Reduce Spring Tree Pests with Dormant Oil in Winter
January 9, 2019
There is one thing certain about Texas winters: They are consistently inconsistent! Temperature and weather quickly swing in different directions. Cold & icy one day, then sunny and 75 ℉ the next. Even though we think our low temps are harsh, they are actually relatively mild and ideal for many insects. Instead of dying off in winter, insects such as scale, aphids, whiteflies, mealybugs, and mites often easily overwinter during Texas winters. That means we need to treat for these insects using dormant oil before they become an issue in the spring.
What is Dormant Oil?
Dormant oil is a spray treatment used to control insects in your landscape - especially large shrubs and trees. It is made by refining petroleum oil until the impurities are removed. Dormant oil can also be made of plant extracts such as neem, cottonseed, or soybean oil. When made from plant extracts we call them horticultural oils. Both are used similarly to control the same types of insects.
How Does Dormant Oil Work?
Dormant oil essentially smothers the overwintering insects that are hiding in your landscape, when it comes in contact with them. Insects typically overwinter on the bark of your trees & shrubs – burrowing into cracks and crevices for protection. Many of the most destructive and difficult to control insects, such as scale, can be successfully treated with dormant or horticultural oils.
Is Dormant Oil Safe?
Because dormant or horticultural oils can be certified as organic products, are contact-only treatments (not systemic in the plant), and don’t have a big impact on surrounding wildlife, they can be a good treatment choice for Eco-conscious homeowners. They are non-toxic to humans, pets, and reptiles. If you have a pond in your backyard, we always cover them during application as dormant oil is toxic to fish.
What Pests Can I Treat?
Dormant and horticultural oils are particularly effective for tent caterpillars, mealybugs, and aphids. Dormant oils are commonly used on shrubs and trees such as hollies, ligustrum, live oak, crapemyrtle, and pecan - specifically to control scale and whitefly insects on these plants. As a bonus, dormant oil is also great at warding off many fungal diseases, such as black spot or powdery mildew.
When to Apply Dormant Oil
Timing is incredibly important when applying dormant oil. We suggest application from late December to early March – but the best application time is always temperature dependent. That might mean earlier applications some years, later applications other years.
Why Apply in Winter?
- Dormant oils should only be applied to plants when temperatures are mild (40-70 ℉) to avoid burning delicate foliage that emerges in spring.
- It’s less likely to harm beneficial insects with dormant oils when applied in the winter.
- It’s more effective to control certain stages of insects in the winter (young scale insects are only mobile certain times of year).
- It suppresses insect populations before they begin to reproduce in the spring.
As good timing is crucial to the success of dormant oil applications, call us as soon as possible to get on the schedule for treatment of your trees and shrubs.