Pesticide Formulations
Insecticides are seldom available in their pure form. The technical grade material or active ingredient is formulated with other components which may increase efficiency, reduce toxicity and improve ease of handling, mixing and application.
Some of the most commonly used pesticide formulations used in urban pest control include:
OIL SOLUTION CONCENTRATES are made by dissolving technical grade material in an oil based solvent. Prior to use, the oil solution concentrate is diluted with another oil based carrier such as dieseline or kerosene by the user to achieve the correct application strength. Oil solutions of an insecticide usually provide faster knockdown and kill, because the solvents often have insecticidal action alone and increase the penetration of the active ingredient into the insects' cuticle. The disadvantages of oil solution include the high cost of diluent, damage to paints, phytotoxicity (damage to plants), increased odour and fire risk.
EMULSIFIABLE CONCENTRATES (EC) are made up of the technical material, solvent and emulsifiers. These formulations are diluted to application strength in water. The resulting emulsion maintains many of the advantages of oil solution concentrates without many of the disadvantages.
WETTABLE POWDERS (WP) are formulations made by adding the active ingredient to a diluting powder and mixing this with wetting agents and dispersing agents to allow the product to mix readily with water. Wettable powders do not dissolve in water, they form a suspension. How long the product will stay suspended is determined by how finely it is ground.
Suspensions of wettable powders require regular agitation to maintain even mixing and to avoid settling to the bottom of the tank. Wettable powder formulations should be mixed and used freshly to avoid settling and degradation. Remember, a wettable powder formulation is just that, a powder which can be mixed with water to make application easier.
With no solvent the odour associated with wettable powder formulations is far less than E.C. formulations, and is less likely to damage plants, furnishings, paint etc. than E.C. formulation. Lack of solvent also means that wettable powders are slower to be skin absorbed, and they are less flammable.
By virtue of the fact that wettable powders are just that - powders, this formulation will provide improved residual control on porous surfaces because the applied spray after the water or carrier has evaporated, will remain on the surface and will not be absorbed into the material as an E.C. would. Depending on the formulation, some wettable powder formulations can leave visible residue, particularly on dark surfaces.
SUSPENSION CONCENTRATES (SC) formulations are highly refined wettable powder type formulations, in which the product is pre- suspended by the manufacturer in a liquid, usually water based.
Suspension concentrate or flowable wettable powders formulations overcomes many of the negative attributes of wettable powders in terms of mixing and suspensibility while maintaining the advantages of low odour, not absorbed by porous surfaces etc. Two big advantages of suspension concentrates formulations is that they are manufactured as a liquid suspension so that when diluted with water for application, are much less likely to degrade in the spray tank between jobs or overnight and are much easier to resuspend by agitation than W.P. formulations.
WATER SOLUBLE GRANULE (WSG) formulation is another variation of the wettable powders, in which the product is formed into dry granules which can be measured by volume as if it were a liquid. Water soluble granules tend to be highly refined powders which mix easily and stay suspended longer lessening the need for agitation.
WSG formulations tend to have a high concentration of active ingredient which reduces the total volume of products required, and this reduces transport costs and also leads to less visible residue problems after application.
DUST FORMULATIONS are ready-to-use formulations usually manufactured by combining the active ingredient with a dust diluent which is usually inert. The concentration of active ingredient in the dust formulation can vary from almost 100% to quite low concentrations such as Coopex Dust which is 1%.
Some dust diluent used, such as diatomaceous earth and silica aerogel, have dessicant or abrasive properties which assist the active ingredient absorption and efficiency. Inert dust diluents are used to simply ease application and the even distribution of what otherwise would be very small quantities of active ingredient.
Dust formulations have many advantages in being able to provide greater distribution of the active ingredient into voids and cavities. They can also be used to apply insecticide around electrical motors and equipment where liquid application is dangerous.
Dust formulations sit loosely on surfaces and so can be picked up on the bodies of pests passing through the area. This characteristic of dusts or powder is exploited to great effect with the use of tracking powder for rodent control, arsenic dust for subterranean termites control and insecticidal dust for cockroach control.
This characteristic is also a disadvantage in that the product can also become airborne, increasing the risk of human exposure or treatment efficiency reduction respectively. Many dust formulations suffer from visible residue problems. In all respects the application of dust formulations needs to be carefully and skilfully applied to ensure human safety and treatment effectiveness.
BAIT FORMULATIONS consist of the active ingredient mixed with a bait attractant, usually a preferred food of the pest. In recent years, pheromone (sex) attractants have been combined with active ingredient to make baits for many pests.
Baits may take the form of granules, pellets, paste or liquids. They are particularly useful when the pests forage widely and where there is little alternative food. Baits are useful for social insects where the food is collected and shared within the colony.
Food based bait can be a major hazard for non-target animals. Careful placement of baits is essential to ensure they are easily accessible for the target pest, but are not accessible to non target animals.
MICROENCAPSULATED formulations are made by suspending or encasing the pesticide in droplets of a polymer (plastic). The release rate will vary depending on the polymer used, the size of droplets formed and the wall thickness of the droplet.
The controlled release nature of microencapsulated formulations may increase the residual effect, the odour, the speed of action and the health and safety characteristics of the products.
Because polymers are not soluble in water, the formulations are generally suspended in water to form a flowable suspension. The general handling and mixing procedures should be similar to that of wettable powders and suspension concentrates.
AEROSOL formulations are generally packed in ready to use containers. Although "aerosol" strictly means very fine spray droplet, over the years it has become synonymous with pressure pack cans and cylinders. Aerosol formulations are therefore basically a convenient method of application, rather than a formulation as such.
An aerosol ready-to-use formulation is made by mixing and placing the insecticide and carrier and propellant into the application container or pressure pack can. In some cases the carrier and the propellant may be one and the same. For example, Pestigas uses carbon dioxide as the carrier and propellant.
LACQUER formulations are another method to prolong the residual effect of the insecticide. The insecticide is dissolved in the lacquer which is applied by paint brush or spray to surfaces. The lacquer dries, leaving a film through which the insecticide migrates to the surface over a period of time.
The advantage of lacquer formulations is in areas regularly washed, since when the insecticide is washed from the surface of the film, another "bloom" will occur from within the film to replace the insecticide that was removed.