7.2 Pesticide Formulations & Their Characteristics

7.2 Pesticide Formulations & Their Characteristics

Technical Definition: A pesticide formulation is a commercial mixture combining a biologically active pesticidal ingredient (technical grade chemical) with inert ingredients—such as liquid solvents, dry mineral carriers, surfactants, dispersing agents, and stabilizers—to render the product safe, stable, and practical for field application.

Pure active ingredients are rarely applied in their raw chemical state; many are insoluble crystalline solids or thick, viscous oils that cannot be distributed evenly across a treatment site. Formulation chemistry dictates how the product behaves inside the spray tank, its penetration into target pests and plant cuticles, its wear on pumps and nozzles, and the specific exposure hazards it presents to the applicator.

---

Liquid Formulations: Chemistry, Strengths, and Vulnerabilities

+-------------------------------------------------------------------------+
|                    MAJOR LIQUID FORMULATION TYPES                       |
|                                                                         |
|  EMULSIFIABLE CONCENTRATE (EC)     FLOWABLE / SUSPENSION CONCENTRATE (SC)|
|  - Active in petroleum solvent     - Insoluble solid ground in liquid   |
|  - Forms milky emulsion in water   - Forms suspension; needs agitation  |
|  - High dermal & phytotoxic risk   - Low solvent risk; abrasive         |
|                                                                         |
|  SOLUTIONS (S / SL)                MICROENCAPSULATED (ME / CS)          |
|  - True molecular solution         - Active encased in plastic capsules |
|  - Clear; zero agitation needed    - Extended residual; bee pollen risk |
+-------------------------------------------------------------------------+

1. Emulsifiable Concentrates (EC or E)

• Composition: A lipid-soluble active ingredient dissolved in an organic, petroleum-based hydrocarbon solvent, combined with an emulsifying agent.
• Behavior in Water: When poured into water, the emulsifier allows the water-insoluble oil droplets to disperse uniformly, forming a milky white, opaque emulsion. Requires mild tank agitation to prevent phase separation.
• Advantages: Highly concentrated (often containing 2 to 8 pounds of A.I. per gallon); easy to measure and pour; non-abrasive to pumps and spray nozzles; leaves little visible residue on treated foliage.
• Disadvantages & Hazards:
  • Dermal Absorption: Petroleum solvents readily penetrate human skin lipids, drastically accelerating the transdermal absorption of the active ingredient into the bloodstream.
  • Phytotoxicity: High risk of chemical burning (foliar phytotoxicity) on sensitive ornamental plants, seedling crops, or during high ambient temperatures (>85°F).
  • Equipment Degradation: Solvents cause rapid deterioration, softening, and swelling of rubber and synthetic neoprene pump impellers, spray hoses, and tank gaskets.
  • Flammability: Organic solvents possess low flash points and present fire hazards during storage.

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

• Composition: The active ingredient dissolves completely in water or an organic carrier, forming a true, uniform molecular solution.
• Behavior in Water: Remains completely dissolved; forms a clear, transparent liquid that will never separate or settle out once mixed.
• Advantages: Requires zero tank agitation once thoroughly blended; non-abrasive to equipment; zero nozzle clogging or strainer blockage.
• Disadvantages: Very few pesticidal active ingredients possess chemical structures that dissolve readily in pure water.

3. Flowables (F) or Suspension Concentrates (SC)

• Composition: An active ingredient that is an insoluble solid is wet-milled into an ultra-fine powder and suspended in a liquid carrier matrix with dispersing agents.
• Behavior in Water: Forms a liquid suspension upon dilution. Requires moderate, continuous mechanical or hydraulic agitation in the spray tank.
• Advantages: Eliminates the dry dust inhalation hazard associated with wettable powders; contains lower concentrations of organic solvents than ECs, reducing dermal absorption and phytotoxicity risks.
• Disadvantages: Tends to settle out into a dense, solid cake at the bottom of containers during prolonged winter storage; abrasive to spray nozzles and pump components.

4. Microencapsulated Formulations (ME or CS)

• Composition: Liquid or solid active ingredient cores encased in microscopic polymer or plastic capsules suspended in a liquid medium.
• Behavior in Water: Disperses as a suspension; the active ingredient releases slowly over days or weeks through diffusion across the porous capsule wall.
• Advantages: Extended residual pest control; reduced acute dermal toxicity and odor for human applicators; reduced volatile vapor loss.
• The Critical Pollinator Hazard: Microencapsulated capsules measure 10 to 30 microns in diameter and carry an electrostatic surface charge virtually identical to natural pollen grains. Foraging honeybees (Apis mellifera) collect the capsules on their pollen baskets and carry them directly back to the hive. Nurse bees feed the contaminated capsules to larvae and the queen, frequently resulting in devastating, complete colony collapse.

---

Dry Formulations: Mechanics, Handling, and Hazards

1. Wettable Powders (WP or W)

• Composition: A dry, finely ground insoluble active ingredient blended with an inert mineral clay or talc carrier, supplemented with wetting and dispersing surfactants.
• Behavior in Water: Does not dissolve. When mixed with water, it forms a suspension of fine solid particles. Requires continuous, vigorous mechanical agitation to prevent particles from settling to the tank floor.
• Advantages: Excellent residual efficacy on porous, unpainted surfaces (wood, concrete); low skin absorption rate compared to ECs; low risk of plant phytotoxicity.
• Disadvantages & Hazards:
  • Inhalation Hazard: Pouring, scooping, and measuring dry WP formulations creates a fine dust plume that presents an acute inhalation hazard to mixers and loaders.
  • Abrasive Wear: Highly abrasive to bronze and plastic pump impellers, pressure relief valves, and spray tips (particularly soft brass nozzles).
  • Clogging: Rapidly clogs line strainers and 50-mesh nozzle screens if agitation stalls.

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

• Composition: Engineered like wettable powders, but the fine particles are agglomerated into small, free-flowing micro-granules.
• Behavior in Water: Disperses rapidly in water, breaking down into a fine suspension identical to a WP.
• Advantages: Combines the low phytotoxicity of wettable powders with zero dust generation, drastically mitigating applicator inhalation exposure during measuring and tank loading.
• Disadvantages: Highly abrasive to nozzles; requires continuous tank agitation.

3. Granules (G) and Pellets (P)

• Composition: Ready-to-use dry formulations where the active ingredient is coated onto or absorbed into coarse mineral particles (clay, corn cobs, walnut shells, or fertilizer granules).
• Application: Applied directly to soil or turf using rotary or drop spreaders; never mixed with water.
• Advantages: Zero spray drift risk; low dermal and inhalation risk; penetrates dense turfgrass canopies to reach thatch and soil-dwelling pests (e.g., grub control).
• Disadvantages: Heavy, bulky shipping; non-target wildlife hazards (ground-foraging songbirds ingest granules mistaking them for grit or seeds); requires rainfall or irrigation to activate.

---

Formulation Comparison Matrix

---