Aphids are small, plant-eating insects that often appear on the leaves, stems and trunks of vegetable plants, fruit trees and flowers. The bugs' tough outer shells make them difficult to kill. In the past, gardeners most frequently used chemical pesticides to control these insects. However, there are several organic pesticides for aphids that are inexpensive to make and simple to apply.
Soap spray is an all-purpose organic pesticide that kills aphids, white flies and spider mites. To make soap spray, combine 1 tsp. of liquid dish soap with 1 cup of vegetable oil. Pour the solution, along with 1 quart of water, into a spray bottle. Spritz the solution onto your plants' stems and leaves every 10 days to control aphids. Soap spray works best on vegetables like carrots, cucumbers and peppers. Test the solution on a single leaf at first to make sure it doesn't burn the plant.
Powerful garlic spray is acidic enough to kill aphids, as well as mosquitoes and onion flies. Pour 2 tbsp. of mineral oil into a non-porous container and add 3 to 4 oz. of chopped garlic. Cover the mixture and allow it to marinate for about 24 hours. Dissolve 1 tsp. of fish emulsion in 1 pint of water and add it to the garlic and mineral oil. Strain the solution to remove the chunks of garlic, then store the solution in a glass jar. To use the garlic spray, mix one part solution to 20 parts water in a spray bottle. Apply the spray to the plants about every two weeks. Garlic spray can be used on just about any plant, but be careful to avoid the edible portions.
Onion spray is the most mild of the organic pesticides for aphids. Peel and slice one large onion, and puree it in a blender or food processor with 1 tbsp. of water. Pour the puree into a bowl, cover it with 1 to 2 cups of warm water and allow it to soak overnight. Strain the puree from the mixture and pour it into a clean spray bottle. Apply the onion spray to roses, fruit trees and flowers as frequently as necessary.