7.1 Pesticide Formulations, Adjuvants & Tank-Mixing Compatibility (WALES & Jar Tests)

7.1 Pesticide Formulations, Adjuvants & Tank-Mixing Compatibility

Pesticide active ingredients (a.i.) in their pure, technical-grade state are rarely suitable for direct field application. Pure active ingredients may be insoluble in water, chemically unstable under ambient ultraviolet light, extremely toxic in concentrated form, or physically impossible to distribute evenly across thousands of square feet of target crop or turf. To transform raw chemical compounds into safe, effective, and marketable pest management tools, chemical manufacturers combine active ingredients with inert carriers, solvents, and surface-active agents to create a pesticide formulation.

For certified applicators in Utah, selecting the appropriate formulation and understanding how different products interact in a spray tank is foundational to achieving biological control while preventing crop phytotoxicity, equipment breakdown, and off-target contamination.

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1. Formulation Chemistry: Active vs. Inert Ingredients

Every commercial pesticide product consists of two distinct components defined under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA):

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|                        ANATOMY OF A PESTICIDE FORMULATION                   |
|                                                                             |
|   +-----------------------------------+---------------------------------+   |
|   |      ACTIVE INGREDIENT (a.i.)     |        INERT INGREDIENTS        |   |
|   +-----------------------------------+---------------------------------+   |
|   | - Biologically active chemical    | - Solvents, carriers, diluents  |   |
|   | - Toxicologically controls pest   | - Wetting agents & emulsifiers  |   |
|   | - Explicitly named on label       | - Preservatives & stabilizers   |   |
|   | - Percentage by weight or volume  | - Anti-caking / anti-foam agents|   |
|   +-----------------------------------+---------------------------------+   |
+-----------------------------------------------------------------------------+

• Active Ingredient (a.i.): The specific chemical or biological agent that prevents, destroys, repels, or mitigates the target pest, or functions as a plant regulator, defoliant, or desiccant. The chemical name and percentage of each active ingredient must be explicitly stated on the front panel of the pesticide label.
• Inert Ingredients: Any substance contained in the pesticide product that is not an active ingredient. Inert substances do not directly control pests, but they serve critical physical functions: dissolving active molecules, enhancing droplet spreading, preventing chemical degradation during storage, or reducing user toxicity. While termed "inert," these ingredients are not necessarily non-toxic; petroleum solvents in liquid formulations can cause severe skin irritation, ocular burns, or plant tissue phytotoxicity.

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2. Liquid Pesticide Formulations

Liquid formulations are packaged as liquids, concentrates, or liquefied gases. When added to water or oil carriers in the spray tank, they behave differently depending on their solubility and physical state.

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|                       LIQUID FORMULATION COMPARISON                         |
|                                                                             |
|   FORMULATION     CARRIER BEHAVIOR     AGITATION NEEDED   NOZZLE ABRASION   |
|   -----------     ----------------     ----------------   ---------------   |
|   EC (Emulsion)   Milky Emulsion       Moderate           Low               |
|   S / SL (Sol.)   True Solution        Initial Only       Negligible        |
|   F / SC (Susp.)  Suspended Solids     Continuous         Moderate-High     |
|   ME (Capsule)    Suspended Capsules   Moderate           Low               |
|   ULV (Ultra-Low) Undiluted Liquid     None               Low               |
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1. Emulsifiable Concentrates (EC or E)

An Emulsifiable Concentrate consists of a liquid active ingredient dissolved in one or more petroleum-based organic solvents, combined with an emulsifier. An emulsifier is a detergent-like chemical that allows oil droplets to remain suspended in water without separating into distinct layers.

• Appearance in Tank: When an EC is poured into water, the emulsifiers disperse the solvent droplets, forming a milky-white liquid emulsion.
• Advantages: Easy to measure and pour; high active ingredient concentration reduces shipping costs; requires only mild agitation once mixed; non-abrasive to sprayer pump impellers and nozzle orifices; leaves little visible residue on ornamental plants or produce.
• Disadvantages & Hazards:
  • Dermal Absorption: Organic petroleum solvents penetrate human skin rapidly, carrying the dissolved active ingredient directly into the bloodstream.
  • Phytotoxicity: Solvents can burn tender plant foliage, especially during hot weather (>85°F) or under bright sunlight.
  • Equipment Deterioration: Petroleum solvents deteriorate rubber and synthetic hoses, pump gaskets, O-rings, and diaphragm seals.
  • Flammability: Solvent vapors present a fire hazard during storage and mixing.

