3.5 Tank Mixing Procedures, Compatibility & Jar Testing

3.5 Tank Mixing Procedures, Compatibility & Jar Testing

Tank mixing is the practice of combining two or more agricultural chemicals—such as multiple herbicides, an insecticide and a fungicide, or a pesticide with liquid fertilizers and adjuvants—in a single spray tank for simultaneous application in a single pass. When performed properly, tank mixing saves labor, fuel, and equipment hours while broadening pest control spectrums and delaying pesticide resistance.

However, tank mixing incompatible products can cause catastrophic results: thick, curdled sludge that ruins pumps and plugs plumbing; chemical deactivation that renders sprays ineffective; or severe foliar phytotoxicity that destroys treated crops. Understanding the precise science of chemical compatibility, jar testing, and the standard WALES addition sequence is an essential competency for all North Carolina certified applicators.

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1. Physical vs. Chemical Incompatibility

Incompatibility occurs when two or more substances combined in a spray tank fail to mix cleanly or react unfavorably.

+-----------------------------------------------------------------------------+
|                     PHYSICAL VS. CHEMICAL INCOMPATIBILITY                   |
|                                                                             |
|   +--------------------------------+   +--------------------------------+   |
|   |    PHYSICAL INCOMPATIBILITY    |   |    CHEMICAL INCOMPATIBILITY    |   |
|   |    (Visible Physical Failure)  |   |    (Invisible Molecular Rxn)   |   |
|   +--------------------------------+   +--------------------------------+   |
|   | - Curdling, clumping, flakes   |   | - Antagonism (zero pest control|   |
|   | - Layering / phase separation  |   | - Synergism / Phytotoxicity    |   |
|   | - Gels, sludge, paste at bottom|   | - Heat generation (exothermic) |   |
|   | - Clogged strainers & nozzles  |   | - No physical separation seen! |   |
|   +--------------------------------+   +--------------------------------+   |
+-----------------------------------------------------------------------------+

1. Physical Incompatibility

• Definition: Products cannot be physically combined or maintained in a uniform, stable dispersion.
• Visible Symptoms: Formation of oily slicks, curdled "cottage cheese" flakes, gelatinous sludge, layering into distinct phases, crystallization, or heavy sediment that settles instantly and cannot be re-suspended.
• Consequences: Immediate clogging of suction strainers, pump failure, plugged spray tips, and non-uniform application rates across the field.

2. Chemical Incompatibility

• Definition: A chemical reaction occurs between active or inert ingredients that alters their molecular structure and pesticidal properties, occurring without any visible physical separation or clumping.
• Antagonism: The mixture reduces or completely destroys the pest control efficacy of one or more components (e.g., mixing certain post-emergence grass herbicides with broadleaf phenoxy herbicides can suppress grass control).
• Synergism & Enhanced Phytotoxicity: The combination causes unexpected foliar toxicity, burning the crop even though individual products applied alone at labeled rates are safe.
• Exothermic Reaction: Chemical reactions may generate heat, noticeable as a warm jar or container during preliminary testing.

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2. The Step-by-Step Jar Compatibility Test Protocol

Never mix products in a 500-gallon spray tank without first verifying physical compatibility on a bench scale. A Jar Test uses proportional amounts of carrier water and pesticide products in a clean glass container to simulate the tank mix.

+-----------------------------------------------------------------------------+
|                        THE JAR COMPATIBILITY TEST                           |
|                                                                             |
|   1. Fill 1-quart glass jar 1/2 to 3/4 full with carrier water from source. |
|   2. Add products in WALES sequence, inverting 10 times after each product. |
|   3. Top off jar with remaining water to full quart volume.                 |
|   4. Observe immediately for heat generation (chemical reaction).           |
|   5. Let stand undisturbed for 15 to 30 minutes.                            |
|   6. Inspect: If smooth and uniform (or easily re-dispersed), COMPATIBLE.   |
|      If curdled, gelled, separated into layers, or gritty, INCOMPATIBLE!    |
+-----------------------------------------------------------------------------+

Required Equipment & Materials

• One clean, clear glass pint or quart jar (1 quart = 32 fluid ounces = 946 mL) with a tight-fitting lid.
• Accurate measuring syringes, pipettes, or graduated medicine droppers (marked in milliliters or fractional teaspoons).
• The exact water intended for the spray tank (from the actual well, pond, or municipal hydrant, at ambient field temperature).
• All planned pesticides, adjuvants, and liquid fertilizers.
• Chemical-resistant PPE (nitrile gloves, safety goggles, apron).

