MECHANICAL PRUNING OF APPLE TREES AS AN ALTERNATIVE TO MANUAL PRUNING

Abstract

High costs of manual pruning and lack of skilled workers incline fruit growers to mechanical pruning. Mechanical pruning gives good results in the case of trees that do not require selective pruning, like citrus trees. This pruning method is also acceptable if the fruit is produced for industrial purposes. Twelve-year-old ‘Pinova’ apple trees grafted on dwarf M.9 rootstocks, spaced at 4 × 1.5 m, trained to the spindle system were mechanically pruned at the pink flower stage (first week of May) and at the fruit setting stage (first week of June). The pruning was done with a STIHL cutting bar as ‘topping’ (trimming  the tops of trees) and ‘hedging’ – pruning of trees from two sides at an angle of 70°. Before the pruning, the trees had a height of 3.5 m and over 2.0 m spread at the bottom part of tree canopy. Control trees were pruned manually using standard methods. The height of the trees was reduced with mechanical and manual pruning to 2.5 m, and the
spread to 2 m at the base of tree canopy. During the three years of the trial, mechanical pruning significantly altered the canopy structure. It developed into a continuous, compact wall without any openings along the row. In the same time, hand pruned trees had free openings in the upper part of tree canopies. Mechanically pruned trees had lower solar irradiation levels than manually pruned trees. In the third year, the trees pruned mechanically gave higher yields than the trees pruned manually, but fruit size, mean fruit weight and the area of the red blush were significantly decreased. The trial indicated that mechanical
pruning of apple trees must be supplemented by hand pruning. More attention is also needed to fruit thinning when trees are pruned mechanically.