Horticultural Oils

Published On: January 4th, 2021

Horticultural Oils have been used in the home landscape and orchard pest control for decades, but their use has increased in recent years as environmental awareness grows.

Years ago, horticultural oil was known as dormant oil and was only applied when plants were dormant. These older oils were very heavy and would cause damage to foliage if applied during the growing season. Today’s horticultural oils are much lighter and safer for plant foliage, but still must be used with caution to avoid burning foliage.

How Horticultural Oils Work

Insects don’t have lungs. They breathe by a different mechanism than mammals; a series of external openings on their body called spiracles. Horticultural oil kills insects by blocking these spiracles, which suffocates the insect. Horticultural oils will also disrupt the metabolism of insect eggs, preventing them from maturing into adults.

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To be effective, coat the insects/eggs thoroughly with a generous application directly to the target pest. To avoid killing beneficial insects and pollinators it’s best to apply oils in the morning or evening when these insects are least active. Also, avoid spraying when plants are in bloom or you notice that beneficial insects are present. Oils are non-toxic and have no residual environmental effects, making them ideal for use on edible crops. Most can be applied up to the day of harvest.

When Not to Use Horticultural Oils

  • Do not apply when temperatures are over 90°F as foliar burning may occur.
  • Do not apply when humidity is high as foliar burning may occur.
  • Do not apply in autumn as fall oil treatment may increase risk of winter damage.
  • Do not apply within 30 days of applying a sulfur fungicide as the combination can be toxic to sensitive plants.
spraying horticulural oils on your houseplants to kill mites

Horticultural Oils at Heyden’s Gardens

All Season Horticultural Spray Oil

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  • Active ingredient: Mineral Oil
  • Mechanism: Kills by smothering
  • Controls: Scale insects, spider mites, aphids, thrips, mealybugs, and overwintering eggs of most insects.

Mite X®

horticultural oils mitex for sale at Heyden's Gardens in cedarburg
  • Active ingredients: Cottonseed Oil, Clove Oil, Garlic Oil
  • Mechanism: Kills by smothering. Highly scented clove & garlic oil also have repellent qualities.
  • Controls: Mites, thrips & aphids. Safe and effective for use on houseplants as well as garden plants.

Neem Oil/ Rose Rx

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  • Active Ingredient: Neem Oil
  • Mechanism: Neem Oil acts as an insecticide, miticide and fungicide. It works as an insecticide and miticide by acting as an antifeedant and disrupting hormone balance, leading to death of insect eggs, larvae, and adults. It is safe for beneficial insects as it will only affect those insects that are feeding on the plant.
  • Controls: Highly effective against sucking insects such as aphids, thrips, whitefly, mealybug, scale, and mites. Some effectiveness against chewing insects such as caterpillars and beetles. Neem Oil also acts as a fungicide and is effective in preventing black spot, powdery mildew, and rust.