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Cotton no-tilled into winter
wheat stubble, such as this crop approaching harvest on Max
Carter’s farm in Coffee County, Ga., contained significantly
more beneficial beetles and spiders than tilled fields compared
in a USDA-Agricultural Research Service study.
Photo by Joe Lewis. |
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Incorporating pest controls at many different stages and limiting
pests’ abilities in many small ways are the foundation of ecological
pest management. Production systems that use ecological principles
to imitate nature, along with multiple tactics and the right information,
can:
 strengthen
individual impacts of strategies when used together,
reduce
the risk of crop failure by distributing the burden of crop protection
across many tactics,
minimize
environmental disruptions and threats to human health,
slow the
rate at which pests adapt or evolve resistance to a given management
tactic because that tactic is used less frequently, and
reduce
operating costs and improve profitability by minimizing the need
for purchased inputs.
Cotton research headed by Joe Lewis at ARS in Georgia has shown
that, like Steve Groff’s vegetable system, combining minimum tillage
with cover crops and cover crop mulch creates enough biological
diversity to stymie pests. Comparing tilled fields to fields planted
using conservation tillage following a winter cover crop like vetch,
winter grains or clover, researchers found that beneficial insect
populations increased. In fact, overall seasonal densities of certain
types of carabid beetles and spiders in the “conservation” fields
were a full 14 times higher than in the conventional fields.
Input costs were nearly identical, but average yields in the conservation
fields were about 100 pounds higher than conventional yields. Moreover,
net returns were $60 per acre higher in the conservation plots.
Improve Management of the Disturbances Created by Agriculture
Agricultural disturbances such as tillage, harvest, and fertilizer
and pesticide application all can provoke pest problems, but you
can avoid stimulating pests at the wrong time. For example, till
fields before final seedbed preparation to stimulate weed germination,
then cultivate before planting to lower the density of weeds infesting
a crop.
Leaving some undisturbed areas on a farm can help maintain the
balance between beneficial and pest organisms. Many predators and
parasites that attack crop pests thrive in the less-disturbed areas
provided by hedgerows, weedy borders, woodlots and riparian buffers
on the farm; in grassed alleyways in orchards and grassed waterways
in field crops; and even in the small areas left between crop rows
by zone tillage. Small sites allow natural enemies to persist and
migrate into crop fields to keep pest populations in check.
In a research project in the Southeast, ground beetles, field crickets,
ants and field mice were important weed seed predators within a
low-input, no-till cropping system in which soybeans were grown
in a surface mulch of wheat straw. Over five weeks in the fall,
the weed seed predators removed more than double the number of seeds
from the no-till system compared to an adjacent conventional tillage
system.
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Applying compost, depicted
in this SARE-funded project evaluating organic soil amendments
to Maine potato fields, builds a healthier soil- and may suppress
soil-borne diseases.
Photo by Greg Porter. |
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Include Perennial Plants in and Near Fields
Perennial plants — such as fruit trees, grassed waterways, trees
growing along stream banks, or forage grasses and legumes harvested
for hay — offer many advantages:
their
roots are more extensive and longer lasting than those of annual
crops,
much more
than annual crops, they support communities of diverse soil organisms
that are more similar to those in soils of natural ecosystems,
they enhance
water infiltration and reduce soil compaction, thus extending
rooting depth,
they serve
as important habitat for beneficial insects, providing both food
and shelter, and
they help
preserve soil and water quality by maintaining living plant cover
above ground and active roots in the soil.
Increase Diversity
Diversity, both in the crops you grow and how you manage them,
can reduce pest problems, decrease the risks of market and weather
fluctuations, and eliminate labor bottlenecks. Enrich diversity:
across
the landscape (within fields, on the farm as a whole and throughout
a local watershed),
throughout
the season (different crops on the same farm at different stages
of growth and managed in different ways), and
from year
to year (rotations of three or more crops).
Ideally, agricultural landscapes will look like patchwork quilts:
dissimilar types of crops growing at various stages and under diverse
management practices. Within this confusing patchwork, pests will
encounter a broader range of stresses and will have trouble locating
their hosts in both space and time. Their resistance to control
measures also will be hampered.
As plant diversity intensifies above ground, diversity builds in
the soil. Through a system of checks and balances, a medley of soil
organisms helps maintain low populations of many pests. Good soil
tilth and generous quantities of organic matter also can stimulate
this very useful diversity in pest-fighting soil organisms.
Researcher Matt Liebman reviewed cropping system studies to get
at how plant diversity deters weeds. His summary of various studies
that grew 27 test crops in rotation compared to monoculture systems
found that:
weed plant
density in rotation was less than in monoculture in 19 out of
25 cases,
weed seed
density in crop rotation was lower in 9 out of 12 cases, and
yields
of test crops were higher in rotation than monoculture in 9 out
of 12 cases.
“These results suggest that crop rotation can be an important component
of strategies to reduce weed density and maintain or increase crop
yield,” Liebman says.
In Oregon’s Willamette Valley, Larry Thompson’s 100-acre fruit
and vegetable farm blossoms with natural insectaries. “To keep an
equilibrium of beneficials and pests and to survive without using
insecticides, we have as much blooming around the farm as we can,”
he says.
Thompson uses cover crops to recruit ladybugs, lacewings and praying
mantises in his battle against aphids. Overseeded cereal rye is
already growing under his lettuce leaves before he harvests in late
summer and fall. “It creates a nice habitat for overwintering beneficials
and you don’t have to start over from ground zero in the spring,”
he says.
Between his raspberry rows, Thompson lets his dandelions flower
into a food source for nectar- and pollen-seeking insects before
mowing them down. Forced out of the dandelions that nurtured them
in early spring, the beneficials pursue a succession of bloom. They
move first into his raspberries, then his Marion berries and boysenberries.
Later in the year, Thompson doesn’t mow his broccoli stubble. Instead,
he lets the side shoots bloom, creating a long-term nectar source
into early winter. “The bees really go for that,” he says.
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