Effects of Mechanical Pruning of Apple Hedgerows with a Slotting Saw on Light Penetration and Fruiting1

Annual cutterbar and slotting saw hedging were compared after 3 years. Fruiting was measured as the number of spurs per twig on 3 year old growth, number of spurs flowering and fruiting, and bushels per tree. Integrated light energy quantities were measured for 6- to 14-day periods for various positions within the tree and correlated with fruiting. A hydraulic “slotting saw” mounted on a boom on a fork lift hedged a slot in the side of the tree. By cycling the slots any one position was cut only once every 4 years, permitting the regeneration of fruiting wood and the penetration of light. ‘McIntosh’ apples pruned as 10 ft high hedges with (a) cutterbar and (b) with a slotting saw, show that annual cutterbar hedging reduces the generation of new fruiting spurs, produces a dense outer periphery shading interior spurs and reduces bearing. The slotting saw mechanical pruning technique increases light penetration into the tree, produces nearly 3 times as many new spurs and about a 4-fold increase in the percentage of spurs flowering. Light measurements within the tree indicate that spur leaves require about 50% of available light for suitable flowering. Light values in trees hedged 3 years with the cutterbar were reduced to less than this value within the outer 2 ft of tree canopy where few spurs exist.