Chapter 4: Pesticide Formulations

Learning Objectives

• Describe what a pesticide formulation is.
• Explain why pesticides are formulated for end use.
• Distinguish between active and inert ingredients.
• State the meaning of abbreviations used for common formulations (WP, EC, G, etc.).
• List the factors to consider when choosing a formulation.
• Discuss the properties and pros/cons of common formulations.
• Explain the roles of adjuvants.

What Is a Pesticide Formulation?

In their pure ("technical grade") form, pesticide active ingredients are often:

• Extremely toxic
• Poorly mixable with water
• Unstable
• Difficult or unsafe to handle, transport, or store

Manufacturers add inert ingredients to make the product safer, easier to handle, and more effective. Inert ingredients have no pesticidal activity, but they're essential to the formulation.

A formulated product may contain:

• The active ingredient (a.i.) — controls the target pest.
• A carrier or diluent — organic solvent or mineral clay.
• Surface-active ingredients — stickers, spreaders.
• Other additives — stabilizers, dyes, safety enhancers.

Solution, Suspension, and Emulsion

Liquid pesticide products are usually one of these three things. Memorize the differences — the exam tests them directly.

Concentrates vs. Ready-to-Use (RTU)

Liquid concentrate examples: LC (Liquid Concentrate), EC (Emulsifiable Concentrate). Solid concentrate examples: WP (Wettable Powder), SP (Soluble Powder), WDG/DF (Water-Dispersible Granules / Dry Flowables).

Formulation Abbreviations

The brand name usually includes an abbreviation and sometimes a number indicating active-ingredient strength. For example, 80 WDG = 80% active ingredient, water-dispersible granule. In a 10-pound bag of 80 WDG, 8 lbs is a.i. and 2 lbs is inert. Liquid formulations usually state the a.i. in pounds per gallon: 4F = 4 pounds a.i. per gallon, flowable.

Choosing the Right Formulation

When more than one formulation is available, base your decision on:

• Legal, labeled uses
• The signal word
• Applicator safety
• Environmental safety
• Pest biology
• Site characteristics
• Target (surface to be treated)
• Appropriate and available application equipment

Ask: Is the intended use on the label? Do I have the right equipment? Can the formulation be applied in these conditions? Will it reach and stay on the target? Might it damage the surface? Is there a less hazardous option that still works?

Cost matters, but pesticide and pest management concerns come first.

Liquid Formulations

Emulsifiable Concentrate (E or EC)

Oil-soluble liquid a.i. + petroleum-based solvent + mixing agent. Usually 2 to 6 pounds of a.i. per gallon. Very versatile — used in agriculture, ornamentals, turf, forestry, structural, food processing, livestock, and public health. Works in many types of spray equipment.

Solutions (S) & Ready-to-Use Low-Concentrate Solutions (RTU)

RTU solutions contain a small amount of a.i. (often 1% or less). No mixing required. Convenient, low exposure risk, but high cost per unit of a.i. and limited availability.

Concentrate solutions (C, LC, WSC, WSL) require dilution with a liquid carrier — usually water, sometimes oil. Relatively easy to handle; no agitation needed; don't plug nozzles; no visible residues.

Liquid Baits

• Liquid insecticide baits — usually concentrated sugar solutions in ready-to-use bait stations for ants and cockroaches.
• Liquid rodenticide baits — mixed with water, placed in bait stations. Useful where sanitation is poor (traditional baits compete with other food) or where water is scarce.

Ultra-Low Volume (ULV)

Concentrates that are nearly 100% active ingredient. Used "as is" or diluted with only small amounts of specified solvent. Applied as very fine droplets at very low rates per area. Good for outdoor agricultural, forestry, ornamental, and mosquito control.

Invert Emulsions

Water-soluble pesticide dispersed in an oil carrier (usually fuel oil). Requires a special emulsifier. Consistency of mayonnaise; applied as very large droplets. Used mainly for weed control on rights-of-way to reduce drift to nontarget plants.

Oil phase doubles as a sticker-spreader — improves rainfastness, coverage, and penetration, reducing runoff.

Flowables (F or AF, sometimes L)

For active ingredients that won't dissolve in water OR oil (insoluble solids). A.i. is impregnated on a carrier (clay), ground to fine powder, then suspended in a small amount of liquid. Thick liquid suspension — combines properties of ECs and WPs.

Aerosols (A)

Active ingredient(s) + solvent. Two types:

• Ready-to-use aerosols — Pressurized sealed containers. Inert gas pushes pesticide through a fine opening to create fine droplets. Good for greenhouses, small indoor areas, localized outdoor spots. Commercial models hold 5-10 pounds and are refillable.
• Smoke or fog generator formulations — NOT packaged under pressure. Used in machines with rapidly whirling disks or heated surfaces to create fine mists. For insect control in structures and outdoor mosquito/biting fly control.

