Pesticide formulations explained

What a formulation is

NPIC describes a pesticide formulation as a mixture of active and other ingredients, also called inert ingredients. The active ingredient is what prevents, kills or repels the pest, or acts as a plant regulator, desiccant, defoliant, synergist or nitrogen stabilizer.^[1][8]

The other ingredients help deliver the active ingredient. Solvents dissolve it, carriers are liquids or solids that help deliver it, and adjuvants often help the pesticide stick to or spread over a surface such as leaves, or help a formulation mix when it's diluted.^[1]

EPA lists some jobs inert ingredients do: helping the active ingredient get through a leaf surface, preventing caking or foaming, extending shelf life, improving safety for the applicator and protecting the pesticide from sunlight. Inerts range from solvents to common food items such as certain edible oils and spices, and natural materials such as beeswax.^[8]

A synergist is an active ingredient that has no pesticidal effect of its own but helps another one kill the pest with a minimum of active ingredient. Insecticides containing pyrethrins, for example, often include piperonyl butoxide.^[1]

Pesticides come in many forms because active ingredients differ in how well they dissolve, how they control the pest and how easy they are to handle and transport. Manufacturers also weigh the surface being treated, the training and equipment of the people using the product, runoff and drift, the pest's habits and safety.^[1]

Labels list the active ingredients and their percentages, but manufacturers usually don't disclose the specific other ingredients, which often make up most of the product.^[4][8]

The name 'inert' doesn't mean non-toxic. EPA must approve every inert ingredient before it goes into a pesticide, and it reviews safety information on each one. UC IPM adds that the effects of undisclosed other ingredients are uncertain and can affect bees.^[8][4]

Formulation codes on the label

EPA's consumer guide says home-use pesticides come as solutions, aerosols, dusts, granules, baits and wettable powders, and that certain formulations work better for some pests and some target areas than others.^[9]

The formulation type may appear on the label as a one- to three-letter abbreviation. These are common ones from NPIC's list:^[4][1]

• RTU: ready-to-use, which needs no dilution^[1]
• A: aerosol; ULV: ultra-low-volume concentrate^[1]
• B: bait; P: pellet; G: granule^[1]
• D: dust^[1]
• E or EC: emulsifiable concentrate; FL: flowable; M: microencapsulated^[1]
• WP: wettable powder; SP: soluble powder; DF: dry flowable; WDG: water-dispersible granule^[1]
• UC IPM's bee ratings also use F or L for liquids, S for solutions and GR for granules, so the same form can carry more than one abbreviation.^[4]

Ready-to-use products

Many products the public buys are ready-to-use formulations that need no dilution and can be applied quickly. NPIC's examples include granules for insect and weed control and baits for rodent control.^[1]

UC IPM suggests buying ready-to-use products when possible, since you don't have to measure and mix them. For many home and garden jobs it calls a ready-to-use product in a trigger pump sprayer the best choice: there's nothing to dilute, no special equipment to buy, and it works well for spot treatments on small plants and shrubs.^[3][9]

The same active ingredient is often sold both ways. Clemson's Home and Garden Information Center notes that insecticidal soaps come as concentrates to dilute before spraying and as ready-to-use pre-mixed bottles, and it advises against homemade soap recipes because they're more likely to injure plants than commercial soaps that have been tested on plants.^[12]

Ready-to-use still means following the label. Wear the shoes, long sleeves, pants, eye protection and any other gear it lists, and never apply more than it allows.^[3][9]

Concentrates: measuring, mixing and leftovers

Concentrated formulations have to be measured and diluted, and UC IPM says proper measurement is essential for safe, effective use. For most insecticides and fungicides, the label gives the rate in ounces per gallon of water; for herbicides and some lawn uses, it gives an amount for a given area, so you'll need to measure the area you're treating.^[3]

EPA's consumer guide gives a worked example. If a label says to mix 8 fluid ounces of pesticide into 1 gallon of water for aphids on tomatoes, and you need only 1 quart of spray for your plants, use a quarter of the product, 2 fluid ounces, in that quart. That makes the same strength the label calls for.^[9]

