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

Grapegrowers in the southern San Joaquin Valley (SJV) struggle to achieve prof­itability due to increased labor costs. Since manual pruning accounts for >30% of production cost, mechanical pruning is an attractive alternative on bilateral cordons. In addition, SJV’s hot climate make it difficult to achieve an optimal berry color for red Vitis vinifera cultivars. To study the effect of mechanical pruning on yield and berry composition, we selected Cabernet Sauvignon and Petite Sirah for a two-way factorial split-plot study in a commercial vineyard located near Kerman, CA, in 2021. Bilateral cordon, spur-pruned, Cabernet Sauvignon and Petite Sirah vines grafted on 1103 Paulsen were chosen. Vines were planted in 2018 and hand-pruned before mechanical pruning was implemented in January 2021. Two cordon heights and two levels of water deficits, replicated three times, were used in this study with five vines designated as an experimental unit. Cordon height is 54” and 68” above the vineyard floor. One water deficit is the sustained deficit irrigation (SDI): 80% ET_c from berry set until harvest and the regulated deficit irrigation (RDI), of 50% ET_c from berry set to veraison, then back to 80% ET_c until harvest. Midday leaf water potential (Ψ) and fruit-zone photosynthetically active radiation (PAR) were measured to assess vine water stress and the fruit-zone light environment. Higher cordons improved berry TSS for both cultivars, but improved berry anthocyanins only in Petite Sirah. Cordon height had no effect on any yield components. RDI reduced the berry size of Cabernet Sau­vignon and the cluster size of Petite Sirah, but improved berry anthocyanins only in Petite Sirah. The study will be repeated in 2022.

Funding Support: No external fund