Aerosol hazards: inhalation risk, flammable/explosive if punctured or heated, hard to direct at a single pest.

Dry or Solid Formulations

Dusts (D)

Most are ready-to-use with 10% or less a.i. (a few are concentrates). Very fine, dry inert carrier (talc, chalk, clay, nut hulls, volcanic ash). Never mix with liquid — always used dry. Common uses: seed treatments, cracks and crevices, spot treatments, pet and livestock external parasites.

Tracking powders — special dusts with an adsorbed stomach poison. Insects and rodents pick it up on feet/fur and ingest it when grooming. Effective where bait acceptance is poor.

Granules (G)

Like dusts, but larger and heavier particles. Not water-soluble — always ready-to-use, never mixed. Carriers are adsorptive (clay) or absorptive plant material (corncobs, walnut shells). Usually 1% to 15% a.i. Most granular products deliver systemic pesticides.

Granules slowly release the a.i. Some need moisture (rain, soil moisture, watering) to activate; others release as they decompose.

Pellets (P or PS)

Very similar to granules, but all particles are the same weight and shape. Made by extruding a slurry under pressure, then cutting to length. Uniform size = precise application. A few fumigants are pellets (clearly labeled to avoid confusion).

Wettable Powders (WP or W)

Dry finely ground solids with wetting/dispersing agents. 5-95% a.i., usually 50%+. Mixed with water and applied as a spray suspension — particles don't dissolve, they settle out without constant agitation.

To prepare: form a slurry (WP + small amount of water), then dilute further. On porous surfaces (concrete, plaster, untreated wood), only water penetrates — the WP stays on the surface.

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

Wettable powders compressed into dust-free granules. Most come with a product-specific measuring device marked in dry ounces/pounds. Mixed with water; granules break into fine powder. Require constant agitation.

Share WP advantages AND disadvantages, but with reduced handler exposure risk because granules are larger, less dusty, and easier to measure.

Soluble Powders (SP or WSP)

Look like wettable powders, but dissolve completely in water to form a true solution. After mixing, no further agitation needed. 15-95% a.i., usually more than 50%. Share WP advantages but only one WP disadvantage: inhalation hazard while mixing. Few a.i.s dissolve in water, so SPs are uncommon.

Baits (B)

A.i. mixed with food or another attractive substance. Usually less than 5% a.i.. Solid (blocks, granules, pellets), liquid, paste, or gel. Used for ants, cockroaches, flies indoors; rodents, snails, slugs, some insects outdoors.

Pastes, Gels & Injectable Baits

Mainly for ants and cockroaches. Insecticide gels/pastes are now the primary formulation for cockroach control. Injected or placed as bead/dot in cracks and crevices with syringes or bait guns.

Advantages: odorless, low human toxicity, long-lasting, low applicator exposure, hidden placement, accurate dosage. Disadvantages: can be contaminated by other pesticides/cleaners, gels run at high temperatures, may stain porous surfaces, repeat applications build up.

Other Formulations

Fumigants

Deliver the a.i. to the target as a gas. Some a.i.s are pressurized liquids that become gas on release; others are volatile liquids; still others are solids that release gas in humid or wet conditions. Used in structural pest control, food/grain storage, regulatory pest control at ports, soil, greenhouses, commodity storage.

Microencapsulated Pesticides (M)

Dry particles or liquid droplets surrounded by a plastic, starch, or other coating. Mixed with water, applied as a spray. Once applied, the pesticide is slowly released from the capsule.

Release can be weather-dependent — cool/dry weather slows it, meaning residues may persist longer than expected. Some products have long REIs and PHIs because of this.

Water-Soluble Packaging (WSB or WSP)

A special film packages a precise amount of WP, SP, or gel a.i. Dropped in the spray tank, the bag dissolves and releases the contents. Greatly reduces handler exposure.

Won't dissolve in organic solvents or undiluted ECs. Must be kept dry. Never handle with damp/wet gloves.

Impregnates

Pesticide a.i. incorporated into a solid material (usually plastic). The pesticide evaporates or is released over time. Examples: livestock ear tags, plastic pest strips, adhesive tapes, pet collars. Fertilizers can also be impregnated.

Animal Systemics

Absorbed by and moved within a treated animal. Applied externally (pour-on liquids, sprays, dusts) or orally (food additives, capsules, pastes, liquids). Control external parasites like fleas AND internal parasites like worms.

Pesticide-Fertilizer Combinations

Usually granule or pellet formulations. Controls pests and delivers nutrients at the same time. Common homeowner lawn products. Dealers may custom-mix for specific crops.

Pesticide Mixtures & Tank Mixing

Benefits: saves time, labor, fuel, and equipment wear; reduces soil compaction and crop damage from multiple passes. Examples: fungicide + insecticide on fruit trees; combining herbicides to expand weed spectrum.

