Dormancy Management Practices for Central Coast Wine Grape Vineyards

Erratic budbreak due to insufficient winter chilling has been observed in several wine grape vineyards located 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 initiated in 1998 to examine the interaction between pruning date and chemical treatment on the budbreak of Chardonnay and Pinot noir grapevines in this region. Main plots within each cultivar consisted of two pruning dates: early January (6 January) and late January (20 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 on 6 January commenced growth in mid-February, several weeks ahead of vines pruned on 20 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 on 6 January, all chemical treatments advanced budbreak compared to the control. In contrast, chemical treatments had less effect on budbreak when vines were pruned on 20 January. Chemical treatments had little effect on shoot and cluster numbers per vine, or on the uniformity of fruit development. The results indicate that pruning timing and dormancy-breaking chemical treatments had little effect on vine performance during the high chill winter of 1998.