4.3 Formulations, Adjuvants & Tank Mixing Compatibility

4.3 Formulations, Adjuvants & Tank Mixing Compatibility

Quick Summary: Pure pesticide active ingredients cannot be applied directly in the field; they must be formulated with inert carriers, solvents, and surface-active agents into usable products. Formulations are divided into liquids (EC, S, F, ME, ULV) and dry materials (WP, SP, DF/WDG, G, P, D, B), each with distinct tradeoffs in agitation, nozzle wear, and dermal versus inhalation hazard. Applicators optimize tank mixes using activator and utility adjuvants and prevent costly tank curdling through the W-A-L-E-S Jar Test protocol.

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Pesticide Formulations: Foundations and Operational Trade-Offs

The technical grade active ingredient (AI) manufactured in chemical synthesis plants is typically an oily, insoluble resin, a crystalline rock, or an unstable chemical powder. In this concentrated state, it cannot be evenly distributed over acres of crops or turf at typical dosages (often measured in ounces per acre).

A formulation is the final commercial product prepared by combining the active ingredient with inert ingredients (carriers, organic solvents, wetting agents, emulsifiers, stabilizing agents, and anti-caking compounds). When selecting a formulation, certified applicators must evaluate five operational tradeoffs:

1. Applicator Exposure & Safety: Inhalation hazard of fine dry powders versus rapid dermal absorption of liquid petroleum solvents.
2. Agitation Demands: True solutions requiring no agitation versus suspensions settling rapidly without constant mechanical agitation.
3. Sprayer Equipment Wear: Abrasive powders rapidly eroding pump impellers and nozzle orifices versus petroleum solvents softening rubber hoses and gaskets.
4. Phytotoxicity: The risk of chemical burning on tender foliage, which is significantly higher with solvent-based concentrates applied in hot weather.
5. Target Drift & Non-Target Hazards: Fine dusts drifting on the wind versus encapsulated beads poisoning honeybee hives.

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Liquid Formulations: Chemistry, Pros, and Cons

                      COMMON LIQUID FORMULATIONS
   [EC] Emulsifiable Concentrate  --> Milky emulsion; high solvent/dermal risk
   [S]  Solution                   --> Clear liquid; true solution; no agitation
   [F]  Flowable / Liquid          --> Insoluble solid pre-suspended; abrasive
   [ME] Microencapsulated          --> Plastic polymer beads; acute bee toxicity
   [ULV] Ultra-Low Volume          --> High concentrate; aerial/vector control

1. Emulsifiable Concentrates (EC or E)

• Chemistry: Contains an oil-soluble active ingredient dissolved in one or more petroleum-based organic solvents, combined with an emulsifying agent.
• Mixing Characteristics: When mixed into water in a spray tank, the emulsifier forces the petroleum droplets to disperse throughout the water, forming a characteristic milky white emulsion. Requires mild to moderate tank agitation.
• Advantages: Easy to measure and pour; high active ingredient concentration reduces shipping volume; leaves little visible chalky residue on foliage or ornamental plants; relatively non-abrasive to nozzles and pump impellers.
• Disadvantages & Hazards:
  • High Dermal Absorption: Petroleum solvents readily dissolve human skin oils, accelerating rapid transdermal chemical absorption into the applicator's bloodstream.
  • Phytotoxicity Risk: High solvent concentration can burn tender plant foliage, particularly when temperatures exceed $85^\circ\text{F}$.
  • Equipment Degradation: Petroleum solvents cause swelling, softening, and deterioration of neoprene rubber hoses, pump diaphragms, and tank gaskets.
  • Flammability: Many EC products are combustible; must be stored away from open flames and heat.

2. Solutions (S or SL)

• Chemistry: The active ingredient (whether liquid or dry) dissolves completely in a liquid carrier (typically water or an alcohol-based solvent), creating a true molecular solution.
• Mixing Characteristics: Forms a completely clear, transparent liquid when poured into the spray tank. Once thoroughly mixed, it will never settle out or separate, requiring zero tank agitation.
• Advantages: Non-abrasive to equipment; does not clog screens, strainers, or nozzles; leaves no visible deposit; low dermal absorption risk compared to petroleum solvents.
• Disadvantages: Limited availability because few active chemical compounds are naturally water-soluble.

