HORTICULTURAL OILS - For a long time refined petroleum oils have been used to manage many plant insect pests.  The oil smothers the insects by plugging the holes though which they breathe, which are spiracles.  The oil may also be toxic to some insects.  There are usually two names used to describe the oil products used in pest management: dormant oil or horticulture oil.  Mixed in a 1 to 3 percent solution, these oils should be sprayed onto the infested plant parts. There is a chance of damaging plants if the oils are used improperly.  Oils can essentially "burn" the leaves of a plant if the solution is to strong, applied in the wrong weather conditions, or when the plant is in a tender stage of growth.  Some plants are especially sensitive to horticultural oils.  Read all labels on the product that you plan to use and make sure you spray the appropriate plants at the correct time. Most commonly oils are used as dormant sprays to control insects that spend the winter on trees and shrubs.  During the growing season, there are refined oils that are effective for controlling whiteflies, young scales, mites and many other familiar plant pests. The one very important point about horticultural oils is that they are quite safe for humans and wildlife.  Beneficial insects are not greatly affected by oil sprays, especially dormant oils.  Dormant oils are applied when most beneficial insects are not present in the garden.  Oils are like soaps in that they act through contactaction and have no residual effects.  These facts make it essential to get thorough coverage when applying an oil to plant needing protection.