I recently laid some new turf (couch). I poisoned the existing "grass" with Roundup (glyphosate) 3 weeks earlier, then put down about 3 inches of topsoil over the area to lay the turf on.

It's now 3 weeks since the turf was laid, and nutgrass (sedge) is starting to come through in patches. It's definitely nutgrass, it said so on the interwebs (no, seriously, I know nutgrass when I see it). Bloody annoying - I suspect the topsoil I bought was contaminated, but who knows.

Does anyone have some tips on the best approach to getting rid of it? I've read that you can dig the bulbs out, but it is a large area and the turf is still fairly new - I don't really want to start hacking holes all over it just yet. I've also read there are nutgrass - specific poisons available for lawns: anyone had any experience with these? Are they OK with couch grass, and should I be spraying it over turf that's only 3 weeks old?

I will seek some advice from our local nursery this weekend, but thought I'd seek the collective and individual wisdom of the membership here as well.

Thanks!

James.