5.2 Pesticide Formulations & Adjuvants

Pesticide Formulations Overview

A pesticide product as purchased from a dealer rarely consists of pure technical active ingredient. Technical active ingredients are typically insoluble, unstable, or too concentrated for direct uniform distribution across target acres. A pesticide formulation is a precise commercial mixture composed of one or more active ingredients (a.i.)—the chemicals responsible for controlling target pests—blended with inert ingredients (solvents, mineral carriers, emulsifiers, wetting agents, dyes, or stabilizers) to render the product safe, stable, and easy to handle and apply.

Formulations are divided into two main categories based on physical state at manufacture: Liquid Formulations and Dry Formulations.

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Liquid Formulations

+---------------------------------------------------------------------------------------+
|                               LIQUID FORMULATIONS                                     |
|                                                                                       |
|  Formulation Type         Physical Form in Tank          Primary Risk / Considerations|
|  ----------------         ---------------------          -----------------------------|
|  Emulsifiable Conc (EC)   Milky emulsion in water        High dermal absorption / Solvents|
|  Soluble Liquid (SL)      True liquid solution           Non-abrasive / Minimal agitation|
|  Flowable / Liquid (F/L)  Solid suspension in liquid     Requires agitation / Abrasive|
|  Solution (S)             True liquid solution           No settling / Fully dissolved|
+---------------------------------------------------------------------------------------+

Emulsifiable Concentrates (EC)

• Composition: An active ingredient dissolved in one or more petroleum-based organic solvents, combined with an emulsifier (a detergent-like compound that allows oil and water to mix).
• Appearance: When added to water in a spray tank, EC formulations form a milky-white emulsion.
• Advantages: Easy to measure and pour; contains high concentrations of active ingredient per gallon; non-abrasive to spray nozzles and pumps; requires minimal tank agitation once mixed.
• Disadvantages: Petroleum solvents are rapidly absorbed through human skin, creating high dermal exposure hazards for handlers; solvents may cause phytotoxicity (leaf burn) on sensitive crops; solvents degrade synthetic rubber hoses, pump diaphragms, and gaskets.

Soluble Liquids (SL)

• Composition: A water-soluble active ingredient dissolved in a water carrier or water-miscible solvent.
• Appearance: Mixes completely with water to form a clear true solution.
• Advantages: Requires no tank agitation after initial mixing; does not settle out when spray equipment pauses; non-abrasive to nozzles and equipment.
• Disadvantages: Readily absorbed through skin; may require addition of surfactants to wet target foliage.

Flowables / Liquids (F or L)

• Composition: A finely ground solid active ingredient suspended in a liquid carrier (often water or oil) with clay or thickening agents.
• Appearance: Thick liquid (resembling mayonnaise or heavy cream) that dilutes in water to form a suspension.
• Advantages: Eliminates dust inhalation hazards during tank loading; easy to handle and measure.
• Disadvantages: Requires continuous moderate-to-vigorous tank agitation to prevent solids from settling; highly abrasive to soft metal nozzle orifices (especially brass); leaves visible powder residue on treated foliage.

Solutions (S)

• Composition: Active ingredients that dissolve completely in water or petroleum solvents without emulsifiers.
• Appearance: Clear liquid that does not separate or settle.
• Advantages: No agitation required; non-abrasive.
• Disadvantages: Application options depend on solvent type (oil-based solutions require specialized low-volume equipment).

Microencapsulated (ME or M)

• Composition: Liquid or solid active ingredient encased in microscopic plastic or polymer capsules suspended in a liquid carrier.
• Advantages: Slow, controlled release extends residual control; reduces acute handler toxicity.
• Disadvantages: Honeybees may collect capsules mistaking them for pollen and carry them back to hives, resulting in severe colony mortality. Special label restrictions apply near bee foraging areas.

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Dry Formulations

Wettable Powders (WP)

• Composition: Dry, finely ground solid active ingredient combined with a mineral carrier (e.g., clay or talc) and wetting agents.
• Appearance: Dry powder mixed into water to form a suspension.
• Advantages: Lower risk of skin absorption compared to EC formulations; less phytotoxic to sensitive foliage.
• Disadvantages: Severe dust inhalation hazard during measuring, opening bags, and tank loading; requires continuous, high-capacity tank agitation to prevent rapid settling; highly abrasive to spray pumps and nozzle orifices.

Dry Flowables (DF) / Water Dispersible Granules (WDG)

• Composition: Active ingredient formulated into small, dust-free granules that disaggregate and break down into a fine suspension when added to water.
• Advantages: Combines the lower dermal hazard of WP with greatly reduced dust inhalation risk during loading; easier to pour and measure than WP.
• Disadvantages: Requires continuous tank agitation; abrasive to pump impellers and spray nozzles.

