Pesticides

Tank mixes of two or more pesticides are commonly applied. Sometimes these pesticides may not mix well in the tank even though each product alone mixes well. Also, there are situations where it is desirable to use a fluid fertilizer or liquid nitrogen as the carrier. Some pesticides are compatible with fluid fertilizers and some are not. Never mix fungicide with fertilizers. By conducting a simple compatibility test before adding the pesticides to the tank, one can usually avoid making "Jello" in the tank. Every batch of fluid fertilizer or liquid nitrogen should be tested for compatibility. Batches can vary in pH, salt concentration, or even temperature. Minor differences may affect compatibility.

Materials Required for a Compatibility Test

Table 1. Amount of pesticides to add for a compatibility test.

 
Pesticide
Formulation

Rate/Acre

Teaspoons to Add
WP or DF

1 lb

1.5
 

2 lb

3.0
 

3 lb

4.5
 

4 lb

6.0
EC, F, L, or S

1 pt

0.5

1 qt

1.0

2 qt

2.0

4 qt

4.0

Procedure

The procedure for a compatibility test is often outlined on a pesticide label. Follow these steps, in order to perform a compatibility test.
1. Add 1 pint of the fluid fertilizer to each quart jar.
2. To the jar marked "with", add 1/4 teaspoon of compatibility agent. Shake gently for 5 to 10 seconds.
3. To each jar, add the appropriate amount of pesticide(s), (table 1). Shake gently for 5 to 10 seconds.
4. Let the jars sit for 5 minutes, then look at them. See if there are any flakes, sludge, gels, or other precipitants. Also see if there is any separation or layering, or small oil particles in solution.
If incompatibility occurs in "without" jar but not in "with" jar, use a compatibility agent.
If incompatibility is observed in the "with" jar, this combination is not compatible and should not be used.
5. If separate layers are formed after sitting up to 30 minutes but can be resuspended by shaking, using agitation in the sprayer will make commercial application possible.
If there is layering, an emulsifiable concentrate will normally rise to the top. Wettable powders will either settle to the bottom or float on top, depending upon the density of the fertilizer carrier.