First soybean aphids of 2022

June 17, 2022 11:09 AM
Blog Post

Today, while scouting for bean leaf beetle south of Ames, my lab found a few early vegetative plants with soybean aphid. Actually, it was Ashley Dean who found them. It was the ants moving on plants that caught her eye. Taking a closer look revealed a few small aphid colonies feeding on the undersides of the trifoliates. That is pretty typical from my experience – finding the first soybean aphids of the season is by seeing ants or lady beetles. It is not unusual to see soybean aphid in mid-June.

soybean aphid.
Soybean aphid colony tended by ants at the ISU Johnson Farm (just south of Ames) on 17 June 2022. Photo by Ashley Dean. 

Soybean aphid is the only species in Iowa that will colonize soybean. After developing on their overwintering host, buckthorn, winged adults will migrate to soybean and potentially product 15+ generations. Initial infestations in soybean are patchy and located near field edges, but winged aphids can quickly disperse within and between fields. Long and short distance immigration is more likely after bloom. Aphids prefer to feed on the undersides of leaves and will colonize on the newest leaves. If a large colony develops and leaves are crowded, soybean aphid will feed on stems.

With the potential of many overlapping generations in a field, scout weekly from plant emergence until seed set to assess population dynamics. The economic threshold for soybean aphid is well established for the north-central region. Consider a foliar application when the average density exceeds 250 per plant (Ragsdale et al. 2007; Koch et al. 2016). Populations should be increasing and most of the plants have to be infested (>80 percent) in order to justify an application. This threshold is appropriate until plants reach mid-seed set (R5.5).


Erin Hodgson Professor

Dr. Erin Hodgson started working in the Department of Entomology, now the Department of Plant Pathology, Entomology, and Microbiology, at Iowa State University in 2009. She is a professor with extension and research responsibilities in corn and soybeans. She has a general background in integrated...

Ashley Dean Agriculture and Natural Resources Extension Specialist II

Ashley is an education extension specialist for field crop entomology at Iowa State University. She coordinates the Iowa Moth Trapping Network, the Regional Corn Rootworm Monitoring Network, and the Iowa Pest Alert Network. She also develops educational resources for field crop pests in Iowa and ...