## 2 Thinning Methods
### Manual Thinning  
Hand/manual thinning may be economically unjustified due to the time and labour it requires [9]. However, it is the most accurate thinning method even if a large number of qualified employees is needed in a short time [63]. Manual thinning can be supported by a portable thinning machine (Effleureuse), which is an intermediate form between mechanical and manual thinning and makes the work more effective and considerably cheaper [15; 16].  
Stone fruit species are thinned manually primarily during flowering. The disadvantage of thinning carried out at this time is that it is hardly selective. The advantage is that the early time of treatment improves the fruit size by reducing competition between generative and vegetative organs [64]. Thinning during flowering is associated with the risk of excessive yield limitation if frost occurs after flowering. This risk can be avoided by thinning after flowering; however, very late thinning may lead to the loss of assimilates, which can negatively affect fruit quality and reduce yield in both the current and subsequent growing season [1].  
Hand removal of 20% of buds or 20% of flowers of 'Ujfehertoi Furtos' sour cherry before or during flowering increased yield efficiency per unit of trunk cross-sectional area (TCSA). However, stronger thinning resulted in a decrease in yield, while fruit mass and diameter and total soluble solids increased linearly. The same study showed no significant differences in the average values of these quality parameters between fruit from trees thinned at bud and flower stages [39]. In addition, experiments conducted on 'Summit' cherries grown on Table(r) Edabriz showed a significant increase in fruit weight after thinning cuts applied to fruiting spurs, whereas the best fruit size was obtained after removal of 30 to 50% of fruiting spurs [65]. Similar results were obtained by selective removal of reproductive buds from spurs, leaving one bud per spur. Thinning results were the best in the years of high crop load [12]. However, it should be remembered that the thinning effect is cultivar-dependent, because thinning of 15 to 50% of buds, spurs, flowers, and fruit of the self-pollinating variety 'Lapins' grown on the bird cherry (_Prunus avium_ L) rootstock did not affect the yield. Nevertheless, 'Lapins' sweet cherry thinning significantly reduced the share of fruit with a diameter of less than 21 mm, i.e., below market standards [33]. In addition, other studies evince that the reduction of the number of flower buds from the natural level (3 to 4 per spur) to 1 to 2 per spur resulted in a yield decrease to 25%, while the average fruit size increased by 43% (Table 2). Soluble solids were found to have increased significantly as well, which proves that the leaf area per fruit ratio is a key factor here [34]. Another crucial variable determining the results of thinning is the vigour of the rootstock and thus the whole tree as demonstrated by a study on the manual fruiting spur thinning of sweet cherries grown on the strongly growing rootstock 'Mazzard F-12/1'. The impact of thinning on fruit size was negligible, which is probably associated with a stronger vegetative than generative development of trees growing on this rootstock [43].