Canopy Separation Did Not Improve Dry-on-Vine Raisin Yield or Quality from Selma Pete Grapevines on Open Gable Trellises

Summary

Goals:

Dry-on-vine (DOV) raisin growers with open gable trellises can use selective cane-pruning and shoot positioning to separate grapevine canopies into distinct fruiting and renewal zones. This practice is thought to improve canopy structure and microenvironment, increasing raisin yield and quality. However, these assumptions have not yet been confirmed by research. Therefore, an experiment was conducted in which Selma Pete grapevines (Vitis vinifera) on open-gable trellises were subjected to one of three canopy separation treatments: non-separated; center-divided, where renewal shoots were gathered in the trellis center and supported by a foliage catch wire; or within-row alternate-bearing (WRAB), where selective pruning left canes and spurs on opposite cordons. The effects of canopy separation treatments on canopy structure, microenvironment and raisin yield, and quality were followed for three years.

Key Findings:

The WRAB canopy separation method generally reduced the number of leaf layers and increased the proportion of leaves on the canopy exterior in renewal shoot zones. In spring, renewal shoots in WRAB canopies had more direct sun exposure than renewal shoots in other canopy types, but light levels in WRAB canopies diminished thereafter, becoming similar to those in other canopies. Despite effects on canopy structure and microenvironment, no canopy separation method tested affected raisin yield or quality consistently.

Impact and Significance:

The WRAB canopy separation method affected canopy structure and microenvironment, but insufficiently to increase the yield or quality of DOV raisins on an open gable trellis. Moreover, the selective pruning required to establish WRAB canopies may reduce yield in the season following establishment, and possibly have negative effects on the fruiting zone microclimate, hindering fruit ripening or drying.