Dormant Oil Spraying
Dormant spraying combines Horticulture Oil to kill overwintering insects (such as scale and mites), insect eggs, and diseases on certain hardy landscape plants.
What Plants Benefit From A Dormant Oil Spray Application?
Dormant Oil are best applied to fruit trees, roses, ornamental shrubs like Highbush Cranberry and European Snowball, evergreens such as Cedars, Green Junipers, and Euonymus, and trees like Hawthorn, Crab Apple, and Honey Locust, Spruce ans Magnolia.
Do not use a dormant spray on Beech, Butternut, Colorado Blue Spruce, Hickory, Holly , Sugar Maple, Japanese Maple, or Walnut.
When To Spray
Spray so the plant will be completely dry by evening. The spray should be frost free for at least six hours.
What I Dormant Oil
This time of year we see the recommendation to spray dormant oil to control insects on everything from fruit trees to lilacs. But is it just any oil sprayed when the plants are dormant? Most commercial dormant oil sprays are refined from petroleum oil. A few are made from cottonseed oil. Unlike home remedies, commercial spray oils have an emulsifier added to allow the oil to mix with water. Many of the newer commercial oils are more highly refined than past dormant oil products. The new formulations are labeled to also be used, usually at a reduced rate, during the growing season. These are generally listed as horticultural, ultrafine or summer oils. Read and follow all label directions for proper timing and rates.
Oils kill exposed insects and mites by either suffocating them (covering up breathing tubes) or by directly penetrating the outside cuticle and destroying internal cells. Spraying trees with dormant oil after bud break and leaves have emerged will still control the pests, but it may kill the young leaves or cause leaf edges to turn black if the correct oil is not used at the proper rate.
The benefits of making an application of dormant oil. Advantages include: (1) a wide range of activity against most species of mites and scales, including some activity on eggs; (2) minimal likelihood of insects' or mites' developing resistance; (3) generally less harmful to beneficial insects and mites than other pesticides (4) relatively safe to birds, humans, and other mammals. Disadvantages of using dormant oil are (1) potential plant damage if incorrect oil is used or used at improper rate during the growing season and (2) minimal residual activity to kill new pest infestations.
Dormant oils are effective in controlling certain scales that overwinter as nymphs or adults such as cottony maple, euonymus, lecanium, and obscure scale. However, dormant oils provide minimal control of oystershell and pine needle scale because both these scales overwinter as eggs. In addition, eggs are generally stacked on top of each other, and the dormant oil may not contact the bottom layer. As a result, applications of summer oils after egg hatch are generally required. Accurate identification of the scale is important for proper control.
Honeylocust mite, European red mite, and spruce spider mite are controlled with dormant oil sprays, because they overwinter as exposed eggs on plants.
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