Aphids are a hot topic of conversation at the AgriLife Extension Office this week! First, we spotted aphids in the vegetable garden! Then several homeowners called with questions about their crape myrtles with black limbs, which is usually caused by sooty mold that colonizes on aphid “honeydew.” Aphids are on the move and they are an interesting pest!
Aphids are small, soft-bodied insects that range from 1/16 to 1/8 inch. They vary in color from black, gray, red, orange, green, yellow, blue-green, or white, depending on the species and the plants they feed on. Most aphids don’t have wings, but there are some species that develop wings in response to environmental conditions. Aphids have long slender mouthparts that they use to pierce stems, leaves, and other tender plant parts and suck out fluids.
Reproduction of aphids happens very quickly. Many aphids can reproduce asexually, and adult females can give birth to live offspring, instead of laying eggs. Some species can give birth to as many as 12 live young each day. Other species mate and produce eggs in fall or winter, and the eggs overwinter on the foliage of perennial plants. Many aphid species can develop from a newborn nymph to mature, reproducing adult in seven to eight days. It’s no wonder that aphids can reproduce faster than any other insect!
Damage from aphids can be extensive. Low numbers of aphids are not usually a problem in a garden or on trees, but a large population of aphids will damage leaves and stunt shoots. Aphids also secrete a sticky substance called honeydew that falls on leaves, trunks, and anything below the plant. If you’ve ever stood underneath a pecan tree on a cloudless day and felt “rain” you probably received some honeydew. Honeydew can be a problem because a fungus called sooty mold (Capnodium spp.) colonizes on surfaces coated in honeydew. Sooty mold keeps sunlight from reaching the leaves of a plant, preventing photosynthesis. Sooty mold is the culprit behind the black limbs on crape myrtles.
The best way to manage aphids is to closely monitor your plants once or twice each week, especially in the spring and fall. Aphids can usually be found on the underside of leaves or on new growth. You can remove a lot of aphids with a strong stream of water from a water hose or by knocking them off. Lady beetles and lacewings are both good predators of aphids and provide some natural, biological control of aphids. Insecticidal soaps or oils are another effective control measure, and you can find many insecticides that are effective against aphids. If you spray insecticides in a fruit or vegetable garden, check the label to make sure the insecticide is approved for food crops.
