Dormancy Management Practices for Central Coast Wine Grape Vineyards
Insufficient winter chilling is a localized problem in several wine grape vineyards in the south-central coast of California. Shoot and cluster numbers per vine, as well as fruit development uniformity, are often reduced as a result. A factorial experiment was conducted in 1999 to examine the interaction between pruning date and chemical treatment on the budbreak of Chardonnay and Pinot noir grapevines grown at a low chill site. Main plots within each cultivar consisted of two pruning dates: early January (5 January) and late January (22 January); sub-plots consisted of the following chemical treatments: untreated control; 2%hydrogen cyanamide (4%Dormex); 0.5%hydrogen cyanamide (1%Dormex) + 2%Agridex (a non-ionic, paraffin based surfactant); and 35%calcium ammonium nitrate (CAN-17) + 2%Agridex. Vines of both cultivars pruned in early January commenced growth in mid-February, several weeks ahead of vines pruned in late January. Budbreak was relatively uniform regardless of time of pruning, and pruning date had no significant effect on the maximum observed budbreak of either cultivar. When vines were pruned in early January, all chemical treatments advanced budbreak compared to the control. Chemical treatments had less effect on budbreak when vines were pruned in late January. Chemical treatments had little effect on the shoot number of Chardonnay vines, but vines treated with 4%Dormex had greater cluster numbers compared to vines treated with 1%Dormex + 2%Agridex and 35%CAN-17 + 2%Agridex. However, chemical treatments also advanced bloom into a period of less favorable weather conditions for fruit set and resulted in a significant reduction in yield compared to the control. Chemical treatments had little effect on shoot and cluster numbers of Pinot noir. Fruit composition was similar among the treatments in both cultivars.