8.4 Compatibility, the Jar Test & Tank-Mixing Sequence
Key Takeaways
- Physical incompatibility shows as curdling, gelling, flocculation or separation; chemical incompatibility degrades the active ingredient without visible change.
- Biological antagonism means the mixture controls the pest less well than either product alone, even when it looks and pumps normally.
- The jar test uses proportional amounts of each product in a quart of the actual carrier water, added in the intended order, then observed for separation.
- The WALES/DALES sequence adds wettable powders and dry products first, then agitate, then flowables, then liquids and solutions, then emulsifiables, then surfactants.
- Fill the tank half to two-thirds full with agitation running before adding any product, and never add a second product until the first is fully dispersed.
Last updated: August 2026
Compatibility, the Jar Test & Tank-Mixing Sequence
Why this matters: Tank mixing saves passes across the field and destroys pumps, booms and crops when it goes wrong. The jar test and the mixing sequence are the two procedures that keep it from going wrong.
1. Understanding Pesticide Compatibility: Physical vs. Chemical vs. Biological
Before combining two or more commercial products in a spray tank, applicators must evaluate three distinct levels of chemical interaction:
+-----------------------------------------------------------------------------------------+
| THE THREE TIERS OF PESTICIDE COMPATIBILITY |
+-----------------------------------------------------------------------------------------+
| 1. PHYSICAL INCOMPATIBILITY (Immediate Visual Failure): |
| * Formulations fail to disperse or remain mixed in carrier water. |
| * Visual Symptoms: Phase separation (creaming), severe curdling ("cottage cheese"), |
| precipitation of crystals, greasy oil layering, or thick bottom sludge. |
| * Result: Instantly clogs suction filters, destroys pump valves, ruins spray batch. |
| |
| 2. CHEMICAL INCOMPATIBILITY (Invisible Reaction Failure): |
| * Chemical molecules react chemically, altering molecular structures. |
| * Visual Symptoms: Often ZERO visible change (or unexpected heat/gas generation). |
| * Result: Complete deactivation of pest control efficacy, formation of illegal toxic|
| breakdown residues, or severe non-target environmental toxicity. |
| |
| 3. BIOLOGICAL ANTAGONISM & SYNERGISM (Field Interaction): |
| * Antagonism: One product reduces the biological efficacy of another. (e.g., mixing |
| broadleaf auxin 2,4-D with grass herbicide clethodim reduces grass control by 50%).|
| * Synergism / Phytotoxicity: Combined mixture destroys non-target crop foliage. |
| (e.g., tank-mixing EC formulations or foliar oils with Captan or Sulfur fungicides |
| within 14–21 days strips leaf cuticle, causing severe necrotic leaf defoliation). |
+-----------------------------------------------------------------------------------------+
2. The Standardized Jar Compatibility Test Protocol
When an applicator intends to mix products whose compatibility is not explicitly documented on the label, performing a small-scale Jar Compatibility Test is mandatory before loading hundreds of gallons into a spray rig.
+-----------------------------------------------------------------------------------------+
| STEP-BY-STEP JAR COMPATIBILITY TEST PROTOCOL |
+-----------------------------------------------------------------------------------------+
| EQUIPMENT NEEDED: |
| * 1-Quart (32 fl oz / 1 Liter) transparent clean glass jar with tight-fitting lid. |
| * Accurate graduated syringes / pipettes (1 mL to 10 mL calibrated increments). |
| * Water from the EXACT field filling source (at actual field application temperature). |
| * Required handler PPE (gloves, protective eyewear, chemical-resistant apron). |
| |
| MATHEMATICAL PROPORTIONING FORMULA (For 20 Gallons Per Acre Carrier Volume): |
| * 1 Quart in a jar = 1/80th of a 20 Gallon field tank mix. |
| * 1 Pint of liquid product per acre = Approximately 1.2 mL in 1 quart of water. |
| * 1 Quart of liquid product per acre = Approximately 2.4 mL in 1 quart of water. |
| * 1 Pound of dry product per acre = Approximately 6.0 grams (or ~1.2 teaspoons). |
| |
| STEP-BY-STEP PROCEDURE: |
| Step 1: Fill the glass jar HALF FULL (16 fl oz / 500 mL) with field source water. |
| Step 2: If testing a water conditioner (AMS), add it first and agitate until dissolved. |
| Step 3: Add products in the EXACT "WALES / DALES" sequence, agitating after each step: |
| - 1. Water-Soluble Packets (dissolve completely) |
| - 2. Dry Powders & Granules (WP, WDG, DF) |
| - 3. Liquid Flowables & Suspensions (SC, F, ME) |
| - 4. Liquid Solubles & Solutions (SL, S) |
| - 5. Emulsifiable Concentrates (EC) |
| - 6. Surfactants & Adjuvants (NIS, COC, MSO, DRA) |
| Step 4: Fill the jar to 1 quart with remaining carrier water, cap tightly, and invert |
| the jar 10 to 15 times to ensure thorough mixing. |
| Step 5: Let the mixture stand undisturbed for 15 TO 30 MINUTES in a safe area. |
| |
| EVALUATION CRITERIA: |
| * COMPATIBLE : Uniform dispersion, stable emulsion, or light separation that readily |
| redisperses with 2 gentle inversions. Mixture is safe to spray. |
| * INCOMPATIBLE : Formation of flakes, oily film, sludge, curds, heavy bottom sediment, |
| or heat generation. DO NOT MIX IN COMMERCIAL SPRAY TANK! |
| * COMPATIBILITY AGENT TEST: If separation occurs, repeat test adding 1/2 teaspoon of a |
| compatibility agent to water first. If it stays mixed, add |
| compatibility agent to the field spray tank first. |
+-----------------------------------------------------------------------------------------+
3. The Universal Tank-Mixing Sequence: WALES / DALES
The physical failure of tank mixtures is most commonly caused not by chemical incompatibility, but by improper mixing order. Introducing an Emulsifiable Concentrate (EC) into the tank before dry wettable powders are fully dispersed coats the dry particles in oil, preventing water from wetting the powder and forming unmixable, sticky blobs ("paste balls").
