4. Organic vegetable production

Davidson and Davidson (1992) give the example of 1000 ibis consuming nearly a quarter of a million pests
during a day.
next instar, or larval, stage. Heliothis
have six instars. At the completion
of the sixth instar, the caterpillar
burrows into the soil to pupate.
Most pupae are found in the top 10
centimetres of soil. If pupation takes
place during summer, the moth will
develop, then crawl to the surface
along the tunnel the caterpillar
dug and, once emerged, repeat
the cycle. In much of temperate
Australia Heliothis have three to
four generations a year. As autumn
progresses an increasing proportion
of the pupae will enter a winter
diapause and will not complete
development until the following
spring.
There are several things to note
from this life cycle:
• The moths are not active in the
day or are not readily observed,
but male moths can be caught in
pheromone traps.
• Eggs are exposed from four
to 30 days, depending on
temperatures.
• Newly emerged larvae often feed
in exposed situations, but later
instars tend to be protected.
• The larvae cause the damage
to the crop, and the later instars
feed the most.
• Moths cannot burrow, so any
damage to the exit tunnel will
prevent moths emerging.
The resulting management options
are as follows:
• monitoring moth flights with
pheromones
• monitoring egg numbers and,
if intervention is required,
targeting treatment to egg hatch
• if larvae are missed, the next
opportunity for management
is to cultivate the soil after
pupation to destroy the exit
tunnels—known as ‘pupae
busting’.
Natural enemies
In natural environments most
organisms’ populations are kept
in check by a range of ‘natural
enemies’, among them bacterial,
viral and microsporidium diseases,
nematode infections, parasites
or parasitoids, and predators.
These natural enemies are called
‘beneficials’. Most insect pests have
a range of specific and generalist
natural enemies that either kill
them or limit their ability to
cause damage or reproduce. In
most agricultural systems—and
particularly those that use few, if
any, insecticides—there are a range
of generalist predators. Davidson
Suitable hosts
and
alternative food
Beneficial Triangle
Beneficial present
and Davidson (1992) give the
example of 1000 ibis consuming
nearly one-quarter of a million pests
during a day.
Populations of specific natural
enemies can build up in the
presence of the pest. If natural
enemies are to thrive they need the
‘beneficial’ equivalent of the ‘pest
triangle’:
• The beneficial must be present.
• There must be suitable hosts
and, in some cases, a nectar or
pollen source.
The environmental conditions must
be favourable.
Shelter, breeding grounds and
year-round food sources encourage
predators. Nectar-producing species
incorporated in pastures and
windbreaks attract parasitic wasps,
which parasitise scarab species
in pastures. On-farm wetlands
encourage predatory waders and,
if correctly located and properly
designed, provide a filter for
nutrients in drainage before it leaves
the farm. Ideally, there are suitable
non-pest hosts for the beneficial
populations to increase, so that if a
pest arrives it finds itself in a hostile
environment.
Step 2: Prevention
Within a pest management system,
it is wise to prevent or limit the
likelihood of pest populations
causing serious damage. A variety
of cultural control methods can be
used to reduce the likelihood of pest
outbreaks.
Favourable
environmental
conditions
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