8.2 Dry and Specialty Formulations (WP, WDG, G, Baits & Fumigants)

Dry and Specialty Pesticide Formulations (WP, WDG, DF, G, P, Baits & Fumigants)

Core Regulatory & Operational Principle: Dry and specialty pesticide formulations deliver active chemical molecules using solid carriers such as talc, kaolin clay, diatomaceous earth, bentonite, synthetic granules, or food attractants. Unlike liquid concentrates, dry formulations introduce unique handling challenges—most notably respirable dust inhalation hazards, abrasive mechanical wear on spray nozzles and pump impellers, wildlife ingestion threats, and volatile gaseous toxicity in fumigation. Understanding the physical behavior of dry particles in spray tanks, master handling protocols for Water-Soluble Packets (WSP), and enforcing strict containment for Granules (G) and Fumigants are mandatory competencies for Oregon certified applicators.

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1. Physical Classification of Dry Formulations

Dry formulations are categorized based on whether they are engineered to be diluted in a liquid carrier (spray tank suspensions) or applied dry in their native solid state.

+-----------------------------------------------------------------------------------------+
|                       CLASSIFICATION OF DRY PESTICIDE FORMULATIONS                      |
+-----------------------------------------------------------------------------------------+
| 1. MIXED WITH WATER & APPLIED AS SPRAY SUSPENSIONS:                                     |
|    * Wettable Powders (WP / W)               : Finely milled powder + clay carrier.     |
|    * Water-Dispersible Granules (WDG / DF)   : Agglomerated dust-free micro-granules.   |
|    * Water-Soluble Powders (SP / WSP)        : True dissolving dry powder crystals.     |
|    * Water-Soluble Packets (WSB / WSP)       : Pre-measured PVA film containment.       |
|                                                                                         |
| 2. APPLIED DIRECTLY IN DRY SOLID STATE (NO WATER):                                      |
|    * Granules (G)                            : Coarse porous particles (clay/corncob).  |
|    * Pellets (P / PS)                        : Extruded uniform cylinder/sphere pellets.|
|    * Dusts (D)                               : Ultra-fine talc powder (1% to 10% a.i.). |
|    * Baits (B)                               : Food attractant matrices + stomach toxin.|
|                                                                                         |
| 3. SPECIALTY VOLATILE CHEMICAL SYSTEMS:                                                 |
|    * Gaseous / Solid Fumigants               : Volatile gas/precursor penetrating space.|
|    * Micro-pelletized Soil Injections        : Moisture-activated chemical fumigants.   |
+-----------------------------------------------------------------------------------------+

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2. Wettable Powders (WP / W)

Wettable Powders represent one of the oldest and most chemically stable dry spray formulations. In a WP, a technical active ingredient (often solid at room temperature) is blended with finely ground inert mineral powders (such as kaolin clay, talc, or diatomaceous earth) and synthetic wetting and dispersing surfactants.

+-----------------------------------------------------------------------------------------+
|                         WETTABLE POWDER (WP) CHARACTERISTICS                            |
+-----------------------------------------------------------------------------------------+
| * Active Ingredient Concentration : Typically high (25% to 80% a.i. by dry weight).     |
| * Behavior in Spray Tank          : Forms an insoluble solid particle SUSPENSION.       |
| * Agitation Requirement           : CONTINUOUS VIGOROUS MECHANICAL AGITATION.           |
| * Nozzle & Pump Erosion           : HIGHLY ABRASIVE to soft metals (brass, aluminum).   |
| * Inhalation Safety Hazard        : EXTREME RESPIRABLE DUST HAZARD during measuring.    |
| * Foliar Safety                   : Very low phytotoxicity (contains NO oil solvents).  |
+-----------------------------------------------------------------------------------------+

Suspension Dynamics and Agitation Demands

Wettable powders never dissolve in water. When introduced to a spray tank, the mineral particles remain suspended only as long as kinetic energy is supplied by mechanical paddle shafts or high-volume hydraulic jet agitation.

