Major Alfalfa Insects

Alfalfa Weevil  (Hypera spp.)

  
Description – Adult approximately ¼ inch long; light brown in color with dark brown strips on back. Larva is light green with black shiny head. Larva feed on new growth and can severely defoliate alfalfa plants. Majority of damage is seen in early spring on first cut.

Control – No resistant varieties are currently available. Severe infestations may require chemical control.

Potato Leafhopper  (Empoasca fabae)

Description- Small light green insect approximately 3 mm long, nymphs are light yellow. Insect characteristically walks sideways and will jump when disturbed. Insect injects a toxin into the alfalfa plant when feeding, resulting in a yellowing or reddening of the plant. Leaf tips may display a "V" Shaped yellowing similar to Verticillium wilt. Severe infestations result in plant stunting. Majority of crop damage occurs in mid to late summer.

Control – New resistant varieties (glandular hair types) can greatly reduce yield losses associated with potato leafhopper infestations. Severe infestations may still require chemical control.

Spotted Alfalfa Aphid (Therioaphis maculata)

Description - Smallest of alfalfa aphids. Yellowish green color with dark spots in rows on its back. Prefers to feed on lower portion of plant, and injects a toxin when feeding that can result in seedling death, severe stunting and yellowing of mature plants. Leaf veins may turn yellow from toxin.

Control – Resistant varieties best control.

Blue alfalfa Aphid  (Acyrthosiphon kondoi)

  
Description – Bluish-green color with uniformly dark antennas. Injects a mild toxin when feeding, resulting in plant stunting. Prefers to feed on terminal leaves or new re-growth. Prefers mild temperatures, with its peak period in late winter or early spring.

Control – Resistant varieties best control

Pea Aphid  (Acyrthosiphon pisum)
    
Description– Largest alfalfa aphid, green color. Antennas have dark bands on the end of each segment. May build up in large numbers up and down plant stems, with minimal plant damage (No Toxin)

Control – Resistant varieties are best control.

Cowpea Aphid  (Aphis craccivora)

Potential New Threat:
This black aphid has historically been considered a very minor pest of alfalfa. Recent outbreaks in western hay fields (California & Arizona) and increased reportings across the U.S., have resulted in a renewed interest in this aphid. It is still too early to know if the recent outbreaks of this aphid is a short-term population fluctuation or the beginning of a new long-term problem.

Clover Root Curculio  (Sitona hispidula)

    
Description – Gray snout beetle about 3/16 inches long, or 2/3 length of alfalfa weevil. White larva feed on bark of alfalfa roots in late spring or summer. Root damage may provide entrance wound for common root pathogens.

Control – No resistant varieties are available. High soil moisture may reduce larva activity. Alfalfa variety selection with strong root disease resistance may be advisable to reduce yield losses following secondary disease infection from insect feeding.

Silverleaf Whitefly  (Bemesia argentifolil)

A relatively new pest to alfalfa. The silverleaf whitefly was the first reported as causing serious damage to alfalfa in 1991, in the southern areas of California and Arizona. Plant breeders are currently working on this new alfalfa pest, and resistant varieties are expected in the next few years.

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Bob O'Donnell - America's Alfalfa