On the morning of August 12, Russ Higgins, University of Illinois Extension Commercial Agriculture Educator, Northern Illinois Agronomy Research Center, sampled soybean fields in DeKalb, Grundy, Kendall, and LaSalle counties. In four of seven commercial soybean fields, he detected soybean aphids in low numbers. Typically, Russ found one to two aphids per leaf. He also noted that beneficial insects were abundant within the soybean fields.

The economic threshold for soybean aphids remains at 250 aphids per plant with 80% of plants infested. A rescue treatment through R5 (beginning seed) may prove worthwhile and should be considered. It is important to recognize that actual economic injury does not generally occur until aphids reach 675 aphids per plant. The economic threshold is designed to enable producers sufficient time to make a rescue treatment if aphid densities are increasing.

Producers are encouraged to scout their soybean fields vigilantly over the next several weeks for soybean aphids. Cool to moderate late-summer temperatures will promote favorable conditions for aphid development and survival. While scouting for aphids, please note whether natural enemies are present and holding aphid densities in check over time.

If aphid densities begin to increase rapidly in your area of the state, please let me know so that I can share these observations with the readers of this Bulletin.