Yorkshire fog/weed grass

Hi all, this is the first of many questions I will be posting on here after finding this great site!

I have quite a large grassed area that is not in the best condition. It's very mossy in places and weedy. There are 4 or 5 patches of yorkshire fog in there that don't look so bad now, but in spring summer it looks awful and it grows so much faster. A friend advised to put weed killer on the areas to get rid and then re-seed it. Each patch is about 1-2 square metres

Is this the best course of action? If so what would be the best type and when should I do it? Then, when can I sew new seed?

If it makes any difference I am planning to scarify (probably the first time it's ever been done) in early March.

Thank you

 

Welcome aboard.
The idea when removing problem grasses is to replace it with a similar type so have a nice even looking lawn which can be a pain as there are so many types of grasses available.
Depending on what you want and in simple terms you either dig up the weed grass, scarify hard, dress with soil and reseed the whole area to try and create an even look or you simply remove the weed grass areas and dress and reseed.
You can kill it with weedkiller which will be best done in the warmer spring weather with a sprayer and hood attached to reduce drift but you still really need to remove the grass by hand as you have large areas that need reseeding.
One problem is that while scarifying is great and reseeding is fine you then can't treat the weed with a herbicide due to new growth and herbicides normally list the time delay on packaging.
You could turf the areas which would be a quick fix and turfing can be done anytime apart from when we have extreme weather conditions.
If your lawn is really is in poor condition with moss you should treat that with iron before scarifying to not only kill or deter the moss but will reduce the waste produced and harden the grass plant. When its really bad the chances are using a domestic scarifier or not having experience with the techniques the lawn will require a dress and seed.
To throw another option in which is aimed at moss you could try products aimed at reducing moss without the need to scarify and without it turning black and simply eat the moss away. MO Bacter is one product aimed at removing moss and also feeding the lawn which is over an extended time but it relies on warm, damp weather and needs to be applied at a heavy rate to work best and will require more than one treatment.
The choice is really how much you want to spend, effort and looks.

 

You can get rid of patches of weed grass completely by using a total kill weedkiller (Glyphosate-based). It is the only way to be sure to get rid of it. Something like roundup, resolver or other weedkiller will do the job. It will kill ALL grass though, so be careful with it.
The good thing about glyphosate is that you can re-seed new grass the same day without any problem.
For your situation, once the lawn starts growing again (About march-april), spray the weed grass with the weedkiller. Then sprinkle grass seed over the top and then cover the whole thing with a layer of topsoil. The weed grass will die back completely while the new grass comes through.
If you have a thick thatch layer you may have problems with germination, but just put a bit more topsoil down if you are worried.
Give it a month and it will be well on it's way.