Chapter 24

Greenhouse Pesticides

Pesticide Formulations

A pesticide formulation is a combination of active and inert ingredients that forms an end-use pesticide product. The active ingredients in a pesticide are the chemicals that control the target pest. Pesticides are formulated to make them safer or easier to use. This is because many pesticide active ingredients, in “pure” (technical grade) form, are not suitable for application. In their concentrated form, some are extremely toxic, many do not mix well with water, some are unstable, and some are difficult (or unsafe) to handle, transport, or store. To address these problems, manufacturers add inert ingredients to end-use pesticide products. Inert ingredients have no pesticidal activity, and some simply serve as diluents or carriers. In many cases, inert ingredients make the formulated product safer, easier to handle and apply, and/or more effective.

Formulation Process

The active ingredients in pesticide products come from many sources. Some, such as nicotine, pyrethrum, and rotenone, are extracted from plants. Others have a mineral origin, while a few are derived from microbes. Regardless of their source, pesticide active ingredients have different solubilities. Some dissolve readily in water, others only in oils. Some active ingredients may be relatively insoluble in either water or oils.


In some cases, it may be necessaryor desirable to adhere a liquid active ingredient onto a solid surface (e.g., a powder, dust, or granule). This process is called sorption and it can be accomplished by two possible mechanisms: 1) adsorption—a chemical/physical attraction between the active ingredient, and 2) the surface of the solid or by absorption—entry of the active ingredient into the pores of the solid.


A solution is made by dissolving a substance in a liquid. A true solution is a mixture, but it cannot be separated by filtration or other mechanical means.


A suspension is also a liquid mixture. However, a suspension is formed by dispersing fine (very small), solid particles in a liquid. These solid particles do not dissolve in the liquid carrier. Suspensions must be agitated to maintain uniform particle distribution. Otherwise, the undissolved parts of suspension mixtures will settle (or float to the top).


An emulsion is a mixture that occurs when one liquid is dispersed (as droplets) in another liquid. Each liquid will retain its original identity and some degree of agitation generally is required to keep the emulsion from separating. The insecticide Demon EC is formulated as an emulsifiable concentrate.

Liquid Formulations

Most liquid formulations are diluted with water to make a finished spray. However, some labels direct users to mix the product with another solvent such as crop oil or other light oil as a carrier.

Liquid Flowables (L or F)

Liquid flowables are made with active ingredients that do not dissolve well in water or oil. The active ingredient is very finely ground and suspended in a liquid along with suspending agents, adjuvants, and other ingredients. The result is a suspension requiring further dilution with water before use.

Emulsifiable Concentrate (EC or E)

An emulsifiable concentrate formulation usually contains an oil-soluble liquid active ingredient, one or more petroleum-based solvents, and a mixing agent. The mixing agent allows the formulation to be mixed with water to form an emulsion. Emulsifiable concentrates are mixed with water and applied as a spray. As their name implies, they form an emulsion in the spray tank.

Solutions (S)

Solutions (water-soluble concentrates) consist of water-soluble active ingredients dissolved in water, for sale to the applicator for further dilution prior to field application. They will obviously form a true solution in the spray tank and require no agitation after they are thoroughly dissolved.

Dry or Solid Formulations

Solid formulations can be divided into two types: ready-to-use; and concentrates, which must be mixed with water to be applied as a spray. The properties of seven solid formulations are described in this publication. Three of the solid formulations (dusts, granules, and pellets) are ready-to-use, and three (wettable powders, dry flowables, soluble powders, and water-soluble packets) are intended to be mixed with water.

Dusts (D)

Dusts are manufactured by the sorption of an active ingredient onto a finely-ground, solid inert such as talc, clay, or chalk. They are relatively easy to use because no mixing is required and the application equipment is lightweight and simple.

Granules (G)

The manufacture of granular formulations is similar to that of dusts except that the active ingredient is sorbed onto a larger particle. The inert solid may be clay, sand, or plant materials. A granule is defined by size: Granule-sized products will pass through a 4-mesh (number of wires per inch) sieve and be retained on an 80-mesh sieve.

Pellets (P)

Pellets are very similar to granules, but their manufacture is different. The active ingredient is combined with inert materials to form a slurry (a thick liquid mixture). This slurry is then extruded under pressure through a die and cut at desired engths to produce a particle that is relatively uniform in size and shape. Pellets are typically used in spot applications.

Wettable Powders (WP)

Wettable powders are finely divided solids, typically mineral clays, to which an active ingredient is sorbed. This formulation is diluted with water and applied as a liquid spray. The mixture forms a suspension in the spray tank; however, they settle out quickly unless constantly agitated to keep them suspended. Furthermore, they can be abrasive to equipment; and they may cause strainers and screens to plug.

Water-dispersible Granules (WDG) or Dry Flowables (DF)

Water-dispersible granules, also known as dry flowables, are like wettable powders except instead of being dust like they are formulated as small, easily measured granules. Water-dispersible granules must be mixed with water before applying.

Soluble Powder (SP or WSP)

This is a dry formulation that contains a high percent active ingredient. Soluble powders look like wettable powders, but they form a true solution when added to water. Agitation in the spray tank will help this formulation to dissolve.

Other Formulations


Fumigants are pesticides that deliver the active ingredient to the target site in the form of a gas. Some active ingredients are liquids when packaged under high pressure but become gases when released. Other active ingredients are volatile liquids.

Microencapsulated Pesticides (M)

Microencapsulated pesticides are dry particles or liquid droplets surrounded by a coating. Coatings may be plastic, starch, or some other material. Microencapsulated pesticides are mixed with water and applied as a spray. In some situations, the encapsulation process can provide “timed” slow release of the active ingredient.

Water-soluble Packets (WSB or WSP)

More and more pesticide products are available in water-soluble bags (WSBs). A special film packages a precise amount of wettable powder, soluble powder, or gel containing the pesticide active ingredient(s).

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