I have adopted Beneficial nematodes for all 'in ground' pests. Applied at the right time in the correct fashion, most, if not all soil dwelling pests will be eliminated.
As most pests spend time in the ground, as larvae, it can prove useful in controlling even Codling moth.

Thanks Beeman, I have used beneficial nematodes around my rhodos and begonias for weevil and the (indoor) nematodes around my daylilies one year when I had a problem with gall midge but hadn't given it a thought to using them anywhere else. Sounds like a plan :).

Annette

You can use row covers or a home-made version for the root maggots (I use tulle from a fabric store). I think the flies like to deposit their eggs by the base of the plant so a barrier method will deter them. Cos once those maggots are in, I don't think anything can be done. Plus they overwinter in the soil and emerge as adults in the spring to wreak more havoc. Gross!

If you have acid soil, you should lime regardless for brassica. They do not grow well otherwise. I much prefer wood ash, though, because of superior mineral content.