Effect of Canopy Angle and Row Spacing on Tree Growth, Yield, Light Interception, and Fruit Quality of Y-trellis-trained Apple Trees

Abstract

`Empire'/M.9/MM.106 and `Ace Delicious'/MM.106 apple trees were planted in 1985 at three between row spacings (3.0 m, 4.25 m and 5.5 m) and were trained as either free standing central leaders or as Y-shaped hedgerows for 13 years. The Y hedgerow arms had varying angles from 40° to 80° above the horizontal. Final scaffold length, canopy volume, trunk cross-sectional area, and above-ground canopy weight were positively correlated to the angle of the Y arms. 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 vertical 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. 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. There was also a strong positive relationship between tree density and yield. `Empire' fruit size was smaller from the Y-shaped trees than from the central-leader trees. The optimum angles for fruit size were the intermediate angles. Fruit color was poorest on the flattest angles and best on the most-vertical angles. The best yield efficiency was at intermediate angles (50° 70°). This resulted in the best balance of vegetative growth and cropping.