Effects of trellising, crown bunch handling, and the number of oil emulsion and gibberellic acid sprays on harvest-pruned sultanas

Abstract

Effects of trellising together with the use of various foliage wire arrangements on the production and quality of harvest-pruned sultanas were studied over 4 years. In one experiment a single wire and four narrow 0.4 m 'T' trellis systems, and in a second experiment four 0.9 m wide 'T' trellis and one 0.4 m narrow 'T' trellis system, were tested. Other treatments superimposed on all trellises included crown bunch removal in early spring or at harvest pruning, one and two alkaline oil-in-water sprays (oil sprays) and gibberellic acid (GA) or no GA spray. There were no differences between the four narrow trellises. Dried fruit yield of these four trellises was greater than that of the single wire by an average of 27%, because of higher bunch and cane numbers. There were also no differences between the four wide trellises except that two of the complex ones had more canes. The narrow trellis NTI (used in both experiments) yielded 27% less than the wide trellises because of fewer bunches per vine, caused by lower cane numbers and fruitfulness. Trellising had no effect on fruit quality and only marginal effects on rate of fruit drying, most probably due to low vigour of the experimental vines. As the complex trellis systems had no advantage over the simpler two wire 'T' trellises, their use in harvest pruning is not advocated. In both experiments two oil sprays produced slightly better fruit quality with faster drying of fruit. Use of two oil sprays is warranted where fruit has to be dried rapidly to minimise risk due to rain damage. Early crown bunch removal did not reduce yield and the best time for bunch removal was 6 weeks after bud burst. Use of GA in harvest pruning is not recommended as it does not improve fruit quality and in some years leads to slower fruit drying.