close up of a hemlock branch infested with woolly adelgid

Oils of all sorts have been used for centuries to control pests from destroying trees, fruit trees and small woody plants. Today these oils have been refined to be used on vegetables, house plants, and even flowers. They used to be called dormant oils because for many years, they were harsh and could only be used during the plant’s dormant season. Today’s oils may now be used throughout the growing season, and have become a reliable way to control a broad variety of plant pests. There are a number of different types of oils:

  • Mineral oil
  • Summer (foliar) oil
  • Supreme oil
  • Superior oil
  • Vegetable oils
  • Neem oil

How Do Dormant Oils Work?

Dormant and horticultural oils work by suffocating them, clogging the breathing holes (spiracles) of the insects attempting to invade your hard work. These oils also destroy the eggs of many garden invaders by penetrating the shells and interfering with basic metabolic and respiratory processes.These are just some of the pests that dormant oils can kill:

  • aphids
  • caterpillar eggs
  • ealy bug
  • mites
  • spider mites
  • whiteflies
  • woolly adelgid

Oils also work as an excellent preventative measure against viruses, as they kill aphids known to carry them. Oils are also highly effective against the spread of viruses transmitted by people via mechanical means. And some oils are effective against powdery mildew and rust. One of the best parts of using oils to solve your pest issues is that they are safe for the wildlife in your yard. Compare this to other, more toxic methods of pest control, and you can see why this is a method worth considering.

How and When to Use Dormant Oils

With advances in refinement, many different oils have been developed for a wide variety of uses. “Dormant” oil today refers to the time in which you would use it, namely the plant’s dormant season. The best time to spray your plants is before your buds begin swelling. Ideally, you’ll want to spray on a clear day when you can expect temperatures to remain between 40 and 70 degrees Fahrenheit for at least 24 hours after application. Spray on the plants when they are dry. You’ll also want to ensure that you do not spray when freezing temperatures are expected within the next three to four days.

Words of Caution

At Environmental Turf Management, our pest control professionals apply dormant oils as part of our program of tree and shrub care. As with any insecticide, make sure you fully read the label and follow any precautions listed.