Test your sprayer with water first to see whether you cover the recommended area with the recommended amount of spray, and adjust your pace if not. For fruit and ornamental trees, where labels often say to wet plants to the dripping point instead of giving square feet, a water test shows how much to mix.^[3]

Never use more than the label says. UC IPM notes the pest won't be controlled faster, and the extra wastes pesticide and money while risking plant injury and contaminating the environment. EPA's guide puts it the same way: twice the amount won't do twice the job.^[3][9]

Mix only as much as you need right away, and don't store leftover solution. Diluted pesticide may change in quality at high or very low temperatures, be affected by minerals in the water or settle out.^[3][9]

Keep a set of measuring spoons or cups only for pesticides, labeled 'PESTICIDE ONLY' and stored far from food preparation areas. If you spray herbicides, keep a separate sprayer marked 'WEEDS ONLY', because herbicide residue can injure plants if the same sprayer is used for another product. EPA adds to use level spoonfuls and never to use pesticide measuring tools for food, even after washing them, and to mix outdoors or in a well-ventilated area.^[3][9]

The concentrate itself can call for more protection than the diluted spray. One professional bifenthrin concentrate label requires everyone who mixes, loads or applies it to wear a long-sleeved shirt, long pants, socks, shoes and chemical-resistant gloves; once the product is diluted according to the label, waterproof gloves are sufficient.^[5]

When you're done, EPA suggests rinsing the mixing tools in a bucket and pouring the rinse water into the sprayer, then applying it according to the label.^[9]

Mixing two products

Check the label before combining products: it lists what the product shouldn't be mixed with, and incompatible pesticides can separate, gel, curdle or clog equipment. NPIC says pesticides that are physically different, such as a dust and a liquid, are typically incompatible.^[1]

NPIC says ready-to-use liquids and concentrates already diluted according to the label can be mixed together, but undiluted concentrates shouldn't be combined. Flowables, wettable powders and water-dispersible granules need regular shaking to reduce incompatibility problems.^[1]

Mixing can raise the hazard to bees. UC IPM says tank mixes can increase bee toxicity through synergistic effects, and advises checking each active ingredient's bee rating and following label instructions for mixing.^[4]

Dusts, granules, baits and pellets

Dust labels name the equipment. One deltamethrin dust label calls for a hand or power duster, or a bulbous duster for cracks and crevices, applied lightly and uniformly, and bars applying it into air handling systems or ducts, including heating, ventilation and air conditioning equipment that moves air into rooms people use.^[6]

The same deltamethrin dust label says to apply it in living areas in a way that avoids deposits on exposed surfaces or putting the material into the air, and to cover or wash food processing surfaces and utensils and to cover or remove exposed food.^[6]

Granules for insect and weed control are among the ready-to-use products homeowners buy. Granules, baits and pellets also rank among the formulations least hazardous to bees, with low direct exposure unless dust or water contamination occurs.^[1][4]

UC IPM lists bait stations among the least toxic products that target a pest, and names ant bait stations as one way to limit environmental contamination.^[3][12]

Clemson HGIC explains why: a bait station holds the insecticide inside a chamber that insects enter to feed, which reduces exposure for people, pets and other animals. It suggests them where children or pets are present or food is prepared or stored.^[12]

Rodent bait stations are sold ready to use with the bait inside. EPA sorts them into tiers: stations shown to resist tampering by young children and dogs and to be weather-resistant can be used indoors and outdoors within 50 feet of buildings, while stations not shown to be tamper-resistant may be used only indoors where young children and pets have no access.^[10]

Whatever the form, EPA says never to put insect or rodent bait where small children or pets can reach it.^[9]

Aerosols and total release foggers

Aerosol cans carry their own hazards. The label on one wasp and hornet spray says it's extremely flammable and under pressure: keep it away from fire, sparks and heated surfaces, don't puncture or incinerate the can, and know that temperatures above 130°F may cause it to burst.^[7][9]

EPA's guide says never to smoke or eat while mixing or applying pesticides, partly because some products are flammable, and never to puncture or burn a pressurized or aerosol container because it could explode.^[9]

