Applying Ecological Principles
|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.
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.
|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.
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.
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.