Claire Villasenor, Dylan Ellis, Michael Anderson, M. Andrew Walker, and Jean Peterson *
*California Polytechnic State University, One Grand Avenue, San Luis Obispo, CA 93407 (jdodsonp@calpoly.edu)

Cordon-trained, spur-pruned grapevines frequently display variation in development as a function of position along the cordon. Discrepancies in shoot growth and/or cluster ripeness can impact the timing and success of vineyard management activities such as leaf and cluster thinning and eventual fruit maturity indices at harvest. The objective of this research is to determine the role that shoots/meter manipulation has on berry chemistry and on the homogenization of shoot development down the length of a cordon. The study was conducted in Oakville, CA, on bilateral cordon-trained, spur-pruned Cabernet Sauvignon vines on 1.8 × 2.5 meter spacing. Vines were pruned to either 5.5 shoots/meter or 11.1 shoots/meter for a total of 12 or 24 buds per vine, respectively.  Parameters measured include shoot length, internode length, cane diameter, and pruning and cluster weights. Berry sampling was performed as a function of position along the cordon (head, middle and end) and encompassed soluble solids, pH, titratable acidity (TA), and total phenolics. In the first and second year of the study, implementation of 5.5 shoots/meter resulted in uniform shoot internode length, diameter, and berry chemistry down the length of the cordon. The 11.1 shoots/meter treatment demonstrated variable development as a function of position with respect to both shoots and clusters. In year three, the 5.5 shoots/meter treatment began showing trends similar to that of the 11.1 shoots/meter with respect to berry chemistry, in that non-uniformity was an issue as a function of position along the cordon. Specifically, cluster soluble solid accumulation in the 5.5 shoots/meter treatment was higher at positions originating from the head of the vine than at the end. The 5.5 shoots/meter treatment also exhibited higher berry pH at positions originating from the head and lower pH at the end cordon positions.

Funding Support: Funding for this project was generously provided by the California State University Agricultural Research Institute and the CSU College of Agriculture, Food and Environmental Sciences Summer Undergraduate Research Program.