Increased number of soybean aphids have been reported in early July in some parts of Southern Minnesota, as well as in adjoining areas of Iowa and Wisconsin. In 2003, soybean aphids caused considerable soybean yield reduction and dollar loss in Minnesota and Iowa. Warm, dry conditions have been favorable for soybean aphid development in recent weeks. Soybean growers should scout their fields at least a couple times a week for soybean aphids in the coming weeks, as aphid populations can increase quite rapidly in just a few days under ideal conditions. The effects of the soybean aphids and the resulting yield reduction to the soybeans are usually greatest under hot, dry weather conditions. The University of Minnesota recommends treatment for soybean aphids when a threshold level of 250 or more aphids per plant are counted, and more than 80% of the plants are infested. There are several good insecticide options available to treat soybean aphids; however, timeliness of application is a key to getting good control and preventing yield loss. For more information on management of soybean aphids, farm operators should contact their agronomist or crop consultant, or visit the University of Minnesota Soybean Web site at: www.soybeans.umn.edu.
Editors note: Kent Thiesse is a former University of Minnesota Extension educator and now is Vice President of MinnStar Bank, Lake Crystal, MN. You can contact him at 507-726-2137 or via e-mail at firstname.lastname@example.org.