Aphids

There are a number of different aphid species that attack landscape plants, including the green peach aphid (Myzus persicae), melon or cotton aphid (Aphis gossypii), foxglove aphid (Aulacorthum solani), chrysanthemum aphid (Macrosiphum rosae) and potato aphid (Macrosiphum euphorbiae).

Certain plant species and cultivars are more susceptible to aphids than others. And distribution varies depending on the plant species or cultivar.
 

BIOLOGY.
Aphids typically feed on new terminal growth and the undersides of leaves. Its color varies depending on the host plant and should not be used for identification.

Aphids cause direct plant injury by removing plant fluids with their piercing-sucking mouthparts. Feeding on new growth results in young leaves appearing distorted or curled (upward or downward). They may also cause plant stunting. Many aphids are also capable of transmitting viruses.

The pest produces a clear sticky liquid material referred to as honeydew, which serves as a growing medium for black sooty mold fungi. The presence of black sooty mold detracts or reduces the aesthetic quality of plants. High aphid populations may lead to the presence of white cast or molting skins that can also reduce plant aesthetics.

Aphids can be major insect pests of landscapes, particularly early in the season when new succulent growth is expanding.

CONTROL.
Controlling aphids involves implementing cultural, insecticidal and biological strategies; preferably using all three. Proper watering and fertilization practices can effectively minimize potential aphid problems.

Aphids are attracted to and feed on plants receiving excess amounts of nitrogen, so avoid overfertilizing. Aphid reproduction increases when they feed on plants that have been overfertilized.

Sanitation is an important means of avoiding aphid problems. Remove plant debris and old stock plants from landscapes or place into containers with tight-sealing lids because winged aphids may abandon desiccating plant material and migrate onto the main crop.

Weed removal eliminates potential sources of aphids since many broadleaf and grassy weed species commonly found in and around landscapes serve as a reservoir for aphids and can support large populations.

Aphids are susceptible to contact, translaminar and systemic insecticides. There are a number of insecticides that have both translaminar and systemic properties. Be sure to rotate insecticides with different modes of action in order to avoid resistant aphid populations from developing.

If biological controls are going to be used, it is important to identify the aphid species. Various parasitoids are specific to the aphid species they will attack.

Parasitoid or predator releases must be made before aphid populations are “high” and plant damage is evident. Biological control agents for aphids include the parasitoids, Aphidius colemani, A. matricariae and A. ervi; the predatory midge Aphidoletes aphidimyza; the green lacewings Chrysoperla carnea and C. rufilabris; the ladybird beetle Hippodamia convergens and the beneficial fungus Beauveria bassiana.
 

The author is a professor and extension specialist in ornamental entomology/integrated pest management at Kansas State University. He can be reached at rcloyd@ksu.edu.