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Dormant oil spray is one of the most effective insect control materials, and best of all, its environmental impact is low. It’s just highly refined, very dilute petroleum jelly. If that sounds like a medication you put on burns and other injuries, that’s because it is. Dormant oil is one formulation in a class of insecticides known as horticultural oils.
The use of horticultural oils in our battle to keep insects from destroying our valuable trees and shrubs isn’t new. Arborists have been using it for decades, maybe even centuries. As more and more property owners are concerned with the environment when making plant health decisions, dormant oil has risen to the top.
Dormant oil spray is particularly effective against aphids, mites and scale. These 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, while they’re dormant, kills the insects while they’re still asleep. Dormant oil can also coat gypsy moth and spotted lanternfly egg masses to prevent the eggs from hatching.
I’m urging you to sign up for this treatment because we have a very small window of opportunity to apply dormant oil. It needs 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. Consequently, applying this material to foliated plants can interfere with photosynthesis.
The dormant oil target insects that 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 onto 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.
