Disclaimer: This article is geared towards a Tulare County audience and may not be applicable to other geographical areas.

Vine Growth and Rootstocks

Depending upon soil type and growing conditions, Autumn Royal exhibits moderate to high vigor when planted on its own roots. Specific information on cultivar performance when grafted on rootstocks is unavailable, but rootstocks are generally recommended for replant situations or when nematodes or phylloxera are present. Depending upon soil type and specific pest pressures, Harmony, Freedom, 5C and 1103-P are likely rootstock choices.

Pruning and Training Systems

Spur pruning is suggested to obtain maximum fruit quality; spur pruned vines normally produce larger clusters and berries than cane pruned vines. Fruit ripening and color development is normally more uniform on spur pruned vines as well. Differences in fruit quality between cane and spur pruned vines are due primarily to crop load effects, as well as to cluster location on the cane. Basal nodes (nodes 1, 2 and 3) generally produce larger clusters and berries than nodes in the mid (5 or 6) or apical (>10) sections of the cane.

If spur pruning is employed, quadrilateral cordon training (or similar divided curtain training configuration) is suggested for maximum productivity. Depending upon vine vigor and size, 24 to 32, 2-bud spurs are normally retained per vine (based on standard 8' x 12' spacing). Compared to vines trained to a divided curtain system, the productivity of bilateral cordon trained vines is lower since fewer buds or spurs are retained per vine. If cane pruning is used, heavy cluster thinning must be performed to avoid the potential for overcropping. As noted above, cane pruned vines typically produce smaller clusters and berries, and reduced fruit color, compared to spur pruned vines.

Productivity

Long-term productivity records are not available for this cultivar. Data collected in a small test plot located near Delano indicated that yields ranged between 700 and 800 boxes per acre on unmanipulated, bilateral cordon trained over a four year period. However, the cultivar has also exhibited somewhat erratic fruitfulness, and in one season yields dropped to 400 boxes per acre. The reason for this yield fluctuation is unknown, but may be related to climatic conditions during the fruit bud differentiation period. We are currently examining the effects of pruning method and cultural practices on the productivity of this cultivar in greater detail.

Cluster and Fruit Characteristics

Autumn Royal produces large clusters, with natural cluster weight averaging between 3 to 4 pounds in many vineyards. Clusters are conical in shape, and loose to well-filled. In some cases berry set is excessive, and clusters become compact or too tight. A potential problem with the cultivar is that its cluster framework or rachis is relatively weak. The attachment between the rachis and pedicel is fragile, and berries may separate from the rachis with their pedicel intact during harvest. Fruit should be packed in bags to avoid this problem.

The natural berry size of Autumn Royal is the largest among currently available seedless cultivars. Without gibberellin or girdling, berry weight can average 9 grams or more. In comparison, girdled and gibberellin treated Thompson Seedless berries typically weigh between 6 and 7 grams. Berries are ovoid to ellipsoidal in shape, and purple-black to black in color. The berry flesh is firm and translucent, and the skin low to medium in thickness. In some seasons, prominent seed traces are present in the berry.

Similar to many other black table grape cultivars, Autumn Royal berries are susceptible to berry cracking and rot. A relatively thin berry skin, along with well filled clusters, enhance its susceptible to these problems. Cracking is most commonly observed near the stylar scar of the berry. Clusters may withstand small amounts (1/4") of precipitation during the fall, depending upon post-rain conditions, without suffering significant damage. However, prolonged periods of inclement weather, such as the multiple rains which occurred during the fall of 1997, can result in significant fruit losses due to rot.

Cultural Practices

Canopy management. Canopy management practices, including shoot thinning, basal leaf removal and summer pruning, are similar to those normally performed on other cordon trained/spur pruned cultivars. Open canopies are desired near harvest to reduce humidity and increase wind movement following a rain.

Crop load management. Crop load has a significant impact on the fruit quality of Autumn Royal. Optimum crop load obviously varies among vineyards, depending upon vine vigor, berry set and tipping practices. Initial crop reductions are performed after berry set when shoots are thinned to a single cluster. In some cases, if berry set is excessive, it may be necessary to remove individual shoulders and reduce cluster compactness. Cluster tipping is also practiced to reduce cluster size and further decrease crop load. Untipped clusters may weigh up to 4 pounds at harvest, making them difficult to pack in bags. Clusters tipped to 7 or 8 shoulders typically weigh between 2 and 2.5 pounds at harvest. Based on this estimate, vines adjusted to 25 clusters would produce about 2 packed boxes of fruit per vine or 900 boxes per acre (based on 8' x 12' spacing). The severity of both cluster thinning and tipping are typically reduced in seasons of low fruitfulness.

Summary

Autumn Royal has significant commercial potential, primarily due to its late season market window and large clusters and berries. While information regarding optimum cultural practices will continue to be developed over the next few years, it is clear that effective crop load management is essential to produce high quality fruit. At present, quadrilateral cordon training (or other divided curtain training configuration) and spur pruning may be the best way to assure optimum cropping efficiency and fruit quality. Although further testing is needed to determine long-term effects of GA berry thinning applications on vine productivity, these treatments will likely become a standard practice. GA thinning applications decrease cluster compactness and increase berry size, enhancing fruit quality. The use of GA for berry sizing appears less desirable, not only due to possible detrimental effects on bud fruitfulness, but also to decreased fruit color. Girdles applied at fruit set increase berry size, but also retard fruit color development and delay harvest. However, fruit set girdles have the additional benefit of improving berry firmness.

^zNumbers followed by the same letter within columns are not significantly different at the 5% level (Duncan's Multiple Range Test).

^zNumbers followed by the Fame letter within columns are not significantly different at the 5% level (Duncan's Multiple Range Test).

^ZNumbers followed by the same letter within columns are not significantly different at the 5% level (Duncan's Multiple Range Test).

^ZNumbers followed by the same letter within columns are not significantly different at the 5% level (Duncan's Multiple Range Test).