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How to Use Dormant Oils - Tree & Shrub Care

By DoMyOwn staff

A dormant oil application can help keep your trees and shrubs healthy and protect your ornamental plants from insect infestations in the spring.

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Video Transcript

Hey guys I'm Amber! I'm here at DoMyOwn and i'm going to talk to you today about dormant oils: why you use them, what they are, and when to apply them.

Dormant Oils are primarily a lightweight petroleum-derived oil that's used for a myriad of things including controlling and preventing insects and diseases on trees and a variety of ornamental shrub species.

Scale as well as a variety of other insects are going to be ones that the dormant oil can control. Things like aphids, white flies, immature stages of mites, or even caterpillar eggs or things of that sort as well as mealy bugs and even some diseases such as scab, blight, and mildew are all great options that you could use the dormant oil to try and prevent and control.

The primary time to apply dormant oils, hence its name, is when your plants are going to be in a dormant state or transitioning out of or into that dormancy. When the plants have very little foliage of any on the tree is going to be ideal for the fall and winter months. You also want to make sure that you're paying attention to the growth cycles on the trees if you're going to be applying it. In the spring, between bud swell and first leaf emergence is normally going to be a great time to apply that to make sure that you're controlling all those unwanted pests and still allowing the tree plenty of time to fruit out before any of the beneficial insects like pollinators start becoming active. Anytime that temperatures are 40 degrees or higher you should be safe to apply to the tree. That being said, make sure you're not applying them when temperatures are too high, say over 75, because we want to make sure that when you're applying an oil while beneficial to the trees and limbs, that you're not doing it in excess or when temperatures are too high to potentially cause burn. Look at the weather forecast and make sure that no rain is expected and preferably when using oils it's better to do it on a day when your relative humidity is a little bit on the lower end.

Now typically you want to use a hand pump or backpack-style tank sprayer we don't really want to use hose-end sprayers unless it's absolutely necessary because often the oils are too thick to run through that type of equipment make sure that you're getting thorough coverage and you're spraying the limbs completely until they have sort of a shiny look to them from the oils and then cut that off before it starts to drip. And if you have any type of beneficial predatory mites or any type of beneficial insects that tend to overwinter in lower parts of trees you can always skip spraying the bottom parts of the trunk and just focus on the upper areas and the backsides of leaves if your plant still has some on it and requires an application at that growth stage.

One word of caution is that if you've applied any type of sulfur-based pesticides in the last 30 days, that you hold off on that horticultural or dormant oil application certain oils and sulfur products may not mix so well and could cause a toxic combination to the plant. So let's make sure the plants are safe and give that space that we need between applications.

There are other insecticides that you often can pair up with it to be more beneficial to your treatment process depending on the particular pest you're treating for or disease and the overall severity of it. You may need other products to get the complete control you're looking for. Insects like scale for instance often require a systemic application, one that you pour around the root zone of the tree, as well as a topical or foliar application with something like a dormant oil. This two-factor application can really make sure that you're getting the complete control you need especially if you already have a well-established and mature aged scale that is on the tree. IGR stands for insect growth regulator are basically a fancy way of saying birth control for bugs.

In some cases you may need to mix this in with your dormant oil application if your pest populations are extremely high and you want to help reduce some of those future generations to contend with this season and next season.

So make sure you're checking those product labels so that anything you're planning to use on your plants is going to be safe all the way through.

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