Training Systems for Hybrid Winegrapes in Subtropical Climates

Vine productivity is a function of adequate shoot growth, disease management, and light penetration into the canopy.  High vigor, prevalent in a humid climate, can lead to decreased vine productivity and fruit yield by increasing shading in the canopy.  Reduced light penetration into the fruit zone reduces fruit bud initiation, resulting in declining yield over subsequent years.  The objective of this project was to address declining yields in Florida hybrid bunch grapes by improving vine balance with the application of different training and renewal systems.  In 2011 and 2012, six-year-old ‘Stover’ grapevines were trained to two different pruning systems, a bilateral cordon (control) or four-arm kniffen (4AK).  In addition, the existing bilateral cordon system was altered in two separate treatments to renew cordons [1/2 of vine each year; cordon renewal (CR)] or extend cordon length, in which every other vine was removed [alternate vine removal (AVR)]. All treatments were pruned to approximately 100 buds/vine during the dormant season.  Total yield per vine, berries per cluster, berry weight, fruit quality assessments [°Brix, pH, and titratable acidity (TA)], dormant pruning weights, and calculated Ravaz index was collected each year. In 2011, the average yield per vine was greatest in control, followed by AVR, while in 2012, vines in the AVR had the greatest average yield per vine.  In both years, extending the cordon length in the AVR treatment resulted in the highest number of buds per vine, contributing to the higher average yield per vine.  Berry weight was not affected in either year; however berries per cluster were reduced in the control when compared other training or renewal systems in 2011. The °Brix, pH, and TA were not affected by training system in either year.  Retraining or renewing vines reduced pruning weight in the 4AK treatment when compared to CR or AVR treatments in 2011 only. The Ravaz index, a measure of vine balance, indicated that all treatments were undercropped in both 2011, with ratios of yield (kg):pruning weight (kg) approaching the ideal (i.e., 5–10) in only the 4AK and AVR treatments. It appears that fruit quality is not compromised with shifts in either the training or renewal process in ‘Stover’ bunch grapes; however the Ravaz index indicates that either extending the cordon length or spreading the canopy vertically with a 4AK system improves vine balance in Florida.  Further monitoring of these training and renewal systems is required to determine long-term effects.