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I park my car under the canopy of a large bur oak
tree. For the past several weeks my car has been covered in a sticky
substance: honeydew. Aphids are sucking insects that feed on plants by
thrusting their long beaks into plant tissue and withdrawing sap from the
plant. Aphids excrete large amounts of sugary honeydew, leaving the plant
and everything it falls on — patio furniture, sidewalks, automobiles
— sticky.
Aphids — slow-moving, pear-shaped insects that
range from 1/16 to 1/8 inch long — may be green, black, brown, red,
pink, or another color, depending on the sap of the host plant. They have
long, thin legs, long antennae, and a pair of tubelike structures on the
end of the abdomen. Various sizes of wingless aphids may be found in dense
colonies on stems, the undersides of leaves, and flowers. Heavily infested leaves of plants may be distorted
— twisted or curled — or turn yellow as the aphids remove the
sap, and a fungus called sooty mold often grows on honeydew deposits,
blackening the stems and leaves. Most aphid attacks inflict only temporary aesthetic
damage. An established plant, growing vigorously, can usually tolerate a
small population of aphids; newly transplanted or otherwise stressed plants
are more vulnerable to damage. The life cycle of the aphid is complex. These tiny
insects are masters of reproduction. Females give birth to live young
without fertilization. The young nymphs start feeding immediately and
mature in seven to 10 days, after which they are ready to produce live
young of their own. Each female is capable of producing 40 to 60 offspring,
generally female. Several generations can result in a population explosion.
Early-season generations are generally wingless; later generations may have
wings. Winged aphids are able to migrate to new host plants. In the fall,
aphids switch from asexual reproduction to sexual. Gardeners have several options for dealing with
aphids. The first is to let nature take its course and encourage natural
predators such as lady beetles, lacewing, aphis lions, and parasitic wasps
to dispose of them. Late in the season, aphids can usually be controlled
effectively by such predators. You can also knock aphids off plants with a
steady, forceful stream of water. When a population becomes too large on a
new or stressed plant, consider spraying the foliage with insecticidal
soap, malathion, acephate, or imidacloprid, but be sure to check first for
natural predators that may already be taking care of the aphid population. Although the aphids are probably not stressing my oak
tree, I will not miss the chore of washing my car window each morning. For more information, go to the University of Illinois
Integrated Pest Management Web site’s page on aphids:
ipm.uiuc.edu/landturf/ insects/aphids/index.html.
Jennifer Fishburn is a horticulture educator with the
University of Illinois Extension Sangamon Menard Unit. Contact her at
www.extension.uiuc.edu/Sangamon.
This article appears in Aug 9-15, 2007.
