THE ROLE OF SPUR AND BOURSE LEAVES OF 3 APPLE CULTIVARS ON FRUIT-SET AND GROWTH AND CALCIUM CONTENT

Individual flowering spurs on mature wood of 'Cox's Orange Pippin', 'Golden Delicious' and 'Crispin' apple trees were modified by removing the spur leaves, the bourse shoot, or both, at full bloom and two, four and eight weeks afterwards. Leaf removal reduced fruit set, yield (as fruit number and not size), fruit calcium level at harvest, and return bloom. Defoliation had its greatest effect on fruit calcium level when done early in the season and plots of this against treatment time suggested a curvilinear relationship. Return bloom was dependent on the presence of the bourse shoots on the spur but not on spur leaves. Return bloom of all three cultivars declined with the number of fruitlets per spur four weeks after full bloom.