Autumn King is a late-season white-skinned table grape (Vitis vinifera L.), typically ripening in late October in the San Joaquin Valley. It is notable for its very large berries (>9 g natural berry weight), and high yield potential. Head-training and cane-pruning is recommended. Preliminary reports suggested Autumn King vineyards will yield 700-800 22 lb boxes of fruit per acre each year (Hashim-Buckey and Ramming), but more recently it was suggested the variety could produce 1,800 19 lb boxes/acre annually (Fidelibus et al., 2018). The difference in yield estimates depends, in part, on berry size, as original yield estimates were based on natural berry size of approximately 10 g, but optimal cultural practices can substantially increase berry size. Autumn King is patented and licensed exclusively to the California Table Grape Commission.
Origins and History
Autumn King originated from a planned cross of Vitis vinifera L. selections designed by David Ramming, USDA-ARS. A US plant patent (USPP16284P2) was awarded in 2006, and the variety is licensed to the California Table Grape Commission.
Autumn King grape vines are described in detail in the plant patent (Ramming and Tarailo, 2006). In short, the vines are relatively late to break bud, and young shoots are light yellow-green in color, though the shoot tips may show occasional red on the sun-exposed side. Leaf blades have an orbicular shape with five lobes. The petiole sinus is lyre-shaped, and usually half overlapped. Leaves are dark green, with light green veins, having occasional red on main veins near the center of the leaf. Vines are moderately vigorous with an upright growth habit.
Head-training and cane-pruning are recommended to ensure adequate yield. Depending on vine vigor and trellising system, 5-8 canes with 12 to 15 nodes per cane, are retained after pruning, along with up to four 2-node spurs for cane renewal. Modern table grape vineyards in California typically use open-gable trellis systems, which are Y-shaped trellises typically spanning 10 feet and supporting three foliage wires on each crossarm.
Shoot thinning, sterile shoot removal, and leaf removal around clusters is recommended (Hashim-Buckey and Ramming). However, excessive fruit exposure promotes the development of yellow fruit color, which is undesirable. Because Autumn King is harvested very late, it is susceptible to heavy rain and frost, and may benefit from the protection of plastic vine covers (Hashim-Buckey and Ramming; Fidelibus et al., 2016). Autumn King is particularly susceptible to powdery mildew, and requires a season-long control program.
Clusters are medium in size, and conical to cylindrical in shape. Berries are cylindrical to ovoid in shape and pale green in color. Acidity is low, and seed traces are present but not noticeable. Natural berry size is approximately 10 g, but cultural practices including the use of plant growth regulators (PGRs) and girdling, can substantially increase berry size and weight. A typical PGR program includes a gibberellic acid (GA3) thinning spray of 1 ppm at 60 to 80% bloom, followed by a sizing spray of 10 ppm GA at 8-10 mm diameter (Fidelibus et al., 2018). Forchlorfenuron (CPPU) can be used to further increase fruit size. The rate for such an application is approximately 8 ppm. Supraoptimal rates of CPPU may delay ripening. Vines may be girdled approximately two to three weeks after fruit set. and cluster tipping and hand thinning may be done in early June to loosen clusters and adjust cluster length and crop load.
Hashim-Buckey, J., and D. Ramming. Cultural practices for Autumn King. UCCE, Kern County.
Ramming, D.W., and R.E. Tarailo. 2006. Grapevine denominated ‘Autumn King’. USPP16284P2
Fidelibus, MW, SJ Vasquez, and SK Kurtural. 2016. Late-season Plastic Canopy Covers Affect Canopy Microclimate and Fruit Quality of ‘Autumn King’ and ‘Redglobe’ Table Grapes. HortTechnology 26:141-147.
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.