4.4 Adjuvants, Tank Mixing Compatibility & Jar Testing

Adjuvants, Tank Mixing Compatibility & Jar Testing

Maximizing pesticide efficacy while preventing costly application failures requires a deep understanding of spray tank chemistry, formulation interactions, and adjuvant technologies. Applying a pesticide with hard or alkaline water, mixing incompatible products, or adding formulations in the wrong physical sequence can cause chemical deactivation, severe crop phytotoxicity, or catastrophic tank curdling that clogs spray lines and ruins equipment.

Certified applicators in South Carolina must master adjuvant classifications, compatibility testing protocols (the Jar Test), and the universal WALES tank mixing sequence.

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1. What is an Adjuvant?

An adjuvant is any chemical substance added to a pesticide spray mixture (either included in the formulated product or added separately to the spray tank) to improve the physical properties of the spray liquid, enhance application performance, or increase pesticidal efficacy.

[!NOTE] Regulatory Distinction: Adjuvants themselves possess no standalone pesticidal activity and are not registered as pesticides under FIFRA Section 3. However, many pesticide labels contain mandatory instructions requiring the addition of specific adjuvants (e.g., "Always add a non-ionic surfactant at 0.25% v/v"), making the inclusion of that adjuvant a legally binding requirement under FIFRA Section 12(a)(2)(G).

+-----------------------------------------------------------------------------+
|                        MAJOR ADJUVANT CLASSIFICATIONS                       |
|                                                                             |
|   [UTILITY ADJUVANTS]                    [ACTIVATOR ADJUVANTS]              |
|   (Modify spray liquid properties)       (Directly enhance pest control)    |
|   - Buffers & Acidifiers                 - Surfactants (Wetters/Spreaders)  |
|   - Water Conditioners (AMS)             - Stickers & Extenders             |
|   - Drift Retardants / Thickeners        - Crop Oils & Penetrants (COC, MSO)|
|   - Anti-Foaming / De-foaming Agents     - Foliar Nutrients                 |
|   - Compatibility Agents                                                    |
+-----------------------------------------------------------------------------+

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2. Adjuvant Classes & Functional Roles

1. Surfactants (Surface Active Agents)

• Mechanism: Water molecules possess high surface tension, causing spray droplets to form spherical beads that roll off waxy leaf cuticles. Surfactants reduce the surface tension and contact angle of water droplets, allowing the spray to flatten, spread uniformly across the leaf surface, and cover a much larger surface area.
• Non-Ionic Surfactants (NIS): Possess no electrical charge; compatible with virtually all pesticides; the most widely prescribed surfactant on agricultural and turf labels.
• Organosilicone Surfactants: Advanced synthetic surfactants that produce super-spreading by reducing surface tension to ultra-low levels, enabling stomatal infiltration.

2. Stickers and Extenders

• Mechanism: Adhesives that physically bond pesticide residues to plant foliage, preventing the chemical from being washed off by rainfall, overhead irrigation, or degraded by ultraviolet (UV) sunlight.

3. Penetrants & Crop Oil Concentrates (COC / MSO)

• Crop Oil Concentrates (COC): Contain 80–85% petroleum-based oil plus 15–20% non-ionic surfactant. They dissolve and soften the epicuticular wax layer on mature weed leaves, dramatically increasing foliar penetration of systemic postemergence herbicides.
• Methylated Seed Oils (MSO): Chemically modified vegetable oils (e.g., methylated soybean oil) that provide even greater cuticular penetration than COCs, especially on drought-hardened weeds.

4. Buffers, Acidifiers & Water Conditioners

• Alkaline Hydrolysis Prevention: Many insecticides (organophosphates, carbamates, pyrethroids) and herbicides undergo rapid chemical decomposition called alkaline hydrolysis when mixed with alkaline water ($\text{pH} > 7.0$). In water with a pH of 8.5 to 9.0, certain chemicals lose 50% of their active potency within 30 to 60 minutes inside the spray tank.
• Buffers / Acidifiers: Lower and stabilize spray solution pH to an optimal slightly acidic range (typically $\text{pH } 5.0\text{--}6.5$), preventing active ingredient breakdown.
• Water Conditioners (Ammonium Sulfate / AMS): Neutralize hard water cations (such as $\text{Ca}^{2+}$, $\text{Mg}^{2+}$, and $\text{Fe}^{3+}$) that bind to and deactivate weak-acid herbicides like glyphosate and 2,4-D.

