3.1 Conventional Liquid and Dry Formulations

3.1 Conventional Liquid and Dry Formulations

Exam Focus: Pesticide applicator licensing examinations place substantial weight on formulation abbreviations, physical states in water (true solutions vs. emulsions vs. physical suspensions), agitation requirements, equipment abrasiveness, and primary handler exposure routes.

Every commercial pesticide product purchased by an applicator is a specialized chemical mixture known as a formulation. Pure pesticidal active ingredients are rarely applied in their raw, concentrated technical form because many are highly toxic viscous oils, crystalline solids, or insoluble precipitates that cannot be distributed evenly across target acres without specialized carriers and blending agents.

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Anatomy of a Pesticide Formulation

A formulated pesticide consists of two distinct components defined by federal and state pesticide statutes:

1. Active Ingredient (AI): The specific chemical or biological agent in the product that controls, repels, mitigates, or eliminates the target pest (e.g., weeds, fungi, insects, nematodes). The active ingredient is always identified by its common chemical name and percentage by weight or volume on the pesticide label.
2. Inert Ingredients: Auxiliary substances intentionally added to the formulation that possess no direct pesticidal activity against the target pest. Far from being "inactive," inert ingredients serve vital operational functions:
   • Carriers: Liquid or solid media (such as water, organic solvents, talc, clay, or pulverized corn cobs) that dilute the active ingredient to safe, usable concentrations.
   • Solvents: Liquid compounds (commonly petroleum distillates, aromatic hydrocarbons, or alcohols) that dissolve solid or oily active ingredients.
   • Emulsifiers: Surface-active agents that allow immiscible liquids (such as oil and water) to disperse into stable droplets without separating into distinct phases.
   • Wetting Agents & Spreaders: Compounds that reduce surface tension, allowing dry powders to hydrate or spray droplets to spread over waxy leaves.
   • Stabilizers & Preservatives: Anti-foaming agents, ultraviolet inhibitors, dyes, and anti-caking compounds that maintain chemical shelf-life.

+-------------------------------------------------------------+
|                 COMMERCIAL PESTICIDE PRODUCT                |
+-------------------------------------------------------------+
                               |
        +----------------------+----------------------+
        |                                             |
 [Active Ingredient (AI)]                     [Inert Ingredients]
 • Toxicant killing pest                      • Solvents & Carriers
 • Chemical percentage stated                 • Emulsifiers & Wetting Agents
 • Determines biological efficacy             • Anti-caking & Stabilizers

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Conventional Liquid Formulations

Liquid formulations are manufactured for dilution in water or liquid fertilizer, though a few are engineered for direct application. Their physical interaction with carrier water dictates both tank agitation and equipment maintenance protocols.

1. Emulsifiable Concentrates (EC or E)

An Emulsifiable Concentrate consists of a liquid active ingredient or oil-soluble solid active ingredient dissolved in one or more petroleum-based organic solvents, combined with an emulsifying agent.

• Behavior in Water: When added to water, the emulsifier forces the petroleum-oil phase to break into millions of microscopic oil droplets dispersed throughout the aqueous carrier, creating an opaque, milky white emulsion. The emulsion remains stable under light to moderate agitation, though prolonged stagnation will cause oil droplets to coalesce and float toward the surface ("creaming").
• Operational Advantages:
  • Easy to measure and pour accurately using graduated cylinders or volumetric jugs.
  • Non-abrasive to pumps, pressure regulators, strainers, and spray nozzles.
  • Leaves little to no visible powdery residue on harvested agricultural commodities, ornamentals, or structural surfaces.
• Disadvantages & Operational Hazards:
  • High Acute Dermal Absorption: The organic petroleum solvents dissolve the natural protective lipid and sebum barrier of human skin. If splashed, the active ingredient penetrates dermal tissue and enters the applicator's bloodstream far more rapidly than dry or water-based formulations.
  • Equipment Wear on Soft Components: Petroleum distillates degrade, soften, swell, and crack rubber and neoprene hoses, pump diaphragms, Viton seals, and polycarbonate sight gauges over time.
  • Phytotoxicity: Solvents can cause chemical burn (leaf chlorosis, necrosis, and leaf drop) on sensitive crop foliage, particularly when applications occur in intense sunlight and temperatures exceeding 85°F to 90°F.
  • Flammability: Many EC products have low flash points, requiring explosion-proof storage and separation from ignition sources.

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

Solutions and Soluble Liquids consist of water-soluble or alcohol-soluble active ingredients dissolved in an aqueous or polar solvent system.

