Questions

I have recently put in raised beds. The first layer of soil is made up of the grass / lawn sods taken from the area. Followed by mulch. The beds are 20" high. Cutworms are appearing and eating through all stems of salad and leafy veg. only thing that they have not eaten are onions of any sort! When I lift the root of a salad there are 3 or 4 of them embedded in the roots! Is there any solution apart from digging everything out and starting again.