Dry and Liquid Formulations, Adjuvants, Surfactants, and Compatibility

Dry and Liquid Formulations, Adjuvants, Surfactants, and Compatibility

Pesticide active ingredients (a.i.) are rarely applied in their pure chemical form. Technical-grade active ingredients must be combined with liquid carriers, dry diluents, emulsifiers, or inert binding agents to create a commercial pesticide formulation. Choosing the correct formulation and understanding spray tank additives (adjuvants) directly impacts application safety, equipment wear, biological efficacy, and compatibility.

1. Liquid Pesticide Formulations

Liquid formulations are packaged as concentrated fluids that are dissolved, emulsified, or suspended in liquid carriers (typically water).

Common Liquid Formulations

• Emulsifiable Concentrates (EC or E): Consists of an oil-soluble liquid active ingredient dissolved in a petroleum solvent with emulsifying agents. When mixed with water, it forms a milky-white emulsion.
  • Advantages: Easy to handle, non-abrasive to pumps/nozzles, stays in suspension with minimal agitation.
  • Disadvantages: Petroleum solvents cause high dermal absorption hazard, skin/eye irritation, potential phytotoxicity to sensitive foliage, and rubber hose deterioration.
• Solutions (S or Deliverables): Active ingredient dissolves completely in water or solvent carrier, forming a true transparent solution.
  • Characteristics: Requires no tank agitation once thoroughly mixed; will not settle out or clog nozzles.
• Flowables / Liquid Suspensions (F or L): Finely ground solid active ingredients suspended in a liquid base. Functions similarly to a liquid Wettable Powder.
  • Characteristics: Requires continuous moderate tank agitation; moderate nozzle wear and screen clogging potential.
• Microencapsulated (ME or M): Liquid or solid active ingredient encased in microscopic plastic polymer capsules suspended in a liquid carrier.
  • Characteristics: Provides extended slow-release pest control and improved safety to applicators. High hazard to honeybees if worker bees collect capsules mistaking them for pollen grains.

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2. Dry Pesticide Formulations

Dry formulations are manufactured as powders, dusts, granules, or dispersible granules.

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3. Adjuvants and Surfactants

An Adjuvant is any substance added to a pesticide spray tank to modify spray physical characteristics or enhance chemical performance. Adjuvants fall into two primary functional categories:

                             SPRAY ADJUVANTS
                                    |
         +--------------------------+--------------------------+
         |                                                     |
UTILITY MODIFIERS                                    PERFORMANCE ENHANCERS
(Modify Physical Spray Properties)                   (Enhance Biological Activity)
  - Buffers & Acidifiers (pH control)                  - Surfactants (Surface tension)
  - Drift Control Agents (Droplet size)                - Crop Oil Concentrates (Cuticle penetration)
  - Antifoaming Agents (Foam suppression)              - Stickers (Rainfastness / Adhesion)

Surfactant Physics and Categories

Surfactants (Surface Active Ants) reduce the surface tension of water spray droplets. Natural water surface tension causes droplets to bead up on waxy leaf cuticles, rolling off target foliage. Surfactants allow droplets to flatten, spread out, and penetrate leaf stomata.

1. Non-Ionic Surfactants (NIS): Carry no electrical charge. They are the most common and versatile surfactants used with herbicides, insecticides, and fungicides because they do not react chemically with active ingredients or hard water minerals.
2. Anionic Surfactants: Carry an electrical negative charge. Used primarily in industrial formulations.
3. Cationic Surfactants: Carry a positive electrical charge. Highly phytotoxic to plants; rarely used in crop protection.
4. Crop Oil Concentrates (COC): Petroleum or vegetable-oil based concentrates with 15-20% NIS. Excellent for penetrating thick, waxy weed cuticles in hot, dry climates.

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4. Tank Mixing Protocols and Compatibility

Combining multiple pesticides and fertilizers in a single tank load saves labor and application passes. However, mixing incompatible chemicals leads to physical clumping, nozzle clogging, phytotoxicity, or chemical neutralization (loss of efficacy).

The W-A-L-E-S Mixing Sequence

When tank-mixing products, always add materials to the spray tank in the standardized W-A-L-E-S Order while keeping the agitation system running with the tank filled to $50-75%$ capacity with water:

1. W - Water-Soluble Packets and WDG / DF Formulations: Add water-soluble packets first, allowing them to dissolve fully. Then add dry flowables (WDG/DF) and allow complete dispersion.
2. A - Agitate Thoroughly and Add WP: Maintain vigorous tank agitation and add Wettable Powders (WP).
3. L - Liquid Flowables and Suspensions: Add liquid suspensions (F or L) and microencapsulated (ME) products.
4. E - Emulsifiable Concentrates: Add Emulsifiable Concentrates (EC).
5. S - Surfactants, Soluble Liquids (SL/SP), and Adjuvants: Add liquid solutions, surfactants, drift agents, and soluble liquid fertilizers last.

The Jar Compatibility Test

If chemical compatibility is unknown, perform a Jar Test prior to filling large spray equipment:

• Fill a 1-quart glass jar with 1 pint of carrier water from the intended spray source.
• Add proportionate drops or teaspoons of each pesticide and adjuvant in the exact W-A-L-E-S sequence.
• Cap jar, invert 10 times, and let stand for 15-30 minutes.
• Compatibility Check: If the mix remains uniform, the components are compatible. If heat evolves, phase separation occurs, or clumps, sludge, or heavy flakes form, the mix is physically incompatible and must not be used.