We have a small farm in the Western Cape, and have been hit in the last 2 months by these little buggers called Cabbage root flies.

Essentially these flies lay their eggs at the stem of a plant (cabbage, broccoli, cauliflower) and when the larvae Hatch, they proceed to eat the roots of the host plants.
This damages and even kills the plants because their root structure is compromised.

So we are desperately looking for a fix for this issue for a couple of thousand cabbage plants that we have in the ground currently.

So are there any people out there with experience in getting rid of these pests once they've set in?

Things that are suggested (that we know of) :

• putting a cover over plants to stop the adult flies
• having a plastic cover or sheet on the ground with slots in them for the plants
• mulch and other items to cover ground
  

These are preventative measures, but we already have the issue and are looking to kill them in the ground without hurting the plants further....if that's possible.

Or else it's just nursing them to get through the fly 'season'.

Is there any advice please?

Much appreciated.