Influence of Mechanical String Thinning Treatments on Vegetative and Reproductive Tissues, Fruit Set, Yield, and Fruit Quality of ‘Gala’ Apple

Abstract

<jats:p>The objectives of this experiment were to test the efficacy of a mechanical string thinner (Darwin PT-250; Fruit-Tec, Deggenhauserertal, Germany) on apple and to identify an optimal range of thinning severity as influenced by spindle rotation speed. Trials were conducted in 2010 and 2011 at the Pennsylvania State University Fruit Research and Extension Center in Biglerville, PA, on five-year-old ‘Buckeye Gala’/M.9 apple trees that were trained to tall spindle. A preliminary trail on five-year-old ‘Cripps Pink’/M.9 was conducted to determine the relationship between string number and thinning severity. As the number of strings increased, the level of thinning severity increased. A range of spindle speeds (0 to 300 rpm) was applied to the same trees for two consecutive years. As spindle speed increased, blossom density (blossom clusters per limb cross-sectional area) was reduced as was the number of blossoms per spur. In 2010, leaf area per spur was reduced 9% to 45%. In 2011, the fastest spindle speed reduced leaf area per spur 20%. Although increased spindle speed reduced cropload, injury to spur leaves may have inhibited increases in fruit size. The largest gain in fruit weight was 28 g (300 rpm) compared with the control. In both years, the most severe thinning treatments reduced yield by more than 50%. There was no relationship between spindle speed and return bloom. Severe thinning treatments (240 to 300 rpm) caused significant reductions in spur leaf area, yield, and fruit calcium and did not improve fruit size or return bloom. Spindle speeds of 180 and 210 rpm provided the best overall thinning response and minimized injury to spur leaves, but cropload reduction was insufficient in years of heavy fruit set. Therefore, mechanical blossom thinning treatments should be supplemented with other thinning methods. Mechanical string thinning may be a viable treatment in organic apple production, where use of chemical thinners is limited.</jats:p>

Yield, Labor, and Fruit and Juice Quality Characteristics of Machine and Hand-harvested ‘Brown Snout’ Specialty Cider Apple

“…Although spur and limb damage were generally low due to machine harvest, they were almost twice as great as compared with hand harvest. Although this amount of tree damage may not directly impact yield, open wounds may be sites for infection of important diseases such as fire blight (Erwina amylovora), leading to significant effects on long term orchard health and yield (Kon et al, 2013).…”

Screening of eco-friendly thinning agents and adjusting mechanical thinning on ‘Gala’, ‘Golden Delicious’ and ‘Fuji’ apple trees

“…Mcclure and Cline (2015) with a Darwin ® machine at 3.2 km•h -1 and 180-240 rpm did not observe a significant yield reduction on 'Royal Gala ® '. Both Kon et al (2013) with a Darwin ® , and Damerow et al (2007) with a Baum ® machine, reported higher blossom removal as rotational speed increased. On the other hand, a study conducted by Sinatsch et al (2010) on 'Pinova cov ', did not reveal significant differences when maintaining a tractor speed at 3.2 km•h -1 , and rotational speeds from 200 to 220 rpm.…”

“…Seehuber et al (2014b) suggested E2 to F2 as the ideal timing window for mechanical thinning, whereas a wider window was suggested by Veal et al (2011) (E2 to G). Hence, reference studies have been performed at different stages like F1 (Basak et al, 2016;Mcclure and Cline, 2015), pink bud (E2) to full bloom (F2) (Miranda Sazo et al, 2016;Solomakhin et al, 2012;Veal et al, 2011), at full bloom (F2) (Hehnen et al, 2012;Kirstein, 2015;Kon et al, 2013;Solomakhin and Blanke, 2010), or even at 30% of petal fall (Kirstein, 2015). The fact that mechanical thinning is less dependent on phenological stage than timing of chemical thinners will allow more time to manage different spring situations, like spring frost forecasts, in order to delay the treatment for safety reasons.…”

Tree-adapted mechanical flower thinning prevents yield loss caused by over-thinning of trees with low flower set in apple

“…Dashed line marks the mean value. J o u r n a l o f H o r t i c u l t u r a l S c i e n c e to our knowledge, applied in practice ranging from 2.5 km h -1 to 12.0 km h -1 (Kon et al, 2013). At rotational frequency of 380 rpm, this difference in tractor speed caused a maximum spread of 0.19 J, regarding the angle of the string at 135° to the driving direction.…”

“…As an alternative, devices for mechaniyears with more reliable effects (Schröder, 1996 , 1998;Damerow et al, 2007). The principle is based on a driven by a mechanical or hydraulic system, which allows the length of strings, the rotational frequency and the speed of er removal (Zoth, 2011;Kon et al, 2013;Penzel et al, 2020) by the enhanced kinetic energy (E kin ), which is transferred by the strings into the canopy. The speed of the tractor inand Blanke (2010) regards most of these factors and also incompared to the effect of the thinning intensity.…”