A few fields in southern Minnesota recently were treated for soybean aphids after a new “speed scouting” system was employed to determine if the infestation warranted treatment. The new speed scouting system was developed by entomologists at the University of Minnesota. It reduces the time spent scouting fields because every insect is not counted. Instead, once 40 aphids/plant are counted, the plant is considered infested.

“But remember that the 40-aphid figure is just a sampling criteria and not an economic threshold number,” says Ken Ostlie, entomologist with the University of Minnesota Extension Service. “The economic threshold for soybean aphids that’s been determined from Minnesota research is 250 aphids per plant through pod set. Late-maturing, or late-planted, soybean might benefit from controlling heavy infestations after soybeans begin setting seed, but no thresholds are available for these later stages.”

As of August 5, a few fields in the St. James, Comfrey, Springfield and New Ulm areas of Minnesota had reached economic threshold levels of 250 aphids/plant and were being treated with insecticides, according to Bruce Potter. Potter is an integrated pest management (IPM) specialist at the university’s Southwest Research and Outreach Center near Lamberton. “We expect only scattered areas of Minnesota to reach economic threshold levels and require treatment in the next couple of weeks,” Ostlie says. “The good news is that aphids in fields with low infestations are literally running out of time to develop into economic infestations. However, given their potential to increase in number, it’s important to continue scouting fields over the next two weeks.”

Details on using the new scouting plan, including worksheets, are available at www.soybeans.umn.edu.