Various types of oils have been used for many centuries to control hard-to-kill insects like aphids, scale and spidermites on fruit trees, providing good control of these insects with little risk to the plant, beneficial insects or the applicator. Oils kill insects in several ways, most importantly by blocking the air holes through which the insects breathe, causing them to suffocate. Oils may also acts as poisons by interfering with insect metabolism or disrupt insect feeding. They are also effective against powdery mildew and some aphid-transmitted viruses. In fact, oils can easily be worked into an organic spray program for fruit trees as well as small fruit plants, vegetables, flowers, tree and shrubs.

Before the development of current oil refining techniques, oils were used primarily on fruit trees during the dormant season, before the spring bud break. The application was timed to kill insects overwintering on the trees but also to avoid burning or damaging the leaves, which frequently happened with heavier, less highly refined oils. These oil products could not be used on plants during the growing season due to their phytotoxic effects. For this reason, the term 'dormant oil' was coined. Oil products currently available are more highly refined and the leaf damaging components including sulfur have been largely removed. Products like Sunspray® , Volck® and superior oil can be used both in summer and during the dormant season. Summer foliage applications of horticultural or 'summer oils' can control such insects as aphids, leafhoppers, whiteflies, scale and spidermites.

To get the best results from a horticultural oil application, follow these precautions. First, read and follow all label directions, paying particular attention to which plants are listed on the label as sensitive to the product. Do not apply oils to sensitive plants or allow the product to drift onto them. Do not combine oil applications with sulfur or pesticides containing sulfur like Captan. Do not apply horticultural oil when temperatures are above 100 degrees or below freezing. Do not apply oils to quickly expanding shoots in spring. Finally, allow plants to harden off well in fall before making dormant oil applications; this avoids increased susceptibility to winterkill.