3.2 Liquid and Dry Formulations

Liquid and Dry Formulations

A pure, manufactured pesticide active ingredient is known as the technical-grade material. Technical-grade pesticides rarely exist in a form that can be directly applied to crops, turf, or structures—many are insoluble solids, thick waxy oils, or highly concentrated liquids that would be impossible to meter evenly across an acre. To make them usable, manufacturers combine technical active ingredients with inert ingredients (solvents, emulsifiers, dry carriers, wetting agents, and stabilizers) to produce a formulation.

Selecting the proper formulation requires balancing biological efficacy against target pests, crop safety (phytotoxicity), applicator exposure risks, equipment wear, agitation capabilities, drift potential, and cost.

+-----------------------------------------------------------------------------+
|                   PHYSICAL BEHAVIOR OF MIXTURES IN WATER                    |
|                                                                             |
|     [TRUE SOLUTION]             [EMULSION]              [SUSPENSION]        |
|       (S / SL / SP)             (EC / E)                (WP / WDG / SC)     |
|                                                                             |
|     +-------------+          +-------------+          +-------------+       |
|     | *  *  *  *  |          | o  o  o  o  |          | .  .  .  .  |       |
|     |  *  *  *  * |          |  o  o  o  o |          |  .  .  .  . |       |
|     | *  *  *  *  |          | o  o  o  o  |          | .  .  .  .  |       |
|     +-------------+          +-------------+          +-------------+       |
|     - Dissolves 100%         - Oil droplets in        - Solid particles     |
|     - Transparent/clear        water                    suspended in liquid |
|     - Never separates        - Milky white            - Opaque/cloudy       |
|     - NO agitation           - Minimal agitation      - CONSTANT vigorous   |
|       needed once dissolved    once mixed               agitation required  |
+-----------------------------------------------------------------------------+

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1. Liquid Formulations

1. Emulsifiable Concentrates (EC or E)

• Composition: An oil-soluble active ingredient dissolved in one or more petroleum-based organic solvents, combined with an emulsifying agent that allows oil and water to blend.
• Behavior in Tank: When added to water, the emulsifier forces the petroleum-chemical solution to disperse into microscopic oil droplets, forming a distinctive milky-white emulsion.
• Advantages: Easy to measure, pour, and handle; requires only moderate initial agitation (remains suspended with minimal agitation); non-abrasive to sprayer pump impellers and nozzle orifices; leaves no visible chalky residue on treated turf or ornamentals.
• Disadvantages & Hazards:
  1. High Dermal Absorption: The organic petroleum solvents rapidly penetrate human skin, carrying the active pesticide directly into the applicator's bloodstream.
  2. Foliar Phytotoxicity: Petroleum solvents can burn tender foliage, blossoms, and young crop shoots, especially during high ambient temperatures ($>85^{\circ}\text{F}$).
  3. Equipment Degradation: Solvents cause rapid swelling, softening, and deterioration of rubber and synthetic neoprene hoses, O-rings, pump diaphragms, and plastic tank fittings.
  4. Flammability: Organic solvents possess low flash points and must be stored away from open flames, pilot lights, and high heat.

2. Solutions (S, SL, or Concentrated Solutions - C / LC)

• Composition: Water-soluble or alcohol-soluble active ingredients dissolved completely in a liquid carrier.
• Behavior in Tank: Blends completely with water to form a true, transparent solution.
• Characteristics: Molecules never separate or settle out once mixed; requires no mechanical agitation after initial blending; non-abrasive; low phytotoxicity risk; leaves no visible surface residue.

3. Suspension Concentrates / Flowables (SC, F, or L)

• Composition: Insoluble solid technical-grade active ingredients finely ground into microscopic powder and pre-mixed into a liquid carrier with suspending agents.
• Behavior in Tank: Forms a liquid suspension when diluted in water, behaving similarly to a wettable powder in liquid form.
• Advantages: Eliminates the hazardous dust inhalation risk associated with measuring and pouring dry powders; easy to handle and measure.
• Disadvantages: Requires continuous mechanical agitation in the spray tank to prevent particles from settling; moderate abrasive wear on nozzle tips; can settle into an intractable, concrete-like cake in the bottom of original jugs or spray tanks if stored for prolonged periods without shaking.

4. Microencapsulated Formulations (ME or CS)

• Composition: Liquid or solid active ingredients encased within microscopic plastic polymer capsules (10 to 30 microns in diameter) suspended in a liquid carrier.
• Behavior in Tank: Forms a suspension in water requiring moderate continuous agitation.
• Advantages: Provides controlled, timed release of the active ingredient for extended residual pest control; significantly reduces acute dermal toxicity to the applicator because the plastic capsule prevents direct skin contact during handling; lowers odor and volatility.
• Critical Environmental Hazard (Pollinators): Microcapsules are identical in physical diameter and electrostatic charge to pollen grains. Foraging honeybees mistakenly collect microcapsules from treated flowers, pack them into their pollen baskets (corbiculae), and transport them back to the brood nest. Inside the hive, worker bees feed the capsules to larvae and the queen, causing catastrophic colony collapse.

