Reducing Pest Pressure
|Creating refuge strips of flowering plants amid field crops, such as this row of anise growing in soybeans in Ingham County, Mich., attracts beneficial insects that prey on insect pests. |
Photo by Doug Landis.
Reducing pest problems relies on many 'little hammers,' each contributing to one or more of the following general strategies:
producing healthy crops
increasing stress on pests
You can redesign the farm to become a more complex agricultural ecosystem. Maximize the farm's favorable ecological processes, such as nitrogen fixation, nutrient mineralization from organic matter and beneficial insect populations. Minimize undesirable processes, such as nutrient loss, disease development and feeding damage by crop pests.
'We're not trying to turn farms into completely natural systems,' says Teasdale. 'In a natural system, no one species becomes dominant. In an agroecosystem, the crop is going to dominate. But within that much simpler, very managed system, we can apply many principles from natural ecosystems to make it easier to control pests.'
Produce Healthy Crops
Vigorous crops compete better with weeds and tolerate more insect damage and disease. Growing crop varieties that are resistant to particular pests, such as a fungal disease, usually results in more vigorous crops that are better able to resist other pests. Reducing environmental stresses through better soil and crop management helps plants better compete with or resist pests.
Build and maintain soil health. The link between healthy soils and healthy plants remains fundamental to ecologically based pest management. The ability of a plant to resist or tolerate pests is grounded in favorable physical, chemical and biological properties of soil. Adequate moisture, good soil tilth, appropriate pH, the right amounts and balance of nutrients, and a diverse and active community of soil organisms all contribute to plant health. (See Resources for information about the SAN book, Building Soils for Better Crops.)
Conserving and building soil organic matter encourages soil fertility and promotes more complex food webs among soil organisms. Healthy plants depend on healthy root systems. 'Creating aerobic soil conditions increases the health of plant roots,' says John Luna, extension specialist in integrated farming systems at Oregon State University. 'By maintaining good drainage, good tilth and good aerobic condition, you're able to promote a whole array of beneficial microorganisms and to discourage the pestiferous ones.'
Beneficial bacteria and fungi that colonize root surfaces can prevent infection by such disease-causing organisms as Pythium and Rhizoctonia, especially in biologically diverse systems with more complex food webs. Beneficial soil fungi, nematodes and insects also can be more effective in complex than in simple soil systems.
Scientists are finding that contact with pest invaders can actually mobilize resistance mechanisms in plants. For example, a leaf infection by a plant pathogen or a bite by an insect can prompt resistance to future attacks by these or very different pests. This 'systemic acquired resistance' occurs throughout the plant, even in tissue far away from the initial site. Farming practices can enhance it. Amending soil with compost, for example, has produced systemic resistance within cucumber to anthracnose. Similarly, inoculating transplants with beneficial mycorrhizal fungi has protected roots from root rot fungi such as Cylindrocarpon and Pythium.