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Identifying Aphids

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  • Blue alfalfa aphid
  • Cowpea aphid
  • Pea aphid
  • Spotted alfalfa aphid

Four aphids commonly cause damage in alfalfa hay. Cowpea aphid is the only black aphid in alfalfa and may occur whenever alfalfa is actively growing. Pea aphid and blue alfalfa aphid are similar looking, both green in color (except for the pink pea aphid biotype), and are a problem primarily in the spring. Spotted alfalfa aphid is a yellow, hot-weather aphid and is a problem only on a few cultivars. Aphids in alfalfa have many natural enemies. Also see the key to aphids common to alfalfa.

Names link to more information on identification and management.

Click on photos to enlarge


Blue alfalfa aphid
Blue alfalfa aphid
Identification tip: A large green aphid with long legs and antennae that closely resembles the pea aphid. The blue alfalfa aphid is more damaging to alfalfa.
Blue alfalfa aphid antennae
Blue alfalfa aphid antennae
Identification tip: Blue alfalfa aphid antennae are uniformly brown.
Cowpea aphid
Cowpea aphid adult (black) and nymphs (gray)
Identification tip: The cowpea adult is the only black aphid found infesting alfalfa; it is relatively small and shiny. Nymphs are slate gray; the appendages are whitish with blackish tips.

Pea aphid
Pea aphid
Identification tip: A large aphid with long legs and antennae. Most common form is green. Distinguished from blue aphid by antennae.

Antennae of the pea aphid
Pea aphid antennae
Identification tip: Antennae have narrow dark bands at the tip of each segment. (Those of the blue alfalfa aphid are uniformly brown.)

Pink pea aphid
Pink pea aphid
Identification tip: A pink biotype of the pea aphid is sometimes seen.
Adult spotted alfalfa aphid
Spotted alfalfa aphid
Identification tip: A small, pale-yellow or grayish aphid with four to six rows of spined black spots on its back.

Statewide IPM Program, Agriculture and Natural Resources, University of California
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