Agriculture Reference
In-Depth Information
PEST BARRIERS
In some tropical areas, birds and fruit bats can cause extensive losses of fruit
near harvest. Numerous bird species, from solitary species to large fl ocks
of parrots, will eat fruit. Various approaches are used to reduce these losses,
including propane-fi red cannons to scare the birds and permanent net
enclosures (Fig. 3.9). The propane-fi red cannons produce loud, unexpected
blasts at random intervals, which are generally not less than 3 min apart.
The noise keeps the birds nervous, while they will become accustomed to
cannons that are always located in the same spot in a fi eld, if the fi rings occur
at regular intervals or fi re very rapidly. Other electronic devices produce
electronic synthetic sounds to repel birds by reproducing distress calls that
mimic individual bird species. Visual repellents, such as balloons, streamers
and fl ashing lights, are not as ef ective as acoustical devices. Bird netting is
available that is lightweight and draped over the tree and, once over, harvest-
ing is possible, to heavier, ultraviolet-resistant protective materials fastened
to an overhead structure that totally encloses the orchard. The overhead
structure has a very high initial cost. Netting comes as rigid or stretch
materials in dif erent widths and mesh sizes. The material chosen depends
upon the crop and layout, expected material life and the equipment available
for installation and removal.
In Asia, structures are built and covered with fi ne nylon mesh to exclude
aphids that carry viral diseases. An example would be a mesh structure in
which papaya is grown to protect it from ringspot virus. These structures
cover hectares of land and are rather light in structure and frequently suf er
considerable damage from hurricanes (typhoons) during the warm season.
(a)
(b)
Fig. 3.9.
Birds and fruit bats cause signi
fi
cant damage to fruit and may require the
use of a protected shelter to protect the crop (a). Protective shelters are also used
to protect papaya and other crops from insect-borne viruses (b); these lightweight
shelters are made of very
fi
ne mesh nylon.
