Today, I received a report of corn leaf aphids being found in some corn that is beginning to tassel. There is little research that has been conducted on management of corn leaf aphid in corn. Often we find the aphid in low numbers pre-tassel and consider them to be beneficial because they serve as a food source for predacious and parasitoid insects.
If I had to choose a treatment threshold, I would probably treat a field if more than 30% of the plants had over 50-100 aphids per leaf at or above the ear. It is important to check for beneficial insects and parasitized aphids. If more than 10-20% of the aphids are parasitized (golden-brown aphids), the population is likely to crash quickly.
Corn leaf aphids were a problem in some corn fields in 2024. We were able to conduct a research test is a corn field near Port Lavaca and determined the field populations were great enough to cause yield losses. Below is a summary of this research.
2024 Field Research Summary
Corn leaf aphid has long been found in corn and sorghum fields of Texas, but in 2024, aphid populations greatly exceeded the levels found in recent years. A trial was conducted to evaluate the insecticide bifenthrin and to determine the effect of the aphid on corn production. Treatment with bifenthrin did not significantly reduce the aphid population and, if this result is repeatable, bifenthrin would not be considered and effective insecticide for corn leaf aphid control in corn.
Corn Leaf Aphids. Photo by S. Biles
The comparison of uninfested and infested plants showed surprising results. The average kernel weight from ears of infested plants was 71.13 g less per ear than uninfested plants: a 43.9% reduction in grain weight per ear. Further research should be conducted to evaluate insecticidal control of corn leaf aphid and investigating the economic threshold of corn leaf aphids and effects of the timing of infestation in corn production.
For the complete report follow this link: https://agrilife.org/mid-coast-ipm/files/2025/04/2024-Corn-Leaf-Aphids-in-Corn.pdf
Recommendations from Extension Entomologists across the corn belt vary in suggested treatment thresholds.
I have linked many of them here:
Kansas State: https://entomology.k-state.edu/extension/crop-protection/corn/cla.html
Illinois: https://farmdoc.illinois.edu/field-crop-production/illinois-crop-update-july-26-2024.html
Utah: https://extension.usu.edu/vegetableguide/sweet-corn/corn-leaf-aphid
Iowa State: https://crops.extension.iastate.edu/cropnews/2023/08/corn-aphids-observed-iowa
Kentucky: https://entomology.ca.uky.edu/ef126
Minnesota: https://extension.umn.edu/corn-pest-management/aphids-corn-post-pollination
Nebraska: https://cropwatch.unl.edu/2023/watch-aphids-corn/
