Pruning Style and Long Term Irrigation Regime Effects on ‘Sunpreme’ Raisin Quality and Fruitfulness

Abstract

Crop harvest suitability and raisin quality were examined for the new natural dry-on-the-vine raisin cultivar ‘Sunpreme’ as influenced by irrigation and pruning style. Cane- and spur-pruned vines were evaluated under three irrigation regimes: full evapotranspiration (ET), 50% ET and a further reduced “Shock” treatment. Irrigation regimes were established on the vines in 2007, six years prior to the onset of the test in 2013. Vine fruitfulness and dormant pruning mass were compared during each of the study years, as were product moisture content and raisin quality. Vines irrigated at Full ET, both cane- and spur-pruned, were consistently lower in juice total soluble solids as compared with other irrigation treatment x pruning style combinations during 2014. Full ET treated vines had significantly higher product moisture content at harvest as compared with Shock-treated vines in both years of the study. ‘Sunpreme’ raisin quality was very high (> 93% B or Better) across irrigation plots during 2013 when crop load was adjusted to 62% of available clusters. A higher percentage of crop load (81%) was allowed in 2014, and B & better percentage was 91% for Full ET treated vines, but was considerably lower in other irrigation plots. B & better percentages did not differ significantly across pruning styles in either study year, but the percentage of substandard raisins was lowest for Full ET in 2014 when there was a higher crop load.