This is an old fact sheet from Stephen Brown, our Lee County FL extension horticulture agent.
Topic: Making insecticidal soap
Question: Would you please tell me what horticultural oil is and when it can be applied? Also insecticidal soap, how does this differ from Joy or Dove dish soap? Are these items I can make in my home? - Glen, email
Answer: Horticultural oils are “soft” insecticides derived either from petroleum or plant oils. The oils are used to control sucking pests such as aphids, mites, scales and whiteflies. These oils destroy insects and insect-like pests by suffocation. Insecticidal soaps target many of the same pests by disrupting their cell membranes. Commercial Insecticidal soaps are available at most garden centers. You can also make your own insecticidal soap by using 2.5 tablespoons of dishwashing liquid and 2.5 tablespoons of vegetable oil per gallon of warm water. Do not use dishwashing liquids containing a degreaser or an automatic dishwashing soap or detergent. Dawn and Lemon Joy seem to be the liquid dishwashing soaps of choice. Make only what is needed in a day’s treatment. Both Insecticidal oils and soaps are generally nontoxic to many organisms, including humans. Their limitations are that thorough and repeated cover-age of the affected plants are required. They can be used at any time of the year.
However, don’t spray either oils or soaps if temperature is 90°F or above as this could cause leaf burn.
