Soybean aphids are making a very strong appearance in Story and Boone counties in central Iowa. It is not uncommon to find small areas across fields with thousands of aphids per plant. These areas often attract large numbers of lady beetles, flies, and ants. Leaves typically are dark because of sooty mold growing on the honeydew secreted by the aphids, and infested plants may be stunted compared with plants without aphids. Aphid populations may continue to build and fields should be scouted.

Enlarge

Soybean aphids.

Information was presented on scouting, a nominal economic threshold, and recommended insecticides in the July 1 Integrated Crop Management newsletter, pages 127-128. Briefly, it was suggested that an insecticide should be used to control soybean aphid in July when five criteria in the field were met:

1. soybean plants are in the R1 stage (first bloom) or later,
2. aphid populations are heavy and cover the upper trifoliate leaf on a majority of plants,
3. lower leaves are not yet covered with aphid honeydew or turning black from sooty mold,
4. infested plants do not yet appear stunted, and
5. a majority of aphids are not winged or developing wings.