ABSTRACT
Ten test emulsifiers and one commercial product (Actipron®, B.P. Chemicals) were evaluated as adjuvants for use with two herbicide-mineral oil-water mixtures. The two herbicides were phenmedipham and quizalofop-ethyl. Effects on emulsion stability were determined by a simple standing test and by measuring oil droplet size in the emulsion. Stability was influenced by the herbicides (and any formulation components present in the herbicide concentrates) and/or the type of emulsifier. All phenmedipham emulsions were fully stable over the 16-h experimental period, including those formulated with oil but no emulsifier. The stability of the quizalofop-ethyl mixtures, however, depended upon the type of emulsifier used. The smallest oil droplets were observed in the phenmedipham mixtures, and the type of emulsifier had no influence on this. Oil droplets in the quizalofop-ethyl mixtures were approximately 125 times larger (by volume) than those in the phenmedipham emulsions, and none of the test emulsifiers produced droplets smaller than those formed using Actipron. The influence of emulsifier on herbicide efficacy was determined by spraying Chenopodium album L. (common lambsquarters) and Hordeum vulgare L. (barley) with phenmedipham and quizalofop-ethyl emulsions, respectively. Phenmedipham performance was significantly improved by five of the test emulsifiers, whereas, with quizalofop-ethyl, only two test emulsifiers enhanced performance compared with the Actipron treatment. In vivo and in vitro tests established that none of the test emulsifiers was phytotoxic to a typical broadleaved crop species Beta vulgaris L. (sugar beet).
