University of Illinois Extension

University of Illinois Extension

Hort Answers

Insect Damage


Aphids on spirea. P.Nixon
Aphids on spirea. P.Nixon
3 (1 = rare 5 = annual)
2 (1 = very little damage 5 = plants killed)
Many types of annuals and perennials especially various ornamental milkweeds (Asclepias spp.). On Asclepias, aphids commonly become heavy enough to cause wilting and distorted growth.

Plants Affected





Aphids have peircing sucking mouth parts. On tender shoots and leaves, the feeding can cause the shoots and leaves to become distorted and leaves may pucker. The aphids suck sap from the plants. As the sap moves through the insect, the aphid removes any necessary nutrients. The concentrated sap is passed as honeydew (insect fecal matter). A fungus called sooty mold will grow on this honeydew any place the honeydew becomes thick enough. The sooty mold turns things black and reduces photosynthesis.

Life Cycle
Aphids over-winter as eggs. The eggs hatch in spring. All newly emerging aphids are females who give birth to live young when they mature in a few days. These aphids in turn give birth to live young. When the aphid population becomes over crowded, the aphids wll give birth to live young who have wings. The winged aphids then fly to another part of the plant or to another plant where they give birth to live young. Lengthening nights and falling temperatures will stimulate the females to start giving birth to live males and egg laying females. The males mate with egg laying females only.

There are numerous insect predators such as lady beetles, lacewings, and syrphid flies, as well as parasitic wasps. There are diseases that kill aphids. Plain water from a hose can be used to wash aphids off the plants. In addition, organic and chemical insecticides can be used to kill aphids. Read and follow all directions and precautions on the label when using any pesticide.

Related Resources
Home, Yard & Garden Pest Guide
Illinois Commercial Landscape and Turfgrass Pest Management Handbook
U of IL - Distance Diagnosis through Digital Imaging
U of IL - Plant Clinic