As a follow-up to the article in issue no. 18 on insecticidal soaps, examples demonstrating the effectiveness of various dishwashing liquids and detergents on insect and mite pests are provided here:
- Palmolive, Dawn, Joy, Ivory, and Dove effectively reduced the numbers of sweet potato whitefly (Bemisia tabaci), green peach aphid (Myzus persicae), cabbage aphid (Brevicoryne brassicae), and twospotted spider mite (Tetranychus urticae) on a variety of vegetable crops.
- Dawn Ultra dishwashing liquid was found to be effective on German cockroach (Blattella germanica), causing 100% mortality.
- Ivory liquid dishwashing soap tested at 0.4 to 3.0% concentrations was effective in controlling spider mites, aphids, and psyllids.
- Ivory liquid dishwashing soap was effective against aphids, spider mites, psyllids, and thrips at 1 and 2% concentrations.
- New Day dishwashing detergent, when used at 2.0 ml/L, was highly active on whiteflies, providing 95% mortality of silverleaf whitefly (Bemisia argentifolii) nymphs.
- Aqueous solutions (0.1 to 2.0% concentrations) of two “soft” soaps caused nearly 100% mortality on two household insect pests: cricket and cockroach.
- Ivory liquid dishwashing soap and Tide detergent were effective in reducing populations of aphids, citrus red mite (Panonychus citri), psyllids, and greenhouse thrips (Heliothrips haemorrhoidalis) on landscape plants.
Soaps may be combined with fish, whale, vegetable, coconut, corn, linseed, or soybean oil. For example, “Green Soap” is a potassium/coconut oil soap that was used widely as a liquid hand soap in public restrooms. It is now available as a hand soap or shampoo and has been shown to be effective, as an unlabeled insecticide, in controlling soft-bodied insects.
Despite these examples, however, dishwashing liquids and laundry detergents are primarily designed to dissolve grease from dishes and clean clothes, not to kill insects. These materials may cause plant injury by dissolving the waxy cuticle on the leaf surfaces. They should not be used for insect control. Registered, commercially available insecticidal soaps are less likely to dissolve plant waxes than are household cleaning products.