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Ch. 6, pp. 6 - 9

[Pesticide Formulations: formulations | label ]

The formulation describes the physical state of a pesticide and determines how it will be applied. Pesticides are rarely applied full strength. The chemical in the pesticide formulation that actually kills the pest(s) is termed the active ingredient. The added chemical(s), those which make the product easy and safe to formulate or apply, are termed the inert ingredients. Common pesticide formulations follow.
Emulsifiable concentrates (EC or E)
The active ingredient is mixed with an oil base (often listed as petroleum derivatives) forming an emulsion which is diluted with water for application. ECs are common in the home garden trade, being easy to mix and use. They can cause a minor surface bronzing of light-colored fruit. They should be protected from freezing temperatures which can break down the emulsifier.
Solutions (S)
These formulations are premixed, ready to use. They are often used in household pest products.
Flowables (F or L)
A flowable, or liquid, can be mixed with water to form a suspension in a spray tank.
Aerosols (A)
These are very low-concentrate solutions, usually applied as a fine spray or mist. They are generally sold in aerosol cans and are a very expensive source of pesticide.
Dusts (D)
Made by adding the active ingredients to a fine, inert powder or talc; generally used dry.
Granules (G)
Granular formulations are made by adding the active ingredient to coarse particles (granules) of inert material like fired clay particles.
Wettable powders (WP or W)
Wettable powder formulations are made by combining the active ingredient with a fine powder. They look like dusts, but they are made to mix with water. These formulations need continuous agitation to maintain a suspension and are thus difficult for home gardeners to use. When mixing a WP, first mix the measured quantity with a small amount of water, forming a slurry, (a paper cup with a popsicle stick makes a good disposable mixing container) then add it and the additional water to the spray tank. The spray tank must be frequently shaken to maintain the suspension.
Soluble powders (SP)
Made of an active ingredient in powder form; dissolves in water.
Baits (B)
A bait formulation is made by adding the active ingredient to an edible or attractive substance. Baits are often used to control slugs, snails, ground-dwelling insects, and rodents.
Gardeners often attempt to compare a spray with a dust. It should be noted that dusts are a type of formulation, but sprays are not a formulation; they are one means of applying several different formulations such as wettable powders or emulsifiable concentrates that are mixed with water.


When added to a pesticide, a surfactant reduces the surface tension between two unlike materials, such as a spray film and a solid surface. For example, by adding a surfactant to a sprayer, oil and water will mix and can be sprayed on plant surfaces. With increasing emphasis on safe application of pesticides, such factors as droplet size, spray pattern, and pesticide drift have focused more attention on surfactants to give ideal coverage for pesticides.
Surfactants include: activators; compatibility agents; deflocculators; detergents; dispersants; emulsifiers; foam and drift suppressants; and spreading, sticking, and wetting agents. These materials are added to a spray mix to help keep the pesticide in suspension; improve cohesiveness and dispersion of the spray; and increase the wetting (or coverage) of the leaves, fruits, and stems.
This section focuses on surfactants that act as spreading, sticking, and wetting agents. They are most useful when spraying the hard-to-wet foliage of such plants as azalea, boxwood, camellia, carnation, conifer, euonymus, gardenia, gladiolus, holly, iris, narcissus, peony, rose, and yew. Whether a spray rolls off or sticks to a plant surface depends on the physical and chemical properties of the spray mixture and the physical properties of the surface itself. If the surface tension of the mixture is high, or if the plant surface is waxy, the spray droplets will roll off.
A spreader or film extender (spreader-activator) is a substance that, when added to a pesticide mix, increases the area that a given volume of spray will cover and improves the contact between the pesticide and the plant surface. A spreading agent builds spray deposits and improves weatherability. Most wettable powder insecticides benefit from the addition of a spreader.
A sticker or adhesive is a material that, when added to a spray mix or dust, improves the adherence (tenacity) to a plant surface rather than increasing the initial deposit. Commercial sticking agents are oily in consistency and increase the amount of suspended solids retained on plant surfaces by coating the particles with a resin or varnish-like film. Most fungicides, especially wettable powders, benefit greatly from the use of stickers. Stickers may be judged in terms of resistance to wind and water, length of adherence, and mechanical or chemical action.
A wetting agent is a material that, when added to a pesticide, lowers the interfacial tension between a liquid and a solid; in this case, a plant surface. Effectiveness is measured by the increase in spread of a liquid over a solid surface and the ability of the spray film to make complete contact with it. When a wetting agent reduces surface tension, spreading naturally occurs.
The pesticide label should state whether a surfactant is needed or should be added to a spray mix for certain applications and should indicate restrictions in the selection of compatible surfactants. In many cases, surfactants have been designed specifically for use with fungicides, insecticides, or herbicides.
All commercial spreading, sticking, and wetting agents should be mixed strictly according to label directions. Adding more surfactant than recommended may cause excessive runoff, resulting in a poor spray deposit and reduced pest control. In general, if the spray mix contains one or more pesticides produced or formulated by the same company, use a surfactant sold or recommended by that company. Surfactants are sold separately from pesticides and are not subject to EPA registration.
Although choosing an effective surfactant to accompany a specific pesticide is no simple task, the label will state whether a surfactant is needed and the brand that should be used.

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