3.3 Pesticide Formulations, Compatibility & Adjuvants

Formulation Chemistry: Active vs. Inert Ingredients

A pesticide product in its pure commercial synthesis—the active ingredient (AI)—is rarely suitable for direct field application. Pure technical-grade chemicals are frequently insoluble in water, chemically unstable under sunlight, difficult to handle safely, or impossible to meter evenly across large acreages. Manufacturers blend technical active ingredients with inert ingredients (solvents, mineral carriers, emulsifiers, wetting agents, stabilizers, and dyes) to produce a formulation that can be safely measured, mixed with a carrier, and distributed uniformly.

How Formulations Behave in the Spray Tank

When added to water in a spray tank, all formulations behave as one of three physical mixtures:

1. True Solution: The active ingredient dissolves completely in water at a molecular level (like table salt in water). Solutions are transparent, never settle to the bottom, and require no agitation once thoroughly dissolved.
2. Suspension: Insoluble solid particles of active ingredient are suspended throughout the liquid carrier (like fine sand in water). Suspensions are cloudy or opaque, do not dissolve, settle rapidly to the bottom of the tank if agitation stops, and cause mechanical abrasion to pumps, regulators, and nozzle orifices.
3. Emulsion: One liquid is dispersed as microscopic droplets within another immiscible liquid (like oil in water), facilitated by an emulsifier. Emulsions are milky-white in appearance. If chemical destabilization occurs, the emulsion "breaks," causing an oily film or curds to separate on the liquid surface.

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Survey of Liquid and Dry Formulations

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Tank Mixing: Physical vs. Chemical Incompatibility and the Jar Test

Applicators frequently combine two or more pesticide products, fertilizers, and adjuvants in a single tank load to save labor and broaden pest control spectrums. However, improper mixing can result in incompatibility.

Incompatibility Types

• Physical Incompatibility: The formulations fail to mix physically, resulting in clumping, curdling, phase separation, layering, crystallization, or thick gelatinous sludge ("mayonnaise") that clogs suction screens, lines, and nozzles.
• Chemical Incompatibility: The chemical molecules react together, altering the biochemical properties of the active ingredients without necessarily displaying visible physical changes. This leads to antagonism (loss of pesticidal efficacy), synergism (unintended severe crop phytotoxicity), or rapid chemical degradation.

The Standard Jar Test Protocol

Before mixing untested products in a 500-gallon spray tank, the applicator must perform a compatibility jar test:

1. Use a clean 1-quart glass jar and the exact water carrier source (and temperature) intended for the application.
2. Add approximately 1 pint (500 mL) of the carrier water to the jar (representing half the final spray volume).
3. Add proportionate quantities of each product based on their labeled application rates (e.g., approximately 1 teaspoon per quart for a rate of 1 pint per 100 gallons).
4. Add products in the strict WALES / DLABS sequence, stirring or inverting the jar gently after each chemical addition.
5. Fill the jar to nearly full with remaining water, add final surfactants or adjuvants, and secure the lid.
6. Invert the jar 10 times and let it stand undisturbed for 15 to 30 minutes.
7. Evaluation: If the mixture remains smooth, uniform, or easily resuspended with gentle swirling, the mix is physically compatible. If the jar feels warm (exothermic chemical reaction), forms flakes, curdles, separates into distinct oil/water layers that resist mixing, or forms gritty sediment, the mixture is incompatible and must not be loaded into the spray tank.

+--------------------------------------------------------------------------+
|                       COMPATIBILITY JAR TEST OUTCOMES                    |
|                                                                          |
|   [COMPATIBLE]                    [INCOMPATIBLE: Separation / Sludge]    |
|   +------------+                  +------------+                         |
|   |            |                  |~~~~~~~~~~~~| <-- Oily / Cream Layer  |
|   |  Uniform   |                  |            |                         |
|   | Dispersion |                  |   Clear    |                         |
|   | (Pass)     |                  |   Water    |                         |
|   |            |                  |............| <-- Gritty Curds/Flakes |
|   +------------+                  +------------+                         |
+--------------------------------------------------------------------------+

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The Standard Tank Mixing Sequence: WALES / DLABS Protocol

Adding products in the wrong sequence is the primary cause of tank mix clumping. When wettable powders are added to a tank that already contains oily emulsifiable concentrates, the oil coats the dry powder particles, preventing them from wetting and dispersing, forming unresolvable sludge. Applicators must adhere to the standardized WALES (or DLABS) order:

