I live in a rampant cow parsley area with all the carrot fly problems that entails. I use flyaway or resistafly seed. Plant in June to miss the early batch of fly, [early carrots in bucket in poly],cover carefully with mesh and now have a lovely crop with carrots well over 8 ins long [ must try to take photo and learn how to get it on line..] Have now taken mesh off and hope the mild weather hasn't allowed a super late hatching. I intend to leave them in the ground unless the local rodents start getting their teeth in. Then I'll be off for a bag of sharp sand...