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A jar test is a crucial procedure for evaluating the compatibility of various ag chem before tank mixing.
This test helps prevent undesirable reactions such as precipitation, gelling, or separation, which can lead to clogged equipment, reduced efficacy, and crop damage. Performing a jar test ensures a homogeneous and effective spray solution.
Pro Tip: When you hear an agronomist talk about "antagonism,” they’re describing a scientific phenomenon where two or more items mixed together have an overall reduced effect simply from being combined. It’s important to know that mixing two products or ingredients together doesn’t always mean they retain their effectiveness.
Clear Glass Jars: At least one quart-sized (or liter-sized) clear glass jar per chemical in the proposed mixture, plus one for the final mixture. Mason jars are ideal.
Measuring Devices: Accurate measuring spoons and syringes (e.g., 1 mL, 5 mL, 10 mL) for precise measurement of small liquid volumes.
Water Source: The same water source intended for the actual spray application (e.g., well water, pond water, municipal water). Water quality (pH, hardness) can significantly impact compatibility.
Agricultural Chemicals: Samples of each product to be mixed, including herbicides, insecticides, fungicides, foliar fertilizers, adjuvants, and surfactants.
Stirring Rods: Separate stirring rods for each chemical or a method to clean between uses to prevent cross-contamination.
Timer: To monitor agitation and settling times.
Labels/Markers: For clear identification of jars and contents.
Personal Protective Equipment (PPE): Gloves, eye protection, and appropriate clothing as recommended on product labels.
Calculate the exact amount of each product to add to the jar based on the intended spray volume and tank size.
A common scaling factor is 1:100 (e.g., pint per 100 gallons becomes 1 teaspoon per gallon). For a 1-quart (0.25-gallon) jar, this means scaling to 0.25% of the field rate.
Example: If a product is applied at 1 quart per 100 gallons, and your jar holds 1 quart (0.25 gallons), you would add (1 quart/100 gallons)×0.25 gallons=0.0025 quarts, or 0.075 mL (since 1 quart≈946 mL). Precision is critical for small volumes.
Fill the test jar with the exact amount of water determined by your scaling factor (e.g., 1 quart, or 946 mL). Use water from the actual spray source.
Always add products in the recommended mixing order. A common order is:
Adjusters (pH buffers, water conditioners)
Wettable powders (WP), Dry flowables (DF), Water-dispersible granules (WDG)
Agitate thoroughly after each addition.
Flowables (F), Suspension concentrates (SC)
Agitate.
Emulsifiable concentrates (EC)
Agitate.
Solutions (S), Soluble liquids (SL)
Agitate.
Surfactants/Adjuvants
Agitate.
Foliar fertilizers (if not already added as a solution)
Agitate.
Add each product individually, stirring thoroughly for 30−60 seconds after each addition to ensure complete dispersion before adding the next.
Immediately after mixing all components, observe the mixture for any signs of incompatibility:
Precipitation: Formation of solids or flakes.
Gelling: Mixture thickens into a gel-like consistency.
Layering/Separation: Distinct layers forming, indicating insolubility.
Foaming: Excessive, persistent foam.
Color Change: Significant and unexpected color changes.
Secure the lid on the jar and shake vigorously for 30 seconds to simulate pump agitation.
Let the mixture stand undisturbed for 15−30 minutes. This allows for observation of slower reactions or settling.
After the settling period, re-examine the mixture.
Look for any of the incompatibility signs mentioned in Step 4.
Gently swirl the jar to see if any settled material easily re-suspends. If solids remain at the bottom and do not re-suspend, this indicates poor compatibility.
Compatible: The mixture remains uniform, with no significant precipitation, gelling, or separation. Any slight settling should easily re-suspend with gentle agitation. This mixture is likely safe for tank mixing.
Incompatible: Any persistent signs of precipitation, gelling, layering, or difficulty in re-suspending settled material indicate incompatibility. Do not proceed with this tank mix combination. Adjust the order of addition, consider alternative products, or consult with an agronomist or chemical representative.
Record all observations, including product names, order of addition, water source, and results. This documentation is valuable for future reference and troubleshooting.
Remember that a compatibility jar test will only reveal physical incompatibility between products in your tank mix. They will not reveal any other form of antagonism.
The only way to know for sure is to apply the mix to a few test plants. You can use a spray bottle and apply your test to a few plants in the field. Look for signs of crop damage, such as yellow or brown spots on leaves.
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