3. Flowables / Suspension Concentrates (F, L, or SC)

• Chemistry: An insoluble, solid active ingredient is micro-milled into an ultra-fine powder and suspended in a liquid carrier with dispersing agents.
• Mixing Characteristics: Viscous, thick liquid (consistency of latex paint or a milkshake). When added to water, it forms a mechanical suspension.
• Advantages: Eliminates the inhalation and dust hazard of dry powders during measuring and tank loading; easy to handle and pour.
• Disadvantages & Hazards: Requires constant, moderate tank agitation; if agitation ceases, solids settle into a dense cake at the bottom of the spray tank that is difficult to resuspend; moderately abrasive to spray nozzles and pump impellers.

4. Microencapsulated Formulations (ME or CS)

• Chemistry: Particles of liquid or dry active ingredient are encased in microscopic plastic or polymer capsules, which are suspended in a liquid carrier.
• Mixing Characteristics: Mixes with water to form a liquid suspension; requires moderate tank agitation.
• Advantages: The polymer capsule provides controlled, slow-release residual activity, extending pest control over weeks; reduces handler acute toxicity because the active chemical is physically encased; reduces chemical volatilization and odor.
• Critical Environmental Hazard: Honeybee Toxicity. Microcapsules are roughly the size of pollen grains. Foraging bees can pick them up with pollen and carry them back to the hive, where stored contaminated pollen can poison brood and adult bees long after the application. For this reason, many microencapsulated insecticide labels carry strict bee-protection statements.

5. Ultra-Low Volume (ULV) & Aerosols (A)

• ULV Formulations: Contain extremely high concentrations of active ingredient (often 80% to 100%) designed to be applied at total spray volumes of 0.5 gallon per acre or less. Utilized primarily in public health mosquito vector management and forestry spraying. Requires specialized rotary atomizers or mist blowers; presents high drift hazards.
• Aerosols (A): Low percentage of active ingredient dissolved in volatile solvents inside pressurized metal cans with gas propellants, or applied through thermal fog generators for structural and greenhouse applications.

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Dry Formulations: Handling, Performance, and Worker Exposure

                      COMMON DRY FORMULATIONS
   [WP]  Wettable Powder      --> Insoluble dust; constant agitation; abrasive
   [SP]  Soluble Powder       --> Dissolves to true solution; no agitation
   [WDG] Water-Dispersible    --> Granules disperse in water; low dust hazard
   [G/P] Granules & Pellets   --> Applied dry directly to soil; bird hazard
   [D/B] Dusts & Baits        --> D = high drift; B = attractant matrix

1. Wettable Powders (WP or W)

• Chemistry: Dry, finely ground, insoluble active ingredient blended with an inert mineral carrier (such as talc or bentonite clay) and wetting/dispersing agents.
• Mixing Characteristics: Does not dissolve in water. It forms a mechanical suspension of microscopic mineral flakes suspended in water.
• Operational Demands: Requires continuous, vigorous mechanical or hydraulic tank agitation. If the sprayer's bypass agitator fails, particles rapidly settle to the bottom of the tank, causing wildly uneven application rates.
• Abrasiveness: Highly abrasive to application equipment. WP slurries act like liquid sandpaper, rapidly enlarging soft brass and aluminum nozzle orifices, requiring frequent nozzle recalibration and replacement.
• Handler Hazard: Severe inhalation hazard to mixers and loaders when pouring the dry, fine powder into the tank. Handlers must wear NIOSH-approved particulate respirators.

2. Soluble Powders (SP or WSP)

• Chemistry: Dry, finely ground active ingredient that dissolves completely and irreversibly in water to form a true solution.
• Characteristics: Requires initial stirring to dissolve, but once dissolved in the tank, no further agitation is required. Non-abrasive to nozzles and equipment.
• Packaging: Often packaged in pre-measured Water-Soluble Packets (WSP). The applicator drops the sealed PVA packet directly into the spray tank, where the packet dissolves in minutes, completely eliminating the dry inhalation hazard.

