I have'nt had much problems with the root fly ...maybe about 5% loss.I have always read the interplant them with onions and from what I have harvested of my carrots so far (about 50 carrots) I have only seen one carrot with the tell tail hole in it...so maybe it might work in my case but with an infestation like yours it's hard to say.

I am an ardent organic gardener so I don't reealy beleive in mixing even natural pesticides into the soil, but you can get neem pellets that come from the neem tree bark and it kills some insects,you will have to look into if they are affective with carrot root fly.My farther-in-law used them and does'nt have a worm to be found in his soil ,don't know if it's the neem pellets or not but I would'nt use them.

Hope that helps some

Hmmm... Neem, funny you should mention that. A couple of years ago, I rushed out and ordered some to combat some nasty that was driving me nuts, on the strenghth of it being "organic". I did the real reading on it after it arrived, and promptly put it in the cupboard, where it has stayed ever since! Maybe if this grass method doesn't work, I might consider trying it next year. About the only thing I use, other than garlic (and "treepel" on the roses) is B.T. on the brassicas, which unfortunately doesn't seem to be available to us proles any more.

One way to help, not that I have ever grown carrots, is that you sow them extra thinly and when you thin or harvest them do it in the evening, then water same so the fly does not get the scent of freshly dug carrots. I read that somewhere.
Heather

I heard something about (though I don't grow carrots so haven't tried it)using crushed garlic, mixed with water to spray the plants. Supposedly this disguises the smell of carrots to the little blighters. Might be worth a try...

Getting some good things to try here, thanks. Maybe a combination of all suggestions will do the trick. I hope so, as I'm desperate to have good, spray-free carrots growing in my garden again!