Proportional Mixing Math

To accurately simulate tank concentrations in a 1-quart (32 oz) jar, use standard volumetric conversion ratios based on your target carrier rate per acre (e.g., 25 gallons per acre):

Step-by-Step Execution

1. Fill Jar: Add 1 pint (16 fl oz, or 1/2 of final volume) of carrier water to the clean quart jar.
2. Sequential Addition: Add products one at a time following the WALES sequence. Cap the jar and invert 10 times after adding each individual product.
3. Top Off: Add remaining water to bring the total volume to 1 quart; cap and invert 10 final times.
4. Immediate Check: Feel the jar exterior. If noticeable heat is generated (an exothermic reaction), chemical incompatibility is occurring.
5. Stand & Observe (15 & 30 Minutes): Place the jar in a secure location out of direct sunlight. Inspect the mixture at 15 minutes and 30 minutes for:
   • Uniform cloudiness or dispersion (Compatible).
   • Curdling, clumping, flake formation, or oily film on top (Incompatible).
   • Severe layering or sludge formation on bottom.
6. The Re-Dispersion Test: If slight phase separation or settling occurs at 30 minutes, invert the jar gently 2 to 3 times. If the mixture readily re-disperses into a smooth, uniform liquid, the mix is physically compatible with continuous tank agitation. If flakes, curd, or gritty sludge remain stuck to the bottom, the mixture is incompatible and must not be used.

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3. The Standard WALES Mixing Sequence

The most frequent cause of physical tank mixing failure is adding products in the wrong sequence. When dry powders are added after oily solvents, the solvent coats the powder grains with a water-repellent oil film, forming greasy, insoluble lumps that permanently clog strainers. To prevent this, applicators must follow the industry-standard WALES (or W-A-L-E-S) protocol.

+-----------------------------------------------------------------------------+
|                        THE STANDARD WALES MIXING PROTOCOL                   |
|                                                                             |
|   [W]  WATER-SOLUBLE PACKETS & WETTABLE POWDERS (WP, WDG, DF)               |
|        * Add dry products first; pre-slurry if needed; allow WSP to dissolve|
|                                                                             |
|   [A]  AGITATION STARTED & TANK FILLED TO 1/2 - 3/4 VOLUME                  |
|        * Start mechanical/hydraulic agitation and maintain continuously     |
|                                                                             |
|   [L]  LIQUID FLOWABLES & SUSPENSIONS (F, SC, ME)                           |
|        * Add finely ground solids suspended in liquid carriers              |
|                                                                             |
|   [E]  EMULSIFIABLE CONCENTRATES (EC)                                       |
|        * Add petroleum solvent-based products; forms milky emulsion         |
|                                                                             |
|   [S]  SOLUBLE LIQUIDS, SOLUTIONS & ADJUVANTS (SL, SP, NIS, COC, AMS)       |
|        * Add true water solutions, then surfactants, oils, and fertilizers  |
+-----------------------------------------------------------------------------+

Detailed Breakdown of the WALES Steps

1. W — Water-Soluble Packets & Wettable Powders (WP, WDG, DF)

• Add clean carrier water until the tank is 1/3 to 1/2 full.
• If using Water-Soluble Packets (WSP), add them first and allow 2 to 3 minutes of mild agitation until the PVA packet shell completely dissolves in clean water.
• Next, add dry products: Wettable Powders (WP), Water-Dispersible Granules (WDG), and Dry Flowables (DF). If recommended on the label, pre-slurry powders in a bucket of water before pouring.
• Critical Rule: Dry formulations MUST hydrate and disperse in water BEFORE any petroleum solvents (ECs) are introduced into the tank.

