Pea Aphids Reported in Alfalfa - UNL CropWatch, April 6, 2012

Pea Aphids Reported in Alfalfa - UNL CropWatch, April 6, 2012

April 6, 2012

We have received several reports of pea aphids in alfalfa in southeastern Nebraska. These aphids are often the first to appear each spring in alfalfa.

Pea aphids are comparatively large (3/16 inch long), bright green aphids, with long legs, antennae, and cornicles (paired "tails" near the end of the body). These aphids over-winter as eggs. After hatching in the early spring, the nymphs feed on the first growth, and are usually found on the growing tips of the plants. High populations may cause wilting or death of the plant. Dry, cool conditions (55-60°F) favor the development of dense populations. Infestations are most likely to occur during spring or late summer.

To identify the aphids in your alfalfa and view comparative photos, see Alfalfa Insects II (EC1577)

To see insecticides available in Nebraska for aphid control in alfalfa, see the Guide to Weed Management in Nebraska with Insecticide and Fungicide Information, EC 130,

After scouting, to determine whether treatment is warranted, see the economic thresholds in Table 1.

Bob Wright
Extension Entomologist

 Table 1. Economic thresholds for pea, blue, spotted and cowpea aphids per alfalfa stem at seedling and three growth stages. (Source: High Plains IPM Guide)
 Growth Stage  Pea aphid  Blue alfalfa aphid  Spotted alfalfa
 Cowpea aphid
 Seedling 5 1 1 5
 <10 inches 40  10  10  40
 10 -20 inches  75  30  30  75
 >20 inches  100  50  100  100