5. Drift Retardants / Deposition Aids

• Synthetic polymers that increase the viscosity (thickness) of the spray liquid. By increasing the Volume Median Diameter (VMD) of spray droplets, they minimize the formation of ultra-fine droplets ($< 105,\mu\text{m}$) most prone to airborne drift.

6. Anti-Foaming / De-Foaming Agents & Compatibility Agents

• Anti-Foaming Agents: Dimethicone or silicone-based emulsions that eliminate excessive foam caused by vigorous hydraulic agitation of surfactant-rich solutions.
• Compatibility Agents: Specialized surfactants that physically stabilize complex tank mixtures (e.g., liquid fertilizer mixed with EC formulations), preventing phase separation and curdling.

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3. Physical vs. Chemical Incompatibility

Tank mixing involves combining two or more pesticide formulations, or pesticides with liquid fertilizers, in a single spray tank. When products do not mix successfully, the result is tank incompatibility.

+-----------------------------------------------------------------------------+
|                        TANK MIXING INCOMPATIBILITY                          |
|                                                                             |
|   [PHYSICAL INCOMPATIBILITY]             [CHEMICAL INCOMPATIBILITY]         |
|   - Visible physical failure             - Non-visible chemical reaction    |
|   - Curdling, clumping, flakes           - Alkaline hydrolysis / breakdown  |
|   - Layer separation / stratification    - Antagonism (reduced pest kill)   |
|   - Dense sludge blocking strainers      - Synergistic phytotoxicity (burn) |
+-----------------------------------------------------------------------------+

1. Physical Incompatibility

• Symptoms: The mixture forms visible precipitate flakes, greasy curd-like masses, gelatinous sludge, or separates into distinct un-mixable layers (stratification).
• Consequences: Severe plugging of suction strainers, intake screens, and nozzle orifices; erratic application rates; inability to drain or clean the spray tank.
• Common Causes: Inadequate carrier volume, improper mixing order, attempting to mix oil-based formulations directly with liquid fertilizers without a compatibility agent, or extreme cold water temperatures.

2. Chemical Incompatibility

• Symptoms: Products mix cleanly with no visible physical changes, but a chemical reaction occurs between the active ingredients or carriers that alters their biological activity.
• Consequences:
  • Antagonism: The mixture significantly reduces or eliminates pesticidal effectiveness against the target pest (e.g., mixing postemergence grass herbicides with broadleaf phenoxy herbicides can suppress grass control).
  • Phytotoxicity: The chemical reaction creates phytotoxic compounds that cause severe foliar burn, chlorosis, or death of the desirable crop or turfgrass.
  • Alkaline Hydrolysis: Chemical deactivation caused by carrier pH.

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4. The Jar Test Procedure

Whenever an applicator intends to combine formulations or fertilizers that have not been previously tested or explicitly recommended on product labels, the applicator must perform a small-scale compatibility test: The Jar Test.

+-----------------------------------------------------------------------------+
|                         THE 6-STEP JAR TEST PROTOCOL                        |
|                                                                             |
|   [STEP 1] Fill a clean 1-quart glass jar with 1 pint of carrier (water or  |
|            liquid fertilizer) from the exact source to be used in spraying. |
|                                                                             |
|   [STEP 2] Add products in the exact WALES mixing sequence, using           |
|            proportional teaspoon/milliliter rates matching field dosages.   |
|                                                                             |
|   [STEP 3] Cap the jar tightly; invert gently 10 to 15 times to mix.        |
|                                                                             |
|   [STEP 4] Let the jar stand undisturbed for 15 to 30 minutes.              |
|                                                                             |
|   [STEP 5] Inspect for signs of physical incompatibility:                   |
|            - Clumping, curdling, gel formation, precipitate sludge          |
|            - Phase separation or oily slick that cannot be re-dispersed     |
|            - Excessive heat generation (exothermic chemical reaction)       |
|                                                                             |
|   [STEP 6] Evaluation: If mixture remains uniform or easily re-suspends     |
|            with gentle swirling, the combination is physically compatible.  |
+-----------------------------------------------------------------------------+

