Shijian Zhuang,* Qun Sun, Kaan Kurtural, and Matthew Fidelibus
*University of California Cooperative Extension, Suite 210-B, 550 E Shaw Ave, Fresno, CA, 93710 (gzhuang@ucanr.edu)

Cabernet Sauvignon and Petite Sirah are the top red winegrape cultivars in CA; however, the hot climate in Fresno is not ideal for red Vitis vinifera, particularly for berry color development. Mechanical pruning and water deficit have been studied previously in this region, but there is a lack of research on cordon height and irrigation in mechanically-pruned vineyards. A two-way (2 × 2) factorial split block design, replicated three times, was implemented in Fresno in 2021 and 2022, with the same experimental design applied to both cultivars. The two levels of water deficit were regulated deficit irrigation (RDI) and sustained deficit irrigation (SDI). Water deficit in RDI plots was maintained at 60% ETc from berry set to veraison and 80% ETc from veraison to harvest, while water deficit in SDI plots was maintained at 80% ETc from berry set to harvest. The two cordon heights were 52 and 68 inches above the vineyard floor. In Cabernet Sauvignon, the high cordon, with >20% more leaf area, increased total soluble solids (TSS) by 2 Brix and anthocyanins by 11% above the low cordon without affecting yield. The effect of water deficit was mainly on berry size and the yield reduction was due to smaller berry size in RDI. There was no interactive effect of cordon height and water deficit on yield performance and berry chemistry. Similar results were found in Petite Sirah, with high cordon increasing berry anthocyanins by 30%. High cordon and water deficit can be used in mechanically-pruned vineyard systems in a hot climate; however, given the potential yield reduction from RDI, a high-cordon trellising system is preferred to improve berry TSS and anthocyanins, with no negative impact on yield.

Funding Support: No external funding