New lawn going brown

No flowering, just similar to grass, only a browny red color, with a bit of a head on top. Agritox is basically NCPA, which is supposedly good for killing buttercups, which is why I sprayed it. I know it wasnt the best time of the year to be treating. I might try the fertiliser in spring and then try and get rid of the weeds once they are growing strongly. I will try and get some way of identifying the type of plant that is in those pictures as well before i treat it.

I'm sure you have to deal with amateurs like me all the time who dont know what they are doing, but I like to figure out and know what the problems are and how to solve them.

 

I find Weedol works well on Creeping Buttercups @dsburny. These weeds put out runners so it will need to be applied wherever they pop up. With perseverance they can be eliminated.

 

We all started off green, its part of the joys of gardening. What you may find best is the weed may be local to your area and you might be able to track it down that way which local lawn companies will know.
The Herbicide you used should not be used on lawns under a year of age and this Herbicide is not to be used in via a hand sprayer as per info below.
More info can be found here but its not really for domestic use.
http://technical.nufarm.co.uk/documents/Herbicide/Label/Agritox_labelinfo.pdf

Sheal has mentioned a domestic product that can be used and these really are the ones you should look at or again use a company that are trained in use of professional pesticides.
You may have to pay once but a good company will give you plenty of tips like controlling buttercups by scarification if non chemical use is required. I do a fair bit of consultation in my year of work and its a good start for customers wanting to be more hands on.
Some times chemicals cause more damage to turf than other aspects of turf related problems.