"Devlin" wrote

what can I buy to prevent cabbage root fly larve

Nothing available on the chemical shelf these days for the gardener. Only
way is to use a collar around the stem so the fly can't get to the earth
around the stem to lay it's eggs. You can purchase these or make them out of
anything that will last a season, roofing felt, carpet....... hole in the
centre for the stem and slit so you can put it on/take it off.

--
Regards
Bob Hobden
W.of London. UK