• Rapid Gravitational Settling: If agitation ceases (e.g., during equipment breakdown or transit to the field), solid WP particles settle rapidly to the bottom of the tank, forming a dense, hard cake. Re-suspending settled WP cake requires vigorous manual scraping and prolonged high-shear agitation.
• Plugging of Filters and Screens: WP suspensions require coarse filtration (50-mesh strainers). Attempting to spray WP mixtures through fine 100-mesh nozzle screens results in instantaneous particulate bridging, pressure spikes, and clogged nozzles.

Mechanical Abrasiveness and Equipment Wear

Because mineral carriers (clays, silicates) possess high hardness ratings on the Mohs scale, WP suspensions act as liquid sandpaper when pumped under pressure.

• Nozzle Wear Rates: Brass and aluminum nozzle orifices wear rapidly when spraying WP suspensions, increasing output volume by $10%\text{ to } 25%$ within 20 to 50 hours of operation. This uncalibrated wear results in massive chemical overdosing and crop damage. Applicators spraying WP formulations must use hardened stainless steel, ceramic, or polymer nozzle tips.
• Pump Selection: Roller pumps and internal gear pumps suffer rapid internal scoring from WP grit. Diaphragm pumps and centrifugal pumps are strongly preferred for wettable powder applications.

Operator Safety & Respiratory Protection

The primary occupational hazard of wettable powders is inhalation exposure during package opening, weighing, and hopper loading. Fine airborne dust particles ($< 10\ \mu\text{m}$) bypass upper airway filtration and enter the deep pulmonary alveoli. Under OSHA and EPA Worker Protection Standard (WPS) mandates, handlers mixing and loading dry WPs must wear a NIOSH-approved particulate filtering respirator (TC-84A, such as an N95, R95, or P100 mask) along with protective eyewear and chemical-resistant gloves.

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

Water-Dispersible Granules (WDG), often termed Dry Flowables (DF), represent a major engineering advancement designed to overcome the dust inhalation hazards and poor pouring characteristics of wettable powders.

+-----------------------------------------------------------------------------------------+
|                        WDG / DF vs. WETTABLE POWDER (WP)                                |
+-----------------------------------------------------------------------------------------+
| FEATURE                   | WETTABLE POWDER (WP)        | WATER-DISPERSIBLE GRANULE(WDG)|
+---------------------------+-----------------------------+-------------------------------+
| Physical Form             | Ultra-fine dusty powder     | Small, dust-free granules     |
| Measuring & Pouring       | Generates airborne dust     | Pours like dry liquid / beads |
| Operator Inhalation Risk  | High inhalation exposure    | Extremely low dust generation |
| Packaging Cleanout        | Clings to interior jug walls| Empties cleanly & completely  |
| Tank Behavior             | Forms solid suspension      | Disintegrates into suspension |
| Agitation Needed          | Continuous vigorous         | Continuous vigorous           |
| Abrasiveness to Nozzles   | Highly abrasive             | Highly abrasive (once broken) |
+---------------------------+-----------------------------+-------------------------------+

Granule Disintegration in Water

When WDG/DF granules are poured into water, the hydrophilic binders within each granule rapidly absorb water, causing the granule to spontaneously swell, burst, and disperse into micron-sized individual particles. The resulting spray tank suspension is physically and operationally identical to a wettable powder suspension, requiring continuous agitation and hardened nozzle tips.

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4. Water-Soluble Packets (WSP / WSB)

Water-Soluble Packets (WSP)—also designated as Water-Soluble Bags (WSB)—utilize specialized packaging engineering to achieve complete operator isolation from highly toxic dry active ingredients.

+-----------------------------------------------------------------------------------------+
|                     WATER-SOLUBLE PACKET (WSP / WSB) TECHNOLOGY                         |
+-----------------------------------------------------------------------------------------+
| [Outer Protective Foil Pouch] ──> Cut open carefully; keep dry; do NOT puncture WSP.   |
|               │                                                                         |
|               └──> [Inner PVA Film Packet] (Contains Pre-Measured WP or WDG Chemical)   |
|                            │                                                            |
|                            └──> Dropped INTACT into spray tank water carrier            |
|                                         │                                               |
|                                         └──> Polyvinyl Alcohol (PVA) Dissolves in Water |
|                                              Releasing chemical safely with ZERO DUST!  |
+-----------------------------------------------------------------------------------------+

