Aphids are found throughout the United States. These small, soft-bodied insects may be pale green, pink, black, or yellow, depending on the species. Some stages of the life cycle are winged, others wingless. Aphids feed on a wide variety of plants, including most edible and ornamental plants. Clustering on tips of new growth and leaf undersides, they suck plant juices causing leaves to become distorted and yellow.
Aphids secrete a sugary fluid called honeydew that attracts ants and may cause the growth of a sooty black fungus on leaves. In small numbers aphids do little damage, but they reproduce rapidly. They can also spread diseases among plants.
Start by rinsing plants with a strong spray of water to reduce the population. If aphids return, spray with insecticidal soap or horticultural oil. When spraying, be sure to cover the undersides of leaves. A variety of natural insect parasites and predators also reduce aphid populations, which is the main reason to not be overly aggressive with sprays.
Photography by Whitney Cranshaw, Colorado State University, Bugwood.org