Adjuvants and volatility of hormone herbicides

Abstract

AbstractThe aim of this study was to develop a rapid and reliable method for detecting the effect of adjuvants on the volatility of herbicides and to assess the efficacy of locally available adjuvants. Bioassays, using seed germination, were unsatisfactory for assessing the reduction of the volatility of the iso‐octyl ester of 2,4‐dichlorophenoxyacetic acid (2,4‐D IOE) by adjuvants.Field trials and parallel trials under controlled conditions, together with chromatographic analyses of trapped herbicide vapour, were effective in assessing the efficacy of adjuvants. The adjuvants used were: a molasses‐based developmental sample of a feeding attractant and antidrift agent; a wax emulsion contributing to control of droplet size; an anionic gel‐based sticker and spreader made from kelp; an alkoxylated‐fatty alkylamine polymer marketed as a wetter and penetrator; an aqueous dispersion of waxes and surfactants which reduces drift and evaporation; a polyvinyl polymer for drift reduction; an emulsifiable beta‐pinene polymer and two different formulations of an adjuvant with buffering action. Experimental grass plots were sprayed with herbicide with or without adjuvants (used as controls). 2,4‐D vapour in the air above the plots was sampled and analysed by gas chromatography. Field trial results indicated that weather factors influenced the volatility of 2,4‐D IOE and that only the polyvinyl polymer decreased volatility for the duration of the trial. The adjuvant consisting of a dispersion of waxes and surfactants had no effect on the volatility of 2,4‐D IOE. The molasses‐based, wax emulsion, and beta‐pinene polymer‐based adjuvants caused an initial increase in 2,4‐D IOE vapour, but the volatility decreased after two hours. Trials performed in a portable glasshouse showed similar results, and also showed that a new formulation of an existing adjuvant with buffering action reduced volatility.