Effect of timing and concentration of rest breaking agents on budburst in 'Bing' sweet cherry under conditions of inadequate winter chilling in South Africa
The effect of timing of various rest breaking agents (RBAs) on vegetative and floral budburst, and production efficiency was investigated on 4-year-old 'Bing' sweet cherry trees on 'Gisela® 5' rootstock. Two experiments were conducted, near Clarens (28°28'S; 28°19'E, 1860 m.a.s.l) and Reitz (28°0'S; 28°28'E; 1717 m.a.s.l) in the eastern Free State, during 2005 and 2006, respectively. The 2005 experiment evaluated five treatments; 1 % and 2% Dormex® (49% hydrogen cyanamide, HCN); 1% Dormex® + 3% Budbreak® oil (869.3 g L-1 mineral oil); and 3% Lift® (thidiazuron and mineral oil) sprayed on whole trees on three dates preceding expected "green- tip", and an unsprayed control. In 2006 four treatments were evaluated; 1 % Dormex®; 1 % Dormex® + 3% Bud- break® oil (869.3 g L-1 mineral oil); 3% Lift® applied on three dates, and an unsprayed control. Compared to the control, RBAs were most effective at improving vegetative budburst during both seasons while results of floral budburst and production efficiency varied between seasons indicating that time of RBA application should be based on chilling accumulation and bud development stage and not only calendar date. The time of application of RBAs had the most significant influence on budburst and production efficiency. No interaction was observed between time and treatment.