Abstract
Apricot trees usually bear more fruits than they can adequately support. Crop load adjustment through fruit thinning is a routine practice adopted by fruit growers to obtain a marketable product. Manual thinning, although effective, is a labor-intense and expensive operation, accounting for over 30% of the production costs; chemical thinning, on the other hand, provides inconsistent results and, though relatively inexpensive, is an unreliable practice.The aim of this study is to test a new thinner machine on apricots fruitlets, identifying the most suitable working speed combining thinning with the lack of visible damage on branches and on the remaining fruits.
The machine is composed by a rotor equipped with radial rods on a central axe mounted in a rear tree point linkage of a tractor. Trials were carried out in April 2016 in an apricot orchard sited in Cesena (FC). The experiment aimed to compare mechanical thinning at different working speeds (1.11 and 0.83 m s-1) and hand thinning on green fruits (2 ≤ Ø ≤ 2.5 cm). The thinning effect was evaluated by counting the remaining fruits from 40 randomly chosen branches in the upper and down part of four plants replicates. After the mechanical thinning, a manual thinning of finishing was performed, aimed to eliminate the fruits too close together on the branch and, in general, to ensure a uniform fruit set on the tree. The time required for thinning was measured in the mechanically thinned trees and compared with the ones thinned only by hand (control).
The two different working speeds gave two different thinning intensities: at 0.83 m s-1 fallen fruits counted for 44 % of the total while 47 % at 1.11 m s-1 . The thinning effects depended on the branch length: the highest fruit reduction was recorded (50.3 %) in more-than-35-cm long branches at 1.11 m s-1 while the lowest one (44.4 %) was recorded in less-than-15-cm long branches. The results obtained in the thesis at 0.83 m s-1 were different. The percentage of fruit reduction varied, indeed, from 47.5 % recorded in more-than-35-cm long branches and 41.3 % recorded in less-than-15-cm long branches.
Mechanical thinning can produce a net economic impact on apricot cultivation and, in some cases, can replace manual thinning and reduce the labor costs considerably.
