6.3 Tank Mixing Procedures, Compatibility Testing & The W-A-L-E Sequence

6.3 Tank Mixing Procedures, Compatibility Testing & The W-A-L-E Sequence

In commercial agriculture, turfgrass management, and structural pest control, applicators frequently combine two or more pesticide products—or tank mix pesticides with liquid fertilizers and adjuvants—in a single spray tank application. When executed correctly, tank mixing improves operational efficiency, expands the spectrum of controlled pests, reduces equipment field passes, and supports resistance management. However, improper mixing procedures can produce severe physical clumping, equipment damage, active ingredient deactivation, or catastrophic crop injury.

---

1. Rationale, Benefits, and Legal Boundaries of Tank Mixing

Commercial applicators employ tank mixtures to achieve three primary agronomic and operational objectives:

1. Broad-Spectrum Pest Suppression: A single treatment can simultaneously target unrelated pest complexes. For example, a commercial turf manager may combine a selective post-emergent broadleaf herbicide, a pre-emergent annual grass herbicide, and a systemic fungicide to treat turf diseases and weeds in a single operational pass.
2. Labor, Fuel, and Soil Compaction Reductions: Combining treatments eliminates duplicate trips across fields, golf courses, or rights-of-way. This drastically reduces labor costs, fuel consumption, machinery wear, and undesirable soil compaction that impairs root growth.
3. Resistance Management: Co-applying two active ingredients with different biochemical Modes of Action (MOA) targeting the same pest population reduces the selection pressure for resistant biotypes. Pests possessing genetic mutations conferring resistance to one mode of action are controlled by the companion active ingredient.

The Legal Standard Under FIFRA Section 2(ee)

Under federal law (FIFRA Section 2(ee)), tank mixing two or more federally registered pesticides is legally permissible, provided that:

• The mixture is not expressly prohibited on any of the participating product labels.
• All active ingredients are applied strictly within their labeled target crops, sites, or host plants.
• The dosage rate of each individual product does not exceed the maximum labeled rate per application or per season.
• The applicator adheres to all personal protective equipment (PPE), worker re-entry intervals (REI), pre-harvest intervals (PHI), and environmental buffer restrictions across all labels. Where label requirements differ, the most restrictive label rule always governs the entire application.

---

2. Physical Incompatibility vs. Chemical Incompatibility

When multiple chemical products fail to combine properly in the spray tank, the failure stems from either physical or chemical incompatibility.

                                    TYPES OF TANK MIX INCOMPATIBILITY
                                    
                     ┌──────────────────────────────┴──────────────────────────────┐
                     ▼                                                             ▼
       ┌───────────────────────────┐                                 ┌───────────────────────────┐
       │  PHYSICAL INCOMPATIBILITY │                                 │  CHEMICAL INCOMPATIBILITY │
       ├───────────────────────────┤                                 ├───────────────────────────┤
       │ • Visible physical failure│                                 │ • Molecular reaction      │
       │ • Curdling, flakes, sludge│                                 │ • No visible warning      │
       │ • Layering & separation   │                                 │ • Active ingredient loss  │
       │ • Clogs nozzles & strainers│                                │ • Antagonism / Deactivat. │
       │ • Equipment destruction   │                                 │ • Severe crop phytotox.   │
       └───────────────────────────┘                                 └───────────────────────────┘

Physical Incompatibility

Physical incompatibility occurs when products cannot physically blend or remain uniformly suspended in the carrier liquid. It is caused by formulation antagonism, improper order of addition, carrier temperature extremes (mixing in near-freezing well water), or high mineral hardness in the carrier.

• Observable Symptoms:
  • Flocculation: Particles aggregate into visible flakes, curds, or fluffy clumps that float on the surface.
  • Precipitation: Insoluble solids drop out of suspension, accumulating as heavy sand, sludge, or crystalline grit at the bottom of the tank.
  • Phase Separation / Layering: The mixture stratifies into distinct, immiscible liquid layers (resembling unmixed oil and vinegar salad dressing).
  • Curdling and Gelling: The formulation converts into an intractable, thick, mayonnaise-like gel or rubbery mass.
• Operational Consequences: Severe physical incompatibility plugs suction strainers, destroys pump impellers, blocks 50-mesh nozzle screens, and produces uneven application rates (pure water sprayed first, followed by a toxic slug of concentrated sludge). Applicators are forced to shut down operations and undertake costly, hazardous tank clean-outs.

Chemical Incompatibility

Chemical incompatibility occurs when a chemical reaction takes place between active ingredients, adjuvants, or carrier minerals, fundamentally altering the molecular structure and biological properties of the compounds.

