|Authors: ||C. Seehuber, L. Damerow, M.M. Blanke|
|Keywords: ||apple (Malus domestica Bork.), alternate bearing, crop load management, fruit quality, sustainability|
Thinning is a pre-requisite for the majority of fruit crops worldwide in order to overcome or prevent alternate bearing (high and low yields in alternating years) and to provide regular yields of high quality fruit in terms of size, taste, color and constituents, as required by the market.
Chemical thinning, a widely used practice, usually relies on compounds that are commonly referred to as hormones, are temperature-dependent for efficacy, and are often criticized by the consumer.
Hence, a new device was developed to achieve a wide variety of three-dimensional thinning motions in orchard systems, consisting of three variable horizontal rotors with rotating tines.
The objective was to achieve removal of individual flowers from the five-flower apple cluster; otherwise, multiple flowers in a cluster lead to many small, hard, green and unripe fruits.
The device was tested on the canopy of ten-year-old 'Pinova' and 'Braeburn' apple trees.
Overall, the success of the selective thinning depended on the interaction between branch angle and singlet portion, Branches were classified as to their position on a horizontal plane as 0° (along the tree row), 45° and 90° (perpendicular to the tree row). Branches at 45° from the tree row facing the thinning device were more severely thinned.
Selective thinning led to the removal of individual flowers out of a flower cluster (rather than removing complete clusters) and increased the portion of the desired singlets from, i.e., flower bunches with one single flower with less fruit, to fruit competition for photo-assimilates and, subsequently, better fruit quality.
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