Surfactants and Additives

An adjuvant is any material added to a herbicide spray solution to enhance or modify the performance of the solution. Adjuvants can be divided into two general categories: spray modifiers and activators (Kirkwood, 1994). Spray modifiers are those adjuvants that change the wetting, spreading or sticking characteristics of the spray solution. This is primarily accomplished by a modification in the surface tension of the spray solution. Activator adjuvants primarily influence the absorption of the herbicide by a direct interaction with the plant cuticle. The most common types of adjuvants are surfactants (surface active agents). Surfactants can be defined as spray additives that facilitate or enhance the emulsifying, dispersing, spreading, sticking or wetting properties of liquids (spray modifiers). However, surfactants also directly influence the absorption of herbicides by changing the cuticle characteristics (activators). Surfactant types receiving significant attention in the past few years are organosilicones. Another commonly used adjuvant type is oil. In addition to oils being used as adjuvants they can also be used as contact herbicides and as carriers for synthetic herbicides. A third adjuvant type, salts commonly used as fertilizers, is rapidly gaining in popularity. A final adjuvant grouping are buffers which are used to adjust the acidity of the spray solution. The most commonly used buffers are for reducing the pH of water.