• Antagonism (Efficacy Loss): One active ingredient deactivates or degrades the companion chemical. For example, mixing certain post-emergent grass herbicides (graminicides) with broadleaf herbicides (such as 2,4-D or dicamba) can cause severe chemical antagonism, rendering the grass herbicide completely ineffective.
• Synergism & Enhanced Phytotoxicity: The chemical reaction creates unexpected phytotoxic compounds or accelerates cuticular penetration to a degree that causes catastrophic foliar burning, stunting, defoliation, or complete death of the desirable crop or turfgrass.
• The Insidious Hazard: Chemical incompatibility often produces no visible physical changes in the spray tank. The solution may appear clear, uniform, and sprayable, yet pest control fails entirely or valuable crops are destroyed.

---

3. The Small Jar Compatibility Test Protocol

Before mixing unfamiliar pesticide formulations, new adjuvant combinations, or pesticides with liquid fertilizers in a 300-gallon commercial spray tank, the applicator must conduct a small jar compatibility test.

Required Equipment and PPE

• One clean, transparent glass quart jar (approx. 1 liter) with a leak-proof, chemical-resistant lid.
• Calibrated measuring droppers, syringes, or graduated pipettes.
• Personal Protective Equipment: Chemical-resistant nitrile gloves, safety goggles, and protective apron.
• Source carrier water or liquid fertilizer drawn from the exact source and at the exact temperature planned for field application.

Step-by-Step Test Procedure

1. Measure Carrier: Pour one pint (16 fl oz / approx. 500 mL) of the spray carrier (water or liquid fertilizer) into the clean glass quart jar. This volume represents a standard spray volume baseline (approximately 25 gallons per acre).
2. Calculate Proportional Ratios: Determine the proportional amount of each pesticide to add to the pint of carrier, matching labeled field application rates:
   • Dry Formulations (WP, WDG, DF): For each 1 pound per acre recommended on the label, add 1 rounded teaspoon (approx. 5 grams) to the pint of carrier.
   • Liquid Formulations (EC, F, S): For each 1 pint per acre recommended on the label, add 1/2 teaspoon (approx. 2.5 mL) to the pint of carrier.
3. Add Ingredients in Strict Sequence: Add products one at a time in the standard W-A-L-E order. Seal the jar and shake gently for 5 to 10 seconds between additions.
4. Invert and Mix: After all components and adjuvants are added, secure the lid tightly and invert the jar 10 to 15 times to thoroughly blend all phases.
5. Initial Observation: Inspect the jar immediately for abnormal heat generation (exothermic chemical reaction), gas bubbling, immediate phase separation, or curdling.
6. Standing Period: Allow the sealed jar to stand undisturbed for 15 to 30 minutes.
7. Final Evaluation:
   • Compatible: If the mixture remains uniformly dispersed, or if minor settling occurs but redisperses smoothly with gentle jar inversion, the combination is physically compatible.
   • Incompatible: If flakes, sludge, curdling, oil separation, or mayonnaise-like gels form that refuse to redisperse, the mixture is physically incompatible and must not be mixed in the field.
   • Compatibility Agents: If physical incompatibility occurs, prepare a second test jar adding a commercial compatibility agent (typically 6 to 8 drops per pint, representing 1 to 2 pints per 100 gallons) to the carrier before adding pesticides. If this resolves separation, the mixture can be safely applied using the compatibility agent.

---

4. The Standard W-A-L-E & W-A-M-L-E Mixing Sequence

The order in which chemical formulations are introduced into the spray tank is non-negotiable. Dry products must be completely wetted and dispersed before oily liquids are added.

The Scientific Principle: Dry formulations (WP, WDG) require direct access to free water molecules to hydrate, wet, and disperse. If an Emulsifiable Concentrate (EC)—which contains petroleum solvents and oils—is added to the tank before dry powders, the oil coats the dry particles with a water-repellent film. This prevents the powder from wetting, transforming it into greasy, floating clumps that can never be dispersed.

Applicators follow the W-A-L-E sequence (or the expanded W-A-M-L-E sequence):

                                     THE W-A-M-L-E TANK MIXING SEQUENCE
                                     
       ┌─────────────────────────────────────────────────────────────────────────────┐
       │ 1. [ W ] WATER / CARRIER                                                    │
       │    Fill tank 1/4 to 1/2 full of clean water or carrier; start agitation     │
       └──────────────────────────────────────┬──────────────────────────────────────┘
                                              ▼
       ┌─────────────────────────────────────────────────────────────────────────────┐
       │ 2. [ A ] AGITATE & ADD DRY FORMULATIONS                                     │
       │    Add Wettable Powders (WP), WDG, Dry Flowables, and Water-Soluble Packets │
       │    Maintain continuous, vigorous agitation for 3-5 minutes until dispersed │
       └──────────────────────────────────────┬──────────────────────────────────────┘
                                              ▼
       ┌─────────────────────────────────────────────────────────────────────────────┐
       │ 3. [ M ] MICROENCAPSULATED & FLOWABLES                                      │
       │    Add Flowables (F/SC) and Microencapsulated (ME/CS) liquid suspensions    │
       └──────────────────────────────────────┬──────────────────────────────────────┘
                                              ▼
       ┌─────────────────────────────────────────────────────────────────────────────┐
       │ 4. [ L ] LIQUIDS & WATER-SOLUBLE CONCENTRATES                               │
       │    Add true Solutions (S) and Soluble Liquids (SL); mix thoroughly          │
       └──────────────────────────────────────┬──────────────────────────────────────┘
                                              ▼
       ┌─────────────────────────────────────────────────────────────────────────────┐
       │ 5. [ E ] EMULSIFIABLE CONCENTRATES                                          │
       │    Add EC formulations; agitation shears oil into milky emulsion            │
       └──────────────────────────────────────┬──────────────────────────────────────┘
                                              ▼
       ┌─────────────────────────────────────────────────────────────────────────────┐
       │ 6. REMAINING ADJUVANTS & TOP OFF                                            │
       │    Add Surfactants, Crop Oils, Drift Control Agents; fill to final volume   │
       └─────────────────────────────────────────────────────────────────────────────┘

