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Dormant Oil Kills Many Pests As They Sleep

Petroleum jelly is good for treating burns and other human injuries. It’s also good for treating trees and shrubs for insect pests while they sleep. In the case of trees and shrubs, I’m referring to dormant oil spray.

Dormant oil spray is particularly effective against aphids, mites and scale. This material is highly refined oil – like very dilute petroleum jelly. Thus, the analogy above. The insects hibernate for the winter in the deciduous trees or shrubs whose leaves provide them with food in season. Spraying the trees/shrubs with dormant oil in early spring kills the insects while they are still asleep. Dormant oil can also coat gypsy moth egg masses to prevent the eggs from hatching.

We have a very small window of opportunity to apply dormant oil. That’s why we’re starting to schedule our applications now. It has to be applied after the temperature rises above 40 degrees and before the plants leaf out. Dormant oil coats the insects, smothering them. But plants transpire water through their leaves. Applying dormant oil to foliated plants can interfere with photosynthesis.

The dormant oil target insects are very small, scarcely visible to the naked eye. Aphids are small (adults are no more than an inch long), soft body insects that suck nutrients from the leaves. Mites pierce leaves and suck out the chlorophyl. Mite damage is easier to see than the mites themselves. Mites are black specs the size of a grain of pepper. Sucking the chlorophyl out of leaves results in yellow spots that are clearly visible. The best way to check for mites is to hold a piece of white paper under a branch and shake it. The mites will fall on the paper just like shaking pepper on food. Scale insects also pierce and suck the chlorophyl, leaving yellow spots.

A dormant oil application is part of our Plant Health Care (PHC) program. If you’re on a PHC program, you don’t have to do anything. We’ll apply it at the proper time. But we also offer it as a single application for those who aren’t on a PHC program. Time’s running short for you to arrange for an application. Act now if you want this environmentally sound protection for your valuable trees and shrubs.

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