Figure 1. Pea aphids from 30 sweeps. Courtesy: Brady Hauswedell
While scouting alfalfa this week we observed a field that had pea aphids at population densities that greatly exceeded the economic threshold of 400 pea aphids per 30 sweeps in alfalfa that is taller than 10”. The populations were so extreme that in 30 sweeps we were collecting approximately 1,000-3,000 pea aphids (Figure 1). The field in question was beginning to have shiny, sticky leaves, which is caused by the aphid excrement, honeydew. In addition, while walking through the field we noticed that our shoes and pants became covered in pea aphids and honeydew (Figure 2).
Figure 2. Pea aphids and honeydew on boot from a heavily infested alfalfa field. Credit: A. Varenhorst
Pest Development & Management
Although pea aphid development is typically not favored during periods when temperatures exceed 90°F it appears that these populations are doing fine. It may be partially due to the cooler temperatures that have been occurring off and on for the last week. For more information regarding pea aphid scouting and management, please refer to our earlier article Scouting Recommendations for Pea Aphids in Alfalfa.