Critical Operational Rules for Water-Soluble Packets

While WSPs eliminate inhalation hazards, improper mixing practices cause severe operational failures:

1. Never Cut or Puncture the Inner Packet: The PVA packet must be placed into the tank completely intact. Cutting or puncturing the packet exposes the handler to toxic dust and destroys the pre-calibrated dosage unit.
2. Add to Tank Water FIRST (Clean Water Carrier): WSP packets MUST be introduced into clean water before adding any other chemical products. The tank should be filled $1/3\text{ to } 1/2\text{ full}$ with clean water, agitation engaged, and the WSP packets allowed to dissolve completely (typically 3 to 5 minutes) before proceeding.
3. Avoid Cold Water Shock: Water temperatures below $45^\circ\text{F} (7.2^\circ\text{C})$ dramatically slow PVA dissolution, requiring extended agitation times up to 10–15 minutes.
4. The Chemical Cross-Linking Trap (Oils, Boron & Electrolytes):
   • If an applicator adds Emulsifiable Concentrates (EC), crop oils, or boron-containing liquid fertilizers into the tank before the PVA packet dissolves, the boron or organic solvents chemically react with the polyvinyl alcohol film in an irreversible cross-linking reaction.
   • This reaction transforms the PVA film into an insoluble, rubbery, gummy mass that encapsulates the dry chemical, fails to dissolve, and instantly plugs suction strainers, pumps, and spray lines.

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5. Granules (G) and Pellets (P)

Granular (G) and Pellet (P) formulations are dry solid systems engineered for direct application to soil, turfgrass thatch, aquatic sediment, or right-of-way zones without liquid dilution.

+-----------------------------------------------------------------------------------------+
|                      ANATOMY OF A GRANULAR / PELLET FORMULATION                         |
+-----------------------------------------------------------------------------------------+
| * Inert Carrier Core      : Dense mineral particles (calcined clay, attapulgite,        |
|                             bentonite) or organic cores (crushed corncobs, walnut shells|
| * Active Ingredient Load  : Relatively low concentration (typically 1% to 15% a.i.).   |
| * Binder / Impregnator    : Polymer adhesive fixing chemical to carrier surface.        |
| * Release Mechanism       : Soil moisture, rainfall, or microbial degradation.          |
+-----------------------------------------------------------------------------------------+

Operational Advantages of Granular Formulations

• Zero Spray Drift: Granule particle mass ($300\text{ to } 2,000\ \mu\text{m}$) is hundreds of times greater than hydraulic spray droplets, completely eliminating off-target wind drift under normal operating conditions.
• Canopy Penetration: Heavy granules drop cleanly through dense plant canopies, turfgrass blades, and forest brush to deliver active ingredients directly to the soil surface or root zone.
• Low Operator Toxicity: Eliminates liquid splash hazards and hydraulic spray mist inhalation.

Critical Environmental Hazard: Wildlife and Avian Ingestion

The greatest environmental threat associated with granular pesticides is secondary poisoning of birds and wildlife.

• Seed and Grit Mimicry: Songbirds, upland game birds (pheasants, quail), and waterfowl actively seek out small hard particles to serve as gastric grit in their muscular gizzards for grinding food, or mistake pesticide granules for agricultural seeds. Ingesting just a few granules of an organophosphate or carbamate insecticide (e.g., terbufos, ethoprop) delivers a lethal oral dose within minutes.
• Mandatory Spill Cleanup & Soil Incorporation: Under Oregon and federal law, any granular pesticide spilled during loading, hopper filling, or equipment turning on row ends MUST be immediately swept up and recovered, or fully incorporated into the soil via mechanical tillage or heavy discing to eliminate wildlife exposure.

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6. Dusts (D) and Baits (B)

Dust Formulations (D)

Dust formulations consist of low concentrations of active ingredient ($1%\text{ to } 10%\text{ a.i.}$) blended with an ultra-fine, lightweight inert carrier such as talc, pyrophyllite, or diatomaceous earth.