3. Dry Flowables (DF) / Water-Dispersible Granules (WDG)

• Chemistry: Active ingredient formulated into small, dry, dust-free granules that disintegrate rapidly into a suspension upon contact with water.
• Operational Profile: Functionally identical to a wettable powder in the spray tank (requires continuous tank agitation and exhibits abrasiveness to nozzles), but eliminates the fine airborne dust and inhalation hazard during weighing, measuring, and tank loading.

4. Granules (G) and Pellets (P)

• Chemistry: Dry, coarse particles made of absorbent inert materials (calcined clay, crushed walnut shells, ground corn cobs) impregnated with low concentrations of active ingredient (typically 2% to 15% AI). Pellets are uniform cylindrical extruded matrices.
• Application: Applied dry directly to soil or turf using rotary spreaders, drop spreaders, or specialized aerial equipment without water.
• Advantages: Low drift potential; minimal handler inhalation hazard; simple mechanical spreaders; penetrates dense crop or turf canopies to reach the soil surface.
• Hazards & Limitations: Requires soil moisture or irrigation to activate; non-target wildlife hazard—ground-feeding songbirds, quail, and doves often ingest granular pesticides mistaking them for food seeds or gizzard grit.

5. Dusts (D) and Baits (B)

• Dusts (D): Low percentage of active ingredient (1% to 10%) blended with extremely fine talc, pyrophyllite, or chalk. Applied completely dry. Highly susceptible to wind drift; primarily restricted to indoor crack-and-crevice structural applications or seed treatments.
• Baits (B): Active ingredient mixed with an edible food attractant matrix (such as grain meal, peanut butter, sugar, or soybean oil) at low concentrations (typically < 5%). Pests are drawn to the bait, ingest the chemical, and die. Highly targeted; minimizes broad-spectrum environmental contamination.

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Comprehensive Pesticide Formulation Comparison Matrix

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Adjuvants: Chemistry, Classifications, and Functional Roles

An adjuvant is any chemical substance added to a pesticide spray tank (or incorporated into a formulation by the manufacturer) to modify the physical properties of the spray solution, enhance application performance, or increase biological target efficacy.

                             ADJUVANT CLASSES
      ACTIVATOR ADJUVANTS                   UTILITY ADJUVANTS
   (Enhance Biological Activity)         (Modify Physical Solution)
   - Surfactants / Wetting Agents        - Buffers & Acidifiers
   - Spreaders & Stickers                - Compatibility Agents
   - Penetrants                          - Drift Control Agents
   - Crop Oil Concentrates (COC/MSO)     - Antifoaming Agents (Defoamers)

1. Activator Adjuvants

Activator adjuvants directly improve the biological uptake, coverage, and efficacy of the active ingredient:

• Surfactants (Surface Active Agents) & Wetting Agents: Pure water has high surface tension (approximately 72 dynes/cm), causing spray droplets to form spherical beads that bounce or roll off waxy plant leaves. Surfactants possess both hydrophilic (water-loving) and lipophilic (oil-loving) molecular poles. They reduce water surface tension down to approximately 30 dynes/cm, allowing spray droplets to flatten out and spread into a continuous liquid film across the leaf surface.
• Spreaders: Increase the total surface area covered by each spray droplet on hard-to-wet, hairy, or glaucous (waxy) foliage.
• Stickers: Substances that increase the adhesive properties of spray droplets, binding the chemical film to the leaf surface to resist wash-off by rain, heavy morning dew, or wind abrasion.
• Penetrants: Assist systemic herbicides and fungicides in penetrating the thick, waxy cuticle layer of target plant leaves and moving into cellular tissues.
• Crop Oil Concentrates (COC) and Methylated Seed Oils (MSO): Blends containing 80% to 85% phytobland petroleum or esterified vegetable oil and 15% to 20% surfactant. They soften and partially dissolve the crystalline epicuticular wax on mature weeds, dramatically boosting herbicide penetration under hot, drought-stressed summer conditions. Caution: Applying COCs or MSOs in temperatures exceeding $85^\circ\text{F}$ substantially increases crop phytotoxicity and leaf burn.