Step-by-Step Sequence Breakdown

---

5. Container Stewardship: The Mandatory Triple-Rinse Protocol

Under federal FIFRA provisions, the Resource Conservation and Recovery Act (RCRA), and Rhode Island Department of Environmental Management (RIDEM) regulations, an unrinsed pesticide container is legally classified as hazardous waste.

Unrinsed containers retain toxic residues that endanger waste handlers, contaminate groundwater, and prevent plastic recycling. When properly triple-rinsed or pressure-rinsed immediately upon emptying, the container is reclassified as clean, non-hazardous solid waste suitable for recycling or sanitary landfill disposal.

The Standard Triple-Rinsing Protocol

Applicators must execute the triple-rinsing procedure immediately after emptying a liquid pesticide container, while residue remains fluid:

                                     THE MANDATORY TRIPLE-RINSE PROTOCOL
                                     
    ┌───────────────────────────┐         ┌───────────────────────────┐         ┌───────────────────────────┐
    │ Step 1: DRAIN 30 SECONDS  │         │ Step 2: ADD 1/4 WATER     │         │ Step 3: SHAKE 30 SECONDS  │
    │ Invert container over     │ ──────> │ Fill container 1/4 full   │ ──────> │ Replace cap tightly;      │
    │ tank; drain until drip    │         │ of clean carrier water    │         │ shake/rotate vigorously   │
    └───────────────────────────┘         └───────────────────────────┘         └─────────────┬─────────────┘
                                                                                              │
                                                                                              ▼
    ┌───────────────────────────┐         ┌───────────────────────────┐         ┌───────────────────────────┐
    │ Step 6: PUNCTURE BOTTOM   │         │ Step 5: REPEAT 2X MORE    │         │ Step 4: DRAIN 30 SECONDS  │
    │ Puncture base & sidewall; │ <────── │ Repeat steps 2, 3, & 4    │ <────── │ Pour rinsate into spray   │
    │ recycle (ACRC) or landfill│         │ for 3 complete rinses     │         │ tank; drain 30 seconds    │
    └───────────────────────────┘         └───────────────────────────┘         └───────────────────────────┘

1. Initial Drainage (30 Seconds): Empty the pesticide concentrate into the spray tank. When flow ceases, hold the container vertically inverted over the tank fill opening for at least 30 seconds until steady flow degrades to individual drips.
2. Add Water Carrier (1/4 Volume): Add clean water to the container until it is approximately one-fourth (1/4) full.
3. Seal and Agitate (30 Seconds): Replace the container closure/cap securely. Vigorously shake, rotate, and invert the container for at least 30 seconds, ensuring the rinsate washes all interior surfaces, corners, threads, and handle recesses.
4. Drain Rinsate into Tank (30 Seconds): Remove the cap and pour the rinsate directly into the spray tank. Allow the container to drain for at least 30 seconds into the tank.
5. Repeat Twice More: Repeat steps 2, 3, and 4 two additional times, completing a total of three separate rinse cycles.
6. Puncture and Render Unusable: Using a utility knife, punch, or spike, puncture the bottom and sidewall of the plastic container. Puncturing permanently prevents the container from being illicitly reused to store human drinking water, food, animal feed, or fuel.
7. Recycling and Disposal: Deliver clean, dry, punctured containers to an authorized Ag Container Recycling Council (ACRC) collection facility, or dispose of them in an approved municipal solid waste sanitary landfill.

Pressure Rinsing Alternative

Applicators may utilize an approved high-pressure rinsing nozzle attached to a pressurized water hose (minimum 40 PSI):

• Invert the container over the spray tank opening.
• Insert the sharp probe nozzle directly through the bottom of the container.
• Rinse for at least 30 seconds, allowing the pressurized rinsate to drain continuously into the spray tank.
• Pressure rinsing punctures the container during the cleaning process, satisfying both rinsing and destruction requirements simultaneously.