The effect of the physico‐chemical stability of emulsions of an ester of 2, 4‐D on their biological activity

The phytotoxicity of oil‐in‐water emulsions containing the ‘iso‐octyl’ ester of 2, 4‐D [(2, 4‐dichlorophenoxy)acetic acid], prepared by the dilution of emulsifiable concentrates, to Phaseolus vulgaris, was found to be independent of the surfactant concentration (‘Synperonic NPE 1800’ + ‘Ethoduomeen T20’) and of the emulsion stability. Moreover, spray retention was also independent of the surfactant concentration within the range studied (0.01‐150 g litre−1); this could be accounted for in terms of the energetic processes involved during impaction, and the subsequent adhesion of the spray droplets to the target surface. However, the independence of the phytotoxicity of the surfactant concentration and emulsion stability was not expected, and some tentative explanations are given for these results.