Don't know if anyone knows this tip.
Grow your carrots in blue barrels or tubs this year. You won't get carrot fly.
Carrot fly only fly around 15" off the ground so won't get your carrots.
A little tip from Terry on the BBC lottie :)
Would that work for raised beds too. I am thinking of very raised beds, ie waist height as used for senior citizens on our site. They have glass fibre moulds raised up on concrete blocks.