The use of insecticides to control the soybean aphid has become a predominant management practice for growers. Before the confirmation of the soybean aphid in 2000, less than 0.1% of soybean was treated with insecticides. However, soybean aphid management has resulted in a 130-fold increase of insecticide applications in less than a decade. An estimated 1,400% increase of Iowa soybean acres were treated with a foliar insecticide in 2009 compared to 2000. Growers are also increasing the use of insecticidal seed treatments to control early-season establishment of insects on soybean. Approximately 73% of Iowa soybean had an insecticidal seed treatment in 2009. Our laboratory researches the efficacy of insecticide products and their applications for soybean aphid management.
Since 2005, we have evaluated foliar and seed-applied insecticides for soybean aphid. We have recently incorporated single gene host plant resistance for soybean aphid (Rag1) into our evaluation program. The general protocol has remained the same every season, and includes evaluating 20-35 different insecticides per year. We evaluate insecticide efficacy on at least one Iowa State University (ISU) Research Farm per year. Each insecticide is compared to multiple entries with at least four replications comprised of small plots within a randomized complete block design. Soybean aphid populations are monitored throughout the season. Insecticides are applied to foliage with a backpack sprayer at either the economic threshold or, if aphid populations are not expected to exceed this threshold, within the first 2 weeks of August. Cumulative aphid days (CAD) are calculated to provide a measure of seasonal aphid exposure experienced in each plot, and plots are harvested with a small plot combine. A summary of CAD and yield are published in an ISU Yellow Book publication each year.