Agriculture Reference
In-Depth Information
FIGURE 7.2
Citrus Tree Hedger by Northern Motors.
Figure 7.3 illustrates a rotating string thinner designed by H. Gessler, a German
grower, to remove apple blossoms in organic orchards (Schupp, 2008). The string
thinner consisted of a tractor-mounted frame with a 3-m-tall vertical spindle in the
center of the frame. Attached to the spindle were 36 steel plates securing a total of
648 plastic cords each measuring 50 cm long. The speed of the rotating spindle was
adjusted by a hydraulic motor. The height and angle of the frame was adjustable to
conform to the vertical inclination of the tree canopy, and the intensity of thinning
was adjusted by changing the number of strings and the rotation speed. In the 2007
commercial orchard trial, the string thinner effectively reduced flower density in
the upper canopy part as compared with hand thinning. It was also observed that
the string thinner had a much greater blossom removal on branches parallel to the
drive row. Access to the interior canopy and blossoms were limited. The researchers
suggested refinements in both machinery and canopy design to obtain maximum
efficacy.
7.2.2.1 Selective Thinning and Pruning Automation
Even though various attempts have been made using chemical and mechanical meth-
ods, neither has been successful enough to be used commercially. The concerns for
current mechanical thinning techniques include poor fruit removal—over- or under-
thinning, most fruit removal occurs at the tree top, too many large fruit are removed,
and the difficulty of achieving evenly spaced fruit.
