It could definitely be army worms. It's easy to tell though. You can probably still find some in the field if they're the culprit. They're small caterpillar looking worms with black strips (most species) and will hide in decaying foliage just above the ground. If you see not animal tracks, etc., and confirm army worms, I'd recommend using Sevin. I prefer the powder form. It'sa systemic insecticide...meaning you sprinkle the powder on the plant, the plant absorbs the powder, thus becoming poisonous to the worms. Hope this helps somewhat.