Aphids Infesting Corn in South Dakota

Aphid populations are taking off in some southeastern South Dakota corn fields (Figure 1). The two aphid species that are commonly observed in corn include the corn leaf aphid (Figure 2) and the bird cherry oat aphid (Figure 3). Infestations of both species are possible on the same corn plant. So far in 2025, the colonies present on corn are the bird cherry oat aphid (Figure 4).

Identification

Bird cherry oat aphids are dark green with a rusty orange patch present at the end of their abdomens. Bird cherry oat aphids will infest almost any area of the corn plant. During early infestations, they will often be present on the stalk near the ears. Once the population increases, aphids can be found on the stalks, leaves, and ears. In some cases, the aphids can be present under layers of the husks.

Management Considerations

There are currently no treatment thresholds for aphid populations in corn. Although aphid populations can reach high densities in corn, their presence doesn’t indicate guaranteed yield loss. Typically, these populations show up in South Dakota following harvest of small grains and don’t reach large populations or feed enough to cause concern. Dr. Erin Hodgson, Professor at Iowa State University, recommends sampling 30 corn plants for every 50 acres of a field to determine the average aphid density present. In addition, below are some factors Dr. Hodson suggests considering prior to insecticidal management of aphids in corn.

1. Determine if aphid infestations are primarily occurring around the field edge.
2. Determine if infestations are present on 80% or more of the scouted plants.
3. After scouting for more than one week, determine if the aphid populations are increasing.