Post-Pollination Insect Pests to Look Out For

Pollination is complete for most cornfields in Iowa, but it is still important to continue scouting for insect pests that may be robbing corn yields as the season progresses. We do not recommend using foliar insecticides unless scouting determines a need to spray. Some pests are resistant to older active ingredients, such as pyrethroids, and careful identification will determine what product would be more effective. In addition, prophylactic use of insecticides will limit any benefits that natural enemies may provide. 

If pollination is complete, we are not concerned about clipped silks or feeding on the tassel. Any injury that has occurred or any pests still feeding in these areas are no longer impacting pollination success and do not need to be managed.

This article will guide you through scouting for a few key late-season corn pests and discuss whether treatment is worthwhile after pollination.

Corn aphids

We have heard several reports across the state of aphids colonizing corn plants. There are a few species that could be present, and often, there are mixed populations on a single plant. The most prominent species we have seen in 2026 is corn leaf aphid. Most of these populations have been found in the upper canopy, but some areas have started to see them on lower leaves and on stalks. 

If pollination is complete, it is probably not worthwhile to treat the field for corn aphids, regardless of where they are feeding on the plant. It is difficult to see a return on investment (ROI) for insecticide applications made after pollination, and aphids tend to leave corn after the dough stage (R4), which is where many fields are right now. One exception might be if plants are stressed (moisture) and sooty mold is developing on upper leaves and interfering with photosynthesis. If aphid populations are patchy, a targeted application may be warranted.

Spider mites

In corn, there are a few species of spider mites that could be present, but twospotted spider mites are the most common 

in Iowa. We received a few reports of fields with spider mite issues, primarily in areas of western Iowa with prolonged heat and drought conditions. These populations were not widespread, but areas of the field had plants with spider mite injury up to the ear.

Again, it is likely not worthwhile to treat for spider mites at this point in the season, especially if rainfall is expected soon, which is not favorable for spider mite populations. If an application is warranted, we highly discourage the use of insecticide products like bifenthrin and dimethoate, as these products are ineffective on mite eggs and would decimate populations of natural enemies in the field. Instead, choose a miticide product, especially one that kills eggs before they hatch (e.g., abamectin or etoxazole).

Caterpillars

It is not uncommon to find caterpillars feeding in corn ears at this time of year, but scouting should also focus on finding eggs on leaves or silks prior to caterpillars making their way into ears. Once caterpillars are inside, insecticides are no longer effective. A few other things to watch for if you find caterpillars or evidence of injury in the ear are: 1) secondary pests, like sap beetles, that feed on the damaged kernels, and 2) ear molds that develop as a result of feeding injury and frass left behind. Some common culprits include:

• Corn earworm: Look for single eggs laid on corn silks, especially if the field is late-planted or late-maturing. Once eggs hatch, larvae travel down silks to feed on the tip of the ear. Larvae have an orange head capsule, stripes down the body, and bumps with hairs. Corn earworm larvae are resistant to pyrethroids through several mechanisms (target site mutations and enhanced metabolism) and are also resistant to several Bt traits.
• Western bean cutworm: Look for egg masses laid on the top of upper leaves (if you can see them). Eggs turn purple as they are about to hatch, and larvae make their way down the plant to the ear. Larvae have tan-to-orange head capsules, usually with two dark stripes directly behind the head. They have stripes down the body and are smooth. Western bean cutworm also has documented resistance to several Bt traits.