6.2 Pesticide Formulations & Physical Properties

6.2 Pesticide Formulations & Physical Properties

Every commercial pesticide product is a precise chemical mixture designed to deliver a toxicant effectively to a target pest while maintaining stability during storage, handling, and application. Understanding pesticide formulations—their physical states, behavior in spray tanks, risks to application equipment, and hazards to human handlers and non-target organisms—is a foundational requirement for Ohio commercial pesticide applicators.

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Active vs. Inert Ingredients

A pesticide product as sold in the container consists of two distinct components:

1. Active Ingredient (AI): The chemical component that produces the biological effect against the target pest (e.g., killing weeds, repelling insects, or inhibiting fungal growth). The active ingredient is always clearly identified on the front panel of the pesticide label by its common chemical name and chemical percentage by weight.
2. Inert Ingredients: Additives included by the manufacturer to dilute the active ingredient, improve handling, enhance storage stability, aid in mixing, or facilitate application. Inert ingredients may include liquid solvents, dry clays, emulsifiers, wetting agents, dyes, or preservatives. Although termed "inert" because they do not harm the target pest, these ingredients are not necessarily non-toxic to humans or non-target wildlife; many organic solvents in liquid formulations increase skin penetration or flame hazards.

The ratio of active ingredient to total weight determines the product's concentration. For example, a 4EC formulation contains 4 pounds of active ingredient per gallon of liquid product, while an 80WP contains 80% active ingredient by weight in dry powder form.

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Liquid Formulations

Liquid formulations are popular because they are easy to measure and pour. However, their liquid carriers and petroleum solvents introduce specific dermal absorption and equipment degradation risks.

Emulsifiable Concentrates (EC or E)

• Composition: Active ingredient dissolved in an organic petroleum solvent with an added emulsifier (a detergent-like agent that allows oil and water to mix).
• Appearance: Clear brown or amber liquid that turns milky white when mixed with water in the spray tank.
• Advantages: Easy to measure, pour, and mix; requires minimal tank agitation; non-abrasive to pump impellers and spray nozzles; leaves little visible residue on treated foliage.
• Disadvantages & Hazards: High dermal absorption hazard because petroleum solvents readily penetrate human skin; high risk of phytotoxicity (plant burning) in hot weather; causes rubber hose and gasket swelling or degradation; flammable.

Solutions (S)

• Composition: Active ingredient that dissolves completely in water or a specified liquid carrier, forming a true chemical solution.
• Behavior: Once mixed, the pesticide will not settle out or separate. Requires no agitation after initial thorough mixing.
• Use: Common for systemic herbicides and indoor pest control applications.

Flowables / Suspensions (F or L)

• Composition: Finely ground, insoluble solid active ingredient suspended in a liquid carrier (essentially a pre-wetted wettable powder in liquid form).
• Behavior: Requires moderate agitation in the spray tank to prevent settling. Leaves a visible film on leaves and can cause moderate nozzle wear.

Ultra-Low Volume (ULV)

• Composition: Near 100% active ingredient applied in extremely fine droplets at rates less than 0.5 gallons per acre.
• Hazards: High vapor drift hazard; requires specialized application equipment; presents severe dermal absorption and inhalation risks to applicators.

Microencapsulated (ME or M)

• Composition: Liquid or solid active ingredient encased in microscopic plastic capsules suspended in a liquid carrier. Upon application, the active ingredient slowly diffuses through the capsule shell over time.
• Advantages: Provides prolonged residual pest control; significantly reduces acute applicator dermal toxicity.
• Disadvantages: Severe hazard to honeybees. Foraging honeybees mistake the microscopic capsules for pollen grains, carrying them back to the hive where the brood is poisoned.

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Dry Formulations

Dry formulations are manufactured as powders, dusts, or granules. They eliminate petroleum solvent hazards but often introduce dust inhalation and pump abrasion challenges.

Detailed Breakdown of Key Dry Formulations

• Wettable Powders (WP): Dry, finely ground formulations that do not dissolve in water; instead, they form a suspension. They require continuous mechanical tank agitation to prevent the powder from settling to the bottom. WPs are non-phytotoxic and less readily absorbed through skin than ECs, but the dry dust poses a critical inhalation hazard during measuring and mixing, and the suspended mineral particles severely abrade brass and aluminum pump impellers and nozzle orifices.
• Water-Dispersible Granules (WDG) / Dry Flowables (DF): Formulated as small, dust-free granules that break apart into a fine suspension when added to water. WDGs offer the safety benefit of reduced dust inhalation during tank loading while retaining the storage stability of dry products.
• Granules (G) and Pellets (P): Coarse particles designed for direct dry application to soil or turf without water. Granules exhibit minimal drift hazard but require specialized dry spreaders and present ingestion hazards to seed-eating birds.

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Aerosols & Fumigants

• Aerosols (A): Contain active ingredients dissolved in solvent under high gas pressure or generated via thermal foggers. Used primarily for structural space treatments; high inhalation and flammability risk.
• Fumigants: Pesticides that form toxic gases or vapors when applied. Fumigants (such as aluminum phosphide or chloropicrin) are non-selective, penetrating soil, wood, or grain to kill all living organisms. They require specialized Category 10 (Fumigation) certification, specialized gas-tight PPE, and continuous gas detection monitoring.

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Spray Tank Adjuvants

An adjuvant is a chemical added to a pesticide spray tank mixture to modify physical properties or enhance performance. Adjuvants do not possess pesticide activity on their own.

1. Surfactants (Surface Active Agents): Reduce the surface tension of water spray droplets, allowing them to spread out into a thin, uniform film over waxy leaf surfaces or insect cuticles rather than beading up and rolling off.
2. Stickers: Increase the adherence of spray droplets to plant foliage, preventing the pesticide from being washed off by rain or irrigation.
3. Spreaders-Stickers: Combine wetting and adhesive properties into a single additive.
4. Anti-Foaming Agents: Suppress excessive foam creation caused by tank agitation when mixing liquid or powder formulations.
5. Drift Retardants / Thickeners: Increase spray droplet size and fluid viscosity, significantly reducing the formation of microscopic fines (<150 microns) that drift off-target.
6. Buffers / Acidifiers: Adjust and stabilize spray water pH. Many organophosphate and carbamate insecticides undergo alkaline hydrolysis (rapid chemical breakdown) when mixed in alkaline water (pH > 7.5); acidifying buffers maintain optimal pH (5.5–6.5) to preserve pesticide potency.