Vegetative and Reproductive Responses of Mature Cabernet Sauvignon Grapevines Converted from Spur Pruning to Cane Pruning at Five-Foot In-Row Vine Spacing

Summary Goals: Once established, vineyards are generally constrained by vine and row spacing and trellis configuration, which restricts how these variables can be modified. Regardless, such post-planting modifications may be desirable. This project chronicles vine performance following the conversion of seven-yr-old, cordon-trained, spur-pruned vines (“spur-pruned”) to head training and cane pruning (“cane-pruned”) with vines spaced 5 ft (1.5 m) apart in the row. While there are both pros and cons with either system, head training and cane pruning has an operational advantage in that less labor is expended on shoot-thinning because of retention of far fewer basal buds with cane-pruned vines. At issue, though, is a perception or reality that relatively wide in-row vine spacing (e.g., ≥4 or 5 ft) leads to uneven shoot development and nonuniform fruit ripening on long canes. We hypothesized that nonuniformity of shoot growth and development would lead to increased variability of fruit maturity at harvest with the conversion from spur pruning to cane pruning, with mature vines planted 5 ft (1.5 m) apart in the row. Key Findings: In comparison to spur pruning, the cane-pruned vines exhibited: (i) delayed budbreak and bloom; (ii) fewer, but more fruitful shoots; (iii) lower cane-pruning weights; and (iv) similar canopy architecture, primary fruit chemistry at harvest, and uniformity of pruned cane weights. Impact and Significance: Although we hypothesized that a 5 ft (1.5 m) in-row vine spacing might lead to nonuniform shoot development and fruit ripening on bilateral canes, this proved not to be the case. Although there was variation in components of yield for cane-pruned vines compared to spur-pruned vines, fruit maturity indexed as soluble solids concentration was similar between the two systems in the four seasons after conversion. While spur pruning has some advantage from the standpoint of reduced or eliminated time to tie canes following dormant pruning, the disadvantage, at least with Cabernet Sauvignon, as used here, is the propensity of cordon training to produce abundant basal shoots, which add excess crop and canopy density or additional labor to remove those shoots. A closer in-row spacing might be advised for cane pruning in new vineyards; however, it is possible to effectively convert spur-pruned vines back to cane pruning even for mature vines spaced 5 ft (1.5 m) apart in the row should that conversion be desired for labor savings, anticipated fruit quality improvements, or other reasons.