+-----------------------------------------------------------------------------+
|                 MICROENCAPSULATED (ME) POLLINATOR HAZARD                    |
|                                                                             |
|   [SPRAY APPLICATION] ---> Microcapsules (10-30 microns) deposit on flowers |
|                                  |                                          |
|                                  v                                          |
|   [HONEYBEE FORAGING] ---> Electrostatic charge causes capsules to adhere    |
|                            to bee hairs; packed into pollen baskets         |
|                                  |                                          |
|                                  v                                          |
|   [BROOD NEST COLLAPSE] -> Transported to hive; fed to brood & queen;       |
|                            timed-release toxin destroys entire colony       |
+-----------------------------------------------------------------------------+

5. Ultra-Low Volume (ULV)

• Composition: Highly concentrated active ingredient (often approaching 100% a.i.) applied in extreme low volumes (less than 0.5 gallons per total acre) without dilution.
• Characteristics: Applied using specialized aerial or vehicle-mounted high-speed rotary atomizers generating microscopic aerosol droplets ($10\text{--}50\text{ microns}$). Primarily used for municipal mosquito abatement and rangeland grasshopper control. Poses severe spray drift hazards and rapid dermal penetration.

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2. Dry Formulations

1. Wettable Powders (WP or W)

• Composition: Dry, insoluble technical pesticide combined with finely ground talc or clay carriers and wetting/dispersing agents.
• Behavior in Tank: Does not dissolve; forms an opaque suspension of solid mineral particles floating in water.
• Advantages: Widely available; excellent residual control on porous structural surfaces (unpainted wood, concrete, brick) because particles remain on the surface rather than soaking in; lower foliar phytotoxicity than petroleum-based ECs.
• Disadvantages & Hazards:
  1. Severe Inhalation Hazard: Pouring, measuring, and dumping fine powder generates airborne chemical dust that is easily inhaled into the applicator's lungs.
  2. Continuous Agitation Required: Insoluble particles rapidly settle to the tank bottom if agitation stops, resulting in uneven application.
  3. High Equipment Wear: Abrasive mineral particles rapidly erode soft metal nozzle tips (brass and aluminum) and pump impellers, enlarging nozzle orifices and causing severe over-application.
  4. Strainer Clogging: Particles easily clog fine mesh suction and nozzle strainers ($50\text{ to }100\text{ mesh}$).

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

• Composition: Active ingredient formulated into small, uniform granules using dry carriers and wetting agents.
• Behavior in Tank: When added to water, granules rapidly break apart and disperse into a fine suspension identical in performance to a wettable powder.
• Key Advantage over WP: Low-dust formulation. Eliminates the dangerous chemical dust clouds during measuring and pouring, substantially improving applicator respiratory safety while retaining the low phytotoxicity benefits of WP.

3. Soluble Powders (SP or WSP)

• Composition: Dry, finely ground powder containing active ingredients and carriers that dissolve 100% in water.
• Behavior in Tank: Forms a clear true solution. Requires no agitation after complete dissolution; non-abrasive to nozzles.
• Packaging Innovation (WSP): Often packaged in pre-measured Water-Soluble Packets (WSP) made of polyvinyl alcohol film. Applicators drop the unopened packet directly into the spray tank where the outer bag dissolves, completely eliminating human contact with chemical dust.

4. Granules (G) & Pellets (P)

• Composition: Coarse, solid carrier particles (clay, corncob grits, walnut shells, or extruded polymer) impregnated with $2%\text{ to }15%$ active ingredient. Pellets are extruded under pressure to ensure uniform weight and cylindrical shape.
• Application Method: Applied completely dry using rotary broadcast spreaders, drop spreaders, or tractor-mounted in-furrow granular boxes; never mixed with water.
• Advantages: Zero spray droplet drift; no water hauling or mixing required; provides excellent systemic root uptake against soil-dwelling insects and pre-emergent weed seedlings.
• Disadvantages & Wildlife Hazards: Bulky packaging; requires rainfall or mechanical soil incorporation for activation; ingestion hazard to wildlife—ground-feeding songbirds frequently mistake pesticide granules for food grains or necessary gizzard grit.

5. Dusts (D) & Baits (B)

• Dusts (D): Very low concentration active ingredient ($1%\text{ to }10%$) on finely ground talc or chalk, applied dry. Used primarily for structural crack-and-crevice voids, crawlspaces, livestock dust bags, or seed treatments. Outdoors, dusts pose unacceptable wind drift and inhalation hazards.
• Baits (B): Low concentration active ingredient blended with highly palatable food attractants (grains, proteins, sugars, pheromones). Pests ingest the bait and receive a lethal dose. Minimizes broad-scale environmental chemical loading; widely used for rodents, termites, cockroaches, and nuisance ants.

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3. Formulation Comparison Matrix