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Dormant Oil in Winter Helps Prevent Spring Pests

You might think winter is the time when you don’t have to worry about things like pests and diseases in your trees. Everything goes dormant, right? That’s not the case in our mild climate. Many pests and diseases are able to persist through the winter months, only to become a bigger problem come spring. If you don’t take the opportunity to treat for certain pests in winter, you’ll miss a good opportunity to prevent spring pests. Now would be the time to schedule your tree’s mid-winter application of dormant oil.

089 Scale Red Oak Trunk

Scale on a red oak tree.

What is dormant oil?

Dormant oil is a horticulture grade oil that essentially smothers pests it comes in contact with. We apply it by spraying it onto the foliage and bark of your trees and shrubs when temperatures are just right. Because the dormant oil we use is approved by Organic Materials Review Institute (OMRI), it is safe to use around birds, reptiles, pets, and other wildlife. However, we do recommend covering nearby ponds if you plan to apply dormant oil yourself, or have us apply it for you.

How does dormant oil work?

If you have hollies, ligustrum, red oak, live oak, pecan, or maple
trees in your landscape, you more than likely will have a problem with
scale insects at some point. Scale is a common insect that survives
through winter by hiding in the cracks and crevices of your trees and
shrubs. When dormant oil is applied, it suffocates the insects so they
don’t emerge and breed once warmer weather arrives. Dormant oil is also
incredibly effective against other insects such as whiteflies, aphids,
leafhoppers, leafrollers, mealybugs, mites, scale, and tent
caterpillars. Growing roses? Apply dormant oil to roses in winter to
ward off fungal diseases such as black spot.

Timing is everything!

Late December through early March are the prime times to apply dormant oil. But it all depends on actual temperatures during the season.

Why winter?

  • When weather is consistently cool, there is less risk of the oil burning new foliage that emerges in spring, when the insects are still active.

  • We have the best chance of killing off insects that overwinter in trees and cause the most damage in spring and summer.

  • There are fewer beneficial insects to be concerned about harming during winter months.

  • Applications in winter mean you have less risk of having to use a stronger pesticide in spring if an infestation occurs later in spring. Prevention is key!

Because timing is everything when it comes to using dormant oil, call your arborist soon, before you get too wrapped up in the holidays. If you’ve had scale, whiteflies or other persistent pests in your trees and large shrubs, give us a call and schedule this important tree care.

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