• Behavior in Water: When mixed into the spray tank, the product forms a true chemical solution. Once the molecules disperse uniformly, they will never settle out, precipitate, or separate, even if the spray rig sits without agitation for days.
• Operational Advantages:
  • Completely non-abrasive to pump components, impellers, and nozzle orifices.
  • Requires no continuous tank agitation once thoroughly mixed.
  • Will not clog fine nozzle screens (100-mesh) or tip orifices.
• Disadvantages & Operational Hazards:
  • Limited availability: only a small percentage of pesticide active ingredients have sufficient water solubility to formulate as concentrated true solutions.
  • Certain soluble liquids are corrosive to metal fittings, requiring poly or stainless steel plumbing.

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

A Suspension Concentrate, frequently designated as a Flowable (F or L), is manufactured by milling an insoluble solid active ingredient into a microscopic, micronized powder and pre-suspending it in a liquid carrier (typically water) containing wetting and anti-caking agents.

• Behavior in Water: In the spray tank, the liquid product forms a physical suspension of solid particles dispersed in water. While the liquid pours easily like a thick cream or latex paint, it does not dissolve.
• Operational Advantages:
  • Eliminates the dangerous inhalation dust hazard associated with measuring and pouring dry wettable powders.
  • Non-flammable and generally contains minimal or no petroleum solvents, substantially reducing crop phytotoxicity and dermal absorption hazards.
• Disadvantages & Operational Hazards:
  • Requires moderate, continuous agitation during transport and application to keep the heavy solid particles suspended.
  • Can settle into an immovable, solid "cake" at the bottom of containers if stored under freezing conditions or held in long-term warehouse storage without periodic shaking.
  • Causes mild to moderate abrasive wear on pump impellers and nozzle orifices over extended operational hours.

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Conventional Dry Formulations

Dry formulations are packaged as powders, granules, or pellets. Some are mixed with water carriers to form sprayable suspensions or solutions, while others are applied dry through specialized spreaders or dusters.

+-------------------------------------------------------------------------+
|                        CONVENTIONAL DRY FORMULATIONS                    |
+-------------------------------------------------------------------------+
                                      |
        +-----------------------------+-----------------------------+
        |                                                           |
 [Diluted in Water Carrier]                                  [Applied Dry]
 • Wettable Powders (WP)                                     • Granules (G)
 • Water-Dispersible Granules (WDG/DF)                       • Pellets (P)
 • Soluble Powders (SP)                                      • Dusts (D)

1. Wettable Powders (WP or W)

A Wettable Powder is a dry, finely ground formulation consisting of an insoluble solid active ingredient blended with an inert mineral carrier (such as bentonite clay or talc) and surface-active wetting and dispersing agents.

• Behavior in Water: Wettable powders do not dissolve. When mixed with water, the wetting agents allow the dry mineral particles to absorb water and disperse into a physical suspension.
• Agitation Mandate: Continuous, vigorous mechanical or hydraulic agitation is mandatory. If tank agitation stops for even a few minutes, the heavy mineral and pesticide particles settle out into a dense layer at the tank bottom, leading to severe under-dosing initially followed by nozzle-clogging and massive crop burn when the concentrated sludge reaches the spray boom.
• Equipment Abrasiveness: The mineral carriers (clay and talc) are highly abrasive. Pumping WP suspensions causes rapid abrasive wear to roller pumps (roller pumps should never be used with WP formulations; centrifugal or diaphragm pumps are required) and brass or aluminum nozzle tips. Orifices erode rapidly, increasing flow rates and distorting spray patterns.
• Primary Handler Exposure: Severe inhalation dust hazard. During bag opening, measuring, and dumping into the spray tank, fine airborne particles are easily inhaled by the applicator, requiring strict use of particulate respirators (NIOSH N95 or better).

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

Water-Dispersible Granules and Dry Flowables are essentially wettable powders compressed during manufacturing into small, uniform, dust-free granules or beads.

• Behavior in Water: Once added to the spray tank water, the granules break apart rapidly and disperse into a fine particulate suspension identical in behavior and performance to a wettable powder.
• Operational Advantages:
  • Drastically reduces the inhalation dust hazard to the handler during hopper loading and pouring.
  • Pours cleanly from plastic jugs or foil bags without clinging to container walls, making measuring and triple-rinsing far simpler and more accurate.
• Agitation and Equipment Demands: Exactly like WPs, WDGs require continuous mechanical or hydraulic agitation and cause abrasive wear on soft nozzle tips.

3. Soluble Powders (SP or WSP)

A Soluble Powder consists of a finely ground dry active ingredient and inert carriers that completely dissolve in water to create a true solution.

