The first observation of soybean aphids in research plots near Harwood were found this week at very low densities and <1% of the plant infested.

Now is the time to start scouting fields for soybean aphids in the V3 to V4 crop stage. This small aphid is yellowish-green, about ¹/₁₆ inch long, and pear-shaped with two black cornicles. They are commonly found feeding on the underside of the leaf and in the top ‘tender’ leaves of vegetative soybeans. Aphids suck fluid from plants. When infestations are large, infested leaves are wilted, yellowed or curled. All aphids excrete honeydew, a sweet substance that accumulates on surfaces of lower leaves and promotes the growth of black sooty mold.

Here’s a reminder of the correct Economic Threshold for soybean aphids:  R1 (beginning of flowering) to R5 (beginning seed) = average of 250 aphids per plant and when populations are actively increasing in 80% of field.

Janet J. Knodel

Extension Entomologist