Mechanically Pruning Apple and Sweet Cherry Increases Efficiency

Pruning is a labor- and time-demanding operation that generally represents the second greatest annual expense for tree fruit growers worldwide. Previous research into mechanized pruning in traditional orchard architectures yielded negative results. As orchardists adopt new two-dimensional, planar systems there is improved potential for the adoption of automation and mechanization technologies, including pruning. To date, there are few studies on the effectiveness of mechanical pruning in the top two tree fruit crops in the Pacific Northwest (PNW)—apple (Malus domestica Borkh.) and sweet cherry (Prunus avium L.). The goal of this project was to determine best management practices for pruning PNW apples and sweet cherry with a commercial sickle bar mechanical pruner.  Trials were initiated in 2014 in a commercial ‘Tieton’/‘Gisela®5’ sweet cherry orchard trained to the Upright Fruiting Offshoot (UFO) system. Mechanical pruning (hedging and topping) was 23 times more efficient compared to standard manual pruning practices; however, hand pruning removed twice as much wood as mechanical pruning. Additionally, experiments comparing hand pruning (dormant only) with mechanized pruning at 3 stages (dormant, or summer at 15 or 20 leaves) were established in commercial ‘Fuji’/‘Nic 29’ and ‘Pink Lady’/‘M9-337’ orchards trained to the slender spindle system.  Dormant mechanical pruning in ‘Pink Lady’ reduced yield 13% compared to hand pruning.  Neither timing of mechanical summer pruning affected yield.  Dormant mechanical pruning on ‘Fuji’ was twice as fast as hand pruning (9 s/tree versus 21 s/tree); however, the latter removed three times more wood. Manual pruning was more selective than the hedger, and most of the cuts performed by hand were thinning cuts—a key reason that more wood was removed by hand pruning. After mechanical summer pruning, up to 6.5% of fruit were damaged, though these were removed during green fruit thinning. The results of this first year of research suggest that mechanization can improve pruning efficiency with minimum effects on yield and fruit damage.