Applicators must memorize and strictly execute the DALES / WALES sequence:
+-----------------------------------------------------------------------------------------+
| THE UNIVERSAL DALES / WALES MIXING SEQUENCE |
+-----------------------------------------------------------------------------------------+
| |
| [ D / W ] ───> DRY FORMULATIONS & WATER-SOLUBLE PACKETS |
| * Step 1: Fill tank 1/2 to 3/4 full with clean water; start AGITATION. |
| * Step 2: Add Water Conditioners / Ammonium Sulfate (AMS) first. |
| * Step 3: Add Water-Soluble Packets (WSP/WSB); allow to fully DISSOLVE. |
| * Step 4: Add Wettable Powders (WP) & Water-Dispersible Granules (WDG). |
| |
| [ A ] ───────> AGITATION & SUSPENSION FLOWABLES |
| * Maintain continuous high-shear agitation. |
| * Add Suspension Concentrates (SC), Flowables (F), Capsule Suspensions |
| (ME / CS). Allow 2-3 minutes for thorough dispersion. |
| |
| [ L ] ───────> LIQUID SOLUTIONS & SOLUBLES |
| * Add Soluble Liquids (SL), Solutions (S), and water-soluble salts. |
| |
| [ E ] ───────> EMULSIFIABLE CONCENTRATES |
| * Add Emulsifiable Concentrates (EC) and Microemulsions. |
| * Watch for spontaneous milky-white emulsion bloom formation. |
| |
| [ S ] ───────> SURFACTANTS, ADJUVANTS & TOPPING OFF |
| * Add Non-Ionic Surfactants (NIS), Crop Oils (COC/MSO), Drift Retardants|
| * Add foliar micronutrients / liquid fertilizers. |
| * Fill spray tank to final target water volume while maintaining run. |
+-----------------------------------------------------------------------------------------+
4. Summary Table: Tank Mix Troubleshooting & Problem Prevention
| Tank Mix Problem | Physical / Chemical Mechanism | Root Cause / Mistake | Mandatory Corrective Action |
|---|---|---|---|
| "Mayonnaise" / Curdled Sludge | Oil droplets encapsulating unwetted dry powder | Added EC formulation into tank before WP or WDG had fully dispersed | Drain/clean tank; rebuild mix following strict WALES sequence |
| Gummy Plastic Lumps in Filter | Polyvinyl alcohol cross-linking reaction | Dropped WSP packet into tank containing EC solvents, crop oil, or Boron fertilizer | Dissolve WSP in clean water FIRST before adding any oils or electrolytes |
| Pesticide Deactivation in Tank | Alkaline Hydrolysis ($OH^-$ cleavage of chemical bonds) | Using alkaline carrier water ($\text{pH} > 8.0$) for organophosphates/carbamates | Test source water pH; add acidifying / buffering agent to reach $\text{pH } 5.5\text{--}6.5$ |
| Herbicide Failure on Weeds | Cation Antagonism ($\text{Ca}^{2+}, \text{Mg}^{2+}$ binding) | Spraying weak-acid herbicides (glyphosate) in hard water without conditioning | Add spray-grade Ammonium Sulfate (AMS) to water BEFORE adding herbicide |
| Foam Overflowing Tank Neck | High-shear pump agitation of surfactant mixture | Agitation running vigorously while adding surfactants without defoamer | Add silicone anti-foam agent to tank water prior to loading surfactants |
Loading diagram...
Test Your Knowledge
An applicator is mixing a complex tank batch containing: (1) an Emulsifiable Concentrate (EC) insecticide, (2) a Water-Dispersible Granule (WDG) herbicide, (3) a Non-Ionic Surfactant (NIS), and (4) Ammonium Sulfate (AMS) water conditioner. According to the standardized WALES / DALES tank-mixing sequence, in what exact order must these components be added to the spray tank?
A
B
C
D
Test Your Knowledge
An applicator conducts a 1-quart Jar Compatibility Test to evaluate a proposed tank mix of a new liquid fertilizer and an EC fungicide. After inverting the jar and letting it stand for 20 minutes, the applicator observes a thick, greasy layer of curdled sludge resembling cottage cheese on top of the liquid that will not redisperse upon shaking. What does this test indicate?
A
B
C
D