Total release foggers empty the whole can at once. NPIC says using more foggers than the label gives for the space won't control pests better and could raise your risk, that they may not be effective on all indoor pests, especially bed bugs, and that some contain substances that drive pests deeper into hiding.^[11]

Keep foggers away from ignition sources. EPA lists ovens, stoves, air conditioners, space heaters and water heaters; NPIC says to turn off pilot lights and unplug electrical appliances. Both say not to use foggers in small enclosed spaces such as closets and cabinets.^[9][11]

A CDC report counted 466 cases of fogger-related illness or injury in eight states from 2001 to 2006, mostly mild and mostly respiratory. The most common reasons were not leaving before the fogger went off, going back in too soon, using too many foggers for the space, setting one off by accident and not warning others nearby.^[13]

How formulation changes the risk

All pesticides have some risk, which depends on the amount of exposure and the toxicity of the ingredients, and NPIC notes that the formulation, whether a liquid, dust, gel or bait, may affect that risk.^[2]

For bees, UC IPM ranks dusts, dry flowables and water-dispersible granules, liquids, microencapsulated products and wettable powders as most hazardous, because the small particles stick to bee hairs, get carried to hives and may be fed to brood. Emulsifiable concentrates, soluble powders, solutions and systemics are a moderate hazard, and baits, granules, pellets and seed treatments without a systemic pesticide are the lowest.^[4]

Some formulations can discolor or pit the surface of plants or other surfaces. Rain soon after an application can wash a pesticide into lakes, rivers, streams or ponds, and wind can carry it onto neighboring property, water, people or animals.^[1]

Advice on wind differs. UC IPM says not to spray when winds are 5 mph or more, while EPA's consumer guide says never to apply pesticides outdoors when winds are higher than 10 mph. UC IPM also says not to spray when rain is forecast, and EPA says never to water your lawn after applying pesticides.^[3][9]

UC IPM's minimum protective gear for any pesticide, even a least toxic one, is chemical-resistant gloves made of nitrile, neoprene, butyl or rubber, eye protection, a long-sleeved shirt, long pants and closed shoes. Cotton gloves and lightweight dust masks can absorb liquid sprays and keep them against your skin.^[3][9]

EPA's guide adds to wear what the label requires, such as nonabsorbent gloves instead of leather or fabric and rubber footwear instead of canvas or leather. If the label lists no clothing, it recommends gloves, a long-sleeved shirt, long pants and closed shoes.^[9]

Choosing a formulation for a home job

• Identify the pest first; a local Cooperative Extension office or UC Master Gardener program can help. NPIC notes that how a pest feeds, reproduces and develops is what guides a manufacturer's choice of formulation for it.^[1][3][9]
• Pick the least toxic product that targets your pest, such as bait stations, insecticidal soaps and oils, or a microbial insecticide like Bacillus thuringiensis (Bt).^[3][12][9]
• Choose the form, such as aerosol, dust or bait, that best suits the place you're treating and the pest, as EPA's consumer guide advises.^[9]
• For small areas and spot treatments, a ready-to-use product saves measuring and mixing.^[3][9]
• Check the signal word. Clemson HGIC suggests products labeled 'caution', which are least likely to harm the user and the environment.^[12][9]
• Make sure you have the equipment the label calls for before you buy; the label lists it.^[1][3]
• Buy only as much as you need for the current problem, so you don't have to store leftovers for a long time.^[3]
• Treat where the pest is most prevalent instead of spraying the whole garden or house.^[3]

Common questions

What does EC mean on a pesticide label?

EC stands for emulsifiable concentrate. It's a concentrate, so it has to be measured and diluted exactly as the label directs.^[1][3]

Is a ready-to-use spray safer than a concentrate?

It skips measuring and mixing, which is why UC IPM and EPA both describe ready-to-use products as easier. The concentrate itself can need more protection: one bifenthrin concentrate label requires chemical-resistant gloves for mixing and loading and accepts waterproof gloves once the product is diluted.^[3][9][5]

Can I save leftover mixed spray for next time?

