Not sure what you mean by pendulous sedge, Whit, but its fair to say that lawn weed treatments aren't that effective against quite a lot of invasive lawn weeds. Might be better to dig out whatever weed you mean and reseed the area

you find that with a lot of these apparent cures dont you bamboo ?

Well these days, yes - everything they bring out that works turns out to have some awful effect on people or the environment, so is then removed a few years later, and what we're left with in terms of weedkillers isn't that effective, truth be told, Noseyp.

money money money .it seams like the goverment must run the garden centres lol.

hi bamboo, pendulous sedge is an oramental grass ,looks good ,it appeared in my garden (unasked )a few years ago if i`d known what was going to happen i would have dug it out then,it self seeds every where lawns, cracks in crazy paving,any where there is a bit of soil,as for digging from the lawn that is a no go my lawn is 400sq yards .im a bit old for doing that amont of work iam keeping it dow by mowing

Ah, you mean Carex pendula, I didn't recognise it from that name, Whit. Given that its a sedge, or a form of grass, no lawn weedkiller will work on it - they're designed not to kill grass or grass like plants. You could try using glyphosphate, sprayed on, then reseed after its given up the ghost, just don't get the spray on your lawn grass.

BAMBOO ,slight mistake on lawn size it is 400sq feet not yards ,
i had some one dig out the main plant from a flower bed ,what i am left with is hundreds of seed lings about 2inches high (until i mow them), so it would be impractical to re seed the full lawn i suppose its keep on mowing

If they're that small, it should be possible to hoick them out with a sharp knife - cut round and pull them out - if you can bend down for long enough, that is, something I find increasingly difficult these days, oh woe is me...

same for me, but there is hundreds of these things and from what ive read about them their roots are like ground elder tiniest piece left and they`re growing better than ever