Spreaders, Wetting Agents, and Surfactants
Discussion
We are talking here about three related classes of adjuvants that often overlap in the same material, but not always.
A spreader increases the area covered by a liquid on a solid or another liquid.
A wetting agent increases the ability of a liquid to wet, or make real contact, with a solid surface. The liquid might replace another contaminant on the solid surface. Wetting is measured by retention of a liquid on a tilted surface.
A surfactant (surface active agent) helps mix polar solvents, such as water, with non-polar solvents, such as oil. Each surfactant molecule has a hydrophilic end attracted to the polar solvent and a hydrophobic end attracted to the non-polar solvent. The surfactant molecules line up in a film between the two solvents, allowing them to mix as small droplets. An example is a detergent.
Many wetting agents are also penetrants, which help materials move across waxy coverings of plants or arthropods. Some spreaders are also stickers, which bind materials to surfaces.
Spreaders, wetting agents, and surfactants can improve the efficacy of insecticides, fungicides, and herbicides. But they can also leave an unsightly residue or increase the risk of injury to a crop, especially for fruit with fragile skin, such as grapes. Care must be taken in the selection and concentration of these adjuvants. High temperatures can increase the risk of crop injury.
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