Horticultural oils, soaps and Bacillus thuringiensis (Bt) products may provide a more environmentally-friendly approach to landscape pest control. These materials are relatively nontoxic to the user, are relatively safe to beneficial insects and it is difficult for pests to develop resistance to oils and soaps.
Horticultural oils and soaps will control egg, immature and adult stages of soft-bodied pests such as aphids, thrips, whiteflies, mites and scales. Bt products are used to control caterpillars.
Horticultural oil is formulated with an emulsifier that allows it to be mixed with water. Oil-based products kill insects on contact by disrupting respiration, cell membrane function or structure.
Horticultural oils are classified as dormant oils, summer oils or superior oils. Dormant oils are the heaviest of the horticultural oils and are formulated for use on dormant plants. Apply these oils during dormancy but before plants begin spring growth. Do not use dormant oils during the growing season unless the label specifically states that such use is safe. Summer oils are lighter than dormant oils and are formulated for use during spring and summer. Superior oils are the most refined and can be used for pest control in any season. Superior oil products allow greater flexibility in their use and have been tested at temperatures in the mid 90s with no damage to shrubs.
Only a few of the many manufactured soaps are effective insecticides. Insecticidal soaps are made from potassium salt of oleic acid, which is present in high quantities in olive and other vegetable oils. The mode of action of insecticidal soaps is unclear. Soaps do disrupt an insect’s outer body covering (cuticle). Some evidence indicates that soaps enter the insect’s respiratory system and cause internal cell damage.
Horticultural oils are sold under various descriptive names such as “dormant oil,” “oil emulsion,” “safety-side,” “summer oil,” and “superfine oil.” There are several soaps available for purchase, such as Safers Insecticidal Soap and M-Pede.
Thorough spray coverage is essential when using oils and soaps. All plant surfaces, tops and bottom sides of leaves and stems must be coated with spray for best results.
Another environmentally friendly product for controlling caterpillars is Bt (Bacillus thuringiensis). Bt is a bacterium that paralyzes the digestive system of caterpillars. It’s best used when caterpillars are young. After ingesting a lethal dose, the caterpillar stops feeding and will die within several hours to days. Bt can be found under several brand names such as Dipel, Thuricide and Sok-Bt.
Though horticultural oils, soaps and Bt products are less toxic than many insecticides, it is important to use them with caution. Read and follow the label carefully.
Larry Williams, UF/IFAS Extension Agent, Okaloosa County, June 13, 2014