Adjuvants for use with fungicides have been known since the first studies on formulation efficiency and it is now well known that the activity of systemic fungicides can be improved by a proper choice of additives and/or adjuvants. Several studies have clearly demonstrated that these improvements result from changes in such factors as droplet formation, surface contact and behaviour of the deposit, penetration into the leaf (transcuticular or stomatal) and transport within the plant, as well as interactions within the fungal cell. The transfer of these results from laboratory studies to field trials often yields inconsistent results and simulation models often fail to predict the behaviour of adjuvants under field conditions. This is probably because many factors are involved which cannot be controlled in the field. For example, droplet formation can be very different, leaf structure and canopy formation can interfere, and results for one particular fungicide/crop/fungus/adjuvant combination cannot be translated to another situation. This multiplicity of very complex interactions is probably the main reason why there has been no general breakthrough in practical adjuvant use with fungicides. More applied research is needed to optimise the specific application conditions for each crop/fungicide/fungus combination. There are still some unresolved problems associated with the use of adjuvants such as loss of selectivity and the occurrence of phytotoxic side-effects. Also some unexpected specific interactions between adjuvants and formulation constituents can influence the activity which necessitate more fundamental studies on the biochemical and physicochemical background of their mode of action.
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