The Norman Transcript

July 19, 2013

Aphids are prevalent on Crapemyrtles

The Norman Transcript

NORMAN — Do you have plants that appear shiny or oily or have ants crawling all over them? Aphids could be your problem. I’ve seen aphids in abundance on Crapemyrtles this summer, but they may attack other plants as well.

Aphids are soft-bodied, slow-moving insects that reproduce rapidly. They also are called “plant lice” for their ability to cover a leaf or stem surface. Aphids are most commonly green or yellow, but they can be brown, red or black. They have piercing, sucking mouthparts and feed by sucking sap from plant tissues.

Aphids may be winged or wingless, although wingless forms are most common in Oklahoma. A typical aphid species may produce several wingless generations in the spring, followed by a generation of winged forms.

The winged forms can fly to other plants where many more wingless generations can be produced. Because aphids don’t require males to have offspring, aphid populations can increase rapidly in a short period of time. During warm weather, some species can complete a generation in less than two weeks.

Many aphids prefer to feed on young, succulent growth. Some feed in sheltered locations, such as inside leaves they have caused to curl or become distorted. Aphids attack trees and shrubs of all kinds but do not usually cause serious injury.

Aphids and other plant sap-sucking insects excrete large amounts of honeydew, a sticky substance often seen on leaves, pavement, automobiles and other surfaces below the infested foliage.

Honeydew consists mainly of excess sugars ingested by the insects and passed through the body. Ants are attracted to the sugary honeydew and occasionally tend the aphids like people tend cattle. Some ants even carry the aphids to new plant parts to establish more colonies.

A black fungus called sooty mold will sometimes grow on the honeydew deposited on foliage. It may look as though the leaves have been dipped in fireplace ashes. This fungus can detract from the plant’s appearance and reduce the amount of light reaching the leaves, thus reducing photosynthesis. Sooty mold is a purely cosmetic problem.

Aphids can infest most plants, generally at non-injurious levels. The excreted honeydew may be the first noticeable sign you have aphids. These insects are often controlled by natural forces, such as driving rains and low or high temperatures.

In addition, natural predators may keep the population in check shortly after the aphids are noticed. These beneficial insects include ladybird beetles, lacewings, syrphid flies and parasitic wasps.

Residents should search the aphid colonies for these natural enemies. High numbers of these beneficial insects usually indicate that aphid problems are being controlled without intervention.

Do not apply traditional chemical insecticides on plants to control aphids, since these also will kill off the beneficial insects and the aphid population will come back with a vengeance.

Insecticidal soap is an organic control that may be used in extreme cases, but this kills any insect it contacts, good or bad. The best option to remove the insects is to wash the plant with a firm stream of water.

Tracey Payton Miller is Cleveland County’s horticulture extension educator for the Oklahoma Cooperative Extension.