Soybean aphids are usually a problem only in northern Illinois and surrounding states. But this year, because of the cooler temperatures and other factors, it has become a problem in southern Illinois.

"The first recommendation is to not panic," says Doug Jones, University of Illinois Extension pest management specialist. "This pest has been around for several years now and lots of research has been conducted about its impact and control."

Scout your soybeans before applying any insecticide. Proper scouting procedure is to take a W-shaped trip across the field and examine at least 30 plants, estimating the total number of aphids per plant. Examine the lower leaves as well as the upper leaves. If you only examine the upper leaves, you may end up with a higher estimate of the population infesting the soybean plant.

The published economic threshold for soybean aphids is 250 aphids per plant. However, the actual population level needed for a real economic loss to occur (economic injury level, EIL) is 675 aphids per plant. Additionally, these recommendations apply only to soybeans that have not reached the R5 to R6 level of maturity

Once soybeans have reached R6 maturity, Jones says that insecticidal treatments are of questionable value.

Later planted beans that are still in earlier stages of development may respond well to a rescue treatment once the economic threshold of 250 aphids per plant has been exceeded.

Another important factor to consider is the pre-harvest interval (PHI). Some insecticides have a PHI that may not allow a timely harvest of the soybeans this fall.

For more complete information along with insecticide options, get our Soybean Aphid Fact Sheet at franklin.extension.uiuc.edu. If you don't have internet access, call 439-3178 for a print copy.