Surfactants are classified by how they split apart into charged atoms or molecules, called ions.
Anionic surfactants have a negative (-) charge. They are most often used with contact pesticides, which control the pest by direct contact instead of being absorbed into it systemically.
Cationic surfactants have a positive (+) charge. Do not use them as stand-alone surfactants often, they are phytotoxic.
Nonionic surfactants have no electrical charge. They are often used with systemic products to help pesticides to penetrate plant cuticles. They are compatible with most pesticide products. A pesticide can behave very differently in the presence of an anionic, cationic, or nonionic surfactant. For this reason, you must follow label directions when choosing one of these additives. Selecting the wrong surfactant can reduce efficacy and damage treated plants or surfaces.
The terms used with pesticide additives can be confusing. People sometimes use the words adjuvant and surfactant interchangeably. However, an adjuvant is ANY substance added to modify properties of a pesticide formulation or finished spray. A surfactant is a specific kind of adjuvant one that affects the interaction of a spray droplet and a treated surface. All surfactants are adjuvants but not all adjuvants are surfactants. For example, drift control additives and safeners are not surfactants.