Modern monoculture planting has created situations where insect infestations can grow to unnatural population numbers. When natural controls break down and a population explodes, the pests self-destruct by eating themselves out of their (and our) food supply. Safe remedies for large problems, therefore, are very attractive.
Essential oils are a natural way to organically treat a variety of insect infestations. For centuries, they have been used safely because they work by utilizing natural metabolic pathways to either discourage or eradicate pests on crops. Historically growers have used companion planting—placing plants with natural repellent properties, such as garlic and marigolds, between crops susceptible to particular types of pests.
Due to their relative safety, essential oils can be used to control preharvest and postharvest insects without increasing the risk of toxic exposure for downstream customers of a grower. With only a few exceptions, these oils have low animal toxicity and last only briefly in the environment because of their chemical construction (they were created in a plant, not a beaker in a laboratory).
Most essential oils are safe to use on ornamental plants, but only some are safe and legally allowed on food and ingestible herb crops. For example, essential oils from geraniums, lemongrass and citronella are noted for their repellent action on mosquitoes and other biting insects; however, these oils are not allowed for food crops according to the EPA rules. Still, essential oils are general safer than using the typical diluted neurotoxins in chemical insecticide products.
The United States have more approved essential oils than any other country, but there are some restrictions regarding their use. Therefore, checking labels is important to know when and where to use them and how to advise customers. The FIFRA (25b) compliance list is an easy way to determine use. Below is the list showing those oils that can and cannot be used on food and ingestible herb crops—only those essential oils that have an astrix (*) after their name can legally be used use on food and herb crops.
Active Ingredients Exempted Under 25(b) of the Federal Insecticide, Fungicide, & Rodenticide Act:
(*) indicates exempt active ingredients that are also exempt from pesticide residue tolerance requirements
- Castor oil (U.S.P. or equivalent)*Linseed oil
- Cedar oilMalic acid
- Cinnamon and cinnamon oil*Mint and mint oil
- Citric acid*Peppermint and peppermint oil*
- Citronella and Citronella oil2-phenethyl propionate
- Cloves and clove oil*Potassium sorbate*
- Corn gluten meal*Putrescent whole egg solids
- Corn oil*Rosemary and rosemary oil*
- Cottonseed oil*Sesame (includes ground sesame plant) and sesame oil*
- Dried BloodSodium chloride (common salt) *
- EugenolSodium lauryl sulfate
- Garlic and garlic oil*Soybean oil
- Geraniol*Thyme and thyme oil*
- Geranium oilWhite pepper
- Lauryl sulfateZinc metal strips (consisting solely of zinc metal and impurities)
- Lemongrass oil
The FDA and EPA state inspectors closely watch products and their claims based on their labeled ingredients and have in-store spot checks to determine if these restricted oils are being promoted on food and ingestible herbs.
Using the list above, a store owner can safely advise customers what essential-oil-based products to use and on what type of plant. With this is mind, it is probably a good idea to have a closer look at the active ingredients of the miticides on your store shelves to double check their ingredients against the manufacturer’s claims.