• Application Scope: Applied exclusively in dry form using specialized power or hand dusters. Utilized primarily in structural crack-and-crevice treatments, enclosed wall voids, livestock dust bags, and agricultural seed box treatments.
• Operational Hazards: Dusts represent an extreme off-target drift hazard outdoors due to minute particle mass ($< 30\ \mu\text{m}$). Outdoor agricultural dusting is largely obsolete. Dusts create high inhalation risks and readily irritate mucous membranes and ocular tissue.

Bait Formulations (B)

Baits blend a low concentration of active ingredient ($0.05%\text{ to } 5%\text{ a.i.}$) with an edible, highly palatable food attractant matrix (proteins, sugars, cereal grains, peanut butter oils, or grain meals) designed to entice target pests into ingesting a lethal dose.

• Target Pests: Rodents (rats, mice, voles), gastropods (slugs, snails), pest ants, cockroaches, yellowjackets, and vertebrate pests.
• Safety Mandates (Tamper-Resistant Stations): Because baits are engineered to be palatable food substances, they present severe poisoning hazards to non-target children, domestic dogs, cats, livestock, and predatory wildlife (via secondary toxicosis). Federal and Oregon regulations mandate that outdoor rodenticide baits and urban baits must be secured inside EPA-certified, tamper-resistant, anchored bait stations.

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7. Gaseous and Precursor Fumigants

Fumigants are specialized, non-selective chemical formulations that exist as a gas or generate volatile chemical vapors at ambient field temperatures and pressures. They are applied to soil, structural buildings, enclosed grain silos, or shipping containers to eradicate nematodes, soil-borne fungi, weed seeds, wood-boring beetles, and stored-product insects.

+-----------------------------------------------------------------------------------------+
|                             FUMIGANT CHEMICAL CATEGORIES                                |
+-----------------------------------------------------------------------------------------+
| 1. TRUE GASEOUS FUMIGANTS (Pressurized Cylinders):                                      |
|    * Sulfuryl fluoride (Vikane®) : Odorless structural/wood-destroying insect fumigant. |
|    * Methyl bromide              : Restricted quarantine & pre-shipment fumigant.       |
|                                                                                         |
| 2. VOLATILE LIQUID PRECURSORS (Soil Injected):                                          |
|    * 1,3-Dichloropropene (Telone®) : Injected liquid; volatilizes into nematicidal gas.  |
|    * Chloropicrin                  : Severe lachrymator (tear gas); warning agent.      |
|    * Metam sodium / Metam potassium: Hydrolyzes in moist soil to generate MITC gas.     |
|                                                                                         |
| 3. SOLID PRECURSOR FUMIGANTS (Moisture-Activated):                                      |
|    * Aluminum phosphide / Magnesium phosphide pellets: React with atmospheric humidity  |
|      to generate highly toxic, flammable Phosphine gas (PH3).                           |
+-----------------------------------------------------------------------------------------+

Strict Regulatory Controls and Fumigant Management Plans (FMP)

Fumigants fall under EPA Toxicity Category I (DANGER - POISON) and are among the most hazardous chemicals used in agriculture and structural pest control.

1. Fumigant Management Plan (FMP): Before initiating any agricultural soil or structural fumigation in Oregon, the certified applicator must author a legally binding, site-specific Fumigant Management Plan (FMP) documenting soil moisture, soil temperature, application depth, buffer zone distances, notification logs, emergency response protocols, and air monitoring schedules.
2. Buffer Zones & Posting: Buffer zones extending hundreds of feet from the treatment boundary must be calculated using EPA buffer look-up tables. Buffer zones must be posted with multi-lingual warning signs prohibiting entry.
3. Respiratory Equipment: Applicators and handlers must utilize positive-pressure Self-Contained Breathing Apparatus (SCBA) or supplied-air respirators, combined with real-time direct-reading gas detection devices (e.g., colorimetric detector tubes or photoionization detectors).
4. Tarping Engineering (TIF): Modern soil fumigation mandates high-barrier plastic tarps—specifically Totally Impermeable Film (TIF)—to trap fumigant vapors in the root zone and prevent toxic atmospheric venting.

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8. Dry and Specialty Formulation Comparative Summary