2. Solutions (S) and Soluble Liquids (SL)

Solutions contain water-soluble active ingredients dissolved in a liquid carrier (typically water). When mixed with water in the spray tank, they form a true chemical solution that is completely transparent and homogeneous.

• Characteristics: The active ingredient molecules disperse completely at the molecular level; once mixed, they will never settle out or separate, even if agitation is shut off for days. They are non-abrasive and do not clog strainers or nozzle tips.

3. Flowables (F) / Suspension Concentrates (SC) / Liquid Flowables (L)

Flowables are designed for active ingredients that are solid compounds insoluble in both water and organic solvents. The technical material is finely ground into microscopic solid particles and suspended in a thick liquid carrier with dispersing agents.

• Characteristics: When added to water, they form a liquid suspension. Flowables require continuous tank agitation to prevent solid particles from settling to the bottom. In long-term storage, flowables can settle into a dense, cement-like cake at the bottom of the container; containers must be vigorously shaken prior to measuring. Solid particulates are moderately abrasive to pump components and nozzle tips.

4. Microencapsulated Formulations (ME or CS)

In a Microencapsulated formulation, liquid or solid active ingredient particles are enclosed inside microscopic plastic or polymer capsules, suspended in a liquid carrier.

• Mechanism & Benefits: Following application, the polymer capsule slowly breaks down or allows the active ingredient to diffuse through its wall over days or weeks, providing extended residual pest control, lower volatility, reduced user dermal toxicity, and reduced crop phytotoxicity.
• CRITICAL EXAM HAZARD (Honey Bee Toxicity): Microcapsules are manufactured to a size range (15 to 50 microns) that mimics natural pollen grains. Microcapsules readily pick up electrostatic charges, causing them to adhere to the hairs of foraging worker honey bees. Bees carry the toxic capsules back to the hive and pack them into brood comb cells with pollen, resulting in catastrophic poisoning of larvae, nurse bees, and the entire colony.

5. Ultra-Low Volume (ULV)

ULV concentrates contain extremely high concentrations of active ingredient (often approaching 100%) and are applied undiluted or in very low carrier volumes (less than 0.5 gallons per acre). Used primarily in broad-area mosquito abatement and rangeland grasshopper control. ULV produces fine aerosol droplets that present severe inhalation and drift hazards.

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2. Dry and Solid Pesticide Formulations

Dry formulations are packaged in bags, cartons, or drums as powders, granules, pellets, or dusts.

1. Wettable Powders (WP or W)

Wettable powders are dry, finely milled particles consisting of an insoluble active ingredient blended with a mineral clay carrier and wetting/dispersing agents.

• Behavior in Water: WPs do not dissolve. When added to water, they form a mechanical suspension of solid particles.
• Agitation: Requires constant, vigorous mechanical agitation. If agitation stops, the powder rapidly precipitates to the bottom of the spray tank, creating a dense sludge that clogs suction strainers and causes uneven application.
• Abrasiveness: Highly abrasive to sprayer pumps (especially roller pumps) and nozzle orifices (rapidly widening brass and plastic tips).
• Inhalation Risk: Measuring and dumping dry wettable powders creates airborne dust clouds, presenting a severe acute inhalation hazard for the handler.

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

WDGs and DFs are dry formulations where the active ingredient and clay carrier are formed into small, dust-free granules or beads.

• Operational Advantage: When added to water, the granules break apart and disperse into a suspension identical to a wettable powder. However, because they are granular rather than fine powder, they generate virtually no airborne dust, dramatically reducing applicator inhalation hazards during measuring and tank loading.

3. Soluble Powders (SP) and Water-Soluble Packets (WSP)

• Soluble Powders (SP): Finely ground dry active ingredients that dissolve completely in water, forming a true, clear solution. Once dissolved, no ongoing agitation is required.
• Water-Soluble Packets (WSP): Pre-measured quantities of WP or SP enclosed in water-soluble polyvinyl alcohol (PVA) film bags. The applicator drops the sealed packet directly into the spray tank without opening it. The PVA film dissolves rapidly, completely eliminating handler exposure to chemical dust during mixing.

