Sulfur acts by competing with oxygen in the blood stream. Horticultural Oils Various horticultural oils are also considered alternative chemicals. They were used before the pesticide revolution and some can be safely used around humans and pets. Examples of petroleum oils used for pest control on ornamental plants are summer oils , dormant oils and horticultural oils . Horticultural oils and summer oils are synonymous terms.
Confusion arises in unfortunate wording on the labels of many oils.
Some labels carry directions for winter or dormant applications first and in fairly large type, making the product appear to be a dormant oil when it is actually a horticultural oil that can be applied during the dormant season. Three factors distinguish summer oils from dormant oils. These factors determine the effects of the oil sprays on the plant to be treated. Oils have saturated and unsaturated hydrocarbons. Unsaturated hydrocarbons are more unstable than saturated hydrocarbons and, when sprayed onto plants, they tend to form substances toxic to plants.