Aphids

Aphids are small insects, 0.04 to 0.2 inches (1–5 mm) long that come in a variety of colors. The two most common species encountered on beans are the cowpea aphid and the bean aphid.

• The adult cowpea aphid has a shiny black body with whitish legs and antennae ending in black tips, while the younger cowpea aphid nymph is a lighter gray.
• The bean aphid is slightly larger and less shiny than the cowpea aphid. The adult bean aphid is dark purplish-black with light-colored legs, while the younger bean aphid nymph has a slightly reddish tint.
• The pea aphid is a relatively large (4 mm), green, long-legged aphid.
• The green peach aphid is dark green to yellow and lacks a waxy covering.

Refer to the photo identification key, Key to the common aphids of cowpeas in California (PDF) for more detailed information.

Ways that aphids damage plants:

• Suck plant sap which stunts plants and causes heavily infested leaves to curl
• Excrete honeydew, a sugary substance that causes sticky, shiny leaves and black sooty mold growth
• Spread plant diseases (a large number of viruses are vectored by aphids)
• Inject toxins which can stunt plants

Infestations are frequently localized with heavily infested leaves curled downward.

Assess levels of biological control when evaluating aphid numbers. Frequently, natural enemies prevent aphid infestations from becoming established throughout a field. Temperatures greater than 85°F can slow down increase of pea and green peach aphid numbers.

(View photos to identify natural enemies of aphids)

Common predators of aphids in beans include lady beetles, syrphid flies, and lacewings. Parasitic wasps also attack aphids, turning them into hard, aphid-shaped shells called mummies. Plant field edge habitat that attracts natural enemies and avoid the use of broad-spectrum pesticides known to harm natural enemies.

Planting hedgerows of native California flowering shrubs along field crop edges will enhance natural enemy activity, helping to manage this pest. For more information about planting hedgerows, see Establishing Hedgerows on Farms in California, (PDF) UC ANR publication 8390. Organically approved pesticides are not likely to provide economically viable levels of pest control in dry bean production.

Aphid control in beans is not always necessary. The decision to apply an insecticide for aphids is based mainly on visual inspection and the stage of crop development. Measurable thresholds are not available. Begin inspecting for aphid problems when the crop emerges. Continue monitoring through the vegetative growth and flower bud to bloom stages. Apply an insecticide to seedling plants if they appear to be stressed by aphid populations. Older plants can tolerate low to moderate numbers of aphids.

• Photos of natural enemies of aphids