Can we manage light interception levels above 70% in apple orchards?

Abstract

For the last 20 years we have recommended that orchards be designed to intercept a minimum of 70% light interception. Replicated field plantings at Geneva have shown that when tree height is about 90% of the between row spacing light interception is about 75%. This has become our standard recommendation in designing new orchards. However, in recent years three developments have led us to question this rule. First the development of the Tall Spindle planting system and the use of mechanical summer pruning has resulted in very narrow canopy profiles (fruiting walls), which have very good light distribution within the canopy. This could allow taller trees relative to the between row spacing with a height to row spacing ratio of 1:1. A second development has been the use of V-shaped canopies, which are very thin and shoot growth in the middle of the V is controlled with plant growth inhibitors. These V-shaped canopies can intercept more than 75% of available light depending on the open gap at the top of the V. This tree shape allows even the lowest part of the canopy to receive adequate light during the middle of the day with good fruit quality in the bottom of the canopy but also imposes the greatest energy load on the tree and hence transpiration compared to vertical tree shapes. A third trend is the use of reflective films to enhance the light exposure level of the lower part of the canopy. This practice with the use of V-shaped canopies could utilize 80-85% of available light energy resulting in higher yield.