Dormant Oil Spray

Here we are with another thing to do in the garden! Who said there is nothing garden-wise to do during the winter months? It is nearing the time for dormant oil spray, which is also known as horticultural oil, superior oil and natural oil depending on the formulation and brand. Those plants especially in need of dormant oil spray include fruit trees and vines, and deciduous trees and shrubs – especially those prone to certain insect issues.

Dormant oil is considered an ecologically friendly way to manage garden insect pests and consequently, some diseases. Many available oil products are made from mineral oil, but there are others made from vegetable oils such as cottonseed, canola, or soybean. These oils are usually mixed with some kind of emulsifying agent, which allows it to be mixed with water and used as a spray.

Dormant oil, used at a time when the plants are dormant or resting, is a good way to reduce pest numbers during a season where pollinators are not present. Insect pests such as aphids, mites, scales, leafhoppers, mealybugs, thrips, whiteflies, caterpillar eggs, and others tend to overwinter in the various cracks and crevices of the plant’s trunk and branches. Dormant oils work by suffocating the pests by blocking the spiracles through which the insects breathe. The oils can also disrupt the metabolism of insect eggs and the ability of some insects to feed. Many insects such as aphids vector diseases, so by controlling the aphids, some diseases may also be controlled.

Dormant oils should be applied just before the leaf and/or flower buds show signs of swelling or breaking open. You don’t want to spray too early or the insects won’t be active and breathing.

Dormant oils should not be applied in freezing temperatures or when the temperature is over 100 degrees F. During freezing temperatures, the oils don’t hold together well and coverage becomes uneven. If the plants are drought-stressed, they can be more susceptible to damage from the oil. The oils should also not be sprayed on windy days or when it is raining. Some lighter versions of these oils can be used in the summer months, but extra care needs to be taken to not burn the foliage. Some species of plants, including redbud, smoketree and spruce, are sensitive to dormant oils and are usually listed on the product’s label.

Dormant oils are fairly safe and are not poisons, but are still considered pesticides and should always be used according to the label’s instructions. Use only when absolutely necessary as it can kill both good bugs and bad bugs. It is considered safe around humans and pets because it has no toxic residue.