Effect of application date of rest breaking agents on growth and production of 'Royal Gala' and 'Granny Smith' apple
2012
North, M.S. | De Kock, K. | Cook, N. | Allderman, L. | Booyse, M.
The efficacy of chemical Rest Breaking Agents (RBA’s), used to reduce the negative effects of insufficient winter chilling, depends on application date, concentration, chemistry and cultivar. As environmental concerns increasingly limit the use of agricultural chemicals, RBA’s must be applied more efficiently. The depth of dormancy during RBA application was determined by the rate of bud break of one-year-old shoots forced at 25°C. Shoots were excised six times during August and September 2008 and 2009 from mature ‘Royal Gala’ (RG) and ‘Granny Smith’ (GS) apple trees. During 2008, these same trees, on the same six occasions, were treated with either Dormex(R)/oil (0.5%/3% v/v), Lift(R) (3% v/v), Symphony(R) (½ and ¼ volume). During 2009, the same trees were again treated with the same RBA’s except Oil (5% v/v) replaced Symphony (¼ volume). Control trees were left untreated. Bud break (BB) on one-year-old pre-marked shoots and yield/tree were recorded during both seasons. Depth of dormancy varied with cultivar and season and had little effect on BB caused by the RBA. Dormex(R)/oil and Lift(R) increased bud break of RG but application date had no effect. RBA’s applied during early August in both seasons increased yield of larger, redder RG fruit, but no treatment increased total yield. Bud break of GS was increased by Dormex(R)/oil and Lift(R) applied during early September. Neither RBA nor application date influenced GS yield during both seasons.
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