Soaps can be used to control a wide range of plant pests. Small, soft-bodied arthropods such as aphids, mealybugs, psyllids and spider mites are most susceptible to soap treatments. Insecticidal soaps are considered selective insecticides because of their minimal adverse effects on other organisms. Lady beetles, green lacewings, pollinating bees and most other beneficial insects are not susceptible to soap sprays. Predatory mites, often important in control of spider mites, are an exception--they are a beneficial group of organisms easily killed by soaps. Soaps and detergents act strictly as contact insecticides, with no residual effect. To be effective, sprays must be applied directly to the insects with thoroughly cover. Several insecticidal soaps are distributed for control of insects and mites and are available under a variety of trade names. The active ingredient of all products is potassium salt of fatty acids. Soaps are chemically similar to liquid hand soaps; however, there are many features of commercial insecticidal soap products that distinguish them from the dishwashing liquids or soaps that are sometimes substituted. Commercial insecticidal soaps have a manufactured consistency designed to control insects and minimize potential plant injury. Dry dish soaps and all clothes-washing detergents are too harsh to be used on plants. But some household hand soaps and liquid dishwashing detergents can be used as insecticides; however, there is increased risk of plant injury with these products. Certain plants are more sensitive to these sprays and may suffer permanent damage; for example, most commercial insecticidal soaps list plants such as hawthorn, sweet pea, cherries and plum as being sensitive to soaps. Portulaca and certain tomato varieties also can be damaged by insecticidal soaps. The risk of plant damage is greater with homemade preparations; identifying safe and effective combinations for insect control requires experimentation. When in doubt, test soap-detergent sprays for phytotoxicity (plant damage) problems on a small area a day or two before an extensive area is treated. Regardless of what product is used, soap-detergent sprays are always applied diluted with water, typically at a concentration of around two to three percent. Plant injury can be reduced by using sprays that are diluted more than the two to three percent suggested on label instructions. To reduce leaf injury, wash plants within a couple of hours after the application. Limiting the number of soap applications can also reduce problems, as leaf damage can accumulate with repeated exposure; however, because of their short residual action, repeat applications may be needed at relatively short intervals (four to seven days) to control certain pests, such as spider mites and scale crawlers. Because application must be thorough and completely wet the pests, this usually means spraying undersides of leaves and other protected sites. Insects that cannot be completely submerged, such as aphids within curled leaves, will not be controlled with insecticidal soaps. Environmental factors also can affect use of soaps. In particular, soaps (but not synthetic detergents) are affected by the presence of minerals found in hard water, which results in chemical changes producing insoluble soaps (soap scum). Control decreases if hard-water sources are used. Insecticidal soaps may also be more effective if drying is not overly rapid, such as early or late in the day. Soaps and detergents can offer a relatively safe and easy means to control many insect pests. As with all pesticides, however, there are limitations and hazards associated with their use. Understand these limitations, and carefully follow all label instructions. For more information see the fact sheet, Insect Control Soaps and Detergents.

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