Influence of Canopy Density on the Performance of Vertically Shoot Positioned Grapevines in the Central Coast
The purpose of this study is to examine the effects of leaf area density on the performance of vertically shoot positioned Chardonnay grapevines in coastal regions. The primary objective is to develop quantitative guidelines for optimum canopy density and vine performance for vertically shoot positioned canopies. The experiment was established in 1996 in a mature, vertically shoot-positioned Chardonnay vineyard located near Greenfield in the Salinas Valley. The vines are bilateral cordon trained and spur pruned. Primary shoot density was adjusted to 14, 28 or 40 shoots per vine (approximately 10 to 26 shoots per meter) following budbreak. Additional adjustments were performed as needed during the growing season to maintain treatment integrity. Each treatment was replicated eight times using seven vine plots. The middle three vine spaces in each plot were used for light, canopy assessment, and vine performance measurements. In the first season of study, cluster number and yield per vine improved with shoot density. Vines thinned to 14 shoots produced approximately 2 tons per acre, while vines with 40 shoots produced about 5 tons per acre. Despite producing lower yields and having the greatest leaf area:fruit weight ratio among the treatments, fruit from vines thinned to 14 shoots had the lowest soluble solids in the experiment. Total leaf area per vine increased with shoot density (7 to 9 m2 for vines thinned to 14 shoots and 40 shoots, respectively), while pruning weight was lowest for vines thinned to 14 shoots. Vines with 14 shoots had lower leaf layer numbers, greater numbers of canopy gaps, and higher percentages of exterior leaves and clusters, compared to vines with 28 and 40 shoots per vine. Light penetration within the canopy declined as shoot number per vine increased. Cluster counts will be collected in spring 1997 to determine treatment effects on return fruitfulness.