• Operational Characteristics: Unlike WPs, SPs dissolve fully. Once initial agitation achieves complete dissolution, no further agitation is required, and the spray mix will not settle out. Soluble powders cause no abrasive wear on pumps or nozzles.
• Water-Soluble Packets (WSP): Many modern SP and WP products are pre-measured and sealed inside water-soluble polyvinyl alcohol (PVA) film bags. The applicator drops the entire unopened outer packet directly into the water-filled spray tank, where the film dissolves within 60 to 90 seconds. This technology virtually eliminates handler chemical exposure during the mixing and loading phase.

4. Granules (G) and Pellets (P)

Granules and Pellets are dry formulations designed for direct application without water. Coarse particles of clay, ground corncobs, crushed peanut hulls, or walnut shells are impregnated with active ingredient (typically 1% to 15% AI).

• Operational Advantages: Ready to use directly from the sack; no water haulage, mixing, or tank agitation is involved. The large, heavy particles produce virtually no spray drift, making them ideal for soil-applied pre-emergence weed control, turf insect treatments, or mosquito larviciding in standing water.
• Environmental & Wildlife Hazards: Granules present a severe non-target wildlife ingestion hazard. Seed-eating birds, songbirds, and waterfowl frequently mistake pesticide granules and pellets for weed seeds or grit needed in their muscular gizzards to grind food. In agricultural row crops, granules applied in-furrow or banded must be incorporated into the soil immediately to prevent bird poisoning.

5. Dusts (D)

A Dust is a ready-to-use dry formulation containing a low percentage of active ingredient (usually 1% to 10%) blended with an ultra-fine, lightweight inert carrier such as talc, chalk, or clay.

• Operational Hazards: Dusts represent the highest drift hazard of all pesticide formulations. In arid western states like New Mexico, spring winds quickly carry dust clouds miles away from the intended target site. Dusts also represent an intense inhalation hazard and eye irritant. Consequently, dusts are largely restricted to specialized structural crack-and-crevice treatments, enclosed greenhouse applications, poultry dusting, or agricultural seed box treatments.

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Formulation Comparison and Equipment Selection Matrix

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Practical Field Scenario: Pecan Orchard Spray in the Mesilla Valley

Consider a commercial agricultural applicator managing a 200-acre mature pecan orchard in Doña Ana County, New Mexico. In late June, temperatures reach 98°F with 12% relative humidity, and the orchard requires treatment for yellow pecan aphids (Monelliopsis pecanis).

The chemical distributor offers the recommended insecticide in two distinct formulations: an Emulsifiable Concentrate (EC) and a Water-Dispersible Granule (WDG).

1. Evaluating the EC Formulation: While the EC pours easily and requires minimal agitation, applying petroleum solvents under 98°F desert heat presents an extreme risk of phytotoxicity (foliar leaf burn) to tender pecan leaves and developing nut clusters. Furthermore, the intense heat causes applicators to perspire heavily, which accelerates the dermal absorption of petroleum-based solvents.
2. Evaluating the WDG Formulation: The WDG carries zero petroleum solvents, completely avoiding high-temperature phytotoxic burn on pecan foliage. The granulated particles eliminate the inhalation dust hazard of old wettable powders during mixing. However, the applicator must ensure that the orchard airblast sprayer's mechanical agitation system is functioning properly and that the spray nozzles are fitted with hardened stainless steel or ceramic tips rather than soft brass, which would rapidly erode under the abrasive suspension.
3. Operational Decision: The certified applicator selects the WDG formulation, mitigating both crop injury in extreme desert heat and dermal toxicity hazards for the spray crew, while confirming that sprayer agitation and hardened nozzles handle the physical suspension effectively.

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Key Takeaways Summary

• Active Ingredients (AI) provide pesticidal activity, while Inert Ingredients provide carrying, dissolving, emulsifying, wetting, and stabilizing functions.
• Emulsifiable Concentrates (EC) form milky emulsions; their petroleum solvents accelerate dermal absorption, degrade rubber hoses, and pose phytotoxicity hazards in hot weather.
• Suspension Concentrates (SC/F) suspend insoluble solids in liquids, eliminating powder dust hazards while requiring continuous moderate agitation.
• Wettable Powders (WP) form suspensions requiring vigorous mechanical agitation, erode pumps and nozzles, and pose serious handler inhalation dust hazards.
• Water-Dispersible Granules (WDG/DF) deliver the performance of wettable powders while drastically suppressing inhalation dust during measuring and loading.