By Dr. Kelley Tilmon and Dr. Andy Michel, OSU Extension Entomology, Adapted from C.O.R.N. 2023-23
You know how at the end of the horror movie there’s always some hint that the monster may come back? We don’t know if this year will be “Soybean Aphid 11: The Return,” but there are some hints that you might want to pay attention to your beans and keep an eye out for this pest. We have been hearing reports of unusually high numbers of various aphid species on various types of plants – fruits, vegetables, weeds. This trend appears to be regional, and is being detected in other states as well. Why? It’s probably due to the unusual late spring/early summer weather which was very dry. Wetness is the enemy of aphids because it creates conditions that favor the insect-killing fungi that help keep them in check. We suspect that aphids got off to a great [great for them] start early this season because of the dry conditions, and now they’re unusually abundant in many settings.
Soybean aphid never really went entirely away. When we look hard enough for research purposes we can usually find a few here and there. While we don’t know if we will see soybean aphid problems in soybean this season, the general happiness of other aphid species this summer suggests that vigilance is appropriate.
Soybean aphid damage is not visually apparent until populations are much higher than you want them to be; plants must be examined closely to find early populations. Starting near the end of July, walk a zig-zag through your field and carefully inspect the undersides of leaves on at least 20 plants. The aphids are sometimes attended by ants, so ant activity is one tip-off to look more closely for aphids. Keep count of the number of aphids per plant – if at least 80% of the plants you examine have 250 aphids or more, a spray is warranted. We really don’t recommend spraying an insecticide before this point – not because we are tree-hugging hippies, but because (a) extensive research has shown that it does pay off even with a low-cost generic product, and (b) it can actually cause non-problematic aphid populations to flare when it kills beneficials like ladybeetles that help suppress them (aphid produce a lot faster than ladybeetles, and a few remaining aphids can turn into many a lot faster than a few remaining ladybeetles to rebound).
For more information about soybean aphid scouting and biology based on soybean-checkoff funded Land Grant research, visit https://soybeanresearchinfo.com/soybean-pest/soybean-aphid/