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Designing a Habitat Management Strategy
The most successful examples of ecologically based pest management
systems are those that have been derived and fine-tuned by farmers
to fit their particular circumstances. To design an effective plan
for successful habitat management, first gather as much information
as you can. Make a list of the most economically damaging pests
on your farm. For each pest, try to find out:
 What
are its food and habitat requirements?
What
factors influence its abundance?
When
does it enter the field and from where?
What attracts it to the crop?
How
does it develop in the crop and when does it become economically
damaging?
What
are its most important predators, parasites and pathogens?
What
are the primary needs of those beneficial organisms?
Where
do these beneficials overwinter, when do they appear in the field,
where do they come from, what attracts them to the crop, how do
they develop in the crop and what keeps them in the field?
When
do the beneficials’ critical resources — nectar, pollen,
alternative hosts and prey — appear and how long are they
available? Are alternate food sources accessible nearby and at
the right times? Which native annuals and perennials can compensate
for critical gaps in timing, especially when prey are scarce?
See
Resources and/or contact your county
extension agent to help answer these questions.
CAUTION: Converting to organic production is no guarantee
that your fields will be pest-free, even if you surround them with
natural vegetation. Pest levels are site-specific: they depend on
which plants are present, which insects are associated with them and
how you manage both.
The examples below illustrate specific management options to address
specific pest problems:
In
England, a group of scientists learned that important beneficial
predators of aphids in wheat over-wintered in grassy hedgerows
along the edges of fields. However, these predators migrated into
the crop too late in the spring to manage aphids located deep
in the field. After the researchers planted a 3-foot strip of
bunch grasses in the center of the field, populations of over-wintering
predators soared and aphid damage was minimized.
Many
predators and parasites require alternative hosts during their
life cycles. Lydella thompsoni, a tachinid fly that parasitizes
European corn borer, emerges before corn borer larvae are available
in the spring and completes its first generation on common stalk
borer instead. Clean farming practices that eliminate stalk borers
are thought to contribute to this tachinid fly’s decline.
Alternative
prey also may be important in building up predator numbers before
the predator’s target prey — the crop pest —
appears. Lady beetles and minute pirate bugs can eventually consume
many European corn borer eggs, but they can’t do it if alternative
prey aren’t available to them before the corn borers lay
their eggs.
High
daytime soil temperatures may limit the activity of ground-dwelling
predators, including spiders and ground beetles. Cover crops or
intercrops may help reduce soil temperatures and extend the time
those predators are active. Crop residues, mulches and grassy
field borders can offer the same benefits. Similarly, many parasites
need moderate temperatures and higher relative humidity and must
escape fields in the heat of day to find shelter in shady areas.
For example, a parasitic wasp that attacks European corn borers
is most active at field edges near woody areas, which provide
shade, cooler temperatures and nectar-bearing or honeydew-coated
flowering plants.
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