3.3 Dry & Specialty Formulations: Physical Characteristics & Safety

3.3 Dry & Specialty Formulations: Physical Characteristics & Safety

Dry pesticide formulations are widely manufactured for both spray-applied tank mixtures (requiring water carrier) and direct dry-applied soil, structural, or bait treatments. The physical characteristics of the inert carrier—ranging from fine talc and attapulgite clay to coarse walnut shells and granulated corn cobs—dictate how the product behaves in storage, during mixing, in the sprayer tank, and across the outdoor environment.

For North Carolina pesticide applicators, mastering dry formulations requires understanding the distinction between products that dissolve (forming true solutions) and those that suspend (forming abrasive slurries), as well as managing the severe inhalation hazards of fine powders and the unique wildlife hazards of dry granules.

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1. Wettable Powders (WP / W)

A Wettable Powder (WP or W) is a dry, finely divided formulation containing 25% to 80% active ingredient blended with an inert mineral carrier (such as bentonite, attapulgite clay, or diatomaceous earth) and synthetic wetting and dispersing agents.

+-----------------------------------------------------------------------------+
|                      WETTABLE POWDER (WP) TANK BEHAVIOR                     |
|                                                                             |
|   [ MEASURING / LOADING ]                 [ IN SPRAY TANK ]                 |
|   +-----------------------+              +-----------------------+          |
|   | Dry Insoluble Powder  |   + Water    | Insoluble Particles   |          |
|   | (Fine Mineral Carrier)| -----------> | Suspended in Water    |          |
|   | * Severe Inhalation   |   Strong     | (Forms Cloudy Slurry) |          |
|   |   Dust Hazard!        |   Agitation  | * Abrasive to Nozzles |          |
|   +-----------------------+              +-----------------------+          |
|   * MUST be pre-slurried; settles rapidly to tank bottom if agitation stops  |
+-----------------------------------------------------------------------------+

Physical Behavior & Suspension Mechanics

• Insoluble in Water: Wettable powders do NOT dissolve in water. When added to a tank, the wetting agents allow water to penetrate the dry carrier, creating a physical suspension of microscopic solid particles.
• Agitation Mandate: Requires continuous, aggressive mechanical or hydraulic agitation. If agitation stops, the heavy mineral particles settle rapidly to the bottom of the tank. Restarting agitation after settling can be difficult and may cause clogged suction lines.
• Pre-Slurrying Protocol: Applicators should always mix wettable powders with a small volume of water in a clean bucket to form a smooth, lump-free slurry before pouring the mixture into the partially filled spray tank.

Hazards & Equipment Wear

• Severe Inhalation Hazard: During measuring, weighing, and tank loading, fine toxic dust becomes airborne. Handlers must wear NIOSH-approved particulate respirators (TC-84A approved, such as N95, R95, or P95 filters) to prevent pulmonary poisoning.
• Abrasive Wear on Equipment: Suspended clay and mineral particles are highly abrasive under pressure. They rapidly enlarge nozzle orifices on brass and aluminum tips, erode pump rollers in roller pumps, and score pressure relief valves.
• Strainer Clogging: Particles can quickly clog fine line strainers and nozzle screens. Screens finer than 50-mesh should generally not be used with high-concentration WP mixtures.
• Visible Residue: Leaves a chalky, visible white film on foliage and fruit, which may be undesirable for ornamental landscape plantings or fresh-market produce.

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

Water-Dispersible Granules (WDG), also marketed as Dry Flowables (DF), are dry formulations developed specifically to overcome the severe inhalation dust hazards associated with wettable powders.

+-----------------------------------------------------------------------------+
|                   WATER-DISPERSIBLE GRANULES (WDG / DF)                     |
|                                                                             |
|   [ POURING / MEASURING ]                 [ IN SPRAY TANK ]                 |
|   +-----------------------+              +-----------------------+          |
|   | Granular Agglomerates |   + Water    | Granules Disintegrate |          |
|   | (Pours Like BBs/Grain)| -----------> | Into Fine Micro-WP    |          |
|   | * Dust-Free Handling! |   Agitation  | Suspension in Water   |          |
|   +-----------------------+              +-----------------------+          |
|   * Same suspension/abrasion properties as WP, but safe to pour without dust|
+-----------------------------------------------------------------------------+

Comparison: WDG/DF vs. WP

• Physical Form: Formulated as small, uniform, dust-free granules or pellets that pour cleanly from the container like tiny BBs or grain.
• Dispersion in Water: Upon contact with water in the spray tank, the binding matrix dissolves, causing the granules to disintegrate into microscopic particles that form a suspension identical to a wettable powder.
• Agitation & Abrasion: Requires continuous, vigorous mechanical/hydraulic agitation and exhibits the same abrasive nozzle wear characteristics as wettable powders.
• Safety Advantage: Dramatically reduces handler inhalation exposure during measuring and loading because there is virtually no airborne chemical dust.

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3. Soluble Powders (SP / WSP)

A Soluble Powder (SP) is a dry formulation containing 50% to 90% active ingredient that dissolves completely in water to form a true, transparent chemical solution.

