Using soap and water on plants for pest control is an age-old remedy that's been passed down through generations. According to the Online Information Service for Non-Chemical Pest Management in the Tropics (OISAT), many soaps contain fatty acids and salts that act as selective pesticides. Using a simple solution of dishwashing detergent and water, you can reduce or eliminate many common pests from your garden including ants, aphids, fruit flies, spider mites, whiteflies, rust, powdery mildew and more.
Harvest any mature fruits or vegetables from your plants before spraying.
Start with a small amount of soap to see how your plants respond, then increase if needed. Mix 1 tablespoon mild liquid dishwashing soap such as Dawn or Palmolive with 1 gallon of water.
Put the mixture into a spray bottle or fertilizer spreader attachment on your garden hose.
Spray plants fully in the early morning or late afternoon. Be sure to spray both the top and bottom of the leaves.