Pest of the week – Soybean Aphids

Soybean Aphids

The soybean aphid, a native of Asia, has been in the Midwest since 2000 and has quickly become a serious pest of soybeans in parts of the Midwest.



Nymph: Nymphs look similar to wingless adult aphids but are smaller. White flakes may be present near aphids; these are cast skins from nymphs molting.

Adults: The soybean aphid is a small, yellow to green aphid with distinct black tailpipes, or cornicles, on the abdomen.


As with many aphids, the soybean aphid has a complicated life cycle, that requires the presence of its overwintering host, buckthorn. One important feature of the lifecycle is the ability of female soybean aphid to reproduce live, female offspring (clones) parthenogenically during the summer months. This means that soybean aphid numbers can often increase rapidly when conditions are favorable in a soybean field. Soybean aphid are usually found in soybeans from late May through August.

Sampling: Sample 20 plants from different locations throughout the field and count the number of aphids per plant.

Economic Threshold: The economic threshold for soybean aphid is 250 soybean aphids per plant, with an increasing population density. Thus, at least two samples are needed to determine whether the population size is rising. After the R5 growth stage there is no economic return to treating.

Management Options: There are several predators, including lady beetles, which may help take care of this aphid. If populations reach 250 aphids per plant and the density is rising, then the use of an insecticide might be needed. Resistant soybean varieties are now available that offer partial control of soybean aphid, although those fields should still be scouted. For more information, visit and

Impact in Knox County: Soybean aphids have rarely reached economic threshold levels in Knox County.  Could this be the year??  Click here to see the most recent information from OSU Entomologists Kelley Tilmon and Andy Michel.

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