ADJUVANTS AND VOLATILITY OF HORMONE HERBICIDES

The aim of this study was to develop a rapid and reliable method for d etecting the effect of adjuvants on the volatility of herbicides and t o 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 aci d (2,4-D IOE) by adjuvants. Field trials and parallel trials under con trolled conditions, together with chromatographic analyses of trapped herbicide vapour, were effective in assessing the efficacy of adjuvant s. The adjuvants used were: a molasses-based developmental sample of a feeding attractant and antidrift agent; a wax emulsion contributing t o control of droplet size; an anionic gel-based sticker and spreader m ade from kelp; an alkoxylated-fatty alkylamine polymer marketed as a w etter and penetrator; an aqueous dispersion of waxes and surfactants w hich reduces drift and evaporation; a polyvinyl polymer for drift redu ction; an emulsifiable beta-pinene polymer and two different formulati ons of an adjuvant with buffering action. Experimental grass plots wer e 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 g as chromatography. Field trial results indicated that weather factors influenced the volatility of 2,4-D IOE and that only the polyvinyl pol ymer decreased volatility for the duration of the trial. The adjuvant consisting of a dispersion of waxes and surfactants had no effect on t he 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 IO E vapour, but the volatility decreased after two hours. Trials perform ed in a portable glasshouse showed similar results, and also showed th at a new formulation of an existing adjuvant with buffering action red uced volatility.