The neem oil shouldn't have hurt the corn if applied via directions, not sure though if it pooled up in the corn swirls and sat a while. For a few number of corn plants just using tweezers to pluck out the corn loopers would be fairly easy. First time I've seen corn in containers, ear production may be questionable.

That is a very unusual method of trying to grow corn. Have you had success with this approach in the past?

I agree that Neem shouldn't create a problem if label directions are followed. But if over-applied and in the heat of the day or harsh sun most any sprayed chemical can cause some leaf damage.

But it shouldn't effect the new growth in any way. Deformed, discolored new growth is almost always a nutrient issue, primarily nitrogen. And since corn is such a heavy nitrogen user, even under ideal circumstances, it would be quite difficult to provide enough of it and keep it readily available to the plants in your situation. In such small containers it would leach righ out every time you water the plants.

Dave