Indiana Prairie Farmer publishes a column written by Tom Bechman with the help of CCAs for CCAs and their clients. With permission from Prairie Farmer we are posting these Soybean and Corn Pest Beat articles on the CCA website. Many thanks to the authors and the support of Indiana Prairie Farmer.
Corn Pest Beat Articles
Don’t pull trigger on corn aphid control too soon
Answers are from the Indiana certified crop adviser panel: Gene Flaningam, Flaningam Ag Consulting, Vincennes; Carl Joern, Pioneer, Lafayette; Greg Kneubuhler, G&K Concepts, Fort Wayne; and Dan Quinn, Purdue Extension corn specialist.
Corn aphids were a problem last year, especially in midseason. Could they show up this year? When should I scout for them? Should I spray?
Flaningam: Corn aphid pests vary yearly. Environmental conditions like dry weather, wind currents and crop stage are all factors that must be considered for aphids to develop. Treatment may be justified if 50% of the tassels are covered by aphids and their honeydew before 50% of the field pollination has occurred.
Joern: Corn aphids could appear, but they do not overwinter in Indiana. That said, you should scout for them! Whether or not to spray is a more complex decision.
Prior to last year, corn aphid infestations in northwest Indiana typically occurred after pollination. Insecticide applications were generally recommended only if honeydew excreted by the aphids threatened to gum up tassels or silks. However, last year’s severe infestations proved that even post-pollination, aphids could significantly reduce yield if their honeydew and resulting sooty mold impaired the canopy’s photosynthetic capacity.
Begin scouting in the late vegetative stages, a few weeks ahead of tasseling. A rough threshold for concern is around 10 aphids per plant across multiple sampling spots. If populations are increasing, an insecticide application may be warranted.
The best way to assess the situation is to be in your fields regularly. Always double-check your insecticide’s label. Not all products are approved for corn leaf aphids.
Kneubuhler: It’s not all that likely that you’ll have aphids this year just because you had them last year. Most generally, they are carried in on storm fronts. It’s hard to predict whether they will be here or not until we scout or follow weather patterns.
It takes a large aphid infestation to affect corn plants to the point of impacting yield, but it can happen. Scout just before and during pollination to observe populations. Their excrement, which is also referred to as honeydew, can affect pollination.
If you find them, they need to be treated rather soon. Pyrethroid insecticides don’t have the best efficacy against them but can help. The best active ingredient against aphids is methomyl, which is Lannate.
Quinn: Yes, aphids could show up again this year, but it is very hard to predict. Scouting and monitoring cornfields throughout the growing season is important. In 2024, corn aphid severity in fields was likely a combination of growth stage, hybrid susceptibility, weather patterns and geography. Corn leaf aphids can be carried into the Midwest via storms from the South. The outbreaks were also largely observed after pollination, meaning control methods in 2024 likely did not help much.
It takes a very severe aphid infestation to cause yield reductions, and it often looks much worse than it is. In addition, plants under moisture stress are more susceptible to yield reductions. A good time to start scouting is two to three weeks prior to tassel emergence and throughout the pollination period. Current Purdue University recommendations for determining if you should spray include: 15 aphids per plant whorl three weeks before tasseling and/or 50% of tassels covered prior to 50% pollination.
