7.2 Pesticide Formulations
Key Takeaways
- Active ingredient (AI) is the pesticidal chemical; the formulated product is what you actually buy, mix, and apply.
- Emulsifiable concentrates (EC) mix with water to form a stable emulsion but are flammable and penetrate skin easily.
- Wettable powders (WP) and water-dispersible granules (WG/DF) require constant agitation and can abrade nozzles.
- Granular (G) and dust (D) formulations are ready-to-apply dry products; granules are safer for baiting, dusts drift easily.
- Adjuvants and surfactants are added to spray tanks to improve mixing, spreading, or sticking but must be label-approved.
7.2 Pesticide Formulations
Quick Answer: A formulation is the commercial mix of the active ingredient (AI) with inert ingredients that determines how a pesticide mixes, sprays, and behaves. Common formulations include emulsifiable concentrate (EC), wettable powder (WP), soluble powder (SP), flowable (F/L), granular (G), dust (D), bait, microencapsulated (M), water-dispersible granule (WG/DF), and soluble liquid (SL). The label — not the applicator — decides which formulation may be used on a given site.
Active Ingredient vs. Formulated Product
This is a calculation-critical distinction. The active ingredient is the pesticidal chemical itself. The formulated product is what you pour out of the jug; it contains the AI plus solvents, carriers, surfactants, and stabilizers. When a label states "apply 1 lb active ingredient per acre," you must convert to product using the percentage of AI in the formulation (see Section 7.3). Mixing up the two is one of the most common — and most dangerous — application errors, because concentrated AI is far more toxic per unit weight than the diluted formulated product.
Why Formulation Choice Matters
The formulation controls:
- Mixing behavior: does it dissolve, suspend, or emulsify in water?
- Droplet behavior: does it drift, evaporate, or stick to the leaf?
- Skin and inhalation hazard: how easily does it enter the body during handling?
- Equipment compatibility: will it abrade nozzles, clog screens, or settle in the tank?
- Storage stability: how long does it last, and under what temperature range?
- Environmental behavior: will it leach, bind to soil, or volatilize?
A formulation that performs well in a boom sprayer may be wrong for an air-blast sprayer or a backpack unit. The label's Directions for Use section lists the allowed formulations and equipment combinations for each use site.
Comparison of Common Formulations
| Code | Formulation | How It Mixes | Key Properties | Main Hazards / Limits |
|---|---|---|---|---|
| EC | Emulsifiable Concentrate | Emulsifies in water to milky solution | Easy to mix, penetrates waxy leaves and insect cuticles | Flammable, solvent odor, skin absorption high, may harm plants (phytotoxic) |
| WP | Wettable Powder | Suspends in water, needs agitation | Less phytotoxic than EC, easy to package | Inhalation hazard as dust, settles fast, abrades nozzles |
| SP | Soluble Powder | Dissolves fully in water | True solution, no agitation needed | Inhalation of dry powder, limited products available |
| F / L | Flowable / Liquid | Suspends as fine particles, needs agitation | Pourable like a liquid, mixes like a WP | Settles in storage, can clog screens |
| G | Granular | Ready-to-apply dry, no mixing | Low drift, bait-able, easy to calibrate | Needs calibrated spreader, can be mistaken for fertilizer |
| D | Dust | Ready-to-apply dry | Penetrates crevices, light coverage | Drifts badly, inhalation hazard, seldom used outdoors |
| Bait | Bait | Ready-to-apply (dry or gel) | Target-specific, low AI content | Pets and children may ingest, must keep dry |
| M | Microencapsulated | Suspends, slow release | Time-released AI, longer residual | Bee hazard if foraging during release — read label |
| WG / DF | Water-Dispersible Granule | Disperses in water, needs agitation | Low dust, pourable, less nozzle abrasion than WP | Measure by weight, not volume |
| SL | Soluble Liquid | Dissolves fully in water | True solution, easy to handle | May be expensive, limited active ingredients |
Adjuvants and Surfactants
Adjuvants are additives that improve how a spray performs. They are not active ingredients and do not themselves kill pests. Common types:
- Surfactants reduce surface tension so droplets spread on waxy leaves.
- Stickers keep the deposit on the leaf through rain.
- Spreaders widen the contact area.
- Penetrants help the AI move into the leaf tissue (translaminar).
- Drift-control agents thicken the spray to reduce fine droplets.
- Compatibility agents allow mixed products to stay in solution.
The label is the controlling document. Many labels explicitly state "add a non-ionic surfactant at 0.25% v/v" or forbid certain adjuvants. Adding an adjuvant that the label does not authorize is a label violation under FIFRA and Part 83, even if it seems to improve performance. Never add an adjuvant to a formulation that is already premixed with its own.
Choosing the Right Formulation
Match the formulation to the site, pest, and equipment:
- Foliar pest on a waxy leaf, boom sprayer: EC or WG with a surfactant.
- Soil insect on row crop, granular applicator: G banded at planting.
- Structural crack-and-crevice treatment: D or bait gel, never broadcast.
- Backpack spot-spray of herbicide: SL or EC for ease of mixing small batches.
- Bee-sensitive bloom period: avoid M and dusts; choose a short-residual SL if a spray is unavoidable.
Storage and Handling Notes
- ECs store in a cool, dry place away from ignition sources (they are flammable).
- WPs and WGs absorb moisture — keep sealed; caking means it has spoiled.
- Flowables settle over time; invert the container several times before pouring, and never store below freezing.
- Granulars keep dry — moisture causes clumping and uneven metering.
- Baits must stay palatable; once stale, pests reject them and the application fails.
Common Exam Scenarios
- Scenario A: A label lists only an EC formulation for use on a crop. The applicator has a WP of the same AI on hand and applies it. This is a label violation — the formulation is part of the use directions, not interchangeable.
- Scenario B: An applicator adds a silicone surfactant to a spray mix because the product "spreads better." The label does not mention any adjuvant. This is a label violation.
- Scenario C: A granular bait is stored in an open shed over a humid Michigan summer. The bait cakes and is applied anyway; pest counts do not drop. The failure is formulation mismanagement, not the active ingredient.
Summary
Formulation is how a pesticide reaches the pest. The AI does the killing, but the formulation decides whether the product mixes, sticks, drifts, or abrades the equipment. Always confirm the formulation is label-approved for the site and equipment, never add an adjuvant the label does not authorize, and convert AI rates to product rates using the AI percentage on the label.
A pesticide label lists only the emulsifiable concentrate (EC) formulation for use on a crop. The applicator has a wettable powder (WP) of the same active ingredient and applies it instead. Under FIFRA and Michigan Part 83, this is:
Which formulation mixes as a true solution in water and requires no tank agitation once mixed?
An applicator adds a drift-control adjuvant to a spray mix. The product label does not mention any adjuvant. Under Michigan and federal rules, this is: