The U.S. Department of Agriculture's organic regulations restrict pesticide use to those of a natural origin, eliminating many of the synthetic remedies that gardeners have come to rely on. Controlling insects and diseases in the organic garden, however, goes beyond using pesticides. Organic methods seek to improve whole-system health, thus improving a plant's ability to withstand pests and diseases without pesticides. (See References 1) A system known as integrated pest management guides pest- and disease-control decisions in the organic garden.
Integrated Pest Management
At the heart of IPM lies an understanding of the garden as an ecosystem in which multiple organisms interact. When an insect or disease becomes a problem, practitioners of IPM seek to understand why and to correct the cause of the problem rather than resorting to a pesticide that will eliminate the problematic organism. For example, poor soil fertility may leave a plant unable to resist a fungal disease, or the lack of plants attractive to pest predators may allow pest populations to escalate. While IPM doesn't forbid the use of organic pesticides, these are typically regarded as a last resort. (See References 2)
Monitoring and Identification
Because IPM requires understanding of a pest within an ecological system, you must monitor pest populations in your garden and correctly identify or diagnose potential pests. Agricultural extension agents, master gardeners or experienced garden center employees can help with pest and disease identification. You should expect to see pest organisms in your garden. Only when they begin to adversely affect the production of your plants do control methods become necessary. (See References 2)
Insect control begins with plant selection and biodiversity. Choose plants that problematic local pests don't like. Planting a variety of plants prevents pests from homing in on your garden as a one-stop source for their favorite food. Take care to remove those weeds that act as alternate food sources for insect pests.
In nature, predators keep pest numbers under control. Attracting these predators --- called beneficial insects or beneficials --- to your garden can moderate insect pest problems. Ensure that you have plants near your garden that act as food sources for beneficials, including weeds like dandelions. If these methods don't bring a pest under control, you may be able to use a biological pesticide to control the organism; diseases and parasites afflict the pest while leaving beneficials alone. Finally, organic insecticides may control pests. (See References 3)
Disease control for the organic garden takes an approach similar to insect control: improving the health of the ecosystem and individual plants and avoiding conditions that favor disease. Whenever possible, select plants that are bred to resist a particular disease. Avoid wetting plant foliage as much as possible, as this can encourage the development of fungal diseases. Water at the base of the plant or water overhead early in the day, giving the foliage time to dry, and maintain enough space between plants so that airflow keeps foliage dry.
When you grow the same plant two years in a row in the same soil, plant diseases often overwinter in the soil and infect the next year's crop. Crop rotation prevents these diseases from taking hold. Finally, organic pesticides, such as botanical oils and sulfur, can control some diseases. (See References 4)
- U.S. Department of Agriculture: Organic Production and Organic Food
- National Sustainable Agriculture Information Service; Biointensive Integrated Pest Management (IPM); Rex Dufour; 2001
- Sustainable Agriculture Research & Education; How Ecologically Based Pest Management Works; Miguel A. Altieri, et al.; 2005
- National Center for Appropriate Technology: Plant Diseases
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