13 - The Use of Emulsions in the Application of Pesticides

Abstract

Abstract Emulsions are widely used as a vehicle for the application of pesticides, both to crops and to livestock. They are usually supplied as an “emulsifiable concentrate”, i.e. a solution of the pesticide in an organic solvent, containing suitable surface-active agents so that a stable oil-in-water emulsion can be formed simply by mixing with water using the minimum of agitation. The development of emulsifiable concentrates of most pesticides is a relatively straightforward task. The fundamental principles are understood in general terms, and certain semi-empirical concepts such as hydrophile–lipophile balance (HLB) can be utilized. A vast range of emulsifier blends, usually of anionic and nonionic species, is available, and it falls to the skill and experience of the formulator to select from these to produce a formulation of the desired properties. However, it is questioned whether sufficient attention is given to deciding just what these properties should be. At present, the main emphasis is almost invariably directed towards achieving a high level of emulsion stability in the final dilution. Sight is often lost of the fact that the emulsion is merely a vehicle for conveying the pesticide to the foliage, or other substrate where it is to act. The interaction of the emulsion with this substrate may be of vital importance in determining the biological effectiveness of the application. This interaction may arise from the properties of the emulsion itself or from the surface-active agents present. In the past, any advantages that might be obtained in this way have usually been sacrificed to the need for emulsion stability. However, with modern spray machinery, a high degree of emulsion stability may no longer be required, and it should be possible to adapt a more flexible approach to produce emulsions which have the characteristics required for satisfactory application and optimum biological efficiency.