A mixture that contains no more than 1 to 2 percent mild dish washing detergent or hand soap will generally control whiteflies and other pests sufficiently. Blend the liquid soap and water together at a rate of 2 to 5 tablespoons of soap per 1 gallon of water, instructs Clemson Cooperative Extension.

Can soapy water kill whiteflies?

A simple solution made from liquid dish soap and water will kill adult whiteflies without harming plants. Add 1 tablespoon of liquid dish soap to 1 gallon of water and mix well. Pour the solution into a plastic spray bottle and spray it on all infested plants, saturating the leaves' upper and undersides and the stems.

Is washing up liquid harmful to plants?

If they use liquid hand soap, the fatty acid salts are made from short chain fatty acids which are phytotoxic to plants – they damage plants. You can't make insecticidal soap using things you find around the house.