Federal law allows tank mixing UNLESS a label specifically prohibits it. If no prohibitions exist, you may mix:

• Pesticide with fertilizer
• Two or more pesticides

When tank-mixing, each individual product must be at or BELOW its labeled rate — you never exceed any single component's rate.

Products must be compatible. Compatibility testing procedures are in Chapter 10.

Adjuvants

Most end-use pesticide products already contain adjuvants — especially those applied to foliage. Applicators may add more to a tank mix if needed.

EPA does NOT register adjuvants because they have no pesticidal activity. There are no standards for composition, quality, or performance. For questions, contact the manufacturer.

Types of Adjuvants

• Antifoaming / defoaming agents — reduce foaming caused by surfactants or vigorous agitation.
• Buffers / pH modifiers — adjust water pH. Most pesticides are stable between pH 5.5 and 7.0. Water outside this range degrades pesticides, sometimes rapidly. Add buffers to tank water FIRST, before pesticides.
• Compatibility agents — help combine pesticides or pesticides + fertilizers.
• Drift control additives / deposition aids — reduce drift by increasing droplet size and reducing "fines."
• Emulsifiers — allow petroleum-based pesticides (ECs) to mix with water.
• Extenders — keep pesticides active longer on a target. (Sometimes called stickers.)
• Invert emulsifiers — allow water-based pesticides to mix with petroleum carrier.
• Plant penetrants — help pesticide pass through leaf surface.
• Safeners — reduce toxicity of a pesticide to the handler or the treated surface.
• Spreader — allows pesticide to form a uniform coating over a treated surface.
• Stickers — keep pesticide on the treated surface; reduce wash-off, evaporation, and photodegradation.
• Thickeners — increase viscosity of spray mixtures. Reduce drift, slow evaporation.
• Wetting agents — allow WPs to mix with water.

Surfactants

Surfactants (surface-active ingredients) alter the dispersing, spreading, and wetting properties of spray droplets. They reduce surface tension, making droplets spread out instead of beading up. Critical for treating waxy or hairy leaves.

Examples of surfactants: wetting agents, spreaders.

Choosing the Right Adjuvant

• Read and follow the label. Is an adjuvant recommended or prohibited? Don't substitute.
• Use only agricultural/horticultural adjuvants — NEVER industrial products or household detergents.
• No adjuvant is a substitute for good application practices.
• Be skeptical of vague performance claims unless backed by research.
• Test adjuvant-added spray mixes on a small area first.

Key Terms Cheat Sheet

• Formulation — combination of a.i. and inerts forming an end-use product.
• Active ingredient (a.i.) — the chemical that controls the pest.
• Inert ingredients — no pesticidal activity; carriers, diluents, additives.
• Solution — dissolved mixture; transparent; no settling; no agitation needed.
• Suspension — solid particles in liquid; cloudy; needs agitation; settles.
• Emulsion — liquid droplets in another liquid; milky.
• Concentrate — needs dilution before use.
• Ready-to-Use (RTU) — applied without dilution.
• EC (Emulsifiable Concentrate) — oil-based liquid; forms emulsion with water; 2-6 lb a.i./gal.
• ULV — ~100% a.i., very fine droplets, very low volume; high drift.
• Invert emulsion — water-based a.i. in oil carrier; low drift; mayonnaise-like.
• Flowable (F, AF) — insoluble solids suspended in a thick liquid.
• Dust (D) — dry, ≤10% a.i.; never mix with liquid; high inhalation risk.
• Granule (G) — larger/heavier than dust; 1-15% a.i.; common for systemics.
• Pellet (P) — uniform size and shape; more precise than granules.
• Wettable Powder (WP) — 5-95% a.i.; mixed with water; forms suspension; needs agitation.
• Water-Dispersible Granule (WDG/DF) — dust-free WP; reduced exposure risk.
• Soluble Powder (SP) — dissolves in water to form a solution; no agitation after mixing.
• Bait (B) — a.i. (less than 5%) in attractive food/substance.
• Gel/Paste — primary formulation for cockroach control.
• Fumigant — pesticide delivered as a gas; needs enclosed site.
• Microencapsulated (M) — coated particles; timed release; bee hazard.
• WSB/WSP — water-soluble bag/packet.
• Tracking powder — dust with stomach poison for rodents and insects.
• Tank mix — combining two or more products in one application.
• Adjuvant — non-pesticidal additive that changes how a pesticide works.
• Surfactant — adjuvant that alters surface tension; wetting agents and spreaders.
• Anionic surfactant — negative charge; for contact pesticides.
• Cationic surfactant — positive charge; phytotoxic if used alone.
• Nonionic surfactant — no charge; for systemic pesticides; most compatible.
• Buffer — adjusts pH of tank water.
• Sticker — keeps pesticide on treated surface.
• Extender — prolongs pesticide activity on target.
• Thickener — increases spray mixture viscosity; reduces drift.
• Safener — reduces pesticide toxicity to handler or surface.
• Phytotoxicity — damage to plants caused by the pesticide.