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Dormant Oil – Insects’ Worst Nightmare

It may be the middle of winter but that doesn’t mean your trees and shrubs are free from insects. You may not see them at this time because both the insects and the plant are dormant. Come spring, though, the insects will be active again, feasting on the leaves of your trees and shrubs. And, after their long winter nap, they are going to be mighty hungry.

This would be a good time to schedule an early spring dormant oil treatment to destroy overwintering insects in their sleep. Many insects “breathe” through their skin. Coating them with dormant oil while they sleep will clog their air intakes and smother them. Dormant oil is a highly refined oil, much like the petroleum jelly we put on wounds. However, dormant oil is diluted so that it flows through a hose and spray nozzle.

Aphids, mites and scale are the leading targets for dormant oil treatment. Although they can hardly be seen, it’s a safe bet that they are fast asleep in your trees and shrubs. Since properly applied dormant oil won’t harm the plant, this treatment lets you get a leg up on the most common spring and summer pests. Dormant oil will also destroy overwintering egg masses, including gypsy moth and hemlock woolly adelgid (pictured). The oil coats the buff colored gypsy moth egg masses and the white, cotton like hemlock woolly adelgid egg masses by preventing air from penetrating.

The window of opportunity to apply dormant oil is very small. We can’t apply it until the temperature rises above 40º and stays there. Otherwise the oil will become too viscous (thick) to spread properly and coat the whole plant and the insects. However, it also has to be applied while the tree is still dormant, before the leaf buds break. Applying dormant oil after a plant leafs out can damage the leaves.

One comment on “Dormant Oil – Insects’ Worst Nightmare

  1. Although we do not have such a problem, is oil safe on foliage while the weather is cold?

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