Aphids or plant lice are small, soft-bodied slow moving insects which feed by sucking juice from plants. They can usually be recognized by the pear-shaped body and fairly long antennae.
Aphids vary in color - white, gray, green, brown, red, yellow or black (Figure 1.) They are usually found in large numbers (colonies) on the underside of leaves or on stems (Figure 2.) There are both winged and wingless aphids in most species. As the aphids feed, they secrete honeydew - a sweet sticky shiny substance seen on leaves. Honeydew consists mainly of excess sap ingested by the insect and passed through the body.
Aphids may damage many plants including fruits, vegetables and ornamental trees and shrubs. The major damage is caused by the aphids sucking the juices from the stems and leaves causing a reduction in vigor, curling and distortion, and reduction in yield. Some species inject saliva into the plant tissue as they feed and may transmit virus diseases from one plant to another.
In addition to the direct damage caused to the plant by the aphids feeding a black fungus, known as sooty mold, grows on the honeydew secreted by the aphids. Sooty mold is unsightly and in association with honeydew it is objectionable to the buyer of affected plant material, fruits or vegetables.
Most species of aphids overwinter in the egg stage. The eggs hatch in the spring to produce a generation of females. These female aphids give birth to living young. Generally the first young aphids are wingless, however, when a colony becomes too crowded, winged forms may be produced. The winged forms migrate to new host plants and begin new colonies. Enormous populations are built up from these overlapping generations all summer long.
Late in the season the aphids migrate back to the original host plant, and a generation consisting of both males and females is produced. These individuals mate and the females lay eggs which will overwinter.
Carefully inspect plants for the beginning of an aphid population buildup. Check for natural enemies such as mummies (Figure 3.), which are gray-brown bloated parasitized aphids indicating wasp parasites at work, and the alligator-like larvae of lady beetles and lacewings.
Yellow sticky boards are also used as a monitoring tool for aphid populations. Aphids are attracted to the yellow color and often are visible on the cards before they are detected on the plant.
If there are high numbers of mummies, or large populations of ladybird beetles, or lacewings along with the aphids, additional treatments may not be necessary. Ladybird beetles and lacewings are beneficial because both the adults and larvae actively feed on aphids.
In general, controlling populations early in the season often eliminates the need for later spraying. In a few cases, however, treatment may need to be carried out all season long. Wash off aphids with water occasionally as needed early in the day. A hard stream of water directed at aphids will remove many from plants.
Before using any pesticide, check the label. Both the crops you wish to treat and the pest you are treating for must be listed on the label. If not, do use the pesticide. Also make sure to read the label to determine how long you need to wait before harvest. Harvesting treated vegetables too soon after a pesticide application may result in excessive residue being present when consumed.
For information on controlling aphids on ornamental trees and shrubs, annual and perennial flowers, houseplants, fruit crops, etc. refer to a current copy of Part I Guide to Pest Management Around the Home, Cultural Methods and Part II -- Pest Management Around the Home, Pesticide Guidelines, which are mentioned below.
Pesticide and management recommendations obtained from: Part I Guide to Pest Management Around the Home, Cultural Methods and Part II -- Pest Management Around the Home, 2005-2006 Pesticide Guidelines, Miscellaneous Bulletins 139S74-I and 139S74II, Cornell Cooperative Extension Publications.
This publication contains pesticide recommendations. Changes in pesticide regulations occur constantly and human errors are still possible. Some materials mentioned may no longer be available, and some uses may no longer be legal.