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Rest breaking agents and application date affect bud break but not yield of 'granny smith' and 'Royal Gala' apple

North, M. S., De Kock, K., Booyse, M.
Acta horticulturae 2014 no.1058 pp. 639-644
apples, application timing, budbreak, chemistry, cold treatment, cultivars, farms, fruit trees, knapsack sprayers, oils, orchards, shoots, urea
Rest Breaking Agents (RBA) are used to reduce the negative effects of insufficient winter chilling. Their effectiveness depends on application date, concentration, chemistry and cultivar. In a four year study, RBA were applied five to six times between early August and late September to single-tree plots within mature commercial Royal Gala (RG) and Granny Smith (GS) apple orchards on the same farm. The results from the final year are presented here. Either Dormex®/oil (0.5%/4% v/v), Symphony® (16% N), Oil (5%), Oil/Oil (5%/5% one week later), GAN/Partner® (5%/2%) or Oil/Urea (5%/5% m/v) were applied using motorized knapsack sprayers. Control trees were left untreated. Bud break (BB) on one-year-old pre-marked shoots and fruit/tree and kg/tree were recorded. In GS, Oil and Oil/Urea on the second date (25/8/11); Symphony®, Oil/Oil, GAN/Partner® and Oil/Urea on the third date (7/9/11); DM/Oil, Symphony and GAN/Partner® on the fourth date (21/9/11) and GAN/ Partner® on the fifth date (27/9/11) improved BB relative to the control. No RBA affected yield. Trees receiving the first application (10/8/11) had more fruit/tree than the control. In RG, Symphony®, Oil/Oil and Oil/Urea treatments had higher BB than the control. Higher BB occurred after the third application (7/9/11) than after the first (10/8/11), fourth and fifth applications. In the first harvest, DM/Oil and Oil/Oil treatment trees had higher kg/tree, and the Oil/Urea treatment lower kg/tree than the control. Neither RBA nor application date had any effect on total fruit/tree, kg/tree or fruit size. Although some treatments promoted BB, the final yield of either cultivar was not affected.