2. Utility Adjuvants (Spray Modifiers)

Utility adjuvants do not directly increase pesticidal activity; instead, they modify the physical working characteristics of the spray solution inside the tank and during droplet flight:

• Buffers and Acidifiers: Stabilize spray tank pH. Many organophosphate and carbamate insecticides undergo alkaline hydrolysis—a chemical reaction where water with a pH above 7.0 rapidly splits the pesticide molecule, destroying its pest-killing power within hours. Acidifiers lower the solution pH to the optimal range of 5.5 to 6.5, preserving chemical stability.
• Compatibility Agents: Specialized surfactants that physically blend products that would otherwise separate, curdle, or sludge in the tank—especially when mixing liquid pesticides with liquid commercial fertilizers (such as 28-0-0 or 32-0-0 UAN solutions).
• Drift Control Agents (Thickeners / Deposition Aids): High-molecular-weight polyacrylamide polymers that increase the viscosity (thickness) of the spray liquid. This significantly decreases the percentage of ultra-fine, "driftable" droplets (those smaller than 105 to 150 microns in diameter) produced at the nozzle orifice, ensuring that droplets deposit directly on target foliage.
• Antifoaming Agents (Defoamers): Silicone emulsions that break and suppress surface foam caused by vigorous tank agitation and high-surfactant loads, preventing messy tank overflows.

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Tank Mixing Compatibility: Physical vs. Chemical Incompatibility

Combining two or more pesticides (or a pesticide with liquid fertilizer) in a single spray tank saves time, labor, and fuel. However, combining products without verifying compatibility can lead to catastrophic application failures.

Physical Incompatibility

• Definition: An adverse physical reaction between mixed products resulting in the inability of the materials to stay homogeneously dispersed in water.
• Visual Symptoms: The mixture curdles into a cottage-cheese-like mass, separates into oil-water layers, forms greasy globules, precipitates into crystalline flakes, or forms a thick, sticky sludge at the bottom of the tank.
• Operational Consequences: Severe clogging of pump strainers, in-line 50-mesh screens, and nozzle tips; ruined spray solutions; hours of downtime dismantling and pressure-washing equipment; expensive chemical disposal problems.

Chemical Incompatibility

• Definition: A chemical reaction between mixed ingredients that chemically alters the active molecules, forming entirely new compounds.
• Operational Consequences: Can cause antagonism (complete chemical inactivation of one or both active ingredients, resulting in zero pest control) or severe phytotoxicity (creating unexpected caustic byproducts that cause catastrophic defoliation or crop destruction).
• Critical Risk: Chemical incompatibility often produces no visible clues—the spray solution may look completely clear and normal in the tank, yet the chemical activity is completely destroyed or made violently crop-toxic.

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The Jar Test Protocol & The W-A-L-E-S Mixing Sequence

To prevent tank-mixing disasters, applicators must conduct a standardized Jar Test prior to mixing full-scale commercial loads.

                     THE W-A-L-E-S TANK MIXING SEQUENCE

   [W]  WETTABLE POWDERS & DRY DISPERSIBLES (WP, WDG, DF, dry fertilizers)
         |  --> Add to tank 1/2 full of water; agitate until dispersed
   [A]  AGITATE THOROUGHLY & ADD FLOWABLES (F, L, SC)
         |  --> Maintain continuous agitation; let liquids disperse
   [L]  LIQUID SOLUTIONS & SOLUBLE LIQUIDS (S, SL)
         |  --> Dissolve completely in carrier
   [E]  EMULSIFIABLE CONCENTRATES (EC)
         |  --> Form milky emulsion; allow full dispersion
   [S]  SURFACTANTS & ADJUVANTS (NIS, COC, MSO, Drift Retardants)
         |  --> Add last to prevent excessive tank foaming