+-----------------------------------------------------------------------------+
|                      SOLUBLE POWDER (SP) CHARACTERISTICS                    |
|                                                                             |
|   +-----------------------+              +-----------------------+          |
|   | Dry Soluble Powder    |   + Water    | True Homogenous       |          |
|   | + Soluble Carrier     | -----------> | Chemical Solution     |          |
|   | (Dissolves Molecularly|   Initial    | (Transparent Liquid)  |          |
|   +-----------------------+   Mixing     +-----------------------+          |
|   * Once dissolved, NEVER settles; completely NON-ABRASIVE to nozzles/pumps |
+-----------------------------------------------------------------------------+

Critical Differences Between SP and WP

Water-Soluble Packets (WSP)

Many WP and SP formulations are packaged inside pre-measured Water-Soluble Packets (WSP) made of polyvinyl alcohol (PVA) film. The applicator drops the entire sealed packet directly into the partially filled spray tank. The water dissolves the outer PVA film within 1 to 2 minutes, releasing the product without any handler contact or airborne dust exposure.

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4. Granules (G) and Pellets (P)

Granules (G) and Pellets (P) are dry formulations designed to be applied directly to soil, turf, or aquatic environments without mixing in water.

+-----------------------------------------------------------------------------+
|                         GRANULAR (G) FORMULATIONS                           |
|                                                                             |
|   +---------------------------------------------------------------------+   |
|   | Coarse Inert Core (Clay, Corn Cobs, Walnut Shells, 1-15% a.i.)      |   |
|   +---------------------------------------------------------------------+   |
|        | Applied dry via rotary/drop spreaders                              |
|        v                                                                    |
|   [ Soil Surface ] + Rainfall / Irrigation ---> Releases a.i. to Root Zone  |
|                                                                             |
|   * CRITICAL HAZARD: Ingested as food/grit by birds -> Lethal avian toxicity|
+-----------------------------------------------------------------------------+

Composition & Application Mechanics

• Low Active Ingredient Percentage: Typically contains 1% to 15% active ingredient coated onto or absorbed into coarse, heavy carrier particles (corncob fragments, attapulgite clay granules, recycled paper, or walnut shells).
• Pellets (P): Similar to granules but extruded under high pressure into uniform, dense cylindrical pellets.
• Application Equipment: Applied dry using broadcast rotary spreaders, drop spreaders, tractor-mounted granular hoppers, or specialized aircraft seeders.
• Moisture Activation: Inactive until moisture (rainfall or supplemental irrigation) dissolves the coating, leaching the active chemical into the soil and root zone.

Advantages & Environmental Hazards

• Zero Spray Drift: Because particles are large and heavy, aerial drift is virtually non-existent under normal operating conditions.
• Low Handler Exposure: Pours cleanly with minimal dust, reducing dermal and respiratory exposure hazards.
• Avian & Wildlife Ingestion Hazard (High-Yield NC Exam Topic): Granules and pellets resemble weed seeds, grains, and mineral grit. Granivorous songbirds, waterfowl, and gamebirds (such as mourning doves, quail, and turkeys) actively seek out small hard particles to fill their muscular gizzards for grinding food. Birds that consume pesticide granules suffer acute, lethal poisoning. Applicators must mechanically incorporate granules into the soil or sweep spilled granules from hard surfaces immediately.

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5. Baits (B) and Dusts (D)

Baits (B)

• Composition: An active ingredient (usually low concentration, 0.25% to 5%) blended with an edible, highly attractive food carrier (such as peanut butter, grain meal, sugar, or animal fat).
• Deployment: Placed in targeted harborages, bait stations, or broadcast for controlling rodents, insects (cockroaches, ants, mole crickets), and vertebrate pests.
• Hazards: High risk of accidental ingestion by non-target domestic pets (dogs, cats), children, and non-target wildlife. Must be placed in tamper-resistant, lockable bait stations when applied in areas accessible to children or pets.

Dusts (D)

• Composition: A dry formulation containing a low percentage of active ingredient (1% to 10%) combined with a finely ground, lightweight inert carrier such as talc, chalk, or clay.
• Application: Applied dry using hand bulb dusters, bellows dusters, or power dusters.
• Hazards: Extremely high drift hazard outdoors. Generally restricted to indoor structural crack-and-crevice treatments, wall voids, animal direct treatments, and crawl spaces. Severe inhalation hazard requiring respiratory protection.

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6. Fumigants: Non-Selective Gaseous Biocides

Fumigants are specialized pesticidal chemicals that exist as gases or volatile liquids/solids that vaporize into toxic gases at ambient temperatures and pressures.

+-----------------------------------------------------------------------------+
|                        FUMIGANT CHARACTERISTICS & RISKS                     |
|                                                                             |
|   +-----------------------+              +-----------------------+          |
|   | Liquid/Solid/Gas      |   Release    | Penetrating Gas Phase |          |
|   | Precursor (Cylinder)  | -----------> | (Fills Enclosed Space |          |
|   | * Category I Toxicity |   Ambient    |  Kills All Living Org)|          |
|   +-----------------------+   Temp       +-----------------------+          |
|   * Completely non-selective; highest inhalation danger; requires SCBA/tarps|
+-----------------------------------------------------------------------------+

Key Operational Characteristics

• Non-Selective Action: Fumigants are completely non-selective biocides; they kill insects, nematodes, weed seeds, pathogens, rodents, fungi, and human beings within the treated enclosure.
• Total Gas Penetration: Gaseous molecules penetrate deeply into soil pores, grain mass, wood structures, and commodity packaging where liquid sprays cannot reach.
• Highest Toxicity Rating: Virtually all fumigants are classified as EPA Toxicity Category I (Signal Word: DANGER-POISON with Skull & Crossbones).
• Regulatory Mandates: Requires specialized applicator licensing categories, mandatory gas-tight sealing (tarpaulins/tents), established buffer zones, real-time air monitoring devices, and Self-Contained Breathing Apparatus (SCBA) or supplied-air respirators.

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7. Dry Formulations Comparison Matrix