5.2 Dry & Misc Formulations (WP, WDG/DF, G, P, Fumigants)

5.2 Dry & Misc Formulations (WP, WDG/DF, G, P, Fumigants)

Dry and specialized miscellaneous pesticide formulations are manufactured for application conditions where liquid formulations are impractical, hazardous to target foliage, or ineffective against specific target pests. Dry products range from dry powders and dust-free granules mixed with water in a spray tank to dry granules, dusts, pellets, edible baits, and gaseous fumigants applied directly to the target environment.

Each dry formulation presents unique operational demands regarding applicator inhalation exposure during handling, nozzle erosion, off-target particle drift, and application machinery requirements.

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Wettable Powders (WP or W)

A Wettable Powder (WP or W) is a dry, finely ground formulation consisting of a solid active ingredient combined with dry inert carriers (such as clay or talc) and wetting agents. Wettable powders look like flour or fine talcum powder.

Mixing and Spray Tank Behavior

Wettable powders do not dissolve in water. When mixed with water in a spray tank, the wetting agents allow the dry powder particles to disperse throughout the liquid, forming a suspension.

Inhalation Hazard During Tank Loading

The primary health hazard associated with WP formulations occurs during measuring, opening bags, and pouring dry powder into the spray tank loading hatch. The fine powder easily becomes airborne, creating an extreme inhalation hazard for the applicator. Applicators must wear an approved dust-mist filtering respirator, eye protection, and gloves during all mixing and loading operations.

WETTABLE POWDER (WP) VS. WATER-DISPERSIBLE GRANULE (WDG/DF)

[ WP Container ]  ===> Fine Dusty Powder     ===> High Inhalation Hazard during Loading
[ WDG Container ] ===> Dust-Free Granules   ===> Low Inhalation Hazard, Disintegrates in Water

Agitation and Nozzle Abrasion

• Constant Vigorous Agitation: WP particles are relatively heavy solid grains. They require continuous, aggressive mechanical agitation in the spray tank. If agitation fails even briefly, the powder will rapidly settle to the tank bottom.
• Severe Nozzle Erosion: The dry clay and active ingredient particles are highly abrasive. Passing WP spray mixtures through spray nozzles under high pressure quickly erodes soft nozzle orifices (especially brass, aluminum, and plastic), expanding the orifice size and increasing spray volume output far beyond calibrated rates. Hardened stainless steel, ceramic, or tungsten carbide nozzle tips are recommended for WP applications.

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Water-Dispersible Granules (WDG) and Dry Flowables (DF)

Water-Dispersible Granules (WDG), also termed Dry Flowables (DF), are dry formulations designed to combine the safety advantages of wettable powders with the handling ease of liquid flowables.

Physical Composition and Performance

WDGs are formulated as small, dry granules or extruded pellets. When added to water in the spray tank, the granules absorb water and rapidly break down (disintegrate) into fine particles, creating a suspension identical to a wettable powder.

Advantages over Wettable Powders

• Reduced Inhalation Risk: Because WDG/DF particles are formed into coarse granules rather than fine powder, they produce virtually no airborne dust during measuring and tank pouring, dramatically lowering inhalation risks for applicators.
• Easier Pouring and Measuring: Granules pour cleanly out of containers without clinging to container walls, leaving less chemical residue in empty packaging.
• Tank Behavior: Like WPs, WDGs require continuous mechanical agitation to maintain suspension and cause abrasive wear on soft nozzle tips.

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Dusts (D)

A Dust (D) is a ready-to-use dry formulation containing a low concentration of active ingredient (typically 1% to 10%) mixed with an extremely fine inert carrier such as powdered talc, chalk, clay, or volcanic ash.

Application Characteristics and Off-Target Drift

Dusts are applied completely dry—they are never mixed with water. Specialized dust applicators (such as hand bellows, bulb dusters, or power dusters) blow fine dust clouds onto target surfaces.

• Extreme Drift Potential: Dust particles are extremely light. Even light breezes (under 3 mph) will carry dust particles off-target, creating high drift hazards to nearby crops, livestock, homes, and bystanders.
• Inhalation and Weather Sensitivity: Applicators face high respiratory exposure during application. Furthermore, dusts easily wash off plant foliage during rain and do not adhere well to dry surfaces. Dusts are primarily restricted to indoor crevice treatments, structural voids, livestock dusting, or specialized agricultural spot applications.

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Granules (G) and Pellets (P)

Granular (G) and Pelletized (P) formulations consist of active ingredients applied to or absorbed into dry, coarse particles of inert carriers such as clay, ground corn cobs, walnut shells, or synthetic polymers. Granules are larger and heavier than dust particles, while pellets are dense, uniform molded cylinders.

Operational Advantages of Granular Formulations

1. Minimal Off-Target Drift: Because granular particles are heavy and coarse, they settle rapidly to the ground, virtually eliminating atmospheric spray drift.
2. Low Applicator Hazard: Granules produce minimal dust, presenting very low inhalation hazards and lower dermal absorption risks during loading.
3. Targeted Soil Placement: Granules slide off plant foliage without sticking, falling directly to the soil surface or turf thatch layer to control soil-dwelling pests, weed seeds, or root pathogens.

Disadvantages and Wildlife Ingestion Hazards

• Required Moisture: Granular active ingredients remain trapped in the inert carrier until rainfall or overhead irrigation leaches the chemical out into the soil solution.
• Avian Wildlife Hazard: Birds often mistake granular pesticide particles for grit or food seeds. Ingesting just a few pesticide-coated granules can be fatal to songbirds and upland game birds.

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Baits (B)

A Bait (B) formulation combines a pesticide active ingredient (insecticide or rodenticide) with an edible food attractant (such as grain, sugar, meat meal, molasses, or peanut butter). Pests are attracted to the bait, consume it, and ingest a lethal dose.

Safety Concerns: Secondary Toxicity and Non-Target Ingestion

• Child and Pet Hazard: Edible baits are naturally attractive to non-target domestic pets, livestock, and young children. Baits must always be placed inside tamper-resistant bait stations or in concealed locations inaccessible to non-target organisms.
• Secondary Poisoning: Predators or scavengers (such as hawks, owls, dogs, and cats) that feed on rodents or insects dying from anticoagulant bait ingestion can suffer secondary lethal poisoning.

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Fumigants

Fumigants are specialized pesticide formulations that deliver active ingredients in the form of a gas. Some fumigants are stored under pressure as liquids or solids and vaporize into toxic gas upon release or exposure to atmospheric moisture (e.g., aluminum phosphide reacting with moisture to release phosphine gas).

Characteristics and Operational Requirements

• Non-Selective Penetration: Fumigant gases penetrate deeply into soil pores, grain mass, wood structures, and wrapped commodities, killing all living organisms within the enclosed space (insects, nematodes, weeds, rodents, fungi).
• Extreme Inhalation Fatality Risk: Fumigants present the highest inhalation toxicity of all pesticide formulations. A single breath of concentrated fumigant gas can cause severe lung edema, neurological damage, or immediate fatality.
• Specialized Equipment and Quarantine: Application requires total gastight enclosure (tarping or structural sealing), positive-pressure Self-Contained Breathing Apparatus (SCBA) or supplied-air respirators, calibrated gas detection instruments, and strict multi-day site quarantine and aeration monitoring.

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Summary Comparison of Dry & Miscellaneous Formulations