Colorful California Landscape: A Water-Friendly Garden
Colorful California Landscape:  A Water-Friendly Garden

Natural Pest Control

The central principle of organic gardeing is growing plants in harmony with Nature (Rodale's OrganicLife, August 2010).  Insects, even those that eat your plants, are a crucial part of that system.  When you see insects in your garden, take some time to watch what they're doing.  Are they actually destroying the plant or just nibbling it a bit?  Many plants can outgrow minor damage.  The best defenses against insect attack are preventative measures.  Grow plants suited to the site and they'll be less stressed.  Don't let plants be too wet, too dry or too shaded.  Design a diverse garden, so that pests of a particular plant won't decimate an entire section of the garden.

Chemical Versus Organic Pest Control

In chemical horticulture, a specific insecticide may be applied to quickly kill off a particular insect pest.  Chemical controls can dramatically reduce pest populations in the short term, yet by unavoidably killing (or starving) natural control insects and animals, cause an increase in the pest population in the long term, thereby creating an ever increasing problem.  Repeated use of insecticides and herbicides also encourages rapid natural selection of resistant insects, plants and other organisms, necessitating increased use, or requiring new, more powerful controls.

In contrast, organic horticulture tends to tolerate some pest populations while taking the long view.  Organic pest control requires a thorough understanding of pest life cycles and interactions, and involves the cumulative effect of many techniques, including:

  • Allowing for an acceptable level of pest damage
  • Enouraging predatory beneficial insects to flourish and eat pests
  • Encouraging beneficieal microorganisms
  • Careful plant selection, choosing disease-resistant varieties
  • Planting companion crops that discourage or divert pests
  • Using row covers to protect crop plants during pest migration periods
  • Rotating crops to different locations from year to year to interrupt pest reproduction cycles
  • Using insect traps to monitor and control insect populations

Each of these techniques also provides other benefits, such as soil protection and improvement, fertilization, pollination, water conservation and season extension.  These benefits are both complementary and cumulative in overall effect on site health.  Organic pest control and biological pest control can be used as part of integrated pest management (IPM).  However, IPM can include the use of chemical pesticides that are not part of organic or biological techniques.

The philosopy at High Country Gardens is to use plant that are well suited to your region and David Salman, their chief horticulturist, says: "This is the best way to avoid stressed, insect and disease prone plants. A plant that is ill-suited to its growing environment is always struggling and therefore vulnerable to attack from pests."

Use Mother Nature for Pest Management

Natural Predators

Encourage the natural predators of pest insects to hunt in your garden - beneficial insects (such as the common ladybug), birds, frogs and lizards control pests by eating them (Organic Gardening, August 2010). You can make your garden hospitable for your natural allies by keeping a water source (like a birdbath or even just a dish) nearby for them and not wiping out the entire pest population with a pesticide, sending the beneficials elsewhere in search of food.  Also, grow plants with small blossoms like sweet alyssum and dill, which attract predatory insects who feed on flowers' nectar between attacks on pests.

Aphids are the most common garden pest insect.  They feed on both garden crops and ornamental plants.  They feed in colonies, part of the reason that they are so destructive.  Ladybugs are an excellent predator of aphids. An adult can eat up to a 1000 aphids a day and as a larvae, about half as many.

Decolate snails (see photo below) are 1-1/2" long, conical-shelled predators that attack and kill common brown snails, garden snails and slugs.  You can buy both of these at your local nursery or on the internet.  The Gardens Alive! website sells beneficial nematodes which they claim can be highly effective in killing grubs and fleas.  They also sell Green Lacewings - advertised as being the best all-purpose predator for your garden for controlling aphids, mealybugs, immature scales and whiteflies, thrips, spider mites and other plant pests.  Adult green lacewings are not predators of aphids, but their larvae are.  Other beneficial insects include hover flies, predatory bugs, ground beetles, rove beetles, hunting and parasitic wasps, spiders and tachinid flies. Learn to identify the pests from the beneficial insects and how to attract beneficial insects.

If you need to react quickly to an acute pest invasion you can choose from several natural products that affect specific insects, won't harm humans, pets or wildlife, and that degrade quickly in the environment. Among the best of those products is Bacillus thuringiensis, a naturally occurring bacteria that you apply to your plants to disrupt the digestion of caterpillars and other leaf-eaters. Be sure to identify the pest positively before you buy this product because each strain of Bt affects specific kinds of insects. Horticultural oils, insecticidal soaps and garlic and/or hot pepper sprays also work well against many pests.

After you've enticed the good insects and the nasty ones still persist, the next step is using traps, barriers and the hand-picking of pests. Many natural plant-derived chemicals (such as red pepper, pyrethrins, rotenone and many others) should be used in place of chemical pesticides, which often kill beneficial insects as well as the pests. Insecticidal soaps can be used as well effectively.

Plant and Soil Enhancers

Worm tea is the liquid that drains or "leaches" from the worm bedding and castings.  The end result is a plant and soil enhancer that can be used as a supplement to a complete fertilization program for application on flowers, trees, shrubs, turf, fruits and vegetables.  It can be sprayed directly on plants or appliced to the surrounding soil.  Worm tea is a natural white fly, aphid, and spider mite repellant.

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Stewardship requires the recognition that we are all caretakers of the environment and economy for the benefit of present and future generations. We must balance the impacts of today's decisions with the needs of future generations. - The Minnesota Round Table on Sustainable Development (1998)