Scarlet Royal is a mid-season red-skinned table grape (Vitis vinifera L.), typically ripening in mid to late August, in the San Joaquin Valley of California. This variety produces large (1.8 lb) conical-shaped clusters that are medium to well-filled (Hashim-Buckey and Ramming). Berries are oval in shape and of similar appearance to Crimson Seedless. Natural berry size is moderate to large for table grapes, 5-7 g, and generally color well naturally. Growers may expect 1,600 19-lb boxes of fruit per acre annually (Fidelibus et al., 2018). Scarlet Royal is patented and licensed exclusively to the California Table Grape Commission.
Origins and History
Scarlet Royal resulted from a planned cross of two red seedless grape (Vitis vinifera L.) selections, with embryo rescue technique to develop a seedling from the seedless parents. The variety was first selected as B1, and subsequently released as Scarlet Royal in 2006. A US plant patent was awarded in 2006 (US Plant Patent 16,229), and the variety is licensed to the California Table Grape Commission.
Scarlet Royal grape vines were described in detail by Hashim-Buckey and Ramming. In short, the vines are moderately vigorous on their own roots, and fruitful on basal nodes. Quadrilateral cordon training and spur pruning, on an open-gable trellis, are recommended. Cluster counts of 50-70 per vine were thinned to 40-45 following berry set (Hashim-Buckey and Ramming). Natural color development is better than Flame Seedless or Crimson Seedless, but ethephon may be used if needed. However, ethephon-treated fruit may develop an undesirable purple color.
Scarlet Royal has moderate vigor on its own roots. Pruning weights and yields were increased by grafting onto certain rootstocks (1103P and Freedom; Fidelibus, unpublished). This variety has fruitful basal nodes and is typically trained to quadrilateral cordons and pruned to spurs. Most commercial vineyards use an open-gable trellis (Y) system. Natural berry size is medium to large for table grapes, 5-7 g, and can be increased with the use of gibberellic acid. Gibberellic acid (GA3) is applied twice annually. The first application is a thinning spray, of 2 to 2.5 ppm (GA3) at 40 to 60% bloom, and the second is a sizing spray of 10 ppm at fruit set. Girdling may increase heat damage and berry astringency, and is thus not recommended. Berries generally color well naturally, and the use of plant growth regulators to improve color, such as ethephon or abscisic acid, may promote the development of an undesirable purple color.
Shoot thinning at 8-10”, shoot positioning, and minor leaf removal in the fruit zone can reduce humidity, and improve fruit exposure to the sun and agrichemicals. Canopy management seems to improve color development in this variety. Shoot trimming or hedging in the row middles just prior to harvest helps reduce humidity, which may be beneficial for suppressing bunch rots.
Scarlet Royal generally has large, well-colored, attractive berries, with firm, meaty flesh and a sweet and neutral flavor. However, Scarlet Royal berries can develop an undesirable astringency and bitter flavor if held too long on the vine. Hashim-Buckey and Ramming suggested harvest should begin after fruit is sweet (>17 Brix), and the berries are well colored near the capstem and continue until fruit accumulate > 22 Brix, after which they are more likely to have astringent or bitter flavors.
Hashim-Buckey, J., and D. Ramming. May-June 2008. Cultural practices for Scarlet Royal. UCCE, Kern County. https://cekern.ucanr.edu/files/98672.pdf
Fidelibus, M., A. El-kereamy, D. Haviland, G. Zhuang, D. Stewart, and D.A. Sumner. 2018. Sample costs to establish and produce table grapes. San Joaquin Valley South. Autumn King, Late Maturing. Univ. California Coop. Ext. Dept. Agr. Resource Econ., Davis.