Canopy Separation and Defoliation Do Not Improve the Dry-on-Vine (DOV) Raisin-Making Method for ‘Thompson Seedless’ Grapevines on Traditional Trellises

Abstract

‘Thompson Seedless’ (syn. ‘Sultana’) grapevines ( Vitis viniferaL.) were subjected to canopy separation and defoliation treatments to determine whether either or both of those factors could increase pruning efficiency, the number of clusters per vine, canopy evaporative potential, yield, or quality of dry-on-vine (DOV) raisins. Canopy separation methods included: 1) within-row alternate bearing (WRAB), where fruiting canes and renewal shoots were trained to opposite sides of the trunk such that each were adjacent to similar structures of neighboring vines, 2) Wave, where fruiting and renewal canes were trained to opposite sides of the trunk such that the fruiting canes of one vine were adjacent to the renewal shoots of the next vine, or 3) non-separated. Defoliation treatments, applied near cane severance, included burning or blowing the leaves, application of concentrated solutions of calcium ammonium nitrate (CAN-17), urea ammonium nitrate (UAN-28), or ethephon (750 ppm) to leaves, or no defoliation. None of the canopy separation or defoliation treatments provided any consistent benefit with respect to the variables measured. On the contrary, vines with separated canopies sometimes had more congested fruiting zones, as evidenced by their greater number of cluster layers, than vines with non-separated canopies, and their raisins were often moister at harvest. In one trial, defoliation by blowing or burning enhanced drying of raisins on vines whose canopies were subjected to the WRAB method, but in another trial the use of those defoliation methods resulted in raisins that were too moldy to process. Thus these canopy management methods did not improve the DOV raisin-making method for ‘Thompson Seedless’.