Evaluation of the Effect of Different Budbreak Promoters on Apple Trees ‘Eva’ and ‘Castel Gala’ in Mild Winter Climate Conditions

This study aimed to evaluate the effect of different budbreak promoters on low chilling apple trees, Eva and Castel Gala, in mild winter conditions of Southern Brazil. An experimental design was randomised blocks, with four replications, and the experimental unit was composed of two plants, on 4x2 factorial arrangement (four treatments and two cultivars). This research was carried out during growing season 2014/2015, in an experimental apple orchard located at Palma Agriculture Center, Federal University of Pelotas, Southern Brazil. Four treatments were applied: Erger 3% + calcium nitrate 3%; Erger 5% + calcium nitrate 5%; hydrogen cyanamide 1.5% + mineral oil 3% and control. It was recorded phenological stages: beginning, full and the end of blooming; budbreak of axillary buds and fruit set. The productive parameters were analysed: average fruit weight (g), yield efficiency (kg-cm-2) and yield (Mg ha-1). All treatments reduced blooming period and improved the synchronisation in both cultivars. There was an increase in budbreak of axillary buds, whereas, in ‘Eva' apple trees, the treatments with Erger had higher budbreak rates than hydrogen cyanamide. In ‘Eva', the application of budbreak promoters reduced fruit set and increased the average fruit weight, yield and yield efficiency, when compared to control trees. However, these results were not observed in ‘Castel Gala'. The combination of Erger and calcium nitrate showed similar and higher performance than the combination of hydrogen cyanamide and mineral oil in the budbreak percentage in ‘Castel Gala' and ‘Eva', respectively.