+-----------------------------------------------------------------------------+
|                        THE STANDARD WALES SEQUENCE                          |
|                                                                             |
|   W  ->  WETTABLE POWDERS, Dry Flowables & Water-Dispersible Granules (WDG) |
|   A  ->  AGITATE thoroughly & add Liquid Flowables / Suspensions (SC / F)   |
|   L  ->  LIQUID Solubles, Soluble Powders & True Solutions (S / SP)         |
|   E  ->  EMULSIFIABLE CONCENTRATES (EC)                                     |
|   S  ->  SURFACTANTS, Crop Oils, Adjuvants & Soluble Fertilizers            |
+-----------------------------------------------------------------------------+

1. Tank Fill & Agitation: Fill the spray tank 1/2 to 3/4 full with clean carrier water and start continuous mechanical or hydraulic agitation.
2. W (Wettable Powders & Dry Products): Add water-soluble packets, dry flowables (DF), water-dispersible granules (WDG), and wettable powders (WP). Allow these dry products to fully hydrate, wet, and disperse in the water vortex for 3-5 minutes before adding other chemistries.
3. A (Agitate & Add Suspensions): Maintain vigorous agitation while adding liquid flowables (F) and suspension concentrates (SC).
4. L (Liquid Solubles & Solutions): Add water-soluble liquid concentrates (S) and soluble powders (SP).
5. E (Emulsifiable Concentrates): Add emulsifiable concentrates (EC) and microencapsulated formulations (ME).
6. S (Surfactants & Adjuvants): Add drift control agents, non-ionic surfactants (NIS), crop oil concentrates (COC), and liquid fertilizers. Top off the tank to the final designated volume with water while maintaining continuous agitation throughout transport and spraying.

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Adjuvant Classes and Functional Chemistry

An adjuvant is any substance added to a pesticide spray mixture to modify chemical performance, improve physical handling, enhance coverage, or alter physical properties of the spray solution.

Surfactants (Surface Active Agents)

Water molecules have high surface tension, causing spray droplets to stand as spherical beads on waxy leaf surfaces. Surfactants possess a dual chemical structure with a hydrophilic (water-loving) head and a lipophilic (oil-loving) tail. By aligning at the droplet surface, surfactants break water surface tension, flattening the droplet and expanding the contact surface area across the leaf cuticle.

• Non-Ionic Surfactants (NIS): Carry no electrical charge. They are universally compatible with most post-emergence herbicides, fungicides, and insecticides, enhancing droplet spreading and foliar absorption without destabilizing the mix.

Crop Oil Concentrates (COC) and Methylated Seed Oils (MSO)

• Crop Oil Concentrates (COC): Contain 80-85% petroleum paraffin base oil plus 15-20% non-ionic surfactant. COC dissolves and softens the thick, waxy cutin layer of weed leaves, significantly increasing the penetration rate of systemic herbicides.
  • Operational Warning: In hot (>85-90°F), bright sunny weather, COCs can cause severe phytotoxic burn to desirable crops.
• Methylated Seed Oils (MSO): Chemically modified vegetable oils (e.g., methylated soybean oil) providing even more aggressive cuticular penetration on drought-stressed weeds with thickened waxy barriers.

Utility and Water Conditioning Adjuvants

• Buffers and Acidifiers: In many eastern and southern Colorado water districts, spray water is hard and alkaline ($pH > 7.5-8.5$). Under alkaline conditions, sensitive pesticide active ingredients (especially organophosphates, carbamates, and pyrethroids) undergo rapid alkaline hydrolysis—a chemical degradation reaction that breaks chemical bonds and destroys insecticidal efficacy within hours inside the spray tank. Acidifying buffers lower and stabilize spray tank pH between 5.5 and 6.5, preventing hydrolysis.
• Drift Retardants / Deposition Aids: Long-chain polymer thickeners that increase liquid viscosity, reducing the formation of driftable fine droplets (<105-150 microns) and ensuring that spray particles settle directly onto target foliage.
• Stickers and Extenders: Adhesives that bind pesticide deposits tightly to leaf surfaces, preventing spray washoff from heavy irrigation, rainfall, or mechanical abrasion, while shielding active ingredients from ultraviolet (UV) photodegradation.
• Defoamers (Anti-Foaming Agents): Silicon-based agents (e.g., dimethicone) added to suppress excessive foaming caused by vigorous tank agitation of surfactant-rich mixtures.