Answer: Sounds as though you may have discovered corn borers. Corn borer populations fluctuate from year to year and can be more severe in some fields than others. There are two generations of this insect each year.
The first generation occurs from early June to early July and is most damaging to early-planted corn. Damage is primarily due to borer tunneling in leaf midribs and the stalk. The second generation in August and September is a greater threat to late-planted corn. Borers of this generation tunnel in ears, ear shanks and stalks. Stalk breakage may be serious. Borer entrance holes in corn plants also provide a site for stalk rot pathogens to enter the plant.
I'd hand pick the critters or use Bt (sold as Dipel). It's safe to use in the garden because it targets larvae and is harmless to beneficial insects.
Best wishes with your corn!
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