Soybean aphids have been spotted in several states in the Midwest. Aphids are a pest that has the potential to rob soybean yield. While the pests have not reached the level where treatment is required, Iowa State University Extension entomologists urge farmers to begin scouting their fields.
"Growers should scout now and into August to determine if they will need to manage this pest with an application of insecticide," says Matt O'Neal, a soybean insect specialist and professor of entomology at ISU.
The economic threshold for treating soybean aphids across the Midwest is 250 aphids per plant and increasing. In other words, if you have an average of 250 aphids per plant in a field, and weather conditions favor an increase in that population, it's time to spray an insecticide.
Despite the significant increase in the value of soybeans, entomologists at ISU and other universities are not altering their recommendation. "We have no evidence that soybean aphid populations below 250 per plant reduce yield," says O'Neal. "The density of this pest from year to year, and even from field to field, is remarkably variable. By scouting and using the threshold, growers can avoid an unnecessary application of insecticide."
Following this recommendation also avoids killing the beneficial insects which are predators of the aphids. "The predators can keep populations down until insecticide control is needed, if it is needed at all," he explains. "In the long run, following this 250 threshold recommendation helps reduce the risk of aphids becoming resistant to insecticides."