Insecticidal soaps are a safe, effective and low toxic alternative to the more toxic pesticides used to control many undesirable insects in your garden.
Insecticidal soaps are inexpensive, leave no harsh residue, and among the safest pesticides, are natural products that are virtually non-toxic to animals and birds, and can be used on vegetables up to harvest. Most beneficial insects are not harmed by soap sprays.
Insecticidal soaps kill by suffocation, they disrupt the cellular membranes of the insects, and they remove the protective waxes that cover the insects, which results in dehydration. Insecticidal soaps will kill aphids, thrips, spider mites, mealybugs, and scale crawlers. Insecticidal soaps are also effective at removing honeydew, sooty mold, and other debris from leaves.
The insecticidal soaps are made from a potassium salt of a fatty acid from a plant or animal oil and a strong alkali. Insecticidal soaps are a highly refined version of a liquid dish soap. You could make your own insecticidal soap mixture, but there in a significantly increased risk of plant injury. All clothes-washing detergents and dry dish detergent are too harsh to use on plants because all the additives in them. Some detergents and soaps are poor insecticides, and other additives in the products maybe phytotoxic, meaning it will damage the plant.
Some plants are sensitive to soap sprays and may be seriously injured by them. Read the label to make sure you plant is not one of them. As with any pesticide, the label is the law.
Sensitive plants include: portulaca, hawthorn, sweet pea, cherries, plum, horse chestnut, mountain ash, Japanese maple, bleeding hart, maidenhair fern, crown of thorns, lantana, nasturtiums, gardenias, and Easter lilies. Conifers may be sensitive under drought conditions. Plants with a bluish color caused by a waxy leaf coat may lose their bluish color as the wax is washed away. Somewhat sensitive plants are azaleas, begonias, fuchsias, geraniums, and impatiens. Rinse the plant with clean water if they show signs of wilting or leaf edge brown within a few hours of treatment. To test for plant sensitivity, spray a small area and wait 24 hours to see if any damage occurs. Plants under water stress should not be sprayed.
It is important to read the label completely and follow all directions when applying to plants. Insecticidal soaps are applied at 1-2% solution meaning 2? to 5 tablespoons per gallon. Making a higher concentration can be very harmful for your plants. Do not apply the insecticidal soap above 90F or in full sun because this can damage the plants. High humidity and high temperatures can increase plant stress therefore sensitivity.
It is important to spray both the top and bottom of the leaves because under the leaves this is where the majority of pests are found. Insects must be in contact with the soap to be effective. Repeat applications may be necessary every 4 to 7 days until the pests are eliminated, just make sure to follow the label directions. Excessive applications may cause leaf damage.
The three disadvantages of insecticidal soaps are: the soap solution must wet the insect during application; there is no residual effectiveness because the soap dries or is washed away; and there is a potential for phytotoxicity when the soap residue is affected by high temperature.
Insecticidal soaps are sold as a concentrate or as a pre-mixed RTU (Ready to Use). The following products can be found where garden supplies are sold:
• Bonide Insecticidal Soap Concentrate; &RTU
• Espoma Earth-tone Insecticidal Soap Concentrate; & RTU
• Garden Safe Insecticidal Soap Insect Killer Concentrate; & RTU
• Miracle-Gro Natures’s Care Insecticidal Soap Insect Killer RTU
• Natural Guard Insecticidal Soap Concentrate; & RTU
• Safer Brand Insect Killing Soap Concentrate; & RTU
• Safer Brand Tomato & Vegetable Insect Killer RTU
• Whitney Farms Insecticidal Soap RTU
For more information on insecticidal soaps for garden pest control, please visit the Home and Garden Information Center website at hgic.clemson.edu. Tune in on Tuesday nights to watch “Making it Grow” at 7 p.m. on SCETV or mig.org. Email Outen at callenb@clemson.edu.
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