Step-by-Step 1-Quart Jar Test Procedure

1. Use a clean, transparent one-quart glass jar.
2. Add water or carrier from the exact source to be used in the field (water hardness and mineral content drastically affect compatibility).
3. Fill the jar half full of carrier (approximately one pint, matching a planned 20-gallon-per-acre spray volume).
4. Calculate proportional amounts of each product matching the planned field application rate (typically one teaspoon per quart per pound or pint per acre).
5. Add the ingredients in the strict W-A-L-E-S sequence (described below), gently inverting the jar between each addition to simulate tank agitation.
6. Top off the jar with carrier to full volume, cap securely, and invert 10 times.
7. Allow the capped jar to stand undisturbed for 10 to 15 minutes.
8. Evaluation: Inspect the jar carefully:
   • Compatible: A uniform, smooth liquid suspension or emulsion without separation, flakes, curdling, or layering.
   • Incompatible: Separation into distinct layers, precipitation of grit, sludging at the bottom, or an exothermic generation of heat (indicating a chemical reaction). If heat generates or sludge forms, do NOT mix these chemicals in the spray rig!

The Standard W-A-L-E-S Tank Addition Sequence

When filling the full commercial spray tank, applicators must follow this universal sequence to guarantee proper dispersion:

1. Fill Tank: Fill the spray tank $1/2$ to $3/4$ full of clean water or carrier and engage the mechanical or hydraulic agitator.
2. W - Wettable Powders & Dry Dispersibles: Add dry formulations (WP, WDG, DF, SP). Allow dry materials to disperse completely in the water before adding any liquids.
3. A - Agitate & Add Liquid Flowables: Maintain continuous agitation and add liquid suspensions (F, L, SC). Flowables must disperse in water before encountering oil-based concentrates.
4. L - Liquid Solutions: Add true water-soluble solutions (S, SL).
5. E - Emulsifiable Concentrates: Add petroleum-based emulsifiable concentrates (EC). The petroleum emulsifier needs a well-dispersed water matrix to establish its milky emulsion.
6. S - Surfactants & Adjuvants: Add non-ionic surfactants, crop oil concentrates, and drift retardants last. Adding surfactants early causes severe foaming that interferes with dry chemical wetting and overflows the tank fill well.
7. Top Off: Fill the tank to its final volume with continuous agitation.

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💡 Practical Scenario: Diagnosing Incompatibility & Selecting Adjuvants

Scenario: A commercial agricultural applicator in Central Alabama prepares a 500-gallon tank mix combining a dry-flowable herbicide (WDG), an organophosphate insecticide (EC), a liquid nitrogen fertilizer (28% UAN), and a non-ionic surfactant. The applicator dumps all products simultaneously into an empty spray tank before adding water.

• The Failure: Within three minutes, the tank turns into a thick, curdled sludge that plugs the 50-mesh suction strainer and stops the centrifugal pump. The applicator failed to follow the W-A-L-E-S protocol, failed to conduct a Jar Test, and added oil-based concentrates and fertilizer before hydrating the dry granules in water.
• The Correct Procedure:
  1. Conduct a 1-quart Jar Test using proportionate amounts of the 28% UAN carrier and products, testing whether a compatibility agent is required.
  2. In the spray rig, fill the tank half full with carrier and run the agitator.
  3. Pre-slurry the WDG granules in a 5-gallon bucket of water and add them first (W).
  4. Ensure thorough agitation (A).
  5. Add any soluble liquids (L).
  6. Add the organophosphate EC product (E).
  7. Add the non-ionic surfactant last (S), then top off to 500 gallons.

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💡 Exam Tips for Success

• Microencapsulated Bee Hazard: ME capsules are pollen-sized, so bees can carry them back to the hive with pollen.
• Wettable Powders Wear Equipment: WPs act like liquid sandpaper, rapidly enlarging brass nozzles and requiring vigorous continuous agitation.
• Alkaline Hydrolysis: Organophosphates degrade in alkaline water (pH > 7.0); applicators use buffers and acidifiers to maintain pH between 5.5 and 6.5.
• W-A-L-E-S Mixing Order: Memorize the sequence: W (Wettable powders/dry) $\rightarrow$ A (Agitate/flowables) $\rightarrow$ L (Liquids/solutions) $\rightarrow$ E (Emulsifiable concentrates) $\rightarrow$ S (Surfactants/adjuvants last).