Agriculture Reference
In-Depth Information
Benefits of biological control:
X
Non-toxic to humans, wildlife and pets.
X
Numbers of predators and parasites increase
naturally.
X
A balanced population of predators and parasites is
reached.
X
No build-up of resistant pests and diseases.
Limitations of biological control:
X
Needs careful introduction and knowledge of life
cycles.
X
Can easily be affected by pesticides.
Safe practice and environmental impact. The main
problems with biological control are:
X
Unsuccessful application of biological control
organisms can lead to a severe pest problem (e.g.
late introduction of
Encarsia
wasp used against
glasshouse whitefl y).
X
The incorrect introduction of a biological control
organism can subsequently kill desirable or
benefi cial organisms in the environment (e.g.
accidental introduction of the New Zealand
fl atworm (
Arthurdendyus triangulates
)
in the 1960s
has reduced earthworm numbers in some northern
areas of Great Britain).
Risks can be
minimized
by the following:
X
Understanding both the pest's and predator/
parasite's life cycles in order to achieve reliable
control carefully.
X
Choosing the best predator or parasite for the
problem pest or disease concerned.
X
Taking care that environmentally useful animal
species are not subject to the attacks of the
predators and parasites, such as the earthworms
mentioned above.
Natural balances. In most horticultural situations, there
are important examples of
natural balance
between
species:
X
With pests, their naturally occurring
predators and
parasites
are an important form of crop protection,
as described in this section of the chapter.
X
With diseases, naturally occurring predators
and parasites are less well understood, but the
nutritional
condition of the plant and the resulting
naturally occurring bacterial and fungal populations
on leaf, stem and root surfaces (see
organic
growing
, p. 10) often help to slow a disease's
progress.
X
The garden represents a complex situation. There
may be plant species present from every continent
(see Chapter 2), and any of these plant species
may be accompanied by a specifi c pest from its
country of origin. Plant species that have been
16
Figure 16.5
Tree stumps can be a long-term source
of honey fungus
stump by placing a bird table on a tree stump is not a
recommended activity in gardening (see Figure 16.5).
An environmental point
Removal of dead plant material from gardens can be
considered from the opposite point of view. Many
beneficial species
, such as violet ground beetle,
centipedes and ichneumon wasps, can use the
dead
hollow stems
of garden perennials as overwintering
refuges. Hedgehogs may spend the winter within
piles of dead branches. Gardeners may wish to
consider a
balance
between tidiness and their desire
to achieve natural pest control.
Biological control
Biological control
is the use of natural enemies to
reduce the damage caused by a pest (or disease).
