Soybean aphid, Aphis glycines, is capable of reducing soybean yield by 20-40% during severe outbreaks in the North Central growing region of the U.S. (McCornack et al., 2007). Since soybean aphid was first documented in Wisconsin in 2000, a common University research protocol was adopted by entomologists in six North Central states (MN, IA, WI, MI, ND, and NE) who provided data from 19 yield-loss experiments conducted over a 3-year period. Results of this research validated the soybean aphid economic threshold (ET) recommendation to treat within 7 days when aphid density exceeds 250 aphids/plant.

The ET is the pest density at which management action should be taken to prevent an increasing pest population from reaching the economic injury level (EIL). The EIL is the lowest population of insects that will cause economic damage, i.e., yield loss that equals the cost of control. In 2003, a preliminary EIL of 1,000 aphids per plant was reported based on research from the University of Minnesota. Since then, data from additional states (2003-2005), including Wisconsin, have refined the EIL at 674 (± 95) aphids/plant during the R1 – R5 soybean growth stages (Ragsdale et al., 2007).