When liquid dish soaps were more basic without fragrances, lotions and anti-bacterial agents, they were safer to recommend as a spray control for insects on plants. These added products may cause sensitive plants to die back, become deformed or burn badly. New concentrated formulations of dish soaps make it even harder to give a general mixing ratio per gallon of water that will control pests and not burn plants.

Commercial companies such as Safers® have developed an insecticidal soap made from potassium salt of a fatty acid. This and other similar insecticidal soaps are more expensive than dish detergents, but they are safer to use on plants. Dilutions are clearly marked on the labels, thus decreasing the chance of burn potential.

In today’s world of new and improved, super grease-cutting soaps for washing dishes, it is recommended to use an insecticidal soap for spraying on plants. Saving money on a homemade soap mixture is certainly desirable, but with an awareness of the increased burn potential, homeowners may wish to think twice before reaching for the bottle of dish soap to control plant pests.

Additional Resources
http://okeechobee.ifas.ufl.edu/News%20columns/Clean%20Up%20Pests.htm

http://edis.ifas.ufl.edu/IG013

http://www.extension.iastate.edu/news/2007/nov/071601.htm