ERFORMANCE OF Y-SHAPED APPLE CANOPIES AT VARIOUS ANGLES IN COMPARISON WITH CENTRAL LEADER TRAINED TREES.

‘Empire’/M.9/MM.106 and ‘Ace Delicious’/MM.106 apple trees planted at three between- row spacings (3.0, 4.25 and 5.5 m) were trained as either free-standing central leaders or as Y-shaped hedgerows for 6 years. The Y-hedgerow arms had varying angles from 40° to 80° above the horizontal. Y-shaped trees were trained by tying all scaffold limbs on the tree to a trellis at specific angles in the third year. Each year thereafter, upright shoots arising from the scaffold branches were removed during the summer and counted, measured and weighed. Central leader-trained trees were also summer pruned, and the number and length of shoots removed were measured. As the angle of the Y arms became more horizontal, the amount of growth removed during summer pruning increased. At the flattest angle (40° above horizontal) terminal growth of both cultivars ceased and excessive sucker growth resulted. As the angle of the Y arms became more vertical, more terminal growth was obtained and less shoot growth had to be removed during summer pruning. Final scaffold length was directly related to the angle of the Y arms.

Six-year cumulative yields of the Y-shaped trees were generally greater than those of the central leader-trained trees. Exceptions were the most horizontal and the most vertical canopy angles, which had the lowest yields. The relationship between angle of Y arms and yield showed a broad optimum between 50° and 70° above the horizontal. The difference in yield between Y-shaped trees and central leader trees was greater for ‘Empire’ than for ‘Delicious’, where differences were small. At the optimum angle, ‘Empire’ yielded from 16% to 40% more than the central leader trees, while ‘Delicious’ yielded from 7% to 18% more, depending on the spacing. ‘Empire’ fruit size was smaller from the Y-shaped trees than from the central leader trees, but with ‘Delicious’ the reverse was true. There was no consistent optimum angle for best fruit size. Fruit red color was best at the most vertical angle.