Cedar oil is sometimes effective for pest control, depending on the garden and the type of pests. Cedar oil works by permeating pest insects and affecting their pheromones. Some gardeners claim it works, and some claim it does not.
Pest insects use pheromones to find food and mates. When cedar oil disrupts this process it causes the pest insects to die relatively quickly, as they are unable to eat or procreate. Beneficial insects are generally not driven by pheromones for their activities, and thus are unaffected by the cedar oil. Cedar oil is applied in either a liquid or gas form, and both are lethal to pest insects if they come in contact with the oil for even a brief period of time.
The United States Environmental Protection Agency recognizes cedar oil as a low-risk pesticide. The oil's pungent odor keeps insects at bay, and people have used cedar in many different forms, such as wood and sawdust, to keep insects away for many years. Some claim cedar oil reduces the number of aphids, thrips and scales in a given garden and also works against cucumber beetles; however, regular application is necessary for cedar oil to work properly. Cedar oil derives from a few kinds of juniper and cypress trees. The red cedar tree is its most common source.