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***Please Note: This information was originally provided in conjunction with a presentation at the Organic Growers School Spring Conference. If you have further questions, feel free to contact us.***

“Organic Pest Control in the Garden”

by Linda Blue

Key steps to organic pest control:

  1. Use good cultural practices to avoid pest problems.
  2. Implement mechanical and physical control measures.
  3. Choose organic pesticides.

Integrated pest management:

  1. Monitor plants regularly for potential pests as well as natural enemies.
  2. Learn to identify the good guys and the bad guys.
  3. Learn their life cycles.
  4. Determine your action threshold. (How much damage can you tolerate before taking action?)

**Gardening is a continual learning experience. Be an observant gardener and adjust your practices from year to year.

Insect and Disease Control

Cultural Practices

  1. Good Soil Preparation- Healthy soil produces healthy plants – the basis of organic gardening. A. Soil test: it’s free. This is the only way to correct problems with the soil pH or phosphate levels. B. Organic amendments: Compost, rotted manure, leaf mold, pine bark soil conditioner, cover crops. Organic components improve drainage and aeration and enhance the living organisms in the soil.
  2. Plant selection Look for disease resistant cultivars when possible. Select healthy, insect and disease-free transplants. In the landscape plant the right plant in the right place and avoid plants with known common pest problems.

  3. Rotate crops in the vegetable garden. Rotate by family: nightshades, legumes, cucurbits, brassicas.

  4. Planting dates. Let the soil warm up adequately before planting warm season vegetables. Ex: beans prone to root rot in cold soil. Brassicas planted in spring will have lower insect populations than fall crops. Earlier maturing corn will have less worm problems.

  5. Plant spacing. Good air circulation is important for reducing fungus diseases. Crowding produces weaker plants, enables insects to spread unnoticed and makes spraying difficult.

  6. Irrigation. Water enough for continual growth. Avoid wet foliage by using sprinklers in morning or using drip irrigation.

  7. Weed Control. Weeds can harbor diseases and insects, and reduce air circulation around crops.

Mechanical Control Measures

  1. Search and destroy. Handpick caterpillars, beetles, bugs. Squash them or drop them into a bucket of soapy water to drown. Identify egg masses of squash bugs, Colorado potato beetles, etc. and squash them. Aphid populations can be reduced by smashing.

  2. Barriers. Cutworm collars prevent cutworms from attacking stems. Netting can prevent worms from getting on cabbage or delay been beetles and squash beetles (remove row covers when plants begin to flower).

  3. Sanitation. Remove diseased plants or plant parts. Clean up debris at the end of the season and destroy plants infested with diseases or insects.

Biological Contols

  1. Provide habitat for birds.

  2. Attract and protect the beneficials. Learn to identify them and use care with the use of pesticides.

  3. Releasing beneficial insects into a garden is usually not very cost-effective because parasites and predators are quite mobile.

Organic Pesticides

  • Biological Pesticides

          A. Bacillus thuringiensis (B.t.)

              – B.t. var. kurstaki for numerous caterpillar species.

              – B.t. var. san diego for Colorado potato beetle grubs.

              – B.t. var. israelensis for mosquito larvae.

          B. Bacillus popilliae. Milky spore for Japanese beetle grubs only.

  • Beneficial nematodes Steinernema feltiae, Beauveria bassiana, Heterorhabditis Useful for some soil dwelling insects – black vine weevil larvae, flea larvae, fungus gnats, grubs. They are living organisms, so follow handling instructions.
  • Spinosad (derived from bacteria Saccharopolyspora spinosa) Works best on chewing insects (ingestion), but some effect on contact. May also kill some beneficials, especially immature forms.

  • Serenade (Bacillus subtilis) Disease control – mostly several fungus diseases. Spray preventatively. Combine with copper for tomato late blight.

Inorganic Pesticides

  • Insecticidal Soaps. Potassium salts of fatty acids. Best on small soft bodied insects such as aphids, mites, white flies. Excellent coverage on bottom of foliage required. Follow label for mixing and application precautions.
  • Horticultural oils. Refined petroleum (mineral) oil, some plant derived. Good on small soft bodied insects such as aphids, mites, scale. Good coverage required. Potential for plant burning; follow label.
  • Dormant Oil. Heavier oil used on trees during the dormant season.
  • Kaolin (Surround). Finely ground clay. Repels insects, mostly in orchards. Film washes off fruit.
  • Diatomaceous earth. Silicon dioxide. Do not breathe! (Wear a dust mask.) Mostly for slugs.
  • Copper & Sulfur. Disease control. Weak fungicides. Copper helps for bacterial diseases.

Botanical Pesticides

  • Neem oil Kills many insects and mites. Less damaging to beneficials.
  • Pyrethrum Contact poison. Kills most types of insects (including beneficials).
  • Rotenone Contact and stomach poison. Kills many insects (including beneficials). Use care with honey bees.


Weed Control

Cultural Practices:

  1. Remove weeds before planting.
  2. Do not allow weeds to go to seed.
  3. Keep tilling to a minimum after planting. It brings new seeds to the surface.
  4. Mulch.


  1. Pulling, hoeing, tilling.
  2. Mulch. Apply mulch to weed-free beds. Spread 2 – 3 inches deep. Vegetable beds: straw or chopped leaves. Ornamental beds: Bark mulches, pine needles, wood chips, chopped leaves.

Organic Herbicides:

  1. Pre-emergent – prevent seeds from germinating. Corn Gluten Meal. Relatively ineffective in our climate. Plentiful spring rains cause it to break down quickly and prevent the necessary seedling root desiccation. 10% nitrogen.
  2. Post-emergent – kill existing weeds. All burn leaves but have no effect on roots. All work best on young plants, and when applied in warm sunny conditions.
  • A. Acids. Acetic acid (vinegar), citric acid. Young grasses. Strong acids can lower soil pH if used frequently. Also use caution to avoid eye or nose irritation.
  • B. Oils. Eugenol (clove oil). Young broadleaf weeds.
  • C. Soaps. Potassium salts of fatty acids.




Author: OGS

Organic Growers School is a non-profit organization providing organic education since 1993. Our mission is to inspire, educate, and support people in our region to farm, garden, and live organically.

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