4. Granules (G), Pellets (P), Dusts (D), and Baits (B)

• Granules (G) & Pellets (P): Coarse, dry particles with active ingredients bound to inert carriers like clay, ground corn cobs, or walnut shells. Applied dry directly to soil or foliage using drop or broadcast rotary spreaders. Minimizes drift hazards; however, granules left on soil surfaces can be consumed by foraging birds (e.g., pheasants, songbirds) mistaking them for seeds or grit.
• Dusts (D): Low-concentration active ingredients (1% to 10%) bound to ultra-fine talc or chalk carriers. Used primarily in structural crack-and-crevice pest control and seed treatments. Highly prone to drift and easily inhaled.
• Baits (B): Active ingredients blended with an edible food attractant (e.g., grain, sugar, meat proteins) at low concentrations. Pests consume the bait and die. Must be placed in tamper-resistant bait stations to prevent poisoning of pets, livestock, and non-target wildlife.

5. Fumigants

Fumigants are non-selective pesticides that form poisonous gases when applied. They penetrate porous materials, grain bins, and soil matrices to kill insects, nematodes, fungi, and rodents. Fumigants represent the highest acute inhalation toxicity category and require specialized closed-system application rigs, monitoring equipment, and canister respirators or self-contained breathing apparatus (SCBA).

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3. Spray Adjuvants & Surfactants

An adjuvant is any chemical substance added to a pesticide spray mixture to modify the physical characteristics of the liquid, enhance biological activity, or correct water quality deficiencies. Adjuvants do not have pesticidal properties of their own.

+-----------------------------------------------------------------------------+
|                        MAJOR CATEGORIES OF ADJUVANTS                        |
|                                                                             |
|   1. ACTIVATOR ADJUVANTS (Enhance Biological Efficacy)                      |
|      - Non-Ionic Surfactants (NIS): Reduces surface tension, aids wetting.  |
|      - Crop Oil Concentrates (COC): Penetrates heavy leaf cuticles.         |
|      - Spreaders & Stickers: Increases leaf coverage & rainfastness.        |
|                                                                             |
|   2. UTILITY ADJUVANTS (Improve Application & Handling)                     |
|      - Buffers / Acidifiers: Lowers pH to prevent ALKALINE HYDROLYSIS.      |
|      - Anti-Foaming Agents (Defoamers): Eliminates surface foam.            |
|      - Compatibility Agents: Prevents curdling/clumping in tank mixes.      |
|      - Drift Reduction Agents (DRAs): Increases droplet size, limits fines. |
+-----------------------------------------------------------------------------+

Activator Surfactants

Surfactants (Surface Active Agents) alter the interfacial tension of spray droplets:

1. Non-Ionic Surfactants (NIS): Surfactants with no electrical charge. Safe for most crops; reduces droplet surface tension, allowing spherical water droplets to flatten and spread across waxy leaf surfaces.
2. Crop Oil Concentrates (COC): Formulated with 80% to 85% petroleum or vegetable oil plus 15% to 20% non-ionic surfactant. COCs soften and penetrate thick, waxy leaf cuticles (especially useful for mature weeds under drought stress), but increase the risk of crop phytotoxicity in hot weather (>85°F).
3. Stickers: Substances that increase the adhesive properties of spray droplets, preventing pesticide wash-off caused by rain, overhead irrigation, or heavy dew.

Utility Modifiers: Buffers, Defoamers & Drift Retardants

• Buffers and Acidifiers (Crucial Utah Practice): In Utah, municipal water supplies, irrigation canals, and well waters are naturally alkaline, frequently displaying pH values between 7.8 and 8.8 due to dissolved calcium and magnesium carbonates. In high-pH water, sensitive pesticides (particularly organophosphates, carbamates, and certain sulfonylureas) undergo alkaline hydrolysis—a chemical reaction where hydroxyl ions split molecular bonds, neutralizing the active ingredient within hours. Adding an acidifying buffer lowers the spray water pH to an optimal slightly acidic range (pH 5.5 to 6.5), stabilizing the active ingredient.
• Anti-Foaming Agents (Defoamers): Suppresses excessive foam generated by mechanical or hydraulic bypass agitation when mixing surfactants and flowables.
• Drift Reduction Agents (DRA): Long-chain synthetic polymers that increase the viscosity of the spray solution, reducing the proportion of fine, driftable spray droplets (<105–150 microns).

