4.1 Formulation types (EC, WP, D, G, etc.) & compatibility

What a Formulation Is

A pesticide formulation is the product as it comes from the manufacturer: the active ingredient (a.i.) that actually controls the pest, blended with inert ingredients such as solvents, carriers, wetting agents, stickers, and emulsifiers. Technical-grade active ingredient is rarely usable by itself; it may be too concentrated, unable to mix with water, or impossible to apply evenly. The manufacturer therefore formulates it into a product that can be measured, diluted, and applied safely and effectively. The label states the percentage of active ingredient and the formulation type, usually with a letter code after the product name.

Choosing the right formulation is one of the most important decisions an applicator makes. The same active ingredient may be sold in several formulations, and each behaves differently in the tank, on the target surface, and in terms of applicator hazard. Factors to weigh include the application equipment, the surface being treated (porous surfaces soak up sprays), the pest and its habits, the risk of drift, cost, and the hazard to the applicator and the environment.

Liquid Formulations

Emulsifiable concentrates (EC) are active ingredient dissolved in an oil-based solvent with an emulsifier added so the oil mixes with water to form a milky emulsion. ECs are versatile and easy to handle, need only moderate agitation, and leave little visible residue. Their drawbacks: the solvents are readily absorbed through the skin, they can be phytotoxic, they may soften rubber, plastic, and painted surfaces, and they are often flammable.

Solutions (S or SL, soluble liquids) dissolve completely in water and stay in solution, so they need little or no agitation and will not clog or abrade equipment.

Flowables or liquids (F or L) are finely ground solid active ingredients suspended in a liquid. They need moderate agitation to stay mixed, are less abrasive than wettable powders, but can leave a visible residue and settle if left standing.

Ultra-low-volume (ULV) products are nearly 100 percent active ingredient applied as extremely small droplets with special equipment.

Dry and Solid Formulations

Wettable powders (WP) are dry, finely ground powders mixed with water to form a suspension. They require constant agitation to stay suspended, are abrasive to pumps and nozzles, and create an inhalation hazard when the concentrated powder is measured and poured. On the plus side, WPs are absorbed through the skin less readily than ECs and work well on porous surfaces.

Soluble powders (SP) look like WPs but dissolve completely in water, so they need little agitation and pose no settling or abrasion problem, though the dry powder is still an inhalation hazard when measured.

Water-dispersible granules / dry flowables (WDG or DF) are like WPs but formed into granules that break apart in water. They pour easily and create far less dust than WPs.

Dusts (D) are ready-to-use, low-concentration formulations. They need no mixing but drift easily and are hard to keep on target.

Granules (G) carry the active ingredient on or in coarse particles of clay, corn cob, or a similar carrier. They are ready to use, drift very little, and are commonly applied to soil; applicator hazard is relatively low, but they need moisture to release the active ingredient.

Baits (B) combine a small amount of active ingredient with food or another attractant to draw the pest to the pesticide.

Adjuvants and Ready-to-Use Products

Some products are sold ready to use (RTU) at the final dilution so no mixing is needed, and aerosols (A) package the active ingredient with a propellant. Adjuvants are additives that improve performance: surfactants (wetting agents) help a spray spread and stick, stickers hold residue on the surface, and drift-control agents reduce fine droplets. Add only the adjuvants the label allows, because the wrong one can cause plant injury or reduced control.

Compatibility and Mixing Order

Applicators often want to combine two or more products in one tank to save time. Products are compatible when they can be mixed without reducing effectiveness, forming clumps, or damaging plants. Physical incompatibility shows up as clumping, curdling, layering, or a sludge that clogs nozzles; chemical incompatibility reduces pest control or increases plant injury without an obvious visible sign. Always check the label first, because many labels list known incompatibilities.

When the label does not settle the question, run a jar test: mix the products in the correct proportions in a small jar, shake, and watch for separation, precipitate, gel, or heat. Add products in the correct order with the agitator running and the tank part-filled with water: wettable and dry products first, then flowables, then liquids and solutions, then emulsifiable concentrates, and finally surfactants and adjuvants. A compatibility agent can sometimes keep an otherwise borderline mixture uniform.