2. A — Agitation Started & Tank Filled to 1/2 to 3/4

• Engage mechanical paddle or hydraulic venturi agitation.
• Continue filling the spray tank with carrier water to approximately 1/2 to 3/4 of final volume, ensuring vigorous, continuous fluid movement throughout the tank.

3. L — Liquid Flowables & Suspensions (F, SC, ME)

• Add liquid suspensions: Flowables (F), Suspension Concentrates (SC), and Microencapsulated (ME / CS) formulations.
• These finely suspended solids disperse readily into the water phase under active agitation.

4. E — Emulsifiable Concentrates (EC)

• Add solvent-based Emulsifiable Concentrates (EC).
• The emulsifiers in the EC interact with the water to create a stable, milky white oil-in-water emulsion. Because the dry powders (W) and flowables (L) are already fully hydrated, the petroleum solvents will not coat them.

5. S — Soluble Liquids, Solutions & Adjuvants (SL, SP, NIS, COC)

• Add Soluble Liquids (SL), Solutions (S), and Soluble Powders (SP).
• Finally, add remaining adjuvants (Non-Ionic Surfactants, Crop Oil Concentrates, Drift Reduction Agents, and liquid micronutrient fertilizers).
• Top off the spray tank with water to the final calibrated volume, maintaining agitation.

[!NOTE] Special Exception: Water Conditioners (AMS) & Defoamers When using Ammonium Sulfate (AMS) water conditioners to treat hard water, or silicone defoamers to suppress early foam, they should be added to the raw water BEFORE step W to condition the water and prevent foaming.

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4. Preventing Back-Siphoning & Equipment Protection

Contaminating a public water supply, agricultural wellhead, or surface stream during spray tank filling is a severe violation of the North Carolina Pesticide Law of 1971 and federal law.

+-----------------------------------------------------------------------------+
|                   BACK-SIPHONING PREVENTION: THE AIR GAP                    |
|                                                                             |
|            Water Supply Hose (Diameter = D)                                 |
|            +=============+                                                  |
|            |             |                                                  |
|            +====     ====+                                                  |
|                 |   |                                                       |
|                 |   |  <=== AIR GAP (Minimum 2 x Hose Diameter "D")         |
|                 |   |       (Unbroken physical air separation)              |
|                 v   v                                                       |
|       +-----------------------+                                             |
|       | Spray Tank Rim        |                                             |
|       | +-------------------+ |                                             |
|       | | Pesticide Liquid  | |   * NEVER submerge the fill hose below      |
|       | | Level             | |     the spray tank fluid level!             |
|       +-----------------------+                                             |
+-----------------------------------------------------------------------------+

Mandatory Anti-Backflow Standards

1. The Physical Air Gap: The applicator must maintain an unbroken, vertical physical air gap between the end of the water fill hose and the top rim of the spray tank. The air gap distance must be at least twice (2x) the inside diameter of the fill hose (e.g., a 2-inch fill hose requires a minimum 4-inch vertical air gap).
2. Backflow Prevention Devices: If an air gap cannot be maintained, an approved, certified anti-siphoning device or reduced-pressure backflow preventer must be installed on the water supply line.
3. Prohibited Practice: Never submerge the fill hose directly below the surface of the spray solution inside the tank. A sudden drop in water supply pressure will cause reverse atmospheric siphoning, sucking hundreds of gallons of concentrated pesticide directly into the drinking water well or municipal system.

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5. Carrier Water Temperature & Agitation Dynamics

• Cold Well Water Impact: In early spring, groundwater pumped from deep wells in North Carolina is often cold (40°F to 50°F). Frigid water drastically slows down the dissolution of PVA water-soluble packets and retards the hydration of dry flowables (WDG). Applicators must allow extra agitation time (5 to 10 minutes) or pre-slurry dry products in warmer water before adding them to cold tanks.
• Agitation Balance: While continuous agitation is essential for suspensions (WP, WDG, F), excessive agitation of tank mixes containing high concentrations of surfactants can generate violent foaming that overflows the tank manhole and cavitates the spray pump. Add a silicone defoamer before foaming begins.

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6. Comprehensive Tank Mixing Reference Summary