APPLE TREE BUDBREAK PROMOTERS IN MILD WINTER CONDITIONS

The 400 to 600 h below 7.2°C of chilling, which is experienced in the main growing area in Southern Brazil, is marginal for apple production. Erratic budbreak and blooming occurs under these conditions, which is characterized by low breaking of lateral buds, small leaves and long periods of budbreak and blooming. Budbreak promoters, such as hydrogenated cyanamide (Dormex™) and mineral oil, have been successfully used to overcome the chilling deficiency, but the lack of alternative products and/or active ingredients keep apple growers very dependent on these products and consequently rather insecure. The objective of this study was to test the technical and economical efficiency of new budbreak promoters such as inorganic hydrogen compounds (Erger™), Busan 30 (2-(tiociometiltio) benzotiazol 30%), calcium polisulfide, and TDZ + mineral oil (Lift™), as alternatives to Dormex™. Dormex™ and EgerTM treatments advanced budbreak and blooming in relation to the other treatments tested. The percentage of budbreak on laterals was greater when treated with Erger™ (5-7%) + calcium nitrate (5-10%) than with Dormex™ + mineral oil. Calcium polysulfide had low efficiency in breaking lateral buds. The best break of lateral buds would result in more flowers for the following season. This was more evident with Erger™ treatments. The treatments of Erger™ reduced the fruit set of ‘Gala’ and, to a smaller extent, also on ‘Fuji‘. Lift™ was efficient in stimulating the break of lateral buds, but it reduced leaf size in the current year, and promoted very small fruits in the following growing season. Among the tested promoters, Erger™ was the most promising for commercial use under the climatic conditions of Southern Brazil.