511 Budbreak Induction in Apple Trees by Erger and Calcium Nitrate Application F.J. Hawerroth J.L. Petri and G.B. Leite UFPel – Universidade Federal de Pelotas EPAGRI/Estação Experimental de Caçador C.P. 354, 96010-900 Pelotas, RS C.P. 591, 895000-000 Caçador, SC. Brazil Brazil Keywords: Malus domestica, budbreak promoters, dormancy Abstract In mild winter climates, the budbreak promoters application is one of main management strategies used to decrease problems of insufficient winter chilling on temperate fruit trees. Despite of the high efficiency of some chemicals on budbreak induction, the high toxicity showed by these compounds is one problem related to its use. Erger, an organic nitrogen compound, combined with calcium nitrate, has a similar effect to that of hydrogen cyanamid, with the advantage of being less dangerous to the environment. The objective of this study was to evaluate the effects of Erger and calcium nitrate combinations on budbreak induction of ‘Imperial Gala’ and ‘Suprema’s Fuji’ apples. The experiments were carried out in Caçador, Santa Catarina, Brazil (26°46’S, 51°W), at 960 m a.s.l., during two growing seasons (2006/2007 and 2007/2008). The treatments tested were control, standard (mineral oil 3% + Dormex ® 0.7%), and Erger + calcium nitrate at concentrations of 3, 5, and 7%. Full bloom date, axillary and terminal budbreak, fruit set, and mean fruit weight were evaluated. All Erger + calcium nitrate concentrations anticipated the full bloom date in relation to control treatment, but were not observed differences with mineral oil 3% and Dormex ® 0.7%. The budbreak promoters increased significantly axillary and terminal budbreak and increasing the uniformity of budbreak. Fruit set was not affected by Erger + calcium nitrate concentration in relation standard treatment. The combinations of Erger and calcium nitrate showed similar uniformity and performance to mineral oil and hydrogen cyanamide on budbreak, showing to be an efficient alternative to budbreak induction in ‘Imperial Gala’ and ‘Suprema’s Fuji’ apples. INTRODUCTION Deciduous fruit trees and other woody perennials of temperate climates require a certain amount of winter chilling to overcome their dormancy (Garaglio et al., 2006; Albuquerque et al., 2008). When deciduous fruit trees, like apple trees, are cultivated in regions with insufficient winter chilling, these plants show low intensity of flowering and budbreak. In mild winter climates, the budbreak promoters application is one of main management strategies used to decrease problems of insufficient winter chilling in temperate fruit trees. Despite the high efficiency of some chemicals on budbreak induction, the high toxicity showed by these compounds is one problem related to its use. Growth regulators and nutritional compounds can be used on budbreak induction of temperate fruit trees (Mohamed, 2008), although little options are available for commercial use. Hydrogen cyanamid (Dormex, a.i. 49%) and mineral oil are the main substances used to decrease problems caused by insufficient winter chilling in the Brazil apple industry (Petri et al., 2006). These compounds have great efficiency on apple budbreak induction. Although the high toxicity showed by hydrogen cyanamid is one problem related to its use. Preliminary results (Petri, 2005; Petri et al., 2008) indicate Erger, an organic nitrogen compound, combined with calcium nitrate, has a similar effect to that of hydrogen cyanamid, with the advantage of being less dangerous to the environment. The aim of this study was to evaluate the effects of Erger and calcium nitrate combinations on budbreak induction of ‘Imperial Gala’ and ‘Suprema’s Fuji’ apples in Southern Brazilian Proc. XI th IS on Plant Bioregulators in Fruit Production Ed.: G. Costa Acta Hort. 884, ISHS 2010