Aphids

Aphid nymphs and adults suck sap from plants by inserting their needle-like stylets into the plants. Curled, yellow leaves are often left behind, along with a sticky substance and the possible development of black sooty mold. Flowering and yields may be reduced.
Insecticidal soap available at garden centers kills the bugs by clogging their breathing holes. According to Oregon State University Extension Service, you can get similar results by mixing 1 teaspoon of vegetable oil, 1 teaspoon of dishwashing liquid, and 1 cup of water. Another option is to make a 1 percent soap solution by mixing 3 tablespoons of dishwashing liquid with a gallon of water. Spray thoroughly on plants, including the undersides. After a few hours, wash the solution off with a garden hose.