Agriculture Reference
In-Depth Information
Fig. 4.6
Mechanical blossom
thinning performer in an
apple orchards in Germany.
(Damerow and Blanke
2009
)
activates for the survival of the species. The process, controlled primarily by auxin
and ethylene, leads to activation of the fruit abscission zone. In the presence of
an abundant flowering and optimal conditions during blooming, the physiological
fruit drop may not be sufficient to ensure commercially-acceptable fruit sizes that
can be achieved only with a further reduction of fruit load. This is achieved with
flower or fruitlet chemical thinning depending upon the climatic characteristics of
the growing areas. As a results of the inconsistency and the cost of some of the
methods (chemical and manual) used in apple and peach, mechanical thinning was
introduced in the practice.
In northern areas where frost damages frequently occur, fruitlet thinning is
preferred and should be performed promptly because the persistence of an ex-
cessive load on the tree fruit can negatively affect flower bud differentiation.
In apple, thinning must be performed within 30 days after full bloom, when the
development of king fruitlet reach a diameter of maximum 15 mm (Dal Cin et al.
2005
; Botton et al.
2011
). When thinning is performed, aspects related to tree
habitus, training system, light interception, leaf/fruit ratio, etc., should be taken
into consideration.
The mechanical thinning can be performed either on flowers or fruitlets. As
far as flower thinning is concerned, a machine called Darwin, consisting of a
rotary body carrying whips that hit the flowers, was recently tested (Fig.
4.6
).
In order to optimize the intervention, it has been recommended to develop wall
training system where the flowers are more uniformly exposed to the action of
the rotating device. Fruitlet mechanical thinning is done by limb- (operating
on branches) or trunk-shakers. The operation is cheaper than the manual one,
although it requires specific adaptation of the training system. The chemical thin-
ning in principle would be the less costly if properly performed and in presence
of varieties which respond to the thinners. It is successfully performed on some
apple varieties, while in stone-fruit, the lack of reliable chemical thinners is still
one of the main problem.
