Horticultural Oil: What Is It And How To Use It In The Garden

The use of horticultural oil is a common way to eliminate pest issues for fruit trees and landscape plants. 

Many people struggle to control the garden pests such as caterpillars, spider mites, scales, aphids, whiteflies, mealybugs, leafhoppers, slugs, thrips., and snails and keep them at bay.

spraying horticultural oilPin

Generally labeled for pest mites, thrips, whiteflies, scale (soft and armored), plant bugs, lace bugs, caterpillars (webworms, codling moth, armyworm, hornworm, leafrollers, etc.), and other soft-bodied insects (aphids, adelgids, psyllids, sawfly larvae, leaf beetle larvae, and leafminers). 

After exhausting other means of pest control, such as insecticidal soaps, natural neem insecticide, pesticides, and fungicides, many turn to horticultural oils, also called spray oil.

The majority of pest control oils are some type of mineral oil, a refined petroleum product. There are a few vegetable oils that are also effective pesticides, such as cottonseed oil and soybean oil. 

You must remember not all insects are pests. Lady Bugs are a natural enemy of some soft-bodied insect pests, for example, helping to control aphid populations.

Unfortunately, oils will harm both the good beneficial insects and the bad insects, so take care and evaluate the situation before using horticultural sprays.

What Is Horticultural Oil?

When it comes to pest or insect control, you’ll find several types of horticultural oils to use, which can eliminate garden pests like spider mites on your fruit tree and shrubs.

Is neem oil a dormant oil?

Neem oil makes one of the best insect-repelling essential oils that exist. It is made up of many components, but azadirachtin is the most active insecticidal active ingredient.

Several neem-derived insecticides have been developed. A number of compounds found in neem seeds, notably azadirachtin, have proven useful as insecticides. 

Derived from petroleum, oils work by coating the outside of a bug (armored scale insects) and preventing them from proper breathing and eating, suffocating them.

The highly refined vegetable oils extracted from plants (soybean oil & cottonseed oil) can also naturally eliminate pests and insect eggs.

Mix the oil with water and a little Dawn dish soap into a sprayer or a spray bottle and apply on plants struggling with insect issues.

You’ll hear several names get thrown around to describe the oil:

When and How To Use Horticultural Oil Application Spray In The Garden?

Reach for horticulture oil after exhausting all other insect pest control options. Oils work very well on most plants; however, always check the labeling before applying them. 

Some oils perform better when applied during the dormant season and only under specific conditions (temperature as well as humidity).

Applying a “dormant oil” helps kill off any wintering insects like mites and scales and gives aphid control without harming the plant.

Horticultural spray oils, when first introduced, were heavy oils. Today, this type of oil is highly refined and “lightweight,” like Bonide All Seasons Spray Oil (amazon) now allows safe use on many plants throughout the entire growing season as needed. 

Apply the oil. It dries up and becomes non-toxic to plants but is effective in pest control. Also, use oils to help control powdery mildew or black sooty mold.

The term “dormant spray” refers to the proper time of application to use the oil and not the kind of oil utilized. Always refer to the label for application directions.

Use Spray Oils On What Type Of Plants?

Using homemade horticultural oils to kill plant scale and other soft insects on woody ornamental plants makes for a lethal combo.

Most oil products work the same way: you spray them on plant foliage where you see pests or the beginnings of a fungal infection.

Unfortunately, they also kill off many beneficial insects as well. Take great care to ensure the proper application and use of any spray solution on plants that can tolerate the oils.

The oils don’t harm the plant, just the bugs. They work by suffocating the insects as well as the insect eggs.

They also affect how the insects eat and can poison the insects as well as suffocate them. Additionally, one insect may carry the oils to other insects and contaminate the entire nest.

 While plant-safe under the right conditions, horticultural oil can cause phytotoxicity (plant tissue damage, especially on foliage) if applied during high heat or when evaporation is reduced due to cloudy, rainy, or very high humidity. 

The summer rate per gallon of water is given in bold (and the dormant season rate per gallon of water is given in plain text in parentheses). 

Horticultural oil for Scale – In order for the horticultural oil to work effectively, insects like scale need to be totally covered. Good spray coverage is important. Once the oil dry’s on the plant, the oils no longer work on the insect pests.

Related Reading

Plants NOT To Use Oils On?

Never use oils with any aquaponic gardening. The oils are toxic to fish. Don’t use oils on plants such as:

  • Maples
  • Junipers
  • Spruce
  • Cedar or other such Evergreen plants
  • Japanese as well as Red Maples
  • Hickory and Black Walnut plants
  • Plume cedar
  • Smoke Tree – very sensitive plants

If plants show yellowing of leaves or needles after application, do not use them again on the plant. This usually indicates a burn and could cause further plant injury if used again.

So, you’re probably thinking, “Horticultural oil vs. neem oil“.

Make every effort to eliminate pests with other organic pest control methods, such as neem oil, before seeking horticultural oil, such as insecticides or biorational pesticide. 

Never apply oils in freezing temperatures, droughts, or extreme heat, and ALWAYS read the chemical label for the application rates.

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