Submitted to: Journal of American Pomological Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2015
Publication Date: 1/15/2016
Citation: Ledbetter, C.A. 2015. ‘Sunpreme’ raisin quality and timing as affected by irrigation treatment and pruning style. Journal of American Pomological Society. 70(1):36-44.
Interpretive Summary: Winter rains can bring an abrupt end to the raisin season if the arrival is prior to removal of dry product from the vineyard. Raisin harvest timing is influenced by many factors: crop load, degree days received during the growing season, irrigation regime, and the specific grape cultivar used for drying. ‘Sunpreme,’ a recently-bred raisin cultivar from the Crop Diseases, Pests and Genetics Research Unit in Parlier, CA, is capable of drying naturally on the vine without cane cutting. It is a vigorous vine and heavy raisin producer, factors that generally delay harvest timing. We examined the harvest timing and resulting raisin quality in ‘Sunpreme’ vines when cultured with various irrigation regimes and pruning styles. It was determined that ‘Sunpreme’ could be harvested earlier, and without any loss of product quality, using a reduced or deficit irrigation schedule. Pruning style had little effect on harvest timing or raisin quality. These results are important in terms of irrigation water savings as well as the potential savings in raisin tonnage, through earlier harvests, in years when winter rains come early and have potential to damage product still in the vineyard.
Technical Abstract: Successful raisin production requires that a dry well-matured product be removed from the vineyard prior to the onset of winter rains. Crop maturity timing and raisin quality were examined in the new natural dry-on-the-vine raisin cultivar ‘Sunpreme’ as influenced by irrigation treatment 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. Crop loads were adjusted equally across vines in each harvest season with large differences in crop loads during the two study years. Irrigation treatment significantly influenced dormant pruning weight but not vine fruitfulness. Reduced volume irrigation treatments sped the raisining process, and no significant differences were noted in raisin quality from irrigation treatment or pruning style. Reduced volume irrigation treatments can be used successfully in ‘Sunpreme’ raisin to speed the raisining process without reducing raisin quality or vine fruitfulness. Advanced harvest maturity will reduce crop losses due to early winter rains.