On Thu, 30 Jul 2009 11:59:00 +0100, Peter Donovan wrote:

Yes all treated wood.

OK (BTW we bottom-post in this ng) then all you need do is surround the
bed with a barrier 18inches high: carrot-fly don't fly higher than 13"
off the ground. Some 2-foot laths nailed to the beds and some fine
netting wrapped round should do the trick (and act as a wind-break too).
No need to cover.