Print This Page




Pest Control Products to Use With Caution

I’m often asked whether dormant oil is acceptable insect control and do I recommend its use. It’s a somewhat complicated answer. Oils sprayed in the dormant season are acceptable in an organic program; however, there are several “buts”. I rarely recommend them now and never use myself because they are non-selective and kill over-wintering beneficial insects as well as pests. With proper soil building and healthy plants resulting from the organic program, spraying to kill is rarely needed. If you have insect pressure serious enough to warrant dormant oil spraying, here’s more detail you need to know.

In the past, horticultural oils were heavier and used only when plants were not in their growing seasons (dormant). They were called dormant oils. The old oils killed pests that overwintered on woody plants, but were too heavy to spray on plants with foliage. The term dormant oil is still used, but now generally refers to the application time rather than the product. New, lighter formulations allow use during the growing season. These products, sometimes called summer, superior, or supreme oils, can control pests from spider mites to whiteflies.

Horticultural oils are safe to use around mammals, birds and reptiles but are toxic to fish. Applying oil in freezing conditions or extreme heat, or during drought or periods of new growth, can injure plants. Some plants, including maples, junipers, cedars and spruce are sensitive to these oils. Be cautious when using horticultural oils and apply them only as a last resort. They will potentially damage your plants and will definitely kill beneficial insects.

Types of various oils used to spray for plant pests: 

Horticultural oil - a highly refined complex mixture of hydrocarbons containing traces of nitrogen and sulfur-linked compounds that is used to control plant pests. It is an acceptable alternative to control pests in organic farming, but horticultural oil usage is poorly understood since the product labels give little information on the content.

Dormant oil - was originally a less refined oil used for woody plants during the dormant season. Dormant oil now refers to the time of application rather than the characteristic of the oil.

Mineral oil - oil found in the rock strata. The white mineral oil is the tasteless petroleum used for pharmaceuticals or medicinal purposes.

Narrow-range oil - highly refined that has a narrow range of distillation.

Petroleum oil - same as horticultural oil and a more common term of reference in some circles.

Summer oil - refined oil used on plants when foliage is present as well as in the winter.

Supreme oil - highly refined and distilled oil.

Vegetable oil - derived from the seeds of some oil seed crops.

Botanical plant oil - derived from parts of plants known to have insecticidal properties - garlic oil, chinaberry oil, citrus oil, custard apple seed oil, garlic oil, neem oil and pongam oil spray.

Precautions when using horticultural oils: 
  • Do not apply on sensitive plants and avoid drift onto them.
  • Do not apply on drought-stressed plants.
  • Do not apply during freezing weather or when humidity is above 90% for longer than 36 hours.
  • Do not apply when plant foliage is wet or when rain is expected.
  • Do not spray during shoot elongation and when buds are fully-opened.
  • Do not apply in combination with sulfur or sulfur-containing pesticides.
  • Do not use spray tank that previously contained a sulfur-based fungicide.
  • Do not mix oil with fungicide and do not spray oil within 2 weeks after fungicide treatment.
  • Read and follow the label instructions carefully.
  • Spray in the early morning or late afternoon.
  • Use utensils for the extract preparation that are not used for food preparation and for drinking and cooking water containers. Clean properly all the utensils every time after using them.
  • Make sure that you place out of reach of children and house pets while leaving it overnight.
  • Harvest all the mature and ripe fruits before application.
  • Always test the extract formulation on a few infected plants first before going into large scale spraying. When adding soap as an emulsifier, use a potash-based one.
  • Wear protective clothing while applying the extract.
  • Wash your hands after handling.
To discuss this newsletter or any other topic, tune in each Sunday 8am - 11am central time to the Dirt Doctor Radio Show.The call-in phone number is 1-866-444-3478. Listen on the internet or click here to find a station in your area.

Please share this newsletter with everyone in your address book and all your friends on Facebook and Twitter to help me spread the word on organics.

Naturally yours,

Howard Garrett


  Search Library Topics      Search Newspaper Columns