Gardeners are not the only ones who enjoy fruit trees. Pests — such as scales, aphids and mites — feast on the tender plant parts and overwinter on the fruit trees. Dormant oils control these annoying pests and are safe for use on fruit trees.
Dormant oils once contained heavy oils that had to be applied when the fruit tree was in its dormant stage to prevent damage to buds and foliage. Nowadays newer dormant oils are lighter, allowing them to be applied at anytime during the year without harming buds. Because you can apply newer dormant oils throughout the season, the term “dormant” typically refers to the time at which the oil is applied. Dormant oil consists of refined petroleum oil that — when applied to trees — will smother overwintering insects — such as aphids, scales and mites — and their eggs or will dissolve their protective waxing coating. It is applied in the winter months when fruit trees are in their inactive period. For dormant oil to provide proper control, the oil must come in contact with the pests.
Dormant Oil Recipes
Several dormant oil recipes are available and help control pests on fruit trees. A dormant oil formula developed by scientists at Cornell University controls overwintering pests and foliar diseases. It contains 2 tablespoons of ultrafine canola oil and 1 tablespoon of baking soda mixed with a gallon of water. Cornell University scientists also developed a nourishing formula containing 2 tablespoons of horticultural oil, 1 tablespoon of baking soda, 1 tablespoon of kelp and 1 tablespoon of mild dish soap mixed with 1 gallon of water. Another dormant oil recipe contains 2 tablespoons of baking soda, 5 tablespoons of hydrogen peroxide, 2 tablespoons of castile soap — which is made from an olive oil base — and 1 gallon of water. If you are not one who likes to do DYI, you can buy it premade at the store.
No matter which recipe you use, the application for the homemade dormant oil is the same. During the fruit tree’s dormant stage — which is typically between November and early spring before bud break — fill a pump sprayer with the homemade dormant spray and thoroughly coat the fruit trees — stems and both sides of the leaves — with the oil. Never apply dormant oil when the temperature is below freezing or when fruit trees are stressed. Stressed trees are more likely to become damaged when treated with dormant oil. Furthermore, only apply the oil spray when the fruit tree is dry. Moisture or high levels of humidity lower the effectiveness of dormant oil sprays.
Dormant oils generally won’t harm beneficial insects since they are applied at a time when beneficial insects aren’t present on fruit trees and have a low toxicity level to humans and mammals. Furthermore, dormant oils won’t leave harsh residue behind. It loses its ability to control pests once dried, however, and can harm plants susceptible to oil sprays. Cedars, maples, spruce and junipers are a few susceptible tree species that dormant oil should not be used on.