Dormant Oil Spray

During the dreary winter days, plants go dormant. In February and March, your plants may still be hibernating, but Senske’s expert technicians aren’t! This is the ideal time to spray dormant oil for healthy trees the rest of the year.

Dormant oil spray is recommended to control insects on everything from fruit trees to lilacs. The combination of horticulture oil and copper sulfate kills overwintering insects (such as scale and mites), insect eggs, and diseases on most all landscape plants.

When To Spray

This powerful combination spray is applied when plants are dormant, ideally just before buds begin to swell or break. It’s still beneficial to spray if buds of trees and shrubs have begun to open. Generally, sprays are scheduled in February and March when the temperature will remain at 32°F (0°C) or above long enough for the spray to dry.

What Plants Benefit from a Dormant Spray?

Dormant oil and copper sulfate works great when applied to fruit trees, roses, ornamental shrubs, flowering shrubs, evergreens such as Cedars, Junipers, and Euonymus, and trees like Hawthorn, Crab Apple, and Honey Locust. Don't use a dormant spray on Beech, Birch, Oak, Lynden, Sugar Maple, Japanese Maple, or Walnut.

Pests Fear Dormant Oil Sprays

Dormant oils are effective in controlling certain scales that overwinter as nymphs or adults such as cottony maple, oyster shell, lecanium, and obscure scale. Honeylocust mite, European red mite, and spider mite are controlled with dormant oil sprays, because they overwinter as exposed eggs on plants.

How Does it Work?

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 after leaves open up we switch to contact insecticides that offer longer control.

Proper Application is Critical

The benefits of dormant oil sprays are contingent upon proper applications. Rely on Senske’s expert knowledge and experience. Plants can be damaged if incorrect oil is used or sprayed at an improper rate during the growing season. Applied at an incorrect time, dormant oil sprays can burn leaf buds that have started to swell or show any sign of green. Dormant oil is applied when temperatures stay above freezing long enough for the spray to dry.

Accurate identification of the scale is important for proper control. In some cases, applications of summer oils after egg hatch might be required. Since oystershell and pine needle scale overwinter as eggs, which are generally stacked on top of each other, a dormant oil may not contact the bottom layer. Contact sprays are best used to control slow soft bodied insects.

Not just any oil sprayed when the plants are dormant will do. Senske only uses highly refined oils which spread uniformly on the bark of trees and shrubs to which it is applied and coat non-mobile, dormant insects on the tree smothering them to death. Unlike home remedies, commercial spray oils have an emulsifier added to allow the oil to mix with water.

A Senske expert will identify your trees and shrubs to make sure a dormant oil spray is appropriate. Some trees, such as Japanese maple and Blue Spruce should not be sprayed. The foliage (needles) of Colorado blue spruce can be discolored (change from blue to green) by dormant oil applications.