Sesbania before
of biocontrol of perennial trees. Some of
the better-known introduced tree species in
this country include Acacias, Hakeas, Pines,
Prosopis and Eucalyptus trees. These, along
with many others, are categorised as invasive,
to varying degrees, requiring different levels
of control. But, what dictates whether these
species are targets for control or eradication?
As with many species, but particularly with
tree species, whether they are considered
to be beneficial, be it on a commercial or
small-scale basis, plays an integral role in
their management plan as far as biological
control is concerned. Where there are no
clear benefits to having an invasive tree
species present, it is possible to utilise
control mechanisms that will ultimately
lead to death of the tree. One of the most
successful examples to illustrate this is that
of Red sesbania (Sesbania punicea), which was
considered a serious invader of water-courses
across the country. However, following the
release of three biocontrol agents - two
targeting the reproductive capacity of the plant
Flower galling midge on black wattle
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Sesbania after
and a third, which impacts the growth of the
plant; the abundance and density of this weed
has been reduced to such an extent that the
tree is no longer considered a weed of major
significance. Hakea species would also fall into
this category, and once again biological control
efforts against this invasive group of weeds
make use of the combined efforts of both seed
and flower feeders as well as a stem borer.
On the flip-side of the coin, trees such as
Eucalypts and pines are grown commercially
for their timber, and the former also play
an extremely important role in the apiary
industry. In addition, several acacias (i.e. black
and green wattle), are grown and harvested
to extract tannin from the bark and pulp (for
paper production) from the wood, others (i.e.
blackwood, Acacia melanoxylon) produce high
quality timber for the furniture industry or
are prized for firewood (Acacia cyclops). Lastly,
the wood from Prosopis species is used to
make charcoal, and pods from the plant are
used by farmers as a fodder for livestock, and
even created into prosopis flour for human
Stem boring weevil on Sesbania
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