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Horticultural Oil Sprays for Pest Control | Homemade Pest Oil Spray

Oil sprays, known as horticultural oil or pest oil or white oil, are used to manage pest like scales, aphids,  caterpillars, leaf miners, leafhoppers, mites on fruit, vegetable plants, flower plants and ornamental plants. The oils also can control some plant diseases, such as powdery mildew. The horticultural oils are also known as eco oils, dormant oils, superior oils, or 70-second oils.
Insects on Citrus Tree
Insects on Citrus Tree, Orange bugs on Lime Tree

How Horticultural Oils Spray Works?

  1. Oil sprays are are not poisons, but kill insects and mites by suffocation. Oils block the air holes known as spiracles through which insects breathe, reducing the availability of oxygen causing them to die from asphyxiation. The cause of death is primarily suffocation.
  2. Oil spray will kill only insects it comes in direct contact at the time of application. 
  3. Large insects and animals that breathe by another method are not affected by the oils.
  4. Oil sprays are safe to humans, 
  5. Oils are usually inexpensive compared to many insecticides.

Commercial Horticultural Oils

Most of the commercially available horticultural oils are highly refined petroleum products known as mineral oils, mixed with some emulsifying agent that allows the oil to mix in water. 

Vegetable Based Horticultural Oils

Vegetable oils also can be used as fungicides and insecticides to kill aphids, caterpillars, leafhoppers, leaf miners on citrus trees, scales and mites and powdery mildew. Cottonseed oil, canola oil and soybean oil have been found to be quite effective for this purpose. 

Some herbs and spices like mint, garlic, thyme, peppers, cinnamon, etc. may also be effective as mineral oils. The essential oils derived from these herbs and spices are used in commercial products.

Oil sprays are exceptionally safe to humans, they are not poisons, nor do they have any bad odours. They have little if any effect on ladybugs, parasitic wasps, honey bees, etc.

Neem Based Horticultural Oils

Neem oil can also been used for the control of insects. Neem contains azadirachtin, which works as insecticide.

How to Use Horticultural Oils For Pest Control

  1. Always test horticultural oil on a small portion of foliage to avoid leaf burn.
  2. As horticultural oils work by direct contact with the pest, spray evenly and thoroughly covering both the sides of all leaves, and all the branches, stems and bark. Only those pests that are thoroughly coated by the spray solution at the time of application will be killed. Pest may be hiding on leaf undersides or minor cracks in tree bark.
  3. Spray leaves or flowers at the first sign of new growth.
  4. Spray at any times when pests are observed.
  5. To control citrus leaf miner on citrus trees like on lime, lemon, oranges, etc. spray when new growth of leaves appear, and then repeat every 2 weeks during the growth period.
  6. Apply in winter on deciduous fruit trees and roses and then just before new buds occur to control pests. 
  7. On vegetable plants and ornamental plants spray when pests first appear and then repeat after 2 weeks.
  8. You can also use horticultural oil  on Indoor plants to control scale insects, mealy bugs and spider mites. 

Precautions for Using Pest Oils

  1. Minimize your exposure to pesticides.  Avoid contact with eyes. Always read label of the product for  directions of use.
  2. Do not use on plants that are sensitive to oils.
  3. Do not spray when temperatures are above 30°C to avoide risk of leaf injury.
  4. Only use on healthy plants.
  5. Do not apply to plants suffering water/moisture stress.
  6. Wash the edible produce thoroughly before eating 

The withholding period, When to Consume any produce after spray?

If you use horticultural oil with petroleum oils, consume edible crops after more than 1 day before spray. Plant based oils are safe to use on vegetables and fruits and you can eat then on the same day after washing.

Disadvantages/Limitations of Horticultural Oils

  1. The oil spray is good for controlling aphids, pine needle scale, oyster shell scale, euonymus scale, spider mites and small pine sawfly larvae. 
  2. It is difficult to control larger, faster moving and flying pests as they are unlikely to be coated with oil. Many of the most common garden pests such as apple maggot, white grubs  and cabbageworms, etc. are not killed by oil spray.

Homemade DIY Pest Oil Recipe

The homemade pest oil formula is as under.
  1. Mix 1 cup canola oil with 1/4th cup dishwashing liquid soap in a bottle. Shake well until it becomes white. This makes the concentrated oil spray which keeps good for more than a year in a air-tight bottle.
  2. How to use pest Oil
  3. Mix 10 ml of this concentrate mixture in a litre of water in a spray bottle, and spray on plants.


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References
  1. Insect Control: Horticultural Oils, Colorado State University Extension 
  2. Using Horticultural Oil Sprays for Pest Control, Iowa State University Extension and Outreach