3.2 Dry Formulations, Baits & Fumigants

3.2 Dry Formulations, Baits & Fumigants

Core Principle: Dry pesticide formulations are manufactured by impregnating, coating, or blending active ingredients onto solid inert carriers such as finely ground clays, talc, diatomaceous earth, walnut shells, or synthetic polymer granules. Dry formulations fall into two distinct operational categories: those mixed with water before spraying (WP, SP, WDG/DF, WSP) and those applied directly in dry form without a liquid carrier (G, P, D, B, Fumigants).

Selecting dry formulations involves weighing critical trade-offs between applicator inhalation hazards during mixing, equipment wear, application convenience, and non-target wildlife exposure.

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Dry Formulations Diluted in Water

1. Wettable Powders (WP or W)

A Wettable Powder (WP or W) is a dry, dust-like formulation consisting of a solid active ingredient (typically 25% to 80% a.i.) blended with an inert powder carrier (such as clay or talc) and surface-active wetting and dispersing agents.

• Behavior in Water: Insoluble in water. When added to the spray tank, the wetting agents allow the dry powder to absorb water and disperse into a suspension of fine solid particles.
• Agitation Requirement: Continuous and vigorous mechanical or hydraulic agitation is mandatory. If agitation stops, the insoluble particles will quickly settle to the bottom of the spray tank, creating a dense sludge that plugs lines and leads to uneven application rates.
• Equipment Abrasion: The inert clay and mineral particles are highly abrasive. Pumping a WP suspension causes rapid abrasive erosion of soft pump impellers, pressure relief valves, and soft nozzle tips (brass and aluminum). Applicators must use hardened stainless steel or ceramic nozzles.
• Severe Inhalation Dust Hazard: The greatest danger associated with WPs occurs during measuring, scooping, and dumping into the spray tank. Fine particles become airborne as toxic dust, presenting a severe acute inhalation and eye exposure hazard. Applicators must wear a NIOSH-approved particulate respirator (N95 or higher) and chemical-splash goggles when mixing.
• Slurry Pre-Mixing: Best management practice requires creating a slurry—pre-mixing the measured WP with a small amount of water in a clean bucket to form a smooth, lump-free liquid before pouring it into the partially filled spray tank.
• Phytotoxicity: WPs carry very low phytotoxicity risks because they contain no petroleum-based solvents.

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2. Soluble Powders (SP) & Water-Soluble Packets (WSP)

Soluble Powders (SP)

• Composition & Behavior: A dry formulation containing a finely ground active ingredient (typically 50% to 90% a.i.) that dissolves completely in water to form a true, transparent solution.
• Operational Profile: Unlike WPs, once an SP is thoroughly dissolved, no continuous agitation is required, and the spray mix is completely non-abrasive to nozzles and pump components. It will not clog fine strainer screens.
• Handling Risk: Like WPs, raw dry SPs generate airborne dust during measuring and dumping, posing an acute inhalation risk.

Water-Soluble Packets (WSP)

• Mechanism: To eliminate the severe inhalation and dermal hazards of handling dry powders (WP and SP), manufacturers pre-weigh precise doses of pesticide into pre-sealed bags made of polyvinyl alcohol (PVA) film.
• Mixing Procedure: The unopened packet is dropped directly into the spray tank containing water. Within minutes, the PVA film completely dissolves, releasing the pesticide into the water with zero dust generation and zero applicator contact.
• Handling Precautions: WSPs must be kept dry until placed in the tank. Handlers must wear dry chemical-resistant gloves. WSPs must be added to clean water before any oils, surfactants, or liquid fertilizers are added, as petroleum products or cold water can prevent the PVA film from dissolving properly.

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

Water-Dispersible Granules (WDG) and Dry Flowables (DF) are functionally identical terms describing dry formulations engineered as small, uniform, dust-free granules.

• Composition & Technology: An insoluble solid active ingredient is micro-milled and agglomerated into small granule-sized pellets using water-soluble binders and dispersing agents.
• Behavior in Water: When added to water, the granules break apart rapidly and disperse throughout the liquid carrier, forming an insoluble suspension identical in spray characteristics to a Wettable Powder.
• Advantages over WP:
  • Virtually Dust-Free: Dramatically reduces the inhalation and eye exposure hazards during measuring and tank loading.
  • Pourability: Pours cleanly and smoothly from plastic jugs and measuring cylinders like dry grains of sand, without sticking to container walls.
• Operational Requirements: Like WPs, WDGs/DFs require continuous tank agitation and cause abrasive wear on soft nozzle tips.