No. Mix only as much as you need right away; stored solutions can change in quality at high or very low temperatures, react with minerals in the water or settle out.^[3][9]

Can I mix two pesticides in one sprayer?

Check both labels first. Each lists what it shouldn't be mixed with, and incompatible products can separate, gel, curdle or clog the sprayer. NPIC adds that a dust and a liquid are typically incompatible and that undiluted concentrates shouldn't be combined.^[1]

Are the inert ingredients in a pesticide harmless?

Not necessarily. EPA says 'inert' doesn't mean non-toxic; it approves each inert ingredient after reviewing safety information, but labels usually show only their total percentage, not their names.^[8]

Will using two foggers work better than one?

No. NPIC says more foggers than the label gives for the space won't control pests better and could increase your risk, and CDC found using too many foggers for the space was one of the common causes of fogger-related illness.^[11][13]

Sources

1. National Pesticide Information Center, “Pesticide Formulations Fact Sheet.” npic.orst.edu/factsheets/formulations.html (accessed 2026-11-10)
2. National Pesticide Information Center, “Pesticide Products.” npic.orst.edu/ingred/products.html (accessed 2026-11-10)
3. University of California Statewide IPM Program, “Understanding Pesticides (Home and Landscape).” ipm.ucanr.edu/home-and-landscape/pesticides-safe-and-effective-use-in-the-home-and-landscape/ (accessed 2026-11-10)
4. University of California Statewide IPM Program, “Bee Precaution Pesticide Ratings: Frequently Asked Questions.” ipm.ucanr.edu/bee-precaution-pesticide-ratings/frequently-asked-questions-faqs/ (accessed 2026-11-10)
5. U.S. EPA Pesticide Product Label System, “Bifenthrin TC (alternate name Bifen I/T) label, EPA Reg. No. 53883-118 (EPA-stamped, September 1, 2026).” www3.epa.gov/pesticides/chem_search/ppls/053883-00118-20260901.pdf (accessed 2026-11-10)
6. U.S. EPA Pesticide Product Label System, “K-Othrine Dust Insecticide (alternate brand name DeltaDust) label, EPA Reg. No. 432-772 (EPA-stamped, Aug. 5, 2016).” www3.epa.gov/pesticides/chem_search/ppls/000432-00772-20160805.pdf (accessed 2026-11-10)
7. U.S. EPA Pesticide Product Label System, “RWH 33 wasp and hornet spray (alternate brand name Raid Wasp & Hornet Killer 33) label, EPA Reg. No. 4822-553 (EPA-stamped, Feb. 13, 2026).” www3.epa.gov/pesticides/chem_search/ppls/004822-00553-20260213.pdf (accessed 2026-11-10)
8. U.S. Environmental Protection Agency, “Basic Information about Pesticide Ingredients.” www.epa.gov/ingredients-used-pesticide-products/basic-information-about-pesticide-ingredients (accessed 2026-11-10)
9. U.S. Environmental Protection Agency, “Citizen's Guide to Pest Control and Pesticide Safety (EPA 735-K-04-002).” www.epa.gov/sites/default/files/2017-08/documents/citizens_guide_to_pest_control_and_pesticide_safety.pdf (accessed 2026-11-10)
10. U.S. Environmental Protection Agency, “Choosing a Bait Station Product for Household Use.” www.epa.gov/rodenticides/choosing-bait-station-product-household-use (accessed 2026-11-10)
11. National Pesticide Information Center, “Total Release Foggers.” npic.orst.edu/ingred/ptype/fogger.html (accessed 2026-11-10)
12. Clemson Cooperative Extension, Home and Garden Information Center, “Less Toxic Insecticides for Garden and Landscape Pest Control in South Carolina.” hgic.clemson.edu/factsheet/less-toxic-insecticides/ (accessed 2026-11-10)
13. Centers for Disease Control and Prevention, “Illnesses and Injuries Related to Total Release Foggers: Eight States, 2001-2006 (MMWR 57(41), 2008).” www.cdc.gov/mmwr/preview/mmwrhtml/mm5741a3.htm (accessed 2026-11-10)