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Horticultural oil is made from refined petroleum, which can be mixed with water for pest control application. The use of horticultural oils can be an effective alternative to conventional pesticides. They not only work just as well but are safe for the environment, humans, and most animals. Generally applied as a spray, this type of pest control works by suffocating insects and their eggs. Horticultural oils may also deter pests from laying eggs and protect plants from viral or fungal diseases.
While horticultural oil is considered safe to use, it can be toxic to fish and may adversely affect beneficial insects, like ladybugs and honeybees. Some plants do not tolerate these oil sprays either. For instance, plants with blue-colored foliage or wax-like coatings should not be sprayed with horticultural oil. Horticultural oils are most effective for treating aphids, whiteflies, spider mites, scale insects, and other soft-bodied pests.
Complete coverage of the foliage will increase its overall effectiveness. Proper timing is also crucial. The ideal time to apply this form of pest control is during cool, cloudy conditions, with no wind. Oil sprays should be avoided anytime the humidity is high as well. Although reapplication is usually necessary, there should be about a two-week interval between treatments.
While most plants are unaffected by horticultural oil sprays, some treated leaves may exhibit dark-colored lesions and eventually drop from the plant. There may also be some spotting on open flowers. There are two basic types of horticultural oil sprays: dormant oil and summer oil. Dormant oils are less refined than summer oils. As a result, they evaporate more slowly, remaining on plants for longer periods. This can increase the likelihood of damage.
Dormant oils should be applied in spring just prior to bud break, the time when plants begin blooming. Avoid using dormant sprays in the fall. Summer oils, also known as superior oils, are ultra-refined horticultural oils. They are easier to use and less likely to cause any damage to plants, as they evaporate quickly. Summer oil can be safely used anytime throughout the growing season.
Overall, horticultural oil spray is easy to use and relatively safe with proper application, especially when compared to chemical pesticides. In addition to timing and thorough application, it’s also important to read and follow the label instructions carefully. The oil should be mixed with water at the recommended rate for best results. By mixing baking soda with the horticultural oil solution, it can also be used as an effective fungicide.