David Owens, Extension Entomologist, email@example.com
Congratulations to Greg Dempsey for correctly identifying the cause as the infamous slug. Greg and the numerous other correct responders will be eligible for an end of season prize.
Slug damage can be distinguished from other pests by their irregular, slit like holes and tears on the leaf. If a particularly large slug is present, it can clip the whole plant off in a similar manner to cutworm. You may also see the silvery slime trail left behind on the plant, soil, or residue. If cutworms are in the mix, you may see a row of circular holes across the leaf first. This is caused by small cutworms that drilled into the leaf as it was still folded up. While we are not quite yet at the point of expecting black cutworms large enough to cause cutting (we may reach this point this week in SW DE), there are other species of cutworm that overwinter as larvae and are active.
What is interesting about this picture is that, upon returning to the field this week, this plant looks fine. It pushed out new leaves and the slugs have largely left the regrowth alone. However, the back quarter of the field has large areas in it where the slugs continue to feed and are hammering the seedlings. This goes to show that the front half (some feeding, relatively fine looking plants) might not be completely representative of the entire field. Be sure to scout the whole field. You do not want to come back to this field at side dress to discover stand loss or stunted plants.