Soybean aphid has been almost hard to find in Iowa the last few summers. Growers have benefited from low statewide populations because they save on insecticide application costs. However, this year there have been reports of aphids in Iowa since early June. Aphids have been detected in all parts of Iowa except the southeastern region. At this time, soybean aphid densities are low and the percent of plants infested also remains small. But this aphid can quickly reach outbreak levels under the right growing conditions, so I encourage growers and crop consultants to remain diligent about scouting this year.
Soybean aphid is highly migratory after bloom, and is able to move within and between fields. Begin scouting soybean at bloom to see if soybean aphids are present. Scout every soybean field, even if a seed treatment and host plant resistant seed was used. Keep monitoring fields weekly through seed set to protect yield. Regular monitoring will tell how fast aphid populations are growing and help you make timely foliar applications if needed. The economic threshold for soybean aphid is 250 aphids per plant during flowering through seed set.
Look for soybean aphid on expanding leaves. Photo credit Erin W. Hodgson