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Dry Formulations Applied Directly (Without Water Dilution)

1. Granules (G) and Pellets (P)

Granular (G) and Pellet (P) formulations consist of active ingredient (usually 1% to 15% a.i.) coated or impregnated onto coarse, dry inert carrier particles such as clay, ground corn cobs, walnut shells, or fertilizer granules. Pellets are extruded under pressure into uniform cylinders.

• Application Method: Applied directly to soil, turfgrass, ornamental beds, or water bodies using broadcast granular spreaders, drop spreaders, or specialized in-furrow planting equipment. No water mixing is required.
• Activation: Once applied to the soil surface, granules remain inactive until exposed to soil moisture, rainfall, or supplemental irrigation, which dissolves the active ingredient and leaches it into the soil profile and root zone.
• Advantages: Low drift hazard (large, heavy particles resist wind displacement); zero mixing or liquid handling; low applicator inhalation exposure.
• Avian Wildlife Hazard (Critical Exam Concept): Granular formulations pose a severe poisoning risk to birds (such as quail, pheasants, songbirds, and waterfowl). Birds mistake granules for seeds or intentionally ingest them as digestive gizzard grit to help grind food. A single ingested toxic granule can be lethal. Applicators must ensure proper soil incorporation, avoid surface puddling, and immediately clean up all spills on hard surfaces (driveways, loading pads).

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2. Dusts (D)

A Dust (D) is a ready-to-use dry powder containing a very low concentration of active ingredient (typically 0.5% to 10% a.i.) blended with an inert dry carrier like talc, chalk, or clay.

• Application: Applied completely dry using bulb dusters, hand-pump bellows, or power dusters.
• Uses: Primarily used for crack-and-crevice and void treatments in indoor structural pest control (e.g., treating wall voids, attics, pipe chases for cockroaches, bedbugs, or termites) and localized livestock pest treatments.
• Hazards: Dusts have an extreme drift hazard outdoors because the fine, lightweight particles remain suspended in air currents. They present high inhalation risks and must never be applied outdoors during windy conditions or in broadcast applications.

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3. Baits (B)

A Bait (B) is an edible food attractant (such as grains, sugars, animal fats, proteins, or peanut butter) mixed with a low concentration of active ingredient (usually 0.1% to 5% a.i.).

• Function: Target pests (rodents, ants, cockroaches, flies, slugs) are lured to the bait, ingest the chemical, and die from delayed acute or chronic toxicity. In social insects (ants, termites), worker pests carry bait back to the nest and distribute it to larvae and the queen through food sharing (trophallaxis).
• Safety & Regulatory Requirement: Because baits are formulated with attractive food bases, they present an extreme poisoning hazard to non-target children, domestic dogs, cats, and wildlife. Under Indiana and federal pesticide regulations, rodent baits used outdoors or in accessible indoor spaces must be placed inside certified, tamper-resistant bait stations.

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Fumigants

Fumigants are specialized pesticides that form toxic gases when applied. They are manufactured as pressurized liquefied gases (e.g., methyl bromide, sulfuryl fluoride) or as volatile solids/liquids that chemically react with atmospheric moisture to release lethal gas (e.g., aluminum phosphide pellets releasing phosphine gas).

Operational & Safety Profile

• Non-Selective Lethality: Fumigants are completely non-selective biocides; the toxic gas kills all living organisms within the treated space, including insects, nematodes, fungi, rodents, and humans, by interrupting cellular respiration.
• Total Penetration: Gas molecules diffuse freely into soil pores, grain masses, structural wall voids, wrapped commodity pallets, and raw timber.
• Extreme Acute Inhalation Risk: Fumigants present an immediate, life-threatening inhalation hazard. Gas molecules bypass ordinary clothing and particulate filters.
• Mandatory Safety Protocols:
  • In Indiana, all fumigation — soil, grain, structural, or commodity — falls under a single credential: Category 7d, Fumigation, which 355 IAC 4-1-3(10) requires of every individual using or supervising the use of pesticides that in the gaseous state are designed to kill or repel pests. There is no Indiana "Category 1b" and no separate agricultural-versus-structural fumigation category. A private applicator who uses a fumigant must pass the Core exam and the Category 7d exam. Federal core standards likewise flag that fumigants, aerial application, sodium cyanide, and sodium fluoroacetate all require additional certification beyond the base category (40 CFR 171.103(c)(7)(ii)).
  • Handlers must use specialized Supplied-Air Respirators (SCBA) or specific gas-canister respirators.
  • Real-time electronic gas monitoring instruments (photoionization detectors or colorimetric tubes) must be used to verify safety thresholds.
  • Strict enclosure sealing, warning placarding, security guards, buffer zones, and formal Fumigation Management Plans (FMPs) are legally mandated.

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Comparative Matrix of Dry Formulations