CHEMICAL MANIPULATION OF GRAPE DORMANCY UNDER SIMULATED TROPICAL CONDITIONS
Defoliating chemicals (ammonium thiosulfate, ethrel, and thidiazuron) were evaluated on 8-month-old `Canadice' and `Concord' grapes. The effectiveness of chemical defoliators was determined 20 days after application. Vines were pruned after defoliation and dormancy breaking chemicals (thiourea, cyanamide, and gibberellic acid (GA3) were applied 4 days later. All treatments were applied as sprays. All chemicals were effective in defoliating the vines of both cultivars. Generally, the higher concentrations (ammonium thiosulfate, ethrel, and thidiazuron at 15.15, 3.0, and 0.35 g·liter–1, respectively) were more effective. All chemicals reduced days to maximum budbreak of both cultivars. The higher concentrations (thiourea, cyanamide, and GA3 at 30.3, 15.15, and 0.75 g·liter–1, respectively) resulted in greater reductions in days to maximum budbreak. `Concord' was later in reaching maximum budbreak. Total percent budbreak of both cultivars was increased by all chemicals at the higher concentrations. Cyanamide resulted in greater total percent budbreak in both cultivars.