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4. Tank-Mixing Incompatibility & Jar Compatibility Testing

Mixing two or more pesticides (or a pesticide plus a liquid fertilizer) in a single spray tank saves time, labor, and fuel. However, combining incompatible chemicals can result in catastrophic application failures.

+-----------------------------------------------------------------------------+
|                        TYPES OF INCOMPATIBILITY                             |
|                                                                             |
|   PHYSICAL INCOMPATIBILITY            CHEMICAL INCOMPATIBILITY              |
|   - Visible physical failure          - Invisible molecular reaction        |
|   - Clumping, curdling, gel formation - Chemical degradation / antagonism   |
|   - Separation into distinct layers   - Severe, unexpected crop burn        |
|   - Precipitates that clog strainers  - Zero pest control efficacy          |
+-----------------------------------------------------------------------------+

Physical vs. Chemical Incompatibility

• Physical Incompatibility: The products cannot physically stay blended together. The mixture may curdle, form gel-like flakes, separate into oil and water layers, or precipitate into a heavy sludge that completely clogs pump lines, filters, and nozzles.
• Chemical Incompatibility: A chemical reaction alters the chemical structure of the active ingredients. The mixture may look completely normal and spray cleanly, but the chemicals may neutralize each other (antagonism), destroying pest control efficacy, or create highly phytotoxic reaction products that scorch the crop.

The Jar Compatibility Test Procedure

Before mixing large volumes of unfamiliar pesticides or fertilizers in a spray tank, applicators should conduct a Jar Test:

1. Obtain a clean, transparent 1-quart glass jar.
2. Add carrier water (or liquid fertilizer) from the exact source to be used in the field, filled to approximately half volume (e.g., 1 pint or 500 mL).
3. Calculate proportional amounts of each chemical corresponding to label rates per acre (typically 1 teaspoon of liquid or 1 tablespoon of dry product per quart represents standard field ratios).
4. Add products one at a time in the proper mixing sequence, stirring or inverting the jar after each addition.
5. Fill the jar with remaining carrier water, cap tightly, invert 10 times, and let stand for 15 to 30 minutes.
6. Evaluation:
   • If the mixture remains uniform, milky, or easily re-suspends with gentle shaking, the combination is physically compatible.
   • If the mixture heats up (indicating an exothermic chemical reaction), forms a sludge, precipitates solids to the bottom, curdles into mayonnaise-like clumps, or forms separate oily layers that will not re-disperse, the mixture is physically incompatible and must not be mixed in the field.

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5. The W-A-L-E-S Mixing Protocol

Adding pesticide formulations to a spray tank in an arbitrary order frequently triggers severe physical incompatibility. Applicators must follow the standard industry mixing protocol known by the acronym W-A-L-E-S (or W-A-L-E):

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|                    THE W-A-L-E-S TANK MIXING SEQUENCE                       |
|                                                                             |
|   [START] ---> Fill spray tank 1/4 to 1/2 FULL with water & START AGITATION |
|     |                                                                       |
|   [ W ] -----> WETTABLE POWDERS & DRY FLOWABLES (WP, WDG, DF)               |
|     |          (Pre-slurry in water if required; disperse fully)            |
|   [ A ] -----> AGITATE thoroughly & add WATER CONDITIONERS / ANTI-FOAM      |
|     |          (Allow dry particles to fully suspend before adding liquids) |
|   [ L ] -----> LIQUID FLOWABLES & SUSPENSIONS (F, SC, ME)                   |
|     |          (Thick liquids and microencapsulated formulations)           |
|   [ E ] -----> EMULSIFIABLE CONCENTRATES (EC)                               |
|     |          (Solvent-based liquids; form milky emulsion)                 |
|   [ S ] -----> SURFACTANTS, SOLUBLE LIQUIDS & POWDERS (SL, SP, NIS, COC)    |
|     |          (Add true solutions, surfactants, and foliar fertilizers)    |
|   [END] -----> FINISH FILLING tank with remaining water under agitation     |
+-----------------------------------------------------------------------------+

[!IMPORTANT] Why Sequence Matters: If an Emulsifiable Concentrate (EC) is added before a Wettable Powder (WP) or WDG has fully dispersed in water, the oil and petroleum solvents in the EC will coat the dry powder particles. Once coated in oil, the powder particles become hydrophobic (water-repellent), preventing them from wetting out or dispersing in the water carrier. The result is an insoluble, oily sludge that settles to the tank bottom and ruins the mix.