Larry A. Sagers Regional Horticultural Specialist Utah State University Extension Service Thanksgiving Point Office © All Rights Reserved
What are some less toxic materials that I can use to control pests on my house plants?
Alcohol sprays or alcohol dabbed onto insects is a common recommendation for controlling mealybugs. However, using alcohol on some plants can cause leaf burn injuries. Carefully test a small area of the plant before you attempt to use alcohol as a pest control.
Insecticidal soaps containing potassium salts of fatty acids are commonly available houseplant insecticides. Use these as dilute sprays of one to three percent concentration to help control many houseplant insects and spider mites.
Although many liquid hand soaps and dishwashing detergents also have insecticidal effects, they are not registered pesticides and there is potential for plant injury with such products.
Horticultural oils are petroleum distillates or mineral oils that are diluted with water before application. Diluted sprays of oils are excellent insecticides for houseplant pests and can control scales, whiteflies and spider mites. These highly refined oils primarily act by smothering the pests. Neem insecticides are derived from seed extracts of the neem plant, a common tree in many tropical areas. Neem disrupts insect growth and controls whiteflies and other insects.
Pyrethrins and pyrethroid insecticides. Pyrethins are a common ingredient in many houseplant and garden insecticides. They are an organic product derived from flowers of (pyrethrum) daisy. Pyrethrins act quickly, have a very short persistence of a few hours, and low toxicity.
Several “synthetic pyrethrins,” known as pyrethroids, are also common. These synthetically manufactured insecticides are based on the chemistry of the natural pyrethrins.
Some pyrethroids, such as resmethrin and sumithrin, are fast acting with a short persistence like the natural products. Other pyrethroids, such as permethrin, cyfluthrin, and bifenthrin, may persist in active form on foliage for several days.
Pyrethroids may have differences in their ability to control houseplant pests, such as bifenthrin, which is much more effective than other pyrethroids against spider mites.
Systemic insecticides absorb through the roots into the plants. Those used on houseplants are sold as granules or as stakes that are applied to the soil for the roots to absorb.
Bacillus thuringiensis is a naturally occurring soil bacteria that has the ability to control many insects. It is a commonly used microbial insecticide. Different strains of this bacteria occur which may have different effects on insects. For example, the kurstaki strain is commonly sold to control caterpillars on vegetables and ornamental plants.
Another strain, “israelensis” or “H-14,” can control certain larvae of gnats, blackflies, and mosquitoes. It is sold under the trade names Gnatrol and Knock-Out Gnats to control fungus gnat larvae in houseplants.