Friday, May 30, 2008

Soaps Used as Insecticides

Photograph courtesy of Judy Sedbrook.

Information provided by Whitney Cranshaw, Colorado State University Cooperative Extension specialist, entomology

Soaps have long been used for control of insects and mites. Several "insecticidal" soaps are sold at nurseries and through garden catalogs. These soaps control a variety of garden pests. In addition, some soft hand soaps and liquid dish washing detergents can kill insects. In general, soaps tend to kill small, soft-bodied insects and mites, such as aphids, newly hatched scales (crawlers) and plant bugs.

Insecticidal soaps are used as dilute sprays, typically at a 2 percent dilution -- or about 2 teaspoons per pint. Their advantages are a high degree of safety to the applicator and other "non-target" species, minimal adverse effects to beneficial insects and ease of use. Soaps also have some limitations:

Plants must be covered thoroughly because soaps are effective only if they make contact with the insect.

The treatment doesn't last long. If the insects aren't killed at or soon after application, they'll still be a problem.

Some kinds of plants are injured by soap. If you're using insecticidal soap, check the label for a list of plants that won't tolerate this application.

Soaps work best when applied in soft (or softened) water, preferably during cooler periods when drying is slowed.