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Aphids in Alfalfa Reference Page

Common and scientific names

Pea aphid (Acyrthosiphon pisum)

Alfalfa aphid (Macrosiphum creelii)

Blue alfalfa aphid (Acyrthosiphon kondoi)

Spotted alfalfa aphid (Therioaphis maculata)

 Pest description and crop damage

Light green aphids commonly found on legume plants. They feed by sucking plant juices from the leaves, stems, and pods. The spotted alfalfa aphid is small and pale yellow or grayish, with conspicuous dark spots on the abdomen.   Aphid feeding reduces vigor and produces honeydew that causes stickiness and off-color.

 Sampling and Thresholds  Treat for pea aphid when:

1. The population approaches 100 per sweep, and the plants are less than 1 ft high. Populations of the blue alfalfa aphid may cause damage at levels lower than 100 aphids per sweep.

2. The field is about 2 weeks from cutting, the field is under water stress, and plants are wilting.

3. Predators and parasites are not readily observed.   The spotted alfalfa aphid can damage seedling alfalfa seriously. If aphids average over 10 per stem and honeydew is noticeable, apply an insecticide. Seedlings are very susceptible to injury and one aphid per plant may kill them. 

Management—chemical controls

Alfalfa seeded during late summer or early fall can be protected by a Di-Syston treatment at planting time. This is not a general recommendation, but it may be useful if aphids are abundant in established stands in the area. Apply by drilling or broadcasting (granules only).  Most of the following insecticides are hazardous to bees and should not be used if bees are foraging in the alfalfa.

1. malathion at 1 to 1.5 lb ai/a. PHI zero days. (0)

2. dimethoate at 0.25 to 0.5 lb ai/a. PHI 10 days. Only one application per cutting.

3. Lannate at 0.45 to 0.9 lb ai/a. PHI zero days, 7 for grazing or feeding.

4. methyl parathion at 0.25 to 0.5 lb ai/a. PHI 15 days.

5. Baythroid 2 E at 0.025 to 0.044 lb ai/a. PHI 7 days. One application per cutting. A total of 0.175 lb ai/a (11.2 fl oz/a) may be applied per season. Pea aphid and blue alfalfa aphid only.

6. Furadan at 0.25 to 1 lb ai/a. PHI 7 to 28 days. Blue alfalfa and pea aphid: one application per season.

7. Lorsban at 0.25 to 1 lb ai/a. PHI 7 to 21 days. One application per crop cutting. Do not exceed four applications per year. Minor phytotoxicity may occur on young, tender, rapidly growing plants. Do not graze treated alfalfa within 14 days after application of 0.5-lb rate or within 21 days after application above 0.5 lb. Use 1-lb rate for spotted aphid.

8. permethrin at 0.05 to 0.2 lb ai/a. PHI 1 day if 0.1 lb ai/a or less is used, 14 days if more than 0.1 lb ai/a is used. Do not use more than 0.2 lb ai/a per cutting. No aerial application within 100 yd of aquatic habitats. No ground application within 20 yd of aquatic habitats.

Source: 2002 PNW Insect Management Handbook

Integrated Pest Management Information

Colorado State Aphid Publication

Updated June 6, 2002-jn