Soluble Powders (SP)

• Composition: Dry powder active ingredient that dissolves completely in water to form a true solution.
• Advantages: Creates no abrasive wear on nozzles; requires no tank agitation once fully dissolved.
• Disadvantages: Dust inhalation hazard during bag opening and measuring.

Granules (G)

• Composition: Active ingredient applied onto coarse, dry mineral particles (clay, vermiculite, ground corn cobs, or peanut hulls).
• Application: Applied dry using granular spreaders (seeder/spreader units); never mixed with water.
• Advantages: Ready to use; extremely low drift hazard; minimal handler hazard.
• Disadvantages: Heavy to transport per unit of active ingredient; requires soil moisture for activation; may be ingested by granivorous birds.

Pellets (P) & Dusts (D)

• Pellets: Uniform, molded dry particles larger than granules, used for localized spot treatments or bait applications.
• Dusts: Ultra-fine dry powders containing low percentages of active ingredient on talc or clay carriers, applied dry. High drift hazard and severe respiratory risk; rarely used in agricultural broadcast operations.

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Formulations Summary Comparison

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Tank Mixing & Compatibility Procedures

Mixing multiple pesticides or blending pesticides with fertilizers or adjuvants saves labor and fuel. However, combining incompatible chemicals can result in physical separation, clumping, gel formation, or reduced biological efficacy.

Physical vs. Chemical Incompatibility

• Physical Incompatibility: Materials do not mix properly, forming sludge, cottage-cheese-like precipitates, flakes, or oil layers that clog screens, pumps, and nozzles.
• Chemical Incompatibility: Chemicals mix physically, but a chemical reaction occurs that deactivates the active ingredient or produces phytotoxic compounds that injure host plants.

The Jar Test Procedure

Before mixing large volumes in a spray tank, applicators must perform a small-scale Jar Test:

1. Wear required personal protective equipment (PPE).
2. Fill a 1-quart clear glass jar half-full with the exact water or liquid fertilizer carrier to be used in the field.
3. Add proportionate quantities of each pesticide and adjuvant component in the exact sequence specified by label protocols.
4. Fill the jar to 3/4 full with remaining carrier, cap tightly, and invert 10 to 15 times.
5. Let stand for 15 to 30 minutes and inspect. If heat is generated, or if clumping, precipitation, layering, or curdling occurs, the mixture is incompatible.

Standard Tank-Mixing Sequence: W-A-L-E-S Protocol

When label instructions do not specify a mixing sequence, applicators follow the industry-standard W-A-L-E-S protocol (or alternative W-A-T-E-R protocol):

+-----------------------------------------------------------------------+
|                      W-A-L-E-S MIXING SEQUENCE                        |
|                                                                       |
|  W - Fill tank 1/2 to 3/4 with Water/carrier, begin agitation + WSB   |
|  A - Add Dry Formulations with Agitation (WP, DF, WDG)                |
|  L - Add Liquid Flowables & Suspensions (F, L, ME)                    |
|  E - Add Emulsifiable Concentrates (EC)                               |
|  S - Add Surfactants & Soluble Liquids (SL, SP, Acidifiers)           |
+-----------------------------------------------------------------------+

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Spray Adjuvants

An adjuvant is any chemical substance added to a spray tank mixture to modify the physical or chemical properties of the spray solution, enhancing application performance, coverage, target retention, or environmental safety.

Types of Adjuvants

1. Surfactants (Surface Active Agents):
   • Spreaders: Break the surface tension of water droplets, allowing spray solution to flatten and spread uniformly across waxy leaf cuticles or hairy insect bodies.
   • Penetrants: Enhance active ingredient absorption through waxy plant cuticles.
   • Non-Ionic Surfactants (NIS): The most widely specified surfactant type; neutral charge prevents chemical reaction with active ingredients.
2. Stickers: Increase the adhesion of spray droplets to plant foliage, preventing wash-off from rainfall or overhead irrigation.
3. Buffers & Acidifiers: Modify spray water pH. Water sources with high pH (alkaline water, pH > 7.5) cause alkaline hydrolysis—a chemical reaction that breaks down organophosphate, carbamate, and synthetic pyrethroid insecticides within minutes in the spray tank. Acidifiers lower tank water pH to an optimal range of 4.5 to 6.5.
4. Drift Control Agents (Thickeners): Increase spray solution viscosity, reducing the volume of fine, driftable droplets (droplets smaller than 150 microns in diameter) produced at the nozzle tip.