Use of the starwheel sprayer for applying drying emulsion to sultana grapes to be dried on the trellis

Abstract

The development of the starwheel sprayer for the application of drying emulsion to Sultanas is described. This sprayer consists, in its standard form, of three sets of six radially and horizontally arranged spokes. Each spoke is fitted with three wide angle, solid cone nozzles which spray near and inside the vine canopy. Spraying vines with the starwheel sprayer took one tenth of the time needed to spray the fruit to saturation by hand. Experiments indicated that at least 4000 l ha-1 of spray emulsion containing at least 1.5 per cent oil and 1.875 per cent K2CO3 were needed to obtain sufficient coverage of the fruit for an adequate rate of drying and to ensure good quality of the fruit. The colour of dried sultanas produced by trellis drying after spraying with the starwheel sprayer was darker and less uniform than the colour of fruit produced by rack-spraying and -drying. This appeared to be related to the system of trellis-drying in general rather than to the use of the starwheel sprayer. It is concluded that the starwheel sprayer successfully meets the requirements for applying drying emulsion to Sultanas to be dried on the trellis.