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:
Permitted, because the active ingredient is the same and the rate is adjusted.
Permitted only if the WP is registered for use on a different crop in the same family.
Permitted only if a non-ionic surfactant is added to compensate.
A label violation, because the formulation is part of the use directions and is not interchangeable.
Which formulation mixes as a true solution in water and requires no tank agitation once mixed?
Soluble Powder (SP) or Soluble Liquid (SL)
Wettable Powder (WP)
Flowable (F/L)
Granular (G)
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:
Allowed, because drift-control agents reduce environmental hazard and are always beneficial.
Allowed only if the adjuvant itself is EPA-registered as a pesticide.
A label violation, because adding an adjuvant the label does not authorize is use inconsistent with labeling.
Allowed only if the applicator records the adjuvant in the application log.
Sections you finish are checked off in the contents.