Parasitic nematodes. Some authorities seem to think they are bigger problems in poorly draining soil, soils recently in sod, and soils lacking adequate levels of organic matter. These are the larva of click beetles and the eggs that become these larva are laid each spring and as you have seen crop rotation does little to help control them. Planting later could also help.

I did a great deal of internet searching on this subject last year. A friend has the wireworm problem in his garden. I was unable to find a pesticide that would eradicate them. IIRC, one extention service suggested planting in alfalfa for several years.

My friend tilled during some warm weather, allowed the birds to eat the exposed larvae that weren't chopped up by the tiller, and that he didn't crush under heel. He tilled again just before planting to attempt to destroy more of the vile creatures.

He still has a relatively small infestation. I think it will take years to completely be rid of them.

I do know that wire worms are less apt to drill into potatoes if you plant them whole and do not cut them into pieces.

Wireworms also infect carrots/radish and I have trialed and suggested the following to gardeners dealing with that problem and they report success. Dig planting row. Heavily spread dried molasses (or granulated sugar can be used) down the row. Then spread even handfuls of cheap, fresh, UNCOOKED coffee grounds on top of the sugar. Do not stir to incorporate. Plant potatoes. When you do your first raking in of soil around the potato growth work in handfuls of the dried molasses for extra insurance. Should work. Try it. Let us know, please.