Answer: Wireworms aren't choosy about which roots they like, but the latter critter, which I believe is a cabbage root maggot, sticks to members of the mustard family (turnips, radishes, and all the cole crops).
Wireworms are a toughie. They're usually most problematic in newly turned sod, and for several years thereafter. They're most active in cool soils early in the season. Beneficial nematodes may provide some control, and you can bait some of them away from your crops with pieces of raw potato and carrot on the soil surface. Check these traps frequently and destroy or relocate the pests. Recent research shows that rapeseed (canola) grown as a green manure and allowed to decompose in the soil repells the critters, too!
Cabbage root maggots are easier to foil. You can cover your new plantings with well-secured floating row cover to prevent the flies from laying eggs near your crops. Beneficial nematodes do control these pests. Wood ash and diatomaceous earth heaped around seedling stems are mentioned as repellents for egg-laying flies, but this is useful only where the population of the maggot is fairly low. Since wood ash can also raise soil pH significantly, I'd stay away from that option. I hope this helps!
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