Corn earworms in field corn are not normally associated with yield loss in timely planted corn. This year, our timely planted corn had between 2 and 10% injured ears. However, because of the weather, we had a fair amount of late planted corn that was silking when our major earworm flight began. It wasn’t uncommon to find 2 – 4 earworms in one ear, and I have to think that at these numbers, they could contribute to lower yield through their direct feeding as well as opening the ear up to disease. We sprayed some of our late planted field corn 5 days after silk to no avail. To keep late corn clean chemically, it would require just as many sprays as sweet corn. Once larvae are in the silk channel, they are protected.
At the beginning of the season I shared the link to the handy bt trait table (https://lubbock.tamu.edu/files/2018/01/BtTraitTableJan2018.pdf). This table lists the BT trait packages and what pests they have good efficacy on. If you regularly plant late corn and don’t want to see damaged ears, this may be worth keeping in mind as you select among varieties for next year.