DEVELOPMENT OF A SAFER AND NEW BUD-REST BREAKING AGENT FOR 'GOLDEN DELICIOUS' APPLES GROWN UNDER MARGINAL CLIMATIC CONDITIONS

To reduce the incidence of growth abnormalities associated with insufficient winter chilling, most of the apple (Malus domestica Borkh.) trees grown in the Western Cape, South Africa, receive applications of a chemical bud-rest breaking agent (RBA) at the end of winter. Less hazardous RBA’s are essential to replace products that are currently commercially used. Nitrogen based bud-rest breaking agents tend to be effective only at relatively high concentrations and imbalances between reproductive and vegetative bud-burst may occur. Mixtures of an inorganic and organic nitrogen source, with penetrant and/or humectant adjuvant/s, petroleum or vegetable oils were evaluated against the commercially used control (Dormex^R/oil) on mature ‘Golden Delicious’ apple trees at two sites over five seasons. A formulation that contained 9.38% N from a mixture of 4.8% v/v choline chloride, 6.6% v/v GAN with 1.5% v/v Partner^R and 3% v/v NPX was just as effective in promoting bud burst and improving fruit set and fruit size as the commercial control.