Corn earworms? Fairly common and the best defense is to cover the newly formed ear after it is pollinated. Inspection during growth and if the buggers are found a squairt of mineral oil in the ear helps.

Here is a link that might be useful: Corn Earworms

All that, plus Bt.

I've found that if you have plenty of habitat for birds and predatory inescts then pests in the organic garden rarely cause too much problem.

With an outbreak of pests you also get an out break of predators that will bring equilibreium to the garden.

If we get a few cobs with corn ear worm it's mostly at the top of the cob so we just chop that part off and eat the rest.