When aphids, spider mites, whiteflies and other destructive pests find your tomato and pepper plants to be a tasty meal, you'll want to get rid of them as soon as possible. A variety of pesticides made of toxic chemicals are available, but you can make a homemade pesticide for tomato and pepper plants from safe items in your home that won't harm your growing produce.
Place 1 quart warm water, 1 Tbsp. cayenne pepper and 1 Tbsp. mild liquid detergent in a bowl. Chop the six cloves of garlic and the small onion into small pieces and add to the water in the bowl.
Use a plastic spoon to stir your solution together well without bubbling up the dish liquid. Stir the mixture occasionally, every four to five hours, over the course of a day and let it sit overnight.
Strain the mix through a mesh strainer into another bowl. Set a funnel over the opening of the spray bottle and pour the liquid portion of the mix into the spray bottle.
Spray the undersides and tops of leaves, as well as the stems and anywhere you have seen pests gathering on the tomato and pepper plants. Avoid spraying the actual tomato and pepper fruits themselves. For the most impact, spray the solution in the morning when no rain is expected so the solution is on the plant for as long as possible.
Repeat applications with this solution as often as needed to control infestation and keep your plants healthy.