Alternative products for breaking dormancy in ‘Reubennel’ plum in subtropical regions

Plum is a temperate fruit tree and thus shows abundant vegetative bud percentage and flowering following extended periods of low winter temperatures. When adequate periods of low temperatures do not occur, it is necessary to apply products to stimulate bud dormancy break and uniform leaf and flower appearance. This application is more frequently needed when plum trees are grown in the tropics. The objective of this study was to evaluate alternative products for breaking dormancy in ‘Reubennel’ plum in subtropical regions. The experiment was conducted at a site located at 22°22’S, 43°77’W and 1,173 m altitude, with a Cwa climate type. The following treatments were applied to eight-year-old ‘Reubennel’ plum trees in the 2018 and 2019 production cycles: 1) a negative standard composed of only water (control), a positive standard composed of 2) 1.5% hydrogen cyanamide (HC) (Dormex® commercial product) plus 4.5% mineral oil, 3) Erger G® organomineral fertilizer supplemented with 3% calcium nitrate, 4) 5% potassium nitrate and 5) 0.3% copper sulfate. Two liters of the treatment solutions were applied per plant with a sprayer. The effect of the tested products on vegetative bud percentage and flowering capacity, production cycle reduction and production and quality of ‘Reubennel’ plums was evaluated. It was concluded that the chemicals used to break dormancy affected only the phenology of plum trees in this subtropical region and that the application of copper sulfate can be used to break dormancy in these trees.