Use and mode of action of adjuvants for herbicides: A review of some current work

The use of surfactants, mineral and vegetable oils, emulsifiers and fertiliser salts, such as ammonium sulfate, can greatly enhance the activity of foliage‐applied herbicides. Adjuvant‐herbicide interactions are reviewed with particular reference to the benefits, including dose reduction, enhanced and more consistent herbicide activity, and the nature of underlying mechanisms; the use and role of surfactants receive particular attention. Surfactants are used as activators in commercial formulations of many herbicides to improve their foliar absorption and ultimate biological activity. Current views on their influence are considered in relation to surface phenomena, solubilisation of non‐polar active ingredients, wax dissolution, cuticle penetration, preferential sites of penetration, membrane permeability and possible systemicity. The importance of a number of moderating factors (plant, chemical and environmental) is discussed in the light of current work, with particular regard to herbicide polarity, surfactant type, Hydrophile‐Lipophile Balance and critical micelle concentration. Current studies on the influence of nonionic polyoxyethylene surfactants of differing ethylene oxide (EO) content have underlined the importance of EO number to their activity.