The soybean aphid has completed its march across Iowa and can now be found near the Nebraska border. Hal Tucker (Tucker Consulting, Storm Lake, IA) reported finding aphids in Woodbury County during late August, and I found soybean aphids just east of Correctionville on September 3 and south of Holstein in Ida County. Aphid densities were extremely low, less than one aphid per 25 leaflets.

Enlarge

Asian lady beetle feeding on soybean aphids.

Although it has not been confirmed, I would expect that every county in Iowa probably has soybean aphids. Reports from eastern Iowa indicate that aphid populations are rapidly declining, in part due to feeding by beneficial insects such as the Asian lady beetle, which has been very common in some fields; and in part due to a natural decline in the population as summer ends. No economic damage is expected from this insect during September; therefore, it is unlikely that fields would need to be sprayed for this insect. Winged female aphids will start to abandon soybean fields and fly to buckthorn where they will mate and then lay eggs that will overwinter.