Modifying Apple Tree Canopies for Improved Production Efficiency

Canopy development in perennial crops has a seasonal and a lifetime developmental pattern. The sum of development over individual seasons results in the final canopy dimensions and form. In apple, there is a natural progression from a single-shoot tree toward the tall (10 m), umbrella-shaped tree (Fig. 1). There are many disadvantages to this large umbrella-shaped tree: 1) it is difficult to spray, prune, and hand-harvest; 2) it has poor distribution of light throughout the canopy; and 3) it has a low early life light interception, leaf area index, and fraction of land covered by canopy, leading to delayed cropping. These disadvantages have resulted in widespread efforts to reduce tree size, increase tree density, accelerate canopy and yield development, and improve canopy form to overcome the limitations of the large tree. In apple, there are several practical approaches to tree size control and canopy modification, including the use of rootstocks, scions, pruning, and tree training. Rootstocks are available that will give a wide range of tree sizes ranging from the 10-m tree described above to fully dwarf trees <2 m high. There is also available a range in scion types, ranging from the nonbranching, columnar types to the spreading, nonspur types. In addition, apples respond well to canopy modification by pruning and training. These four variables make possible a myriad of tree forms, planting arrangements, and tree heights, widths, and geometric forms (spheric, rectangular, conic V, T, and A forms). The practical value of canopy modifications depends on their effect on orchard production efficiency.