ORGANOSILICONE SURFACTANTS AS ADJUVANTS FOR AGROCHEMICALS

The literature has been reviewed and 160 references are presented to provide an overview of organosilicones as adjuvants for agrochemicals. Early studies (1973-1981) elucidated the special properties of these compounds, notably their extreme spreading and, by virtue of the exceptionally low surface tensions of their aqueous solutions, the ability to induce infiltration of spray formulations into foliage via stomata. Subsequent research at the New Zealand Forest Research Institute explored these and other properties in-depth, and demonstrated that they enabled the herbicide glyphosate to be used as a cost-effective alternative to 2,4,5-T for the control of forest scrubweeds. As a result, in 1985, 'Silwet' L-77 was the first organosilicone adjuvant to be commercialised, and various other products have subsequently been introduced. The chemistry and synthesis of these organosilicones have been detailed. A mechanistic approach has been adopted to consider the effects of the distinctive properties of organosilicones in each of the processes involved in spray application of agrochemicals. Commencing with spray formulation, the topics of foaming, hydrolytic stability and interactions with co-formulants are discussed. Progressing to spray application, consideration is given to the effects of organosilicones on atomisation and impaction (wetting, adhesion/reflection, spreading, retention/run-off), and the resultant influences on the activity of protectant agrochemicals. An assessment of the use of organosilicones with systemic agrochemicals includes examination of effects on foliar uptake, via both cuticular and stomatal pathways, and the rainfastness which the latter provides. Also considered is the physiological behaviour of organosilicones, specifically phytotoxicity and effects on translocation of active ingredients. The current and potential future use of organosilicones with herbicides, foliar nutrients, growth regulators, insecticides and fungicides is discussed, as is the specificity of their effects. Additionally, the potential application of organosilicone chemistry to adjuvant classes other than the spreader/penetrant type investigated to date is considered. Finally, the issues of registration, handling hazards, both toxicological and chemical, and environmental impact are discussed. The literature reviewed demonstrates the sound science base on which this novel class of organosilicone adjuvant chemistry rests.