[!TIP] Compatibility Agent in Jar Testing: When testing complex mixtures (e.g., dry flowables + emulsifiable concentrates in liquid nitrogen fertilizer), prepare two identical jars: one without a compatibility agent and one with a proportional amount of compatibility agent (typically 1/4 to 1/2 teaspoon per pint). If Jar 1 separates but Jar 2 remains uniformly dispersed, the mix is physically viable with the addition of the compatibility agent.

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5. The WALES Tank Mixing Sequence

The most frequent cause of tank mixing failure and equipment clogging is adding formulations in the wrong sequence. Unless the product labels provide an alternative specific order, certified applicators must always follow the industry-standard WALES (or WALE) Protocol.

+-----------------------------------------------------------------------------+
|                      THE UNIVERSAL WALES MIXING PROTOCOL                    |
|                                                                             |
|   [W] ---> WATER / CARRIER FIRST: Fill tank 1/4 to 1/2 full; start agitation|
|                                                                             |
|   [A] ---> AGITATE & ADD CONDITIONERS: Buffers, AMS, defoamers              |
|                                                                             |
|   [W] ---> WETTABLE / DRY PRODUCTS: WP, WDG, DF, and WSP packets            |
|                                                                             |
|   [A] ---> AGITATE THOROUGHLY: Allow 3-5 minutes for dry products to disperse|
|                                                                             |
|   [L] ---> LIQUID FLOWABLES: Flowables (F), Suspension Concentrates (SC)    |
|                                                                             |
|   [E] ---> EMULSIFIABLE CONCENTRATES: EC formulations & Microencapsulated(ME)|
|                                                                             |
|   [S] ---> SURFACTANTS & SOLUTIONS: Soluble liquids (S/SL), NIS, crop oils, |
|            then finish filling tank with water to final volume              |
+-----------------------------------------------------------------------------+

Step-by-Step WALES Sequence Explained:

1. W — Water / Carrier:
   • Fill the spray tank 1/4 to 1/2 full with clean carrier (water or liquid fertilizer).
   • Engage mechanical or hydraulic agitation immediately before introducing any chemical products. Agitation must run continuously throughout mixing, transport, and spraying.
2. A — Agitate & Add Water Conditioners / Buffers:
   • Add water conditioners (e.g., ammonium sulfate / AMS), pH buffers, acidifiers, and anti-foaming agents. Allow them to circulate and condition the water.
3. W — Wettable Powders & Dry Dispersibles:
   • Add dry formulations: Water-Soluble Packaging (WSP), Wettable Powders (WP), Water-Dispersible Granules (WDG), and Dry Flowables (DF).
   • Critical Rule: Allow dry products to completely dissolve and disperse throughout the water before introducing any liquid or oil-based formulations. If oil products (ECs) are added before dry powders disperse, the oil coats the powder granules, forming impenetrable clumps that cannot disperse.
4. A — Agitate Thoroughly:
   • Maintain vigorous agitation for 3 to 5 minutes to verify complete suspension of all dry materials.
5. L — Liquid Flowables & Suspensions:
   • Add liquid flowables (F), suspension concentrates (SC), and capsule suspensions (CS).
6. E — Emulsifiable Concentrates:
   • Add Emulsifiable Concentrates (EC) and microencapsulated (ME) formulations. As the EC enters the water, it immediately blossoms into a milky emulsion.
7. S — Surfactants, Soluble Liquids & Finish:
   • Add water-soluble liquids (S / SL), non-ionic surfactants (NIS), crop oil concentrates (COC), methylated seed oils (MSO), and drift control retardants.
   • Finally, add the remaining carrier liquid to bring the tank to its final targeted spray volume, maintaining continuous agitation until the application is complete.