Using Horticulture Oil for Insect Control
Horticulture oils have been used to control pests for more than 100 years. Oils target both the egg and adults of aphids, mites, twig borers, pear psylla, scale insects, cutworms & leaf rollers before they can cause problems. Before the development of current oil refining techniques, oils were heavier and caused burning or damage to leaves. These phytotoxic effects limited the use of oil to the dormant season, hence the term ‘dormant oil’. Oil products currently available are lighter grade, more highly refined, and can be used during both the growing season and dormant season without causing damage to most plants. These days, the term dormant oil now refers to the timing of application instead of the product.
Horticulture oils that are sprayed during a tree’s dormancy period are targeting insects that are overwintering on the tree. The ideal time to apply a dormant spray is in early spring, when the flower buds begin to swell, but before the tree blooms. At this time overwintering insects are coming out of dormancy, and are susceptible to suffocation by the oil treatments. The oil must come in contact with the pest in order to be effective, making thorough coverage essential for control of overwintering eggs & adult insects. It’s extremely important to avoid application of oil if a heavy freeze is forecasted. The oil needs at least 12 hours to dry before temperatures drop below freezing in order to avoid damage to the tree. Applying between 50-70 degrees F on a clear day is ideal.
Horticulture oils can be combined with insecticides, but for most backyard fruit growers the oil alone is sufficient. If you were plagued by aphids, scale, or any of the other insects listed above last season a dormant spray this spring may be very beneficial. Dormant sprays are not required every year. If last year’s damage was slight or non-existent, you can skip the dormant spray this year. Horticulture oils can also be used on many other garden & landscape plants, throughout the growing season. If you have questions please call the USU, Iron County Extension office.
Horticulture/Water-Wise Landscape Educator
USU Extension/Central Iron County Water Conservancy District