Chapter 4: Pesticide Formulations

Reading the form off the label

A label often tells you the formulation through a suffix attached to the brand or trade name, and that suffix frequently carries a number. The trick is that the number means different things for solids and liquids:

• For a solid (dust, granule, wettable powder), the number is the percent of a.i. by weight. So BugGone 20WP is a wettable powder that is 20% a.i. by weight.
• For a liquid (liquid flowable, emulsifiable concentrate), the number is the pounds of a.i. per gallon. So WeedXterminator 3.3EC is an emulsifiable concentrate with 3.3 pounds of a.i. per gallon.

Exceptions are common, and not every trade name includes a suffix. When it doesn't, the formulation is spelled out in the Product Information section of the label — so read the label rather than relying on the name alone.

Solubility and the three mixtures

Because so much of formulation comes down to whether the a.i. dissolves, the chapter pauses on solubility — the ability of one substance to dissolve in a solvent, usually water. Salt stirred into water is very soluble; oil won't mix and is insoluble. That single property drives three mixture types you need to keep straight:

• A true solution is a mixture (like salt water) that can't be separated by filtration and doesn't settle out or need shaking. Once made, it stays mixed.
• A suspension is small solid particles that don't dissolve, dispersed in a liquid (like flour in water). Left alone, the particles settle or float, so suspensions require agitation and typically look cloudy.
• An emulsion is a special kind of suspension — droplets of one liquid suspended in another, looking cloudy or milky. An emulsifier is the additive that keeps an emulsion from separating (for instance, keeps the oil from rising to the top).

The formulation types and their trade-offs

The heart of the chapter is a tour of common formulations, each with characteristic strengths and weaknesses. The pattern to internalize is that almost every advantage comes paired with a matching disadvantage, so choosing well means matching the form to the situation.

Emulsifiable concentrates (EC) dissolve an a.i. that is insoluble in water into a petroleum solvent, which is why they smell like solvent; emulsifiers let them mix with water into a milky emulsion. They're easy to handle, pour, and measure and need little agitation — but they're easily absorbed through the skin, corrosive, and flammable, and they can degrade rubber and plastic. Because they carry a high concentration of a.i. and soak into skin, keeping them off your skin matters.

Ultra low volume (ULV) products are near the opposite extreme of concentration — almost 100% a.i., applied as very fine droplets at high pressure, mainly outdoors (mosquito, forestry, ornamental). Those fine droplets bring a high drift hazard and high dermal and inhalation risk.

Wettable powders (WP) are dry solids that don't dissolve; mixed with water they form a suspension. Compared with ECs they carry less skin and eye absorption risk and are gentler on plants and surfaces — but the concentrated powder is an inhalation hazard while mixing, must be weighed rather than poured, is abrasive, clogs nozzles, and needs constant agitation. Soluble powders (SP) look like WPs but actually dissolve into a true solution, so they need no extra agitation; they share the WP advantages with only one disadvantage — inhalation during mixing. Water-dispersible granules (WDG / dry flowables) are WPs pressed into granules, which makes them pour more easily, suspend better, and pose less inhalation risk, while still forming a suspension that needs agitation.

Liquid flowables are thick liquid suspensions with low inhalation risk that seldom clog nozzles, though they need shaking before mixing, require moderate agitation, and can leave a visible residue. Microencapsulated (M) products lock the a.i. inside tiny plastic-coated capsules that break down for slow release, so they stay effective longer — but they need constant agitation and pose a notable hazard to bees, which can carry the capsules back to the hive with pollen.

Among the dry, solid forms: dusts are always used dry, made of a.i. plus a fine carrier like talc, chalk, or clay; they're handy where spray moisture would cause damage but drift easily, adhere poorly, and carry a high inhalation risk. Granules put the a.i. on clay or porous material and are nearly always used to treat soil, releasing slowly (often needing soil moisture). Pellets are like granules but uniform in size and shape (granules vary), used for spot applications, and — like granules — can be a hazard to birds that mistake them for food. Baits mix the a.i. with food or an attractant and usually contain less than 5% a.i.; their advantage is that you needn't cover the whole area since the pest comes to the bait, but rodent baits are often tightly regulated (tamper-proof stations), and old bait must be removed so it doesn't become a food source for pests. Finally, water-soluble bags hold a premeasured dose that lowers exposure to concentrated a.i. — and the one rule to remember is to never puncture or break them open; you add the whole bag to water and let it dissolve.

Adjuvants

Sometimes the label directs you to add an adjuvant (additive) to the tank mix — a material that aids or modifies the action of the formulation or the physical characteristics of the mixture, used most commonly for foliar applications. The most familiar are surfactants — the wetting agents and spreader-stickers applicators add most often — which reduce the surface tension of water and increase how the spray spreads on leaves, much like adding soap to water. Drift reduction (thickening) agents help reduce but not eliminate spray drift, and compatibility agents allow two or more pesticides to be mixed effectively. Adjuvants demand care: some must be added in a specific order, and using too little or too much can make the mixture unusable or injure plants.

Choosing a formulation

The chapter closes by reminding applicators that formulation choice is often overlooked but matters for safety, equipment, and the environment. The number one concern is always the same: make sure the product is labeled for the site, plant, or crop you intend to treat. After that, weigh the signal word (between two products that work, lean toward the less toxic one), applicator safety (some forms are inhaled, others absorbed through skin — have the right PPE), environmental safety (be cautious with drift-prone or volatile products, and with products more toxic to aquatic life), the pest's biology, the surface to be treated (staining, dissolving plastic, damaging foliage), and the equipment (some forms are abrasive or corrosive). Cost is a real consideration, but it comes after safety and pest management.

How to study this chapter

1. Get the big idea: the a.i. is the same across forms; the formulation exists to make that a.i. usable, and the other ingredients aren't automatically safe — the signal word reflects the whole formulation.
2. Drill the suffix rule both ways: on a solid the number is % a.i. by weight; on a liquid it's lb a.i. per gallon.
3. Keep the three mixtures straight: solution (no agitation), suspension (needs agitation), emulsion (special suspension, emulsifier prevents separation).
4. For each formulation, learn its one defining trait and its signature hazard (EC → skin absorption/flammable; ULV → ~100% a.i./drift; WP → inhalation while mixing/abrasive; SP → dissolves, one disadvantage; microencapsulated → slow release/bee hazard; bait → <5% a.i.; WSB → never puncture).
5. Remember the choosing order: labeled for the site first, then safety and pest management, and cost last.