Pesticides Made with Essential Oils
Pesticides made with essential oils are derived from plants that are known to have insecticidal properties. It is important to remember that just because a pesticide is derived from a plant does not mean that it is safe for humans and other mammals or that it cannot kill a wide variety of other life. Many pesticides made with essential oils are formulated with synergists. These have no insecticidal effect of their own, but serve to enhance the insecticidal effect of the botanicals. Carefully read the labels on all products before use to make sure that they do not also contain toxic pesticides. Some botanical pesticides can be quite toxic to humans and should not be used. Neem oil, garlic oil, and sabadilla are some least-toxic botanical pesticides listed below. Others that can also be used as a last resort are citrus oils, mint oil, pine oil, pepper extracts, tree oils and herbal extracts.
Neem oil, extracted from the tropical neem tree, azadirachta indica, contains insecticidal properties that are composed of a complex mixture of biologically active compounds. It has a strong, unpleasant odor. Its various active ingredients act as repellents, feeding inhibitors, egg-laying deterrents, growth retardants, sterilants and direct toxins. Neem has both contact and systemic action in plants. The active ingredients biodegrade rapidly in sunlight and within a few weeks in the soil. Neem oil has very low toxicity to mammals. In India, neem products have been used in toothpaste, pharmaceuticals, and as a grain protectant for centuries without apparent harm to humans.
Garlic oil exhibits antibacterial, antifungal, amebicidal and insecticidal qualities. Although garlic oils kill pest insects and some pathogens, it also kills beneficial insects and microbes. Thus, it is not recommend as an all-purpose spray for outdoor use.
Sabadilla alkaloids, from the dried ripe seeds of a member of the lily family, Schoenoxaulon officinate, are often used as a broad spectrum low-persistence insecticide. Discovered by Native American peoples in northern South and Central America countries ago, it was used in wounds against vermin, and came to be used also by the Spanish invaders as a louse powder. The powdered seeds have been known to require aging to become fully active, but potency can be increased by heat treatment and extraction of the alkaloids into a solvent, like kerosene. The alkaloids are photoreactive or unstable in the presence of light. Reported acute toxicity of the crude dust to mammals is low, with an oral rat LD50=500 mg/kg, but the purified sabadilla alkaloids are known to be toxic to bees. Sabadilla dust is very irritating to the upper respiratory tract, causing sneezing, and is irritating to the skin. Poisoning symptoms include: retching, muscle spasms, and especially, slowed heart beat and decreased blood pressure, not unlike that seen with the drug digitalis. The symptoms are slow to disappear. A researcher noted in 1901 that repeated small doses showed possible cumulative effects.
Resource Center. 1987. "Update: Neem - A New Era in Pest Control Products?"
The IPM Practitioner 9(10). U.S. EPA. 1999. Recognition and Management
of Pesticide Poisonings. EPA 735-R-98-003. Office of Prevention, Pesticides,
and Toxic Substances. Washington, DC.