Pesticides formulations: Wettable powders
A pesticide formulation is a combination of active and inert ingredients that forms an end-use pesticide product. 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.
Wettable powders are dry, finely ground solid materials. Most include wetting and/or dispersing agents. Usually, they must be mixed with water and applied as a spray. A few products, however, may be applied dry or as a liquid suspension.
Wettable powders contain 5% to 95% active ingredient—usually 50% or more. Wettable powder particles do not dissolve in water. When mixed with water, they form a suspension. They will settle out quickly without constant agitation to keep them suspended.
To prepare a spray suspension, you must form a slurry. Mix a WP with a small amount of water, and then dilute this slurry mixture further.
Wettable powders are effective for most pest problems and in most types of spray equipment where agitation is possible. They have excellent residual activity and do not usually harm treated surfaces. When you apply a WP spray suspension to a target, most of the pesticide remains on the surface. This is true even for porous materials, such as concrete, plaster, and untreated wood. In such cases, only the water carrier penetrates the porous material. Wettable powder particles remain on the treated surface.
- Easy to store, transport, and handle.
- Less likely than ECs and other petroleum-based formulations to harm treated plants, animals, and surfaces.
- As a rule, not phytotoxic.
- Less risk of skin and eye absorption than ECs and other liquid formulations.
- Not easy to measure; must be weighed.
- Not easy to mix.
- Inhalation hazard to applicator while measuring and mixing the concentrated powder.
- Suspended particles require good and constant agitation (usually mechanical) in the spray tank and quickly settle out if agitation ceases.
- Abrasive to pumps and nozzles; cause equipment wear.
- Difficult to mix in very hard or very alkaline water.
- If not mixed properly, may clog nozzles and screens.
- Residues may be visible on treated surfaces.